Exploring the shallow structure of the San Ramón thrust fault in Santiago, Chile (~33.5° S), using active seismic and electric methods
Exploring the shallow structure of the San Ramón thrust fault in Santiago, Chile (~33.5° S), using active seismic and electric methods
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使用主动地震和电法探索智利圣地亚哥（~33.5°S）圣拉蒙逆冲断层的浅层结构
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
S. Rebolledo
中科院分区：
文献类型：
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作者：
D. Díaz;A. Maksymowicz;G. Vargas;E. Vera;E. Contreras‐Reyes;S. Rebolledo
抽象的。位于智利中部主要安第斯科迪勒拉山脚下的地壳规模西向的圣拉蒙逆冲断裂系统是一种地质活动构造，在圣地亚哥市东缘的断裂带上表现为第四纪晚期复杂的地表破裂。通过地球物理和地质观测的对比，我们评估了影响跨越断层崖的沉积盖层和岩层地形的地下构造模式，这对于评估相关断层的构造模型和相关的地震危险性是至关重要的。我们使用24个检波器(Geode)阵列，每个剖面25次，进行了平均长度为250米的地震剖面，以产生高分辨率地震层析成像，以帮助解释与变形的沉积盖层相关的阻抗变化。利用二维层析方法对记录的走时折射和反射进行了联合反演，导致了速度和反射在陡峭轴上的变化，这些变化被解释为沉积盖层-岩石底面地形。从断层剖面观察到的地震各向异性与沿断层向西的逆冲构造触发的沉积物变形是一致的。利用跨越两个断层陡坎的电测深建立了地下电阻率层析成像剖面，揭示了上盘较低的电阻率值相对于地质构造下盘的系统差异，并清楚地显示了清晰的东倾电阻率边界。这些边界可以用圣拉蒙断裂的上盘和下盘之间的构造驱动的流体含量变化来解释。总体结果与山前沉积下向西倾~55°E的逆冲构造一致，局部复杂性可能与断裂面破裂传播、断层展布和断层段传递带的变化有关。
Abstract. The crustal-scale west-vergent San Ramon thrust fault system, which lies at the foot of the main Andean Cordillera in central Chile, is a geologically active structure with manifestations of late Quaternary complex surface rupture on fault segments along the eastern border of the city of Santiago. From the comparison of geophysical and geological observations, we assessed the subsurface structural pattern that affects the sedimentary cover and rock-substratum topography across fault scarps, which is critical for evaluating structural models and associated seismic hazard along the related faults. We performed seismic profiles with an average length of 250 m, using an array of 24 geophones (Geode), with 25 shots per profile, to produce high-resolution seismic tomography to aid in interpreting impedance changes associated with the deformed sedimentary cover. The recorded travel-time refractions and reflections were jointly inverted by using a 2-D tomographic approach, which resulted in variations across the scarp axis in both the velocities and the reflections that are interpreted as the sedimentary cover-rock substratum topography. Seismic anisotropy observed from tomographic profiles is consistent with sediment deformation triggered by west-vergent thrust tectonics along the fault. Electrical soundings crossing two fault scarps were used to construct subsurface resistivity tomographic profiles, which reveal systematic differences between lower resistivity values in the hanging wall with respect to the footwall of the geological structure, and clearly show well-defined east-dipping resistivity boundaries. These boundaries can be interpreted in terms of structurally driven fluid content change between the hanging wall and the footwall of the San Ramon fault. The overall results are consistent with a west-vergent thrust structure dipping ~55° E in the subsurface beneath the piedmont sediments, with local complexities likely associated with variations in fault surface rupture propagation, fault splays and fault segment transfer zones.