GEOPHYSICAL RESEARCH LETTERS, VOL. 25, NO. 21, PAGES 4003-4006, NOVEMBER 1, 1998
Crustal
deformation
in the Baikal
rift from GPS measurements
Eric Calais,Olivia Lesne,JacquesD6verch•re
G6osciencesAzur UMR 6526, CNRSFUPMC, Valbonne and Villefranche/Mer, France
Vladimir San'kov, Andrei Lukhnev, Andrei Miroshnitchenko, Vladimir Buddo, Kirill Levi
Instituteof the Earth'sCrust,SiberianBranchof the RussianAcademyof Sciences,Irkutsk,Russia
VjacheslavZalutzky
VS-NIIFTRI, Time andFrequencyServiceDivision,Irkutsk,Russia
Yuri Bashkuev
BuryatScientificCenter,SiberianBranchof the RussianAcademyof Sciences,Ulan Ude,Russia
We processedpseudorangeand phase data in single-day
Abstract. Three yearsand four campaignsof GlobalPositioning
System(GPS) measurements
(1994-1997) in the Baikal rift zone, solutionsusing the GAMIT software (version 9.6, King and
largestactive continentalrift systemin Eurasia,show crustal Bock, 1997). We solvedfor regionalstationcoordinates,satellite
extensionat a rate of 4.5+1.2 mm/yr in a WNW-ESE direction. 'statevectors,13 tropospheric
zenithdelayparameters
per site
A comparison with moment release of large historical and day, and phaseambiguitiesusing doubly-differencedGPS
earthquakes
suggests
thatelasticstrainis currentlyaccumulating phase measurements.We used IGS final orbits, IERS earth
in the Baikal rift zone alongactivefaultsthat currentlyhavethe orientation parameters, and applied azimuth and elevation
potentialfor a M=7.5 earthquake.The GPS-derivedextension dependantantennaphase center models, following the tables
by the IGS. Four primaryandeightsecondaryIGS
rate in the Baikal rift zone is at leasttwo times greaterthan the recommended
prediction
of mostdeformation
modelsof Asia.Thisresultcould
stations (ONSA, GRAZ, TIDB, FAIR, HART, KOKB, TSKB,
reflect the dynamic contribution of the Pacific-Eurasia USUD, TAIW, KITA, $HAO, IRKT) were included in the
subductionto intracontinental deformation in Asia, in addition to
processingto serve as ties with the International Terrestrial
the effect of the India-Eurasia collision.
ReferenceFrame 1994 (ITRF94, Boucheret al., 1996).
Introduction
The Baikal riff zone, located at the northernedge of the
centralAsia intracontinental
deformationzone (Figure 1), is the
largestactivecontinentalrift systemin Eurasia(Tapponnierand
The least squaresadjustment
vectorand its corresponding
variance-covariance
matrix for station positionsand orbital
elementsestimatedfor eachindependent
daily solutionwerethen
passedto a Kalmanfilter (GLOBK, Herringet al., 1990) in order
60'
Molnar, 1979). It extends over a distance of about 2000 km
90'
120'
150'
alongtheS-shaped
paleozoic
suture
thatseparates
theSiberian60.
Platform from the Sayan-Baikalmobile belt (Logatchevand
Zorin, 1992). We presentthe resultsof four campaigns
of Global no.
PositioningSystem (GPS) measurements
in the southernand
westernpartsof the Baikal rift zone.This data set providesthe 20first directmeasurements
of the currentdisplacement
ratesat the O'
boundarybetweenstableEurasiaandEastChina.
!
.
.;•,?
:...,.•..•:
?,.:.:•.,..
ß
.•>x".:
":::"••,
....
ß ,.•.•.,/.-_....::,.•.?,•_•
GPS Measurementsand Data Processing
GPS measurements
in the Baikal
rift zone were initiated
ß . ".
; ,d ..:.... '.?,,.•.'Y
k
•."' "':'.':'
:•'"•
i
in
July 1994 with the installationand first observationof a network
of 11 sitescoveringits southernand westernparts (Figure 1).
The sitesIRKU and ULAN were reoccupiedin August 1995.
The whole network was remeasuredin August 1996 and August
1997. We usedAshtechP12 and Z12 GPS receiverssamplingat
30 seconds.
. Each site was surveyed 22 hours a day for an
average of four consecutivedays during each campaign.We
benefit, since 1996, from the data from the Irkutsk permanent
IGS station(IRKT), located40 m away from the IRKU mark.
