Rupturing process of the M(W)7. 9 Nepal earthquake inverted by the multi-array compressive sensing method

2015年4月25日,尼泊尔地区发生M_W7.9地震,震中位于28.1°N,84.7°E.为了详细地研究此次破坏性极强的地震的破裂过程,本文利用多台阵压缩传感方法,使用了阿拉斯加、欧洲和澳大利亚三个台网的共计179个台站的远场P波垂直分量的数据来反演,结果表明本次地震的破裂过程是一个清晰的南东东方向的单侧破裂,破裂尺度约为105km,整体持续时间约为58s.在破裂初始的前15s,能量辐射基本围绕在震源附近,16s后破裂开始向南东东方向以1.9km·s~(-1)的速度破裂.释放能量最大的时间为第38s,位于距震中70km处.该位置从第29秒开始破裂,并持续释放能量长达30s之久.An M(W)7. 9 earthquake occurred in Nepal on 25 April, 2015. Its hypocenter is located at 28. 1 degrees N, 84. 7 degrees E. In order to investigate the rupturing process of this temblor in detail, we use the multi-array compressive sensing (MCS) method to invert vertical component data of teleseismic P waves recorded by 179 stations of Alaska, Europe and Australia arrays. Traditionally, the compressive sensing (CS) method, based on data from unique array, can recover sparsely distributed source locations in the frequency domain. While the MCS could improve the resolution because of the larger azimuth coverage range than only using data from single array. To apply this method, the first thing is to align the data from each array using cross-correlation respectively. Secondly we stack the aligned data from each array to make the first P wave pulse clear enough to be recognized so that all the data could be aligned. Finally we invert the spatiotemporal rupture process with a sliding window based on the multi-array compressive sensing method. Combining with the discriminant factor (DF), we reduce artifacts and obtain a more credible result. The result indicates that there is a unilateral rupture with orientation of SEE, length of 105 km, and duration time of 58 s. During the first 15 s of failure, the power radiation is mainly distributed around the epicenter. Since 16 s, the rupture propagated toward SEE with a rate of 1. 9 km . s(-1). The largest energy is released at 38 s, 70 km from the hypocenter. The break of this position starts from 29 s and lasts for 30 s. Additionally, we compare the rupture details of the Nepal earthquake and 2008 Wenchuan earthquake because of their same magnitude. Moreover, MCS can offer zones where power radiated intensely, which could provide helpful information for emergency rescue after earthquakes. And we discuss the improvement of resolution because of the larger azimuth coverage range. In the end, based on slip deficit and rate of accumulation of moment deficit, we conclude that this 2015 earthquake could be a repeat of the 1833 M7. 7 Nepal temblor. And the possibility of the occurrence of a larger earthquake in this region cannot be excluded.国家自然科学基金项目SCI(E)EI中文核心期刊要目总览(PKU)中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)liuzhipeng@pku.edu.cn; zge@pku.edu.cn61891-18995