Radon (Rn-222) AS A PRECURSOR Radon (Rn-222) AS A PRECURSOR OF SEISMIC ACTIVITY: A REVIEWOF SEISMIC ACTIVITY: A REVIEW

Krishan Kant Krishan Kant

Principal, Aggarwal Post Graduate Principal, Aggarwal Post Graduate College, Ballabgarh, Faridabad (NCR) -College, Ballabgarh, Faridabad (NCR) -

121 004 (Haryana) India.121 004 (Haryana) India.

National Conference on Natural Hazards and Mitigation at

Eshan College of Engineering, Farah (Mathura) U.P.December 04 – 05, 2012

Earthquake DevastationsEarthquake Devastations

ABSTRACTABSTRACT The analysis of radon and seismicity has established correlation The analysis of radon and seismicity has established correlation

and radon has been used as a precursor in the prediction of and radon has been used as a precursor in the prediction of earthquakes, volcanic activity, fault mapping and earthquakes, volcanic activity, fault mapping and characterization of geothermal sources. characterization of geothermal sources.

Well-established reports indicate that the release of large Well-established reports indicate that the release of large amount of radon depends to a larger extent on the tectonic amount of radon depends to a larger extent on the tectonic disturbance of the host materials. disturbance of the host materials.

Anomalous radon changes in ground water and soil gas have Anomalous radon changes in ground water and soil gas have been reported for several earthquakes at favorably selected been reported for several earthquakes at favorably selected monitoring stations located at distances of several hundred monitoring stations located at distances of several hundred kilometers from their respective epicenters. kilometers from their respective epicenters.

The present paper discusses analytical techniques for The present paper discusses analytical techniques for measurement of radon using Solid State Nuclear Track measurement of radon using Solid State Nuclear Track Detectors (SSNTDs) and reviews the origin and mechanism of Detectors (SSNTDs) and reviews the origin and mechanism of observed anomalies in concentration of radon and their observed anomalies in concentration of radon and their relationship to earthquakes.relationship to earthquakes.

LIST OF SOME SIGNIFICANT EARTHQUAKES IN LIST OF SOME SIGNIFICANT EARTHQUAKES IN

INDIA AND ITS NEIGHBOURHOODINDIA AND ITS NEIGHBOURHOOD DATE EPICENTRE LOCATION MAGNITUDE

Lat( Deg N ) Long( Deg E )

1819 JUN 16 23.6 68.6 KUTCH,GUJARAT 8.0

1869 JAN 10 25 93 NEAR CACHAR, ASSAM 7.5

1885 MAY 30 34.1 74.6 SOPOR, J&K 7.0

1897 JUN 12 26 91 SHILLONGPLATEAU 8.7

1905 APR 04 32.3 76.3 KANGRA, H.P 8.0

1918 JUL 08 24.5 91.0 SRIMANGAL, ASSAM 7.6

1930 JUL 02 25.8 90.2 DHUBRI, ASSAM 7.1

1934JAN 15 26.6 86.8 BIHAR-NEPALBORDER 8.3

1941 JUN 26 12.4 92.5 ANDAMAN ISLANDS 8.1

1943 OCT 23 26.8 94.0 ASSAM 7.2

1950 AUG 15 28.5 96.7 ARUNACHAL PRADESH-CHINA BORDER 8.5

1956 JUL 21 23.3 70.0 ANJAR, GUJARAT 7.0

1967 DEC 10 17.37 73.75 KOYNA, MAHARASHTRA 6.5

1975 JAN 19 32.38 78.49 KINNAUR, HP 6.2

1988 AUG 06 25.13 95.15 MANIPUR-MYANMAR BORDER

6.6

1988 AUG 21 26.72 86.63 BIHAR-NEPAL BORDER

6.4

1991 OCT 20 30.75 78.86 UTTARKASHI, UP HILLS

6.6

1993 SEP 30 18.07 76.62 LATUR-OSMANABAD, MAHARASHTRA

6.3

1997 MAY 22 23.08 80.06 JABALPUR,MP 6.0

1999 MAR 29 30.41 79.42 CHAMOLI DIST, UP 

6.8

2001 JAN 26 23.40 70.28 BHUJ , GUJARAT 6.9

2004 Dec 263.30°N 95.87°E

Off west coast northern

Sumatra, India

9.0-9.3

2005 Oct 0834.493°N 73.629°E

Kashmir Himachal Pradesh

Pakistan India

7.6

2007 Dec 31 DELHI NCR India

2011 Sept 07 28.38°N 77.12°E Sonipat, Haryana; Delhi

4.2

2011Sept 18 27.723°N 88.064°E Sikkim 6.9

2012 March 0528.808°N 76.772°E

Bahadurgarh (New Delhi and

NCR)

