Modeling of the Subsurface Structure from the Seismic Bedrock to the Ground Surface for a Broadband Strong Motion Evaluation

Abstract

Sophisticated predictions of strong ground motion are vital when constructing structure models that enable us to evaluate broadband ground motion features. Such models should integrate subsurface structure models for strata shallower than engineering bedrock and deep structuremodels for strata even deeper. Both such models used to be separately modeled separately so that observation data could be reproduced. In this study, we have created a subsurface structure model applicable from seismic bedrock to ground surface for individual Japanese individual prefectures, e.g., Chiba and Ibaragi, in attempts to sophisticate subsurface structure models. This paper describes how we created these models and reviews our results.

Long-period ground motions in a laterally inhomogeneous large sedimentary basin: observations and model simulations of long-period surface waves in the northern Kanto Basin, Japan

“…Furthermore, we confirmed that the JIVSM did not reproduce the observed excitation of the long-period surface waves at the northern edge of the Kanto Basin (TCG001, TCGH06, and SIT003). In contrast, simulation results of the SBVSM accurately reproduced the observed amplitudes and arrival times (Yamamizu 1996(Yamamizu , 2004Yoshimoto and Takemura 2014a), the waveform analysis using the initial model (Figure 3), the JIVSM (Koketsu et al , 2009, and microtremor surveys (Matsuoka and Shiraishi 2002;Yamanaka et al 2005;Senna et al 2013), respectively. of surface waves at not only stations near the basin edge (GNM.059, TCGH06, TCG001, and SIT003) but also at stations far from the edge (SIT.015, SIT010, and TKY.1220).…”

“…We converted the layered sedimentary structure models from dense microtremor surveys in Saitama, Ibaraki, and Chiba (Matsuoka and Shiraishi 2002;Yamanaka et al 2005;Senna et al 2013) using the same conversion procedure discussed above. Since these models were derived from the dispersion analysis of surface waves, the incorporation of these models may improve the accuracy of long-period ground motion simulations.…”

A Bayesian Approach to Microtremor Array Methods for Estimating Shallow S Wave Velocity Structures: Identifying Structural Singularities

“…The constraints on a velocity model could be strengthened further by also using data sets other than Rayleigh‐wave phase velocities, such as Love‐wave phase velocities (Köhler et al, ; Nishida et al, ; Tada et al, , ), microtremor amplitude information (horizontal‐to‐vertical spectral ratios [HVSRs]; Arai & Tokimatsu, ; Dal Moro, ; Picozzi et al, ), and waveform data of earthquakes (Senna et al, ; Shen et al, ). As an example of strengthening the constraints, Dal Moro et al (, ) conducted “miniature array analyses,” as well as we do in this study, as part of experiments comparing different methodologies which can be used to analyze phase velocities; they performed joint inversions of phase velocities of Rayleigh waves and HVSRs and examined how each data set contributes to the constraints.…”

“…It is customary to fix either one of the S wave velocity and the layer thickness at a prescribed value because a trade‐off exists between those two parameters. For example, it is often the case that the layer thicknesses are fixed and the optimal S wave velocity values are sought in the modeling of shallower portions, whereas the S wave velocities are fixed and the optimal thickness values are sought in the modeling of deeper parts (Senna et al, ).…”

Simple assessment of shallow velocity structures with small-scale microtremor arrays: interval-averaged S-wave velocities

“…We have been working to develop simpler and more robust microtremor methods that use small-scale seismic arrays, such as miniature arrays measuring only 1 m or less in radius and compact arrays of three unevenly spaced sensors measuring only several metres in radius (Cho et al, 2004(Cho et al, , 2008(Cho et al, , 2013. The simpler and more robust microtremor method has enabled large-scale surveys to be conducted in recent years by using large numbers of compact seismic arrays of similar types (Senna et al, 2017).…”