汶川Ms8.0地震前InSAR垂直形变场变化特征研究

利用D-InSAR技术，选用汶川地震前日本ALOS/PALSAR数据，提取了汶川地震前4个条带的形变场，形变场覆盖了映秀镇、茂县、北川县、平武和青川县.结果显示，汶川地震前形变场沿断层呈“凸”状对称形变分布特征，沿发震断层附近出现隆起形变，而远离发震断层两盘均出现下沉，且随着远离断层距离的增加，沉降幅度逐步增加.在断层两侧附近的平武、北川、安县、江油一带出现了大面积形变隆起，幅度为5～10 cm，且断层西侧抬升范围大于东侧.在映秀镇和汶川地震震中附近，沿断层两侧呈现出小范围斑块状隆起，范围在10～15 cm.该隆起区域与汶川震中位置和破裂最强烈段落基本一致.在远离断层的两盘区域出现沉降，绵阳至成都一带沉降范围在0～ -10 cm之间，松潘至文县一带沉降范围在-5～ -10 cm之间.研究表明对于处于闭锁阶段的逆冲断层，震前的垂直变形可能是其主要变形特征.虽然获得的震前形变变化可能存在5 cm的DEM和对流层大气延迟造成的误差，但这种震前垂直形变场变化趋势仍然存在，可能为地震监测预报提供科学依据.

The characteristics of surface vertical deformation before the Wenchuan Ms8.0 earthquake from InSAR

Using the D-InSAR technology, we have analyzed the Japanese satellite ALOS/PLASAR data before the 2008 Wenchuan earthquake and obtained four zones of ground deformation which cover the Yingxiu town, Maoxian county, Beichuan county, Pingwu and Qingchuan county in Sichuan Province. The result shows that before the Wenchuan event, the deformation field was a symmetric convex-shaped pattern around the fault. Vertical uplift appeared nearby the seismogenic fault, while subsidence took place far on its both sides away from the fault which increased in amplitude with increasing distance from the fault. Around Pingwu, Beichuan, Anxian and Jiangyou, a large area of uplift was present on the both sides of the fault with amplitude 5~10 cm. Nearby the Yingxiu town and the epicenter of the main shock, small scale spot-like swelling of 10~15 cm occurred separately, which coincides with the location of the epicenter as well as the most obvious rupture section. In the areas far away from the fault on both sides, there was dominantly subsidence, which was measured 0~-10 cm around Mianyang and Chengdu City and -5~-10 cm from Songpan to Wenxian, respectively. Our study indicates that along the locked thrust fault, vertical uplift is its primary characteristic before the quake. Although the derived deformation before the Wechchuan event from this work probably contains errors of 5 cm related with DEM and the atmospheric delay in the troposphere, such an abnormal change in the vertical deformation field indeed existed which can serve as a line of evidence for earthquake prediction.