Crustal earthquakes in the Cook Inlet and Susitna region of southern Alaska
Crustal earthquakes in the Cook Inlet and Susitna region of southern Alaska
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DOI：
10.1016/j.tecto.2018.08.013
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发表时间：
2018-10
期刊：
影响因子：
2.9
通讯作者：
V. Silwal;C. Tape;A. Lomax
中科院分区：
文献类型：
--
作者：
V. Silwal;C. Tape;A. Lomax
在过去的一个世纪里，阿拉斯加安克雷奇附近发生了几次6级(M≥)大地震。俯冲太平洋板块的存在使得很难确定这些古老地震的起源是地壳、板块或俯冲板块界面。我们对安克雷奇以西的库克湾和苏西特纳地区的历史和现代地震进行了地震学研究。我们首先估计历史上大地震的震源，以评估它们作为地壳、板块或板块界面的起源的可能性。然后，我们研究现代地壳地震活动，以更好地了解断裂的类型和活动构造的位置，包括库克湾和苏西特纳盆地内(和之下)。我们使用高频体波(1-10 Hz)对2007年至2017年发生的中小(M≥2.5)地壳地震(深度≤30 公里)执行双偶矩张量反演。我们的失配函数结合了两个波形的差异以及第一运动的极性，以获得可靠的矩张量解。这三个震源区--白鲸、上库克湾和苏西特纳--表现出地壳地震的主要逆冲机制，表明地壳内部总体上处于与板块会聚方向大致一致的挤压状态。库克湾上游的机制使走向方向与库克湾以前从活动震源地震数据中识别的活动背斜一致。我们的矩张量目录有助于从地震线形结构和从活动震源地震数据的地下图像推断的断层中识别和描述地下断层。
Several large (M≥ 6) earthquakes have occurred in the vicinity of Anchorage, Alaska, within the past century. The presence of the underlying subducting Pacific plate makes it difficult to determine the origin of these older earthquakes as either crustal, slab, or the subduction plate interface. We perform a seismological study of historical and modern earthquakes within the Cook Inlet and Susitna region, west of Anchorage. We first estimate hypocenters for historical large earthquakes in order to assess their likelihood of origin as crustal, slab, or plate interface. We then examine modern crustal seismicity to better understand the style of faulting and the location of active structures, including within (and beneath) the Cook Inlet and Susitna basins. We perform double-couple moment tensor inversions using high frequency body waves (1–10 Hz) for small to moderate (M≥ 2.5) crustal earthquakes (depth ≤ 30 km) occurring from 2007 to 2017. Our misfit function combines both waveforms differences as well as first-motion polarities in order to obtain reliable moment tensor solutions. The three focus regions—Beluga, upper Cook Inlet, and Susitna—exhibit predominantly thrust mechanisms for crustal earthquakes, indicating an overall compressive regime within the crust that is approximately consistent with the direction of plate convergence. Mechanisms within upper Cook Inlet have strike directions aligned with active anticlines previously identified in Cook Inlet from active-source seismic data. Our catalog of moment tensors is helpful for identifying and characterizing subsurface faults from seismic lineaments and from faults inferred from subsurface images from active-source seismic data.