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The Mw 6.5 Bam earthquake of 26 Dec 2003: Precise source parameters from D-InSAR by

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 GeoForschungsZentrum Potsdam Germany. Introduction to D-InSAR Application examples in geosciences The 2003 Bam earthquake

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The Mw 6.5 Bam earthquake of 26 Dec 2003: Precise source parameters from D-InSAR by

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  1. 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 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

  2. Radar: RAdio Detection And Ranging

  3. mountain lake Imaging Radar

  4. SAR: Synthetic Aperture Radar

  5. Envisat Launched March 1st 2002 Differential SAR interferometry Seasat, Cosmos-1870, ALMAZ, SIR-A/B/C ERS-1 ESA C-band 1991-2000 JERS-1 Japan L-band 1992-1998 ERS-2 ESA C-band 1995- Radarsat-1 Canada C-band 1995- SRTM NASA C/X-band 2000 ENVISAT-1 ESA C-band 2002- Radarsat-2 Canada C-band planned launch 2005 ALOS Japan L-band planned launch 2005 TerraSAR-X Germany X-band planned launch 2005 • 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 10-100 meter

  6. 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

  7. Mornitoring of tectonic and/or post-seismic motion I

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

  9. Amelung et al., 2000 Mornitoring of volcano

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

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

  12. Gowk fault The Mw = 6.5 Bam Eq of 26 Dec 2003 C I B Lut Z a g r o s City of Bam Bam Bam fault Makran Baravat 0 10 km The Bam fault system

  13. -7% +40% LOS -90% ENVISAT Surface deformation induced by a pure strike-slip earthquake EW NS Z

  14. Differential ENVISAT ASAR interferogram: descending pass Descending passes: 11-06-2003, 03-12-2003, 07-01-2004 N subsidence Bam earthquake: Mw = 6.5 26 Dec 2003 SE Iran max. subsidence (-18 cm) max. uplift (+30 cm) uplift 10 km

  15. Ascending passes: 16-11-2003, 25-01-2004, 29-02-2004 N 10 km Differential ENVISAT ASAR interferogram: ascending pass uplift uplift subsidence uplift

  16. Teleseismic solutions

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

  18. How evident is the derived second thrust fault? 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 Fault model by Talebian et al. (2004)

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

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

  21. + + 14% 7% 68% of the slip energy 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 The inversion for the slip distribution by the PA approach Sensitivity = Reduction of RMS residual / Magnitude of point dislocation 2. Determine the amplitude of the slip pattern via least-squares fitting 3. Repeat the procedure 1. & 2. to the remaining residual data

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

  23. rms = 1.1 cm 45 km x 45 km rms = 1.4 cm 45 km x 45 km Data Model Residual Comparison between predicted and observed interferograms Descending pass Ascending pass

  24. N IIEES Harvard USGS 10 km Results found for the Bam earthquake • It was a right-lateral strike-slip earthquake as expected for the Bam fault. • The moment magnitude of Mw = 6.4 - 6.5 derived from D-InSar is in agreement with the teleseismic solution. • The total length of the ruptured fault is about 24 km, but • More than 80% moment was released from a 14 km hidden or new fault segment, where • The max. slip > 200 cm at 3-5 km depth, resulting in a stress drop of at least 6 MPa. • The new fault is 4-5 km west to the known main branch of the Bam fault and dips 75-80o to east. • The NW branch of the Bam fault seems to be continued through the city of Bam southwards. • No evidence was found from the InSAR data for the second thrust event as proposed by Talebian et al. (2004).

  25. Progressive Approximation Providing a best-fitting slip model controlled by the sensitivity tests So far, no stability problems Slip resolution as high as possiblefrom the data … Discussion: LS vs. SA Least-Squares Fitting Optimal fitting, but could be unstable, and the derived slip distribution may exhibits non-realistic oscillations Smoothing & Bounding Solving the stability problemsbut at the expense of the slip resolution, and the results may be strongly user-dependent 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…)

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

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

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