Collaborative Research: Deciphering upper plate deformation and faulting processes in Central America with integrated geodetic and seismic analyses

合作研究：通过综合大地测量和地震分析解读中美洲上部板块变形和断层过程

• 批准号: 1822485
• 负责人: Karen Fischer
• 金额: $ 19.94万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1822485&HistoricalAwards=false
• 关键词: Collaborative; Research; Deciphering; upper; plate

In subduction zones, where one tectonic plate descends into the Earth beneath another, a portion of the upper plate called the fore-arc sometimes moves horizontally in a direction that is nearly orthogonal to the direction of convergence between the two plates. For such fore-arc migration to occur, a zone of deformation must exist in the upper plate where movement on faults accomodates the motion of the fore-arc. However, the locations and orientations of faults in the zone of deformation, and their relationship to volcanoes in the upper plate, differ from one subduction zone to the next. This study will improve a global understanding of the processes that enable fore-arc migration by studying them in Nicaragua where the Cocos plate subducts to the northeast beneath the Caribbean plate, and the Caribbean plate fore-arc is moving to the northwest. In particular, this work will test whether the volcanoes in Nicaragua create weak zones in the upper plate that concentrate faulting and earthquakes in the stronger parts of the plate that lie between volcanoes. GPS data will be used to measure where shearing related to fore-arc motion is localized. The locations of large earthquakes and their aftershocks will be improved and used to determine the orientations of active faults. Seismic waves will be used to probe the structure of the upper plate and determine where partial melt rising up to the volcanoes has weakened the upper plate. In addition to improving understanding of fore-arc transport processes, this work will help in assessing where earthquake faults pose hazards to the population of Nicaragua. The project will contribute to the education and career development of graduate students at Penn State and Brown. At least one undergraduate will work on this project through the Leadership Alliance (Brown), and the PA Space Grant (Penn State), programs that recruit students from groups underrepresented in STEM fields. The project will also reach a broader group of students and postdocs at Penn State and Brown through research group meetings and courses, and will be featured in outreach with elementary schools in Providence, RI.Strain partitioning and the formation of migrating fore-arc terranes due to oblique convergence have been documented in numerous subduction zones around the globe, yet major questions remain regarding how the motion of these terranes is accommodated in the upper plate. Studies in different subduction zones have reached varying conclusions about the impact of arc magmatism on upper plate faulting associated with fore-arc transport, and whether and why the apparent geometry of deformation and faulting varies between subduction zones, and in some cases along the strike of a single fore-arc sliver. This project will address these global questions by testing the hypothesis that fore-arc transport in Nicaragua represents an end-member case where crustal weakening due to magma beneath volcanic centers strongly mediates the geometry of faulting and deformation. Along-arc changes in upper plate deformation are revealed by a dramatic rotation in the direction of interseismic velocities from margin-normal in central Costa Rica to margin-parallel in Nicaragua where fore-arc sliver transport is most pronounced. In Nicaragua, evidence for bookshelf faulting and the rotation of fore-arc blocks about vertical axes is provided by margin-normal faults with large earthquakes. However, the distribution of bookshelf faulting versus arc-parallel strike-slip faults, their roles in accommodating fore-arc transport, and the relationship of faulting to a rheologically weak arc, remain uncertain. This project will use geodetic and seismic data to test the hypothesis that zones of rheological weakness associated with magmatic centers significantly alter the mode of upper plate deformation and faulting. Four predictions of this hypothesis will be tested: 1) deformation associated with fore-arc transport is localized in the arc; 2) faulting is localized in zones of strong crust between volcanic centers; 3) deformation is accommodated by bookshelf faulting and margin-parallel strike-slip faulting, where fault orientation is partially controlled by the spacing of volcanic centers; and 4) fore-arc transport is partially accommodated by magmatism. Integrated geodetic and seismic analyses will test the four model predictions. The analysis of new and existing GPS data will indicate the location of the maximum strain gradient (1) and anomalous regions of shear and dilatational strain rates (2-4). GPS-derived coseismic displacements combined with earthquake relocations and analyses of source directivity will indicate fault geometry (2-3). Joint analyses and inversions of surface wave and converted body wave data will improve models of upper plate structure and crust and mantle rheology, including constraints on the distribution of partial melt in the crust (i.e., weak zones associated with the arc). The investigators will work with colleagues at INETER (the agency that monitors earthquakes and volcanoes in Nicaragua) to improve hazard assessment from upper plate earthquakes in relation to population. New GPS network installations will expand the utility of the COCONet GPS network. Another outcome will be software and a workflow to enable the seismologists at INETER to independently carry out double-difference relocation of earthquake sequences.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.

