2015年8月桜島群発地震の振幅を用いた震源推定

Abstract

A rapid ground deformation associated with an intense volcano-tectonic (VT) earthquake swam was observed on August 15, 2015 at Sakurajima Volcano. We applied the amplitude source location (ASL) method to estimate 250 hypocenters of the VT earthquakes. We estimate site amplitude factors using regional earthquakes and the coda normalization method. Vertical component velocity seismograms were corrected with the site factors and converted to the RMS amplitude for input of the ASL method. A plot of the residuals for a hypocenter by the ASL method shows that horizontal locations are well constrained compared to the depths. The epicenters of the VT swarm distribute in and around the dike source, which is estimated by geodetic measurements. The epicenters are also located around northeastern and south-western tips of the dike. The depths of the earthquakes are poorly constrained. The temporal change of the hypocenter distribution is weakly seen. The epicenters are concentrated close to the dike at the first 3 hours of the swarm, after that the epicenter distribution spreads from the dike source to the north-east and south directions.