$
2-.';:
....
'•'•"•"-'
"" "'- '
.
52'
' ß
,..:..:...... :
:.
•. .....
• . .•
'
..
.
:
-.:,ß .......
51'
..
' ß'. 'n.vs.
sta:
.'...':;):.;:.•,..o..•
'•"
""-•\.•
........
: --'."v..'.'
"':
GO
LIA":",
.....
'..7'"re'".''...........
.•..:.'
.........
''
":..'
""•'"
'•:'
' ' •..
ß
100'
102'
104'
106'
108'
Figure1. Tectonicsetting
of thesouthern
Baikalriff zone:major
PapernUmberGRL-1998900067.
active faults (SaF: Sayan fault, TuF: Tunka fault, Mo F:
Morskoyfault,Ob F: Obruchevsky
fault,O1F: Olkhonsky
fault,
Pr F: Primorskyfault), instrumental
seismicity(dots,1962-1980,
M>2.8), historicalearthquakes(stars,see Table 2),-and focal
mechanisms
of major earthquakes.
The trianglesindicatethe
0094-8276/98/GRL-
location of the GPS sites.
Copyright1998by theAmericanGeophysical
Union.
1998900067505.00
4003
4004
CALAIS
ET AL.: CRUSTAL
DEFORMATION
Table 1. Velocities (V, mm/yr) with respect to IRKU and
associatedone standard deviation formal errors (o, mm/yr)
computedby scalingthe 1-o uncertainties
of the final adjustment
by theoverallchi-squared
perdegreeof freedom.
Lon.
Lat.
Vlon
Vlat
cron
cflat
correlation
IN THE BAIKAL
20
RIFF ZONE
' I ' I I I ' t ' I ' I I I I I ' I ' ' ' I ' ' ' I ' ' ' I ' ' ' I ' ' ' I ' ' ' I '
NS component- slope= 3.4 +- 0.2 mrn/yr,wrms= 2.4 mm
10
o
-10
E•'-20 ß,... ,..., ... , ...,... ,... ,. •. ,..., .
ß
Site code
,
108.24 52.97 3.•
-0.0323
TURK
107.62
51.81
2.8
-4.0
1.1 1.4 1.0
1.0
0.6
-0.0693
ULAN
106.58
52.79
-0.7
2.2
1.2
1.0
-0.0430
ANGA
106.49
50.74
3.5
0.2
1.2
1.0
-0.0549
KIAT
106.01
51.17
4.6
-0.8
1.2
1.0
-0.0596
UDUN
105.50
53.06
0.5
0.5
1.2
1.0
-0.0629
BAYA
104.89
51.85
2.2
-0.5
1.4
1.2
-0.0975
LIST
104.32
52.22
0.2
0.4
1.4
1.2
-0.0589
IRKT
104.32
52.22
0.0
0.0
1.0
0.6
-0.0777
IRKU
103.74
51.77
2.3
0.2
1.2
1.0
-0.0517
KULT
103.70
51.65
1.6
0.0
1.4
1.0
-0.0376
SLYU
102.21
51.76
0.1
-2.3
1.4
1.0
-0.0460
BADA
• 20
................
'''''i
•_
•o ''''...........
• '''''
EW component- slope= -3.8 +- 0.2 mm/yr,wrms= 3.6 mm
o
-10
• -20 ß,
,
,
•
,... ,..
• 40'''lii'lliill''l'''
I'''1'''
I'''1'''1'''1•
.C_o
UPcomponent
- slope
= 1.3+- 1.4mm/yr,
wrms
= 11.9mm
• 20
-4•
ßi
ß
i
i ßß' i ßß
49600 49700 49800 49900 50000 50100 50200 50300 50400 50500 50600
julianday number[07/25/94to 08/12/97]
to estimatestation positionsand velocities.We imposedthe
reference frame by minimizing the position and velocity
deviationsof IGS corestationswith respectto the ITRF94 while
estimatingan orientation,translationand scaletransformation.
The height coordinateand velocitywere downweigthed
by a
factorof 10 relativeto the horizontalcomponents.
Figure 3. Baseline time seriesbetween Irkutsk and Ulan Ude.
Each point representsa daily solutionwith its 1-• error bar. The
four setsof point representthe 94, 95, 96, and 97 measurements.
