Strong Motion Estimation for Active Faults with High Earthquake Potential

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Our major objectives are to obtain accurate long-term earthquake prediction by assessing hazard potential of active faults, to clarify physics of the faulting dynamics and to develop the numerical as well as semi-empirical methods for precise ground-motion modeling by computational and observational approaches. Final target is to establish the methodology of predicting strong ground motions for hypothetical active-fault earthquakes and to mitigate earthquake damage from future large earthquakes.We have been developing the above six subjects as follows : (1) Aerial photograph interpretation and paleoseismic trenching were made to date late Holocene earthquakes along the active faults for the seismic hazard evaluation on the Median Tectonic active fault system (MTL). The geometry and average slip rate of seismic source faults were obtained using the analysis of balanced cross sections based on seismic reflection profilings and boring data in some representative areas, Shinjo and Tomakoma … More i. Fault branching and directivity of rupture propagation were studied from rupture patterns of recent earthquake faultings. (2) The arresting mechanism of dynamic crack growth was studied by BIEM and compared with surface geometry of active faults. Strong pulses near the earthquake faults were calculated by near-field expression theory with a dynamic slip-rate time function. Source heterogeneity was studied by combining the results of low-frequency waveform and high frequency envelope inversions using strong ground motion and broadband recordings. Source characterizations of inland crustal earthquakes and large intra-plate earthquake were done using high-quality network data. (3) Accurate 3-D modelings of underground structures are done by joint inversion of refraction and gravity data. Site effects for sedimentary basins and shallow soil layers are well estimated from S-wave profiles derived by microtrmor array measurements, validated by direct evaluations of amplifications from earthquake records. (4) Numerical methods for propagation media with irregular interfaces are developed as a hybrid scheme with the indirect boundary element method and semi-analytical solution for flat interfaces. Seismic anisotropy are confirmed by some observation and numerical simulation in the source region of the 1997 Kagosima-hokuseibu earthquakes. (5) The results of refraction, reflection, and gravity surveys were gathered for deriving the three-dimensional underground structure in the Kobe-Hanshin area. Simulations of strong ground motions in and around heavily-damaged areas were done for examining the relation between strong ground motions and structure damage. Ground motion estimations considering source effects as well as seismic responses due to complex structures in both macro and micro scales were studied in observation and numerical techniques for the subduction and slab earthquakes. (6) Methods of strong motion prediction for future large earthquakes were developed and validated by comparing synthesized results with the observed data and damage distribution during the 1995 Hyogo-ken Nanbu and the 1994 Northridge earthquakes. Estimation of strong ground motions during the 1948 Fukui earthquake was done by hybrid simulation method. The source characterization for large inland earthquakes has been studied from statistical analyses of slip distributions with the waveform inversion.The results of the above six topics was combined to establish the methodology of estimating strong ground motions for hypothetical active-fault earthquakes. We summarize the procedure that is currently used to characterize earthquake rupture models, based on geological investigations of capable earthquake faults and seismological studies of source models. Then we propose a recipe of predicting strong ground motion form scenario earthquakes caused by active faults. Less