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

使用GPS和类似星座的连续空间大地测量观测可以估计地壳的相对运动，很容易精确到毫米/年以下的水平。我们现在有美国10-20年的GPS垂直地表运动记录，精度为1-2毫米/年。这些精确的垂直运动包含了地球深处变形的重要特征。例如，在太平洋西北部Juan de Fuca板块俯冲到北美下方的俯冲带边界附近记录的垂直运动表明，在深部存在相关的地幔对流过程以及与卡斯卡迪亚下方大逆冲地震旋回相关的板块界面粘滑行为过程。该项目将使用一系列数值模型和GPS数据来捕获地震周期和长期地幔时间尺度，并努力将两者分离开来。这些努力将有助于更好地了解地壳是如何变形的，板块边界是如何演变的，以及如何将来自卡斯卡迪亚的数据最好地整合到该地区基于物理的地震危险性估计中。该项目吸引了德州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，旨在增加攻读STEM学位的学生人数。美国西部现今地壳垂直运动的空间大地测量约束对于区分在不同时空尺度上工作的变形过程的相互竞争的假设至关重要。例如，有人提出，来自软流层的小尺度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。这项工作将使用数值模拟和反演来解开深层和浅层贡献。本研究将比较粘弹性旋回变形模型与粘塑性地幔流动预测，建立美国西部地幔黏性模型和地壳弹粘塑性变形与地幔黏性流动相结合的长期变形地球动力学模型。研究人员将探索地壳的永久变形和地幔的瞬态粘性流动，并与大地速度场进行比较，并通过运动学地震周期模型研究地震周期时间尺度上的变形，该模型考虑了由于过去地震和断层间耦合造成的地幔流动。他们将设计技术来整合地球动力学模型和运动学循环模型的结果，以获得垂直表面速度的一致估计。这些努力对了解美国的构造演化以及对太平洋西北地区的地震危险性评估具有重要意义。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.