尼泊尔Mw 7.9级地震同震垂直位移与断层运动模型

2015年4月25日尼泊尔地区发生了Mw 7.9级地震，发震断层位于印度板块与欧亚板块碰撞边界带，此次地震是一次典型的板块逆冲型事件。利用中国境内加密的GPS同震观测资料，融合ALOS-2卫星L波段的InSAR（interferometric synthetic aperture radar）同震形变数据，基于最小二乘方法获得了此次地震的同震垂直位移场。同震垂直位移结果表明，此次地震造成尼泊尔加德满都地区抬升约0.95 m，珠穆朗玛峰地区受地震的影响有所下降，其主峰的沉降量为2~3 cm，中国境内的希夏邦马主峰沉降约为20 cm。地区利用改进的二维弹性半空间位错模型反演了发震断层运动参数，本文模型显示此次地震的断层面破裂宽度约为60 km，平均滑动量达到4 m，相当于Mw 7.89级。

Coseismic Vertical Displacement and Fault Motion Model of the Nepal Mw7.9 Earthquake

The 2015 Nepal Mw7.9 earthquake occurred in the central segment of the Himalayan collision zone, where the rigid Indian plate thrusts beneath the Tibetan Plateau. The published focal mechanism solution shows this earthquake was dominated by thrust slip but minor right-lateral strike slip, so a significant vertical deformation appears on the surface caused by this event. Accurate coseismic vertical displacements in this region provide us a scarce chance to understand the long term uplift of the Himalaya and southern Tibet. By processing the resurvey 'in-situ' GPS data, we obtained a coseismic GPS horizontal displacement field at high precision. In combination with the coseismic GPS displacements and the L-band InSAR line of sight (LOS) observations, we extract the coseismic vertical deformation field due to the Nepal earthquake with a mean uncertainty of 1~2 cm and spatial resolution of 1 km×1 km. The result shows that the Kathmandu was uplifted ~0.95 m after the main shock. In particular, the Mount Everest and Shishapangma subsided~2-3 cm and ~20 cm, respectively. The two-dimensional elastic half-space dislocation model suggests that the mean rupture width of the Nepal earthquake was~60 km and the average coseismic slip reached 4 m. Our results indicate that the slip deficit of this event was equivalent to a moment magnitude of Mw 7.89 assuming a rupture length of 120 km and rigidity of 30 GPa, which is consistent with seismological estimation.The 2015 Nepal earthquake broke the trend of long term uplift in the central segment of higher Himalaya during an interseismic period. Whether this segment will continue to subside or uplift after the event can be discriminated by continuous post-seismic geodetic measurements.