Embed Size (px)
Citation preview
GEOFÍSICA INTERNACIONAL (2011) 502: 211225
Resumen
Inferimos un posible efecto sismomagnético precursor al terremoto (Mw 7.2) del 4 de abril de 2010, cuyo epicentro fue localizado en las estribaciones de las sierras El Mayor y Cucapah en el NE de Baja California, México, el cual ha sido denominado El MayorCucapah. Los datos utilizados corresponden a mediciones de la magnitud del campo magnético total registrados en una base magnética ubicada temporalmente en !"#"$%&'"#('!#'()*+)%#('#,)'-+)".#('#!"#/)'00"#('!#CICESE, en Ensenada, Baja California, México, 1# '-# !%.# %2.'03"&%0)%.# 4"5-6&)+%.# ('# /7+.%-8#Arizona, y Fresno, California, en los EEUU. Estos datos fueron registrados con una taza de muestreo de un minuto del 26 de marzo al 19 de abril de 2010. La comparación de estos ("&%.# 9'04)&):# 3'0)*+"0# ;7'#(70"-&'# '!# 9'0)%(%#de medición las tres estaciones registraron variaciones similares del campo geomagnético.<7'.&0%# "-=!).).# .'# 2"."# '-# !"# ('*-)+):-# 1#90%97'.&"#('#7-"#4'()("#'.&"(>.&)+"#;7'#?'4%.#denominado índice de variación magnética. Este índice, calculado a partir de los datos de una sola estación, nos ha permitido contrastar las variaciones del campo magnético en días previos y posteriores al terremoto, utilizando de forma independiente los datos de las tres '.&"+)%-'.#4"5-6&)+".8# @"+)!)&"-(%# !"# 2A.;7'("#de posibles precursores. A partir de los datos del campo magnético analizados, podemos sugerir ;7'#'!#>-()+'#('#3"0)"+):-#4"5-6&)+"#-%.#9'04)&'#)('-&)*+"0# 7-# 9%.)2!'# '3'-&%# .).4%4"5-6&)+%#;7'#)-)+)"#BC#4)-7&%.#"-&'.#('!#&'00'4%&%#1#&)'-'#una duración de 3 horas, así como la variación anómala del campo magnético causada por una &%04'-&"#4"5-6&)+"#;7'#)-)+):#'!#(>"#D#('#"20)!E
Palabras clave: índice de variación magnética, efecto sismomagnético, terremoto El MayorCucapah, Baja California, México.
Abstract
We describe a possible seismomagnetic pre+70.%0# &%# &?'# FG# HEI# '"0&?;7"J'# %@# K90)!# B8#2010, with epicenter nearby the sierras El Mayor and Cucapah in NE Baja California, México, (El F"1%0L,7+"9"?#'"0&?;7"J'ME#N'#7.'(#&%&"!L*'!(#magnetic intensity data recorded on a temporal magnetic base station on the roof of the Earth Sciences Division of CICESE, in Ensenada, Baja California, México, and magnetic observatories "&#/7+.%-8#K0)$%-"8#"-(#O0'.-%8#,"!)@%0-)"8#PQKE#/?'.'#("&"#G'0'#0'+%0('(#"&#"#."49!)-5#0"&'#%@#one minute from March 26 and until April 19, 2010. A comparison of these data let us verify that during the measurement period the three stations recorded similar variations of the 5'%4"5-'&)+#*'!(EOur analysis is based upon a statistical measure that we call index of magnetic variation, which "!!%G.# 7.# &%# ('&'+&# "-(# ;7"-&)@1# "-%4"!%7.#3"0)"&)%-.#%@# &?'#4"5-'&)+# *'!(# @0%4#("&"#%@# "#.)-5!'# .&"&)%-E# R".'(# 79%-# &?'# 4"5-'&)+# *'!(#data, we suggest that the proposed index %@# 4"5-'&)+# 3"0)"&)%-# )('-&)*'.# "# 9%..)2!'#seismomagnetic event, which begins 40 minutes 2'@%0'#&?'#'"0&?;7"J'#"-(#?".#(70"&)%-#%@#"2%7 hours, as well as anomalous behavior of the 5'%4"5-'&)+# *'!(# +"7.'(# 21# "# 5'%4"5-'&)+#.&%04#2'5)--)-5#%-#K90)!#DE
Key words: index of magnetic variation, seismo4"5-'&)+#'@@'+&8#S!#F"1%0L,7+"9"?#'"0&?;7"J'8#Baja California, México.
211
A possible seismomagnetic precursor of the El MayorCucapah earthquake (Mw 7.2) of April 4, 2010, Baja California, México
Emilia FregosoBecerra and Juan GarcíaAbdeslem
T'+')3'(U#K757.&#IV8#ICWCX#"++'9&'(U#Y"-7"01#ID8#ICWWX#972!).?'(#%-#!)-'U#F"0+?#IZ8#ICWW#
E. FregosoBecerraUniversidad de GuadalajaraCentro Universitario de Ciencias Exactas e Ingenierías(CUCEI)Departamento de Ingeniería CivilBlvd. Marcelino García Barragán Núm. 1421'.;E#,"!$"("#[!>49)+"Guadalajara, Jalisco, México
ORIGINAL PAPER
J. GarcíaAbdeslem,'-&0%#('#\-3'.&)5"+):-#,)'-&>*+"#1#('#S(7+"+):-#Superior de Ensenada (CICESE)])3).):-#('#,)'-+)".#('#!"#/)'00"Departamento de Geofísica Aplicada,"00'&'0"#S-.'-"("L/)^7"-"#<A4E#VZW_Fraccionamiento Zona PlayitasEnsenada, Baja California, MéxicoCorresponding author: [email protected] [email protected]
E. FregosoBecerra and J. GarcíaAbdeslem
212 VOLUME 50 NUMBER 2
Introduction
As part of a series of procedures followed to ensure the reliability and long term performance %@# &G%# 0'+'-&!1# "+;7)0'(# `SF/F# &%&"!L*'!(#4"5-'&%4'&'0.#aCECW#-/#0'.%!7&)%-#"-(#CEI#-/#absolute accuracy), these instruments were set up as basestation magnetometers and deployed at the roof of the Earth Sciences Division building of CICESE at Ensenada, Baja California, Mexico aO)570'# WME# /?).# .)&'# ).# !%+"&'(# "&# 5'%('&)+#+%%0()-"&'.# VWE_bHZº N, 116.6643º W, 47 m above sea level, where a previous survey (Luis Gradilla, personal communication) showed that the site selected to deploy the magnetometers ?".# !%G# ac#CED#4`M# .&"2!'#4"5-'&)+# )-(7+&)%-#effects from 60 Hz electric currents.
/?'.'#4"5-'&%4'&'0.8#.'9"0"&'(#W#4#"9"0&8#G'0'#&70-'(#%-#"&#W_UI_#!%+"!#&)4'#ad/M#%-#F"0+?#26, 2010, just before the eastern vacation period.
,%-&)-7%7.#0'+%0()-5#%@#&?'#5'%4"5-'&)+#*'!(#"&#a rate of 1 minute lasted until April 9, 2010, at WCUBZ#?#ad/ME#K#.'+%-(#9'0)%(#%@#4'".70'4'-&.#G".#.'O#&%#2'5)-#"&#ZUDI#?#ad/M#%-#K90)!#WV8#ICWC8#"-(#!".-&)!#K90)!#WZ8#ICWC#"&#WCUCb#d/E##ad/#e#P-)3'0."!#/)4'#L#H#?ME
K&#WDUBCUBW#d/#%-#K90)!#B8#ICWC8#&?'#S!#F"1%0L,7+"9"?#'"0&?;7"J'#%++700'(# )-# &?'#3)+)-)&1#%@#&?'#Q)'00"#,7+"9"?#"-(#Q)'00"#S!#F"1%0E#/?'#4")-#.?%+J#aFG#HEIM#G".#@%!!%G'(#21#4%0'#&?"-#&'-#&?%7."-(#"@&'0.?%+J.#().&0)27&'(#"!%-5#&?'#-%0&?#western side of Sierra Cucapah and towards the south western side of Mexicali Valley (Figure 1).