4.9

2012 April 1417.4°N 73.8°E

Koyanagar, Maharashtra

4.9

PRECURSORS AND THEIR PRECURSORS AND THEIR SIGNIFICANCE IN SEISMIC ACTIVITYSIGNIFICANCE IN SEISMIC ACTIVITY

PRECURSOR: PRECURSOR: Anomalous events or Anomalous events or processes that may precede an processes that may precede an earthquake are called earthquake are called precursor eventsprecursor events and might signal a coming earthquake.and might signal a coming earthquake.

The art and science of predicting The art and science of predicting an earthquake or volcanic eruption an earthquake or volcanic eruption through precursory methods has through precursory methods has acquired an important role.acquired an important role.

--

There are four different time There are four different time frames for earthquake frames for earthquake

predictionprediction Long term: Long term prediction involves a time frame of a Long term: Long term prediction involves a time frame of a

decade or more and with limited usefulness for decade or more and with limited usefulness for public safety.public safety.

Intermediate term: Intermediate term prediction would fall Intermediate term: Intermediate term prediction would fall into a time into a time span of a few weeks to a few span of a few weeks to a few years, and again it would not be of great years, and again it would not be of great practical usefulness. practical usefulness.

Short term: It is the short term prediction that is specific Short term: It is the short term prediction that is specific information on the time and location of an information on the time and location of an earthquake given within days, weeks, months - earthquake given within days, weeks, months -

not not years - that would be useful for any kind of years - that would be useful for any kind of public public safety. safety.

Impending:Impending:

Among the precursor events that Among the precursor events that may be important are the may be important are the

following:following:

There exist many traditional premonitory signs like There exist many traditional premonitory signs like abnormal behavior of certain species of animals and insects abnormal behavior of certain species of animals and insects (Rikitake, 1976), change of water level in wells before the (Rikitake, 1976), change of water level in wells before the occurrence of earthquake, Ground Uplift and Tilting occurrence of earthquake, Ground Uplift and Tilting (Poitrasson et al, 1999)(Poitrasson et al, 1999) , , Foreshocks Foreshocks  etc., but they have yet etc., but they have yet to receive recognition by scientific community.to receive recognition by scientific community.

On the other hand, there exist some other precursors like On the other hand, there exist some other precursors like emission of seismic electromagnetic signals (Fraser-Smith et. emission of seismic electromagnetic signals (Fraser-Smith et. al., 1990), Change in electrical resistivity of rocks, thermal al., 1990), Change in electrical resistivity of rocks, thermal anomaly, large amount radon emanation from subsoil etc., anomaly, large amount radon emanation from subsoil etc., which rely upon experimental database.which rely upon experimental database.

Precursors help managing and minimizing disasters !Precursors help managing and minimizing disasters !

Foreshocks:One Successful Prediction: The Feb. 4, Foreshocks:One Successful Prediction: The Feb. 4,

1975, magnitude-7.3, Haicheng quake in China1975, magnitude-7.3, Haicheng quake in China

It destroyed half of the city It destroyed half of the city of about 100 million of about 100 million inhabitants, damaged more inhabitants, damaged more than 2,000 bridges, such as than 2,000 bridges, such as this one, as well as homes, this one, as well as homes, transport pipelines, transport pipelines, hydraulic facilities, but hydraulic facilities, but resulted in only a few resulted in only a few hundred deaths because of hundred deaths because of the successful evacuation.the successful evacuation.

In 1976, Chinese earthquake prediction suffered a major blow when the Tangshan earthquake in northern China struck unpredicted and killed at least 240,000 people.

RADON AND MEASUREMENT RADON AND MEASUREMENT TECHNIQUESTECHNIQUES

Radon is distributed in soils,

rocks, sediments,

geofluids, ocean waters and gases in fumaroles.

