The use of regional hydrophone datasets for statistical studies of mid-ocean ridge earthquake populations

Abstract

Seismically generated tertiary (T-) waves can be used to detect and locate the shallow hypocenter earthquakes associated with mid-ocean ridge spreading centers and oceanic transforms. During the last several years, regional seismic catalogs, which contain estimates of T-wave source regions, origin times and acoustic source levels, have been generated from continuous hydroacoustic monitoring along the northern Mid-Atlantic Ridge and equatorial East Pacific Rise. As the mechanics of T-wave generation remain poorly understood, critics of these datasets have questioned the correlation between T-wave source regions and seismic epicenters, as well as the usefulness of acoustic source level as a proxy for earthquake size. Recent analyses, however, suggest that these data provide a reasonably complete record of seismicity within the mid-ocean ridge environment, yielding significant improvements in location accuracy and catalog completeness level, relative to global seismic catalogs. Most importantly, it appears that many fundamental and well-established properties of seismic distributions can be studied using T-wave catalogs, including the modified Omori decay law of aftershocks, a power-law size frequency distribution (Gutenberg–Richter law), a fractal time-clustering behavior (1/f noise) and fractal spatial distribution of epicenters. These observations show that T-wave derived earthquake catalogs can be used for quantitative seismo-tectonic studies in the ridge setting.