The Bam Earthquake of 26 December 2003

The devastating earthquake of 26 December 2003 claimed more than 26,000 lives in the city of Bam and surrounding towns and villages in Southeast Iran, and left the majority of the Bam population homeless. The reason for this tragedy was an unfortunate combination of geological, social and human circumstances. The causative fault practically traversed the city of Bam and the earthquake occurred at a shallow depth. The residential buildings were completely inappropriate for a seismic region, being extremely vulnerable to earthquake shaking, and the earthquake occurred early in the morning when most people were still sleeping. The damage pattern was nearly symmetric about a line 3 km to the west of the surface expression of the Bam fault, and the damage attenuated rapidly with distance from this line. The industrial facilities and the lifelines performed relatively well and experienced slight to moderate damage, but this might have been due to their distance from the earthquake epicentre. However, many of the qanat (traditional subterranean irrigation channels) chains that served the twin cities of Bam and Baravat collapsed. Emergency facilities (hospitals, police and fire stations), schools and the university were destroyed and/or heavily damaged during the earthquake. The geotechnical effects of the earthquake were not significant. There was little evidence that site response effects played a major role in the damage pattern in the city. There were no reports of liquefaction and only minor sliding activity took place during the event. A unique set of strong motion acceleration recordings were obtained at the Bam accelerograph station. The highest peak ground acceleration (nearly 1g) was recorded for the vertical component of the motion. However, the longitudinal component (fault-parallel motion in N–S direction) clearly had the largest energy flux, as well as the largest maximum velocity and displacement.     

3-D velocity structure of the 2003 Bam earthquake area (SE Iran): Existence of a low-Poisson's ratio layer and its relation to heavy damage

To understand the generation mechanism of the Bam earthquake (Mw 6.6), we studied three-dimensional V_P, V_S and Poisson's ratio (σ) structures in the Bam area by using the seismic tomography method. We inverted accurate arrival times of 19490 P waves and 19015 S waves from 2396 aftershocks recorded by a temporal high-sensitivity seismic network. The 3-D velocity structure of the seismogenic region was well resolved to a depth of 14 km with significant velocity variations of up to 5%. The general pattern of aftershock distribution was relocated by using the 3-D structure to delineate a source fault for a length of approximately 20 km along a line 4.5 km west of the known geological Bam fault; this source fault dips steeply westward and strikes a nearly north–south line. The main shallow cluster of aftershocks south of the city of Bam is distributed just under the minor surface ruptures in the desert. The 3-D velocity structure shows a thick layer of high V_S and low σ (minimum: 0.20) at a depth range of 2–6 km. The deeper layer, with a thickness of about 2 km, appears to have a low V_S and high σ (maximum: 0.28) from 6 km depth beneath Bam to a depth of 9 km south of the city. The inferred increase of Poisson's ratio from 2 to 10 km in depth may be associated with a change from rigid and SiO₂-rich rock to more mafic rock, including the probable existence of fluids. The main seismic gap of aftershock distribution at the depth range of 2 to 7 km coincides well with the large slip zone in the shallow thick layer of high V_S and low σ. The large slip propagating mainly in the shallow rigid layer may be one of the main reasons why the Bam area suffered heavy damage.     

一种新的SAR像素偏移量估计流程及其在同震形变监测中的应用

提出了一种无需外部数据的新同震形变偏移量计算流程。以2003年伊朗巴姆里氏6.6级地震为例,利用两景震前无形变数据证明了新方法的精度较传统方法提高了0.224个像素。利用震前震后两景数据计算了方位向同震形变场,与Okada模型模拟得到的方位向同震形变进行了比较。     

D-InSAR在提取地面形变信息中的应用

简要介绍了D-InSAR基本原理和D-InSAR数据处理流程,以双轨差分干涉测量方法处理ENVISAT卫星获取的巴姆地震灾区影像数据提取和分析同震形变场为例子,解释了D-InSAR在提取地面形变信息中的应用。     

Inferring three-dimensional surface displacement field by combining SAR interferometric phase and amplitude information of ascending and descending orbits

Conventional Interferometric Synthetic Aperture Radar(InSAR) technology can only measure one-dimensional surface displacement(along the radar line-of-sight(LOS) direction).Here we presents a method to infer three-dimensional surface displacement field by combining SAR interferometric phase and amplitude information of ascending and descending orbits.The method is realized in three steps:(1) measuring surface displacements along the LOS directions of both ascending and descending orbits based on interferomet...     

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基于D-InSAR技术的伊朗巴姆地震地表形变监测

以伊朗巴姆地区为例,对伊朗巴姆地震造成的地表形变进行了差分干涉测量,得到了垂直向的同震三维形变场,并运用GIS三维分析技术对形变场进行了分析。实验结果表明,地震在巴姆城市的东侧造成了较大形变,在西侧也产生了微量形变。巴姆城市北部地块沉降,南部地块隆起。同时在巴姆城市南部可明显看到地震造成的断层。实验结果验证了基于C波段的SAR数据的D-InSAR技术在干燥地区监测地表形变方面的可行性。本文对产生去相关效应的原因进行了解释,认为对于干燥少植被的地区干涉效果较好。并指出,如果能够通过技术进步提高雷达干涉测量的精度并降低观测成本,同时将该技术与GPS、GIS等技术相结合,从而更好地研究形变机理,这将对地质灾害的研究产生重大意义。     

利用干涉技术定权建立巴姆地区三维形变场

针对传统合成孔径雷达差分干涉测量技术(D-InSAR)只能得到地震区域在雷达视线方向的形变量,即竖直、东西、南北三个方向形变在雷达视线方向的投影,而在研究地震时一维形变量不能满足需求和D-InSAR技术对南北向极不敏感的问题,利用多孔径合成孔径雷达干涉测量技术在监测南北向形变量中的优势与D-InSAR技术在监测垂直方向的形变量中的优势相结合,并用形变图方差法对这两项技术进行定权,建立了伊朗巴姆地区的三维形变场。     

Hybrid stochastic finite fault modeling of 2003, M6.5, Bam earthquake (Iran)

Accelerographic time series of the M ^∗6.5 Bam (Iran) earthquake of December 26, 2003, are used to calibrate the source and propagation path characteristics based on a hybrid stochastic approach, which includes stochastic finite fault and analytical modeling. Estimation of source characteristics is based on the calibration of finite-fault modeling to near-source observed time series, while propagation characteristics are estimated using far-field recorded ones. The distance-dependent Kappa factor is obtained from the slope of smoothed amplitude of acceleration Fourier spectrum at higher frequencies. The estimated zero-distance Kappa value is 0.06. Calibration based on near-source time series indicates a stress drop of 130 bars for the Bam earthquake. The strong impulsive long-period motion, recorded at the only near-source station, is modeled using analytical modeling of Mavroeidis and Papageorgiou (2003).