Some atoms of radon, produced by radium decay

on land, enter the soil gases therefore its

migration is possible only to a few mm or may

escape into the atmosphere.

Factors Controlling Factors Controlling EmanationEmanation

Transmission Characteristics of BedrockTransmission Characteristics of Bedrock Mineralogical EffectsMineralogical Effects Uranium/Thorium ConcentrationUranium/Thorium Concentration Carrier FluidsCarrier Fluids Weather and Soil TypesWeather and Soil Types

Gases measured in soils can be strongly disturbed by Gases measured in soils can be strongly disturbed by environmental variables like atmospheric pressure, soil environmental variables like atmospheric pressure, soil temperature, rainfall, soil moisture etc. temperature, rainfall, soil moisture etc.

MEASUREMENT TECHNIQUESMEASUREMENT TECHNIQUES Methods of measuring radon in general depend upon the amount of time Methods of measuring radon in general depend upon the amount of time

over which the sample to be tested is collected- over which the sample to be tested is collected- grab or spotgrab or spot sampling, sampling, continuouscontinuous sampling and sampling and integratedintegrated sampling. sampling.

Continuous monitoring of radon is done when real-time concentration is Continuous monitoring of radon is done when real-time concentration is required to be known and this involves monitoring through methods like required to be known and this involves monitoring through methods like continuous flask monitor, automated two-filter monitor, diffusion continuous flask monitor, automated two-filter monitor, diffusion electrostatic monitor etc.electrostatic monitor etc.

Integrated type of monitoring yields a single average concentration for an Integrated type of monitoring yields a single average concentration for an extended time, from few days to weeks or more. This involves methods like extended time, from few days to weeks or more. This involves methods like Plastic bag method ; Polonium –218 collection method ; Charcoal method ; Plastic bag method ; Polonium –218 collection method ; Charcoal method ; Semiconductor Detectors and Particle Track-Etch method. Semiconductor Semiconductor Detectors and Particle Track-Etch method. Semiconductor detectors are normally used for real-time measurements and are adorned detectors are normally used for real-time measurements and are adorned with better resolution, stability, and windowless operation and facilitate with better resolution, stability, and windowless operation and facilitate discrimination between different ionizing particles. Another version- discrimination between different ionizing particles. Another version- Alphameter, uses silicon diffused junction semiconductor detector and is Alphameter, uses silicon diffused junction semiconductor detector and is provided with a cavity chamber in which air/gas sample-having radon is provided with a cavity chamber in which air/gas sample-having radon is filled. It can be used to operate at a selected threshold value of energy of the filled. It can be used to operate at a selected threshold value of energy of the ionizing alpha particle emitted from radon or radon daughters which is ionizing alpha particle emitted from radon or radon daughters which is built-up in a closed container or hole. Proportional counters in conjunction built-up in a closed container or hole. Proportional counters in conjunction with with Particle Track- Etch detectorsParticle Track- Etch detectors have also been used. have also been used.

The Particle Track-Etch Method The Particle Track-Etch Method A widely used passive method when integrated radon measurements are A widely used passive method when integrated radon measurements are

required over a required over a longlong periodperiod as precursor for prediction of volcanic, as precursor for prediction of volcanic, seismic activity, and earthquake. seismic activity, and earthquake.

Uses foils known as Uses foils known as Alpha-sensitive Plastic FilmsAlpha-sensitive Plastic Films (ASPFs) which have (ASPFs) which have merits over other methods when used in measurement of radon. merits over other methods when used in measurement of radon.

Technique is a sensitive, portable, low cost, electronics-free, completely Technique is a sensitive, portable, low cost, electronics-free, completely free from gamma-ray and beta –particle interference, besides it free from gamma-ray and beta –particle interference, besides it furnishes more details and larger contrasts than the simpler radiometric furnishes more details and larger contrasts than the simpler radiometric methods.methods.

However, it also suffers from limitations like it is a passive device and However, it also suffers from limitations like it is a passive device and

experience also shows that while using ASPFs, the disequilibrium experience also shows that while using ASPFs, the disequilibrium problems of/and mobility of the immediate parent i.e., Ra-226, and problems of/and mobility of the immediate parent i.e., Ra-226, and other precursors including uranium, or even the leaching of uranium other precursors including uranium, or even the leaching of uranium down dip and leaving radium/daughter products behind, may result in down dip and leaving radium/daughter products behind, may result in as a record of anomalies.as a record of anomalies.

