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

2010年2月智利马乌莱Mw8.8地震提供了一个很好的机会来描述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，皮奇莱穆记录到了最大的余震，震级分别为6.9和6.7级。由于它们是正断层，它们对上板块的同震伸展有贡献，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是弹性的（即，非永久性的），并使用GPS数据来确定大地震的破裂区域，使用弹性模型。然而，Pichilemu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，上板块如何以及为什么会变形以应对大地震;第二，上板块的不连续性是否控制了破裂带沿沿着会聚板块边界的位置。该项目将涉及实地工作，以记录智利马乌莱段弧前正断层的分布和寿命，以及对全球定位系统数据进行数值反演，并对弧前原有地质断层的应力变化进行库仑应力计算。将特别注意一套与马乌莱断裂北方界限重合的NW走向断层带。这些结构在智利俯冲带长期地震分段中的作用将通过对结构的力学分析来确定。太平洋火环周围的大地震，如2010年智利马乌莱和2011年日本东北地震的规模取决于断裂的板块边缘的长度。来自智利的越来越多的证据表明，相同或相似的节段反复断裂。如果知道这些破裂段的平均长度，就可以对任何一个破裂段预期发生的典型地震作出更好的预测;这些预测可以作为建筑规范和防灾准备的基础。该项目将利用2010年2月的马乌莱地震，这是有史以来第六大地震，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中如何反应。由于它们的深度相对较浅，这些弱点上的次生地震可能特别具有破坏性。2010年3月发生在马乌莱地震后的皮奇莱穆余震是与主震相关的最大余震。6.7级和6.9级的地震与海地地震一样大，扰乱了智利总统就职典礼。

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.