TwoTwo ContrastingContrasting InSARInSAR StudiesStudies ofof RecentRecent EarthquakesEarthquakes inin TibetTibet
Barry Parsons Department of Earth Sciences University of Oxford
John Elliott, Wanpeng Feng, James Jackson, Zhenhong Li, Xinjian Shan, Alastair Sloan, Richard Walker, Richard Walters & Peizhen Zhang SignificantSignificant EarthquakesEarthquakes overover thethe PastPast TwoTwo YearsYears
Population Casualties exposed to MMI = Casualities/ Earthquake Date Magnitude VIII (USGS Fatalities+ Exposed PAGER) Missing
L’Aquila, Italy April 2009 6.3 10,000 308 3%
Haiti January 2010 7.0 3,128,000 222,500 7%
Maule, Chile February 2010 8.8 3,649,000 562 0.015%
Sierra El April 2010 7.2 561,000 4 0.0007% Major, Mexico
Yushu, Tibet April 2010 6.9 12,000 2,700 22.5%
Darfield September 2010 7.0 22,000 0 0% New Zealand Christchurch February 2011 6.1 320,000 181 0.06% New Zealand
Tohoku, Japan March 2011 9.0 6,096,000 23,500 0.4% TheThe 20102010 MMww 6.96.9 YushuYushu (Qinghai,(Qinghai, China)China) EarthquakeEarthquake
The earthquake occurred at 23:49 on 13 April, 2010 (UTC; 07:49, 14 April 2010, local) Approximately 70% of houses collapsed. ~2,700 people were killed and over 12,000 injured
Gyegu Monastery SurfaceSurface RupturesRuptures ofof thethe YushuYushu EarthquakeEarthquake
Earthquake occurred on the Yushu-Garzê-Xianshuihe Fault System Surface rupture traced for about 35 km with a peak slip of 1.8m InterferogramsInterferograms forfor thethe YushuYushu EarthquakeEarthquake
PALSAR acquisition 17 April 2010 Interferogram posted 20 April 2010 Envisat acquisition 26 April 2010 Sentinel 1A and 1B will eventually provide mean acquisition time of 3 days. To locate fault for the purpose of modelling, used azimuth and range offsets, phase gradients, interferometric coherence, and SPOT-5 imagery.
Li et al, JGR (in review) SPOTSPOT 55 ImageryImagery forfor thethe YushuYushuYushu EarthquakeEarthquakeEarthquake
Panchromatic, 2.5 m resolution SPOTSPOT 55 ImageryImagery forfor thethe YushuYushuYushu EarthquakeEarthquakeEarthquake SPOTSPOT 55 ImageryImagery forfor thethe YushuYushuYushu EarthquakeEarthquakeEarthquake SPOTSPOT 55 ImageryImagery forfor thethe YushuYushuYushu EarthquakeEarthquakeEarthquake ModellingModelling ofof thethe InterferogramsInterferograms
Also used data from Envisat tracks 498A and 004D in the modelling 3 fault segments; 1 km resolution for the distributed slip model. Modelling showed rupture occurred along a length of about 75 km. SurfaceSurface DisplacementsDisplacements forfor thethe YushuYushu EarthquakeEarthquake
Li et al, JGR (in review) BodywaveBodywave ModellingModelling forfor thethe YushuYushu EarthquakeEarthquake
Main points: Two peaks in the rate at which seismic moment was generated. Seismic moment is the main measure of earthquake excitation and is proportional to the amount of slip and the area on which it occurs. Best fit if assume SE propagation of rupture at ~2.5 km/s Centroid depth of 6 km
MomentMoment ReleaseRelease DistributionDistribution andand SurfaceSurface ObservationsObservations
Li et al, JGR (in review) Majority of moment release above 10 km. Three slip patches. Test hypotheses that NW patch is due to the Mw 6.1 aftershock. TravelTravel TimeTime DifferencesDifferences betweenbetween MMww 6.16.1 AftershockAftershock andand MainshockMainshock DistributedDistributed SlipSlip forfor thethe YushuYushu EarthquakeEarthquake
N
Yushu
Geometry with propagation towards town at end of the fault is same as for the 2003 Bam earthquake.
Slip deficit south of Yushu since last earthquake in 1896 is about 0.7m ( Mw 6.5)
20082008 andand 20092009 MMww 6.36.3 QaidamQaidam BasinBasin EarthquakesEarthquakes
Elliott et al, GRL (2011) FaultingFaulting fromfrom ASTERASTER SatelliteSatellite ImageryImagery FaultingFaulting fromfrom ASTERASTER SatelliteSatellite ImageryImagery EnvisatEnvisat InterferogramsInterferograms forfor QaidamQaidam EarthquakesEarthquakes
Elliott et al, GRL (2011) EvidenceEvidence forfor SegmentationSegmentation ofof aa FaultFault withwith DepthDepth
Elliott et al, GRL (2011) CoulombCoulomb StressStress ChangesChanges duedue toto thethe 20082008 EarthquakeEarthquake
Elliott et al, GRL (2011)
Coulomb stress FaultingFaulting andand FocalFocal MechanismsMechanisms forfor thethe GowkGowk FaultFault
1981 Mw 7.1 Sirch Earthquake 65 km long rupture Max 0.4 m surface offsets 18 km centroid Shallow dipping thrust
1998 Mw 6.8 Fandoqa Earthquake 20 km long rupture Max 3 m surface offsets 5 km centroid Strike slip with normal component
Berberian et al., GJI (2001) ConclusionsConclusions
Combining InSAR and seismology shows that the cause of the relatively large number of casualties from the 2010 Yushu earthquake was probably due to the propagation of the rupture along the fault towards the town, terminating there, combined with the vulnerability of the building stock. A similar scenario occurred for the Bam earthquake. In that case a strong motion accelerometer was available to provide independent evidence for the point of initiation of the rupture and hence the direction of propagation. The InSAR study of the closely separated 2008 and 2009 Qaidam earthquakes indicates segmentation of the fault with depth. Depth segmentation may occur where faults interact and the fault geometry is evolving. In such cases, just because a large earthquake has occurred at same location, it does not mean the immediate seismic hazard has gone away. The occurrence of earthquakes closely spaced in location and time may also lead to incompleteness in the palaeoseismological record.
EstimatingEstimating thethe LengthLength ofof thethe FaultFault fromfrom thethe SeismicSeismic MomentMoment
M0 LW u
Assume: = 3.21010 Pa, W = 15 km,
19 u = 1.5 m, M0 = 2.5 10 N m (GCMT), then L = 35 km
19 W =10 km and M0 = 2.210 Nm L = 42 km SeismicSeismic RuptureRupture inin thethe BamBam EarthquakeEarthquake
Bam
The coloured area is the patch on the fault that slipped in the earthquake as determined by modelling the radar interferometry observations. The circle shows the distance to the initial point of rupture from Bam determined from the recording of an accelerometer in Bam. The location of rupture initiation can be identified (blue circle). The rupture propagated from south to north.
Jackson et al, GJI (2006) SlipSlip DistributionsDistributions
2008 2009