Correlation between coda Q-1 and seismicity in central Japan

Abstract

Coda Q^-1 is a parameter which represents heterogeneities and stress condition in the lithosphere. We determined coda Q^-3 in the frequency range from 1.5 to 24 Hz in two areas, the volcanic and the tectonic areas of the Hida region, central Japan. The data were recorded by a telemetering system for events from 1985 to 1991 (367 events), with magnitudes less than 4.0 and depths shallower than 30km. We found a temporal variation in coda Q^-1, the number of earthquakes and b value, all of which increased with time in the volcanic area. However, we could not find significant temporal variation in such values in the tectonic area. Positive correlation between the coda Q^-1 and the b value was found in the volcanic area, but good correlation was not observed in the tectonic area. We also measured the temporal variation of power of frequency n for coda Q^-1 defined by the formula Q_c^-1=Q_0^-1f^-a, where Q_0^-1 represents Q_c^-1 at 1 Hz and f is frequency. The value of n shows no significant temporal change in the Hida region. We consider the cause of the temporal change in coda Q^-1 in the volcanic area involves aseismic fractures, increasing scatter of creeping cracks, due to magma accumulation.