Strain Partitioning and Active Faulting During Oblique Convergence, Northern Andes, Ecuador

安第斯山脉是海洋与大陆碰撞的典型例子。纳斯卡板块俯冲到南美大陆之下，形成了沿海岸的高山和安第斯山脉中部的大高原。在厄瓜多尔，壮观的安第斯弧分为两个火山链，定义了安第斯山谷的东部和西部边缘，这是一条长而北向南的高海拔低地形。厄瓜多尔首都基多坐落在两条山脉之间的Interandean山谷中。它的150万居民生活在地球上一些更活跃的地质过程和危险之中，包括活跃的、复杂的断层、爆炸性的火山活动，以及由该地区高海拔造成的快速和极端的侵蚀和沉积。厄瓜多尔的Interandean Valley是研究斜辐合过程中应变分配和断层动力学的绝佳地点。地质图很好，该地区构造活动非常活跃，便于观测和量化变形。一个主要的断层系统，德洛雷斯-瓜亚基尔大断层，是一个逆滑的右走滑系统，在瓜亚基尔向陆上延伸，进入安第斯山谷。德洛雷斯-瓜亚基尔大断层在规模和地震活动上与加州的圣安德烈亚斯断层系统相似。和圣安德烈亚斯一样，德洛雷斯-瓜亚基尔大断层也是一个复合断层系统，由许多独立的断层链组成。虽然断层系统的部分已经通过偏移地貌特征、凹陷池和断层陡坡被识别出来，但断层系统还没有在地表被系统地绘制出来。在许多地方，断层的位置被活跃的侵蚀和沉积作用所掩盖。没有任何地方在地下对断层或相关变形进行成像。目前还没有一个连贯的框架来将众多的断层和断层控制构造的发展整合到一个运动学模型中。我们正在进行一个试点项目，在安第斯山谷间的三个战略位置获取高分辨率地震反射剖面，以确定Delores-Guayaquil Megashear的地下断层/褶皱几何形状和变形历史。这项研究的结果将提高我们对跨震环境下应变分配的理解，并与评估厄瓜多尔基多的地震危险性直接相关。该项目是里海伊大学和厄瓜多尔基多国家世俗理工学院地理研究所的合作成果。

The Andes are the type example of ocean-continent collision. The Nazca plate subducts beneath the South American continent, giving rise to the high mountains along the coast and the great plateaus of the Central Andes. In Ecuador, the imposing Andean arc divides into two volcanic chains that define the eastern and western margins of the Inter Andean Valley, a long, north south oriented topographic low at high elevation. Quito, Ecuador's capital city, sits within the Interandean valley between the two chains. Its 1.5 million citizens live amidst some of the Earth's more active geologic processes and hazards, including active, complex faulting, explosive volcanism, and rapid and extreme erosion and sedimentation driven by the high elevations in the area.The Interandean Valley of Ecuador is an excellent place to study strain partitioning and fault dynamics during oblique convergence. The geology is well mapped and the region is extremely active tectonically making it easy to observe and quantify deformation. A major fault system, the Delores-Guayaquil Megashear, a transpressive dextral strike-slip system, trends onshore at Guayaquil and passes into the Inter Andean Valley. The Delores-Guayaquil Megashear is similar in scale and seismic activity to San Andreas Fault system in California. Like the San Andreas, the Delores-Guayaquil Megashear is a composite fault system, composed of a number of individual fault strands. While portions of the fault system have been identified using offset geomorphic features, sag ponds, and fault scarps, the fault system has not been systematically mapped at the surface. In many places the location of the fault is masked by active erosional and depositional processes. Nowhere has the fault or associated deformation been imaged in the subsurface. There is no coherent framework for integrating the numerous faults and the development of fault-controlled structures into a kinematic model.We are conducting a pilot project to acquire high-resolution seismic reflection profiles in three strategic locations in the Inter Andean Valley to determine subsurface fault/fold geometry and deformation history within the Delores-Guayaquil Megashear. The results of this study will improve our understanding of strain partitioning in transpressional settings and are immediately relevant to assessing the seismic hazards for Quito, Ecuador. This project is a collaborative effort between Lehigh University and the Instituto Geofisico at the National Secular Polytechnic National, Quito, Ecuador.