Observations of a newly discovered fault: Tomography, locations and source mechanisms for aftershocks of the M7.1 Darfield, New Zealand earthquake

2010年9月4日达菲尔德发生的里氏7.1级地震和随后于2011年2月22日克赖斯特彻奇发生的里氏6.3级地震是自1931年霍克地震以来新西兰破坏性最大的地震。海湾地震。后者在新西兰基督城造成了巨大的破坏。美国第二大城市。这些地震发生在南岛东部以前未绘制的断层上。这个地震序列的表现导致了许多关于发生地震的断层的基本特征以及当地地质和构造的问题。5台惠灵顿维多利亚大学地震仪和9台帕斯卡尔地震仪在达菲尔德地震发生后两周内被安装在地表破裂周围地区，并于2011年1月中旬被拆除。利用这些临时台站和额外的永久性区域台站记录的数据，研究人员将对达菲尔德地震的余震进行研究，以调查地震活跃断层结构、余震和断层活动的时间演变以及区域地震结构。将根据新西兰GeoNet目录编制一份重新编制的余震目录。调查人员将研究地震活动是如何在整个断层系统中演变的，重点是2011年2月地震前在基督城地下发现的断层。该算法还将用于同时求解断层破裂周围区域的纵波和横波速度。这样做的好处是双重的：改进的3D速度模型将改善余震的位置，并将约束当地的地下结构。例如，断层的速度对比可以用来限制断层的年龄，这是目前一个有争议的话题。余震将计算震源机制。结合余震的位置，震源机制将使研究人员能够约束在余震序列中活跃的各个断层段的运动方向。通过寻找重复地震和非火山震动，他们将能够探索与达菲尔德地震有关的断层移动的各种方式。在大地震之前或之后，一段断层正在经历地震蠕变，可能会引起重复地震。通过研究2010年达菲尔德地震余震序列的前四个月，他们将有助于建立以前未知断层段的断层结构，了解断层活动的演变，并了解导致2011年更具破坏性的克赖斯特彻奇地震的因素。

The Mw7.1 September 4, 2010 Darfield earthquake and the subsequent Mw6.3 February 22, 2011 Christchurch earthquake were the most damaging earthquakes in New Zealand since the 1931 Hawke?s Bay earthquake. The latter event caused enormous damage throughout Christchurch, New Zealand?s second largest city. These earthquakes occurred on previously unmapped faults in the eastern South Island. The behavior of this earthquake sequence has led to many questions about the fundamental characteristics of the fault on which they occurred and the local geology and tectonics.Five Victoria University of Wellington seismometers and nine PASSCAL seismometers were installed in the region surrounding the surface rupture of the Darfield earthquake within two weeks of its occurrence and were removed in mid January 2011. Using data recorded at these temporary stations and additional permanent regional stations, the researchers will study the aftershocks of the Darfield earthquake in order to investigate the seismically active fault structure, the temporal evolution of aftershocks and fault activity, and the regional seismic structure. A relocated aftershock catalog will be developed based on the GeoNet catalog for New Zealand. The investigators will examine how seismicity evolved throughout the fault system, with a focus on faults that had been identified beneath Christchurch prior to the February 2011 earthquake. The algorithm tomoDD will also be used to simultaneously solve for P- and S-wave velocities in the region surrounding the fault rupture. The benefit of this will be two-fold: the improved 3D velocity model will result in improved aftershock locations and it will constrain the local subsurface structure. For example, a velocity contrast across the fault could be used to constrain its age, which is currently a topic of controversy.Focal mechanisms will be calculated for aftershocks.In conjunction with aftershock locations, focal mechanisms will allow the researchers to constrain the directions of motion along the various fault segments that have been active in the aftershock sequence. By searching for repeating earthquakes and non-volcanic tremor, they will be able to explore the variety of ways in which the faults associated with the Darfield earthquake move. Repeating earthquakes may be caused by a section of fault that is experiencing aseismic creep, either before or after a large earthquake. By studying the first four months of the aftershock sequence of the 2010 Darfield earthquake, they will help establish the fault structure of previously unknown fault segments, understand the evolution of activity along them, and understand the factors that contributed to the more devastating 2011 Christchurch earthquake.