TECDOC 0726 Geochemical Precursors of Earthquakes and Volcanic Eruptions

8/13/2019 TECDOC 0726 Geochemical Precursors of Earthquakes and Volcanic Eruptions

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IAEA-TECDOC-726

sotop ic andgeochemical precursorsof earthquakesand volcanic eruptions


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Th e originating Section of this document in the IAEAwas:Section of Isotope HydrologyInternationalAtomic Energy AgencyWagramerstrasse 5P.O. Box 100A-1400Vienna,Austria


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FOREWORDEvery year natural catastrophes, such as earthquakes an d volcanic eruptions, cause

heavydeathtolls, hum an suffering an ddisastrousdamage,despitecontinuousprogressin theunderstanding of natural hazards and the mitigation of their effects. But the prediction ofsuch events within a reasonable time is still aproblem.In recent years, investigations have shown that, under certain circumstances, somegeochemical tools, including environmental isotopes, ca n provide useful indications forpredicting earthquakes and volcanic eruptions. However, the natural processes and thegeological causes which govern the geochemical behaviour of these precursors are still fa r

from being fully understood. The International Atomic Energy Agency therefore convenedan Advisory GroupM eetingon the Isotopicand GeochemicalPrecursorsof Earthquakes andVolcanic Eruptions to review the state of the art in this field, which has such importantpractical implications.The AdvisoryGroupmeeting washeldin Viennafrom9 to 12September1991and wasattended by twenty-three invited experts an d observers from eleven countries and twointernational


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CONTENTS

Summary o f the Advisory Group Meeting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Radonas aprecursorof earthquakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9V.T. D ubin chukGas-geochemical approachesto earthquake prediction . . . . . . . . . . . . . . . . . . . . . . 22Chi-Yu KingRadon measurements in Austria and somebasic problems in earthquakepredictionresearch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37H . FriedmannGeochemical precursors o f earthquakes Experience in Italy . . . . . . . . . . . . . . . . 44M . Valenza, P .M. Nucc ioFluidodynamical andchemical features of radon 222 related to totalgases:Implicationsforearthquake predictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48G . Mart inell iSome isotopic and geochemical anomalies observed in Mexicoprior to largescaleearthquakesandvolcanic eruptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63S. de la Cruz-Reyna, M. A. Armienta-Hernandez, N. SegoviaConclusions on thepossible variations of chemical andisotopic composition ofgroundwater systems inresponse to changed hydrodynamicconditions(based on investigations of deep groundwater systems and thermal-mineralwaters and brines intectonic active areas) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87W . BaldererPrinciples andmethodsof volcanic surveillance:Thecaseof Vulcano, Italy . . . . . . . 108


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SUMMARY OF THEADVISORY GROUPM EETINGThe fluids trapped and segregated in pores, fissures an d fractures of deep geologicalformationsm ay suddenly becomem obile and m igrate into shallow horizonsor to the surfaceunder conditions of tectonic stress an d strain which precede an d eventually causeearthquakes. In fact, the strain to which rocks are subjected determines the opening ofcavities and the fluid release. In general, these fluids have a chemical an d isotopiccomposition different from thoseofother fluids, likeshallow ground water, w ithw hich theymix. Thisproducestheappearanceo fchemicalandisotopic anom alies,whichm ayannounce

the occurrence of an earthquake in the near future.If this is the generalmechanism producing variationsofcertain elementsan d isotopes,the details of their geochemical behaviour, an d therefore their reliability as earthquakeprecursors, are still poorly understood. Radon222 seems to be one of the most promisingprecursors and is the tracer fo r which more data are available: according to statisticselaboratedin China, 70% ofearthquakesareprecededby radon anomaliesdetectablein soil,air and/or in groundwater. However,40% of theradonanomaliesdetectedare not followedby earthquakes.Other isotopes, the variations of which may potentially be suitable fo r earthquakeprediction, are the stable andrad ioactive isotopesof light elements such ashydrogen,helium,oxygen and carbon. For these isotopes, however, the existingdataare still very scarce, an dmuch more research an d observations are necessary to assess their reliability on a statisticalbasis.


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moderate earthquakes at different sites and under different hydrogeological, tectonic an dvolcanic conditions, with a time advance ranging from hours to one year. Among theseindicators one can mention variations in concentration and/or isotopic ratios of hydrogen,helium, carbon, oxygen, neon, radon, radium anduranium .Nevertheless, there are still many scientific questions an d methodological problemswhich need to be solved, in order to extract from the geochemical and isotopic signals aprediction with a high level of reliability. To this end, long term (preferably on-line)monitoring of geochemical, isotopic, hydrological and geophysical parameters should beorganized, and an interdisciplinary approach should be used fo r elaborating the field data,which should lead to the formulation of complex geochemical an d geophysical models.In order to help in tackling these problems and to foster research, the participantsrecommended that further work be done on isotopic and geochemical precursors ofearthquakes and volcanic eruptions. This work should concentrate on:

(i) searching, selecting and using the most informative isotopic and geochemicalprecursors,to bem onitoredalongwithotherhydrologicala ndgeophysicalparam eters;( i i ) analysing precursor behaviour, and formulating theories an d models fo r this;( i i i ) elaborating algorithms fo r data processing and event prediction;( i v ) improving an d developing monitoring networks.


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RADON AS A PRECURSOR OF EARTHQUAKESV . T . D U B IN CH U K *International Atomic Energy Agency,ViennaAbstract

Thisis ashort historical review on the use andstudy o f radonconcentrationvariations in groundwater and soil air as aposs ib le precursorof earthquakes ando thereventsaffected byaccumula tionan dvariationof strainsinrockmassifs. An analysisof the mainfeaturesof radon s igna lsin hydrogeochemical systems is 'presented an dposs ible mechanismso f radonearthquake orerunn ers are discussed. It isassumed tha tth e initialstageofany radon transferf rom a rockmatrix mineralin a s tra inedstatein topo r e luid has athermo-molecular act iva tioncharac ter obey ing general kinetic laws. On this basis a new modelfor radon anomalies hasbeen developed where so-called convertioncoefficients, kinetic complexes, kineticso f radio-active decay , first order transfer processes (sorption, fo r example) and hydraulic transport( turnover) are involved. All of thesek inet i c parameters ar e related to s o m e characteristicresidence timeo r agiven precursorin agivensystem. Bothgroupso fparametersare governingampli tude an dforms of radonprecursoroutputcurves . Th emain character is t icsofprecursorsin hydrogeochemica l sy stems are the residence timedis tr ibutionfunctions for water(R T DFw)an d precursorcomponen ts(RTDFc). Thesefunc t ionscan be evaluatedby m e a nsof we l lblownisotope hydrologytracer techniques. S o m eme thodolog ica l consequences and recommendationshow to use isotope hydrology data ar e givenfor the analysis an d interpretation of the radon( a n d of o ther hydrochemical) precursor s ignalso f earthquakes.1.INTRODUCTIONEarthquakesare amajor threat to humanity and it is a great challengefo rscientistsa ndengineersto makeefforts toprevent their disastrous consequences [9, 42, 57, 58, 65, 73, 7 9 ] .Almosta ll kindso fhumanactivitiesar e mostsensible to anddependo nseismo-tectonican dgeo-dynamicconditions and events [ 5 8 ] . One shouldrememberthatmodern cityagglomerations,roads and pipelines, hydro-, nuclear-, coil- and gas-power stations, chemical and gas-oilindustries, e t c . are vulnerableto geodynamicprocessesconnectedwitho ractivatedby variousstrains insoiland rocks. Th eproblemof earthquakesand othergeodynamicprocessesrequiresan adequateand complexsystemapproach to be analysed[30,58,72,73,75,79].Th emajorproblem to besolvedis the earthquakeforecast, i . e . determinationof strength,place and timeofpossiblefutureearthquakes[8,28,30,43,57,58,75]. It should beemphasizedthatregionalabilityto provideearthquakesafety influences humanactivitiesin adifferent w a y ,

depending on thestateeof the art ofenvironmental monitoring a n d , what ismost important,ofunderstanding seismotectonicprecursorsignalsin ordertomake correctdecision[7,12,28,30,6 0 ] . It istruethatthe greatmajority of catastrophic seismicevents has notbeenforecast, n e v -ertheless the hope of being moresuccessful in future in predicting the site and strength ofearthquakes hasincreased.*Presentaddress:Ail-RussianResearchInstitutefor Hydrology andEngineering Geology, CenterC O for Geoenvironment, 142452 Zeleny Village, NoginskDistrict,M oscow Region, RussianFederation.

