Lg attenuation, frequency dependence and relative site response of the western United States as revealed by the EarthScope Transportable Array
Lg attenuation, frequency dependence and relative site response of the western United States as revealed by the EarthScope Transportable Array
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DOI：
10.1093/gji/ggx145
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发表时间：
2017-06-01
影响因子：
2.8
通讯作者：
Sandvol, Eric
中科院分区：
文献类型：
--
作者：
Gallegos, Andrea;Ranasinghe, Nishath;Sandvol, Eric
美国西部的 Lg 衰减是使用 EarthScope 的可移动阵列、伯克利数字地震仪网络和加州理工学院区域地震网络记录的区域波形来估计的。 Lg 衰减是使用两站法 (TSM) 确定的。使用了 2005 年至 2010 年时间范围内 4 至 6.5 级的 292 个事件。我们通过层析成像绘制了中心频率为 0.5、1、2 和 3 Hz 的窄带内有效 Lg Q 的变化。各个站的相对站点响应是使用这些中心频率处的反向 TSM 确定的。双站和反向 TSM 都具有在绘制地壳横向异质性时无需先验模型即可有效消除位点和源效应的优点。高衰减区域分布在斯内克河平原沿线、加州北部与俄勒冈州边界沿线、整个盆地山脉、沃克巷、瓦萨奇断层和里奥格兰德裂谷。低衰减区域位于科罗拉多高原、落基山脉、内华达中部和哥伦比亚高原。总体而言，Lg Q 被发现具有幂律频率依赖性，中心频率的增加导致 Q 的增加。发现相对站点响应随当地地质情况变化很大。内华达山脉和斯内克河平原等硬岩地区表现出一致的负场地响应模式（即去放大），而沉积程度较高的地区，例如盆地和山脉的地堑，则表现出正场地响应（即放大）。最后，发现站点响应随着频率的变化而变化，随着频率的增加，变化变得越来越小并且更加明显。
Lg attenuation of the western United States is estimated using regional waveforms recorded by EarthScope's Transportable Array, the Berkeley Digital Seismograph Network and the Caltech Regional Seismic Network. Lg attenuation is determined using the two-station method (TSM). 292 events ranging from magnitude 4 to 6.5 in a time range for the years between 2005 and 2010 are used. We have tomographically mapped variations in effective Lg Q at narrow bands with central frequencies of 0.5, 1, 2 and 3 Hz. The relative site responses of individual stations are determined using a reverse TSM at these central frequencies. Both the two-station and reverse TSMs have the advantage of effectively removing site and source effects without requiring a priori models while mapping lateral heterogeneities in the crust. Regions of high attenuation are found along the Snake River Plain, along the northern California-Oregon border, throughout the Basin and Range, Walker Lane, Wasatch Fault and the Rio Grande Rift. Regions of low attenuation are found in the Colorado Plateau, Rocky Mountains, central Nevada and the Columbia Plateau. Overall, Lg Q was found to have a power-law frequency dependence, with an increase in central frequency resulting in an increase in Q. Relative site responses were found to vary strongly with local geology. Hard rock areas such as the Sierra Nevada Mountains and the Snake River Plain show a consistent pattern of negative site response (i.e. deamplification), while areas with a higher degree of sediments, such as the grabens of the Basin and Range, show positive site response (i.e. amplification). Finally, site responses were found to vary with frequency, becoming less variable and more pronounced as frequency increases.