Monitoring of weak earthquakes using hydrophone station in shallow waters

Abstract

The results of hydroacoustic observations of signals from the weak (M<4) earthquakes in natural conditions within the area of South Kuril Islands are presented. A part of the observed earthquakes was registered by seismograph stations as well and another part was registered by the hydrophone station only. The peculiarity of observations was that the record of seismic signals performed in shallow water area that is in conditions of high noise level. Analysis of hydroacoustic records captured from the hydrophone station showed that there was no any evident foregoing response of geological medium on weak distant events. So geoacoustic emission was not detected neither before period of earthquake preparation nor during period of preparation. It is shown that in spite of unfavourable noise conditions even distant weak earthquakes can be confidently registered by hydrophone stations and application of proper signal processing techniques makes it possible to determine the moments of arrival of seismic waves and to measure their parameters. It is also established that frequency spectrum of acoustic signals from weak earthquakes perceived by hydrophone stations has continuous noise-type character in the range up to 90-100 Hz. Low frequency signals fore-running some weak earthquakes and microearthquakes are discovered.