Seismotectonics of the Zagros (Iran) From Orogen-wide Earthquake Relocations

地震是人类面临的最重大的自然灾害之一：在全球范围内，本世纪预计将有数百万人死亡，而在美国，一半的人口面临破坏性震动的风险。然而，地震也提供了关于地球-S构造和构造的有价值的信息。在这个项目中，我们将利用来自地震的信息来了解伊朗扎格罗斯山脉的结构和构造。扎格罗斯山脉是由阿拉伯板块撞击欧亚大陆而形成的年轻大陆碰撞带的典型例子，也是世界上地震最活跃的地区之一。然而，它的许多地震都埋在厚厚的沉积层下，所以用传统的野外测绘方法无法识别产生这些地震的断层线。相反，我们将使用尖端地震学技术非常准确地定位过去半个世纪的地震活动，从而突出埋藏在深处的断层的位置。扎格罗斯山脉可以被用作落基山脉和阿巴拉契亚山脉部分地区的现代类比，这些山脉形成于数千万年前，不再活跃于地震。因此，更好地了解扎格罗山脉将有助于我们了解美国部分地区的结构和构造历史。伊朗的扎格罗斯山脉是一个典型的例子，说明在大陆碰撞的早期阶段，厚重的沉积盆地是如何缩短的。然而，由于埋藏在8-16公里厚的沉积盖层内或之下的陡峭的孕震逆断层的位置不确定，以及对它们在控制主导其地貌的“鲸背”背斜生长方面的作用的相互矛盾的解释，它今天的运动学被掩盖了。扎格罗斯地区流行的地震构造模式是，地震集中在少数大型的基底反向断层上，这些断层在裸露的地层水平上构成离散的台阶，随着剥离沿弱盐层褶皱的剥离，盖层距离主冲断层的缩短。另一种模型认为，地震断层通过扎格罗山广泛分布，通过断层弯曲和断层传播褶皱与单个背斜相关。我们建议对这些相互冲突的模型进行简单的测试，将两个最先进的地震重新定位程序整合在一起，以产生整个约50年前Zagros地区数千次远程地震记录事件的改进震中。第一步是重新定位离散的地震群与位置良好的？校准？？震源独立于InSAR观测和建模或临时本地地震仪部署而知道的事件。第二步使用第一步的结果作为贝叶斯重定位算法的先验约束，该算法更适合于分布在更广泛区域的更大的数据集，并且具有很好的不确定性和最小的位置偏差。震中不确定性将从几十公里(常规目录估计)下降到不超过几公里。如果重新定位的震中聚集成与地层水平上的已知台阶一致的地震活动条带，将证实主要基底断裂的存在和重要性，而如果地震大多位于拟议的基底断裂之外，则支持相反的模型。

Earthquakes are amongst the most significant natural hazards faced by mankind: globally, millions of fatalities are forecast this century, while in the United States half of the population is at risk from damaging shaking. However, earthquakes also provide valuable information on Earth?s structure and tectonics. In this project, we will be using information from earthquakes to learn about the structure and tectonics of the Zagros mountains in Iran. The Zagros are a classic example of a young continental ?collision zone?, caused by the Arabian plate crashing into Eurasia, and are also amongst the most seismically-active regions anywhere in the world. However, its many earthquakes are buried under a thick blanket of sediments and so the fault-lines that generate them cannot be identified using conventional field mapping. Instead, we will use cutting-edge seismological techniques to locate very precisely the past half century of earthquake activity, in doing so highlighting the locations of buried faulting at depth. The Zagros can be used as a modern analog to parts of the Rocky Mountains and Appalachians which formed tens to hundreds of millions of years ago and which are no longer seismically active. An improved understanding of the Zagros will therefore help us understand the structure and tectonic history of parts of the United States. The Zagros range in Iran is a type example of how thick sedimentary basins are shortened during the early stages of continental collision. However, its present-day kinematics are obscured by uncertainties in the locations of steep, seismogenic reverse faults buried within or beneath the 8-16 km-thick sedimentary cover, and by conflicting interpretations of their role in controlling the growth of "whaleback" anticlines which dominate its physiography. The prevalent seismotectonic model for the Zagros has earthquakes concentrated along a small number of large, basement reverse faults which account for discrete steps in the exposed stratigraphic level, with shortening of cover rocks away from the master thrusts accommodated by detachment folding along weak salt layers. An alternative model holds that earthquake faulting is widely-distributed through the Zagros, correlating with individual anticlines through fault bend and fault propagation folding. We propose a simple test of these conflicting models that will integrate two state-of-the-art earthquake relocation procedures to yield improved epicenters for the entire, ~50 year back-catalog of several thousand teleseismically-recorded events in the Zagros. The first step repositions discrete clusters of earthquakes with respect to well-located ?calibration? events whose hypocenters are known independently from InSAR observations and modeling or from temporary local seismometer deployments. The second step uses results from the first as prior constraints in a Bayesian relocation algorithm that is better suited to larger data sets spread over wider regions, and which has well-characterized uncertainties and minimal location bias. Epicentral uncertainties will drop from a few tens of kilometers (for routine catalog estimates) to no more than a few kilometers. The existence and importance of major basement faults will be confirmed if the relocated epicenters aggregate into streaks of seismicity aligned with the known steps in stratigraphic level, whereas the opposing model will be supported if earthquakes mostly lie away from the proposed basement faults.