Calibration of Mainshock Event-terms Using Aftershock Records

초록

To estimate ground shaking level for a specific event, the median of ground motion prediction equation is calibrated by an event term that is the misfit of residuals. For this calibration, the near-source records are important because most damage occurs near the epicenter, but seismic stations are seldom located in this area. Few points cannot ensure the event specific trend near the source. To fill this gap, we investigate residuals from aftershocks and compare with those of mainshock. Ground motions by aftershocks are also recorded by potable network installed after the mainshock, which makes the data points abundant near the source. We see that the residual trends between mainshock and aftershock are similar if aftershock event conditions are close to the mainshock, and the recordings from the portable network ensure the residual bias from the permanent station. Cautions are needed when evaluate aftershock residuals because some aftershock with different conditions from mainshock also have different residual trend.