Collaborative Research: Dynamics of the Southern Rocky Mountains from cross-term estimates of the seismic Green tensor

合作研究：根据地震格林张量的跨项估计得出南落基山脉的动力学

• 批准号: 1142154
• 负责人: Kasper van Wijk
• 金额: $ 20.39万
• 依托单位: Boise State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-03-15 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1142154&HistoricalAwards=false
• 关键词: Collaborative; Research; Dynamics; Southern; Rocky

This project centers on two questions: 1. What props up the Rocky Mountains of Colorado and New Mexico - is the surface elevation high because of extra-thick, buoyant crust underneath, or is the crust no thicker than in the surrounding areas and it is instead hotter than usual mantle sitting underneath that supports the unusually high elevations? To answer this question, we must map the crust-mantle boundary under the Rockies. Conventional methods to do this have so far left a fair amount of ambiguity regarding crustal thickness. We propose to solve this by investigating question 2: Can we use a recently developed method that has been successfully applied to shallow geophysical problems, such as hydrological imaging, to find the much deeper crust-mantle boundary?We will use already collected seismic data sets and apply new analysis techniques to provide constraints on the dynamics of a tectonically enigmatic area. The Southern Rocky Mountain region has recorded a complex history of continental assembly, mountain building far from plate boundaries, and incipient continental rifting. Because the mechanism and timing of uplift of this large area are still under debate, the region has been the subject of intensive study with active and passive source seismic profiles and networks. A recurrent theme from these studies is that the high surface elevations are not mirrored by a thick crustal root, however the most recent crustal thickness estimates still differ by ~10 km. This difference has significant implications for mechanisms to explain the support of high topography in the region, specifically whether the surface elevation is isostatically balanced within the crust or support for the high elevations has to come from deeper in the Earth. Our project is an interdisciplinary collaboration to apply techniques developed by the team for shallow high-frequency seismic applications to lithospheric scale seismology. Specifically, we plan to use diffracted seismic waves, from earthquakes and from ambient seismic noise, to image the Moho (the seismic velocity contrast that can be identified with the crust-mantle boundary). Detection of Moho diffractions is to date limited to earthquakes and explosion sources. Our approach is to perform interstation crosscorrelations of previously recorded explosions and earthquakes and of ocean-generated ambient seismic noise to simulate a signal source at each station location. This technique would allow detection of Moho diffractions and therefore Moho mapping in areas where conventional techniques are not applicable.

这个项目的核心是两个问题：1.是什么支撑了科罗拉多州和新墨西哥州的落基山脉--地表高度高是因为下面有超厚的浮力地壳，还是地壳并不比周围地区厚，相反，它比通常位于下面的地幔更热，从而支撑着异常高的海拔？为了回答这个问题，我们必须绘制落基山脉下的壳幔边界图。到目前为止，这样做的常规方法在地壳厚度方面留下了相当大的含糊不清。我们建议通过研究问题2来解决这个问题：我们能否使用最近成功应用于浅层地球物理问题(如水文成像)的方法来寻找更深层次的壳幔边界？我们将使用已经收集的地震数据集，并应用新的分析技术来提供对构造谜团区域动力学的约束。南落基山脉地区记录了一段复杂的大陆组装、远离板块边界的造山和早期大陆裂谷的历史。由于这一大面积地区的隆升机制和时间仍在争论中，该地区一直是主动和被动震源剖面和台网的深入研究对象。这些研究的一个反复出现的主题是，地表高海拔并不是由厚的地壳根部反映出来的，然而，最新的地壳厚度估计仍然相差约10公里。这种差异对解释该地区高地形的支撑机制具有重大意义，特别是表面高度在地壳内是均衡的还是对高海拔的支撑必须来自地球更深的地方。我们的项目是一个跨学科的合作，将团队开发的浅层高频地震应用技术应用于岩石圈规模的地震学。具体地说，我们计划使用来自地震和环境地震噪声的绕射地震波来成像莫霍面(可以与壳幔边界识别的地震速度对比)。到目前为止，莫霍面绕射的探测仅限于地震和爆炸源。我们的方法是对以前记录的爆炸和地震以及海洋产生的环境地震噪声进行台间交叉相关，以模拟每个台站位置的信号源。这项技术将允许在常规技术不适用的区域检测莫霍面绕射，从而检测莫霍面映射。