5:15 PM - 7:15 PM
[SSS10-P04] Influence of the Shallow Low-Velocity Layer on Fault Rupture Behavior Using a Dynamic Model
Keywords:The 2014 Northern Nagano Earthquake, Dynamic Model, Asperity, Velocity Layer Structure Model
The simulation for dynamic rupture propagation that is based on the force balance is very useful approach to understand the fault behavior especially to the shallow part of the faut for the in-land crustal earthquake. Even the homogeneous medium was assumed for many previous studies, the fault rupture is supposed to penetrate to the shallow part of low velocity layer in case for breaking surface fault. This suggests that the understandings of fault behavior with consideration of low velocity layer is important. Thus, we try to investigate the fault behavior based on the model with low velocity layer and the parameter studies with changing location of asperity as the target of 2014 Northern Nagano Earthquake (Mw 6.2) with breaking surface fault.
At first, we have constructed the model with two (deep- and shallow-) asperities based on homogeneous medium that could reproduce the features of observations, such as earthquake size (seismic moment), spatial distribution of surface displacement, and the near-field ground motions (velocity and displacement time histories) with the adjustments for the stress parameters and frictional parameter (Dc). Based on this model, we have conducted the parameter studies with changing some parameters, such as stress drop, Dc, and location of asperity. The results revealed that the surface displacement is more influenced by the deep asperity than that by the shallow asperity.
The model with the shallow low velocity layer produced the area with large asperity close to the surface and showed more area of the fault surface. On the other hand, the reduction of shear modulus on the shallow part generated little difference in terms of the seismic moment. The amplitudes of the simulated near-field ground motions were amplified by the difference of impedance ratio and their shape showed more complex including reflected waves generated on the boundary of velocity layer.
At first, we have constructed the model with two (deep- and shallow-) asperities based on homogeneous medium that could reproduce the features of observations, such as earthquake size (seismic moment), spatial distribution of surface displacement, and the near-field ground motions (velocity and displacement time histories) with the adjustments for the stress parameters and frictional parameter (Dc). Based on this model, we have conducted the parameter studies with changing some parameters, such as stress drop, Dc, and location of asperity. The results revealed that the surface displacement is more influenced by the deep asperity than that by the shallow asperity.
The model with the shallow low velocity layer produced the area with large asperity close to the surface and showed more area of the fault surface. On the other hand, the reduction of shear modulus on the shallow part generated little difference in terms of the seismic moment. The amplitudes of the simulated near-field ground motions were amplified by the difference of impedance ratio and their shape showed more complex including reflected waves generated on the boundary of velocity layer.