Complex Patterns of Past and Ongoing Crustal Deformations in Southern California Revealed by Seismic Azimuthal Anisotropy
Complex Patterns of Past and Ongoing Crustal Deformations in Southern California Revealed by Seismic Azimuthal Anisotropy
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DOI：
10.1029/2022gl100233
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发表时间：
2022-08
影响因子：
5.2
通讯作者：
Shucheng Wu;Chengxin Jiang;V. Schulte‐Pelkum;P. Tong
中科院分区：
文献类型：
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作者：
Shucheng Wu;Chengxin Jiang;V. Schulte‐Pelkum;P. Tong
利用一种新的伴随状态旅行时层析成像技术，建立了南加州中上部地壳的高分辨率P波方位各向异性速度模型。我们的模型揭示了构造块体之间显著的各向异性变化，清楚地反映了过去和现在的板块边界变形。在地壳浅层，地震各向异性主要受控于与现今N-S挤压应力有关的微裂缝的择优排列，而在深部(>；∼6 km)，地震各向异性主要记录了长寿命法拉隆俯冲及其后期伸展过程中形成的未被现代转换运动完全重置的古面相。有趣的是，我们的模型显示了西横山脉下方与其相邻地块不同的快轴，可能反映了地块大规模的垂直轴顺时针旋转。此外，我们在Salton海槽下发现了具有明显各向异性特征的层状结构，这可能是当前应变的结果。
We present a high‐resolution P‐wave azimuthally anisotropic velocity model for the upper and middle crust beneath southern California by a novel adjoint‐state traveltime tomography technique. Our model reveals significant anisotropy variations between tectonic blocks that clearly reflect both past and current plate boundary deformation. In the shallow crust, seismic anisotropy is mostly controlled by the preferred alignment of microcracks related to the present N‐S compressive stress; while at deeper depths (>∼6 km), seismic anisotropy mainly records paleofabrics formed during the long‐lived Farallon subduction and later extension that have not been fully reset by the present transform motion. Interestingly, our model demonstrates distinct fast axes beneath the western Transverse Ranges from its neighboring blocks, probably reflecting the large‐scale vertical axis clockwise rotation of the block. In addition, we identify layered structures with distinct anisotropy features beneath the Salton Trough, which could be a result of the current transtension.