First result from the GEONET real-time analysis system (REGARD): The case of the 2016 Kumamoto earthquakes

Abstract

We present the initial results of rapid fault estimations for the 2016 Kumamoto earthquake on April 16 (Mj 7.3), and coseismic displacements caused by the two large foreshocks that occurred on April 14 (Mj 6.5) and April 15 (Mj 6.4) from the GEONET real-time analysis system (REGARD), which is based on a Global Navigation Satellite System (GNSS) kinematic positioning technique. The real-time finite-fault estimate (Mw 6.85) was obtained within 1 min and converged to Mw 6.96 within 5 min of the origin time of the mainshock (Mj 7.3). The finite-fault estimate shows right-lateral strike-slip fault along the Futagawa fault segment, which is consistent with the finite-fault model inferred from post-processed GNSS and InSAR analysis. Furthermore, significant coseismic displacements were observed due to the April 14 and April 15 foreshocks at nearby sites, though these earthquakes were smaller than the pre-assigned system threshold. Our results also demonstrate the potential for the GNSS-based earthquake early warning system for inland earthquakes.