Characteristics of the 1983 Tottori earthquake sequence and its relation to the tectonic stress field

Abstract

Good azimuthal coverage of the 1983 Tottori Earthquake sequence provided an opportunity to analyze not only the main shock and aftershock, but also the causal relation between them. Source parameters of the main shock were calculated by the waveform analysis of strong motion seismograms. The fault relevant to the main shock was predominantly strike-slip. The estimated fault parameters are as follows; length 5 km, seismic moment 5.5 × 10 24, average displacement 50 cm and stress drop 3.9 MPa. The spatial distribution of aftershocks was generally consistent with the field of the maximum increase in shear stress after the main shock. Most aftershock sequences occurred in the regions with high maximum shear stress, but there were a few exceptions. Mechanisms of the aftershocks were investigated by comparing the maximum shear stress distribution with the direction of principal axes calculated theoretically from corresponding fault-plane solutions. The results indicate that an ambient tectonic stress is necessary to account for the observed mechanisms of aftershocks. The compressive tectonic stress acting in the Tottori area is estimated to be about 40 MPa or more, and to form an angle of 35–40° with respect to the strike of the fault of the main shock. Precise observations and analysis of the earthquake sequence are shown to be capable of estimating the tectonic stress in a seismotectonic.