PRINCIPLE OF THE PRINCIPLE OF THE TECHNIQUETECHNIQUE

The passage of ionizing particles like alphas, through insulating dielectric materials, popularly known as Solid State Nuclear Track Detectors (SSNTDs), creates narrow, latent damage trails on atomic scale. These trails are known as “tracks”.

The track-core enhanced chemical reactivity and this fact is The track-core enhanced chemical reactivity and this fact is exploited in chemical amplification of these tracks to visible exploited in chemical amplification of these tracks to visible etch-pits or holes to be counted either manually through etch-pits or holes to be counted either manually through optical microscope or to be counted automatically (Spark optical microscope or to be counted automatically (Spark Counter). Counter).

Spark Counter for track counting

Tracks in LR-115 SSNTD)

Optical MicroscopeOptical Microscope

In the present context of radon measurement, In the present context of radon measurement, the SSNTDs selected are alpha-sensitive and also the SSNTDs selected are alpha-sensitive and also known as known as ASPFs.ASPFs. These include thin foils of These include thin foils of Cellulose nitrate (some commercially available Cellulose nitrate (some commercially available ASPFs include Kodak products like CN-85; LR-ASPFs include Kodak products like CN-85; LR-115 type II, Lexan polycarbonate; CR-39(allyl 115 type II, Lexan polycarbonate; CR-39(allyl diglycol carbonate) etc. The chemical used as diglycol carbonate) etc. The chemical used as etchant for post-irradiation track etchant for post-irradiation track amplification(countable through optical amplification(countable through optical microscope) is normally aqueous 2.5 N NaOH, microscope) is normally aqueous 2.5 N NaOH, KOH, LiOH solutions used at temperatures KOH, LiOH solutions used at temperatures ranging from room temperature to 70oC for a ranging from room temperature to 70oC for a period ranging from 1-7 h.period ranging from 1-7 h.

Radon Thoron Twin Chamber Dosimeter

System

DETECTOR USED: LR-115, Type II DETECTOR USED: LR-115, Type II Solid State Nuclear Track Detector Solid State Nuclear Track Detector

(SSNTD)(SSNTD)It Senses and SignalsIt Senses and Signals

The ASPFs used in conjunction with Proportional Counter The ASPFs used in conjunction with Proportional Counter (ASPFs may also be used alone even) for the fieldwork (ASPFs may also be used alone even) for the fieldwork involving radon emanation. A simple device consisting of involving radon emanation. A simple device consisting of plastic cup of about 10 cm height, 3 cm diameter, bottom plastic cup of about 10 cm height, 3 cm diameter, bottom fitted with an ASPF of size ca. 2 cm x 2 cm while open mouth fitted with an ASPF of size ca. 2 cm x 2 cm while open mouth is covered with a plastic membrane to eliminate thoron and is covered with a plastic membrane to eliminate thoron and water condensation.water condensation.

In another version, radon measurement in In another version, radon measurement in soils are carried out by means of a sampler, soils are carried out by means of a sampler, each composed by a thin ASPF (normally each composed by a thin ASPF (normally LR-115 or CR-39) placed in a 30 cm long LR-115 or CR-39) placed in a 30 cm long PVC tube, inside a second 1 m long PVC PVC tube, inside a second 1 m long PVC tube of bigger diameter. Samplers are tube of bigger diameter. Samplers are buried at the site of study about 1m to few buried at the site of study about 1m to few tens of meters below earth’s surface. Alpha tens of meters below earth’s surface. Alpha particles from radon decay are registered.particles from radon decay are registered.

The obse

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the

The obse

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the

radon c

oncentra

tion in

soil

gas and

radon c

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soil

gas and

ground wate

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ground wate

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initi

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vestig

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initi

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vestig

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on

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precu

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on

earthquake

precu

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phenomena.

Radon is one of

the

phenomena.

Radon is one of

the

geophysical

precu

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of

geophysical

precu

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of

earthquakes.

earthquakes.

