Abstract

Continuous monitoring of low-frequency acoustic energy was accomplished in the Flores Sea using three hydrophones strung out astern of the listening ship during seismic refraction profile operations. In addition to energy from the TNT shots, unusual bursts of noise due to “seaquakes” were noted on some of the records. Analysis of these arrivals shows that most of the energy is in the less than 10 cps range, the events last from 0.2 to 4 minutes, occur up to four times per hour, and generally overload the recording system; i.e., the energy was greater than that from the shots that were being recorded. Because the hydrophones were in line, an indication of the direction of propagation of the energy is apparent from the arrival time on individual units. Analysis of the data shows that the majority of the events came from the West, had either emergent or impetus onset, a bimodal distribution in time, and were often followed by a secondary buildup of energy. If the onset is taken as a P arrival and the later phase as T, the TP interval gives an epicentral distance of 50-400 km, or mostly within the western arm of the Flores Sea. Of the 27 seaquakes monitored, only one is noted on the USC & GS cards. The rest may have come from local disturbances or Krakatoa.

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