Eos, Vol. 87, No. 7, 14 February 2006 VOLUME 87 NUMBER 7 14 FEBRUARY 2006 PAGES 73–84 EOS, TranSacTiOnS, amErican GEOphySical UniOn The largest observed displacement of Satellite Data Give Snapshot the LOS displacement field of InSAR around the northern Pakistan earthquake damage of the 2005 Pakistan Earthquake area is ~30 centimeters of LOS movement toward the satellite. However, maps of dis- placement as calculated by InSAR were incoherent near the fault mainly because of The detected crustal deformation was PAGES 73, 77 the high deformation gradients resulting along these active faults and all observations from the large displacement (approximately were consistent with previously known While it is well-known that the collision of several meters): Because the measured directions of past fault movements. Model the Indian subcontinent with the Eurasian phase is only modulo 2 π rad (half of the calculations also showed that the faults continent forms the Himalayas, the real-time wavelength), the phase in the high deforma- slipped a maximum of about nine meters. spatial crustal movement of these plates is tion gradients area changes too rapidly to In addition, analysis using other high-res- difficult to observe. However, scientists can count the phase cycles; in other words, olution images from the Space Imaging, Inc. witness a part of this process of the forma- undersampling occurs. Furthermore, strong IKONOS satellite showed that landslides tion of the Himalayas through an eye in seismic motion near the fault caused a loss occurred along the active faults and were space: synthetic aperture radar (SAR). of coherence over the damaged area. concentrated on the northeastern side. From the European Space Agency’s Envi- Because InSAR cannot measure deforma- sat, a satellite with SAR, the details of tions in areas where deformation gradient crustal deformation resulting from a major Method and Analysis is too large, the displacement fields of the earthquake—a chance snapshot of the two SAR amplitude images taken before and growth of the Himalayas—has been cap- SAR measures ground geometry and the after the earthquake were measured using a tured. Envisat’s SAR has provided important distance between the satellite and the sub-pixel-level offset estimation technique data about the northern Pakistan earth- ground surface with radar waves. By com- [ Tobita et al., 2001]. Its measurement accu- quake (M7.6) of 8 October 2005, which piling several successive radar pulses from racy is lower (~1 meter) than that of InSAR, occurred in the Kashmir region in the a source moving over a target, an image but it succeeded in detecting this deforma- northwestern part of the Himalayas. can be formed of that target that combines tion that is impossible to measure with There are two important findings in this all the received echoes. In particular, inter- InSAR. Figure 1a is a combination map of article. First, the earthquake occurred on ferometric synthetic aperture radar (InSAR) the InSAR and the SAR offset field analyses, pre-existing active faults. This means that from space, which calculates the pixel-by- and it shows several-meter-scale crustal surveying existing faults is important for pixel phase differences between two SAR deformations extending in a strip. In addi- estimating future earthquake hazards and images generated at different times over the tion, it shows that the heavily-damaged area risks. Second, the satellite data show the same location, has become a powerful tool north of Muzaffarabad experienced about ruptured earthquake faults in detail, allow- to monitor deformation of the Earth’s sur- five meters of deformation. ing relief planners to quickly simulate and face because the technique has high mea- A fault model was constructed to estimate the seismically damaged areas and surement accuracy (a few centimeters). simulate the surface displacement of the extent of the damage for prompt rescue However, Envisat’s InSAR uses short- Figure 1a. Using a buried fault model in a and relief operations. wavelength (5.6 centimeter, C-Band) radio homogeneous elastic half-space, as The crustal deformation mapped with waves, which makes it difficult to measure formulated by Okada [1985], the model SAR data from Envisat revealed that the large deformation gradients or make mea- fault was divided into three rectangular newly deformed area occupies a ~90-kilo- surements in precipitous terrain. faults on which slip is uniform. Optimal meter-long northwest-southeast trending In this study, earthquake deformation was fault parameters were estimated using an strip extending from Balakot, Pakistan, found by comparing InSAR and SAR images iterative least squares method. The esti- southeast through Kashmir, the disputed of the same region, one before the earth- mated parameters are listed in Table 1, and areas between Pakistan and India. The heav- quake (17 September 2005) and one after positions of each fault plane are shown in ily-damaged area north of Muzaffarabad (22 October 2005). Figure 2. The calculated moment within the Pakistani-controlled area of The Envisat data collected during this magnitude is 7.6, which matches the U.S. Kashmir has the maximum deformation, as study are from descending acquisitions that Geological Survey estimated magnitude. observed by the satellite. There are known result in an east-southeast line-of-sight active faults stretching to the northwest and (LOS) direction from the ground target to southeast near the epicenter, which reveal the satellite. The measured crustal deforma- Relationship Between Known Active Faults some uplift (on the northeastern side) and tion is the change in length along the radar and Displacement dextral (right-lateral) strike-slip activities. LOS from the ground target to the SAR sat- ellite. The components of displacement in Since most of the areas affected by the each direction (north-south, east-west, and up- earthquake are in mountainous regions and B Y S. F UJIWARA , M. T OBITA , H.P . S ATO , S. O ZAWA , down) have not been directly determined. The access is prevented by landslides that have H. U NE , M. K OARAI , H. N AKAI , M. F UJIWARA , H. Y ARAI , result is an image that is not a traditional Car- blocked the roads, ground survey is limited. T. N ISHIMURA , AND F . H AYASHI tesian map. At the moment, no exposed fault has been
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