基于GPS和InSAR反演汶川Mw7.9地震断层滑动分布

INVERSION OF SLIP DISTRIBUTION OF 2008 WENCHUAN Mw7.9 EARTHQUAKE CONSTRAINED JOINTLY BY InSAR AND GPS MEASUREMENTS

利用汶川8.0级地震野外考察得到的地表破裂带的空间分布及余震精定位结果,构建了两段发震断层的几何结构模型。基于该模型反演汶川8.0级地震GPS和InSAR同震形变场数据,获得了断层滑动分布及部分震源参数。结果表明:1)联合反演能较好地解释GPS和InSAR所获得的同震形变场,数据拟合度达97.27%;2)映秀-北川断裂反演得到的滑动分布主要集中于地下0～20km处,最大滑动量分别位于北川及青川等地区,尤其是多条断裂经过的北川地区在0～20km深处存在较大滑动量,最大可达到10m,青川地区10～15km深处的滑动量最高达6.5m;3)发震断层都以逆冲为主兼有一定右旋走滑分量,其中汶川地区的平均滑动角为103°,北川地区的平均滑动角为121°,青川地区的平均滑动角为138°,灌县-江油断裂的平均滑动角约为105°;4)反演得到的矩张量达8.7×1020Nm,矩震级为Mw7.9。

A two-segment fault model for the May 12,2008 Wenchuan Ms8.0 earthquake based on field investigations and precisely relocated aftershocks had established.The model is consistent with the surface rupture traces seen in the field at most sites along the fault.It contains two fractures with linearly varied dips from 70° to 33° and from 60° to 20°,respectively and they converge into one shear belt at the depth of 28 km.Then use this fault model as the constraint to invert the coseismic slip distribution using GPS data as well as InSAR measurements solo or jointly.The results show a robust slip distribution can be obtained by jointly using GPS and InSAR data.The deformation by forward modeling matches well the GPS data and InSAR deformation,with a relatively small total RMS of 9-11 cm.The inverted slip distribution is confined to a depth range 0-20 km and the maximum slip is 10 m.Among the largest slip areas,the Beichuan area has relatively concentrated slip and shallower depth（0-10 km）than other areas.This may be the reason that the Beichuan area was most severely destroyed by the earthquake.The inverted rake distribution shows that there is a transform of fault slide along the direction of SW-NE.It is primarily thrusting with some right-lateral component from nearby the epicenter to Beichuan,and changes into dominantly right-lateral slip with little thrusting or even pure right-lateral slip at the Qingchuan area in northeast.The mean rakes range from 103°to 121°and 138°.The inverted seismic moment tensor M0 is 8.7×10^20 Nm,and the inverted moment magnitude scale Mw is 7.9.