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

地震是人类面临的最严重的自然灾害之一：在全球范围内，预计本世纪将有数百万人死亡，而在美国，有一半的人口面临破坏性地震的风险。然而，地震也为地球提供了宝贵的信息吗？S构造与构造。在这个项目中，我们将利用地震信息来了解伊朗扎格罗斯山脉的结构和构造。扎格罗斯夫妇是年轻大陆人的典型代表。碰撞区?这是由阿拉伯板块撞击欧亚大陆造成的，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物之下，因此无法用常规的野外测绘来识别产生地震的断层线。相反，我们将使用尖端的地震学技术来非常精确地定位过去半个世纪的地震活动，这样就可以突出隐藏在深处的断层的位置。扎格罗斯山脉可以作为现代版的落基山脉和阿巴拉契亚山脉的一部分，它们形成于几千万到几亿年前，现在不再有地震活动。因此，对扎格罗斯的进一步了解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，沉积盆地的厚度是如何缩短的。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、诱发地震的逆断层位置的不确定性，以及对它们在控制主导其地貌的“鲸背”背斜生长方面所起作用的相互矛盾的解释，它的现今运动学模糊不清。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基底逆断层上，这些断层在暴露的地层水平上造成了离散的台阶，覆盖岩层在远离主逆冲的情况下缩短，这是由沿弱盐层的拆离褶皱所适应的。另一种模型认为，地震断层在扎格罗斯地区广泛分布，通过断层弯曲和断层传播褶皱与个别背斜相关联。我们对这些相互冲突的模型提出了一个简单的测试，该测试将整合两种最先进的地震重新定位程序，以产生更好的震中，为整个约50年来在扎格罗斯地区记录的数千次远程地震事件提供回溯目录。第一步是根据定位良好的校准重新定位离散的地震群。震源独立于InSAR观测和模拟或临时的当地地震仪部署的事件。第二步使用第一步的结果作为贝叶斯重新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大型数据集，并且具有良好的特征不确定性和最小的位置偏差。震中的不确定性将从几十公里（常规星表估计）下降到不超过几公里。如果重新定位的震中聚集成与已知的地层台阶一致的地震活动性条纹，则证实了主要基底断层的存在和重要性，而如果地震大多远离所提出的基底断层，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.