Abstract: We used the radar data from the satellite ALOS/PALSAR of Japan and the differential interferometric synthetic aperture radar(D-InSAR)technology to derive the coseismic displacement field produced by the M_S 8.0 Wenchuan,Sichucan Province,China earthquake on 12 May 2008.Based on processing SAR data of 7 tracks and 112 scenes by the two-pass method,we obtained the interferometric map of 450km×450km covering the causative fault and determined the distribution range of incoherent zones.Proper phase unwrapping was performed to these tracks of continuous and discontinuous phases,yielding digital image of the interferometric displacement field,which is analyzed by displacement contours and the profile across the fault.The result shows that the Wenchuan M_S 8.0 earthquake has produced a vast area of surface deformation along the Yingxiu-Beichuan Fault,primarily concentrated in a near-field range of 100km wide on the both sides of the causative fault.In this field,the 250km-long and 15～35km wide incoherent zone nearby the fault has suffered the largest deformation with surface ruptures,of which the amount is too large to measure by InSAR.The secondary deformed areas are 70km wide on each side of the incoherent zone,where envelope-like fringes are clear,continuous and converging towards the fault,indicative of increasing gradient and amplitude of displacements which exhibit sunk north wall and uplifted south wall in sight line.With respect to the north and south edges of the data track,the maximum subsidence in the north wall is 110～120cm appearing northeast of Wenhcuan and Maoxian,and a big range of descents of 55～60cm occurred nearby the epicenter south of Lixian.The largest uplift 120～135cm in the south wall is present at the epicenter west of Yingxiu,north to Dujiangyan and around Beichuan.The maximum relative displacement between the north and south walls is up to 240cm that appears nearby the epicenter west of Yingxiu and north to Dujiangyan.In the far-field 70km away from the incoherent zones on the both sides of the causative fault,there are sparse fringes indicative of displacements less than 10cm.The profile across the fault indicates a highly variable gradient of deformation with profound heterogeneity near the fault and in its hanging wall,and a relatively uniform deformation in the foot wall.These differences of deformation can be attributed to complicated thrust faulting.Our analysis suggests that the fault rupture of the Wenchuan earthquake is a relative thrust between the two walls of the fault.

Key words: D-InSAR, Wenchuan M_S8.0 earthquake, surface deformation, interferometry

摘要： 基于星载合成孔径雷达差分干涉测量技术(D-InSAR),利用7个条带共112景日本ALOS/PALSAR raw格式雷达数据,采用两通差分干涉处理模式,获取了2008年5月12日汶川M_S8.0地震发震断层周围约450km×500km区域的同震形变干涉纹图。通过对干涉纹图的定性分析,确定了非相干带的分布范围,据此对相位连续条带和相位不连续条带采用不同的相位解缠方案,实现了7个条带的成功解缠,获得了数值化的干涉形变场图像,并通过形变等值线和跨断层形变剖面线等方法对干涉形变场的空间分布和演化特征进行了分析。结果表明:汶川地震造成的地表形变场沿映秀-北川断裂带分布,形变范围很大,但主要集中在发震断层南北两侧各约100km的近场区。其中断层附近由西向东宽约30~15km,长约250km的区域为非相干带,是本次地震中变形最强烈并伴有地表破裂发生的区域,其形变梯度已超出InSAR测度能力。在非相干带两侧宽度各约70km,具有清晰可辨连续完整并向发震断层收敛的包络状干涉条纹区域是次一级形变区,距离发震断层越近,形变梯度和幅度越大,其视线向位移为北盘沉降,南盘抬升。相对于数据条带南北边缘,北盘最大累积沉降量约-110~-120cm,出现于汶川和茂县东北,在理县南震中附近也有一大面积沉降区,沉降位移约为-55~-60cm。南盘最大累积抬升量约120~130cm,出现在映秀西侧震中区,都江堰北及北川附近。南北盘之间的相对最大形变量约240cm,出现在映秀西侧震中附近及都江堰北。在发震断层两侧距非相干带各约70km以外的远场区,干涉条纹稀少,形变量很小,仅在±10cm以下。跨断层形变剖面表明,断层附近及其上盘形变梯度差异大,变形非均匀性突出,而下盘形变过程相对平稳。这些形变差异反映了断层活动的非均匀性及逆断层变形的复杂性。分析认为汶川地震发震断层的运动模式是上下盘相对逆冲运动。

关键词: D-InSAR, 汶川M_S8.0地震, 地表形变, 干涉