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Examining Differences in Basin Amplification Between Interface and Intraslab Subduction Sources From the Kanto Region in Japan

Description: 

The basin amplification models used for subduction sources do not currently distinguish between intraslab and interface earthquakes. However, interface sources may generate stronger surface waves and S-to-surface wave conversions at the basin edge due to the shallower incidence ray path of the incoming waves. In contrast, deeper intraslab sources feature steeper incidence angles that could result in weaker surface waves at the basin-edge. Numerical simulations for sources near the Seattle basin provide support for this hypothesis (Wirth, 2019). We use recordings selected from the NGA-Subduction database in the Kanto Basin, where the city of Tokyo is located and compute the predicted response spectra for spectral periods from 0.01-10s using the four NGA-Subduction GMMs regionalized for Japan. The predictions are for a uniform site condition and without the basin term. We use a mixed-effects regression to partition each set of total residuals into the bias, between-, and within-event terms. The within-event residuals are plotted against the depth to the shear-wave velocity (Vs) horizon where Vs=2.5km/s (Z2.5). We find differences in basin-depth scaling for intraslab and interface sources, with interface earthquakes producing steeper gradients for periods greater than 1s. Basin amplification factors (BAF) are computed using the ratio of the average effective site terms within the Kanto Basin to those in a reference region outside of the basin. The uncertainty in the BAFs is accounted for by selecting random subsets of the recordings and examining the variability across the different subsets. BAFs suggest that interface sources typically show larger amplification than intraslab sources at longer periods (T>1s). We examine the influence of station selection and incidence angles, which have significant effects on the character and amplitude of the BAFs. Our results can inform weights of alternative basin models in the logic trees for subduction regions.

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: James Smith

Student Presenter: No

Invited Presentation: 

Authors