Abstract:
Seafloor earthquakes create seismoacoustic T waves traveling in the oceanic sound channel. T waves are useful to monitor earthquakes in the oceanic environment, allowing a reduction in detection threshold by at least two levels of magnitude. The physical processes involved in T-wave generation are not well understood. For example, in the case of a perfectly flat ocean bottom at a depth greater than the sound channel, it is not clear how energy radiated by the source is coupled to the sound channel. Likewise, the relationship between earthquake source depth and moment, and the T-wave amplitude and duration is not known. This paper investigates the coupling between seismic sources in the solid earth and T waves in the oceanic sound channel. In particular, the extended time duration of the T wave is related to coupling between the source and sound channel over an extended region at the seafloor, and this coupling is shown to be dependent on the seismic source depth. This work builds on previous observations by Schreiner et al. (1995) of variations in T-wave duration and spectral content with source depth associated with the Juan de Fuca ridge seismic swarm of 1993.