Regional tectonic and earthquake hazard implications of a crustal fault zone in southwestern Washington
Regional tectonic and earthquake hazard implications of a crustal fault zone in southwestern Washington
复制标题
华盛顿州西南部地壳断裂带的区域构造和地震灾害影响
DOI：
10.1029/jb088ib12p10371
复制
发表时间：
1983
影响因子：
--
通讯作者：
Stewart w. Smith
中科院分区：
文献类型：
--
作者：
C. Weaver;Stewart w. Smith
圣海伦斯地震带 (SHZ) 是华盛顿州西南部的一个地壳地震带，由中小震级（2.5 至 5.5 级）地震和震源机制定义。该带沿90公里的距离地震活跃，被解释为能够产生中到大震级浅源地震的断层带。自 1977 年以来，在该地震带的北端（考利茨河以北约 15 公里），大片区域的地震静止（3.0 级以上的地震）一直占主导地位。这种静止留下了一个问题：SHZ 是否会继续向北进入普吉特湾南部。沿 SHZ 的地震震源机制表明近乎垂直的走滑断层作用，优先断层面为南北走向。根据这些震源机制，我们推断最大压缩方向是东北方向，与北美板块和胡安德富卡板块之间的板块汇聚方向大致平行。我们将震源机制数据解释为锁定俯冲的证据。这种构造模型提出了发生大规模俯冲地震的可能性。华盛顿目前的地震危险评估中既没有发生中度到大型浅层地壳地震的可能性，也没有发生重大俯冲事件。
The St. Helens seismic zone (SHZ) is a crustal earthquake zone in southwestern Washington that is defined by small- to moderate-magnitude (2.5 to 5.5) earthquakes and focal mechanisms. This zone, seismically active along a distance of 90 km, is interpreted as a fault zone capable of generating a moderate- to large-magnitude shallow earthquake. At the northern end of this seismic zone (about 15 km north of the Cowlitz River) a large area of seismic quiescence (for earthquakes above magnitude 3.0) has predominated since 1977. This quiescence leaves open the question whether the SHZ continues northward into southern Puget Sound. Earthquake focal mechanisms along the SHZ indicating nearly vertical strike-slip faulting with the preferred fault planes striking north–south. From these focal mechanisms we infer that the direction of maximum compression is northeast, approximately parallel with the direction of plate convergence between the North American and Juan de Fuca plates. We interpret the focal mechanism data as evidence for locked subduction. This tectonic model raises the possibility of a large-magnitude subduction earthquake. Neither the possibility of a moderate to large shallow crustal earthquake nor a major subduction event is part of the current earthquake hazard assessment for Washington.