The dashedline is the bestfit linear regressioncomputedfrom a
weightedleastsquaresadjustmentto the data.
verticalcomponent
(Figure3). The GPS-derivedvelocityfield
(Figure 2) showsthat:
Velocity Field
1. ThetwositeslocatedonthestableSiberian
platfo.rm (IRKU,
Our resultsoverthe threeyearperiod1994-1997arelistedon
Table1 anddisplayedin Figure2. The formalerrorshavebeen
computedby scaling the 1-• uncertaintiesof the final
adjustmentby the overall chi-squaredper degreeof freedom.
The uncertaintiesin the horizontalcomponents
of the velocity
estimatesrangebetween0.6 and 1.4 mm/yr (1-•). Long term
baselinerepeatabilities
(weigthedRMS scatteraboutthebestfit
linearregression
to the positiontime series)are on the orderof
2 to 3 mm for the horizontalcomponents
and5 to 10 mm for the
BAYA) showno relativemotionat the 1 mrrdyrlevel.Thisresult
is a goodinternaltestof theoverallqualityof thevelocityfield,
since both sites are located on the same aseismicand undeformed
crustal block with no known active fault between them.
2. The four sites located on the southeastern side of the rift
(UDUN, KIAT, ULAN, TURK) show extensionacrossthe rift
zone at an averagerate of 4.54-1.2mrrdyr(1-•). This resultis in
goodagreement
with geological
estimates
basedon topographic
offsetsin holocenealluvialfansthat indicate5 mrrdyrof total
extension
in thenorthernpartof theBaikalrift zoneduringthe
last 10,000years (Houdry, 1994). The directionof extension
varies between N80 and N140 (relative to IRKU). Given the
100'
102'
104'
106'
108'
54'
smallnumberof observation
epochsavailable,it is not possible
54- to determinewhetherthis variabilityof tectonicoriginor if it
reflects GPS measurement errors. The direction of extension
appears
to be obliqueto thedirectionof themajornormalfaults,
implyingleft-lateralwrench-extensional
faultingin thesouthern
53'
53-partof theBaikal
rift zone.Thisresult
is consistent
with
earthquake focal mechanisms(Figure 1), stress tensor
calculations, and microtectonic measurements in the southern
52'
....ß,,..,
A
T
'"i. •
ULAN
4.•
52- Baikalrift zonethatpredictslipvectors
trending
N105onthe
majoractivefaults(Petitet al., 1996;Delvauxet al., 1997).
3. The five siteslocatedalongthe majoractivefault zonethat
5l- bounds lake Baikal to the northwest and continues westward
51'
along the northernside of the Tunka basin (BADA, SLYU,
50'
MONt30Li A
100'
102'
'"z7q•.....
.....
..-""
104'
'.........
'-.\.
..
106'
108'
KULT, LIST, ANGA) showvelocities
on theorderof 2 mrrdyr
5o- relativeto IRKU. All thesesitesarelocatedin theclosevicinity
Figure 2. Velocities obtained from GPS measurementsin the
centraland southernpartsof the Baikal rift and the Tunka basin.
The arrow length is proportional to the displacementrate,
indicatedin mm/yr next to the sitecodename.The velocitiesare
expressed relative to IRKU. The ellipses represent 95%
confidence intervals.
of a majoractivefault and are thereforelikely to reflectelastic
strain accumulation.
4. We observeno significantrelativemotion(at the 1 mrrdyr
level) betweenKULT and SLYU, located 10 km from eachother
on each side of the Sayan-southBaikal active fault. This
probablyindicates
thattheSayan-south
Baikalfaultis currently
locked.
CALAIS ET AL.: CRUSTAL
DEFORMATION
Discussion
IN THE BAIKAL
RIFT ZONE
4005
parallelfaultsmakesuchpredictionmorequestionable,
but may
indicatea smallerrecurrenceinterval (150 years)for a M=7.5
Comparisonwith SeismicMoment Release
event.
Accordingto the historicalseismicitycatalogsof Solonenko
(1977) and Kondorskayaand Shebalin(1982), six earthquakes Comparisonwith deformationmodelsof Asia
exceeding
M=6TMhaveoccurred
in the southBaikalrift since
1700 (Table 2). Three events most probably occuredon the
Obruchevskyfault, that boundsthe SouthernBaikal basinto the
Severalkinematicmodelshave been proposedrecentlyto
explain the present-daydeformationin centralAsia, basedon
Quaternaryfault rates(Avouacand Tapponnier,1993; Peltzer
north, whereas the other three occured in the Central Baikal
and Saucier, 1996) and sparsegeodeticresults(Molnar and
basin along the Morskoy fault (Figure 1). Following the Gipson,1996;EnglandandMolnar, 1997) or momenttensorsof
empiricalmagnitude-moment
law givenby HanksandKanamori largeearthquakes
(Holt et al., 1995). Whetherthesemodelsusea
(1979), thesetwo subsetsreleasedminimumseismicmomentsof
continuum or a rigid block approach,they all use the
4.8x102øNm
and 2.2x102øNm,
respectively.