A generalized geologic map of the study "0'"# ).# .?%G-# )-# O)570'# WE# /?'# 5'%!%51# %@# &?'#sierras Juárez and Cucapah includes Paleozoic 4'&"4%09?)+# 0%+J.# )-&07('(# 21# ,0'&"+'%7.#granitoids that vary from coarsegrained biotite tonalite to leucocratic granodiorite (Gastil et
Figure 1.#Q+?'4"&)+#4"9#.?%G)-5#.70@"+'#5'%!%51#"-(#4")-#5'%!%5)+# .&07+&70'.# a\<S`\8#WZ_C"X# \<S`\8#WZ_C2X#GarcíaAbdeslem et al.8# ICCWM8# "-(# .').4)+)&1# aY"-7"01#W# &%# Y7!1#WD8#ICWCM# @0%4#,\,SQSLTSQ<[F#aF#f#VM#"-(#PQ`QL<S\,#+"&"!%5.E#/?'#.').4)+)&1#@0%4#,\,SQSLTSQ<[F#+"&"!%5#).#0'90'.'-&'(#7.)-5#+1"-#+)0+!'.E#/?'#.').4)+)&1#@0%4#PQ`QL<S\,#+"&"!%5#).#0'90'.'-&'(#7.)-5#1'!!%G#+)0+!'.#@0%4#Y"-7"01#W#&%#K90)!#B#2'@%0'#&?'#4")-#'"0&?;7"J'8#0'(#+)0+!'.#"@&'0#&?'#4")-#'"0&?;7"J'8#"-(#2!7'#+)0+!'.#"@&'0#&?'#&?)0(#!"05'.&#"@&'0.?%+JE#Q%!)(#.&"0.#.?%G#&?'#&?0''#largest seismic events and the numbers aside indicate its magnitude. Mayor faults are: Laguna Salada (LSF), Cañón Rojo (CRF), Cañada David Detachment (CDDF), Central (CF), Cucapah (CCF), Pescadores (PF) Imperial (IF), and Cerro Prieto (CPF). CPV is Cerro Prieto Volcano. Lithology: Cretaceous Granitoid, KGr, Paleozoic Metamorphic, PM, /'0&)"01#3%!+"-)+8#/Lg8#h7"&'0-"01#3%!+"-)+8#hLg8#<'%5'-'#Q'()4'-&.8#<LQ8#h7"&'0-"01#K!73)%-8#hLKE#/?'#)-.'&#.?%G.#
!%+"&)%-.#%@#4"5-'&)+#2".'#.&"&)%-#"&#S-.'-"("#"-(#4"5-'&)+#%2.'03"&%0)'.#"&#/7+.%-#"-(#O0'.-%E
GEOFÍSICA INTERNACIONAL
APRIL JUNE 2011 213
al., WZHDME# \-# &?'# Q)'00"# S!# F"1%08# 9!7&%-)+#0%+J.# 3"01# @0%4# &%-"!)&'# &%# 4%-$%50"-)&'# "-(#)-&07('# 4'&".'()4'-&"01# 0%+J.# ".# )00'57!"0#.?"9'(#.&%+J.#aR"0-"0(8#WZb_X#Q)'4#"-(#`".&)!8#WZZBME#F)%+'-'#3%!+"-)+#0%+J.#!%+"!!1#%3'0!)'#&?'#+01.&"!!)-'#2".'4'-&#"-(# )&.#'i9%.'(# &?)+J-'..#rarely exceeds a few tents of meters.
/?'# \49'0)"!#"-(#,'00%#j0)'&%# @"7!&.# aO)570'#1) are part of the San AndreasGulf of California .&0)J'L.!)9#@"7!&#.1.&'4#"-(#+%-.&)&7&'#&?'#j"+)*+L<%0&?#K4'0)+"#9!"&'#2%7-("01#)-#&?).#0'5)%-E#/?'#Laguna Salada fault, located over the western margin of Sierra Cucapah, is a highangle fault &?"&#.&0)J'.#-%0&?G'.&#"-(#?".#"-#%2!);7'#-%04"!Ldextral sense of shear that is considered part of &?'#Q"-#K-(0'".#.&0)J'L.!)9#@"7!&#.1.&'4#aF7!!'0#"-(#T%+JG'!!8#WZZWX#F7!!'0#"-(#T%+JG'!!8#WZZDME#/?'# ,"k:-# T%^%# @"7!'05'.# G)&?# &?'# d"57-"#Salada fault at almost right angles and becomes a prominent active normal fault (Figure 1) that acts as a releasing step of the Laguna Salada @"7!&#.1.&'4#aF7'!!'0#"-(#T%+JG'!!8#WZZWME#/?'#Cañada David detachment is a westdipping lowangle normal fault with a curvilinear trace that bounds the western margin of Sierra El Mayor (Siem and Gastil, 1994; Axen et al., 1999; Fletcher and Spelz, 2009).
/?'# S!# F"1%0L,7+"9"?# '"0&?;7"J'# %++700'(#"&# .?"!!%G# ('9&?# al# WC# J4M# "99"0'-&!1# "!%-5#the southeastern segment of the Laguna Salada fault that is concealed by sediments of the F'i)+"!)#g"!!'1E#/?).#).#&?'#!"05'.&#.').4)+#'3'-&#)-#&?'#0'5)%-#.)-+'#O'207"01#IV8#W_ZI8#G?'-#"-#'"0&?;7"J'#%@#"-#'.&)4"&'(#4"5-)&7('#FG#HEW#ruptured segments of Laguna Salada and Cañón T%^%#@"7!&.#aF7'!!'0#"-(#T%+JG'!!8#WZZDX#O!'&+?'0#and Spelz, 2009).
Figure 2 shows the temporal variation of seismicity obtained from NEIC catalogue, for the region shown in Figure 1, from January 1 &%#Y7!1#WD8#ICWCE#O%0#&?'#)-&'03"!#2'@%0'#K90)!#B8#the magnitude Mw varies mostly between 1 and 3 (Figure 2a); the maximum number of events 9'0#("1#aO)570'#I2M#).#"2%7&#WD8#"-(#?19%+'-&'0#('9&?#).#4%.&!1#G)&?)-#IC#J4#aO)570'#I+ME#K@&'0#&?'# S!# F"1%0L,7+"9"?# '"0&?;7"J'# &?'0'# ).# "#notable rise in magnitude and number of seismic events per day, yet the predominant hypocenter ('9&?# 0'4")-.# "&# "2%7&# IC# J4E# /?'#4"i)474#-742'0#%@#'3'-&.#9'0#("1#).#%2.'03'(#%-#K90)!#D#"-(#Y7-'#WDE
Considering the seismic moment, M0 e#HEI_iWC19# <L48# 0'9%0&'(# 21# &?'# 5!%2"!# ,F/#"5'-+)'.8#&?).#'"0&?;7"J'#0'90'.'-&.#&?'#!"05'.&#moment released in the region in more than 100 years. /?'# .').4)+# 4%4'-&# ).# &?'# .+"!"0#parameter of the point source of a double
couple and it is related to the rupture area, A, the average displacement, D, and the shear modulus, !,# 21# &?'# @%!!%G)-5# 0'!"&)%-.?)9# aKJ)8#1966).
M0#e#!DA . (1)
K..74)-5#"#.?'"0#4%(7!7.#@%0#50"-)&)+#0%+J.#of !"e# VEViWC10 N/m2 and an average slip of D e#W48#G'# '.&)4"&'# "# 079&70'# "0'"# %@# "2%7&#I8ICC# J42. Considering the spatial distribution %@#"@&'0.?%+J.#"-(#&?'#().&"-+'#2'&G''-#&?'#&G%#major seismic events that followed the large '"0&?;7"J'#aO)570'#WM8#G'#)-@'0#&?"&#&?'#!'-5&?#%@#&?'#079&70'#).#"2%7&#WIC#J4E#/?'0'@%0'8#@0%4#';7"&)%-# W# G'# '.&)4"&'# &?"&# &?'# 079&70'# "0'"#4"1#'i&'-(#(%G-#&%#"2%7&#W_#J4#@%0#"#3'0&)+"!#@"7!&8#%0#"2%7&#Wb#J4#@%0#"#@"7!&#G)&?#"#()9#"-5!'#of 60oE# /?).# 0%75?# '.&)4"&)%-# %@# &?'# &?)+J-'..#of the seismogenic zone is in good agreement G)&?#"#('9&?#'.&)4"&'#%@#Wb#m#I#J4#&%#&?'#2".'#of the crustal magnetic layer from spectral "-"!1.).# %@# 4"5-'&)+# "-%4"!)'.8# "-(# WZ# J4#from maximum hypocenter depths in this region (GarcíaAbdeslem et al., 2001), suggesting that &?).# '"0&?;7"J'# 20%J'# &?'#G?%!'# 20)&&!'# +07.&"!#layer zone.
