Monitoring Ocean Earthquakes With SOSUS: An Example From the Caribbean

T-phases are acoustic signals in which the primary portion of the propagation path is through the oceans.T-PH. -~,E acoustic signals in ~hich the primm T portion of the propagation path is through tile oceans.Energy sources resulting m the generation of T-phases include earthquakes, submarine volcanism, and under,,vater explosions.Once seismic energy is cot, pled into the water column.T-phases propagate as compressional wa~es primarily through the Sound Fixing and Ranging {SOFAR) Channel.and may be reconverted, at continental shelves, into short-period elastic waves that travel through the sediments and basement of the continents.The ~ave-guide effect of the sound channel combined with the low attenuation of sound m seawater permit T-phases to propagate over great distances through the oceans.It is this fundamental property of T-phases that make them ideal for the study of love-magnitude seismicit'~ within the oceans.The frequency content of T-phases ( I-> I0(1 Hzl is such that attenuation within the crust and upper mantle precludes long-range inland propagation: therefore, the best instruments for the detection and analysis of T-phases are underxvater hydrophones which record seismoacoustic signals that cannot be detected by conventional short-period seismographs t Shurbet.1962 ).The study of T-phases has never been a major research e,npfiasis within the earth sciences: hence, even seismologists are generally unaware of their properties and characteristics.Perusal of some of the well-known text books in seismology reveals brief mention, if at all. of T-phases {e.g.. Aki and Richards.1980: Bullen and Bolt.1985L Much of the early T-phase research was perli~rmed in the late 1960s and early 1970s by a group of investigators at the Ha~vaii Institute of Geophssics ~vfio collected and analyzed data from the permanent.fixed hydrophone arrays of the Pacific Missile Range/Missile Impact Location System installed in the late 1950s by the U.S. Air Force near the islands of Wake.Eni~vetok.Midxvav.and