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

安第斯山脉是大洋-大陆碰撞的典型例子。纳斯卡板块俯冲到南美大陆之下，形成了沿海的高山和中安第斯山脉的大高原。在厄瓜多尔，雄伟的安第斯弧线分成两个火山链，定义了安第斯河谷的东部和西部边缘，这是一个南北走向的、低海拔的长长地形。厄瓜多尔首都基多位于这两个链条之间的Interandes山谷中。厄瓜多尔的150万居民生活在地球上一些较为活跃的地质过程和灾害之中，包括活跃的复杂断裂作用、火山爆发以及由该地区高海拔驱动的快速和极端的侵蚀和沉积。厄瓜多尔的安第斯河谷是研究斜向汇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，该地区的构造极其活跃，因此很容易观察和量化变形。一个主要的断裂系统，德洛雷-瓜亚基尔巨型断裂系统，一个海侵的右行走滑系统，在瓜亚基尔向岸上移动，进入安第斯河谷。德洛雷-瓜亚基尔巨型地震在规模和地震活动上与加利福尼亚州的圣安德烈亚斯断层系统相似。与圣安德烈亚斯一样，德洛雷-瓜亚基尔巨型断层也是一个复合断层系统，由多条单独的断层线组成。虽然利用错位地貌特征、凹陷池塘和断层陡坎识别了断层系统的一部分，但尚未在地表系统地绘制断层系统图。在许多地方，断层的位置被活动的侵蚀和沉积过程所掩盖。断层或相关形变在地下的任何地方都没有被成像。我们正在进行一个试点项目，以便在安第斯河谷的三个战略位置获得高分辨率的地震反射剖面，以确定德洛雷-瓜亚基尔巨型山脉内的地下断层/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压力环境下应变分配的理解，并立即与评估厄瓜多尔基多的地震危险性有关。这个项目是利哈伊大学和厄瓜多尔基多国家世俗理工学院的Geofisico研究所共同努力的成果。

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.