Earthquake prediction is one of the most Important, yet infant disciplineswithin earthsciences and engineering. The history of development of earthquakeprediction studies couldbe subdivided intoth efollowing stages:-intuitive semi-scientific attemptsweremadetillthe end of the 1 9 t h century [ 3 7 , 5 8 ] ;- scientific formulation of theprobleman dpossibleways tosolveitwereelaboratedb yOrlov A . P . , Mushketov I . V . , Golitsyn B . B . , in the early 20thcentury;- thefirst complex studieswere madeafter the Ashkhabad earthquakes by Gam burtsev.His study was predominantly seismological, although there were some indications ofpossible hydrogeochemicaland hydrogeologicalprecursors [ 4 4 ] ;- a "renaissance"ofthisproblem cameafterth eTashkentearthquakeof 1 9 6 6 [4,5,70,73,7 8 ] . At that timeth ehydrogeological parameters (groundwater level, temperature, m i n -eralization, turbidity, flow) and hydrogeochemical tracers ( R n , some other chemicalsoluted gascomponents,m\]fmV, Ra, He)weretriedout toforecastearthquakes. A t thesame time, analogous researchstartedin the USA [ 3 8 , 39, 42,46 , 54, 60, 63, 64, 7 1 ] , inChina [ 3 5 , 74, 75, 8 3 ] , inJapan [ 5 0 , 82] and inothercountries [ 2 3 , 25, see also reviews28,54,57,71,72];- further prognostic studies were greatlyintensified after the Armenian (1987)and theCalifornian (1989) earthquakes.During the last tw o decadesa numbero f hydrochemical precursor indifferent seismo-tectonical regionswere observed. A review of suchobservationscan be found in aseries ofpublications [5, 12, 15, 28, 34, 43, 45, 57, 72, 7 5 ] . In the early 1970s researcherswere veryoptimistic that the prediction problemwould soonb esolved. But the number of precursors,which hasconstantlyincreased,washardto bemonitoredand nearly impossible to be interpreted.There is a lot ofevidencethatsuch groundwater constituentsas Rn, He, C O 2 , C H 4 , Ar ,H 2, O 2, N 2, Na, Cl, Hg, Rb, Cs,S iO2are changing theirconcentrationbefore, duringa nd afteran earthquake[12,15,29-34,44,45,49, 67,75].It wa s noted that not only chemical components,b ut also someisotopes such as D / H ,18O/ 16O, Rn/^Ra,234U/ 238U ,lSC/' 2C, "He/40Ar arevaryingtheircontentorratiosat adetectablelevel[10,12,29-34,39,53].Moreover,it hasbeen recordedthat in experiments bycompressionof rock materials[29, 30, 34, 36, 4 7 ] , in landslidemassifs [ 2 6 , 27, 5 6 ] , in mines andquarriesbefore rock explosions,before and at the end of volcanoeruptions [ 2 0 , 2 2 ] , and by artificialexplosions [ 3 1 ] , somevolatile components ( R n , He, Ar, H2, Hg, CO, CHJ are escaping.Changesin the radon emissionof groundwaterwerefirst observedas a precursory p h e -nomenon of an earthquake. In several publications in theformerSovietUnion [4, 67, 73] anabnormalincrease of radon concentration ingroundwaterprior to the Tashkent earthquake ofApril 26 , 1 9 6 6 was reported. Th e radon concentration of groundwaterobtained from severaldeepwells(1200-2400m) in Tashkent and its surroundings hadgraduallyincreasedfo rseveralyears and reacheda maximum concentration level ( 2 - 3 timeshigherthannormal) justprior to

the earthquake. Immediatelyafterth emainearthquakeevent,withamagnitudeof 5 . 5 , theradonconcentration returnedto thenormallevelofapproximately 5xlO"'Ci/l. Aftermorestudiesandcontinuous monitoring, an apparentcorrelationbetweenth echangesof radonconcentration ingroundwateran dsuccessiveafter-shocks wa sconfirmed.Since theTashkentearthquake,hydrogeochemicalprecursorstudieshavebeen predomi-nantly implementedin groundw ater with increasingintensity indifferent regionsof theRussianFederation:in Uzbekistan [2, 5, 32, 33,67,70,73],in Kirgizia [1, 11-14, 29, 4 1 ] , inDagestan[ 5 3 ] , inUkra ine [15,45, 6 2 ] , in Turkmenia [ 4 4 ] and in Armen ia [ 6 ] , e t c .


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In1975the USGeologicalSurveybegantomonitor radon contentsin subsurfacesoil-gasalong some activefaultsm centralCaliforniain order to test whether thisparametermightshowany useful earthquake relatedchanges[28,38,39,42,46,63,64] American scientiststhoughtthattherewereseveralreasonsforchoosingtomoni torradon msoil-gasinsteadof m g roundwaterTh e first result of it wasthatthe very effectiveand inexpensiveTrackEtch Techniqueha sbeendevelopedItw asobserved thatsoil-gasand gasexhalationsin generalar ecommonly enrichedin Rnin faultzonesan dthatthe nearsurface-air shows significant increasesin itsradon contentm thetime of an earthquakeoccurrence[38,39] However,it isknownthatotherenvironmentalfactorssuch asbarometric pressure,temperature,rainfall,an dwindspeedcan stronglyeffect the radoncontentof the air above and nearthe ground-surfaceIt seems therefore that the observation of radon content m groundwaters is preferablebecausegroundw ater radon is a conservative indicatorwi thregardtoexogemcfactors Alreadyin1979Shapiroet al [63, 64 ]observeda radonanomalywhichcoincidedwith several othergeophysicalandgeochemicalanomalies and appeared tohavebeenassociatedwithanearthquakewhich occurred at a distance of 290 km fromthe siteof the radonanomalies InChinaand theRussian Federation,groundw ater radonanomalies wereobserved50-400km fromthe earthquakeepicentersReports of supposed precursory radon anomalies at great distances (of several tens orhundredsofkilometers)fromthe subsequent earthquakes,werefirst receivedwithconsiderablescepticism, particularly in the USA It was saidthatth e half-lifeof a radon atomis too short

(38days)toallowit to movemorethantensofmetersfromthe site ofproduction, evenifactivesubsurface transportmechanismsare involved[71,72]Even forsoil-airradon content, King[38,39] showed that there were some anomalieswhichappearedto besystematicallyrelated toearthquakeevents above a threshold magnitudeof about 4 0 Thisw asconsideredto bepossibly caused by radonescaping in fault zonesi nresponsetosourcestrainchangesIn China, hydrogeochemical observations related to earthquake prediction research,suchas thestudyof radon variation in groundwater, havebeenmadesince1968 It isworthwhiletonote that radon dataplayed an importantrolein the successful predictionof the LiaotungPen-insula earthquake on February 4, 1975 witha magnitudeof 7 3[75] A review of radon andotherhydrochemicalprecursorstudiesin China can be found in[75]Japanesescientistsstarted the same sort of study in1973 [50,82] byusing the liquidscintillation techniques developed by Noguchi m1964Nowadays, physicists, hydrogeologists and seismologists are usingnetworks of stationsto record several possible precursors in groundwater and soil-gas in an attempt to predictearthquakesof a magnitude greaterthan4 on theRichterscale Neverthelessthe current situationcan be described withthe words of GuyRemer (cited by P Lanoy, 1989) "Thenumber ofear thquakesis sogreat" "that thereis everychance" thatan ykindof monitoring "willleadto something"

2. MEASUREMENT TECHNIQUES USEDJudging b y published literaturethe mostwidely usedtechn iquesto measure radon contentin groundwatera ndsoil-airmay be subdivided intot hefo l lowing groups

-Emanometryby means of lomzationchambersand counters[12,15, 23, 24-27 29-3440]- Liquidscintil lation c ounting[27,50]-Zn(S)scinti llation coun ting[12,27,29-32]-TrackEtchMethod[22,50, 38, 39]-Trap (charcoal, glass) technology[42]Itseemsclearthatdynamical on-line emanometry measurementson thebaseoflomzationand scintillation chambers,plus somevariations of traptechniques[42],are preferable Th eliquid scintillationcounting can be realized in a discret sampling regime as allkinds of traptechniques basedon continuingcounting The TrackEtchMethodusingcellulosefilmsis verycheap andsimplebut can be rather applied in air soilmeasurements and in adiscrete regimeonly Evidently, the measurement techniquechoice dependson goalsand objectives aswellasfieldconditionsTh e requirementsf orearthquake forecast basedon radon m easurement are[12,15, 27,29-32, 50]-Low-level radiation measurementtechniquesare requiredbecauseradon concentrationsingroundwaterare of the order of 1010Ci/1and variations of Rn activityin seismo-tectonicregionsrangein aboutplus/minuson e orderof m agnitude of this value-Thereis aneedfor outgassmgsystems to extract thegas-fraction from natural watersThe outgassmgdevice has to be assimple an drobust aspossible,and it should not beeasilyaffectedby corrosion andprecipitationof calciumcarbonates,organic and suspendedparticles-Therefore caremustbe taken inprocessinggroundwater tomeasureradon in an on-lineregime- Stability of the measuringsytem has to beprovided,and thevariationsof meterologicalconditions (temperature, pressure, air humidityand so on) should be m onitored, to correctthe observationdata- The instruments shouldnot require much maintenance and shouldb e easyt ooperatebecause observation sites(wells, springs, captages)ar e usuallylocated in isolated areas- The relaxation characteristics of the system must not effect the natural variation ofcomponentswhichare beingmeasuredTh emonitoringsystem shouldbe locatedin the moresensitivesiteswhichcan beselectedfrom th eexisting information- The system has to provide a continuous or discrete-continuous regime of measurementswiththe requiredaccuracy3. MAIN FEATURESOF THEOBSERVEDRADON SIGNALSThe analysis of the publishedmaterials allows to formulate some general and specificfeatures of radonand other hydrochemicalprecursors [1,2,5,7, 12-15,28, 33, 45, 50, 51, 57,63,64,67-75,82 84](seealsoFig 1-12, 16 )1 The observed anomalieshavea widespacedistributionwithrespect to the epicentral zones,precursorscan beobserved m a distanceo fseveral tens tohundredskilometers from the


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Fig. l Radon variationsi nTashkent's groundwater(By UlomovV.l.MavashevB.Z., 1967 [78])

Rn

* +S '

Fig. 2

i l l

mn z137 S miumsjiiTaima.1S60 yearsRadon va r ia t ions observed in therraomineral watersat the Ashkhabad station pr ior to the Kopet-Dagearthquakes of 1979-11-14 and 1979-11-27, Turkmenia(B y Atajev S. etal.,[30])

epicenterand atdifferent depthsfromsurfaceup to about 2 km The anomalies havebeenobserved before, during and after the mam events Nevertheless there might be nodetectable anomaliespnorto relatively strong earthquakesThe anomalies occur in shallow anddeepgroundwaters, m springs and insoilair Due togeological, structural andhydrochemical characteristics they mayoccurin cold g round-waters,in mineraland/orthermalwaters,they may be found associatedto faults , fissuredand fractured zones,or belocatedin sedimentaryaquifersA definitepositive correlationexistsbetweenthe earthquake strength(magnitude)and the- distance of the sitewhereprecursorsappear- time of precursor appearance-amplitudeof precursorsignal-shapeo fprecursorrecord

so -

27 2 6 10 III 18 22 IBSE S IR 1977s 10 20 30 10ZT tS7Sl SFig. 3 Radon anomalies priortothe:(a)Tjupearthquakeof1977-08-18(K=9.8,L=73km)observedin theDjety-Oguzthermalwaters,Kirkgizia(wells)(b)Central Tan-Shan earthquakeof1979-09-07(K=11.6,L=200km)

(c) Bakanassearthquakeof1979-09-25 (K=19.2,L=220 km)observed in the wellKurskajaat the shore of theIsyk-Kul lake(ByKalmurzajevK.L. et al. [30])

22 26 JO


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6.106201976 M o n t h - O o t t

Fig 5 Sp ike l ikeg r o u n d w a t er radon a no ma l y observed at the Ku tzanstation 6 days before theM = 7.2Sungpan- P ing nu ear thquake of 1976(Fig. 5-11 ar e ci ted by Teng [74])

I 2' 2.1 210220J.I 31032O1973 M o n l h- D o l e

Fig. 6 Spikelikegroundwater radon anomalyobserved at theKu tzanstation8 day before theM - 7.9Luhuoearthquakeof1973.

