Numerical Simulation of Pulse-Like Ground Motions in the Coastal Area of Osaka Bay During the 2018 Osaka Earthquake

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

In the near future mega crustal and/or subduction earthquakes are expected to strike Osaka City, the second largest city in Japan, causing devastating structural and economic damage. Strong seismic resilience should be constructed in this area, because metropolitan development has been rapidly accelerated for the next World Expo held in Osaka Bay area in 2025. Various previous studies have been carried out for ground motion evaluation in Osaka Bay area in the middle of the Osaka Plain. Recently, the Mw 5.5 inland shallow earthquake occurred in the northern part of the Osaka prefecture on June 18, 2018. The JMA seismic intensity scale lower 6 was observed in the Osaka prefecture for the first time. It has been reported that two types of seismic faults ruptured at the same time. Short-period pulse-like motions with predominant period of less than 1 second were observed in the vicinity of the epicenter. Distinctive pulse motions with large amplitude occurred in the later phase at the KiK-net Konohana site in the Osaka bay area. The same phenomenon also occurred during the 2011 Great East Japan Earthquake and the 2013 Awaji Island Earthquake. In this study, we investigate generation mechanism of peculiar pulse observed in the later phase of ground motions through numerical approach. First, the ground motions in the near-fault area and the coastal area of the Osaka bay are simulated using finite difference method considering long period motions with more than 0.5 second. Then, we examine the influence of these two faults and their contribution to the ground motions. Finally, the generation process of the distinctive pulse in coastal area of Osaka bay is clarified by focusing on the spatial variation of ground motions in observation array crossing the source to the coast of Osaka bay.

Presenting Author: Takuya Kataoka

Authors