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Statistical Green’s Function Method Based on Spectral and Phase Characteristics Estimated by Generalized Inversion Technique for Japanese Data -Case Simulations for the 2011 Ibaraki-Oki Earthquake and Hypothesized Nankai-Trough Megathrust Event

Description: 

We need a method that can predict strong ground motions with sufficient accuracy at any target site for quantitative evaluation of the hazard and subsequent risk of large earthquakes. However, our knowledge of the source, path, and site factors of the observed strong motions has not been fully utilized. First, we performed the analysis to investigate the properties of these factors mentioned above based on a generalized inversion technique on Fourier spectra of strong motion networks deployed in Japan. We tried to model not only spectral amplitude but also phase information in the frequency domain, using the group delay time. Once we obtain statistical properties of the amplitude and group delay time, we can produce ground motions at an arbitrary site from an elemental source at an arbitrary location on the fault surface, which can be used as a Green’s function in the statistical Green’s function method. The statistical Green’s function method is not the same as the stochastic Green’s function method as the former can take into account variabilities in the Green’s functions based on the statistical properties of the separated factors. Next, we constructed a procedure for predicting the strong motions considering both the spectral difference between the whole duration of motion and the S-wave portion and the effects of soil nonlinearity.

As a validation exercise, we confirmed that the proposed method can work well for the reproduction of ground motions generated by the 2011 Ibaraki-Oki earthquake, which was the largest aftershock (Mw7.8) of the 2011 Tohoku earthquake sequence. Matching with data was good because we considered its smaller stress drop as a regional source characteristic. Then we simulated the ground motions in the Kinki region from the hypothesized Nankai-Trough megathrust event based on the scenario proposed by the Central Cabinet Office (2012). As a result, we obtained waveforms with realistic characteristics in the spectra and envelop shapes.

Session: Site-specific Modeling of Seismic Ground Response: Are We Quantitative Enough to Predict? [Poster]

Type: Poster

Date: 4/19/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Kenichi Nakano

Student Presenter: No

Invited Presentation: 

Authors