Changes )-# &?'# +07.&"!# .&0'..# *'!(#"++%49"-1)-5# '"0&?;7"J'# "+&)3)&1# 4"1# induce crustal deformation as well as piezo remanent magnetization of the crustal magnetic layer. /?'0'@%0'8# ".# +?"-5'.# )-# 0'4"-'-+'# +"7.'#+?"-5'.# %@# &?'# S"0&?n.# 4"5-'&)+# *'!(8# 4any efforts have been made since historic times to relate temporal changes in the geomagnetic *'!(#&%#.').4)+#"+&)3)&18#)E'E8#&?'#.').4%4"5-'&)+#'@@'+&#aT)J)&"J'8#WZHbME
/?'# .'"0+?# @%0# 9%..)2!'# .').4%4"5-'&)+#90'+70.%0.# &%# !"05'# '"0&?;7"J'.# ?".# 2''-#conducted in tectonically active regions, such as southern California (Johnston et alE8# WZ_DX#Johnston et al., 1994; Johnston et al., 2006), in Central Italy (Mele et al., 1994; Di Mauro et al., ICCD), and Japan aQ".")# "-(# \.?)J"G"8# WZ_CX#Q".")#"-(#\.?)J"G"8#WZZHX#<).?)("#et al., 2004). In this search, an array of magnetometers is deployed for several years at carefully selected .)&'.# !%+"&'(# )-# 0'5)%-.# %@# !%G# 4"5-'&)+# *'!(#gradient, and across major geologic structures. However, as the main problem detecting seismomagnetic effects is their small amplitude with respect to diurnal variations of the geomagnetic *'!(# a)E'E8# Q&"+'18# WZbBX# Q".")8# WZZBX# Q".")8#ICCWM8# &?'#4"5-'&)+#*'!(#()@@'0'-+'#2'&G''-#"#magnetic station located close to an active fault and a reference station are analyzed (i.e., Sasai "-(#\.?)J"G"8#WZ_CX#F'!'#et al., 1994; Johnston et al., 1994; Nishida et al., 2004; Di Mauro et al., ICCDX#Johnston et al., 2006).
E. FregosoBecerra and J. GarcíaAbdeslem
214 VOLUME 50 NUMBER 2
A considerable research effort on the seismomagnetic phenomena is currently conducted 7.)-5#7!&0"#!%G#@0';7'-+1#aPdOM#'!'+&0%4"5-'&)+#signals (EMS) in tectonically active regions such as California (FraserSmith et al., 1990; Kappler et al., 2010), Japan (Ismaguilov et al., ICCWX# o%&."0'-J%# et alE8# ICCD"X# Q'0)&"# et al., ICCDX# p"1"J"G"# et alE8# ICC_M8# ,?)-"# aIda et al.8# ICC_M8 and Mexico (RamírezRojas et al., ICCBX# o%&."0'-J%# et al.8# ICCBX# o%&."0'-J%# et al.8#ICCD2X#T"4>0'$LT%^".#et al., 2007; RamírezRojas et al.8# ICC_ME# j"0&# %@# &?'# 90%2!'4#G?'-#using ULFEMS is to discriminate the part of &?'#.)5-"!#0'!"&'(#&%#&?'#'"0&?;7"J'#+1+!'8#@0%4#ionosphere signals and cultural noise. A variety of methods have been proposed: polarization analysis, involving measurements of the three magnetic components (Z, H and D) and its 0"&)%.# ap"1"J"G"# et al.8# WZZbX# o%&."0'-J%# et al.8#ICCBX#o%&."0'-J%#et al.8#ICCD"X#Ida et al., ICC_M8#@0"+&"!#"-"!1.).#%@#&?'#9%G'0#.9'+&074#%@#
the geomagnetic signals ap"1"J"G"#et al., 1999; RamírezRojas et al., 2004; RamírezRojas et al., 2007; RamírezRojas et al.8#ICC_X#o%&."0'-J%#et al.8# ICCBX# o%&."0'-J%# et al.8# ICCD"), spectral analysis of geomagnetic resonant structures and micropulsations ap"1"J"G"# et al.8# ICC_X#o%&."0'-J%# et al.8# ICCBX# o%&."0'-J%# et al., ICCD2X# o%&."0'-J%# et al.8# ICC_), and the principal component analysis, which is based in the calculus of eigenvalues from geomagnetic components registered at several stations (o%&."0'-J%#et al.8#ICCD").
\-#%70#+".'8#".#G'#?"3'#%-!1#%-'#&%&"!L*'!(#magnetic station, we analyze our data using a statistical measure that we have called index of magnetic variation (Imv), to search for a possible seismomagnetic effect related to the S!# F"1%0L,7+"9"?# '"0&?;7"J'. /?).# "-"!1.).#).# 90'.'-&'(# )-# &G%# .'+&)%-.E# \-# &?'# *0.&#section we show the consistency between the
Figure 2. Seismicity variables from NEIC catalog: (a) magnitude Mw, (b) number, and (c) depth of seismic events, @0%4#Y"-7"01#W#&%#Y7!1#WD8#ICWCE
GEOFÍSICA INTERNACIONAL
APRIL JUNE 2011 IWD
&%&"!L*'!(# 4"5-'&)+# 4'".70'4'-&.# 0'+%0('(#at magnetometers deployed at Ensenada, hereafter referred as EDAB1 and EDAB2, and their similarity with magnetograms recorded at 5'%4"5-'&)+# %2.'03"&%0)'.# !%+"&'(# "&# /7+.%-#a/P,M8# K0)$%-"8# "-(# O0'.-%# aOT<M8# ,"!)@%0-)"E#\-# &?'# .'+%-(# .'+&)%-#G'# ('*-'# "-(# .&"&'# &?'#assumptions behind the Imv, and use it to search for a possibly seismomagnetic effect related to &?'#S!#F"1%0L,7+"9"?#'"0&?;7"J'E#K&#&?'#+700'-&#state of our analysis, we suggest the possibility of having detected a seismomagnetic effect that .&"0&.#.%4'#BC#4)-7&'.#2'@%0'#&?'#'"0&?;7"J'8#while the large variations in the Imv, observed @0%4# &?'# ("1# "@&'0# &?'# '"0&?;7"J'# G'0'# (7'#&%# "# .&0%-5# .%!"0# G)-(# .?%+J# &?"&# +"7.'(# "#geomagnetic storm.
Reliability of magnetic data recorded at Ensenada
/?'#&%&"!L*'!(#4"5-'&)+#("&"#0'+%0('(#"&#S]KLR1 and EDAB2# "0'# .?%G-# )-# *570'.# V"# "-(# V+8#0'.9'+&)3'!1E# /?'0'# ).# "# +%-.&"-&# ()@@'0'-+'# )-#"49!)&7('#%@#"2%7&#VCC#-/#2'&G''-#&?'#0'+%0('(#data sets, which is attributed to local differences )-#27)!()-5#@0"4'G%0JE#Si+'9&#@%0#&?).#()@@'0'-+'8#&?'#*-'#3"0)"&)%-.#)-#&?'#%2.'03'(#5'%4"5-'&)+#*'!(#"0'#'..'-&)"!!1#&?'#."4'8#".#.?%G-#)-#*570'.#3b and 3d.
