Collaborative Research: Forearc Extension in a Strongly Coupled Subduction System, Northern Chile

对智利北方弧前伸展结构的研究，为深入了解纳斯卡俯冲海洋板块与南美洲大陆板块之间的耦合性质提供了新的视角。这种耦合的性质不仅具有科学意义，而且具有巨大的实际意义，因为这个板块边界是地球上一些最大地震的原因。每隔100到150年，在不同的地区都会发生一次8级以上的地震。该地区最近一次进行研究是在130年前。虽然板块边界似乎强烈锁定之间的大地震和强烈的弹性压缩，在这段时间内，沿海科迪勒拉的地质，它覆盖的板间耦合区，显示只有功能与平行于板块收敛方向的水平延伸。这种延伸表现为北向正断层和一套壮观的张力断裂，由于独特的干燥环境，可以相当完整地绘制。伸展构造可能与大地震期间或之后的弹性回弹或粘弹性松弛、地震期间的震动、板块边界的俯冲侵蚀有关，或者可能与在离岸仅75公里处8公里深处向下延伸到海沟的过于陡峭的大陆坡有关。本项目通过结合野外工作和地质年代学建立正断层的运动学模型，得出伸展的大小、年龄和拆离深度，（2）研究张性断裂的起源、分布和伸展的大小;（3）差分干涉侧孔径雷达，记录前弧的垂直运动，可能包括早期的海岸悬崖崩塌和后退;（4）通过有限元模拟，研究了海岸陡坎和大陆坡地形对区域应力场的影响。

Work on the extensional structures of the forearc of northern Chile is providing new insight into the nature of coupling between the subducted Nazca oceanic plate and the overriding South American continental plate. The nature of this coupling is not only of scientific interest but of tremendous practical importance as this plate boundary is responsible for some of the greatest earthquakes on Earth. Every 100 to 150 years a magnitude 8+ earthquake occurs in various segments. The area in which the research is being carried out last had a major earthquake 130 years ago. Although the plate boundary appears to be strongly locked between great earthquakes and is strongly elastically compressed during that time, the geology of the Coastal Cordillera, which overlies the zone of interplate coupling, displays only features associated with horizontal extension parallel to the plate convergence direction. This extension is manifest both as north-striking normal faults and as a spectacular suite of tension fractures which, due to the uniquely dry environment can be mapped quite completely. The extensional structures may be related to elastic rebound or visco-elastic relaxation during or following great earthquakes, to shaking during earthquakes, to subduction erosion at the plate boundary, or perhaps to an overly steep continental slope going down to the oceanic trench at 8 km depth just 75 km offshore. This project is assessing the relative contributions of these factors by combining: (1) field work with geochronology to construct kinematic models of normal faults to yield magnitude and age of extension as well as depth to detachment; (2) study of the origin, distribution, and magnitude of extension represented by the tension fractures; (3) differential interferometric side aperture radar to document vertical motions in the forearc, including, potentially, incipient coastal escarpment collapse and retreat; and (4) finite element modeling to evaluate the role of the topography of the Coastal Escarpment and the continental slope on the regional stress field.