Seismic Detection and Discrimination Using Ocean-Bottom Seismographs
Annual technical rept. 1 Oct 1979-31 Dec 1980
CALIFORNIA UNIV SAN DIEGO LA JOLLA
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Around January 29, 1980 a mild storm occurred on the Southern California coast. During this time one of our ocean bottom seismographs O.B.S. was periodically recording noise samples at 31 deg N, 119 deg 48 min W, about 370 km offshore in 4 km of water. The noise energy in the 1-3 Hz frequency range correlates most strongly with the wave height on the nearby coast. The local and distant wind data were dissimilar in the durations of the disturbance and in the time of the peak amplitude. We conclude that sea floor noise near 1 Hz comes predominantly from the surf. The nonlinear mechanisms which transfer energy from gravity waves on the sea surface into the sea floor are so inefficient at these frequencies that the contribution from surf a few hundred km away dominates the energy from the sea surface a few km away. An array of 4 ocean-bottom seismometers O.B.S. was operated for one month during June-July, 1977 at 16.5 deg N, 100.5 deg W in the Middle America Trench near Acapulco. The purpose of the experiment was to investigate the seismicity of the accretionary prism and to study the propagation of seismic waves across the continental margin. The location of earthquakes occurring landward of the OBS array was controlled by a 7-station land-based array operated by a team of Mexican seismologists under the direction of Dr. Lautaro Ponce Mori.
- Physical and Dynamic Oceanography