Collaborative Research: Dynamics of the Southern Rocky Mountains from Cross-term Estimates of the Seismic Green Tensor

合作研究：根据地震绿色张量的跨期估计来了解落基山脉南部的动力学

• 批准号: 1142008
• 负责人: Vera Schulte-Pelkum
• 金额: $ 6.42万
• 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: 2012
• 资助国家: 美国
• 起止时间: 2012-03-15 至 2016-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1142008&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.

本项目围绕两个问题展开：1.是什么支撑着科罗拉多和新墨西哥州的落基山脉？地表海拔高是因为下面有特别厚的浮力地壳，还是地壳并不比周围地区厚，而是比下面的地幔更热，从而支撑了异常高的海拔？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，这样做的传统方法在地壳厚度方面留下了相当多的模糊性。我们建议通过调查问题2来解决这个问题：我们能否使用最近开发的已成功应用于浅层地球物理问题（如水文成像）的方法来找到更深的壳幔边界？我们将使用已经收集的地震数据集，并应用新的分析技术，以提供对构造神秘地区的动态约束。 南落基山脉地区记录了大陆组装、远离板块边界的造山和早期大陆裂谷的复杂历史。由于这一大片地区的隆升机制和时间仍在争论之中，该地区一直是主动和被动震源地震剖面和网络的深入研究对象。 这些研究中反复出现的一个主题是，高表面海拔并没有反映出厚的地壳根，但最近的地壳厚度估计仍然相差约10公里。 这一差异对解释该地区高地形的支持机制具有重要意义，特别是地表海拔是否在地壳内均衡平衡，或者高海拔的支持是否来自地球深处。 我们的项目是一个跨学科的合作，应用浅高频地震应用的团队开发的技术，岩石圈尺度地震学。具体来说，我们计划使用来自地震和环境地震噪声的衍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）。莫霍面衍射的探测迄今仅限于地震和爆炸源。我们的方法是执行站间互相关以前记录的爆炸和地震和海洋产生的环境地震噪声，以模拟信号源在每个站的位置。该技术将允许检测莫霍面衍射，从而在常规技术不适用的区域进行莫霍面测绘。