Permanent Upper Plate Deformation Associated with the Mw8.8 Maule, Chile Earthquake of 2010

2010年2月的智利Maule Mw8.8地震提供了一个极好的机会来表征同震反弹期间发生的上板块前弧变形。在主震发生近两周后，在Pichilemu发生了最大的余震，震级为6.9级和6.7级。由于它们是正断层，它们有助于上板块的同震伸展，并且与同震GPS数据非常一致。然而，大多数地震学家认为同震反弹具有弹性（即非永久性），并使用GPS数据利用弹性模型确定大地震的破裂区域。然而，皮奇勒穆正断层余震代表了智利前弧的永久变形。这个研究项目将解决两个问题：第一，上板块是如何以及为什么在大地震中变形的；第二，上板块的不连续是否控制着沿板块边界汇聚的破裂带的位置。该项目将包括实地工作，记录智利前弧上覆盖Maule段的正断层的分布和寿命，并对GPS数据进行数值反演，并对前弧中已有地质断层的应力变化进行库仑应力计算。特别要注意的是一套北西走向的断裂带，这些断裂带与Maule断裂的北部边界重合。这些构造在智利俯冲带的长期地震分割中的作用将通过构造的力学分析来确定。大地震的大小，比如2010年智利Maule地震和2011年日本东北地震，都发生在环太平洋火山带附近，是由板块边缘断裂的长度决定的。来自智利的越来越多的证据表明，相同或相似的部分会反复断裂。如果知道这些断裂段的平均长度，就可以更好地预测任何一个断裂段的典型地震；这些预测可以作为建筑规范和灾害准备的基础。该项目将利用2010年2月的Maule地震（有历史记录的第六大地震）来调查南美洲西部地壳的物理弱点如何控制破裂段的长度，以及这些弱点在大地震期间如何反应。由于它们的深度相对较浅，在这些弱点上发生的二次地震可能特别具有破坏性。2010年3月的皮奇勒木地震余震是所有与主震相关的余震中最大的一次。震级分别为6.7级和6.9级，与海地地震相当，智利总统就职典礼也因此中断。

The Mw8.8 Maule, Chile earthquake of February 2010 presents an excellent opportunity to characterize the deformation of the upper plate forearc that occurs during coseismic rebound. The largest aftershocks were recorded at Pichilemu nearly two weeks after the main shock and had magnitudes of Mw6.9 and 6.7. Because they were normal faults, they contribute to coseismic extension of the upper plate and are very consistent with coseismic GPS data. However, most seismologists consider coseismic rebound to be elastic (i.e., non-permanent) and use GPS data to determine the rupture area of great earthquakes using elastic models. The Pichilemu normal fault aftershocks, however, represent permanent deformation of the Chilean forearc. This research project will address two questions: First, how and why does the upper plate deform in response to great earthquakes and, second, do upper plate discontinuities control the location of the rupture zones along convergent plate boundaries. The project will involve fieldwork to document the distribution and longevity of normal faults in the Chilean forearc overlying the Maule segment and numerical inversions of GPS data and Coulomb stress calculations of the stress changes on pre-existing geological faults in the forearc. Particular attention will be paid to a suite of NW striking fault zones that coincide with the northern limit of the Maule rupture. The role of these structures in long term seismic segmentation of the Chilean subduction zone will be determined through mechanical analysis of the structures.The size of great earthquakes, such as the 2010 Maule, Chile and the 2011 Tohoku, Japan events, around the Pacific Ring of Fire is determined by the length of the plate margin that ruptures. Increasing evidence from Chile suggests that the same or similar segments break repeatedly. If the average length of these rupture segments were known, better predictions of the typical earthquake to be expected in any one segment could be made; these predictions could then be used as the basis for building codes and disaster preparation. This project will use the February 2010 Maule earthquake, the sixth largest on historic record, to investigate how physical weaknesses in the crust of western South America may control the length of rupture segments as well as how those weaknesses respond during major earthquakes. Because of their relatively shallow depth, secondary earthquakes on those weaknesses can be particularly destructive. The March 2010 Pichilemu aftershocks to the Maule earthquake were the largest of any associated with the main shock. At 6.7 and 6.9 magnitudes, they were as large as the Haiti earthquake and they disrupted the Chilean presidential inauguration.