Probable low-angle thrust earthquakes on the Juan de Fuca- North America plate boundary
Probable low-angle thrust earthquakes on the Juan de Fuca- North America plate boundary
复制标题
胡安德富卡-北美板块边界可能发生低角度逆冲地震
作者：
A. Tréhu;J. Braunmiller;J. Nábělek
2004年，卡斯卡迪亚前弧中部发生了两组地震，显示出板块耦合沿走向和下倾变化的若干特征。对每组主震的矩张量分析表明，这两个震级分别为4.9级和4.8级的事件与东倾6°-15°的断平面上的低角度逆冲运动相一致，与板块边界倾角约12°相一致。通过高分辨率二维地壳速度模型追踪射线以匹配二次到达时间（pP和PmP），我们估计M4.9事件的震源深度为9-11 km， M4.8事件的震源深度为15-17 km。我们的结论是，这些地震可能代表了卡斯卡迪亚大逆冲构造名义上的锁定或过渡部分的发震逆冲运动，该逆冲构造的上倾已经记录了间歇性震颤和滑动（ETS）。需要持续的高分辨率地震活动性观测和改进的地壳模型来确认ETS与这些集群中持续地震活动之间的明显时间相关性是否表明沿大逆冲构造的应力转移。
In 2004, two clusters of earthquakes occurred in the central part of the Cascadia forearc, which displays several characteristics indicative of along-strike and downdip variations in plate coupling. Moment tensor analysis for the main shock in each cluster indicates that both events, which had magnitudes of 4.9 and 4.8, were compatible with low-angle thrust motion on fault planes dipping 6°–15° to the east, consistent with the plate boundary dip of ∼12°. By tracing rays through a high-resolution two-dimensional crustal velocity model to match arrival times of secondary arrivals (pP and PmP), we estimate that the source depth was 9–11 km for the M4.9 event and 15–17 km for the M4.8 event. We conclude that these earthquakes probably represent seismogenic thrust motion on the nominally locked or transitional part of the Cascadia megathrust, updip of where episodic tremor and slip (ETS) have been documented. Continued high-resolution observations of seismicity and improved crustal models are needed to confirm whether apparent temporal correlations between ETS and continued seismic activity in these clusters indicate stress transfer along the megathrust.