/%# '-.70'# &?'# 0'!)"2)!)&1# %@# &?'# &%&"!L*'!(#magnetic data recorded at Ensenada, we compare the data recorded at magnetometer EDAB2 with magnetograms recorded at magnetic
Figure 3.#/)4'#.'0)'.#%@#0"G#&%&"!L*'!(#4"5-'&)+#("&"#aF) collected in Ensenada at EDAB1 (a) and EDAB2 (c) base stations, from March 26 to April 19, 2010. Figures (b) and (d) show the data for selected days; highlighted in blue
+%!%0#"@&'0#&?'#4")-#'"0&?;7"J'E
E. FregosoBecerra and J. GarcíaAbdeslem
216 VOLUME 50 NUMBER 2
%2.'03"&%0)'.# /P,# "-(# OT<E# /?'.'# 4"5-'&)+#observatories (see its location in Figure 1) are 4'42'0.# %@# \</STFK`<S/8# "-# )-&'0-"&)%-"!#-'&G%0J# %@# 4"5-'&)+# %2.'03"&%0)'.# G?%.'# ("&"#are available on line (http://www.intermagnet.org). It is worth to mention that the distances 2'&G''-# S-.'-"("L/7+.%-# "-(# S-.'-"("LO0'.-%#"0'#"2%7&#DDC#"-(#bVD#J48#0'.9'+&)3'!18#G?'0'".#the distances between the epicenter zone and S-.'-"("8#/7+.%-#"-(#O0'.-%#"0'#"2%7&#WVD8#BWD#"-(#bBC#J48#0'.9'+&)3'!1E#K@&'0#0'4%3)-5#&?'#(")!1#"3'0"5'8#&?'.'#("&"#G'0'#.'O#)-#"#d/#2".).E#/?')0#comparison (Figure 4) shows that both the long and the short period variations of the geomagnetic *'!(# 0'+%0('(# "&# S-.'-"("# "0'# .)4)!"0# &%# &?%.'#0'+%0('(#"&#/P,#"-(#OT<#4"5-'&)+#%2.'03"&%0)'.8#and thus validate the long term performance of the GEM/F magnetometers.
The search for a seismomagnetic effect
/?'# 0"G# 4"5-'&)+# ("&"# 0'+%0('(# )-# S-.'-"("#by magnetometers EDAB1 and EDAB2, plotted %-#"#d/#(")!1#2".).#"0'#.?%G-#)-#*570'.#D#"-(#b8#0'.9'+&)3'!1E#/?'#("&"#0'+%0('(#2'@%0'#&?'#4")-#'"0&?;7"J'8#".#.?%G-#)-#*570'.#D"#"-(#b"8#?"3'#"#0'57!"0#"-(#.&"2!'#(")!1#3"0)"&)%-E#/?'#.4"!!'.&#variations occur during night time, and a diurnal 4)-)474#).#%2.'03'(#0'57!"0!1#2'&G''-#_#&%#Wb#?E
K.#.?%G-#)-#*570'.#D2L+#"-(#b2L+8#&?'#&%&"!L*'!(# 4"5-'&)+# ("&"# 0'+%0('(# .)-+'# &?'# ("1# %@#&?'#4")-#'"0&?;7"J'#.?%G#"#0'4"0J"2!'#+?"-5'#".# +%49"0'(# &%# 90'3)%7.# ("1.E# /?'# 4"5-'&)+#*'!(#).#9"0&)+7!"0!1#()@@'0'-&#&?'#("1#%@#&?'#4")-#'"0&?;7"J'8# ('-%&'(# 21# &?'# ("0JL2!7'# !)-'# )-#*570'.#D2#"-(#b2E#<%&'#&?"&#&?'#4"^%0#()@@'0'-+'.#
Figure 4.#])@@'0'-+'.#2'&G''-#&%&"!L*'!(#4"5-'&)+#)-&'-.)&1#aF) and its daily average (F), for different time intervals: a"M#@0%4#F"0+?#IH#&%#K90)!#B8#a2M#@0%4#K90)!#B#&%#K90)!#Z#"-(#a+M#@0%4#K90)!#WB#&%#K90)!#WZE#R!"+J#!)-'#+%00'.9%-(.#&%#
EDAB28#2!7'#!)-'#&%#OT<#"-(#0'(#!)-'#&%#/P,E
GEOFÍSICA INTERNACIONAL
APRIL JUNE 2011 217
%++70#2'&G''-#_#"-(#Wb#?E#\&# ).#"99"0'-&# @0%4#*570'.#D+#"-(#b+#&?"&#&?'#4"5-'&)+#*'!(#&'-(.#to recover the variation shown in days before the 4")-#'"0&?;7"J'E
/?'# 4"5-'&)+# ("&"# 0'+%0('(# "&# S-.'-"("#.?%G.#&?"&#!%+"!!18#&?'#5'%4"5-'&)+#*'!(#+?"-5'(#its normal variation since the day of the main '"0&?;7"J'8# .755'.&)-5# "# +"7."!# 0'!"&)%-.?)9#between the physical changes that lead to the seismic activity and changes in the geomagnetic *'!(E# /?'0'@%0'8# G)&?# &?'# 9709%.'# %@# 2'&&'0#describing the changes in the geomagnetic *'!(#(70)-5#&?'#&)4'#2'@%0'#"-(#"@&'0#&?'#4")-#'"0&?;7"J'8#G'# 9'0@%04#2".)+# .&"&).&)+.# %-# &?'#&%&"!L*'!(#4"5-'&)+#("&"#&?"&#).#('.+0)2'(#-'i&E
We assume that the average of the magnetic *'!(8# F A, recorded during the days before &?'# 4")-# '"0&?;7"J'8# 0'90'.'-&.# &?'# ()70-"!#3"0)"&)%-# %@# &?'# 5'%4"5-'&)+# *'!(# (70)-5# "#4"5-'&)+"!!1# ;7)&'L("1E# \&#G".# +"!+7!"&'(#7.)-5#
the magnetic data recorded from March 27 to April 3 at Ensenada, and it was used as a 0'@'0'-+'#&%#;7"-&)&"&)3'!1#%7&!)-'#&?'#4"5-'&)+#*'!(# 3"0)"&)%-.# )-# "!!# %@# &?'# 0'+%0('(# ("&"8#according with the following statistical measure.
N Imv = 100 ! 1 "(Fi - Fi
A)2
(2) N i=1 (Fi
A)2
\-# ';7"&)%-# I8# Imv stands for index of 4"5-'&)+#3"0)"&)%-8#2')-5#&?'#0%%&L4'"-L.;7"0'#of the difference between the recorded magnetic *'!(8#Fi, and the assumed diurnal variation on a 4"5-'&)+"!!1#;7)&'#("18
F A. N is the number of
data used in the calculation.
/%# +%497&'# Imv# G'# .'!'+&'(# &?'# &%&"!L*'!(#magnetic data recorded at EDAB2 shown in O)570'# H"E# /?'# "..74'(# 4"5-'&)+"!!1# ;7)&'#diurnal variation computed from EDAB2 data, is shown in Figure 7b along with the magnetic
Figure 5.#/%&"!L*'!(#4"5-'&)+#)-&'-.)&1#aF) recorded at magnetometer EDAB1#2'@%0'#"-(#"@&'0#&?'#4")-#'"0&?;7"J'U#(a) from March 26 to April 3, (b) from April 4 to April 9 and (c) from April 13 to April 19.
E. FregosoBecerra and J. GarcíaAbdeslem
IW_ VOLUME 50 NUMBER 2
data recorded on April 4 to emphasize their ()@@'0'-+'.E#/?'#3"!7'.#%@#Imv shown in Figure 7c were calculated over 60 minutes segments (N#e#bCM#G)&?%7&#%3'0!"9E#/?).#+"!+7!"&)%-.#.?%G#&?"&#(70)-5#&?'#("1.#2'@%0'#&?'#4")-#'"0&?;7"J'8#@0%4#March 27 to April 3, the Imv is of about 0.02%. O0%4#&?'#("1#%@#&?'#4")-#'"0&?;7"J'8#K90)!#B8#&?'#Imv starts to rise, reaching a maximum greater &?"-#CEWq#%-#K90)!#DE#p'0'"@&'0#&?'#Imv shows strong oscillations while decreases in amplitude "-(#)%'.#2"+J#&%# !%G#3"!7'.#%@#"2%7&#CECIq#on April 17.