5 (Ftb . 19751Dale

Fig 7 Spikelike gro undwa t e r anomaly before the 1973 Hai-cheng earthquake of M = 13, as observed at the Hotang ho t springsiteo f L iaoyang ,L i aonmg provi nce Af te r Th e G ro u po f H y d r o - C hem -istry ( I977|

- langshan Waler Uility Plant ~

15 20 25 30July 1976

Fig 8 G r o u n d w a t e rradonanomaliesobservedatthree stationsbefore the 1976 Tangsh anearthquake( M = 7 8) Top twotracesgivedata from sitesin (heepiccmral region,bottom tracegivesdata fromLangf ang s ta t ion , w hi ch is 130 km from the epicenter After W a n g(1978]

I 10 J O 3OI 10 20 301 10 2O 3OI 10 20 3O1976 JUN E JULY A UGUS T S EP T EM BER

Fig 9 G r o u n d w a t e rradon anomaliesobserved beforetheSun-p a n-P t ngwueanhq uakc showing a much longeranomalousduration.Afte r W a k u a (1978] Cross-hatching indicates above average read-ing s


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D o l e 1 5 ( M o y1 9 7 7 )

M 604 200km1

7 (March 1977)

13 ( H o y , 1977)Do te

Fig 10 Ground water radon anomaliesobservedat twolocationsm Peking byautomaticgroundwaterradon monitoring systems (Top)Peking Shicniao well data before the Lutai event. (Middle) PekingResearch welldata before the Chien-an event (Bottom)Peking Re-search welldata before the Lutaievent After Th e Group of Hydro-Chemistry [1977]a L , hour

F i g . 12 Anexperimentaldischargeo fwater(2), radon(3) and Hg (4)as a function ofstrain value (t) MPa bycompression of abasalt block(By VarshalG. M. etal.,[30])

N M C U u C S K E I)

- ool - ,

Fig 11 Gro undwa t e r radon anomaly observed before the 1978Izu Peninsula ear thquake( M = 7 0) Bot tom t race is anenlargedpor-tion of part of the top trace (H W a k i t a , wri tten communication,1 9 7 8 )

Generally, on the basisofobservationaldata, one can state that the greater themagnitudeof a seismicevent,- thegreateris the distance where precursors can berecorded- the earlier theprecursor signais appear- the larger is the signal amplitudeIt is commonly thought that increasing radon concentrations indicate forthcomingseismo-tectonic events,bu tuntilnow it has notbeendeterminedif there are anyspecificcharactenstics of radonoutput curveswhichcouldserveas an unequivocal indicatorfo rthe timeof earthquake shocksA wide variety of forms, durations and amplitudes of radon output curves have beenrecorded withinthe same regionsand dunngsimilarevents Theremightbe ( s e e also Fig1-12,16)- a singleor severalspikemaximums- amonotonousincrease in radon concentrationwith orwithoutany steady stateplateaubeforeth emainshock- a"wave"-type or faster chaotic fluctuations in radon contentswithout apparent regu-laritiesTh e durationo f precursorvariationscan beshort (severalhours) and long-term (severaldays, months and even years) The time before theshockcan be of the same ord er as thebackgroundvariationduration


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9 It has been noted that there is a wide spectrum of seismic background fluctuations ofprecursorcontent in the pore f luid which ma y deteriorate therecord of useful signalsInvestigations have shown that the background depends on local geological, hydrogeo-logicalan dg eochemicalconditions and on localseismicbackground But thisappearstobe suspicious, m the sense that the background has to be ruledby thesamelaws thata revalid for the 'useful precursorsignals10 Once more this shows the importance of a good knowledge of the aseismicseismichydrogeochemistry characteristics ofhydrogeological systemsselected for monitoringTh e bestar ethosewhich providethe maximu m sensitivity to transform strain variationsin g eochemicalsignals Thismeansthatany observationsystemmustbetunedto the givensite and precursor indicators But so far there are nopreciseguidelinesfor thischoice11 Fromthepointofviewofisotope hydrology,its scientificbackgroundandtechniques[12,21, 27, 29-34,a nd many others] providea widespectrum ofpossibilities to determinewateran dcomponent turnovertimesin hydrogeochemical systems,which couldplay animportant, perhaps even decisive, role As is shownin [17-18 andmanyothers],MeanResidenceTimes(MRT)o fwateran d dissolvedcomponentmay be the keyparametersfor acorrectmonitoring ofhydrogeochem ical precursorsignals12 In fact significant anomalieshave sometimes been observed not in the vicinity of somestrongearthquakeepicenters,but,on the contrary,where someweakseismicevents wererecorded Th eauthorofthis paperbelievesthatthereis nouniquereasonforthis behaviour,but itseemsthatrelaxation timecharacteristicsof the hydrogeochemicalsystemsare veryimportant However,till now thewhole m echanism of theradonvariationingroundwater,soil-air and gas exhalations,has notbeen fullyunderstood nor satisfactorilydescribedfo rprocessinga nd interpreting theobserved anomaliesi n termo fspace-time-strengthpre-diction characteristics

4.ASSUMED MECHANISMSA nu mber of studies havebeenpublished in which an attempt hasbeenmadeto explainradon and otherhydrochemicalprecursoranomalieswiththeoreticalmodels,which should enableto interpretand use them onitoringrecordsf orpredictingearthquakes W ithout pretending togive acompleteoverview, it isworthwhiletonotethe followinghypotheses- rock dilatationan dwaterdiffusion [8, 16,28,43,48],- avalanchefissureforming[8,16,43],-directstrain influenceo nemissiono fprecursorcomponentfromsolid intopore fluids[1, 5, 10, 12-15,29-33, 62 64,67-70,etc ],-activationo fconv ection-diffusion transport [10,11-14,45,68-70,73],- ultra-sonicand/orawiderspectrum of wave extraction(shaking) [12,26,29-33,37,70,73,77],- admixture off luids fromother(deeper)layers [2, 5, 10, 12, 33, 73,77],-changingof fissuresa nd porosity[28,30 33,39,43, 56,59,etc ],- mechanicaldeformations[30,43,77]For a long time, studieso nearthquake prediction wereorientedtowardsth e increaseo fobservation networksand the establishment of new detectors, indicators,etc TheCaliformanearthquake (1989)showed that it is not sufficient to just makepredictions This earthquakeoccurredin an area where thousands of detectors were connectedt o afully computerized tele

metric system even so, thiswas notsufficient Thismeans thatnew and betterconceptsa reneeded morethanadditional new detectors[65]Some specialists(Barsukov V L, et al [30,31 ,60])now thinkthatth eideaof a modernnonlinear dynamics with its concepts of chaos and collective behavior of mhomogeneousstructuredmedia is thepanacea longwaited for If this is so, one should revise all the inter-pretations recentlymadeThis approach may be connected with smergetics [61] as well as with the theory ofcatastropheswhich havebeen recently developed In anycase,n ew information is needed tofully understand the processes which are ruling hydrogeochemical (andother) precursorsMoreover,n ew ideasare required for the interpretation of recordeddata

5. RADONPRECURSORBEHAVIOR IN HYDROGEOCHEMICALSYSTEMS(PERFECTMIXING MODEL)Taking into accountthe relativelyshort life-timeof radon (halflife3 8days)and itsoriginas aradiumdecay product, one can concludethat radonanomaliesobserved in strain areaar eproduced in the vicinity ofobservationsites But,if radonis produced in the earthquakeseatsand then transported to surface and to farobservationsites,it wouldrequire transport velocityan d flow rateoff luidsso high , thatthey wouldbeimpossiblein groundwater[17] Thissupportthe occurrenceofsomeuniqueinitialm echanisms originated, asmentionedabove, by the straininthe earthquakeseatsas wellas at thedistancefrom themAdditionaltectonic straineffectsdecreasetheactivationenergyEaofprocesses (seeFig14) controlling theescapeof chemicalan disotopiccomponents from the rockmatrix into thepore solution Thoseprocesses could be calleddissolution,leaching,emanation, diffusion,formation andtransportof defects in themineral matrixlattice,etc It is wellknown thatdis-solution rate governed by the Arrhemus law,diffusion velocity by theFrenkel-Langmuir-Dashman-law, intensityof defectformationin solidbodiesby theSchottky-law,aswellas anyotherphysico-chemicalreactionsby the Glasstone-Ehnng law , areobeyinganinvariant functionQ ( t ) =Q01 (t) e (1)Q ( t ) is the variation of the componen tinput intoa solutephasefrom amineralmatrix,Tis an absolute temperaturem K ,kis theBoltzmannconstant,kt represents theaveragekineticenergy of a givenparticle( Rn molecule in ourcase) at the absolute temperature T, Q0, is aconstantfor thegivenparticlem a givensystem,If thereis a straino(r),thenthe activation energy (potentialbarner)willchange into[17,55]

(2)E O representsthemeanactivationenergyneededto transfera particlefromt hematrixintothe poresolutionin theunstrained state,an d%is a coefficientThis factis thoroughlyprovedm the thermo-kinetic theory ofbodies[55] Thus,the inputflow rate in thestressedstatemay berecognizedas afunction of theinternalmechanicalstraindevelopedin the body

(3)


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where c^j Kt ..

