10:15 AM - 10:30 AM
[SCG60-06] Current status and issues of shallow fault modeling
Keywords:Kumamoto earthquake, shallow fault, source modeling
The modeling of shallow faults in seismic hazard assessment and fault displacement hazard assessment is an issue that is difficult to evaluate quantitatively because of the large effects of strong ground motions and permanent displacement near the fault zone, together with the geometry of the fault and the subsurface structure near the fault.
Somerville et al. (1997) showed large-amplitude velocity and displacement waveforms of strong ground motions near the epicenter associated with shallow slip, but the response of the fault-normal component was larger than that of the fault-parallel component, leading to the rupture directivity pulse argument. Somerville et al. (1997) showed that the response of the fault-normal component was larger than that of the fault-parallel component. The 1995 Kobe earthquake prompted research on rupture directivity pulses of near-source strong ground motions associated with deep slip and modeling of the source region. In these earthquakes, no strong-motion records were obtained very close to the faults.
During the 1999 Kocaeli earthquake in Turkey and the 2002 Denali earthquake in Alaska, large-amplitude velocity pulses and displacement waveforms associated with shallow slips were observed very close to the fault. However, in both cases, the super-shear rupture of the fault became the main point of contention, and it was pointed out that the fault-parallel component exceeded the fault-normal component during the super-shear rupture (Bouchon et al., 2001; Ellsworth et al., 2004).
In Japan, large amplitude velocity and displacement waveforms were observed very close to the fault during the 2016 Kumamoto earthquake. There is a need for shallow fault modeling that comprehensively reflects factors such as complex fault geometry, source rupture process, and ground amplification more pronounced than existing underground structures. In particular, due to spatiotemporal changes in fault geometries and slip angles, several records have been observed that are difficult to classify clearly into the rupture directivity pulses and fling steps. Although there have been pioneering studies on source modeling along the dip direction of faults for strong ground motion prediction (e.g., Kagawa et al., 2005), there is a need to further understand the spatio-temporal evolution of slip at the top of the fault. In this presentation, we discuss issues of shallow fault modeling, mainly focusing on the 2016 Kumamoto earthquake.
Somerville et al. (1997) showed large-amplitude velocity and displacement waveforms of strong ground motions near the epicenter associated with shallow slip, but the response of the fault-normal component was larger than that of the fault-parallel component, leading to the rupture directivity pulse argument. Somerville et al. (1997) showed that the response of the fault-normal component was larger than that of the fault-parallel component. The 1995 Kobe earthquake prompted research on rupture directivity pulses of near-source strong ground motions associated with deep slip and modeling of the source region. In these earthquakes, no strong-motion records were obtained very close to the faults.
During the 1999 Kocaeli earthquake in Turkey and the 2002 Denali earthquake in Alaska, large-amplitude velocity pulses and displacement waveforms associated with shallow slips were observed very close to the fault. However, in both cases, the super-shear rupture of the fault became the main point of contention, and it was pointed out that the fault-parallel component exceeded the fault-normal component during the super-shear rupture (Bouchon et al., 2001; Ellsworth et al., 2004).
In Japan, large amplitude velocity and displacement waveforms were observed very close to the fault during the 2016 Kumamoto earthquake. There is a need for shallow fault modeling that comprehensively reflects factors such as complex fault geometry, source rupture process, and ground amplification more pronounced than existing underground structures. In particular, due to spatiotemporal changes in fault geometries and slip angles, several records have been observed that are difficult to classify clearly into the rupture directivity pulses and fling steps. Although there have been pioneering studies on source modeling along the dip direction of faults for strong ground motion prediction (e.g., Kagawa et al., 2005), there is a need to further understand the spatio-temporal evolution of slip at the top of the fault. In this presentation, we discuss issues of shallow fault modeling, mainly focusing on the 2016 Kumamoto earthquake.