Following the procedure outlined above, we 7.'#&%&"!L*'!(#4"5-'&)+#("&"#@0%4#OT<#"-(#/P,#%-#"#d/#2".).8#&%#+%497&'#&?'#Imv since March IH#7-&)!#K90)!#WZE#K.#.?%G-# )-#*570'.#_#"-(#Z8#G'# @%7-(#"# 0'4"0J"2!'# .)4)!"0)&1#G)&?# &?'# Imv calculated using EDAB2#("&"E#/?'0'@%0'8#"&#&?'#earlier stages of the analysis we suggested the proposed index of magnetic variation (Imv) as a good measurement of seismomagnetic effects
(GarcíaAbdeslem and FregosoBecerra, 2010; FregosoBecerra and GarcíaAbdeslem, 2010). p%G'3'08#&?"-J.#&%#&?'#.755'.&)%-#%@#&?'#0'3)'G'0.#G'# !%%J# "&# 5'%4"5-'&)+# *'!(# ().&702"-+'.#described by the Dst index. We downloaded the Dst index from Kioto geomagnetic center (fttp://G(+EJ75)EJ1%&%L7E"+E^9ME#/?'#].&#%0#().&702"-+'#storm time index, is a measure of geomagnetic activity used to assess the severity of magnetic stormsE#].&#).#'i90'..'(#)-#-/#"-(#)�'90'.'-&.#the average value of the horizontal component %@#&?'#S"0&?n.#4"5-'&)+#*'!(8#(70)-5#%-'#?%708#"&#@%70#-'"0L';7"&%0)"!#5'%4"5-'&)+#%2.'03"&%0)'.E#/%#%70#.7090).'#G'#@%7-(#&?"&#].&#)-()+"&'.#&?'#%-.'&#%@#"#4"5-'&)+#.&%04#2'5)--)-5#%-#K90)!#D8#"-(#G'#)-+!7('#)&#)-#O)570'.#H8#_#"-(#ZE
O70&?'04%0'8#"&#ZUWD#P/,#%-#K90)!#D8#&?'#Q%!"0#and Heliospheric Observatory (SOHO: http://sohowww.nascom.nasa.gov) reported that a .&0%-5#.%!"0#G)-(#.?%+J#G".#%2.'03'(#"&#Q[p[#"&# HUDZ# P/,# G)&?# .%!"0# G)-(# .9''(# "2079&!1#
Figure 6.#/%&"!L*'!(#4"5-'&)+#)-&'-.)&1#aF) recorded at magnetometer EDAB2#2'@%0'#"-(#"@&'0#&?'#4")-#'"0&?;7"J'U#(a) from March 26 to April 3, (b) from April 4 to April 9 and (c) from April 13 to April 19.
GEOFÍSICA INTERNACIONAL
APRIL JUNE 2011 219
)-+0'".)-5# a@0%4# BDVLDV_# J4r.M# &%# -'"0# HCC#J4r.E# /?'#Q[p[# .9"+'+0"@%3'.# "0%7-(# &?'#Sun in step with the Earth, by slowly orbiting "0%7-(# &?'# *0.&# d"50"-5)"-# j%)-&# adWM8# G?'0'#&?'#+%42)-'(#50"3)&1#%@#&?'#S"0&?#"-(#Q7-#J''9#Q[p[# )-#"-#%02)&# !%+J'(# &%# &?'#S"0&?LQ7-# !)-'E#/?'# dW# 9%)-&# ).# "990%i)4"&'!1# WED# 4)!!)%-# J4#away from Earth (about four times the distance %@#&?'#F%%-ME#<'"0#_UVD#P/,#aCWUVD#d/M#%-#K90)!#D#"#5'%4"5-'&)+#.&%04#G".#)-#90%50'..E
With the aim of discard a global magnetic '3'-Z'3)%7.#&%#&?'#'"0&?;7"J'8#G'#"-"!1$'(#&%&"!L*'!(# 4"5-'&)+# ("&"# @0%4# \-&'04"5-'&#magnetic observatory VIC, located at Victoria, British Columbia, Canada, which is at about W8_HD#J4#"G"1#@0%4#&?'#'"0&?;7"J'#'9)+'-&'0E#
/?'#4"5-'&)+#*'!(#0'+%0('(#"&#g\,#aO)570'#WCM#presents a regular diurnal variation and remains .&"2!'# %-# .'3'0"!# ("1.# 2'@%0'# &?'# '"0&?;7"J'8#but shows a severe change caused by the 4"5-'&)+# .&%04# %@# K90)!# D8#G?'-# &?'#4"5-'&)+#*'!(# ('+0'".'.# (%G-# .%4'# LVCC# -/E# /?'# Imv 0'"+?'.# 79# &%# CEV_q# %-# K90)!# D8# (70)-5# &?'#sudden commence of the magnetic storm and CEW_q#(70)-5# )&.# +!)4"i# %-# K90)!# bE# /?'0'@%0'8#considering both Dst and the Imv calculated from VIC magnetic data, we discard so far the possibility of global magnetic event previous and (70)-5#&?'#S!#F"1%0L,7+"9"?#'"0&?;7"J'E
However, as the geomagnetic storm began "2%7&#WC#?#"@&'0#S!#F"1%0L,7+"9"?#'"0&?;7"J'8#and the Imv indicates a possible seismomagnetic
Figure 7.#a"M#/%&"!L*'!(#4"5-'&)+#)-&'-.)&1#aF) on base station EDAB2 from March 26 to April 9; highlighted in red +%!%0#"0'#&?'#*'!(#3"0)"&)%-.#.)-+'#&?'#&)4'#%@#&?'#4")-#'"0&?;7"J'E#a2M#/?'#"..74'(#4"5-'&)+"!!1#;7)&'#("18#F A, is .?%G-#G)&?#2!"+J#!)-'#"!%-5#G)&?#&?'#4"5-'&)+#("&"#0'+%0('(#&?'#("1#%@#&?'#4")-#'"0&?;7"J'8#)-#0'(#+%!%0#!)-'E#/?'#Imv#3"!7'.#+"!+7!"&'(#7.)-5#';7"&)%-#aIM#@%0#"!!#%2.'03'(#("&"#).#.?%G-#)-#a+M8#G?'0'#&?'#0'(#"00%G#)-()+"&'.#&?'#%0)5)-#
&)4'#%@#&?'#4")-#'"0&?;7"J'E#/?'#].&#)-('i8#)-#-/8#).#.?%G-#)-#a(ME
E. FregosoBecerra and J. GarcíaAbdeslem
220 VOLUME 50 NUMBER 2
event that begins some 40 minutes before &?'# '"0&?;7"J'8# G'# .'!'+&# &?'# 4"5-'&)+# ("&"#0'+%0('(# @0%4# K90)!# V# &%# K90)!# D# "&# S]KLR2, /P,8# "-(# OT<8# "-(# )-+0'".'# &?'# 0'.%!7&)%-# %@#our estimate computing the Imv at 20 minutes intervals (i.e., N# e# ICM# @%0# '"+?# ("&"# .'&E# /?'#computed Imv and the Dst index are shown in *570'.#WW"L28#0'.9'+&)3'!1E
[-#K90)!#V8#"#4"5-'&)+"!!1#;7)'&#("1#G)&?%7&#.)5-)*+"-&# .').4)+# "+&)3)&18# &?'# Imv varies erratically for the three magnetic data sets, with maximum values of about 0.03%. During this day there is only one simultaneous increase (i.e.,
on the three data sets) of the Imv at around IIUBC#?E#/?'#].&#)-('i#@%0#&?).#("1#).#.&"2!'#G)&?#4)-)474#3"!7'.#"0%7-(#LWC#-/E
R'5)--)-5# K90)!# B# "-(# 7-&)!# _UVC# ?# &?'# Imv 3"0)'.#@0%4#CECW#q#&%#"2%7&#CECIqE#O0%4#_UVC#&%#11:30 h the Imv shows a simultaneous increase that is grater in Ensenada (0.03%) and minimum in Fresno (0.02%), which is followed by an erratic 2'?"3)%0# @0%4# WWUVC# &%# WD# ?E# K&# "0%7-(# WD# ?#the Imv starts to rise and simultaneously reach CECVD#q#"&#&?'#&)4'#%@#&?'#'"0&?;7"J'#aWDUBC#?M8#reaching maximum values at 16:10 h. Hereafter the Imv starts to decline having values less than
Figure 8.#/%&"!L*'!(#4"5-'&)+#)-&'-.)&1#aF) on the FRN station is shown in (a) for a continuous period of time from F"0+?#IH#&%#K90)!#WZE#/?'#"3'0"5'#("1#a2!"+J#!)-'M#%2&")-'(#G)&?#&?'#90'3)%7.#("1.#&%#&?'#4")-#'"0&?;7"J'#).#.?%G-#)-#a2M#"-(#&?'#("1#%@#&?'#4")-#'"0&?;7"J'#).#.79'0)49%.'(#)-#0'(#+%!%0E#/?'#Imv#3"!7'.#+"!+7!"&'(#7.)-5#';7"&)%-#aIM#@%0#"!!#%2.'03'(#("&"#"0'#.?%G-#)-#a+M8#G?'0'#&?'#0'(#"00%G#)-()+"&'.#&?'#%0)5)-#&)4'#%@#&?'#4")-#'"0&?;7"J'E#/?'#].&#
)-('i8#)-#-/8#).#.?%G-#)-#a(ME
GEOFÍSICA INTERNACIONAL
APRIL JUNE 2011 221
CECWq#"&#WHUDC#?E#K-%&?'0#.)47!&"-'%7.#0).'#%@#the Imv is observed around 22:30 h. Notice in Figure 11b that on April 4 the Dst index is stable G)&?#4)-)474#3"!7'.#"0%7-(#LWD#-/#E
[-# K90)!# D# &?'# 3"0)"&)%-# %@# &?'# Imv is simultaneous on the three magnetic data sets but presents appreciably larger values in Ensenada. /?'#].&#)-('i#.755'.&.#"#.7(('-#+%44'-+'4'-&#%@#&?'#4"5-'&)+#.&%04#"0%7-(#CW#&%#CI#?#ad/M#)-#good agreement with SOHO forecast. Hereafter the Dst index continuously decreases down to LbC# -/8# )-()+"&)-5# &?'# 2'5)--)-5# %@# &?'# 4")-#phase of the geomagnetic storm.
