Use of Sonobuoys in Ocean Earthquake Studies

Abstract

U.S. Navy anti-submarine-warfare telemetering sonobuoys have recently become an important tool in the study of earthquakes at sea. Earthquake ground motion converts to sub-audio compressional waves in the water and is detected by the sonabuoy hydrophones. The frequency-modulated sonobuoy signals are monitored with commercial VHF receivers on shipboard, aircraft or land, and are recorded on f.m. magnetic tape or strip chart. Subsequent analysis of the seismic signals gives information on location and depth of the earthquake as well as direction of fault motion, stress release and other characteristics of the event. The accuracy of epicenter location is usually limited by the precision of ship navigation but may also be limited by uncertainties in sonobuoy position measured from the ship. Events large enough to be detected on land have been located with better accuracy by sonobuoys than by the land arrays. This paper describes the techniques of using sonobuoys for earthquake research, and gives results of observations of microearthquake swarms in the Gulf of California along the extension of the San Andreas Fault.