Extension on the Tibetan plateau: recent normal faulting measured by InSAR and body wave seismology
Extension on the Tibetan plateau: recent normal faulting measured by InSAR and body wave seismology
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DOI：
10.1111/j.1365-246x.2010.04754.x
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发表时间：
2010-11-01
影响因子：
2.8
通讯作者：
Parsons, B.
中科院分区：
文献类型：
--
作者：
Elliott, J. R.;Walters, R. J.;Parsons, B.
我们利用干涉合成孔径雷达和体波模拟方法，对2008年发生的5次5.9-7.1级正断层地震进行了断层参数的测定，其中包括3月20日于田地震（M-w7. 1），这是大陆上最近发生的最大的正断层事件之一。我们还研究了1992年至2005年发生在藏南的三次较早的正断层地震。用环境卫星、地球资源卫星和高级陆地观测卫星合成孔径雷达数据的上升和下降干涉图测量了这八个事件中每一个事件的同震形变。视线干涉合成孔径雷达位移的弹性位错模型和P波和SH波的体波地震学模型被用来估计故障参数，并发现在所有的事件研究是在良好的协议。使用干涉合成孔径雷达测量变形，除了解决焦平面模糊性外，还可以相对精确地确定断层位置。八个事件中只有五个与清晰的地表地形特征有关，这表明单独使用正断层的地表表达式会导致对伸展量的低估。在所有情况下，观测结果与平面上的滑动一致，倾角在40-50度范围内，穿透地壳最上层10-15公里深。我们没有发现活动的低角度（倾角小于30度）正断层的证据。通过对过去43年地震的地震矩求和估计，正断层对整体延伸的贡献为3-4 mm yr-1，或使用GPS测量整个高原的延伸率的15- 20%。在过去43年中，85%的正断层作用的力矩释放发生在地表高度超过5 km的地区。这一观察结果进一步证实了高原上广泛存在的正断层活动是岩石圈重力势能变化的结果。
P>We use InSAR and body wave modelling to determine the faulting parameters for a series of five M-w 5.9-7.1 normal faulting earthquakes that occurred during 2008, including the March 20 Yutian earthquake (M-w 7.1), one of the largest normal faulting events to have occurred recently on the continents. We also study three earlier normal faulting earthquakes that occurred in southern Tibet between 1992 and 2005. Coseismic deformation for each of these eight events is measured with ascending and descending interferograms from ENVISAT, ERS and ALOS SAR data. Elastic dislocation modelling of the line-of-sight InSAR displacements and body wave seismological modelling of P and SH waves are used to estimate fault parameters and are found to be in good agreement for all the events studied. The use of InSAR to measure deformation allows a relatively precise determination of the fault location in addition to resolving the focal plane ambiguity. Only five of the eight events are associated with a clear surface topographic feature, suggesting that an underestimation of the amount of extension would result from using the surface expressions of normal faulting alone. The observations, in all cases, are consistent with slip on planar surfaces, with dips in the range 40-50 degrees, that penetrates the uppermost crust to a depth of 10-15 km. We find no evidence for active low-angle (dip less than 30 degrees) normal faulting. The contribution of the normal faulting to overall extension estimated by summing seismic moments over earthquakes for the past 43 yr is 3-4 mm yr-1, or 15-20 per cent of the rates of extension measured across the plateau using GPS. 85 per cent of the moment release in normal faulting over the past 43 yr has occurred in regions whose surface height exceeds 5 km. This observation adds weight to the suggestions that the widespread normal faulting on the plateau is the result of variations in the gravitational potential energy of the lithosphere.