Use of temporary seismometers collecting aftershock events for non-ergodic site term development

Abstract

A ground motion model (GMM) predicts intensity measures (IM) at a site given an earthquake scenario, comprising source, path, and site effects. Among these, the site effect is typically constrained by site parameters such as VS30 and site natural period. However, estimating site effects using a single parameter like VS30 can lead to high uncertainties, as it might not adequately represent the complex geological structures at a site. To reduce uncertainties of non-ergodic site effects, accurate geotechnical information or seismic records of the target section are required. Generally, temporary seismometers are installed for earthquake preparation, response, and research purposes following a main earthquake. After the 2017 ML5.4 Pohang event in the southeastern region of the Korean peninsula, several temporary stations were installed near the epicenter, recording multiple aftershock events. Using measurements from temporary seismic stations, we developed non-ergodic site effects for the temporary station locations and could interpolate them to create a more accurate IM map for the mainshock near the epicenter. We validated the developed IM map by comparing records that were not used for generating the IM map. The estimated IM at a test station had less error when compared to the IM predicted directly from the GMM.