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

对新发现断层的观测：新西兰达菲尔德 M7.1 地震余震的断层扫描、位置和震源机制

• 批准号: 1141983
• 负责人: Clifford Thurber
• 金额: $ 11.73万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-01-01 至 2014-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1141983&HistoricalAwards=false
• 关键词: Observations; newly; discovered; fault; Tomography

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.

2010年9月4日达菲尔德7.1级地震和2011年2月22日克赖斯特彻奇6.3级地震是自1931年霍克？S湾地震以来新西兰发生的最具破坏性的地震。后一次事件在整个新西兰克赖斯特彻奇造成了巨大破坏？S是第二大城市。这些地震发生在南岛东部以前未绘制地图的断层上。这一地震序列的行为导致了许多关于它们发生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PASSCAL地震仪在达菲尔德地震地表破裂发生后两周内安装在该地区，并于2011年1月中旬被拆除。研究人员将利用这些临时站和额外的永久地区站记录的数据，研究达菲尔德地震的余震，以调查地震活动的断层结构、余震和断层活动的时间演化以及区域地震结构。将根据新西兰的GeoNet目录编制一个重新定位的余震目录。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，重点是在2011年2月地震之前在克赖斯特彻奇地下发现的断层。算法TOTODD还将用于同时求解断层破裂周围地区的P波和S波速度。这样做的好处有两个：改进的3D速度模型将导致余震位置的改善，并将约束局部的地下结构。例如，断层上的速度差可以用来限制其年龄，这是目前有争议的话题。余震的震源机制将被计算出来。与余震位置相结合，震源机制将使研究人员能够限制余震序列中活跃的不同断层段的运动方向。通过搜索重复的地震和非火山震动，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。重复的地震可能是由一段断层引起的，该断层在大地震之前或之后经历了无地震蠕变。通过研究2010年达菲尔德地震的前四个月余震序列，他们将有助于建立以前未知断层段的断层结构，了解沿这些断层段的活动演变，并了解导致2011年更具破坏性的克赖斯特彻奇地震的因素。