Emanometry Technique

Groundwater Emanometry

Soil-Gas Emanometry

RADON AS PRECURSOR : RADON AS PRECURSOR : MECHANISMS AND MODELSMECHANISMS AND MODELS EXPERIMENTAL REPORTS ON RADON AS A PRECURSOREXPERIMENTAL REPORTS ON RADON AS A PRECURSOR

Various anomalies in the domains of geochemical and hydrological traits preceding Various anomalies in the domains of geochemical and hydrological traits preceding earthquakes have been reported since 1960. earthquakes have been reported since 1960.

Such anomalies have acquired and played a significant role in predicting such events and have Such anomalies have acquired and played a significant role in predicting such events and have also become a part of monitoring seismic activity world wide. also become a part of monitoring seismic activity world wide.

Besides some other pre-cursors, the behaviour of terrestrial gases have been extensively Besides some other pre-cursors, the behaviour of terrestrial gases have been extensively studied in recent years in seismically active regions. studied in recent years in seismically active regions. Soil gasSoil gas concentration and in particular, concentration and in particular, the measurement of subsurface radon may prove to be a useful tool in forecasting eruptions.the measurement of subsurface radon may prove to be a useful tool in forecasting eruptions.

The daily and long –term integrated measurement of radon are carried out in soil and in The daily and long –term integrated measurement of radon are carried out in soil and in ground water alongwith various meteorological parameters viz., temperature, pressure, wind ground water alongwith various meteorological parameters viz., temperature, pressure, wind velocity, rain-fall and relative humidity which help decide the true changes in radon velocity, rain-fall and relative humidity which help decide the true changes in radon concentration unaffected by environmental disturbances. Radon in soil-air investigations using concentration unaffected by environmental disturbances. Radon in soil-air investigations using additional source of radon voluntarily implanted at experimental sites show that radon additional source of radon voluntarily implanted at experimental sites show that radon anomalies are primarily due, if not exclusively, to deeper fluid motion acting as transport anomalies are primarily due, if not exclusively, to deeper fluid motion acting as transport vectors.vectors.

Integrated radon signals have also been found to vary Integrated radon signals have also been found to vary considerably prior to an earthquake. Similarly, it is now considerably prior to an earthquake. Similarly, it is now known that increase in volcanic activities are also known that increase in volcanic activities are also accompanied by a substantial increase in radon accompanied by a substantial increase in radon concentration (Chirkov,1976; Cox and Cuff,1981). concentration (Chirkov,1976; Cox and Cuff,1981).

Since 1927, radon is known to be associated with gases in Since 1927, radon is known to be associated with gases in fumaroles and thermal springs. Radon is constantly fumaroles and thermal springs. Radon is constantly emanated from the earth in minute quantities and larger emanated from the earth in minute quantities and larger emanations have been found either prior to an approaching emanations have been found either prior to an approaching earthquake or after the event had passed. earthquake or after the event had passed.

The analysis of radon emission and earthquake occurrence The analysis of radon emission and earthquake occurrence can be traced back to an analytical investigation made by can be traced back to an analytical investigation made by Okabe (1956) where it was established that Okabe (1956) where it was established that there existed a there existed a positive correlation between the daily variation of atmospheric positive correlation between the daily variation of atmospheric radon content near the ground surface and the local seismicradon content near the ground surface and the local seismic activity at Tottori, Japanactivity at Tottori, Japan. .

The fact that radon signals can be related to earth stresses The fact that radon signals can be related to earth stresses was first put forward by Sodovsky et al. (1972) and King was first put forward by Sodovsky et al. (1972) and King (1978). It was found that the radon content in water samples (1978). It was found that the radon content in water samples drawn from a deep well changed before the occurrence of an drawn from a deep well changed before the occurrence of an earthquake. earthquake.

There are large number of reports available providing evidence of There are large number of reports available providing evidence of radon anomalies (2 to 3 folds the normal range of seasonal, monthly or radon anomalies (2 to 3 folds the normal range of seasonal, monthly or yearly variations) in ground water, and soil as precursory to yearly variations) in ground water, and soil as precursory to earthquakes of moderate to large magnitudes (See for example, Kraner earthquakes of moderate to large magnitudes (See for example, Kraner et al.1964; King 1985;Virk et al.1998;Singh et al.1991;) et al.1964; King 1985;Virk et al.1998;Singh et al.1991;)

Earlier, Ulomov and Mavashev (1967) had also found that the radon Earlier, Ulomov and Mavashev (1967) had also found that the radon concentration in a deep acquifier had changed even a year before an concentration in a deep acquifier had changed even a year before an earthquake of intensity 5.3 occurred in Tashkent. earthquake of intensity 5.3 occurred in Tashkent.