Seems worth to emphasize that the proposed Imv is not a tool to forecast or predict an '"0&?;7"J'E#\&#).#"#.&"&).&)+"!#4'".70'#&?"&#?'!9.#to discriminate magnetic variations that may be related either with the seismic cycle or else with geomagnetic perturbations, from an assumed ;7)&'#"-(#!%+"!#()70-"!#3"0)"&)%-#%@#&?'#5'%4"5-'&)+#*'!(E# /?'# .'"0+?# @%0# "# .').4%4"5-'&)+# '@@'+�'!"&'(#&%#S!#F"1%0L,7+"9"?#'"0&?;7"J'8#2".'(#upon the Imv, suggests the possibility of having detected a seismomagnetic effect that lasted about 3 h, and a precursor event 40 minutes 2'@%0'#&?'#'"0&?;7"J'E
Figure 9.#/%&"!L*'!(#4"5-'&)+#)-&'-.)&1#aFM#%-#&?'#/P,#.&"&)%-#).#.?%G-#)-#a"M#@%0#"#+%-&)-7%7.#9'0)%(#%@#&)4'#@0%4#F"0+?#IH#&%#K90)!#WZE#/?'#"3'0"5'#("1#a2!"+J#!)-'M#%2&")-'(#G)&?#&?'#90'3)%7.#("1.#&%#&?'#4")-#'"0&?;7"J'#).#.?%G-#)-#a2M#"-(#&?'#("1#%@#&?'#4")-#'"0&?;7"J'#).#.79'0)49%.'(#)-#0'(#+%!%0E#/?'#Imv#3"!7'.#+"!+7!"&'(#7.)-5#';7"&)%-#aIM#@%0#"!!#%2.'03'(#("&"#"0'#.?%G-#)-#a+M8#G?'0'#&?'#0'(#"00%G#)-()+"&'.#&?'#%0)5)-#&)4'#%@#&?'#4")-#'"0&?;7"J'E#/?'#].&#
)-('i8#)-#-/8#).#.?%G-#)-#a(ME
E. FregosoBecerra and J. GarcíaAbdeslem
222 VOLUME 50 NUMBER 2
Figure 10.#/%&"!L*'!(#4"5-'&)+#)-&'-.)&1#aF) on the VIC station is shown in (a) for a continuous period of time from F"0+?#IH#&%#K90)!#WZE#/?'#"3'0"5'#("1#a2!"+J#!)-'M#%2&")-'(#G)&?#&?'#90'3)%7.#("1.#&%#&?'#4")-#'"0&?;7"J'#).#.?%G-#)-#a2M#"-(#&?'#("1#%@#&?'#4")-#'"0&?;7"J'#).#.79'0)49%.'(#)-#0'(#+%!%0E#/?'#Imv#3"!7'.#+"!+7!"&'(#7.)-5#';7"&)%-#aIM#@%0#"!!#%2.'03'(#("&"#"0'#.?%G-#)-#a+M8#G?'0'#&?'#0'(#"00%G#)-()+"&'.#&?'#%0)5)-#&)4'#%@#&?'#4")-#'"0&?;7"J'E#/?'#].&#
)-('i8#)-#-/8#).#.?%G-#)-#a(ME
Figure 11. (a) Imv#@0%4#K90)!#V#&%#K90)!#DX#&?'#2!"+J#!)-'#+%00'.9%-(.#&%#S]KLR28#2!7'#!)-'#&%#OT<#"-(#0'(#!)-'#&%#/P,X#&?'#"00%G#%-#K90)!#B#)-()+"&'.#&?'#%0)5)-#&)4'#%@#S!#F"1%0L,7+"9"?#'"0&?;7"J'E#a2M#].&#)-('i#@0%4#K90)!#V#&%#K90)!#DE
GEOFÍSICA INTERNACIONAL
APRIL JUNE 2011 223
Conclusions
N'# "&&'49&# &%# *-(# "# .').4%4"5-'&)+# '@@'+&#+"7.'(#21#S!#F"1%0L,7+"9"?#'"0&?;7"J'8#7.)-5#&%&"!L*'!(# 4"5-'&)+# ("&"# 0'+%0('(# "&# "# .)-5!'#station far away from the epicenter zone. For this endeavor an assumption was made considering that the average of magnetic data on several .').4)+"!!1# ;7)&'# ("1.8# 90'3)%7.# &%# &?'# 4")-#'"0&?;7"J'8#0'90'.'-&.#&?'#()70-"!#3"0)"&)%-#%-#"#4"5-'&)+"!!1#;7)&'#("1E#N'#('*-'#"-(#90%9%.'#the index of magnetic variation (Imv); this statistical measure is robust in the presence of noise, and yields the percent change between &?'# %2.'03'(# 4"5-'&)+# *'!(# "-(# &?'# "..74'(#()70-"!#3"0)"&)%-#%-#4"5-'&)+"!!1#;7)&'#("1E#/?'#Imv calculated on magnetic data recorded at Ensenada, Baja California; Fresno, California, "-(# /7+.%-8# K0)$%-"8# "0'# 0'4"0J"2!'# .)4)!"08#and show a sensible increase the day after the 4")-#'"0&?;7"J'8#G?)+?#+'0&")-!1#).#+"7.'(#21#"#magnetic storm.
/?'#"2.'-+'#%@#.%!"0#G)-(#9'0&702"&)%-.#"-(#;7)'&# (")!1# 3"0)"&)%-# %@# &?'# 5'%4"5-'&)+# *'!(#%2.'03'(# .'3'0"!# ("1.# 2'@%0'# &?'# '"0&?;7"J'8#in contrast with the abrupt and simultaneous change of the Imv observed on April 4, some BC#4)-7&'.#2'@%0'#&?'#'"0&?;7"J'8#.755'.&.#&?'#possibility of having detected a precursor event. /?).#+%-+!7.)%-#).#.799%0&'(#21#&?'#"2.'-+'#%@#"#5!%2"!#4"5-'&)+#'3'-&#&?'#("1#%@#&?'#'"0&?;7"J'8#as inferred from the Imv calculated using VIC magnetic data and by the Dst index.
