ASA 127th Meeting M.I.T. 1994 June 6-10

2pAO12. Comparisons of ridge crest earthquake waveforms recorded on SOSUS hydrophones with ocean bottom seismometers in the near field.

Anthony E. Schreiner

Cooperative Inst. for Marine Resource Studies, Oregon State Univ., 2115 S.E. OSU Dr., Newport, OR 97365

Christopher G. Fox

NOAA/PMEL, Newport, OR 97365

The U.S. Navy's SOSUS network of hydrophone arrays is allowing an unprecedented continuous look at oceanic seismicity. Hydrophones in the SOFAR channel are sensitive detectors of acoustic T-waves resulting from earthquakes in the ocean crust. Since Fall of 1991 a program at the NOAA Pacific Marine Environmental Laboratory has catalogued over 500 seismic events originating on the boundaries of the Pacific, Gorda, and Juan de Fuca tectonic plates. Though extremely sensitive, observations through SOFAR hydrophones have the drawback that the earthquake signal travels long distances though the ocean sound channel. The recorded signal is thus a highly distorted representation of the earthquake. There is as yet no reliably determined relationship between T-wave strength and source magnitude, mainly because many local factors can affect the transfer of energy from the ocean floor into the SOFAR waveguide. We have compared earthquake and explosive events recorded in 1991 simultaneously by the SOSUS network and three small-scale arrays of ocean bottom seismographs placed near the intersection of the Gorda spreading ridge and the Blanco Transform Fault. By this effort, we are attempting to gather enough statistics on long range T-wave strength compared to local measurements to provide a rough magnitude scale.