Seismicity and Fault Structure of Oceanic Detachment Faults

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

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.