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大陆与大陆碰撞带，阿拉伯板块向东北偏北方向移动进入欧亚板块。一座高扎格罗斯山脉由此而建。在其阿拉伯板块一侧，扎格罗斯褶皱逆冲带显示出占据大部分缩短部分的厚沉积盖层的强烈变形。大陆碰撞模型的端元有薄皮情况（无基底参与；例如美国西部的塞维尔造山运动）和厚皮情况（有基底参与；例如美国西部的拉拉米德造山运动）。扎格罗斯褶皱逆冲带可以说是当今地球上年轻大陆碰撞带的最佳例子，我们试图确定扎格罗斯在碰撞模型范围内的位置，以及扎格罗斯的不同部分是否可能在变形过程中发生变形。不同的风格。许多争论取决于沉积物-基底界面相对于地震活动深度的深度。扎格罗斯地区是此类研究的绝佳实验室，因为该地区仪器设备相对完善，并且经常发生中等强度的地震。我们将应用先进的重定位方法来准确确定地震深度，并应用高频接收函数分析来绘制震源区的沉积物-基底界面。我们还将在 S-P 延迟时间空间中使用成像，以避免由于对地壳速度结构的不完全了解而导致估计深度的偏差。在构造活跃的地球上，板块之间相对运动，有些板块碰撞了数千万年。海洋板块的密度足以在这种碰撞过程中沉入地幔中。它们形成了一个狭窄、界限明确的俯冲带，例如最近在日本、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，一个大陆板块不会简单地沉入另一个板块下方；而是会发生碰撞。两侧的浮力地壳碰撞并堆积起来，形成山脉、高原，并引起大范围的地震。喜马拉雅山是长期大陆碰撞的一个例子，这场碰撞吞噬了印度大陆的大部分地区，并使欧亚地壳变形了距板块边界数千公里的范围。伊朗的扎格罗斯是早期大陆碰撞，阿拉伯半岛向东北移动进入亚洲，并在此过程中经历缩短、加厚和折叠。我们项目的目的是确定地壳的哪些层正在吸收变形；研究结果将帮助科学家了解大陆碰撞从开始到晚期（例如以喜马拉雅山为代表）之间是如何发展的。该项目也与地震灾害研究有直接关系。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，并促进该地区30多年来一直缺乏的科学合作。该项目包括美国和伊朗合作者之间的访问以及由美国 PI 为伊朗学生开设的地震学短期课程。