Seismicity and Fault Structure of Oceanic Detachment Faults

大洋扩张中心的板块裂谷是通过断层作用和岩浆注入的共同作用发生的，两者都缓解了与全球构造力相关的累积应力。有时，断层可能占主导地位，导致沿单一平面持续滑动超过一百万年。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丘陵。相反，由于断层上的相对运动，最初很深的岩石被剥离，形成了具有长达几公里的海底起伏的穹顶地貌。这项研究旨在展示滑脱断层在地震中的行为--小地震沿断层的深度发生在哪里，以及这种活动如何横向变化。这项研究获得的新见解可能适用于其他发生伸展构造应力和岩浆作用的地区，如美国盆地和山脉省的部分地区。这项研究由海洋地质和地球物理计划和美国国家科学基金会国际科学与工程部联合支持，将对大西洋中脊13°N和26°N海底地震仪部署6个月期间记录的微震活动数据进行分析，以阐明年轻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的工作重点是先前研究的事件之间的中等规模地震；新的结果将首次详细关注3公里以下的地壳浅层。这两个地区的地震活动模式将进行比较，这两个地区都是海洋核心复合体的所在地。记录地震的分布，以及可能的一些震源机制，旨在评估滑脱断层在三维空间中的行为，以及在断层强度和空间/时间演化方面可能产生的影响。

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.