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

为了更准确地估计地震危险性图，我们发展了一种考虑日本东北地区震源、路径和场地效应的区域差异的强震频谱统计(经验)评估方法。主要研究结果如下：1.研究结果。我们利用DPRI K-Net、Kik-Net、PAI、JMA-87和95型强震台网资料编制了东北地区的强震数据库。我们对同一数据集的S波傅里叶谱和反应谱进行了频谱反演分析，得到了每一次地震的震源谱、传播路径(不同的内陆带和俯冲带)的Q值以及每个场地的场地放大系数。通过绘制布吕恩应力降图和场地放大频度图，发现：(1)宫城县以东地区高频震源辐射强度很高。(2)靠近火山的内陆浅层地震高频辐射强度较低。其他地区内陆地震的应力降与俯冲带浅层地震的应力降相似。(3)日本海一侧0.2赫兹附近的场地放大系数较大，可能是由于鄂尔多山以西的盆地深度大于东部所致。但是，无论是在鄂尔多山以西，还是在东部，如仙台平原，0.5-2赫兹附近的放大幅度都很大，这是低层建筑震害的重要范围。在频谱反演结果的基础上，通过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Vs30的函数，得到了从地表到30m深处的平均S波速。通过引入应力降作为参数，大大减小了地震项的方差。

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.