Investigating Flat Slab Subduction and Plate Edge Tectonics in Northern South America

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The northern South American countries of Colombia and Venezuela have high seismic hazard. These countries are subject to frequent large earthquakes along strike-slip fault systems and subduction zones with the same combined seismic hazard potential as California's San Andreas system, and Oregon, Washington, and Alaska's subduction zones. Recent space geodesy measurements suggest that northwestern South America is overdue for a great (M8) earthquake along the flat Caribbean subduction zone under northern Colombia and the Lake Maracaibo region. Although both countries have modern earthquake monitoring and seismic hazard assessment agencies, Fundación Venezolana de Investigaciones Sismológicas (FUNVISIS) and Servico Geológico Colombiano (SGC), seismic hazard in both nations is exacerbated by poor, unregulated construction practices and a growing population of urban poor. The two nations have a combined population of ~80 million, and rapidly growing urban populations. Both the Venezuelan and Colombian civil and petroleum infrastructures are at risk from large seismic events. For a variety of reasons, including proximity, both Venezuela and Colombia are of strategic significance to the U.S. [Miami and New Orleans are closer to Bogota and Caracas than they are to Seattle, for instance]. Venezuela is of international importance, with hydrocarbon reserves that exceed Saudi Arabia's and extensive hydrocarbon production facilities. Venezuela currently supplies the U.S. with ~ 8% of its oil imports, only slightly less than imports from Saudi Arabia. The U.S. is Venezuela's most important trading partner. Scientific exchange between the U.S. and Venezuela and Colombia is important for developing scientific capacity in these nations, and for training their earth science workforces. Over the course of its history, the Rice Earth Science department has continuously enrolled M.Sc. and Ph.D. students from Venezuela and Colombia. Roughly 10% of modern subduction zones exhibit flat slab segments, including 3-4 along western South American (SA). Geologic history suggests ~70% of the western SA margin experienced flat subduction in the Cenozoic. Slab flattening is attributed to slab buoyancy, mantle wedge properties, and mantle flow dynamics. Flat subduction causes deformation in the overriding plate substantially different than that caused by normal subduction, as seen in seismicity, type and distribution of magmatism, and in some cases, basement cored uplifts. It is now recognized that the Caribbean subducts at low angles under northwestern SA, forming the basement cored uplifts of the Santa Marta, Perija, and Merida Andes ranges. These may be modern analogs to the late Mesozoic-early Cenozoic Laramide basement uplifts of the western United States. With FUNVISIS and SGC, the investigator team will install a large broadband seismograph array to image the subduction zone geometry and measure plate coupling rheology of the northern SA flat slab, with a goal of understanding the geodynamic development of basement uplifts. The local and regional earthquakes recorded by their seismograph array will be used for seismic hazard assessment in northern South America.