Collaborative Research: Vertical signatures of lithospheric deformation in the western US

合作研究：美国西部岩石圈变形的垂直特征

• 批准号: 2045291
• 负责人: Kaj Johnson
• 金额: $ 22.16万
• 依托单位: Indiana University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2045291&HistoricalAwards=false
• 关键词: Collaborative; Research; Vertical; signatures; lithospheric

Continuous space geodetic observations using GPS and similar constellations allow estimating relative motions of the Earth’s crust, easily down to sub-mm/yr levels. We now have long, 10-20 year GPS records of vertical ground surface motions in the United States with precision levels of 1-2 mm/yr. These precise vertical motions contain important signatures of deformation deep in the Earth. For example, recorded vertical motions close to the subduction zone boundary in the Pacific North-West where the Juan de Fuca plate subducts underneath North America imply that there is a signature of the associated mantle convection processes at depth as well as the process of stick-slip behavior at the plate interface associated with the megathrust earthquake cycle underneath Cascadia. This project will use a range of numerical models and GPS data to capture both the seismic cycle and long-term mantle timescales and work toward disentangling the two. These efforts will help to better understand how the crust deforms and plate boundaries evolve in general, and how the data from Cascadia can be best integrated for a physics-based estimate of seismic hazard in the region. The project engages summer students of UT Austin Jackson School's GeoFORCE program, and with Indiana University’s College of Arts and Sciences Undergraduate Research Experience, which are designed to increase the number of students pursuing STEM degrees. Space geodetic constraints on present-day vertical motions of the crust within the western US are critical for discriminating between competing hypotheses of deformation processes working at various temporal and spatial scales. It has been suggested that small-scale convection signals from the asthenosphere may mask some of the expected signatures of the visco-elastic seismic cycle in Cascadia, for example. This proposed work will use numerical modeling and inversions to disentangle deep-seated and shallow contributions. This research will compare visco-elastic cycle deformation models with visco-plastic mantle flow predictions, and build viscosity models of the mantle in the western US and geodynamic models of long-term deformation with elasto-visco-plastic deformation of the crust and viscous flow in the mantle. The researchers will explore both permanent deformation in the crust as well as transient viscous flow in the mantle and compare with the geodetic velocity field, and also examine deformation at the time scale of the earthquake cycle through kinematic interseismic earthquake cycle models which account for mantle flow due to past earthquakes and interseismic coupling across faults. They will design techniques to integrate results from geodynamic models and kinematic cycle models to obtain a consistent estimate of vertical surface velocities. Such efforts have implications for understanding the tectonic evolution of the United States as well as implications for seismic hazard assessment in the Pacific Northwest.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

使用 GPS 和类似星座进行连续空间大地测量可以轻松估计地壳的相对运动，精确到亚毫米/年的水平。我们现在拥有美国 10-20 年垂直地表运动的长期 GPS 记录。这些精确的垂直运动包含地球深处变形的重要特征，例如，胡安所在的太平洋西北部俯冲带边界附近记录的垂直运动。北美下方的德富卡板块俯冲意味着存在相关的深部地幔对流过程以及与卡斯卡迪亚下方的巨型逆冲地震周期相关的板块界面粘滑行为过程的特征。数值模型和 GPS 数据来捕获地震周期和长期地幔时间尺度，并努力解开两者的联系，这些努力将有助于更好地了解地壳变形和板块边界的总体演化，以及数据如何变化。来自卡斯卡迪亚的研究可以最好地整合到该地区基于物理的地震灾害估计中，该项目吸引了德克萨斯大学奥斯汀杰克逊学院 GeoFORCE 项目的暑期学生以及印第安纳大学艺术与科学学院的本科生研究经验，旨在增加学生的研究经验。攻读 STEM 学位的学生数量。目前美国西部地壳垂直运动的空间大地测量限制对于区分不同时间和空间尺度的变形过程的相互竞争的假设至关重要。例如，来自软流圈的小规模对流信号可能掩盖了卡斯卡迪亚粘弹性地震周期的一些预期特征，这项研究将使用数值模拟和反演来区分深层和浅层的贡献。将比较粘弹性循环变形模型与粘塑性地幔流预测，并建立美国西部地幔的粘度模型和长期变形的地球动力学模型研究人员将探索地壳的弹粘塑性变形和地幔的粘性流，并探索地壳的永久变形和地幔的瞬态粘性流，并与大地速度场进行比较，并检查当时的变形。他们将设计技术来整合地球动力学模型的结果，该模型考虑了过去地震引起的地幔流动和跨断层的震间耦合。和运动循环模型来对垂直表面速度进行一致的估计，这些努力对于了解美国的构造演化以及太平洋西北地区的地震灾害评估具有重要意义。该奖项反映了 NSF 的法定使命，并被认为是值得的。通过使用基金会的智力优势和更广泛的影响审查标准进行评估来获得支持。