The physico-geochemicalmeaningofeqs.(l)-(4)is very simple.The transition velocityof aparticle from a solid matrix intoa pore solution (moregenerally, afluid) depends expo-nentially on theratioof theactivationenergyof the given transitionprocessto themeankineticenergyW of thegiven particleattemperature7"K. The parameters 01o r0and0 characterizethe processin unstrainedcondition(0(r)= 0).Y o is an energetico-structural parameterof thesolidmatrix,havingthe dimension of avolume[L3].Th e molecular-kinetictheory hasshownthaty0isproportionalto acharacteristic volume(in average occupiedby the particle ofgiven structural positions)and to alocal overstraino finterparticleconnections[55].The parameter y0stronglydependson the structuralscaleeffects,whereas g and 0do not depend onstructural effects. 0characterizesan activation energy ofdestruction ofinterparticle connectionsin the solidmatrix. Thismeansthat the activation energyfor anycomponent builtin a m ineral latticemusthave thesame orderofmagnitudeof sublimationenergy, dissolution orself-diffusion processes[55].Thismeansthatactivationenergy0mustbe of anorderof :-50-200kcal/moleforthe escapingofparticlesfromcrystallatticesdue to melting, solution,sublimation an ddiffusion;-20-200kcal/molefo rformation and migrationof defectsin crystal latticeas well as formigrationof anyparticleswithdefects throughth esolidbody;- 2-5kcal/molefo rdestructionof Van-der-Waalsbondsbetween m olecules;-2-10kcal/molefor sorption-desorption at thecontactsurface between matrixan dporefluid.In [27]we havealreadytried toevaluateactivationenergiesof radonemanationinmineralsusingpublisheddata on temperature dependency of emanation velocity. They appear in theorder of 8-13kcal/mole (foruranium ores), that is two to three timeshigher thant he bindingenergy i n liquidsa nd adsorbedlayers, but5-10 timesless than the particle contact energy insolid lattices. Thisdata is completely relevant to the energy of defect formation and defectmigration in solidbodies. These facts alsosupport activationenergiesof diffusion of He, Ne,Ar, Kr, Xe is in thesolidmineral phase(seereferencesin [27]).Despite all apparent discrepancies between such a variety ofprocesses as emanation,diffusion, sorption-desorption, solution-precipitation, defect formation-migration,theirkineticsis similar and depend on someparameterslikeQ 0,YO,E 0and a.

In orderto obtain amoreconcreteresultwe can use the solutionof ourearlierpublication[27] to describe the radon behavior in a stationaryhydrological system with perfect mixingregimeof water and its constituents. Additionallyit isassumedthat:- theinitialconcentration of radonin poref luid iszero,e.g.,C0=C(/=0);- theinputo fradoncaused bystrain variationsis describedby eq(3);- theexponentin eq. (3) may besubstitutedby itsTay lor's seriesdevelopmentin the firstapproximation asYo(0 |HF+-.=a,(0+Yo+... (5)

where(6 )

ThisY-valuemay be considered, in theframeworkof themodel,as a generalizedconversioncoefficient of radon transfer fromt hesolidmatrixintothe pore fluid.Using such an approximation of the previously obtained solution for stationary hydro-logical perfect mixing models [17-19], the following expression for time variations of thehydrochemical precursorcan be established:C(t) = / ' /r-O)d0+ (1- /' r-0)d0 (7)Itappearsthat frelatsto theobservationtime moment,but 0 is anintegrating timevariablein th einterval (0,f). Th edifference (t - 0) gives atime0 indays (months,years,etc.)beforethe observationt imet.It shouldb enoticed that \, =q/ V is ahydraulickinetic parameterof thegiven hydro-geological system:q is a recharge-dischargevolumetricflow ratean dV the storage volum e ofwaterin thesystem;th e inversevalue ofX ^is t =A^ '=V lq is the meanresidence (turnover)timeofwatercarryingradonorother components. If aprecursorcomponent isconservativeandstable, then and onlythen is itsresidence timeequal to that of water. A characterizesall possibleprocessesobeying thefirstorderkineticsby which components are lostbecausetheya re non-conservativeand/or unstable. For example,for radon one should takeinto account:- radioactivedecaywithth econstant~ ka;-irreversible lossesby anyphysico-chemicalprocesses like sorbtion, precipitation,etc.,withthe constantX ,pand by thehydraulicdischargewithconstantXw.Thus,

\... (8)

(9)By introducingthe residencetime characteristicof eachprocess,eq. (8)becomes:Now it ispossible to transform eq. (7)from the "X-form" intothe "T-form":

/ rJ rt;'e"A9CX?-0)d0+-c(1 -e""')+ t;1e~a\(r-0)d0 (10)Let usreturnnow to thephysico-hydrogeochemicalmeaning of the solution expressedbyeqs.(7) and(10).Th e firstexponentialterm on therightsideof eqs (7), (10)describesth einfluenceof theinitial content. Thesecond integral term characterizes the action of ahydraulic rechargewi ththe input component concentration Cf t ) . Th e third termgivest he injection of theprecursorcomponent causedby thenormal strain state,i.e. by 0(0 = 0, CJ(t)- 0 andC0= 0. Thelastintegraltermdetermines therequiredseismo-hydrogeochemicalsignal as a reaction of the systemto the strain variation a(f ) in thebulkrock.


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6. SOMEUSEFUL CONSEQUENCESIn spiteof therelativesimplicityof the model we reachsomevery importantconclusions,especiallyfrom theisotope hydrologicalan dgeo-seimologicalpointsof view1 A hydrogeochemical reactionof anysystemo nstrain stressescan be presented as aconvolutionoperationor sum oftimestrainvariations Thesear econverted intoa componentinput from the matrix intoporous fluid bymeansof aweighting function suchas the Green'sfunction for the given system and componentsIt iswellknown insystem analysisthatthisfunctioniscloselyconnectedwith theResidenceTime DistributionFunction(RTDFw)of water [17]

and with theRTDFcof agivenprecursor component(Rn,fo rexample)(12)(13)

These functions are interconnected with each other by the following one-to-one rela-tionshipv_A , _- C (0 are normalized to unit and have allpropertiesneededfor astatistical distribution. The first t-momentsof < 3 > and 4> care tw and T,respectively,whichsupportT ^, and T as themean residencetime ofwaterand componentsin thesystem3 Withalongperiodobservation(f t =A"')any system"forgets" the initialconditionsand,m addition, any "background"term is relaxed to the level ofc/A,whichreflectsa steady"background"state The Q/A valuecan beusedto determineA or (orQ0,and \,) usingth ebackground observationdata4 "Pure" current hydrochemical signals caused only by additional strain cr(r)can bepresentedasAC(0=C(0-

+X '+ V0(r-0)d0 (15)

5 Themaximum signaldepends onmaxima]values of the conversioncoefficienty andthe ratioXJA =^wIt isclearthatwithany otherconstantconditionsa maximal valueof theparameteris 1,whichcan bereachedwhen A - A^, orA.0and A.,, 0, e g whentheprecursor componentisstable ( A . = 0) andconservative( \ =0) like He, for instance Forradona s a noblegas,thecondition\ =0canbeadopted,butX^ 0 This means thatthemaximum valueofaradonsignal is proportional to

6 If the mean residence time of water t, (^40 days, practically), then1 and tne expectedsignals will be rather small. On the contrary,if T: W t an d-I, thent hesignal willb emaximal It is therefore preferableto select the systemwhichhas\, Taasmonitoringsite7 Thereis yetanothercausewhichdecreasesth epossibleuseful hydrochemical signalsThismeans thatthere is aninterrelation betweenth e durationof thestrain impact0(0 and themeanresidence timeTof theprecursorcomponent Supposmgthata strainvariationis animpulseone obtains0(0 = 0, f 0


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00 8 Theformof thehydrogeochemicalsignalsmuststronglydependon the relevantRTDFwand RTDFc(seeFig 15) and on theparameterswhichcan be determined using isotope tracertechniques developedinisotopehydrology For instance, the RTDFw of water($)is determinedby isotopes such a s t r i t ium, 1SO and deuterium To estimate ()> and itsparameterT w (o r Xw ),someartificial tracerscouldalsobe used

9 Suchparametersas Qaan dy (or Q and y0) can be evaluatedby using the hydrogeo-chemical data obtained during aseismic periodsor by interpreting hydrochermcal reactionso fthe system on sinusoidal tidal variations ofstrains10 Th eexperimentalwork shou ldconcentrateon f indingout theactivationenergyE ao fthe transfero fpossibleprecursorcomponents(Rn,He, Ar, Kr, Xe,CH^,etc )fromsolidmatrixinto porefluids That is why it is soimportantto arrange the experimentsin sucha waythatatemperature dependencyof the transferratewouldbe obtained11 Finally,th e resultsgivenherefor perfect mixing modelscan be generalized for anylinear system A reaction of a hydrochermcal system under strain impact is approximatelyproportionalto theconvolution integral of thegiven strain space-timevariation and to theres-idence timedistributionfunctions ofprecursor componentsin thesystem7. CONCLUSIONThereis agreatneed for- elaborating adequatedescriptiveand predictive modelsof formation andtransformationof hydrogeochemicalprecursorsignals,- working outalgorithmsto extract useful information from field data,- evaluating properconversion andrelaxationcharacteristics of the monitored systems inorder topredict earthquakes,- widening isotope hydrology techniquesto measureresidence time parametersof theprecursorcomponents,- generalizing andanalysingtypicalprecursordata inordertounderstandthe mechanismof their formation,- studying and m easuring all the parametersneeded (transporta nd dispersion character-istics,retardation factorsdue to sorption-desorption, emanation and/or leaching velocityand soon),- selecting the criteria for thebest sensitivity of hydrochermcal(andother) prec ursors tothe earthquakes and optimizing observation networksOncemore,itshouldbe emphasizedthata solution of theproblemof hydrogeochemicalearthquake precursors demands consolidatedan dcombinedefforts and developmentsof a widerangeo f specialists misotope hydrology,seismology, hydrogeology,geochemistry, physicochemistry,mechanics,m athematics,system analysis and so on Allthese specialists should begathered togetherwi thint he framework of an internationalp rogramme8. AN EPILOGUETh epresentpaperwasalmostready for publication when two eventsoccurred In Californiaanother strong earthquakeoccurredand in theSovietUnion a new issue of themagazine 'NaukaiZhizn (Scienceand Life)[65 80] published a wide analysis of allaspectsof the catastrophical

