ABSTRACT

The November 12, 2017, moment magnitude (M_w) 7.3 Sarpol-e Zahab earthquake, which occurred after a seismic quiescence, close to the Iran–Iraq border, is one of the largest events recorded in the Zagros fold and thrust belt. In this study, we analyzed strong-motion data of this event from 38 stations within an epicentral distance of 36 to 200 km. Spectral analysis of strong-motion data resulted in an M_w estimate of 7.34, an average rupture velocity of 3.03 km/s, and a stress drop of 154 bars. We estimated that shear dislocation propagated over a rectangular fault area with a length of ~97 km and width of ~17 km. Comparison of the horizontal peak ground-motions from this earthquake with the ground-motion model for active crustal regions indicated overall good agreement; however, the model underestimates ground-motions at stations within distances of approximately 30 km or less. The model appears to underestimate the observed strong-motion recordings from the M_w7.4 September 16, 1978, Tabas and the M_w7.4 June 20, 1990, Manjil earthquakes as well.

Investigation of the observed accelerograms showed that the Sarpol-e Zahab earthquake was nucleated by a sub-event with a local magnitude (M_L) of 4.9 which contributed about 0.02% to the total seismic moment. The empirical data indicated multiple arrivals due to the development of the rupture as two major sub-events. The spatial distribution of stations along with the time difference between the sub-events on the recorded time-series implies their occurrence from the hypocenter toward the S-SE direction which is coincident with the principal directions of the majority of damaged buildings. The estimated M_w of these sub-events is 6.79 and 7.08, respectively. The distinctive characteristics of near-field recordings from Sarpol-e Zahab earthquake (e.g., multiple phase arrivals due to complex source process, forward directivity effect, and blind thrust faulting) make these data a valuable supplement to the recorded ground-motion database. The improved strong-motion database plays a fundamental role in calibrating seismological simulation models, developing ground-motion models that capture near-source effects, and performing nonlinear dynamic structural analyses.

摘要

2017 年 11 月 12 日，矩震级 (M _w ) 7.3 Sarpol-e Zahab 地震发生在地震静止后，靠近伊朗-伊拉克边界，是扎格罗斯褶皱和逆冲带记录的最大事件之一。在这项研究中，我们分析了震中距离为 36 至 200 公里的 38 个台站的强震数据。强运动数据的光谱分析产生了一个 M _w估计为 7.34，平均破裂速度为 3.03 km/s，应力降为 154 bar。我们估计剪切位错在长约 97 公里、宽约 17 公里的矩形断层区传播。本次地震的水平峰值地震动与地壳活动区地震动模型的比较表明总体上吻合良好；然而，该模型低估了大约 30 公里或更短距离内的站点的地面运动。该模型似乎低估了观测到的1978 年 9 月 16 日塔巴斯 M w 7.4 和_{1990年 6 月 20 日 M w} 7.4 曼吉尔地震的强震记录。

对观测到的加速度图的研究表明，Sarpol-e Zahab 地震是由一个局部震级 (M _L ) 为 4.9 级的子事件成核的，它对总地震矩的贡献约为 0.02%。经验数据表明，由于破裂的发展，多次到达是两个主要的子事件。站点的空间分布以及记录的时间序列上子事件之间的时间差表明它们从震源向 S-SE 方向发生，这与大多数受损建筑物的主方向一致。估计的 M _w这些子事件分别是 6.79 和 7.08。Sarpol-e Zahab 地震近场记录的独特特征（例如，由于复杂的震源过程、前向性效应和盲推断层导致的多相到达）使这些数据成为记录的地面运动数据库的宝贵补充。改进后的强震数据库在校准地震模拟模型、开发捕捉近源效应的地震动模型以及执行非线性动力结构分析方面发挥着重要作用。