Open Access

Resistivity and density modelling in the 1938 Kutcharo earthquake source area along a large caldera boundary

Earth, Planets and Space200961:BF03352916

https://doi.org/10.1186/BF03352916

Received: 5 April 2008

Accepted: 14 October 2008

Published: 3 March 2009

Abstract

We present the crustal structure around the fault zone pertaining to the 1938 Kutcharo earthquake (M 6.0), northern Japan, to consider why large earthquakes have occurred around calderas. The study was based on gravity anomalies and magnetotelluric and direct-current (DC) electrical-resistivity survey data. The density structure obtained from gravity anomalies indicated that the fault plane corresponded to the main depression boundary of the Kutcharo caldera. The resistivity section, based on audio-frequency magnetotelluric surveys, indicated that the estimated fault plane was located along the boundary of resistivity blocks, which also corresponded to the depression boundary. A detailed resistivity section in the ruptured zone revealed by a DC electrical-resistivity survey showed a discontinuity of layers, implying cumulative fault displacements. These results indicate that the 1938 earthquake was an abrupt slip along the main depression boundary of the Kutcharo caldera. The most likely hypothesis pertains to fluid intrusion along the depression boundary. However, additional seismic and geodetic studies are required to identify other feasible earthquake mechanisms.

Key words

Magnetotelluricsgravity anomalyDC electrical-resistivity surveyinland earthquakeKutcharo caldera