Strong Motion Estimation for Active Faults with High Earthquake Potential

我们的主要目标是通过评估活动断层的危险潜力来获得准确的长期地震预测，澄清断层动力学的物理学，并开发用于通过计算和观测方法进行精确地震动模拟的数值和半经验方法。最终目标是建立假想的活动断层地震的强地面运动预测方法，以减轻未来大地震的震害。我们开展了以下六个方面的工作：(1)对活动断裂沿线的全新世晚期地震进行了航片解译和古地震槽化，以进行中等构造活动断裂系统(MTL)的地震危险性评估。根据地震反射剖面和钻井资料进行平衡剖面分析，得到了震源断层的几何形状和平均滑动速率，并在…新津和托马科马等代表性地区进行了观测。根据现代地震断裂的破裂图象，研究了断层的分支和破裂传播的方向性。(2)用BIEM方法研究了动态裂纹扩展的止裂机理，并与活动断裂的地表几何形状进行了比较。地震断层附近的强脉冲用近场表达理论和动态滑移率时间函数计算。利用强地面运动和宽带记录，结合低频波形和高频包络反演的结果，研究震源的非均质性。利用高质量的台网数据对内陆地壳地震和板内大地震的震源特征进行了研究。(3)利用折射和重力联合反演法对地下结构进行了精确的三维建模。沉积盆地和浅层土层的场地效应可以从由微管阵列测量得到的S波剖面中很好地估计出来，并得到地震记录放大系数的直接评估。(4)发展了非规则界面传播介质的数值方法，将间接边界元方法与平板界面的半解析解相结合，形成了混合格式。1997年鹿儿岛-河西部地震震源区的观测和数值模拟证实了地震各向异性。(5)综合折射、反射和重力测量结果，得出神户-阪神地区的三维地下结构。为研究强地震动与结构破坏之间的关系，对重灾区及周边地区的强地震动进行了模拟。在俯冲地震和板状地震的观测和数值技术中，研究了宏观和微观尺度上考虑震源效应和复杂结构地震响应的地面运动估计。(6)通过与1995年兵库县南部地震和1994年北岭地震的观测资料和震害分布的对比，建立了未来大地震的强震预报方法，并对其进行了验证。用混合模拟方法对1948年福井地震期间的强地面运动进行了估计。通过对滑动分布的统计分析和波形反演，研究了内陆大地震的震源特征，并结合上述六个主题的结果，建立了假设的活动断层地震的强地面运动估计方法。基于对可能的地震断层的地质调查和震源模型的地震学研究，我们总结了目前用于表征地震破裂模型的方法。然后，我们提出了一个从活动断裂引起的情景地震中预测强地面运动的配方。较少

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