Fig. 15 Typical variation of radon and other hydrochemicalprecursor's concentrations in hydrogeological systemswith a perfect mixing regime. Reactions on:a--stressb-constant impulse stressc-linear increasing strainstressThe curves arerelatedto differentmeanresidencetimesi of thecomponenti nporous fluid: t = =T =T


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R" , r e l a t i v , u n i t M-7

TW8Fig 16 Rn concentration variation in subsoil atmosphereprior to andaf ter the Spitak earthquake,Armenia,1988

Spitak earthquake m Armeniaon December 7,1988 Thisenables us to addsomedatato thosealready shownIn Fig 16, a variation of theradon concentrationin the subsoilatmosphereis given whichwa srecordedbeforea nd aftert hemainshockm Lenmakan (Armenia),bu tanalysedonlyafterthe earthquake Itseemsvery likelythatthe earthquakecouldhavebeen forecast on grounds ofthe radon anomalies which were easily detectable and which were similar to other strongearthquakeforerunners liketheTashkentone Therewas aremarkableincrease of subsoilradonwhich started to increase 3months beforethe earthquakeTh elastmeasurement beforethe main shock was taken on the earlymorning ofD ecember7,1988and afterthat,measurementsweretaken againon December15,1988 In themiddleofNovemberthe radonconcentrationstabilized to a level of 30% abovethe background thiswasan almost definitive signal ofwarning of a forthcoming earthquake The radon signalswereaccompanied by groundwater level variations Accord ing to thedata of G Vartanian fromVSEGINGEO,Moscow,detectablevariationsof regionalgroundwaterlevel distributionswereobserved which reflected the strainstate of theregionbeforethe shock Unfortunately,thesedatawerenot known andinterpretedin time,but onlyaposterioriTh e Califonuaninformation from[66]clearly demonstratesthatit is not sufficientto havehundreds ofdifferent monitorswhich are connectedw ith computerized systemsfor theon-lineprocessing ofobserveddata it isalso necessarytohavegoodconceptualmodelsand algorithmsfor interpreting precursor records, anddrawingcorrectconclusionswithrespectto time, placeand strength of an earthquakeFrom thispoint ofviewth eauthorbelievesthat withoutusingthe latestdevelopmentsmisotopehydrologym order to evaluateproper relaxation parametersof thesystem it will not bepossibleto make adecisivesteptowardsa reliableapplication of hydrogeologicala nd hydrogeochermcal earthquakeprecursors

10.

11.

12.

13.CD

REFERENCESAbdullajevA.U.,MedjitovaZ.A.,KrigerL.P.,Nurgazijeva V.V ,Consequencesof theappearingofprecursorsbeforet hestrong earthquakein northern Tian-Shan (inRussian),FizikaZemli,1988, N7,p.23-32AbduvalijevA.K.,VoitovG.I.,EudakovV.P.,Radon precursorbeforesomestrongearthquakes in CentralAsia(i nRussian),Doklady AkademiiNaukSSSR,1986,291, N4,p.924-927AndrewsJ.N., Radiogenic and inertgases ingroundwaters,paper presentedat 2nd InternationalSymposiumon Water-RockInteraction, Strasbourg,France, Univ.LouisPasteur,CentreNat. RechercheSei., Inst.Geol.,A u g . 17-25,1977AntsilevichH.G.,An attempt to forecast themomentoforiginofrecenttremorsof theTashkentearthquake through observations of the variationof radon(inRussian), Akad.Nauk.Uzb.SSR,1971,p.188-200AsimovM.S.,YerzhanovZ.S., KalmurzaevK.Y., KurbanovM.K.,MavlyanovG.A.,Negmatullaev S . K . NersesovI.L., UlomovV.l.,The state of earthquake prediction research in the SovietRepublics ofCentral Asia(inRussian), International Symposium onEarthquakePrediction,Rep.11-12, UNESCO,Paris,1979, p.20BasentsianM.M., KuchminO.A., RudakovV.P.,Somefeaturesof dynamics ofsubsoilradon fields in theconditionof an Armenian prognostic poligone.Izvestija AkademiiNaukArm. SSR, aukioZemleXLI, Nl ,1988,p.65-67BirchardG.F., LibbyW.F., Soil radon concentrationchangespreceding andfollowing four magnitude4.2-4.7earthquakes on the SanJacinto faultinsouthern California,J.Geophys.Res.,85,1980,p.3100BraceV.F.,MiacbkinV.l.,DietrichG.H.,SobolevG.A.,Two models toexplainearthquakeprecursors.Collection ofSoviet-Americanworksonearthquake prediction,Dushanbe-Moscow,1976, p.9-21BrandesK., Earthquakeprediction- interdisciplinaryco-operationatBerlinonearthquakeprotection.Amts.-Mitteilungsbl. Bundesanst.Materialpruef.1988,V.18(4),p.623-628BulashevichY.P.,ChalovP.I-, TuzovaT.B., etal.,Helium contentsa ndrelations between the uraniumsria isotopesin waters onfaultzones innorthern Kirgizia(inRussian).Fizika Zemli,1976,NI,p.78-84ChalovP.I., KomissarovV.V.,VasiljevI.A.,Radonmigration duringdetermination in theaquifer-well-systemby accumulation of its decayproducts(in Russian).Geokhimia,1986, N7,p.1049-1052ChalovPI., TuzovaT.V., Al'okhinaV.M.,Isotopeparametersingroundwatersof theearth crustfaults.1980,Him, Frunze,p. 104ChalovP.I.,uzovaT.V.,l'ochinaV.M.,Short-timevariationsofradioisotope parameters offault waterin theearth crust(i nRussian).FizikaZemli,1977, N8,p.62-71


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29. Hydrogeochemical andhydrodynamicalstudiesat the prognosticpoligonesof Kirgizia(inRussian).Frunze,"Him", 198830. Hydrogeochemical precursorsof earthquakes (inRussian).1985, Moscow,Nauka ,p.28631. Hydrogeochemistry studies at prognost icpoligones.Alma-Ata, Nauka ,1983,p.11232. Hydrogeoseismologicalstudiesin easternFergana,1978, Tashkent, Fan ,p.18933. Isotopesinhydrology(inRussian).1977,Tashkent,Fan,p.29234. Isotopeinhydrosphere(inRussian).Abstractsof the 3rd All-UnionSymposium(29 May - 1June,1989,Kaunas),p.33635. JiangF., Li G., The applicationof geochemical methods inearthquakeprediction in China,report,W.K. KelloggRadit.Lab., Calif.Inst,ofTechnol.,Pasadena,198036. KaboV.A.,MusinY.A.,IdrisovaS., Some features of radon escape intowater atlong termuniaxial compressionof rocks (inRussian).IzvestiaAkad. NaukSSR, FizZemli,1989, 7,p.103-10637. KeilhakK.,Groundwaters(inRussian). Transi,fromGerman,Leningrad-Moscow,ONTINKTPUSSR,1935, p.49438. KingC.Y.,Episodoic radonchangesin subsurface soil gasalongactivefaults andpossiblerelationtoearthquakes,J.Geophys.Res.,85,1980,p.306539. King.C.Y.,Geochemical measurements pertinent to earthquake predicti on.Journ.Geoph.Res., 980,85,NB6,p.305140. KomissarovV.V.,ChalovP.I., On utilizat ion of the water-gassystemtoseismoprediction goals(inRussian).Geokhimia,1987,6,p.904-99741. Materials of the IXRepublic Scientific Conferenceofyoungscientists(inRussian).Frunze,"Him",198842. MelvinJ.D.,ShapiroH.H.,CoppingN.A.,Anautomated radon-thoronmonitor for earthquakepredictionresearch,Nucl.Instrum.Methods,1978,p.153,23943. MiachkinV.l., Preparing processeso f earthquakes (inRussian).M., Nauka,1978,p.23244. MilkisM.P., Hydrogeologicalandhydrometeorological precursorsof thecatastrophical earthquakeinAshkhabad.DokladyAkademiiNaukSSSR,1983,273,5,p.1091-109445. Modern geodynamicsandearthquakeforcast(inRussian).1987,Kiev


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groundwaterradoncontent.Northwest SeismolJ.,1984,6, NY,p. 83-88

GAS-GEOCHEMICAL APPROACHEST OEARTHQUAKE PREDICTIONChi-Yu K IN GU SGeological Survey,Menlo Park, California,UnitedStates of AmericaAbstractConcentrations of a wide range ofterrestrial gases inground water and soil air have commonly been found tobeanomalouslyhighalongactivefaults,suggestingthatthefaults may bepathsofleast resistancefor theoutgassingpro-cessofthe"solid" earth. Anomaloustemporalgas-concentra-tion changeswithdurationsof afewhoursto many monthshavebeen recordedbefore manylargeandsome smaller earth-quakesatstationsmostlylocated alongactivefaults at epi-centraldistancesof asmuchasseveral earthquake-sourcedi-mensions wherethe associated coseismicstrainchanges areestimated to be assmallas10~8.This result suggeststhattheearthquakesand the associated anomalies are bothinci-dentalresultsof some small butbroad-scaleepisodicstrainchanges in thecrust. Suchstrainchangesmay beamplifiedat theearthquakeand anomalysitesand,ogether wi th su f-ficient pre-existing stresses,may reach some critical levels(above half fracture strengths) forgenerationof the earth-quakesand anomalies. Significantgas-concentration changeshave also been observed at times of other known crustaldisturbances, suchasundergroundexplosions, ground-waterpumping, andearth tide,and from stressed rocksamplesinlaboratory experiments. Theseresultssuggest severalpos-sible mechanismsfor the deformation-related gas-emissionchangesthatinvolvemovementofcrustal fluidsofnon-uni-formchemical composition or enhanced water/rockreactionat newly created rocksurfaces. However,gas-concentrationchanges mayalsobecausedbyvariousnon-tectonicenviron-mentalchanges, which mustbe recognized in the searchoftrue earthquakeprecursors.

