Development of statistical strong-motion evaluation method based on regional variation of source and path effects in the Tohoku region, Japan

为了更精确地估计地震危险图，我们在日本东北地区开发了一种考虑震源、路径和场地效应区域差异的强运动谱统计（经验）评估方法。主要研究结果如下：利用dpi K-NET、KiK-net、PARI、JMA type-87和type-95强震台网数据编制了东北地区强震数据库。我们对同一数据集的s波傅立叶谱和响应谱进行了频谱反演分析，得到了每次地震的震源谱、传播路径q值（内陆和俯冲带不同）以及各震点的放大系数。通过绘制布鲁纳应力降图和频率相关场址放大图，发现了以下趋势：(1)宫城县以东地区高频源辐射强度很高。(2)位于火山附近的浅层内陆地震高频辐射强度较低。其他地区的内陆地震的应力下降与发生在俯冲带的浅层地震相似。(3)日本海侧0.2Hz左右的站点放大因子较大，可能是由于欧胡山脉西部的盆地深度比东部深。尽管如此，0.5-2Hz左右的放大幅度（这是低层建筑震害的重要范围）不仅在欧胡山脉西部，而且在仙台平原等东部地区都很大。基于谱反演结果，将地震项模拟为矩震级和应力降的函数，评价了PGA、PGV、反应谱的衰减关系，并将场地放大系数模拟为地表至30m的平均横波速度Vs30的函数。加入应力降作为参数，可以大大减小地震项的方差。

Toward more precise estimation of earthquake hazard maps, we developed a statistical (empirical) evaluation method of strong motion spectra considering regional variation of source, path, and site effects in the Tohoku region, Japan. The main results are as follows.1. We compiled strong-motion database over the Tohoku region from DPRI K-NET, KiK-net, PARI, JMA type-87 and type-95 strong-motion network data.2. We conducted spectral inversion analyses for both S-wave Fourier and response spectra for the identical dataset, and obtained source spectrum of each earthquake, Q-value of propagating path (inland and subduction zones, differently), and site amplification factor at each site. By drawing maps of the Brune's stress drop and frequency-dependent site amplifications, the followings tendencies are found :(1)high-frequency source radiation strength is very high at east of Miyagi prefecture area.(2)shallow inland earthquakes located near volcanoes show lower high frequency radiation strength. Inland earthquakes at the other area have stress drops similar to the shallow earthquakes occurred in subduction zones.(3)site amplification factors around 0.2Hz are large at Japan-Sea side, probably due to the basin depth of west of Ohu mountains are deeper than the east area. Still, amplifications around 0.5-2Hz, which is very important ranges for the earthquake damage for low-rise building, are large not only in the west of Ohu mountains but in the east area, such as Sendai plain.3. Based on the results of spectral inversion, we evaluated attenuation relations of PGA, PGV, response spectrum by modeling earthquake term as a function of moment magnitude and stress drop, and also modeled site amplification factor as a function of Vs30, averaged S-wave velocity from the ground surface to 30m-deep. The variance of earthquake term is largely decreased by adding stress drop as a parameter.