Modelling of 2016 Kumamoto earthquake by integrating site effect in semi-empirical technique

The 2016 Kumamoto earthquake (M(JMA)7.3) struck central area of Kyushu Island, Japan. The presence of near surface low velocity layer greatly amplified the ground motions and caused severe damage in this region. Therefore, it is essential to study the site characteristics of Kumamoto region. For this purpose, the present research article describes the modification in existing semi-empirical technique of strong motion simply by incorporating the site effect. These site effects are calculated using Horizontal to Vertical ratio (H/V) method. The estimated predominant frequencies (f(peak)) for these stations varies between 2.5 and 7.5 Hz. The sites with low f(peak) indicate higher soil thickness cover and hence, locations are more susceptible to damage. The station KMMH06 used in this work lies in close proximity to one of the major landslide locations (Minami Aso Village), triggered during this earthquake. The low to intermediate f(peak) value estimated at KMMH06 proposes the area prone to site amplification and severe damage. Also, the initial location and parameters of rupture model of this earthquake are considered based on past seismicity and other empirical relations available. The detailed analysis proposes nucleation point in extreme NW corner of the rupture plane. Afterwards, the developed source model and modified technique compositely used to simulate high frequency records at eight near field stations. This includes time histories, response spectra, predominant period (T-p) and mean period (T-m). The above comparison successfully validates modified semi-empirical and source model for 2016 Kumamoto earthquake. As far as we are aware, this work is the first to model rupture plane of 2016 Kumamoto earthquake by means of modified semi-empirical technique. It provides adequately reliable results which will be advantageous for seismic hazard assessment of this region.

Automated summary

This research successfully simulated the seismic characteristics of the 2016 Kumamoto earthquake by modifying the semi-empirical technique and utilizing a source model. The study provides important insights for seismic hazard assessment in the Kumamoto region.