Is continental collision thick- or thin-skinned? Combining local seismicity with receiver functions in the Zagros Fold-and-Thrust Belt

大陆碰撞是厚脸皮还是薄脸皮？

• 批准号: 1246287
• 负责人: Vera Schulte-Pelkum
• 金额: $ 18.46万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1246287&HistoricalAwards=false
• 关键词: continental; collision; thick; thin; skinned

The Zagros region of Iran is an early-stage continent-continent collision zone, with the Arabian plate moving north-northeastwards into the Eurasian plate. A mountain range, the High Zagros, has been built as a result; on its Arabian plate side, the Zagros Fold-and-Thrust belt shows strong deformation of the thick sedimentary cover that takes up much of the shortening. Models of continental collision have as end-members the thin-skinned case (no basement involvement; e.g., the Sevier orogeny in the Western U.S.) and the thick-skinned case (basement involvement; e.g., the Laramide orogeny in the Western U.S.). The Zagros Fold-and-Thrust Belt is arguably the best example of a young continental collision zone on Earth today, and we seek to determine where on the spectrum of collisional models the Zagros lies, and whether different parts of the Zagros may be deforming in different styles. Much of the debate hinges upon the depth of the sediment-basement interface relative to the depth of seismicity. The Zagros region is an excellent laboratory for such a study because it is relatively well instrumented and experiences frequent seismicity at moderate magnitudes. We will apply advanced relocation methods to accurately determine earthquake depths and high-frequency receiver function analysis to map the sediment-basement interface in the source regions of the earthquake. We will also use imaging in S-P delay time space to avoid biases in estimated depths due to incomplete knowledge of the velocity structure of the crust. On the tectonically active Earth, plates are in movement relative to each other, with some plates colliding for tens of millions of years. Oceanic plates are dense enough to sink into the mantle during such a collision; they form a narrow, well-defined subduction zone, such as the ones that gave rise to recent megaquakes in Japan, Chile, and Indonesia. Continental plates are more buoyant, and when two continental plates meet, one does not simply sink underneath the other; the buoyant crustal blocks on each side collide and stack up, building mountains, high plateaus, and causing a wide zone of earthquakes. The Himalaya is an example of a long-lived continental collision that has consumed much of the Indian continent and deformed the Eurasian crust for thousands of kilometers from its plate boundary. The Zagros in Iran is an early-stage continental collision, with Arabia moving northeastwards into Asia and experiencing shortening, thickening, and folding in the process. Our project's aim is to determine which layers of the crust are absorbing the deformation; the results will help scientists understand how continental collisions develop between their onset and a late stage such as represented by the Himalaya. The project has direct relevance to research in earthquake hazards as well. This project involves an international collaboration between two U.S. seismologists, an Iranian seismologist, and a French geologist. Consequently, this research is funded jointly by NSF-Geophysics and the Office of International Science and Engineering (OISE). The international collaboration allows us to apply newly developed analysis techniques to difficult-to-access seismic data and to promote scientific cooperation in a region where it has been lacking for over 30 years. The project includes visits between the U.S. and Iranian collaborators and a short course in seismology for Iranian students, taught by the U.S. PIs.

伊朗扎格罗斯地区是早期陆-陆碰撞带，阿拉伯板块向北东北方向移入欧亚板块。因此，形成了一个山脉，即扎格罗斯高地;在其阿拉伯板块一侧，扎格罗斯褶皱和冲断带显示出厚沉积盖层的强烈变形，这些变形占据了大部分缩短。大陆碰撞模型将薄皮情况作为端元（不涉及基底;例如，美国西部的塞维尔山脉）以及厚皮病例（基底受累;例如，美国西部的拉腊米山脉）。扎格罗斯褶皱冲断带可以说是当今地球上年轻大陆碰撞带的最好例子，我们试图确定扎格罗斯在碰撞模型谱中的位置，以及扎格罗斯的不同部分是否可能以不同的方式变形。大部分的争论取决于沉积物-基底界面的深度相对于地震活动的深度。扎格罗斯地区是进行这种研究的一个极好的实验室，因为它的仪器设备相对较好，经常发生中等震级的地震。我们将采用先进的重新定位方法准确确定地震深度，并采用高频接收函数分析绘制震源区沉积物-基底界面图。我们还将使用成像在S-P延迟时间空间，以避免偏差估计深度由于不完整的知识的速度结构的地壳。在构造活跃的地球上，板块彼此相对运动，一些板块碰撞了数千万年。海洋板块的密度足以在这样的碰撞过程中沉入地幔;它们形成了一个狭窄的、界限分明的俯冲带，比如最近在日本、智利和印度尼西亚引发大地震的俯冲带。大陆板块的浮力更大，当两个大陆板块相遇时，其中一个板块不会简单地沉入另一个板块之下;两侧有浮力的地壳块体相互碰撞并堆积起来，形成山脉、高原，并引起大范围的地震。喜马拉雅山是一个长期存在的大陆碰撞的例子，它消耗了印度大陆的大部分地区，并使欧亚大陆的地壳变形了数千公里。伊朗的扎格罗斯是一个早期的大陆碰撞，阿拉伯半岛向东北移动进入亚洲，并在此过程中经历缩短，增厚和折叠。我们的项目的目的是确定地壳的哪些层正在吸收变形;结果将帮助科学家了解大陆碰撞在其开始和后期阶段（如喜马拉雅山）之间是如何发展的。该项目也与地震灾害研究直接相关。该项目涉及两名美国地震学家、一名伊朗地震学家和一名法国地质学家之间的国际合作。因此，这项研究由NSF地球物理学和国际科学与工程办公室（OISE）联合资助。国际合作使我们能够将新开发的分析技术应用于难以获取的地震数据，并促进该区域30多年来一直缺乏科学合作。该项目包括美国和伊朗合作者之间的访问以及由美国PI教授的伊朗学生地震学短期课程。