Locations of mid‐oceanic earthquakes constrained by seafloor bathymetry

Abstract

Earthquakes associated with the creation of new oceanic crust are difficult to locate precisely because they normally occur far away from seismic stations. We assume that epicenters of these events can be constrained by seafloor topography and use the Harvard centroid moment tensor (CMT) focal mechanism of an interplate earthquake to relate the event to either a transform fault (a parallel in a coordinate system defined by the pole of rotation between two plates) or a mid‐oceanic ridge (a meridian). Using arrival times from the International Seismological Center (ISC) Bulletin, we have relocated about 1500 globally distributed events for the time period 1976–1998. The ISC locations can be as much as 70 km away from appropriate topographic features. Our new locations support that large interplate earthquakes occur on or very close to the primary bathymetric features. For earthquakes with unknown mechanism or magnitude below the CMT threshold or predate the CMT catalog, we use a simultaneous Joint Hypocenter Determination procedure with respect to the already relocated Master Events (JHDME). We invert for earthquakes first for the Romanche Fracture Zone (RFZ) and then for a region extending from 30°N to 30°S. Seismicity agrees well with the main active ridge or transform. However, a small number of events might be related to the secondary bathymetry features. The improved locations for mid‐oceanic earthquakes based on bathymetry could help improve our understanding of the oceanic crustal and deep Earth structure, seismic slip and budget constraint along plate boundaries, and dynamics of plate tectonics.