My research was strongly influenced by ongoing Next Generation Attenuation projects (NGA), which is sponsored by Pacific Earthquake Engineering Research Center (PEER). This far, PEER has sponsored two landmark national projects for developing NGA relationship in active tectonic regions. The result of these two projects will be incorporated into national hazard maps developed by United States Geological Survey (USGS). However, since the national seismic hazard maps include stable continental regions and subduction zones, it is desired to ex- tend those studies to other tectonic regions. NGA-Subduction project has recently been initiated to address Subduction Zones (SZ).
For this project, I collaborated with PEER researcher for processing the data of main shock recordings of the Tohoku earthquake. I also analyzed the data to evaluate the implications of this data set with respect to magnitude-, distance-, and site-scaling in existing GMPEs for SZs. The Mw = 9.0 Tohoku-oki Japan earthquake produced approximately 2000 ground motion recordings. We consider 1238 three-component accelerograms corrected with component-specific low-cut filters. The recordings have rupture distances between 44 and 1000km, time-veraged shear wave velocities of Vs30 = 90 to 1900ms−1, and usable response spectral periods of 0.01 to > 10 s. The data support the notion that the increase of ground motions with magnitude saturates at large magnitudes. High frequency ground motions demonstrate faster attenuation with distance in backarc than in forearc regions, which is only captured by one of the four considered ground motion prediction equations for subduction earthquakes. Recordings within 100 km of the fault are used to estimate event terms, which are generally positive (indicating model under-prediction) at short periods and zero or negative (over-prediction) at long periods. We find site amplification to scale minimally with Vs30 at high frequencies, in contrast with other active tectonic regions, but to scale strongly with Vs30 at low frequencies.
It is envisioned that the research outlined herein could help earthquake engi- neering community to design infrastructures which are more resistant to earth- quakes by improving ground motion prediction capabilities.
