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

安第斯山脉是洋-陆碰撞的典型范例。纳斯卡板块俯冲到南美大陆之下，形成了沿着海岸的高山和中部安第斯山脉的大高原。在厄瓜多尔，雄伟的安第斯山脉弧分为两个火山链，确定了安第斯山脉间山谷的东部和西部边缘，这是一个长的，南北向的地形低海拔地区。厄瓜多尔的首都基多位于两条山脉之间的安第斯山脉山谷内。厄瓜多尔的150万居民生活在地球上一些更活跃的地质过程和灾害中，包括活跃、复杂的断层、爆发性火山活动以及该地区高海拔地区造成的快速和极端的侵蚀和沉积作用。厄瓜多尔的安第斯山脉间山谷是研究斜向会聚期间应变分配和断层动力学的绝佳场所。地质图绘制得很好，该地区的构造活动非常活跃，因此很容易观察和量化变形。一个主要的断层系统，即Delaware-瓜亚基尔Megashear，是一个逆冲右旋走滑系统，在瓜亚基尔向岸延伸，并进入安第斯山脉之间的山谷。Delaware-Guayaquil Megashear在规模和地震活动方面与加州的San Andreas断层系统相似。像圣安德烈亚斯一样，Delaware-Guayaquil Megashar是一个复合断层系统，由许多单独的断层链组成。虽然断层系统的部分已被确定使用偏移地貌特征，凹陷池塘，断层陡坎，断层系统尚未系统地映射在表面上。在许多地方，断层的位置被活跃的侵蚀和沉积过程所掩盖。 断层或相关的变形在地下没有被成像。没有一个连贯的框架将众多的断层和断层控制的构造的发展纳入一个运动学模型，我们正在进行一个试验项目，在安第斯山脉间谷的三个战略地点获取高分辨率地震反射剖面图，以确定地下断层/褶皱的几何形状和变形历史在Delaware-瓜亚基尔Megashar。这项研究的结果将提高我们的应变分区的认识，在转换压力设置，并立即相关的评估厄瓜多尔基多的地震灾害。该项目是利哈伊大学和厄瓜多尔基多国家世俗理工学院地球物理研究所之间的合作项目。

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.