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 - PowerPoint PPT Presentation
The Mw 6.5 Bam earthquake of 26 Dec 2003: The Mw 6.5 Bam earthquake of 26 Dec 2003: Precise source parameters from D-InSAR Precise source parameters from D-InSAR by by R. Wang R. Wang , Y. Xia, H. Grosser, H.-U. Wetzel, H. Kaufmann, , Y. Xia, H. Grosser, H.-U. Wetzel, H. Kaufmann, M. Motagh, M. Motagh, J. Zschau J. Zschau GeoForschungsZentrum Potsdam GeoForschungsZentrum Potsdam Germany Germany Introduction to D-InSAR Introduction to D-InSAR Application examples in geosciences Application examples in geosciences The 2003 Bam earthquake The 2003 Bam earthquake Precise location of the fault segments Precise location of the fault segments The progressive approximation approach for inversing The progressive approximation approach for inversing the slip model the slip model Discussion and conclusions Discussion and conclusions
Transcript
The Mw 6.5 Bam earthquake of 26 Dec 2003:The Mw 6.5 Bam earthquake of 26 Dec 2003:
Precise source parameters from D-InSARPrecise source parameters from D-InSARbyby
R. WangR. Wang, Y. Xia, H. Grosser, H.-U. Wetzel, H. Kaufmann, , Y. Xia, H. Grosser, H.-U. Wetzel, H. Kaufmann, M. Motagh,M. Motagh, J. ZschauJ. ZschauGeoForschungsZentrum PotsdamGeoForschungsZentrum Potsdam
GermanyGermany
Introduction to D-InSARIntroduction to D-InSAR
Application examples in geosciencesApplication examples in geosciences
The 2003 Bam earthquakeThe 2003 Bam earthquake
Precise location of the fault segmentsPrecise location of the fault segments
The progressive approximation approach for inversing the slip modelThe progressive approximation approach for inversing the slip model
Discussion and conclusionsDiscussion and conclusions
Radar: RAdio Detection And Ranging
2
2
r tct r
c
Imaging Radar
lake
mountain
SAR: Synthetic Aperture Radar
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
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 10-100 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
SubsidenceJune 2003- 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-InSARDry and arid area, perfectly suited for D-InSAR
Excellent quality of the D-InSAR data providingExcellent quality of the D-InSAR data providing strong constraints on the source parametersstrong constraints on the source parameters
High-resolution of earthquake’s fault by a newHigh-resolution of earthquake’s fault by a new inversion approachinversion approach
Implications for earthquake hazard assessmentImplications for earthquake hazard assessment
0 10 km
Bam faultBam fault
Gowk faultGowk fault
City of Bam
Baravat
The Mw = 6.5 BamEq of 26 Dec 2003
The Bam fault system
Bam
Lut
Makran
C I BZ 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
Teleseismic focal solutions differential SAR interferogram
Strike: 188o, Dip: 81o, Rake: 165o (CPPT)Slip: 180 cm
Strike: 173o, Dip: 63o, Rake: 164o (Harvard)Slip: 200 cm
Strike: 174o, Dip: 88o, Rake: 178o (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 TechniqueThe 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 BamSurface rupture north of Bam
Surface rupture south of BamSurface rupture south of BamTalebian et al., 2004
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
A new Progressive ApproximationProgressive 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%
+
0
2
4
6
8
10
12
Alo
ng
dip
[km]
0 2 4 6 8 10 12
Along strike [km]
0
25
50
75
100
125
150
175
200
225
0 2 4 6
[km]
0 2 4
[km]
0
2
4
6
8
10
12
Alo
ng
dip
[km]
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
Des
cen
din
g p
ass
Data Model ResidualA
scen
din
g p
ass
45 km x 45 km
45 km x 45 km
rms = 1.1 cm
rms = 1.4 cm
It was a right-lateral It was a right-lateral strike-slipstrike-slip earthquake as expected for the Bam fault. earthquake as expected for the Bam fault.
The moment magnitude of The moment magnitude of Mw = 6.4 - 6.5Mw = 6.4 - 6.5 derived from D-InSar is in derived from D-InSar is in agreement with the teleseismic solution.agreement with the teleseismic solution.
The total length of the ruptured fault isThe total length of the ruptured fault is about about 24 km24 km, but, but
More than 80% moment was released fromMore than 80% moment was released from a a 14 km14 km hidden or new fault segment, where hidden or new fault segment, where
The max. slip The max. slip > 200 cm> 200 cm at 3-5 km depth, 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 The new fault is 4-5 km west4-5 km west to the known main to the known main branch of the Bam fault and branch of the Bam fault and dips 75-80dips 75-80oo to east to east..
The The NW branchNW branch of the Bam fault seems to be of the Bam fault seems to be continued through the city of Bam southwards.continued through the city of Bam southwards.
No evidenceNo evidence was found from the InSAR data was found from the InSAR data for the second thrust eventfor 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 FittingLeast-Squares Fitting
Optimal fittingOptimal fitting, but could be , but could be unstableunstable, and the derived slip , and the derived slip distribution may exhibitsdistribution may exhibitsnon-realistic oscillationsnon-realistic oscillations
Smoothing & BoundingSmoothing & Bounding
Solving the stability problemsSolving the stability problems but at the expense of thebut at the expense of theslip resolutionslip resolution, and the results , and the results may be stronglymay be stronglyuser-dependentuser-dependent
Discussion: LS vs. SA
The common problem:The common problem:
The solution may be The solution may be un-uniqueun-unique. Additional constraints from geology and . Additional constraints from geology and seismology are usually needed (e.g., lower boundary of the rupture area, seismology are usually needed (e.g., lower boundary of the rupture area, max. stress drop…)max. stress drop…)
