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Lessons from a Small Local Earthquake (Mw 3.2) That Produced the Highest Acceleration Ever Recorded in Mexico City
Seismological Research Letters ( IF 2.6 ) Pub Date : 2020-11-01 , DOI: 10.1785/0220200123
Shri Krishna Singh 1 , Luis Quintanar-Robles 1 , Danny Arroyo 2 , Victor Manuel Cruz-Atienza 1 , Victor Hugo Espíndola 1 , Delia I. Bello-Segura 1 , Mario Ordaz 3
Affiliation  

A reliable estimation of seismic hazard‐facing Mexico City from local earthquakes has suffered from poor seismic instrumentation, complex crustal structure, large and variable site amplification, and lack of knowledge of recurrence period of earthquakes on the mapped faults. Owing to recent improvement in local seismic networks, an earthquake swarm activity, which occurred in June–August 2019, was well recorded. The largest event of the sequence, an Mw 3.2 earthquake, caused panic in the city and produced peak ground acceleration (PGA) exceeding 0.3g at the closest station (MHVM) about 1 km away. An analysis of the event shows that it had normal‐faulting focal mechanism, consistent with northeast–southwest‐oriented mapped faults in the region. It was located at a depth of ∼1 km and had a low stress drop (⁠∼0.1 MPa⁠). We find that the high PGA for this low stress‐drop event resulted from high‐frequency amplification at MHVM (about factor of ∼6 around 13 Hz), likely due to topographic site effects, superimposed on a pervasive broadband amplification of seismic waves at hill‐zone sites in the Valley of Mexico (up to ∼10 in the frequency band of 0.2–10 Hz). Simulation of ground motion for a scenario Mw 5.0 earthquake, using an empirical Green’s function technique, reveals that such an event may give rise to significant seismic intensities in the lake‐bed zone of Mexico City. The results emphasize the need to re‐evaluate the seismic hazard to Mexico City from local crustal earthquakes in the Valley of Mexico.

中文翻译:

发生在墨西哥城的有史以来最高加速度的小地震(Mw 3.2)的教训

由于地震仪器差,地壳结构复杂,站点放大幅度较大且变化多端,以及对所绘断层的地震复发期缺乏了解,因此无法可靠地估计当地地震对墨西哥城的地震危险。由于最近当地地震网络的改善,记录了2019年6月至2019年8月发生的地震群活动。该序列中最大的事件是3.2级Mw地震,在该城市引起了恐慌,并在大约1公里外的最近站点(MHVM)产生了超过0.3g的峰值地面加速度(PGA)。对事件的分析表明,它具有正常的断裂震源机制,与该地区东北-西南方向的地图断裂一致。它位于约1 km的深度,应力降低(⁠〜0.1MPa⁠)。我们发现,这种低应力下降事件的高PGA是由于MHVM的高频放大(大约13 Hz处约6%的因子)造成的,可能是由于地形的现场效应所致,叠加在山丘地震波的普遍宽带放大上墨西哥谷的区域区域(在0.2-10 Hz的频带中最多约10个)。使用格林函数经验技术对Mw 5.0地震场景的地面运动进行仿真,结果表明,此类事件可能会在墨西哥城的湖床区引起明显的地震烈度。结果强调需要重新评估墨西哥谷当地地壳地震对墨西哥城的地震危害。叠加在墨西哥谷丘陵地带的地震波无处不在的宽带放大上(在0.2-10 Hz的频带中约10处)。使用格林函数经验技术对Mw 5.0地震场景的地面运动进行仿真,结果表明,此类事件可能会在墨西哥城的湖床区引起明显的地震烈度。结果强调需要重新评估墨西哥谷当地地壳地震对墨西哥城的地震危害。叠加在墨西哥谷丘陵地带的地震波无处不在的宽带放大上(在0.2-10 Hz的频带中约10处)。使用格林函数经验技术对Mw 5.0地震场景的地面运动进行仿真,结果表明,此类事件可能会在墨西哥城的湖床区引起明显的地震烈度。结果强调需要重新评估墨西哥谷当地地壳地震对墨西哥城的地震危害。揭示了这样的事件可能会引起墨西哥城湖床区的强烈地震烈度。结果强调需要重新评估墨西哥谷当地地壳地震对墨西哥城的地震危害。揭示了这样的事件可能会引起墨西哥城湖床区的强烈地震烈度。结果强调需要重新评估墨西哥谷当地地壳地震对墨西哥城的地震危害。
更新日期:2020-11-04
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