INTRODUCTIONScientificmeasurementsforearthquake predictionhavebeen made extensivelysince the mid-1960'sinmanyseismicallyactivecountriessuch as USSR ,China,Japan, an d U S A . Th e geophysical an d geochemical data often show temporalchanges interpreted to bepremonitory to some largeormoderate earthquakes.


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Some of the reported anomalies are considered by other investigators to bemarginal in their tectonic significance, because similar changes may be causedby other concurrent environmental variations such as rainfall or groundwaterpumping. In a previous paper (King, 1986)13' I gave an overview ofgas-geochemical studies carried out in various seismic regions of the world anddiscussed possible effects of various environmental changes. In the presentsupplementary paper, Ishowa collectionof representativegas-geochemical datasetspublishedin theliteratureandsuggestaphysicalbasisfor someof the observedfeaturesin thedata,whichmaystillneedto besubstantiatedbyfur ther studies.

SPATIAL ANOMALIES AND ACTIVEFAULTSActivefaultsa recommonlycharacterizedb yanomalouslyhighconcentrationsof a widevariety ofterrestrially generated gases (e.g., radon,helium, hydrogen,mercury, and carbon dioxide) in ground water and soilair. This observationsuggeststhatthe faultsmay bepathsofleast resistanceforgasesin the "solid"earth to escapeto the atmosphere. Figure 1shows, forexample, the result ofIsraeland rnsson (1967)8' whomeasured radon and thoronconcentrationinsoil air at 1-m depthalongtransectsperpendicularto the strikes of several faultsnear Aachen. They attributed the radon anomalies that were accompanied by

thoron anomaliestoenrichmentofparentnuclides,and theotherradon anomaliesto upward migration ofradon. Irwin and Barnes (1980)6' showed that theworldwide distributions of springs in which the groundwater HCOj1 contentexceeded 1,000ppm generally coincided with major seismic belts (Figure 2).Figure 3showsheliumanomaliesalongactive faults, especiallyatintersectionsoffaults,observed by Yanitskiy et al.(1975)28\ wh omeasuredheliumconcentrationingroundwaterat depthsof30-50m innorth Kazakhstan. Similar anomalieswerealsoobserved fo rseveralothergases (e.g., H2,C2,Rn, andHg).

TEMPORALVARIATIONSASSOCIATED WITH KNOWNCRUSTALDEFORMATIONA number of field experiments have been conducted in which the gasconcentrations in ground water or soil air were found to change in response tok n ow ncrustal strain changescaused by such events as underground explosions,ground-waterpumping,andearthtide. Figure4showssoil-airradonanomaliesobserved by Wollenberg et al. (1977)26> at fivemonitoringsites near the nuclearexplosion Esrom in the NevadaTest Site. The anomaly amplitudes decreasedwithincreasing distance from ground zero, an d wereapparently no t related tobarometric pressurevariations recorded nearby.

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Distance of ampling point from fault,mtrFigure 1. Concentration of radon and thoron at 1-m depthinsoilair over faultsnear Aachen.The concentration was measured intransectsat rightangle to thestrike of the faults, which ha d previously been located by geological methods.A section of the bedrock under each transect isschematically indicated. (AfterISRAELa n d B J R N S S O N , 1967.)8>


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N)

[zuSeismiczone COZ localityFigure2.W orldwidedistributionofseismic zones (shaded)andlocalitiesofspringswith high CO2 discharges (HCO"1 content > 1000 ppm). (After IRWIN andBARNES,1980)6'.

Figure5showsthe resultofSugisaki (1981)23\who observed a correlationbetween tidal strain and the He/Ar concentrationratioin gas bubbles from amineral spring in Japan. Similar results werealsoobserved forother gases atseveral other "sensitive11 sites,suggesting that terrestrialgasemissions at suchsitesmay beresponsivetocrustal strainchanges as low as10~8.

(A, Sbttskiy otfc looriunt

Stepay*k lyncllDollarn M km

Figure 3. Anomalous high helium concentration in groundwater at depths of30-50 malong consolidated and slightly permeable fault zones (dashed lines)(A), and along active fault zones (B),especially at intersections of faults innorthKazakhstan. The helium content in 1 0 ~ ~ 4 m/is


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1000 ina330 -

3 4 6 6August 1878Ga*d ""Pnerlctemprature3 4 5 6Strainandatmospheric pressure

uo102'If-2 Too ~2IID

po01

13 14 16 t6 17 18December 1979 Ga* Ind tmoapherle temperature. . . . . . i . - , . . i ... i . . . . . . . . . .t .13 14 15 16 17 18Strain and atmospher icpressureFigure 5. Comparison oftemporal variations of He/Ar concentration ratio inga s bubblesi n a mineral spring at ByakkoSpa,Japan (circles) with theoreticaltidalstrain(areal dilation;dottedcurve), atm ospheric pressure (solid curve), andtemperature(dashed curve)for twotimeperiods. (After SUGISAKI,1981.)23)

EARTHQUAKE-RELATED GASCHANGESGas-concentration changeshavebeen reportedlyobserved before manylargeand somesmallerearthquakesin variouspartsof theworld.Someofthesechangesmight be coincidental, caused by non-tectonicenvironmental changes, such asrainfall andground-water pumping, or byinstrumentalor humanerror. Others

are probably trulyrelatedtoearthquakes,andtheyappear to showsome generalfeaturesincommon: (1)They tendto occurmostly alongactive faults,especiallyat theintersectionsandbendsoffaults,at epicentral distances up toseveral timesthe corresponding earthquake-sourcedimensions. (2) Thedurationsrange froma fewhoursto manymonths. The occurrence,or theincreasingoccurrences, oftheshort-term (spike-like) anomaliesappearsto be usefulto predict the time ofearthquakes (perhapswithina fewdaysto a fewweeks). (3) Thespatialextentand thedurationofthe intermediate-termanomalies generallyappeartoincreasewith, and thus may be useful forpredicting,earthquake magnitude. (4) Theamplitudeof theanomalies doesnot appear to show consistent correlationwitheither earthquakemagnitudeor epicentral distance (incontrast to the case ofexplosion shown in Figure 4). Following are some representative examples ofearthquake-relatedgaschanges,whicharedeemed relativelyreliable,becausetheywererecorded in multiplecomponents,by independent methods orobservers,oratmultiplesites,orbecausethey can be comparedwi tha reasonablylongset ofbackgrounddata.Radon AnomaliesBeforethe Tangshan Earthquake

Radon contentof ground water hasbeenmonitored at m anywellsinnorthernChina shortly after the magnitude 7.2 Xingtai earthquake in 1966 (see K i n g(1985)12',for a reviewof radonstudiesin China). Figure6 shows the locationofthemagnitude7.8Tangshanearthquake in1976and monitoringstations.Most ofthestations that recorded thesupposedly intermediate-termand/or short-termanomalies(increases, whicharesometimes difficult to recognize, inFigures7 and9) werelocated alongmajoror secondary faultzones up to anepicentraldistanceofabout500 km (Figures 8 and10). Theintermediate-termanomalies (gradualincreasesbeginning inlate 1973andlastingup to several years) may berelatedtoboth the Haicheng (1975, magnitude7.3)an dTangshanearthquakes on account oftheir proximityintime(1.5years)andspace(350km). Onestation(Guanzhuang)was inoperationlong enough tocoverthemagnitude7.4Bohai earthquakein1969also; the associated anomaly, whichpeaked after the earthquake, is shorterin duration but comparable inamplitude. The anomaly amplitudes are small,ranging from 10 to100%and do notdependsignificantlyonepicentral distance(Figures 8 and10). Short-termanomalies (spike-like increasesmostly,Figure 9)wererecordedinincreasingnumbers at the wellsa fewdaysto weeksbeforetheTangshan main shock and severalstrongaftershocks (Figure11). However,veryfew ofthemwererecorded in theimmediate epicentralareas.


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roO) 7.4*

Figure6. Locationsofmonitoringstationsthatshowedintermediate-termground-water radon-concentrationchanges (circles with horizontal stripes), short-termchanges (circles with vertical stripes), and no significant change (small circles)beforethe1976Tangshanearthquake (solidcircle) innorthern China. Thick solidanddashed linesindicateobservedand inferred major faults,respectively. (AfterYINGetal., 1978.)29'

The above-mentionedradon anomaliestypifythose observedelsewhere in theworld.Figure12 shows aplotof anomalyamplitudesv s.epicentraldistancefor aworldwidedata set compiled byHauksson (1981)4^. Th earealextentsof anomalyoccurrences are unexpectedly large, andincreasewi thmagnitudesoftheassociatedearthquakes. However, the anomaly amplitudes do not depend significantly onepicentral distanceor earthquake magni tude. Thethresholdof therelated strainchanges wasestimatedto be~10~8, comparablewith tidalstrainchanges.

HAICHENG TANGSHAN7.3 T.S* rA SCO 4O KM

HAICHENG TANGSHAN7.3 7 8i ;

Figure 7. Time series of groundwater radon concentration (monthly averagevalues)recorded at sensitivestationsin northernChina. Arrowsindicatethe timesof1975Haichengand 1976Tangshan earthquakes. (After Y I N Getal.,1978.)29'

10 0 18 I S U I C E UK)Figure8. Ampl i tudeofintermediate-term ground-waterradon anomalies (relativeto background levelinmonthlyaveragevalues) as afunctionofepicentral distancefrom the 1976Tangshanearthquake.(Based on data inYINGetal.,1981.)30)


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1 0 0 0p

10 20 30J U L . H 7 6

( b )

12 16 20 24 ISJ U L ,1976T I M E ( O A T )

tosi

Figure9. Timeseriesofground-water radon concentration,showingshort-termchangesbeforethe1976Tangshanearthquake. (After YINGetal.,198l.)30' (a)Daily readings, (b) Continuousdataat Langfangstation.

