Collaborative Research: Stratigraphic, Geomorphic, and Paleoseismologic Record of Coseismic Fold Growth in Western Argentina

逆冲断层是世界范围内主要的地震灾害。对逆冲断层的地震危险性评估取决于对过去地震的时间、频率和大小的了解。逆冲断层地震常伴有浅层地下褶皱。褶皱是多次地震的累积产物。因此，了解在单个地震中褶皱生长的程度、频率和几何形状，对于确定褶皱生长与逆冲断层上的地震大小之间的关系至关重要。在阿根廷西部的两个地区，生长地层和地貌表面包含了有关褶皱的信息，代表了相关逆冲断层地震历史的两个储存库。对这两个地区的构造、地貌和古地震学研究揭示了同震和长期变形的详细记录，并为地震时间尺度上的褶皱地貌和地层特征提供了新的认识。目前正在根据1944年一次破坏性大地震的地表影响，开发一种在个别逆冲地震中产生地貌面或生长层的实地校准模型。此外，这些新数据直接有助于阿根廷国家地震危险性评估计划。门多萨（Mendoza）和圣胡安（San Juan）两市的人口加起来超过150万，位于地震活跃断层附近，对过去的地震活动和未来发生地震的可能性几乎没有限制。该研究为褶皱古地震识别提供了模板，为逆冲地震危险性识别提供了新方法。该项目得到地球科学局和国际科学与工程办公室的支持。

Thrust faults are a major seismic hazard worldwide. Seismic hazard assessment for thrust faults depends on understanding the timing, frequency, and size of past earthquakes. Thrust fault earthquakes are often accompanied by folding in the shallow subsurface. Folds are the cumulative product of repeated earthquakes. Thus, knowledge of how much, with what frequency, and with what geometry folds grow in individual earthquakes is essential for determining how fold growth relates to earthquake size on thrust faults. In two areas in western Argentina, growth strata and geomorphic surfaces contain information about folding and represent two repositories of the earthquake history of the associated thrust faults. Structural, geomorphic, and paleoseismologic study of the two areas is revealing a detailed record of coseismic and long-term deformation and providing new insight into the geomorphic and stratigraphic signature of folding on earthquake timescales. A field-calibrated model of the production of geomorphic surfaces or growth strata in an individual thrust earthquake is being developed based on the surface effects of a large and damaging earthquake in 1944. Moreover, the new data are contributing directly to the Argentinean national seismic hazard assessment program. The cities of Mendoza and San Juan have a combined population of more than 1.5 million people and are located near active earthquake faults with little constraints on their past activity or future potential for earthquakes. This study is providing a template for the recognition of paleoearthquakes from folds and a new method of thrust earthquake hazard recognition. This project is being supported by the Geosciences Directorate and the Office of International Science and Engineering.