微小地震反射波の観測と溶融体をともなう地殻深部不連続面の検出

概要

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Microearthquake seismograms recorded by stations located in or bordering 1) the Rio Grande rift near Socorro, New Mexico, USA, 2) the Nikko-Ashio region, northern Kwanto district, Japan and 3) the Wakayama region, northwestern part of the Kii Peninsula, Japan, frequently have two sharp impulsive phases following the direct S. In each of these three regions, the two phases recorded at very small epicentral distances are identified as SxP and SxS reflections from a velocity discontinuity in the deeper part of the earth's crust. Travel times of the reflected phases provide a reliable information of the depth of the discontinuity, while amplitude ratios of the reflected phases can be used to estimate the velocity contrast across the discontinuity. The use of the reflected phases on the microearthquake seismograms proved to be a practical and highly promising method for the detection of unusual crustal discontinuity underlain by molten material with very low rigidity.
1981-03-07