Gas-geochemicalanomaliesin southernCalifornia during1979Gas-geochemicalmeasurementsweremadeextensively in southernCaliforniaby several research groups. Figure 13shows helium and radon concentrationsrecorded by C h u n g (1985) and colleagues at Arrowhead hot spring on the SanAndreas fault. These concentrationsvaried synchronously and were anomalousat the timeof several significant local earthquakes includingthe magni tude 4.8Bi g Bear earthquake in 1979,but not the magni tude 4.1earthquake in 1983.

I E P I C E I T I A l D I S T M C E U 1 0 0 9

Figure 10. Amplitude ofshort-term ground-water radon anomalies (relativetobackground levelin daily readings) as a functionofepiceutraldistancebeforethe1976 Tangshan earthquake. (Based ondatainYINGetal.,198l.)30)

nnr iA iMiimyL i i f l i i t * i I I nfFiiiiiiV1- ] diMM im n u n n i f i n i 1980

110'i l ' i i 'Figure 11. Frequency of occurrence ofshort-term radon anomalies recorded atwaterwellsin northern China.Indicatedare occurrences of Tangshanearthquakean d larger aftershocks (magnitude> 6 0 ,circles) (A f t e r Y A N G etal.,1982~ >


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to00 soo

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1/77 7/77 1/76 7/7 1/7 7/79 1 /80BARROWHEAD SPRINGS

s :/v"Vv\r-1/77 777l/T778179779

MORMONSPRINGS C

1/77 7/77t/70T/78 1/78778/BOFigure14. Timeseriesofradon concentrationsin watersamples takenfromthreeUSCstationsalong the SanAndreasfault within20 km of themagnitude4.8 BigBear earthquake (indicatedby arrows) in southern California. (AfterTENG andSUN, 1986.)25)

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Figure 15. Timeseriesof ground-water radon concentrations recorded at fourCaltechstationsin southern California. (After SHAPIROetal.,1985.)22)

whichmay beresponsiblealsofor theincreased number ofmoderateearthquakesin southern California, includingth e magni tude6 .6 ImperialValleyearthquakeonOctober 15, 1979about 290 km away fromtheir sensitive stations.Geochemicalanomaliesduring1980incentralCalifornia

King e t cd.(1981)16) and O'Neil and King(1981)19) recorded some gas andrelatedchemicalchangesin groundwaterat twowellsalongthe SanAndreasfaultnear San JuanBautista,California (Figure 16) at the beginningof a sequence ofearthquakesin1980; the largestof the earthquakeshas a magnitude of 4.8 andepicentraldistancesofseveralkilometers. Figure 17 showsthe resultofin situmeasurementsofwater level,temperature,salinity, electricconductivity,and pHat a30-mdeepartesian well(MissionFarmCampground). Thewater levelhadgenerally beenrising sincetwoyearsbeforetheearthquake;itreachedthe groundsurface (thewellbecame self-flowing) at aboutthesame timeas amagnitude4.0earthquakethatoccurred25 kmaway,orabouttwomonthsbeforethemagnitude4.8 earthquake at an epicentral distance of 6 km. Simultaneously, the watertemperature becamemoresteady,and thesalinity/conductivityincreased bymanystandard deviationsfromthe background level.Similar resultswereobtainedfromchemicalanalysesofwater samples (taken from the wellat thesame timeas theinsitumeasurement) in the laboratory, especiallyforcontentsofCa++,Mg++,F-, Cl-, NOJ,SO^- ,andHCOJ (Figure 18) andstableisotopes


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COo MISSION FARM CAMPGROUND1 9 7 7 ; 1976| 1979

Figure17. Time seriesof water level,temperature,salinity, electric conductivity,and pH at the MFCwell. Horizontallines indicate pre-anomaly mean value onestandarddeviation.Verticallines indicateoccurrence ofearthquakesofmagnitude>4.0; labeledare magnitude and epicentraldistancein km. (After KINGet al.,

' 2 4 > > 10 > atseveral stations near the magnitude 6.8 earthquake on September 14, 1984in

5 ""P* *ooL

'- "C r L

v 1100to

.- JJJl..'.:'1 9 7 9 . 1980 .198'Figure 18. Time series of ionconcentrations (mg/L) in watersamples from theMFC well. NOJ' are inmg/LN. Symbols as in Figure 16. (After KINGetal.,198l.)16'

th e western Nagano Prefecture ofcentral Honshu,Japan. Sugisaki an dSugiura(1986)24' observed conspicuousgas anomaliesat a fumarole and threespringsabout1-3 monthsbeforethe earthquake. Figure23showstheHe/Ar,N2/Ar ,andCH4/Ar concentrationratiosin bubblegases from a mineral spring (Byakko)onan activefault about50 kmfromtheepicenter.Theyattributedthe anomalies tochanges in the emissionrateofsome deep-seatedgas due to earthquake-relatedchangesinporepressure.The gasbubblesalsoshowed someanomalousincreasesin hydrogenconcentrationbeginningaboutone monthbeforethe earthquake. TheH2 anomaly w asattributed to reactionbetween groundwater an d newly formedcrack surfaces in the rocks. S a n o et al.(1986)20) observed some post-earthquakeincreases (comparedwi th valuesobtainedi nNovember1981)o f3He/4Heratiosinbubblegases from several hot springs located lessthan10 km from a fault that


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(a) MISSION FARM CAUPGftOUND

8 0

-}III1I1

40 48 41K t 12

j A S O K o l J F M A K j j A i o i i t i l j ritr i**o IMI(b) MSSION FARM CAMPGROUN3

Figure 19. (ajTime seriesof 6D and618Oinwater samplesfrom the MFCwell,(b) AD vs. 6'8Ofor the water samples collected before and after the isotopicanomalyrelated to the largest andclosestearthquake to the MFCstation. Thestraightlineis the "meteoricwaterline". (After O'NEILandK I N G ,1981.)19)

wa s possibly formed at the time of the earthquake. They suggested thatthe earthquake w as triggered by an upward migration of some3He-rich fluidsassociated wi thmagmaintrusion beneaththesourceregion. Katohet al.(1986)10'observed anomalousincreases ofradon concentration in soil ga s (superposed onsomeapparentlyseasonalchanges) at severalmonitoringstationslocated onthreeactive faultsabout25 to 100 km away from the epicenter,beginningabout 1 to2yearsbeforethe earthquake (Figure 24). Theseanomalies coincided withcoda-waveduration anomalies observed bySato(1988)21'.They are similar inshapetosoil-gasradon anomalies recorded elsewhere(seee.g., King,1978)n'.

ST FRANCS RETfCAT

Figure20.Timeseriesof water level,temperature, salinity, electricconductivity,and pH at the SFR well.Symbolsas in Figure 16. (After K I N Getal.,198l.)16'XT F R ANC I S R E T R E ATI 9 T T , 1976 19

X OO-V ::- T - ot

aooi- 100-

:E"rtt

lU " , .. i . .J..1-1.J . 11^i injjL-iT 1979l I98O 1981Figure 21 . Timeseries of ion concentrations (mg/L) inwatersamples from theSFR well. NO^ and NOJ are in mg/L N (After KING et al , 1981 )16 >


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COto SAINT fftANCIS RETRET

Figure 22. Time series of CD and A180 in water samples from the SFR well.Symbolsas in Figure 16. (After O'NEILan d K IN G ,1981.)19>

POSSIBLEMECHANISMSFOREARTHQUAKE-RELATEDGAS-GEOCHEMICAL ANOMALIESSeveral possiblemechanisms havebeenpostulatedbyvariousinvestigators toexplain theearthquake-relatedgas anomalies, mostinvolvingtectonicallyinducedmovement of crustal fluids of different concentrations or enhanced water/rockreactionat newlycreated rock surfaces. They includeincreased upward flow ofdeep-seated fluids to the monitored aquifer or holes, gas-richpore fluidsbeingsqueezedout of rockmatrix intothe aquifer,mixing ofwaterfromanotheraquiferthrough tectonically created cracks in theintervenient aquiclude,increased water/rock interactions,andincreasedgas emanationby or from newlycreatedcracksin the rocks to the pore fluids. Some of these possibilities have been testedin laboratoryexperiments. For example, Holub an d Brady (1981)5) monitoredradonemanationand microcrackingactivity in auranium-bearinggranitesampleunderuniaxial loading. Theyobservedaninitial decreasein emanationpossiblyassociated with closure of pre-existing cracks in the rock an d then significantincreasesin both theemanationandmicrocracking activityat aloadof about one-

half of theultimatestrength (Figure 25). Suchincreaseswereobserved repeatedlyuntil largerincreasesoccurred at time of fracture. Kita et ai. (1982)17> crushedgraniteandquartzsamplesunder moistconditions at temperatureof25-270C,and found increased Hbrelease wi thtemperatureup to about 200C; at highertemperaturestherelease decreased wi thtemperature (seeFigure26 forgranite).Theyattributedthe H2generation to chemicalreactionbetween water and Si andSi-O radicalson the fresh surfacesof the crushedrocks.

