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

利用全球定位系统和类似星座进行连续空间大地测量观测，可以估计地壳的相对运动，很容易达到毫米/年以下的水平。我们现在有长期的，10-20年的GPS记录垂直地面运动在美国的精度水平为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，胡安·德富卡板块在北美洲下面俯冲的俯冲带边界附近记录的垂直运动意味着，在深度上存在相关地幔对流过程的特征，以及在卡斯卡迪亚下面与巨型逆冲断层地震周期相关的板块界面处的粘滑行为过程。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，并致力于解开两者。这些努力将有助于更好地了解地壳变形和板块边界的一般演变，以及如何最好地整合卡斯卡迪亚的数据，以便对该地区的地震危险进行基于物理的估计。该项目吸引了UT奥斯汀杰克逊学校GeoFORCE项目的暑期学生，以及印第安纳州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不同时间和空间尺度上变形过程的竞争假设至关重要。例如，有人认为，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。这项拟议的工作将使用数值模拟和反演来解开深层和浅层的贡献。本研究将比较粘弹性循环变形模型和粘塑性地幔流动预测，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与地壳的弹粘塑性变形和地幔中的粘性流动。研究人员将探索地壳中的永久变形以及地幔中的瞬态粘性流动，并与大地速度场进行比较，还将通过运动学震间地震周期模型来检查地震周期时间尺度上的变形，该模型考虑了由于过去的地震和断层间耦合引起的地幔流动。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，以获得对垂直表面速度的一致估计。这些努力对理解美国的构造演化以及对太平洋西北地区地震危险性评估的影响都有意义。该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.