Seismicity and Fault Structure of Oceanic Detachment Faults

在大洋扩张中心的板块裂谷作用是通过断层作用和岩浆注入的结合而发生的，这两种作用都减轻了与全球构造力有关的累积应力。有时断层作用会占主导地位，导致沿着单一平面持续沿着超过一百万年。在这种“拆离断层”时期形成的海底不同于海底普遍存在的典型的线性火山山。相反，当最初的深层岩石由于断层的相对运动而被掀顶时，形成了具有高达几公里海底起伏的穹隆特征。这项研究的目的是展示拆离断层在地震中的表现--小地震是如何沿着断层沿着深度发生的，以及这种活动是如何横向变化的。这项研究中获得的新见解可能适用于发生伸展构造应力和岩浆作用的其他地区，例如美国盆地和山脉省的部分地区。这项研究得到海洋地质学和地球物理学方案以及国家科学基金会国际科学和工程科的联合支助，将对在大西洋中脊北纬13度和北纬26度部署海底地震仪6个月期间记录的微震活动数据进行分析，以阐明年轻的海洋核心复合体的断层活动。13°N的工作是更广泛的英国-法国-美国合作项目的一个组成部分; 26°N的工作重点是以前研究的事件之间的中等规模的地震;新的结果将首次详细关注地壳浅于3公里。这两个地区的地震活动模式，这两个主机的海洋核心复合体，将进行比较。记录地震的分布以及可能的一些震源机制，旨在评估拆离断层在3-D中的表现以及断层强度和空间/时间演化的影响。

Plate rifting at oceanic spreading centers occurs through a combination of faulting and injection of magma, both of which relieve built-up stress associated with global tectonic forces. At times faulting can dominate, leading to sustained slip along a single plane for over a million years. Seafloor formed during such periods of 'detachment faulting' differs from the typical, linear volcanic hills that are ubiquitous on the seafloor. Instead domal features, with up to a few km seafloor relief, develop as initially deep rock is unroofed by relative motion across the fault. This study aims to show how detachment faults behave seismically- where small earthquakes occur with depth along the fault and how that activity varies laterally. New insights gained in this study could be applicable to other regions where extensional tectonic stress and magmatism occur, such as parts of the U.S. Basin and Range province. This study is jointly supported by the Marine Geology and Geophysics Program and the International Science and Engineering section of NSF.Analysis of microseismicity data recorded during 6-month deployments of ocean bottom seismometers at 13°N and 26°N on the Mid-Atlantic Ridge will be conducted in order to elucidate fault activity at young oceanic core complexes. The 13°N work is one component of broader UK-French-US collaborative project; the 26°N effort focuses on earthquakes intermediate in size between events that were previously studied; new results will focus in detail on crust shallower than 3 km for the first time. The seismicity patterns of these two areas, that both host oceanic core complexes, will be compared. Documentation of the distribution of earthquakes, and possibly some focal mechanisms, aims to assess how detachment faults behave in 3-D and what the implications might be in terms of fault strength and spatial/temporal evolution.