In spiteof large India/Eurasia
convergence
as a kinematicboundaryconditionto
uncertainties due to crude estimates of seismic moments for the
the south.They predictan extensionrate that variesbetween0period 1700-1900, thesevaluesare comparableto the 0.9 to 1 mm/yr(PeltzerandSaucier,1996)anda maximumof 2 mm/yr
2.6x10•øNm seismicmomentreleaseover the last 85 years (England and Molnar, 1997) in the Baikal rift zone, which is
proposed
from long-termand short-termkinematicdeformation significantly
smallerthanourGPSresults.An alternatemodeling
models of Asia (Holt et al., 1995).
In order to convert this cumulated seismic moment release
into total slip on each fault, and since active faults in the
southern and central Baikal basins are well delineated, we use
approachhas recentlybeenproposedby Kong and Bird (1996)
who useda dynamicthin-shellfinite-element
modeltakinginto
accountboth the India-Eurasiaand Pacific-Eurasia
convergence
as boundaryconditions.
Their bestfit modelpredicts19 mm/yr
the approachproposedby Brune (1968). Using a seismogenic of extensionin the Baikal rift zone,whichis four timeshigher
thicknessof 25 km (D6vercht:reet al., 1993), the fault dip angles than our GPS results. The high heat flow values (and
givenin Table2, anda rigidityof 3.3x10
• dyn/cm
•, wefinda consequentlylow lithosphericthickness)usedby theseauthors
cumulatedslip of 3.3 m alongthe SouthBaikal fault and 1.0 m fortheBaikalrift (110to 130mW/m
•) compared
to theaverage
on the centralBaikal fault, corresponding
to averagehorizontal valueof 70to 90mW/m
• givenby Lysak(1992)couldpartly
slipratesof 5.6 mm/yrand2.1 mm/yrrespectively.
Theserates, explainsucha discrepancy.
that reflect seismic moment released over 3 centuries, are
comparable
to the 4.5 mm/yr far-fieldextensionrate acrossthe
rift obtainedfrom GPS measurements
over 3 years.This result,
The fact that the GPS-derived extension rate in the Baikal rift
zone is fasterthan the predictionsof kinematicmodelsbasedon
the hypothesisthat present-daydeformationin central Asia is
enterely driven by the India/Eurasiacollision suggeststhe
togetherwith GPS resultsshowingthatthe Sayan-south
Baikal
faultis locked,suggests
thatlittle or no aseismic
slipis occurring existenceof an additionalprocessparticipating
in the presentalongactivefaultsin thesouthern
andwestern
partsof theBaikal day openingof the Baikal rift zone.It haslong beensuggested
rift zone, which are therefore currently accumulatingelastic thatthe Baikalrift zonewasthe restlitof "activerifting",with
strainto be releasedin futureearthquakes.
