Numerical Study on the Characteristics of Abyssal T-wave Envelopes Controlled by Earthquake Source Parameters

Abstract

Hydroacoustics has been successfully applied to detect and locate small to intermediate submarine tectonic activities infrequently recorded in land-based seismic arrays. However, to extend the utilization of T-waves to extract other important earthquake source parameters, such as source strength, the roles of earthquake focal mechanisms and source depths in T-wave envelopes must be thoroughly understood. We performed 3-D numerical modeling considering anisotropic source radiation and realistic scattering in the oceanic crust for two focal mechanisms (normal and strike-slip faults) and three depths (5, 10, and 15 km) to investigate the effect of source radiation and focal depth on abyssal T-waves. By analyzing the synthetic Twave envelopes, we showed that stronger SV-energy radiation from a normal-fault earthquake event generates higher-intensity T-waves of the same source magnitude. The anisotropic source radiation of a double-couple source causes azimuthal changes in the shapes of T-waves, and deeper earthquakes cause gentle sloped envelopes; however, the slopes also vary with respect to the azimuths of receivers and focal mechanisms. Temporal changes in the slopes of T-wave envelopes of magmatic swarm events near Wordie Volcano, Bransfield Strait, Antarctic Peninsula, imply that the depth dependency can be utilized to determine relative depths for hydrothermal-vent events or sequenced earthquakes.