However, it is of interest to note that even reports confirming the fall in However, it is of interest to note that even reports confirming the fall in concentration of radon prior to earthquake are also available (Birchard et concentration of radon prior to earthquake are also available (Birchard et al.1980; Talwani et al.1980).al.1980; Talwani et al.1980).

Monin and Seidel (1991) have described an experiment involving a Monin and Seidel (1991) have described an experiment involving a network of 35 in-soil measuring stations operating track detectors of network of 35 in-soil measuring stations operating track detectors of radon in the southern part of Ecuador where radon was constantly radon in the southern part of Ecuador where radon was constantly measured and monitored for nine months. An earthquake of M6.1 measured and monitored for nine months. An earthquake of M6.1 occurred near Reventador. It was found that 14 stations out of 35 occurred near Reventador. It was found that 14 stations out of 35 produced a clear abnormal signal at the same time in spite of the fact produced a clear abnormal signal at the same time in spite of the fact that they were scattered over an area of 400 km2 and a few of them also that they were scattered over an area of 400 km2 and a few of them also showed negative anomalies as reported by others (Cai et showed negative anomalies as reported by others (Cai et al.,1984;Wakita et al.1985). It is interesting to note that at the time of al.,1984;Wakita et al.1985). It is interesting to note that at the time of the event, no visible changes in the atmospheric parameters were the event, no visible changes in the atmospheric parameters were observed which could have been used as an explanation to the observed which could have been used as an explanation to the happening of the event.happening of the event.

Anomalous changes in radon concentration before an earthquake Anomalous changes in radon concentration before an earthquake suggest that radon monitoring can serve as an additional suggest that radon monitoring can serve as an additional technique in the earthquake prediction programme (Virk et al. technique in the earthquake prediction programme (Virk et al. 1990).1990).

Increased levels of radon gas (222Rn) in wells is a precursor of Increased levels of radon gas (222Rn) in wells is a precursor of earthquakes recognized by the IASPEI.earthquakes recognized by the IASPEI. Spring at Bad Brambach Spring at Bad Brambach (Vogtland, Germany), (U.Koch & Jens Heinicke, 1994) and radon (Vogtland, Germany), (U.Koch & Jens Heinicke, 1994) and radon levels in Ground water in in the southern part of Nishinomiya levels in Ground water in in the southern part of Nishinomiya city, Japancity, Japan (Igarashi, 1995).(Igarashi, 1995).

Connection between the radon concentration in groundwater and Connection between the radon concentration in groundwater and springs and earthquakes might be used for earthquake prediction springs and earthquakes might be used for earthquake prediction by using ionisation chamber (Friedmann and Hernegger; 2001).by using ionisation chamber (Friedmann and Hernegger; 2001).

Data collected along the Hayward and Anatolian faults near Data collected along the Hayward and Anatolian faults near Berkeley, California convincingly supports the notion that a Berkeley, California convincingly supports the notion that a relationship between radon outgassing and seismic activity does relationship between radon outgassing and seismic activity does indeed exists (Holtmann-Rice and Cuff; 2003).indeed exists (Holtmann-Rice and Cuff; 2003).

Spring water and soil radon gas monitoring: A search for possible Spring water and soil radon gas monitoring: A search for possible precursors of earthquake activity in the Marmara region (NW) precursors of earthquake activity in the Marmara region (NW) Inan,  (Setal, 2003).Inan,  (Setal, 2003).

PROPOSED MECHANISMS AND PROPOSED MECHANISMS AND

MODELSMODELS Although several constraints from laboratory experiments, mathematical Although several constraints from laboratory experiments, mathematical

modelling and modelling and insituinsitu hydraulic experiments have also been described hydraulic experiments have also been described but the but the physical mechanisms responsible for these variations are still under investigation.physical mechanisms responsible for these variations are still under investigation.

Initially, the Initially, the Dilatancy Diffusion ModelDilatancy Diffusion Model and several other similar models and several other similar models suggested that radon anomalies were related to mechanical crack growth in the suggested that radon anomalies were related to mechanical crack growth in the volume of dilatancy, or to changes in the flow rate of ground water. volume of dilatancy, or to changes in the flow rate of ground water.

