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，其中一个构造板降落到另一个侧面的地球，上板的一部分称为前弧，有时会朝着几乎正交与两个板之间的收敛方向进行水平移动。 为了发生这种前进的迁移，上板中必须存在一个变形区域，其中断层运动可容纳前弧的运动。 但是，变形区域中断层的位置和方向及其与上板中的火山的关系，从一个俯冲带到另一个俯冲带不同。 这项研究将通过在尼加拉瓜进行研究，在尼加拉瓜中研究它们，在该过程中，在尼加拉瓜的过程中，Cocos板块俯冲到加勒比海板下方的东北部，而加勒比海板前的前方正在移动到西北。 特别是，这项工作将测试尼加拉瓜的火山是否在上板上产生弱区，在火山之间的板块较强部分中浓缩断层和地震。 GPS数据将用于测量与前ARC运动相关的剪切位置的位置。 大地震及其余震的位置将得到改善，并用于确定活动断层的方向。 地震波将用于探测上板的结构，并确定部分融化到火山到火山的位置已削弱了上板。 除了提高对前进运输过程的理解外，这项工作还将有助于评估地震断层对尼加拉瓜人口构成危害。该项目将有助于宾夕法尼亚州立大学和布朗的研究生的教育和职业发展。至少有一个本科生将通过领导力联盟（Brown）和PA太空赠款（Penn State）进行该项目，这些计划是从STEM领域中占人数不足的团体中招募学生的计划。该项目还将通过研究小组会议和课程在宾夕法尼亚州和布朗的一群学生和博士后访问，并将在与普罗维登斯的小学进行宣传，RI.STRAIN分区以及由于倾斜的倾斜而形成的偏向于全球范围内的越来越多的问题，但仍有一些动作，这些越来越多。 在不同俯冲带中的研究得出了关于弧岩浆对与前弧传输相关的上板断层的影响的结论，以及为什么俯冲带的明显几何形状以及在某些情况下沿着单个阿拉伯式滑动的打击。 该项目将通过测试以下假设来解决这些全球问题，即尼加拉瓜的前进运输代表了一个结束成员的案例，在该案例中，由于火山中心下方由于岩浆而削弱了地壳，强烈介导了断层和变形的几何形状。沿弧形变形的弧变化，通过在哥斯达黎加中部的边缘正常到尼加拉瓜的边缘正常到尼加拉瓜的边缘正常的方向上的急剧旋转揭示了，在那里，前空的sliv sliver sliv sliv sliv sliv sliv sliv sliv sliver的传输最为明显。在尼加拉瓜，书架断层的证据和垂直轴的前弧块的旋转是由大地震的边缘正常断层提供的。然而，书架断层与弧线平行滑移断层的分布，在容纳前进运输方面的作用以及断层与流变学弱弧的关系，仍然不确定。该项目将使用地震数据和地震数据来检验以下假设：与岩浆中心相关的流变学弱点区域会显着改变上板变形和断层的模式。 将测试该假设的四个预测：1）与前ARC转运相关的变形位于ARC中； 2）断层位于火山中心之间强层强的区域中； 3）变形由书架断层和边缘平行滑移断层构成，其中断层方向通过火山中心的间距部分控制； 4）前交通的部分是通过岩浆作用的部分来容纳的。综合的大地测量和地震分析将测试四个模型预测。对新的和现有的GPS数据的分析将指示最大应变梯度（1）和剪切和扩张应变率异常区域的位置（2-4）。 GPS衍生的同震位移结合了地震重新定位和源方向性的分析将表明故障几何形状（2-3）。表面波和转化的人体波数据的联合分析和反转将改善上层板结构的模型以及地壳和地幔流变学，包括对地壳中部分熔体分布的约束（即与ARC相关的弱区）。调查人员将与Ineter的同事（监视尼加拉瓜的地震和火山的机构）合作，以改善与人口相关的上板地震的危害评估。新的GPS网络安装将扩展Coconet GPS网络的实用性。另一个结果将是软件和一个工作流程，以使Ineter的地震学家能够独立地进行地震序列的双向重新分配。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的智力优点和更广泛的影响评估的评估来支持的。

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
• 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.