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，新西兰南岛坎特伯雷地区发生基督城6.3级地震，距2010年9月4日的达菲尔德7.1级地震约6个月，并产生了一系列重要的余震，其中许多余震被认为是6.3级地震。目前尚不清楚后来的M6.3事件在技术上是否是余震，因为它与去年9月以来正在进行的活动有关，或者它是一个单独的事件，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破坏区的复杂地下结构，在NSF-RAPID的支持下，与新西兰研究人员合作，调查人员在2010年达菲尔德7.1级地震和2011年6.3级余震区破裂的格林德尔断层上部署了由12台PASSCAL地震仪组成的2个短线性地震阵列基督城地震。从2011年5月5日开始，两个台阵工作了4个月，记录了约1,000次M2余震，其中包括一次M6.0和五次M5+大余震。在本项目中，PI将对两个跨断层阵列记录的波形数据进行系统检查，以识别余震产生的断层带陷波（FZTW），并使用三维有限差分代码模拟这些FZTW，以记录（1）地下结构和材料特性达菲尔德和基督城地震破裂带的宽度、深度延伸、速度降低、Q值和同震岩石破坏程度;（2）破裂在孕震深度处的分段和分支;（3）多次余震的断层岩在主震后的愈合;（4）将本研究结果与我们在加州地震破裂带上的结果进行比较。通过比较新西兰和加利福尼亚板块边界活动断层上的大地震，有关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灾害。地下破裂分割和/或连接的达菲尔德和基督城地震的结果将有助于解决的问题，如果第二个事件是第一个？的余震或一个单独的主震，并评估未来地震的可能性在基督城地区。

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.