The Relationship Between Seismicity and Fault Structure on the Discovery Transform Fault, East Pacific Rise

TitleThe Relationship Between Seismicity and Fault Structure on the Discovery Transform Fault, East Pacific Rise
Publication TypeJournal Article
YearSubmitted
AuthorsWolfson-Schwehr, ML, Boettcher, MS, McGuire, JJ, Collins, JA
JournalGeochemistry, Geophysics, Geosystems
PublisherAGU
Place PublishedWashington, DC

There is a global seismic moment deficit on mid-ocean ridge transform faults, and the largest earthquakes on these faults do not rupture the full fault area. We explore the influence of physical fault structure, including lateral offsets in the fault trace, on the seismic behavior of the Discovery transform fault, 4S on the East Pacific Rise. One year of microseismicity recorded during a 2008 ocean bottom seismograph deployment (24,377 0 ≤ ML ≤ 4.6 earthquakes) and 24 years of Mw ≥ 5.4 earthquakes obtained from the Global Centroid Moment Tensor (CMT) catalog, are correlated with fault structure delineated from high-resolution multibeam bathymetry. Each of the 15 5.4 ≥ Mw ≤ 6.0 earthquakes that occurred on Discovery between January 1, 1990 - April 1, 2014 was relocated into one of five distinct rupture patches using a teleseismic surface wave cross-correlation technique. Microseismicity was relocated using the HypoDD relocation algorithm. The western fault segment of Discovery (DW) is composed of three distinct zones of varying structure and seismic behavior, including a zone with no large events and abundant microseismicity, a fully-coupled zone with large earthquakes, and a complex zone with multiple fault strands and abundant seismicity. In general, microseismicity is reduced within the large, repeating rupture patches. While the extent of the large rupture patches on DW correlates with physical features in the bathymetry, lateral offsets in the primary fault trace are not observed at patch boundaries, suggesting along-strike heterogeneity in fault properties controls the size and location of the large events.