Attenuation models (QP and QS) in three dimensions of the southern California crust:: Inferred fluid saturation at seismogenic depths
Attenuation models (QP and QS) in three dimensions of the southern California crust:: Inferred fluid saturation at seismogenic depths
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DOI：
10.1029/2005jb003947
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发表时间：
2006-05-02
影响因子：
3.9
通讯作者：
Shearer, PM
中科院分区：
文献类型：
--
作者：
Hauksson, E;Shearer, PM
[1]我们分析了高动态范围波形频谱，以确定南加州地震的P波和S波的t*值。我们对三维(3D)频率无关的地壳区域模型Q(P)和Q(S)的t*值进行了反演。这些模型的水平网格间距为15公里，平均垂直网格间距为4公里，深度为22公里，从美墨边境延伸到南部的海岸山脉和北部的内华达山脉。总体而言，Q(P)和Q(S)随深度迅速增加，与地壳密度和速度一致。三维Q(P)和Q(S)模型反映了南加州地壳的主要构造结构，其次是热结构。近地表低Q(P)和Q(S)带与主要的沉积盆地重合，如圣贝纳迪诺、奇诺、圣加布里埃尔山谷、洛杉矶、文图拉和圣玛丽亚盆地和索尔顿海槽。相反，在半岛山脉、莫哈韦沙漠南部和塞拉斯南部之下的浅层，我们看到的是高Q(P)和Q(S)带，它们对应着山脉的致密和高速岩石。几条快速变化的Q(P)和Q(S)明显的过渡带与晚第四纪的主要断裂重合，连接着Q(P)和Q(S)的高低区域。在中地壳深度，Q(P)和Q(S)在略高和略低的Q(P)或Q(S)带内变化不大，这与已报道的地壳反射率一致。总体而言，南加州地壳的Q(S)/Q(P)大于1.0，表明部分流体饱和的地壳。Q(S)/Q(P)小于1.0的少数有限区域对应于主要沉积盆地以外的地区，包括圣哈辛托断裂周围地区，表明剪切模数比体积模数或几乎完全流体饱和度的降幅更大。
[ 1] We analyze high dynamic range waveform spectra to determine t* values for both P and S waves from earthquakes in southern California. We invert the t* values for three-dimensional (3-D) frequency-independent Q(P) and Q(S) regional models of the crust. The models have 15 km horizontal grid spacing and an average vertical grid spacing of 4 km, down to 22 km depth, and extend from the U.S.-Mexico border to the Coast Ranges in the south and Sierra Nevada in the north. In general, Q(P) and Q(S) increase rapidly with depth, consistent with crustal densities and velocities. The 3-D Q(P) and Q(S) models image the major tectonic structures and to a much lesser extent the thermal structure of the southern California crust. The near-surface low Q(P) and Q(S) zones coincide with major sedimentary basins such as the San Bernardino, Chino, San Gabriel Valley, Los Angeles, Ventura, and Santa Maria basins and the Salton Trough. In contrast, at shallow depths beneath the Peninsular Ranges, southern Mojave Desert, and southern Sierras, we image high Q(P) and Q(S) zones, which correspond to the dense and high-velocity rocks of the mountain ranges. Several clear transition zones of rapidly varying Q(P) and Q(S) coincide with major late Quaternary faults and connect regions of high and low Q(P) and Q(S). At midcrustal depths, the Q(P) and Q(S) exhibit modest variation in slightly higher and lower Q(P) or Q(S) zones, which is consistent with reported crustal reflectivity. In general, for the southern California crust, Q(S)/Q(P) is greater than 1.0, suggesting partially fluid-saturated crust. A few limited regions of Q(S)/Q(P) less than 1.0 correspond to areas mostly outside the major sedimentary basins, including areas around the San Jacinto fault, suggesting a larger reduction in the shear modulus compared to the bulk modulus or almost complete fluid saturation.