The Mw 6.5 Bam earthquake of 26 Dec 2003: Precise source parameters from D-InSAR by R. Wang, Y. Xia, H. Grosser, H.-U. Wetzel, H. Kaufmann, M. Motagh,J. Zschau R. Wang, Y. Xia, H. Grosser, H.-U. Wetzel, H. Kaufmann, M. Motagh, J. Zschau GeoForschungsZentrum Potsdam Germany  Introduction to D-InSAR  Application examples in geosciences  The 2003 Bam earthquake  Precise location of the fault segments  The progressive approximation approach for inversing the slip model  Discussion and conclusions

Radar: RAdio Detection And Ranging

Imaging Radar lake mountain

SAR: Synthetic Aperture Radar

Differential SAR interferometry Seasat, Cosmos-1870, ALMAZ, SIR-A/B/C ERS-1 ESA C-band JERS-1 Japan L-band ERS-2 ESA C-band Radarsat-1 Canada C-band SRTM NASA C/X-band 2000 ENVISAT-1 ESA C-band Radarsat-2 Canada C-band planned launch 2005 ALOS Japan L-band planned launch 2005 TerraSAR-X Germany X-band planned launch 2005 Envisat Launched March 1st 2002 SAR: A data recording and processing technique to improve the resolution of point targets in both azimuth and range direction Typical image resolutions of remote sensing spaceborne SARs are meter

D-InSAR: Application potentials and limitations Application: High-resolution DTMs Pre, Co and Post-seismic displacement maps Volcanic building monitoring before eruptions Land subsidence monitoring Land slides detection in mountainous areas Dynamics of glacier and ice motion Atmospheric studies Advantage: High spatial sampling No field campaign Inexpensive Limitation: Temporal decorrelation Atmospheric noise Poor temporal resolution 1D-displacement field

Mornitoring of tectonic and/or post-seismic motion I

Mornitoring of tectonic and/or post-seismic motion II Wright et al., 2001 Motagh et al., 2006

Mornitoring of volcano Amelung et al., 2000

Application in hydrology Amelung et al. (1999) Las Vegas Subsidence June August2003 Mexico City Strozzi et al. (2003) Motagh et al., 2006 Mashhad Basin in NE Iran

Application to the 2003 Bam earthquake Dry and arid area, perfectly suited for D-InSAR Dry and arid area, perfectly suited for D-InSAR Excellent quality of the D-InSAR data providing Excellent quality of the D-InSAR data providing strong constraints on the source parameters strong constraints on the source parameters High-resolution of earthquake’s fault by a new High-resolution of earthquake’s fault by a new inversion approach inversion approach Implications for earthquake hazard assessment Implications for earthquake hazard assessment

010 km Bam fault Gowk fault City of Bam Baravat The Mw = 6.5 Bam Eq of 26 Dec 2003 The Bam fault system Bam Lut Makran C I B Z a g r o s

Surface deformation induced by a pure strike-slip earthquake Z NS EW ENVISAT -7% -90% +40% LOS

Differential ENVISAT ASAR interferogram: descending pass max. subsidence (-18 cm) N max. uplift (+30 cm) Descending passes: , , km uplift subsidence Bam earthquake: Mw = Dec 2003 SE Iran

Differential ENVISAT ASAR interferogram: ascending pass N Ascending passes: , , km uplift subsidence uplift

Teleseismic solutions

Teleseismic focal solutions  differential SAR interferogram Strike: 188 o, Dip: 81 o, Rake: 165 o (CPPT) Slip: 180 cm Strike: 173 o, Dip: 63 o, Rake: 164 o (Harvard) Slip: 200 cm Strike: 174 o, Dip: 88 o, Rake: 178 o (USGS) Slip: 190 cm

Fault model by Talebian et al. (2004) Talebian et al. (GRL, 2004):  A main strike-slip fault of 20 km dipping to east  A second thrust fault (10 sec. after the the main shock) with 20% of the seismic moment and dipping to west  Least-squares fitting with smoothing and bounding How evident is the derived second thrust fault?

Harvard USGS IIEES N 10 km The Sobel-Edge-Filter Technique Principle: max. gradient should be near and along the ruptured segment Detection of the ruptured segment 10 km

Field observations of surface faulting 10 km Surface rupture north of Bam Surface rupture south of Bam Talebian et al., 2004

The inversion for the slip distribution by the PA approach 68% of the slip energy Sensitivity = Reduction of RMS residual / Magnitude of point dislocation Progressive Approximation A new Progressive Approximation approach 1. Assume: slip  sensitivity of the data to a single point dislocation at the same position (the “acupuncture” approach) => prediction of the slip pattern 2. Determine the amplitude of the slip pattern via least-squares fitting 3. Repeat the procedure 1. & 2. to the remaining residual data 14% + 7% +

The slip model derived from D-InSAR data cm The strike-slip component (right-lateral) The dip-slip component (thrust)

Comparison between predicted and observed interferograms Descending pass DataModelResidual Ascending pass 45 km x 45 km rms = 1.1 cm rms = 1.4 cm

It was a right-lateral strike-slip earthquake as expected for the Bam fault. It was a right-lateral strike-slip earthquake as expected for the Bam fault. The moment magnitude of Mw = derived from D-InSar is in The moment magnitude of Mw = derived from D-InSar is in agreement with the teleseismic solution. agreement with the teleseismic solution. The total length of the ruptured fault is about 24 km, but about 24 km, but More than 80% moment was released from More than 80% moment was released from a 14 km hidden or new fault segment, where a 14 km hidden or new fault segment, where The max. slip > 200 cm at 3-5 km depth, The max. slip > 200 cm at 3-5 km depth, resulting in a stress drop of at least 6 MPa. resulting in a stress drop of at least 6 MPa. The new fault is 4-5 km west to the known main The new fault is 4-5 km west to the known main branch of the Bam fault and dips o to east. branch of the Bam fault and dips o to east. The NW branch of the Bam fault seems to be The NW branch of the Bam fault seems to be continued through the city of Bam southwards. continued through the city of Bam southwards. No evidence was found from the InSAR data for the second thrust event No evidence was found from the InSAR data for the second thrust event as proposed by Talebian et al. (2004). as proposed by Talebian et al. (2004). Results found for the Bam earthquake Harvard USGS IIEES N 10 km

Least-Squares Fitting Optimal fitting, but could be unstable, and the derived slip distribution may exhibits non-realistic oscillations Smoothing & Bounding Solving the stability problems but at the expense of the slip resolution, and the results may be strongly user-dependent Discussion: LS vs. SA The common problem: The solution may be un-unique. Additional constraints from geology and seismology are usually needed (e.g., lower boundary of the rupture area, max. stress drop…) Progressive Approximation Providing a best-fitting slip model controlled by the sensitivity tests So far, no stability problems Slip resolution as high as possible from the data …

A test with synthetic data 3D data: 7800, fitting errors: < 1%, inversion method: PA Data (synthetic) Ux Uy Uz Model

Uncertainties of the inversed slip models Slip distribution (input) Without slip bounding Fitting errors < 1% With slip bounding (200 cm) Fitting errors < 5%