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.

西加州西部与板块构造运动相关的当前速度场的特征是使用全球定位系统（GPS）测量测量。积极变形区域中测量测量记录的确切性质仍然是一个重要的问题，因为该技术记录了扳手无国界中可回收（弹性）和永久性（准塑料）菌株（与主要的走滑断层相邻的块）。该提案的目的是通过同时研究San Andreas断层系统的两个不同部分，评估扳手边境变形中可回收和永久组件的相对大小。中部加利福尼亚州的爬行段：仅大地测量值通常无法区分可回收和永久变形，因为断层上的滑移发作之间的间隔很长（50年）。相比之下，在圣安德烈亚斯断层的爬行中央部分中，滑动发作之间的间隔是短的（几周到几个月的）。通过在爬行段中的整个短震动周期中收集大地的数据，PI将能够评估故障附近位移场的可回收和永久成分的相对大小。他们建议检查目前积累的永久测量值，以根据地质和古磁数据确定的长期平均值。先前的工作表明，中新世和扳手无国会中中新世和年轻沉积物的顺时针旋转。 记录各个区域的区域范围，区域分布和旋转量将使他们能够计算长期的永久变形平均值。该提案的这一部分涉及永久的GPS站和监视，运动风格的GP，古磁性和地质映射。南加州索尔顿·沃尔顿（Salton Trough）的杜米德山（Durmid Hill）：在这一地区，以前的工作确定了永久性压力的量。 PI提议完成对变形沉积岩的逐步，三维的逆转性。为了将这些增量应变数据转换为变形率的估计值，必须具有精确的变形时间知识。在这一极好的暴露区域中，与0.76 Ma Bishop Tuff相关的烟灰层的存在提供了变形时间的一个方面。其他信息将由古流磁技术产生，这些技术记录沉积过程中磁场。 PI利用不同沉积层的各种年龄来提供微分垂直轴旋转，可以通过确定哪些单元受到影响，可以确定次要结构的时机（例如，关节，断裂和小褶皱）。通过比较地质速率（包括可回收和永久性应变成分）与地质速率（仅记录永久性应变成分）的比较，他们可以评估该区域中可回收应变的积累量。该提案的这一部分涉及地质映射，古磁性和竞选风格的GPS。通过结合我们两个田间区域的地质，大地磁和古磁研究的结果，PI将评估扳手无国界中可回收（弹性）和永久性（准塑料）菌株的相对贡献。解决这个问题的解决方案对地震力学，边境变形的地质含义以及对主要断层的潜在滑移具有根本性。