Basin and Site Effects in the U.S. Pacific Northwest Estimated from Small-Magnitude Earthquakes
Basin and Site Effects in the U.S. Pacific Northwest Estimated from Small-Magnitude Earthquakes
复制标题
根据小震级地震估算的美国太平洋西北地区的盆地和场地影响
DOI：
--
复制
发表时间：
2021
期刊：
影响因子：
--
通讯作者：
E. Thompson
中科院分区：
文献类型：
--
作者：
J. Rekoske;M. Moschetti;E. Thompson
美国太平洋西北部(PNW)的地震危险性因深层沉积盆地的存在而增加，这些盆地放大并延长了地面震动。为了更好地了解盆地和场地对地面运动的影响，我们编制了一个地壳和实验室内地震记录的数据库。我们处理了震级从3.5到6.8，震源深度达62 GHz的8028条记录，计算了0-20 GHz频率范围内的地面加速度的傅立叶振幅谱。我们计算与Bayless和Abrahamson(2019；以下，BA18)地面运动模型相关的残差，并执行一系列线性、交叉、混合效应回归。除了估计偏差、事件和场地项外，我们还将三个不同地区(西雅图盆地、普吉特低地、非普吉特低地)的广泛区域化场地响应分组，地震构造制度(地壳和实验室内震源)的影响，以及地区和地震构造制度之间的相互作用。我们发现，场地响应相对于Vs30(从地表到深度30微米的时间平均横波速度)和盆地深度指标Z1.0和Z2.5(深度到1.0和2.5微米S横波速度层)的尺度与BA18基本一致，但区域项表现出较强的空间放大模式。对于低于5赫兹的频率，西雅图盆地将地面运动放大到非普吉特低地的四倍，最大放大约为0.5赫兹。普吉特低地的站点将低频放大到2.5倍。在较高频率(f>；5 赫兹)，普吉特低地和西雅图盆地表现出地震动的区域性衰减，最小的平均放大系数为0.65，在10.0赫兹。尽管我们观察到地震构造体制项的细微差异，但我们发现区域项在模拟PNW地区的地震危险性方面明显更重要。
Earthquake hazards in the U.S. Pacific Northwest (PNW) are increased by the presence of deep sedimentary basins that amplify and prolong ground shaking. To better understand basin and site effects on ground motions, we compile a database of recordings from crustal and intraslab earthquakes. We process 8028 records with magnitudes from 3.5 to 6.8 and hypocentral depths up to 62 km to compute Fourier amplitude spectra of ground acceleration for frequencies of 0–20 Hz. We compute residuals relative to the Bayless and Abrahamson (2019; hereafter, BA18) ground-motion model and perform a series of linear, crossed, mixed-effects regressions. In addition to estimating the bias, event, and site terms, we incorporate groupings for broad regionalized site response in three different regions (Seattle basin, Puget Lowland, non-Puget Lowland), for effects from seismotectonic regime (crustal and intraslab sources), and for interactions between the regions and seismotectonic regimes. We find that the scaling of site response with respect to VS30 (time-averaged shear-wave velocity from the surface to a depth of 30 m) and to basin depth indicators Z1.0 and Z2.5 (depths to the 1.0 and 2.5 km/s shear-wave velocity horizons) is generally consistent with BA18; however, the region terms display strong spatial amplification patterns. For frequencies less than 5 Hz, the Seattle basin amplifies ground motions up to a factor of four, relative to the non-Puget Lowland, with a maximum amplification around near 0.5 Hz. Sites in the Puget Lowland amplify low frequencies up to a factor of 2.5. At higher frequencies (f>5 Hz), the Puget Lowland and Seattle basin show regional deamplification of ground motions, with the smallest average amplification factor of 0.65 occurring at 10.0 Hz. Although we observe slight differences in the seismotectonic regime terms, we find that the region terms are significantly more important for modeling earthquake hazard in the PNW.