在俯冲带中，一个构造板块下降到另一个构造板块下方的地球中，称为前弧的上板块的一部分有时会沿与两个板块之间会聚方向几乎正交的方向水平移动。 为了发生这种弧前迁移，上板块中必须存在变形区域，其中断层上的运动适应弧前的运动。 然而，变形带中断层的位置和方向以及它们与上板块火山的关系因俯冲带而异。 这项研究将通过在尼加拉瓜进行研究，提高全球对弧前迁移过程的理解。尼加拉瓜科科斯板块在加勒比板块下方向东北俯冲，而加勒比板块弧前正在向西北移动。 特别是，这项工作将测试尼加拉瓜的火山是否在上板块形成薄弱区域，使断层和地震集中在火山之间板块的较强部分。 GPS 数据将用于测量与弧前运动相关的剪切的局部位置。 大地震及其余震的位置将得到改进，并用于确定活动断层的方向。 地震波将用于探测上板块的结构，并确定上升到火山的部分熔体在何处削弱了上板块。 除了增进对弧前输运过程的了解之外，这项工作还将有助于评估地震断层对尼加拉瓜人口造成危害的位置。该项目将为宾夕法尼亚州立大学和布朗大学研究生的教育和职业发展做出贡献。至少一名本科生将通过领导力联盟（布朗大学）和宾夕法尼亚州立大学空间资助项目（宾夕法尼亚州立大学）从事该项目，这些项目从 STEM 领域代表性不足的群体中招收学生。该项目还将通过研究小组会议和课程，覆盖宾夕法尼亚州立大学和布朗大学的更广泛的学生和博士后群体，并将在罗得岛州普罗维登斯的小学的推广活动中进行重点介绍。由于应变划分和迁移弧前地体的形成全球许多俯冲带都记录了倾斜会聚的情况，但关于这些地体的运动如何在上板块中适应的主要问题仍然存在。 不同俯冲带的研究对于弧岩浆作用对与弧前输运相关的上板块断层的影响，以及变形和断层的表观几何形状是否以及为何在俯冲带之间以及在某些情况下沿着俯冲带的走向有所不同，得出了不同的结论。单个前弧条子。 该项目将通过测试以下假设来解决这些全球性问题：尼加拉瓜的弧前迁移代表了一种端元情况，其中火山中心下方的岩浆导致的地壳弱化强烈介导了断层和变形的几何形状。上板块变形的沿弧变化是通过震间速度方向的剧烈旋转揭示的，从哥斯达黎加中部的边缘法向到尼加拉瓜的边缘平行，其中弧前条子输送最明显。在尼加拉瓜，大地震的边缘正断层提供了书架断层和弧前块体绕垂直轴旋转的证据。然而，书架断层与弧平行走滑断层的分布、它们在调节弧前输运中的作用以及断层与流变弱弧的关系仍然不确定。该项目将使用大地测量和地震数据来检验与岩浆中心相关的流变薄弱区显着改变上板块变形和断层模式的假设。 将测试该假设的四个预测：1）与弧前传输相关的变形位于弧内； 2）断层作用仅限于火山中心之间的坚固地壳区域； 3）变形由书架断层和边缘平行走滑断层调节，其中断层方向部分受火山中心间距控制； 4）弧前输运部分由岩浆作用调节。综合大地测量和地震分析将检验四个模型的预测。对新的和现有的 GPS 数据的分析将指示最大应变梯度 (1) 的位置以及剪切和膨胀应变率的异常区域 (2-4)。 GPS 得出的同震位移与地震重定位和震源方向性分析相结合将指示断层几何形状 (2-3)。表面波和转换体波数据的联合分析和反演将改进上板块结构和地壳和地幔流变学的模型，包括对地壳中部分熔融物（即与弧相关的薄弱区）分布的约束。研究人员将与 INETER（尼加拉瓜地震和火山监测机构）的同事合作，改进上板块地震与人口相关的危险评估。新的 GPS 网络安装将扩展 COCONet GPS 网络的实用性。另一个成果是软件和工作流程，使 INETER 的地震学家能够独立进行地震序列的双差重定位。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查进行评估，被认为值得支持标准。

项目成果

Cascading Hazards in a Migrating Forearc‐Arc System: Earthquake and Eruption Triggering in Nicaragua

迁移的前弧系统中的级联灾害：尼加拉瓜的地震和火山喷发触发

• DOI: 10.1029/2022jb024899
• 发表时间: 2022-12
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Higgins, M.;La Femina, P. C.;Saballos, A. J.;Ouertani, S.;Fischer, K. M.;Geirsson, H.;Strauch, W.;Mattioli, G.;Malservisi, R.
• 通讯作者: Malservisi, R.