Seismic Documentation of Subsurface Damage Zones of the M7.2 Darfield and M6.3 Christchurch Earthquake Sequence in New Zealand Using Fault-Zone Trapped Waves

2011年2月22日，6.3级克赖斯特彻奇地震袭击了新西兰南岛的坎特伯雷地区，距离2010年9月4日同一地区发生的7.1级达菲尔德地震大约6个月后，并产生了一系列明显的余震，其中许多余震被认为是6.3级地震。由于与去年9月以来的持续活动有关，目前尚不清楚后来发生的6.3级地震是技术上的余震，还是单独的事件，因为它位于基督城南部的一个单独的盲断层上。为了研究新西兰这一系列地震造成的复杂地下结构，在NSF-RAPID的支持下，在新西兰研究人员的合作下，研究人员在2010年7.1级达菲尔德地震和2011年6.3级克赖斯特彻奇地震的余震区破裂的格林德尔断层上部署了2台由12台帕斯卡尔地震仪组成的短线性地震阵列。从2011年5月5日开始，两个阵列共工作了4个月，共记录到约1000次M2级余震，其中包括1次6.0级和5次5级以上大型聚集余震。在这个项目中，PI将对记录在两个跨断层阵列上的波形数据进行系统检查，以识别余震产生的断裂带困波（FZTWs），并使用三维有限差分代码模拟这些FZTWs，以记录(1)达菲尔德和基督城地震破裂的断裂带的地下结构和材料特性（宽度、深度扩展、速度降低、Q值和同震岩石破坏震级）；(2)孕震深度的断裂分割和分支；(3)多次余震对断层岩石的震后愈合；(4)将本研究结果与加州地震破裂带的结果进行比较。通过对新西兰和加利福尼亚板块边界上活动断层的主要地震的比较，关于断层带原位状态的最基本信息将有助于进一步了解全球地震过程和危害。达菲尔德和克赖斯特彻奇地震的地下破裂分割和/或连接结果将有助于解决第二次地震是否是第一次地震的问题。余震或单个主震，并评估基督城地区未来发生地震的可能性。

The M6.3 Christchurch earthquake struck the Canterbury region in New Zealand's South Island on 22 February 2011, following ~6 months after the September 4, 2010 M7.1 Darfield earthquake in the same region, and has generated a significant series of aftershocks, many of which are considered big for a M6.3 earthquake. It is not known whether the later M6.3 event is technically an aftershock because of relationship to the ongoing activity since September last year, or it is a separate event, given its location on a separate blind fault south of Christchurch. In order to study the complicated subsurface structure of damage zones caused by this sequence of earthquakes in NZ, under the support of an NSF-RAPID and with collaboration of New Zealand researchers, the investigators deployed 2 short linear seismic arrays of 12 PASSCAL seismographs across the Greendale fault that ruptured in the 2010 M7.1 Darfield earthquake and the aftershock zone of the 2011 M6.3 Christchurch earthquake. Two arrays worked for 4 months starting from May 5th, 2011 and recorded ~1,000 M2 aftershocks, including a M6.0 and five M5+ large aftershocks with clustered events. In this project the PI will conduct a systematic examination of the waveform data recorded at the two cross-fault arrays to identify fault-zone trapped waves (FZTWs) generated by aftershocks, and simulate these FZTWs using a 3-D finite-difference code to document (1) the subsurface structure and material properties (width, depth extension, velocity reduction, Q value and co-seismic rock damage magnitude) of fault zones ruptured in Darfield and Christchurch earthquakes, (2) the rupture segmentation and branching at seismogenic depth, (3) the post-mainshock heal of fault rocks from repeated aftershocks, and (4) compare the results from this study with those we have obtained at rupture zones of California earthquakes. With a comparison of major earthquakes at active faults on the plate boundaries in NZ and CA, the most basic information on the in-situ state of the fault zone will aid further understanding of earthquake processes and hazards globally. Results of subsurface rupture segmentation and/or connection of the Darfield and Christchurch earthquakes will help to address the question if the second event is the first one?s aftershock or an individual mainshock, and evaluate the possibility of a future earthquake in Christchurch areas.