Consideringthe date crustalextension
primarilycausedby thediapiricupwellingof a
ofthelastmajorevent(1742event,
M=7TM,
whichreleased
about mantleasthenolithor plume(e.g. Zorin, 1981). However,recent
50% of the seismic moment of the South Baikal region in the
past 300years) and a constantfar-field extensionrate of
4.5 mm/yr, we can infer that the South Baikal fault has
accumulated
2.7 m of potentialslip (averagedisplacement)
since
that time. This would correspondto a M=7.5 earthquakeif it
results from gravity models (van der Beck, 1997; Petit et al.,
1997), finite-elementdeformationmodels(Lesneet al., 1998), P-
wave delay-time tomography(Petit et al., in press), and
geochemistry
of mantlexenoliths(Ionovet al., 1995) showvery
little mantleuplift undertheBaikalrift zoneandsuggest
thatthe
were to be releasedin a singleevent (Wells and Coppersmith, present-dayextension is mostly driven by horizontal forces
1994).If magnitude
7.5-7.7 earthquakes
(about3 m of potential related to the far-field kinematics.If local processesdo not
slip accumulation)
are characteristic
of the SouthBaikalfault significantly contribute to the force balance in the Baikal rift
zone (an assumption
that is compatiblewith our historical zone,the additionaldynamiccontributionsuggested
by our GPS
knowledgeandwith its 150km longcontinuous
rectilineartrace resultsmustbe soughtin boundaryforcesnot accountedfor in
asunderlined
by theinstrumental
seismicity),
a constant
far-field classical deformation models, in particular at the Pacific
extensionrate of 4.5 mm/yr would imply a 350-yr recurrence subduction
zone,whosedynamiceffectson lithosphericstresses
interval for such events. In the central lake, the numerous sub-
and strain in continentalAsia are poorly known. Possible
processesthat could significantly influence the force balance
several
thousands
of
kilometers
inland
from
the
Pacific
subduction include the effect of shear traction in the subduction
Table 2. List of large historical earthquakesand main border
faults in the South Baikal rift. Estimatedmagnitudes(M) are
taken from Solonenko (1977). Seismic moments (Mo)
are
expressed
in 1020
Nm. SB=SouthBaikal,CB=Central
Baikal.
SeeFigure 1 for fault and eventlocations.
Conclusions
Area Eventdate M
Mo Associated
fault LengthDip
SB 06/27,1742 7TM 3.7 Obruchevsky150km 60ø
SB 10/24,1769 7TM 0.9 Obruchevsky
150km 60ø
SB
04/11, 1902 6.9
0.2
CB 01/12,1862 71/2 1.8
CB
zone (Kong and Bird, 1996) and the influenceof the sinking
oceanic lithosphere on the neighboring subcontinental
convectionby a lateralcoolingeffect (Nataf et al., 1981).
Obruchevsky150km 60ø
Three years of GPS measurementsshow that the Baikal rift
zoneis currentlyopeningat a rateof 4.5+1.2mrn/yrin a NW-SE
direction.Sincethe entirenetworkhasonly be measuredthree
Morskoy 200km 50ø
times (only IRKU and ULAN have been measuredfour times),
6.8
0.2
Morskoy
CB 08/29,1959 6.8
0.2
Morskoy 200km 50ø
theseresultsare still preliminary.They are howeverin good
agreementwith recentgeologicalestimates
of fault slip ratesand
11/26, 1903
200 km 50ø
with the strainand stresspatterndeducedfrom instrumental Holt, W.E., M. Li and A.J. Haines, Earthquakestrain rates and
instantaneousrelative motions within central and eastern Asia,
seismicity.
Geophys.J. Int., 122, 569-593, 1995.
VLBI resultsat Shanghai(Heki, 1995; Molnar and Gipson,
Houdry, F., M6canismesde l'extensioncontinentaledans le rift nord1996) show8_+0.5
mm/yr of eastwardmotionof SouthChina
Baikal,Sib6rie:contraintes
desdonn6es
d'imagerie
SPOT,de terrain,
relative to Eurasia.Zhang et al. (1998) determinea Plio-
de sismologieet de gravim6trie,PhD Thesis,UniversitdPierre et
Quaternary
extension
rateof 54-2mm/yrin a NW-SEdirection
Marie Curie,Paris VI, 356 pp., 1994.
across
theOrdosgrabensystem,
thatprobablyaccounts
for part Ionov, D.A., S.Y. O'Reilly, and I.V. Ashchepkov,Felspar-bearing
of the South China-Eurasia relative motion. Our GPS results
show4.5-+1.2mm/yrof NW-SE extension
across
theBaikalrift
zone,a valuethatis consistent
with the resultsmentionedabove.
The strainin the Baikalregionis howeverlocalizedon a narrow
lherzolite xenoliths in alkalibasaltsfrom Hamar-Daban, southern
Baikal region,Russia,Contrib.Mineral. Petrol., 122, 174-190, 1995.
King, R.W., and Y. Bock, Documentationfor the GAMIT GPS software
analysis,release9.4, unpublished,
1997.
(50 to 100km wide) rift structurewhich appearsto be Kondorskaya,N.V., and N.V. Shebalin,New catalog of strong
earthquakes
in theUSSRfromancienttimesthrough1977,608 pp.,
concentrating
thepresent-day
deformation
between
Eurasiaand
WorldData Cent.A Solid-EarthGeophys.,
Boulder,Colorado,1982.
East China.