Another model suggests that the radon anomalies be due to Another model suggests that the radon anomalies be due to slow crack growthslow crack growth controlled by stress corrosion in a rock matrix saturated by ground water. It is controlled by stress corrosion in a rock matrix saturated by ground water. It is argued that crack growth by stress corrosion should precede any mechanical argued that crack growth by stress corrosion should precede any mechanical crating in a wet environment. crating in a wet environment.

Atkinson and Wilkins (1979) had confirmed experimentally that geological Atkinson and Wilkins (1979) had confirmed experimentally that geological materials can suffer crack growth at very low strain rates in the presence of materials can suffer crack growth at very low strain rates in the presence of high humidity while mechanism of stress corrosion suggests that high humidity while mechanism of stress corrosion suggests that the occurrence the occurrence of radon variations may depend upon strain rate and local conditions like rock of radon variations may depend upon strain rate and local conditions like rock type, elasticity of the media present, pattern of micro earthquakes, degree of type, elasticity of the media present, pattern of micro earthquakes, degree of saturation, temperature, stress intensity factors and other hydraulic properties.saturation, temperature, stress intensity factors and other hydraulic properties.

Haukson and Goddard (1981) have given an empirical relationship between Haukson and Goddard (1981) have given an empirical relationship between magnitude M and distance D where an earthquake can be predicted on the magnitude M and distance D where an earthquake can be predicted on the basis of radon anomalies as M = 2.5 log basis of radon anomalies as M = 2.5 log 1010D - 0.43D - 0.43

King (1985) had suggested King (1985) had suggested Compression MechanismCompression Mechanism for radon for radon release according to which release according to which the anomalous high radon the anomalous high radon concentration may be due to an increase in crustal compression concentration may be due to an increase in crustal compression before an impending earthquake that squeezes out the soil gas into before an impending earthquake that squeezes out the soil gas into the atmosphere at an enhanced rate which in turn may perturb the the atmosphere at an enhanced rate which in turn may perturb the vertical subsurface radon concentration profile such that thevertical subsurface radon concentration profile such that the deeper deeper soil gas having more radon is brought to the detection level.soil gas having more radon is brought to the detection level.

Such behaviour is likely to support the Such behaviour is likely to support the PORE COLLAPSEPORE COLLAPSE (PC) (PC) model generating an upward motion of pore fluids acting as model generating an upward motion of pore fluids acting as radon careers. radon careers.

However, a theoretical model, devised on the basis of analysis of However, a theoretical model, devised on the basis of analysis of transient states show that large amounts of radon are expected to transient states show that large amounts of radon are expected to show during a short duration prior to an earthquake or an show during a short duration prior to an earthquake or an eruption. eruption.

On radon origin various competitive models have been discussed On radon origin various competitive models have been discussed and number of successful earthquake predictions have been made and number of successful earthquake predictions have been made by measuring pre and post –seismic events as a function of time by measuring pre and post –seismic events as a function of time period and environmental parameters.period and environmental parameters.

Thomas (1988) suggested a model on radon anomalies in ground water based Thomas (1988) suggested a model on radon anomalies in ground water based upon the phenomenon- the upon the phenomenon- the Increased Reactive Surface AreIncreased Reactive Surface Area (IRSA) model. a (IRSA) model. According to this model, microfracturing prior to major seismic events is According to this model, microfracturing prior to major seismic events is responsible for precursory increases in ion and gas concentrations.responsible for precursory increases in ion and gas concentrations.

The substantial variations observed in the nature are due to the fact that radon is The substantial variations observed in the nature are due to the fact that radon is transported at faster or slower rate by careers. The variations can be explained transported at faster or slower rate by careers. The variations can be explained quantitatively by using the curves as proposed by Kraner et al. (1964) and later quantitatively by using the curves as proposed by Kraner et al. (1964) and later by Fleischer and Mogro-Campero (1979). by Fleischer and Mogro-Campero (1979).

The experiment conducted by Tidjani et al. (1990) is worth mentioning which The experiment conducted by Tidjani et al. (1990) is worth mentioning which established that the behaviour shown is an evidence of a mechanism based upon established that the behaviour shown is an evidence of a mechanism based upon the variation of pore fluids motion induced by stresses occurring at depth rather the variation of pore fluids motion induced by stresses occurring at depth rather than by a dramatic sudden increase of radon released from the bedrock.than by a dramatic sudden increase of radon released from the bedrock.

