近日，美国密苏里科技大学Fatima Reyes团队提出了1976年危地马拉莫塔瓜7.5 Mw地震的方向性古地震证据。2025年9月10日出版的《地质学》杂志发表了这项成果。

1976年2月4日，沿危地马拉莫塔瓜断层发生的7.5级地震使北美和加勒比板块边界断裂约230公里。今天，对板块边界的监测仍然很差，1976年的地震仍然没有完全了解。

研究组分析了莫塔瓜断裂带周围六个湖泊的地震反射剖面和放射性定年沉积物岩心数据，以及破坏报告和准动态破裂模型，表明1976年地震经历了强烈的指向性，影响了震动的分布。地震在六个研究湖泊中的五个留下了事件沉积物（EDs）的详细记录。在靠近地震破裂终点的Atitlán湖中存在较厚的能谱，而在离破裂方向轴的湖泊中发现较薄的能谱。研究组认为能谱可以用来约束地震时震动的不对称分布，古地震研究应考虑指向性作为控制能谱厚度的一个因素。

附：英文原文

Title: Paleoseismic evidence of directivity for the 1976 Mw 7.5 Motagua earthquake, Guatemala

Author: Jonathan Obrist-Farner, Jeremy Maurer, Derek Gibson, Trenton McEnaney, Andreas Eckert, William F. Kenney, Jeffery Beeson, Nigel Wattrus, Quin Stangeland, Fatima Reyes

Issue&Volume: 2025-09-10

Abstract: On 4 February 1976, a Mw 7.5 earthquake along the Motagua fault, Guatemala, ruptured ～230 km of the North American and Caribbean plate boundary. Today, the plate boundary remains poorly monitored, and the 1976 earthquake is still not fully understood. Here, we present seismic reflection profiles and radiometrically dated sediment core data from six lakes around the Motagua fault, together with reports of destruction and a quasi-dynamic rupture model, which show that the 1976 earthquake experienced strong directivity that impacted the distribution of shaking. The earthquake left behind a detailed record of event deposits (EDs) in five of the six study lakes. Thicker EDs are present in Lake Atitlán, near the terminus of the earthquake rupture, whereas thinner EDs were found in lakes off-axis of the rupture direction. We argue that EDs can be utilized to constrain asymmetrical distribution of shaking during earthquakes and that paleoseismic studies should consider directivity as a factor controlling the thickness of EDs.

DOI: 10.1130/G53449.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G53449.1/661137/Paleoseismic-evidence-of-directivity-for-the-1976