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Crustal structure and seismicity distribution adjacent to the Pacific and North American plate boundary in southern California

机译:加利福尼亚南部太平洋和北美板块边界附近的地壳结构和地震活动分布

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摘要

New three-dimensional (3-D) V_P and V_P/V_S models are determined for southern California using P and S-P travel times from local earthquakes and controlled sources. These models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the Pacific-North America plate boundary. The models extend from the U.S.-Mexico border in the south to the southernmost Coast Ranges and Sierra Nevada in the north and have a 15-km horizontal grid spacing and an average vertical grid spacing of 4 km, down to 22 km depth. The heterogeneity of the crustal structure as imaged by V_P and V_P/V_S models is larger within the Pacific plate than the North American plate. Similarly, the relocated seismicity deepens and shows more complex 3-D distribution in areas of the Pacific plate exhibiting compressional tectonics. The models reflect mapped changes in the lithology across major geological terranes such as the Mojave Desert, the Peninsular Ranges, and the Transverse Ranges. The interface between the shallow Mono of the Continental Borderland and the deep Moho of onshore California forms a broad zone to the north beneath the western Transverse Ranges, Ventura basin, and the Los Angeles basin and a narrow zone to the south, along the Peninsular Ranges. The near-surface increase in velocity, from the surface to up to 8 km depth, is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins. At midcrustal depths a rapid increase in V_P is imaged beneath the sediments of the large sedimentary basins, while beneath the adjacent mountain ranges the increase is small or absent.
机译:使用来自当地地震和受控震源的P和S-P传播时间,确定了加利福尼亚南部的新三维(3-D)V_P和V_P / V_S模型。这些模型证实了现有的构造解释,并为太平洋-北美板块边界的地质结构构造提供了新的见解。这些模型从南部的美国-墨西哥边界延伸到最南端的海岸山脉和北部的内华达山脉,水平网格间距为15公里,平均垂直网格间距为4 km,深度最低为22 km。由V_P和V_P / V_S模型成像的地壳结构的异质性在太平洋板块内要比北美板块大。同样,搬迁后的地震活动在显示压缩构造的太平洋板块区域加深并显示出更复杂的3-D分布。这些模型反映了跨主要地质地形(如莫哈韦沙漠,半岛山脉和横向山脉)的岩性映射变化。大陆边界地区的浅莫诺与加利福尼亚沿海陆上的深莫霍河之间的界面在西部横向山脉,文图拉盆地和洛杉矶盆地的北部形成了一个广阔的区域,在半岛山脉的南部则形成了一个狭窄的区域。从地表到近8 km深度的近地表速度增加是快速的,对于稳定的块体和山脉具有对数形状,而对于沉积盆地则是缓慢的线性关系。在地壳中部深度处,V_P的快速增加显示在大型沉积盆地的沉积物下方,而在相邻山脉以下,则增加幅度很小或不存在。

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    Hauksson Egill;

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  • 年度 2000
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