Unearthing earthquakes and their tsunamis using multiple proxies: the 22 June 1932 event and a probable fourteenth-century predecessor on the Pacific coast of Mexico

Tsunami deposits have been widely studied in temperate latitudes, but the intrinsic difficulties associated with tropical coastal environments, and the intensity of bioturbation in these habitats, limit the possibilities of analysing these formations. Here, we investigate the deposits on the Colima coast of Mexico, which overlies the subducting Rivera and Cocos Plates, in order to reconstruct the tsunami inundation history and related hazard. We developed a multi-proxy study aimed to recognize and date historical and palaeotsunami deposits, including historical data on the effects of a known tsunami, geomorphological mapping, stratigraphic, grain size, organic matter content, diatoms, geochemical composition, magnetic susceptibility, and anisotropy of magnetic susceptibility, together with radiometric dating (²¹⁰Pb and ¹⁴C). We identified two probable tsunami deposits at Palo Verde estuary including a historical event associated with the Mw 6.9 earthquake on 22 June 1932 and a palaeotsunami most likely generated by a similar event in the fourteenth century. This work shows that it is possible to identify both historical and palaeotsunamis in the tropical environment of Mexico’s Pacific coast. These data will serve to enhance our understanding of tsunami deposits in tropical environments and of the regional tsunami hazard.

温带纬度地区的海啸沉积已得到广泛研究，但热带海岸环境固有的研究难点，加之这类生境中生物扰动（bioturbation）作用强烈，极大限制了此类沉积构造的分析可行性。本研究聚焦墨西哥科利马海岸——该区域位于俯冲的里维拉板块与科科斯板块之上——的沉积层，旨在重建海啸淹没历史与相关灾害风险。本研究构建了一套多代用指标研究方案，用于识别并定年历史海啸与古海啸（palaeotsunami）沉积层，研究手段涵盖：已知海啸影响的历史记录、地貌填图、地层学分析、粒度分析、有机质含量测定、硅藻分析、地球化学成分分析、磁化率测试、磁化率各向异性分析，以及放射性定年（²¹⁰Pb和¹⁴C）。研究团队在帕洛维德河口识别出两处疑似海啸沉积层：其一为与1932年6月22日矩震级（Mw）6.9级地震相关的历史海啸事件沉积，其二为大概率由14世纪同类地震引发的古海啸沉积。本研究证实，在墨西哥太平洋沿岸的热带环境中，可同时识别历史海啸与古海啸沉积记录。本研究数据将有助于深化对热带环境下海啸沉积特征以及区域海啸灾害风险的认知。