Kong, X., and P. Bird, Neotectonicsof Asia: thin-shell finite-element
modelswith faults, in "The Tectonic Evolution of Asia", An Yin and
A comparison
betweenthe GPS resultsand the seismic
momentreleased
by historicalearthquakes
suggests
thatelastic
T. Mark HarrisonEds,CambridgeUniversityPress,19-34, 1996.
strainis currentlyaccumulating
in the Baikalrift zonealong Lesne,O., E. Calais,and J. D6verch•re,Finite elementmodelingof
activefaultsthathavethe potentialfor a M=7.5 earthquake
if
crustaldeformationin the Baikal rift zone:new insightsinto the
thatelasticstrainwereto be releasedin a singleeventtoday.If
active-passive
debate,Tectonophysics,
289, 327-430, 1998.
aseismic
slipisneglected,
wehypothesize
recurrence
intervals
of Logatchev, N.A. and Y.A. Zorin, Baikal rift zone: structure and
geodynamics,
Tectonophysics,
208, 273-286, 1992.
150-350yearsfor large (M~7.5-7.7)eventsalongthe lake
rifts, Tectonophysics,
shoreline,
whichcouldimplytheoccurrence
of a strongshockin Lysak,S.V., Heat flow variationsin continental
208, 309-323, 1992.
the near future.
The ratherhigh extensionrate found here for the Baikal rift
zone comparedto the predictionof mostdeformationmodelsof
Asia could reflect the dynamic effect of the Pacific-Eurasia
subduction in addition to the well-kown
effect of the the India-
Eurasia collision. This hypothesisneedsto be confirmedby
additionalGPS measurementsand further testedusing dynamic
deformation
Molnar, P., and J.M. Gipson,A boundon the rheologyof continental
lithosphere
usingvery longbaselineinterferometry:
The velocityof
SouthChinawith respectto Eurasia,J. Geophys.
Res.,101,545-553,
1996.
Nataf, H.C., C. Froidevaux,J.L. Levrat, and M. Rabinowicz,Laboratory
convection
experiments:
Effectsof lateralcoolingandgeneration
of
instabilitiesin the horizontalboundarylayers,J. Geophys.Res., 86,
643-6154, 1981.
models.
Peltzer,G. and F. Saucier,Present-daykinematicsof Asia derivedfrom
Acknowledgments.
We are particularlygratefulto Academician
N.A.
Logatchev,
formerdirectorof the Instituteof theEarth'sCrust,Siberian
Branchof the RussianAcademyof Sciences,for his strongsupportof
this work. We thank all the field operatorswho participatedin the
acquisition
of the GPS data.Insightfulcomments
from G. Peltzerand
S. Wdowinskyhelpedimprovethe first versionof this paper.This
researchwas supportedby the French Ministry for Educationand
Research ("DSPT3"), the French Ministry of Foreign Affairs
CEnveloppe Echanges Scientifiques 1994-1997"), CNRS-INSU
Programs
("Tectoscope-Positionnement
94", "Int6rieurde la Terre97"),
NATO (grant LG#961302), and the SiberianBranchof the Russian
Academyof Sciences.
Contribution
G6osciences
AzurNo. 215.
geologic
faultrates,J. Geophys.
Res.,101,27,943-27,956,
1996.
Petit, C., E.B. Burov, and J. D6verch•re, On the structure and
mechanicalbehaviorof the extendinglithospherein the Baikal rift
fromgravitymodeling,
EarthPlanet.Sci.Lett.,149,29-42,1997.
Petit,C., J. D6verchb•re,
F. Houdry,V.A. Sankov,V.I. Melnikova,andD.
Delvaux,Present-day
stressfield changesalongthe Baikal rift and
tectonicimplications,
Tectonics,
1171-1191,1996.
Petit, C., I. Yu. Koulakov,and J. D6verchb•re,
Velocity structurearound
the Baikal rift zonefrom teleseismicandlocalearthquaketraveltimes
andgeodynamic
implications,
Tectonophysics,
inpress,1998.
Solonenko,V.P., (Ed.), Seismic zoning of Eastern Siberia and its
geological
andgeophysical
base,Nauka(in Russian),
303pp.,1977.
Tapponnier,
P. andP. Molnar,Activefaultingandcenozoic
tectonics
of
the Tien Shan,Mongoliaand Baikal regions,J. Geophys.Res.,84,
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(ReceivedJune8, 1998;revisedJuly 31, 1998;acceptedAugust6, 1998)