Singh et al. (1991) have also reported on the occurrence of an earthquake of Singh et al. (1991) have also reported on the occurrence of an earthquake of magnitude M3.8 at an epicentral distance of 100 to 400 km at Amritsar and magnitude M3.8 at an epicentral distance of 100 to 400 km at Amritsar and Kangra valley, Himachal Pradesh, India. It was concluded that observed radon Kangra valley, Himachal Pradesh, India. It was concluded that observed radon anomalies were mainly earthquake related and the observed radon concentration anomalies were mainly earthquake related and the observed radon concentration patterns during the earthquake events are similar and may be explained by the patterns during the earthquake events are similar and may be explained by the IPE ModelIPE Model suggested by Mjachkin et al.,1975. suggested by Mjachkin et al.,1975.

By and large, the radon in case of By and large, the radon in case of anomalies correlated with a anomalies correlated with a geophysical event may be geophysical event may be considered having considered having two possible two possible originsorigins-either it comes from a deep -either it comes from a deep origin( the degassing of the magma origin( the degassing of the magma in case of a volcanic eruption or in case of a volcanic eruption or the crushing of uranium rich the crushing of uranium rich minerals of the bedrock in case of minerals of the bedrock in case of an earthquake) or only being an earthquake) or only being locally displaced by other pore locally displaced by other pore fluids whose motion is triggered by fluids whose motion is triggered by the forthcoming eventthe forthcoming event..

CONCLUSIONCONCLUSION Despite the array of possible precursor events that are possible Despite the array of possible precursor events that are possible

to monitor, successful short-term earthquake prediction has so to monitor, successful short-term earthquake prediction has so far been difficult to obtain.   This is likely because:far been difficult to obtain.   This is likely because: The processes that cause earthquakes occur deep beneath the surface and The processes that cause earthquakes occur deep beneath the surface and

are difficult to monitor.are difficult to monitor. Earthquakes in different regions or along different faults all behave Earthquakes in different regions or along different faults all behave

differently, thus no consistent patterns have so far been recognized.differently, thus no consistent patterns have so far been recognized. Possible correlation between pre-seismic or pre-eruptive Possible correlation between pre-seismic or pre-eruptive

radon concentration anomalies and actual events have radon concentration anomalies and actual events have been an issue of serious discussion among the scientific been an issue of serious discussion among the scientific community and the first reaction to the positive results community and the first reaction to the positive results triggered some hope that a simple method was on the verge triggered some hope that a simple method was on the verge of reliable utilization. of reliable utilization. However, further investigations have However, further investigations have shown that the method is not as straight forward as it shown that the method is not as straight forward as it seemed.seemed.

The opinion which has emerged is that radon measured in the top soil is The opinion which has emerged is that radon measured in the top soil is due to the local origin and most of the part, if not all of it, comes from a due to the local origin and most of the part, if not all of it, comes from a rather small region from the point of probing. This statement is based rather small region from the point of probing. This statement is based upon a critical analysis of radon physical properties, soils structure and upon a critical analysis of radon physical properties, soils structure and laboratory experiments. laboratory experiments.

Most of the radon anomalies are correlatable with seismic Most of the radon anomalies are correlatable with seismic events and are precursory in nature. events and are precursory in nature. However, there does not However, there does not exist exact formulation and correlation that completely fits the exist exact formulation and correlation that completely fits the radon data so as to use it as a reliable precursor in the matters radon data so as to use it as a reliable precursor in the matters relating to volcanic eruption or seismic activity.relating to volcanic eruption or seismic activity.

Post-earthquake anomalies also address a question to the scientific Post-earthquake anomalies also address a question to the scientific community.community.

Need not to be overemphasized that more experimentation work and a Need not to be overemphasized that more experimentation work and a

wider database on radon anomalies are required to clinch the issue of wider database on radon anomalies are required to clinch the issue of use of radon as a precursoruse of radon as a precursor..

Earthquake prediction is one of the most rewarding scientific challenges, Earthquake prediction is one of the most rewarding scientific challenges, and if attained, a monumental scientific and technological achievement.and if attained, a monumental scientific and technological achievement.