Collaborative Research: Comparing Deformation Rates in Wrench Borderlands from Geodetic and Geologic Data to Evaluate the Permanent and Recoverable Components

合作研究：根据大地测量和地质数据比较扳手边界的变形率，以评估永久和可恢复的组成部分

• 批准号: 0208416
• 负责人: Bernard Housen
• 金额: $ 8.55万
• 依托单位: Western Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-07-01 至 2007-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0208416&HistoricalAwards=false
• 关键词: Collaborative; Research; Comparing; Deformation; Rates

The current velocity field associated with plate tectonic motion in western California is well characterized by geodetic measurements using Global Positioning Systems (GPS). The exact nature of what geodetic measurements record in actively deforming zones remains a significant problem, as this technique records both recoverable (elastic) and permanent (quasi-plastic) strains in wrench borderlands (blocks adjacent to major strike-slip faults). The goal of this proposal is to evaluate the relative magnitudes of the recoverable and permanent components in the deformation of wrench borderlands, by simultaneously studying two different sections of the San Andreas fault system. Creeping segment, central California: Geodetic measurements alone are generally unable to distinguish between recoverable and permanent deformation, because of the long (50 yr) interval between slip episodes on faults. In contrast, intervals between slip episodes are short (weeks to months) in the creeping central section of the San Andreas fault. By collecting geodetic data throughout the short seismic cycle in the creeping segment, the PI's will be able to evaluate the relative sizes of the recoverable and permanent components of the displacement field in the vicinity of the fault. They propose to check the estimates of currently accumulating permanent measurements against long-term averages determined from geologic and paleogmagnetic data. Prior work suggests clockwise rotation of the paleomagnetic signal of Miocene and younger sediments in the wrench borderlands. Documenting the areal extent, regional distribution, and amount of rotation throughout this area will allow them to calculate a long-term average for permanent deformation. This part of the proposal involves permanent GPS stations and monitoring, campaign-style GPS, paleomagnetism, and geologic mapping. Durmid Hill, Salton Trough, southern California: In this area, previous work has determined the amount of permanent strain. The PI's propose to complete a step-wise, three-dimensional retro-deformation of deformed sedimentary rocks. In order to convert these incremental strain data into estimates of deformation rates, one must have precise knowledge of time of deformation. In this region of excellent exposure, one aspect of deformation timing is provided by the presence of an ash layer correlated with the 0.76 Ma Bishop tuff. Additional information will result from paleomagnetic techniques that record the magnetic field during deposition. Utilizing the variety of ages of the different sedimentary layers to provide differential vertical axis rotations, The PI's can determine the timing of minor structures (e.g., joints, fractures, and small folds) by determining which units are affected. By comparing geodetic rates (which include both recoverable and permanent strain components) with geologic rates (which record only a permanent strain component) they can assess the amount of recoverable strain accumulation in this area. This part of the proposal involves geologic mapping, paleomagnetism, and campaign-style GPS. By combining the results of geological, geodetic, and paleomagnetic investigations from our two field areas, the PI's will assess the relative contribution of recoverable (elastic) and permanent (quasi-plastic) strains in wrench borderlands. Resolution of this issue has fundamental implications for earthquake mechanics, geological implications of borderland deformation, and potential slip magnitudes on major faults.

使用全球定位系统 (GPS) 进行的大地测量可以很好地表征与西加州板块构造运动相关的当前速度场。在活跃变形区域中大地测量记录的确切性质仍然是一个重大问题，因为该技术记录了扳手边界（邻近主要走滑断层的块体）中的可恢复（弹性）和永久（准塑性）应变。该提案的目标是通过同时研究圣安德烈亚斯断层系统的两个不同部分来评估扳手边界变形中可恢复分量和永久分量的相对大小。加利福尼亚州中部蠕动段：由于断层滑动事件之间的间隔很长（50 年），仅靠大地测量通常无法区分可恢复变形和永久变形。相比之下，在圣安德烈亚斯断层的蠕动中部部分，滑动事件之间的间隔很短（几周到几个月）。通过在爬行段的整个短地震周期中收集大地测量数据，PI 将能够评估断层附近位移场的可恢复分量和永久分量的相对大小。他们建议根据地质和古地磁数据确定的长期平均值来检查当前累积的永久测量值的估计值。先前的工作表明，扳手边界地区中新世和较年轻沉积物的古地磁信号呈顺时针旋转。 记录整个区域的面积范围、区域分布和旋转量将使他们能够计算永久变形的长期平均值。这部分提案涉及永久性 GPS 站和监测、活动式 GPS、古地磁学和地质测绘。南加州索尔顿槽杜米山：在该地区，之前的工作已经确定了永久应变的大小。 PI 建议完成变形沉积岩的逐步三维逆变形。为了将这些增量应变数据转换为变形率的估计值，必须精确了解变形时间。在这个暴露良好的区域，变形时间的一个方面是由与 0.76 Ma Bishop 凝灰岩相关的灰层的存在提供的。记录沉积过程中磁场的古地磁技术将产生更多信息。利用不同沉积层的不同年龄来提供不同的垂直轴旋转，PI 可以通过确定哪些单元受到影响来确定次要结构（例如节理、裂缝和小褶皱）的时间。通过比较大地测量速率（包括可恢复应变分量和永久应变分量）与地质速率（仅记录永久应变分量），他们可以评估该区域的可恢复应变累积量。该提案的这一部分涉及地质测绘、古地磁学和战役式 GPS。通过结合我们两个现场区域的地质、大地测量和古地磁调查结果，PI 将评估扳手边界地区可恢复（弹性）和永久（准塑性）应变的相对贡献。这个问题的解决对于地震力学、边界变形的地质意义以及主要断层上的潜在滑移幅度具有根本性的影响。