'

/ V ^ ' * j I \1^

wv,92 )

T i m eFigure 23. Time seriesof He/Ar, Nj/Ar, CH4/Ar concentration ratios (dailyaverage valuessmoothed witha sliding10-day window) in bubblegases at theByakko Spring, Japan. Arrows indicate the occurrence of the magnitude 6.8WesternNagano ear thquake in 1984. (AfterSUGISAKI andSUGIURA ,


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to c200

to T"""")V *rMitmhiro

T.D

Figure24. Timeseriesofradonconcentration in soil gas (TD: a-particletrackdensityin weeklyexposed cellulose nitrate film; MA:movingaverage) at threesites locatedon the MedianTectonic Line, the Matsushiro fault, and the Aterafault, which are, respectively, 100, 100, and 25 kmaway from the 1984WesternNaganoprefectureearthquake. (After KATOHet al., 1986.)10)

5,000l

23 24 21 26

COCO Figure 25.Radonemanation (uppercurve) froma uranium-bearinggranitic rockunderuniaxialstress (lower curves). (After H O L U Band B R A D Y , 1981.)5>

1*

granit

10 0 200 300

Figure 26. Amount of Hj release from crushed granitic rocks at varioustemperaturesand in two different atmospheres. (AfterKITA et aL,1982.)17)

King(1978)n) invokedatectonically-inducedverticalflowofcrustal gasestoexplainsoil-gasradon anomalies recorded along the San Andreas fault incentralCalifornia. As shownschematically in Figure27,radon concentrationgenerallydecreasesslowlywith heightinnear-surface atmosphere,andincreasesrapidly (by3 orders of magnitude) with depth in near-surface soilgas, approachingamaximum at a depth of several meters. Because of the high subsurfaceconcentration gradient,asmall upward/downward flowcan significantly increase/decreasethe radonvalue monitoredat afixedshallowdepth ofabout1/2 m.Ki ngconsidered aone-dimensionalmodel inwhichthesoilistreatedas ahomogeneousporoushalf-spacewith uniformradon productionrate. On the assumption thatradon migratesbymoleculardiffusiongovernedby Pick'slaw and byflowgovernedbyDarcy's law andthatthe radon concentration isnegligiblysmallat thesurface,it was shownthatthe steady-stateconcentrationCis afunction ofdepth zasMows (e.g., , Clements , 1974)2> :

where2(eAJ9)1/2

(1)

(2) f> isradon productionrate,A s itsdecayconstant,ei ssoilporosity,D ismoleculardiffusion coefficient ofradon in the soil, an d v isapparent soil-gas flow velocity


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CO

R A D O N CONCENTRATIONFigure27.Schematic diagramofradon concentrationinatmosphereand soilairnear thegroundsurface as afunctionofelevationand depth. C,0is concentrationin undisturbed soilair atgreatdepth;Ca


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COCJ 1

*.*Figure3 0. Schematicrepresentationo f flowpores ( 4 > p ) , diffusionpores (AD),andresidual pores ($R)in rock. Fluid usually flowsthrough th e flow pores but notthe diffusion or residual pores, unless the rock is significantly stressed. (AfterNORTON and KNAPP, 1977.)18>

values in 1979 may be partlyrelatedto the magnitude 5.9Coyote Lakeearthquakeon August 6 ,1979about27 km awayon the samefault.Similar modelsmay explainearthquake relatedanomalies in other soil-gascomponents (He,HS, Hg,etc.) that have similar concentration-versus-depthprofiles. Concentration gradients ma yalsoexist in wall rocks of aquifers, whichma y b econsidereda sconsistingof networksof "flowpores" (Figure30; seeN or t onand Knapp, 1977)18' that transportmeteoric waters fromrecharge areas to the

monitoredspringsorwells. Since groundwaterin theflowporesusuallyhasshorterresidencetunein thegroundandless reactionwithrocks,itcontainsless dissolvedterrestrialgas (and other chemicalsubstances) thanthe fluidsin the "diffusion"and "residual"pores in the wall rocks(Figure30).Thus thetectonically inducedflow from the normally diffusive and isolated pores to the flow pores isexpectedto introducewatersofanomalously highgas and ion content.The samemodelsmay explain theresultsof somelarge-scalepumpingtestsconducted in China, where the radon contents in the pumped wells tended toincrease,whereasthose in thesurroundingobservationwellsto decrease (seeKing,1985)12> .

STRAIN FIELD RESPONSIBLE FOR EARTHQUAKESAND ANOMALIESThe general observation that gas-geochemical (andother) anomalies arewidely spread hi space but confined mostly to active fault zonessuggests thatthey (and he associated earthquakes) are possibly incidental results of some

be produced by a number ofprocesses, including magma intrusion and episodicfault-creep eventsbelowseismogenicdepths. The amplitudesofchangeneed notbe very large (> 10~8), but may be greatly amplified alongpre-existing faultzonesand especially at their intersections andbends. The localstrainincreasesat such places, when combined with sufficient pre-existing strains, may reachcritical levels(above half fracturestrengths) togeneratetheobservedtectonic andphysical anomalies (as defined byIshibashi)7) andearthquakes. The anomaliesm ay disappear beforeor after theearthquakesfor avarietyofreasons, includingstress relaxation associated withthe earthquakes, healingof the fault zone, andexhaustionof gas supply (in thecaseof gas anomalies). The concept ofmultiple-pointconcentration of abroad-scaleepisodic strain changemayalsoexplainwhyearthquakesand the variousanomalies sometimesoccurindistinctyetapparentlyrelatedclustersinspaceandtunealong the same or different faults,why itseemsdifficult topredict earthquake location wi threasonable precision, whythereis alackofdetectableseismic-wavevelocityanomalies (the dilatant zonesmay be toothincompared with seismicwave lengths and too widely distributed), and whythere is a lack of observedone-to-one correspondence between earthquake andanomalyoccurrences.O ne pieceo fevidence supporting thepossibility ofstrain amplification alonga faultzoneiscoseismicstepsrecordedoncreepmetersalongthe SanAndreasfault(King et al, 1977)14). If interpreted asstrainsteps (seeexample inFigure31),1556 UTFEBRUARY 24,1972

g


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COO)

IO KO 3O 40'LOCATION A L O N G FAULTT R A C E (km)

Figure 32. Theoretical shear strain steps alongthe surface trace of a verticalstrike-slip fault in a uniformhalf-spacecausedby aun i form offset of 16 cm overarectangular faultarea10 kmlongand 2 to 10 km in depthrange. (After KINGetal-,1977.)14)their amplitudesare about 2ordersofmagnitude larger than expectedfor thestrain fieldof the associated earthquake, based on a dislocation modelon theassumptionof ahomogeneouscrust (Figure32).

AcknowledgementsThispaperbenefitted from reviewsbyW.P. Irwin,J.C.SavageandespeciallyW.R.Thatcher.

REFERENCES1. Chung,Y., RadonVariationat Arrowheadand MurrietaSprings:ContinuousandDiscreteMeasurements, PAG EOPH,122,294-308,1985.2. Clements,W.E.,Theeffectofatmosphericpressure variationon thetransportof 222Rn from the soil to the atmosphere, Ph.D. thesis, New Mexico Inst.MiningTechnol.,1974.3. E, X., and Yang, Y.,Characteristicsofradon anomalies before largeearth-quakes,in Collected Reports in Seismo-Hydrogeochemistry, pp.93-107,StateSeismologicalBureau, Division of Scientific Research, Beijing (in Chinese),1978.

4. Hauksson, E., Radon content of groundwater as an earthquakeprecursor:Evaluation ofworldwidedataandphysicalbasis, J. Geophys.Res.,86, 9397-9410,1981. ~5. Holub, R.F.,and Brady, B.T.,The effect ofstress on radonemanation, J.Geophys.Res.,86,1776-1784,1981.6. Irwin,W.P.,and Barnes,L,Tectonic relationsofcarbon dioxide dischargesandearthquakes, J.Geophys.Res.,85,3115-3121,1980.7. Ishibashi,K., Twocategoriesofearthquakesprecursors,physicaland tectonic,andtheirrolesin intermediate-termearthquakeprediction, PAGEOPH,126,687-700,1988.8. Isreal, H., and Bjrnsson, S., Radon (Rn-222) and Thoron (Rn-220) in soilair over faults, Z.Geophys.,33,48-64,1967.9. Junge, C.E., Ai rchemistry and radiochemistry, Academic Press, Ne wYorkand London,1963.10. Katoh,K.,Takahashi,M., and Yoshikawa,K., Anomalousincreaseofradonconcentrationasprecursoronsomeactivefaultsnearepicenterof the westernNagano prefecture earthquake, 1984using cellulosenitrate film, Zisin (inJapanese)39,47-55,1986.11. Ki ng ,C.-Y., Radonemanationon SanAndreas fault ,Nature,271, 516-519,1978.12. King,C.-Y.,Radon monitoring forearthquake predictioninChina, Earth-quakePrediction Research, 3,47-68,1985.

13. King,C.-Y.,Gas geochemistry applied to earthquake prediction: Anoverview,J. Geophys.Res.,91, 12,269-12,281,1986.14. Ki ng , C.-Y., and Slater,L.E.,A comparison ofsoil-gas radon and crustalstraindata (abstract),EarthquakeNotes, 49(4),44 ,1978.15. King, C.-Y., Nason, R.D.,and Burford,R.O.,Coseismicsteps recorded oncreepmeters along the San Andreas fault, J. Geophys.Res.,83, 1655-1662,1977. ~~16. King,C.-Y.,Evans,W.C.,Presser,T., andHusk,R.H., Anomalous chemicalchanges inwell waters and possible relation to earthquakes, Geophys.Res.Lett., 8, 425-428,1981.17. Kita,I.,Matsuo,S., andWakita,H., I2generationbyreactionbetweenEyOand crushed rock: An experimental study on I2degassing from the activefaul t zone,J. Geophys.Res.,87,10,789-10,795,1982.18. Norton,D., andKnapp, R.,Transport phenomenain hydrothermalsystems:Thenatureofporosity,Am. J. Science,77,913-916,1977.19 . O'Neil,J.R.,andKing ,C.-Y.,Variationsinstableisotope ratiosofgroundwa-tersinseismically active regionsofCalifornia,Geophys.Res. Lett-,8,429-432,1981.20 . Sano,Y.,Nakamura ,Y.,Wakita,H.,Notsu,K., and Kobayashi,Y.,3He/4Heratio anomaliesassociatedwiththe1984 western Naganoearthquake: possiblyinducedby a diapiric magma, J. Geophys.Res.,91, 12291-12295,1986.


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TECDOC 0726 Geochemical Precursors of Earthquakes and Volcanic Eruptions