A Method for Measuring Small to Large Scale Coseismic Deformation of Earthquakes Using Strong-motion Records: Application to Moderate Earthquakes in the Korean Peninsula

Abstract:

Coseismic deformation of an earthquake provides various information with understanding of rupture kinematics regarding to source mechanism, slip distribution, and total seismic moment. Geodetic estimations derived from GPS and InSAR data are widely utilized to measure the permanent displacement, but still their sampling rates and spatial coverages are limited. Strong motion seismometers record ground motions in zero-frequency band range and are densely distributed over near- and far-field areas from an earthquake source. Static offset in the displacement field can be obtained by double integration of accelerogram. Preceding to the integration of velocigram, suitable baseline correction should be applied to retrieve the correct offset in the displacement field. Linear or quadratic regression corrections of pre-event and after-event trends are generally applied for large earthquakes. However, it is hard to stably estimate a small (e.g. unit of mm scale) amount of permanent displacement using those method. We developed a new baseline correction method to stably estimate a small amount of permanent displacement. We estimated the measurable amount and distance of coseismic deformation of the M_w 7.0 Kumamoto earthquake in 2016, which is rich in reports of coseismic deformation from strong motion, GPS and InSAR data. In addition, we found the possibility of measuring permanent displacement in mm up to the 300 km of epicentral distance when the strong motion signal has relatively good signal-to-noise levels. This method is applied to the recent moderate earthquakes (M_L 5.8 and 5.4) in the southeastern part of the Korean Peninsula. We interpret the outcomes considering the focal mechanisms of events and compare our results with the geodetic observations.