Subducting oceanic basement roughness impacts on upper-plate tectonic structure and a backstop splay fault zone activated in the southern Kodiak aftershock region of the Mw 9.2, 1964 megathrust rupture, Alaska
Subducting oceanic basement roughness impacts on upper-plate tectonic structure and a backstop splay fault zone activated in the southern Kodiak aftershock region of the Mw 9.2, 1964 megathrust rupture, Alaska
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DOI：
10.1130/ges02275.1
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发表时间：
2021-02
期刊：
影响因子：
2.5
通讯作者：
A. Krabbenhoeft;R. Huene;John J. Miller;D. Klaeschen
中科院分区：
文献类型：
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作者：
A. Krabbenhoeft;R. Huene;John J. Miller;D. Klaeschen
1964 年，阿拉斯加边缘在一场 9.2 级逆冲大地震中破裂，这是全球仪器记录以来的第二大地震。 1977 年至 1981 年对科迪亚克岛近海的同震滑动和余震区域进行了调查，以了解该地区的构造。我们使用当前标准基尔霍夫深度偏移和/或 MCS 走时断层扫描重新处理多道地震 (MCS) 现场数据。 1994 年的额外勘测增加了来自广角地震线和多波束测深的 P 波速度结构。已发布的区域重力、后向散射和地震汇编也已在此时推出。海沟下方，粗糙的洋壳被约 3-5 公里厚的沉积物覆盖。俯冲板块上的沉积物调节板块界面起伏。增生棱柱的叠瓦状逆冲断层具有复杂的纵波速度结构。向陆地方向，纵波速度的加速增加以逆止张开断层带（BSFZ）为标志，该断层带标志着从棱柱体到中坡和上坡下方刚性较高的岩石的过渡。与该特征相关的结构可以指示流体流动。继续上坡，另一个断层沿着中坡延伸超过 100 公里。海山俯冲的侵蚀在额棱柱上留下了海湾。板块界面粗糙度沿俯冲带变化。在下坡和中坡下方，2.5D 板块界面图像显示出适度的起伏，而海洋基底图像则较为粗糙。 1964 年地震滑移最大值与俯冲海山和 BSFZ 的前缘和/或向陆侧翼一致。 BSFZ 是一个潜在的活跃结构，应在海啸灾害评估中予以考虑。
In 1964, the Alaska margin ruptured in a giant Mw 9.2 megathrust earthquake, the second largest during worldwide instrumental recording. The coseismic slip and aftershock region offshore Kodiak Island was surveyed in 1977–1981 to understand the region’s tectonics. We re-processed multichannel seismic (MCS) field data using current standard Kirchhoff depth migration and/or MCS traveltime tomography. Additional surveys in 1994 added P-wave velocity structure from wide-angle seismic lines and multibeam bathymetry. Published regional gravity, backscatter, and earthquake compilations also became available at this time. Beneath the trench, rough oceanic crust is covered by ∼3–5-km-thick sediment. Sediment on the subducting plate modulates the plate interface relief. The imbricate thrust faults of the accreted prism have a complex P-wave velocity structure. Landward, an accelerated increase in P-wave velocities is marked by a backstop splay fault zone (BSFZ) that marks a transition from the prism to the higher rigidity rock beneath the middle and upper slope. Structures associated with this feature may indicate fluid flow. Farther upslope, another fault extends >100 km along strike across the middle slope. Erosion from subducting seamounts leaves embayments in the frontal prism. Plate interface roughness varies along the subduction zone. Beneath the lower and middle slope, 2.5D plate interface images show modest relief, whereas the oceanic basement image is rougher. The 1964 earthquake slip maximum coincides with the leading and/or landward flank of a subducting seamount and the BSFZ. The BSFZ is a potentially active structure and should be considered in tsunami hazard assessments.