AcknowledgementS
N'#"+J-%G!'(5'#&?'#0'3)'G#"-(#+%44'-&.#%-#"-#'"0!)'0#3'0.)%-#%@#&?'#4"-7.+0)9#SG"# !%G"+J"#Nita, Mario González Escobar and Luis Munguía Orozco. We are in debt with two anonymous reviewers who suggested the use of the disturbance storm time index and provided a list %@#.)5-)*+"-�'@'0'-+'.E#O)570'#W#G".#4"('#G)&?#the generous help of Victor M. Frías Camacho. We "!.%#&?"-J#,[<K,s/#"-(#,\,SQS#@%0#.799%0&)-5#the operation of RESNOM (Red Sismológica del Noroeste de México), to USGS for supporting the operation of NEIC (The National Earthquake Information Center) and magnetic observatories "&#/7+.%-#"-(#O0'.-%8#&%#\</STFK`<S/#aGGGEintermagnet.org) for promoting high standards of magnetic observatory practice, to NASAESA for SOHO space weather forecast, and Kyoto geomagnetic center.
Bibliography
KJ)# oE8# WZbb8# `'-'0"&)%-# "-(# 90%9"5"&)%-# %@#`LG"3'.#@0%4#&?'#<))5"&"#'"0&?;7"J'#%@#Y7-'#Wb8# WZbBE# j"0&# IE# S.&)4"&)%-# %@# '"0&?;7"J'#moment, released energy, and stressstrain
drop from the Gwaves spectrum, Bull. Earthquake Res. Inst., Tokyo Univ., BB8#HVL__E
Axen G.J., Fletcher J.M., Cowgill E., Murphy M., o"99# jE8# F"+F)!!"-# \E8# T"4%.Lg'!=$;7'$# SE8#ArandaGómez J., 1999, Rangefront fault scarps of the Sierra El Mayor, Baja California: Formed above an active lowangle normal fault?, Geology8#IH8#IBHLIDCE
R"0-"0(#OEdE8#WZb_8#Q&07+&70'#"-(#&'+&%-)+.#%@#&?'#Sierra Cucapah, Northeastern Baja California and Imperial County, California, Ph. D. thesis. University of Colorado, Boulder.
Di Mauro D., Lepidi S., Meloni A, Palangio P., ICCD8#F"5-'&)+# "-(# S!'+&0%4"5-'&)+# .)5-"!.#related to tectonic activity: updates and new analyses on measurements in Central Italy, Nat. Haz. Earth Sys. Sci.8#D8#ZIDtZVCE
Fletcher J.M., Spelz R.,M., 2009, Patterns %@# h7"&'0-"01# ('@%04"&)%-# "-(# 079&70'#propoagation associated with an active lowangle normal fault, Laguna Salada, Mexico: evidence of a rolling hinge?, Geosphere8# D8#V_DLBCHE
FraserSmith A.C., Bernardi A., McGill P.R., Ladd M.E., Helliwell R.A., Villard O.G. Jr., 1990, d%GL@0'+7'-+1#4"5-'&)+#*'!(#4'".70'4'-&.#near the epicenter of the Ms 7.1 Loma Prieta '"0&?;7"J'8# Geophys. Res. Let.8# WH8# WBbDLWBb_E#
FregosoBecerra E., GarcíaAbdeslem J., 2010, Efecto sismomagnético relacionado al terremoto El MayorCucapah (Mw 7.2) del 4 de Abril de 2010. Reunión Anual 2010, Unión Geofísica Mexicana (Resumen), GEOS, 30, p. 146, Puerto Vallarta, Jalisco, México del 7 al 12 de noviembre de 2010.
`".&)!# TE`E8# j?)!!)9.# TEpE8# K!!).%-# SE,E8# WZHD8#Reconnaissance geology of the State of Baja California, Geol. Soc. Am., Memoir 140.
GarcíaAbdeslem J., EspinosaCardeña J.M., MunguíaOrozco L., WongOrtega V.M., RamírezHernández J., 2001. Crustal structure from 2D gravity and magnetic data modeling, magnetic power spectrum inversion, and seismotectonics in the Laguna Salada basin, northern Baja California, México, Geofísica Internacional, 40, bHL_DE
GarcíaAbdeslem J., FregosoBecerra E., 2010, Seismomagnetic effect from El Mayor,7+"9"?# '"0&?;7"J'# aFG# HEIM# %@# K90)!# B8#2010, in NE Baja California, México (Abstract). S!'+&0%4"5-'&)+# .&7()'.# %@# '"0&?;7"J'.# "-(#3%!+"-%'.# aSFQSg# G%0J.?%9ME# ,?"94"-#
E. FregosoBecerra and J. GarcíaAbdeslem
224 VOLUME 50 NUMBER 2
University, Schmid College of Science, Orange County, California, USA, October 36, 2010.
p"1"J"G"#FE8#o"G"&'#TE8#F%!+?"-%3#[EKE8#s74%&%#K., 1996, Results of ultralowfrecuency 4"5-'&)+# *'!(# 4'".70'4'-&.# (70)-5# &?'#`7"4#'"0&?;7"J'#%@#_#K757.&#WZZV8#Geophys. Res. Let., 23, 241244.
p"1"J"G"#FE8#\&%#/E8#Q4)0-%3"#<E8#WZZZ8#O0"+&"!#analysis of ULF geomagnetic data associated G)&?#&?'# 7"4#'"0&?;7"J'#%-#K757.&#_8#WZZV8#Geophys. Res. Let.8#Ib8#I8HZHLI8_CCE
p"1"J"G"# FE8# <)+J%!"'-J%# KEjE8# Q'J)57+?)# FE8#s"4".?)&"#oE8#\("#sE8#s"-%#FE8#ICC_8#K-%4"!%7.#ELF phenomena in the Schumann resonance band as observed at Moshiri (Japan) in possible "..%+)"&)%-#G)&?#"-#'"0&?;7"J'#)-#/")G"-8#Nat. Haz. Earth Sys. Sci., _, 1,3091,316.
INEGI (Instituto Nacional de Estadística Geografía '# \-@%04=&)+"M8# WZ_C"E# ,"0&"# 5'%!:5)+"#/)^7"-"8#\WWLWW8#'.+"!"#WUIDC8CCCE#Q'+0'&"0>"#de Programación y Presupuesto, México, D.F.
INEGI (Instituto Nacional de Estadística Geogra@>"# '# \-@%04=&)+"M8# WZ_C2E# ,"0&"# 5'%!:5)+"#F'i)+"!)8#\WWLWW8#'.+"!"#WUIDC8CCCE#Q'+0'&"0>"#de Programación y Presupuesto, México, D.F.
\("#sE8#s"-5#]E8#d)#hE8#Q7-#pE8#p"1"J"G"#FE8#ICC_8#Detection of ULF electromagnetic emissions ".#"#90'+70.%0#&%#"-#'"0&?;7"J'#)-#,?)-"#G)&?#an improved polarization analysis, Nat. Haz. Earth Sys. Sci.8#_8#HHDLHHHE
\.4"57)!%3# gEQE8# s7E# KE# o%91&'-J%8# p"&&%0)# oE8#g%0%-%3#jEFE8#F%!+?"-%3#[EKE8#p"1"J"G"#FE8#2001, ULF magnetic emissions connected G)&?# 7-('0# .'"# 2%&&%4# '"0&?;7"J'.E# Nat. Haz. Earth Sys. Sci., 1, 2331.
Johnston M.J.S., Silverman S.A., Mueller R.J., R0'+J'-0)(5'# oEQE8# WZ_D8# Q'+7!"0# 3"0)"&)%-8#crustal contribution, and tectonic activity in ,"!)@%0-)"8#WZHbtWZ_B8#J. Geophys. Res., 90, _8HCHt_8HWHE
Y%?-.&%-# FEYEQE8# F7'!!'0# TEYE8# Q".")# sE8# WZZB8#F"5-'&)+#*'!(#%2.'03"&)%-.#)-#&?'#-'"0L*'!(#%@#&?'#I_#Y7-'#WZZI#FG#HEV#d"-('0.8#,"!)@%0-)"8#'"0&?;7"J'8# Bull. Seism. Soc. Amer.8# _B8#HZItHZ_E
Y%?-.&%-#FEYEQE8#Q".")#sE8#S52'0&#`E]E8#j"0J#QEoE8#2006, Seismomagnetic effects from the long"G")&'(#I_#Q'9&'42'0#ICCB#F#bEC#j"0J*'!(#'"0&?;7"J'8 Bull. Seis. Soc. Am., 96, 206220.
Kappler K.N., Morrison H.F., Egbert G.D., 2010, Longterm monitoring of ULF electromagnetic
*'!(.# "&# j"0J*'!(8# ,"!)@%0-)"8# J. Geophys. Res.8#WWD8#RCBBCbE
o%&."0'-J%# KE8# j60'$LS-0>;7'$# TE8# d:9'$L,07$LK2'10%#YEKE8#o%.?'3"1"#QE8# 0)4"!.J1#gE8#uA-)5"#F.R., 2004, Analysis of the ULF electromagnetic '4)..)%-#0'!"&'(#&%#.').4)+#"+&)3)&18#/'%!%17+"-#5'%4"5-'&)+# .&"&)%-8# WZZ_LICCWE# Nat. Haz. Earth Sys. Sci., B8#bHZtb_BE
o%&."0'-J%# KE8# F%!+?"-%3# [E8# p"1"J"G"# FE8#o%.?'3"1"#QE8# 0)4"!.J1#gE8#j60'$LS-0>;7'$#TE8#d:9'$L,07$LK2'10%#YEKE8#ICCD"8#\-3'.&)5"&)%-#of ULF magnetic anomaly during Izu '"0&?;7"J'# .G"04# "-(# F)1"J'^)4"# 3%!+"-%#eruption at summer 2000, Japan. Nat. Haz. Earth Sys. Sci.8#D8#bVtbZE
o%&."0'-J%# KE8# F%!+?"-%3# [E8# j'0'$LS-0>;7'$#R., LópezCruzAbeyro J.A., Koshevaya S., `0)4"!.J1#gE8#o0'4'-'&.J1#\E8#ICCD28#j%..)2!'#seismogenic origin of changes in the ULF EM 0'.%-"-&# .&07+&70'# %2.'03'(# "&# /'%!%17+"-#5'%4"5-'&)+# .&"&)%-8# F'i)+%8# WZZZtICCWE#Nat. Haz. Earth Sys. Sci.8#D8#HWWtHWD.
o%&."0'-J% A., 0)4"!.J1#gE, Koshevaya S., PérezEnrí;7'$# TE, s7&.).# gE, LópezCruzAbeyro J.A., Villegas Cerón R.A.8# ICC_8#Evidence of a new electromagnetic resonance discovered "&#/'%!%17+"-#5'%4"5-'&)+#.&"&)%-8#F6i)+%v8#Geofísica Internacional8#BH8#I_HtIZV.
Mele J., Meloni A., Palangio P., 1994, A tectonomagnetic effect detected in Central Italy, !""#$%&'%&()*+,%-#8#VH8#WHLIDE
F7'!!'0#oEYE8#T%+JG'!!#/ETE8#WZZW8#d"&'#h7"&'0-"01#structural evolution of the western margin of the Sierra Cucapa, Baja California Norte: in ]"79?)-8#YE8#"-(#Q)4%-')&8#RE8#a'(M#/?'#`7!@#and Peninsular Province of the Californias, AAPG Memoir 47, 249260.
F7'!!'0#oEYE8#T%+JG'!!#/ETE8#WZZD8#d"&'#h7"&'0-"01#activity of the Laguna Salada fault in northern Baja California, Mexico, Geolog. Soc. Am. Bull.8#WCH8#_W_E
<).?)("#sE8#Q75)."J)#sE8#/"J"?".?)#oE8#P&.75)#FE8#[.?)4"# pE8# ICCB8# /'+&%-%4"5-'&)+# .&7(1#)-# &?'# '".&'0-# 9"0&# %@# p%JJ")(%8# <S# Y"9"-U#Discrepancy between observed and calculated results, Earth Plan. Space8#Db8#W8CBZtW8CD_E
RamírezRojas A., MuñozDiosdado A., PavíaMiller C.G., AnguloBrown F., 2004. Spectral and multifractal study of electroseismic time .'0)'.#"..%+)"&'(#&%#&?'#FGebED#'"0&?;7"J'#of 24 October 1993 in Mexico, Nat. Haz. Earth Sys. Sci., 4, 703709.
GEOFÍSICA INTERNACIONAL
APRIL JUNE 2011 IID
T"4>0'$LT%^".#KE8#O!%0'.LF=0;7'$#SEdE8#`7$4=-Lg"05".#dE8#F=0;7'$L,07$#YE8#j"3>"LF)!!'0#,E`E8#AnguloBrown F., 2007, A comparison of ground geoelectric activity between three regions of different level of seismicity, Nat. Haz. Earth Sys. Sci.8#H8#DZWLDZ_E
T"4>0'$LT%^".#KE8#O!%0'.LF=0;7'$#SEdE8#`7$4=-Lg"05".#dE8#`=!3'$L,%1&#`E8#/'!'.+"#dE8#K-57!%LR0%G-# OE8# ICC_8# Q&"&).&)+"!# @'"&70'.# %@#seismoelectric signals prior to M7.4 Guerrero["i"+"#'"0&?;7"J'#aF6i)+%M8#Nat. Haz. Earth Sys. Sci.8#_8#W8CCWLW8CCHE
T)J)&"J'#/E8#WZHb8#S"0&?;7"J'#90'()+&)%-E#S!.'3)'08#Amsterdam.
Q".")#sE8#WZZB8#j)'$%4"5-'&)+#*'!(.#90%(7+'(#21#dislocation sources, Surv. Geophys.8#WD8#VbVLV_IE
Q".")#sE8#ICCW8#/'+&%-%4"5-'&)+#4%('!)-5#2".'(#on the piezomagnetism: A review, Annali di ()*+,%-#8#BB8#VbWtVb_E
Q".")# sE8# \.?)J"G"# sE8# WZ_C8# /'+&%-%4"5-'&)+#'3'-&# 90'+'()-5# "# FDEC# '"0&?;7"J'# )-# &?'#\$7#j'-)-.7!"tK.').4)+#.!)9#%@#"#270)'(#@"7!&v8#Bull. Earthq. Res. Inst., Univ. Tokyo8#DD8#_ZDL911.
Q".")# sE8# \.?)J"G"# sE8# WZZH8# Q').4%4"5-'&)+#4%('!.# @%0# '"0&?;7"J'.# )-# &?'# '".&'0-# 9"0&#of Izu Peninsula, Central Japan, Annali di ()*+,%-#8#BC8#BbVtBH_E
Q'0)&"# KE8# p"&&%0)# oE8# s%.?)-%# ,E8# p"1"J"G"#FE8# \.'$"J)# <E8# ICCD8# j0)-+)9"!# +%49%-'-&#analysis and singular spectrum analysis of ULF geomagnetic data associated with '"0&?;7"J'.8# Nat. Haz. Earth Sys. Sci.8# D8#b_DLb_ZE
Q)'4# FE# SE8# `".&)!# TE`E8# WZZB8# F)(L/'0&)"01#to Holocene extension associated with the development of the Sierra El Mayor metamorphic core complex, northeastern Baja California, Mexico. In: F+`)!!8#QE#OE#"-(#T%..8#/E#M., eds. Geological investigations of an active margin, Geol. Soc. Am. Cordilleran Section 57)('2%%J8#T'(!"-.8#,"!)@%0-)"8#Q"-#R'0-"0()-%#County Museum Association, 107119.
Q&"+'1#OE8#WZbB8#/?'#.').4%4"5-'&)+#'@@'+&8#Pure Appli. Geophys.8#D_8#ILIIE
