Geodetic Constraints on Arc Dynamics and Coupling on the Plate Interface in the Lesser Antilles

小安的列斯群岛弧动力学和板块界面耦合的大地测量约束

• 批准号: 1063246
• 负责人: Glen Mattioli
• 金额: $ 3万
• 依托单位: University of Texas at Arlington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-08-01 至 2011-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1063246&HistoricalAwards=false
• 关键词: Geodetic; Constraints; Arc; Dynamics; Coupling

PROJECT SUMMARYAlong obliquely convergent plate boundaries, the relative plate motion vector frequently is partitioned into arc-normal and arc-parallel components. Complete separation of the normal and parallel components leads to arc-parallel thrusts and folds in the forearc and arc-parallel strike-slip faults in the volcanic arc. The forearc thus translates relative to the interior of the overriding plate. Partial separation of the two components, however, is more common, particularly when coupling occurs across the plate interface. In addition, changes in obliquity of convergence along the plate boundary can create arc- parallel gradients in shear stress to produce internal deformation of the forearc. Either arc-parallel extension or compression may occur. The northeastern Caribbean corner affords an excellent opportunity to use Global Positioning System (GPS) geodesy to examine strain partitioning, coupling along the plate interface, and arc-parallel extension in a slow subduction zone. Caribbean-North American relative plate motion is ~20 mm/yr. Thetrend of the plate boundary changes from NNW in the Lesser Antilles to EW along the eastern Greater Antilles. The ENE azimuth of the convergence vector predicts near normal subduction at Martinique and near strike-slip motion at Puerto Rico. Horizontal slip directions derived from shallow-thrust earthquakes east of the Lesser Antilles lie between the predicted convergence direction and the normal to the subduction trace, suggesting that some partitioning occurs. The focus is on the northern Lesser Antilles for four reasons. First, The PI's have collected GPS data in the region since 1994 and have developed a Caribbean reference frame. Second, GPS-derived velocities for the southern Lesser Antilles agree within error with those predicted for Caribbean motion relative to North America at those locations, implying little or no deformation of the overriding plate. In contrast, a simple elastic half-space model shows that preliminary GPS geodetic results from the northern Lesser Antilles are consistent with coupling along the plate interface. Third, the northern Lesser Antilles arc consists of two concentric island chains that provide subaerial exposure closer to the trench and over a greater arc transverse distance than do the islands in the south. Fourth, NE-trending structures transverse to the arc in the northern Lesser Antilles accommodate a component of arc-parallel extension. In addition, volcanic centers on individual islands have migrated parallel to the arc at rates equivalent to those of the arc-parallel component of convergence. Finally, EW-oriented extension along NS-trending structures has been measured by GPS geodesy for the EW-trending eastern Greater Antilles. The slow relative plate motion in the northeastern Caribbean requires long GPS time-series to yield robust velocities to assess potential arc-parallel strain gradients. This five-year proposal, therefore, builds on data collected in the northeastern Caribbean since 1994.If no motion of the islands of the northern Lesser Antilles relative to the Caribbean plate can be detected over temporal scales of a decade or longer a scenario that is unlikely given our preliminary dataset these sites will be used to provide additional constraints for the Caribbean reference frame formulation. The proposed work includes: collection and processing of GPS data; noise analysis, which is particularly important where motion is slow such as the Caribbean; and modeling of results. The questions to be addressed are: Is oblique slip partitioned into trench parallel and normal components in slow subduction zones, i.e. the northern Lesser Antilles? If partitioning occurs, does it depend upon obliquity of convergence? What is the degree of coupling along the plate interface in the northern Lesser Antilles? Is arc-parallel extension of sufficient magnitude for detection by GPS geodesy? If so, does it increase in magnitude as obliquity of subduction increases? Are the rates of arc-parallel slip and/or arc-parallel extension consistent with rates of migration of volcanic centers within the northern Lesser Antilles? What are the implications of this for the dynamics of deep magmatic processes? Determining whether the leading edge of the Caribbean plate corner in the eastern Greater Antilles and the Lesser Antilles is composed of distinct block(s)that move relative to the Caribbean interior also will constrain seismic hazard in the northeastern Caribbean, an area that is little studied and particularly at risk for seismogenic tsunamis.

沿着斜向会聚的板块边界，相对板块运动矢量常常被划分为弧法向分量和弧平行分量。 正常和平行分量的完全分离导致弧前的弧平行逆冲断层和褶皱以及火山弧中的弧平行走滑断层。 因此，前弧相对于覆盖板的内部平移。 然而，两个组件的部分分离更常见，特别是当耦合发生在板界面上时。 此外，沿着板块边界的会聚度的变化可以产生剪切应力的弧平行梯度，从而产生前弧的内部变形。 可能发生弧平行延伸或压缩。加勒比海东北角提供了一个极好的机会，使用全球定位系统（GPS）大地测量检查应变分区，耦合沿着板块界面，并在缓慢俯冲带弧平行延伸。 加勒比-北美板块相对运动约为20毫米/年。 板块边界的走向从小安的列斯群岛的NNW向大安的列斯群岛东部的沿着EW变化。 ENE方位角的收敛矢量预测附近的正常俯冲在马提尼克岛和附近的走滑运动在波多黎各。 水平滑动方向来自小安的列斯群岛东部的浅冲地震之间的预测收敛方向和正常的俯冲痕迹，这表明发生了一些分割。 重点放在小安的列斯群岛的北方有四个原因。 首先，PI自1994年以来一直在该地区收集GPS数据，并制定了加勒比参考框架。 第二，GPS导出的小安的列斯群岛南部的速度与加勒比运动相对于北美在这些位置的预测误差一致，这意味着很少或没有变形的覆盖板块。 相比之下，一个简单的弹性半空间模型表明，从北方小安的列斯群岛的初步GPS大地测量结果是一致的耦合沿着板界面。 第三，小安的列斯群岛的北方岛弧由两个同心岛链组成，与南部的岛屿相比，这些岛弧在更靠近海沟的地方和更大的岛弧横向距离上提供了陆上暴露。 第四，在小安的列斯群岛北方，横向于弧形的NE向构造容纳了弧形平行伸展的分量。此外，个别岛屿上的火山中心平行于弧迁移的速度相当于那些弧平行的收敛组件。 最后，通过GPS大地测量法测量了大安的列斯群岛东部东西向沿着NS向结构的东西向延伸。在加勒比海东北部的缓慢相对板块运动需要长的GPS时间序列，以产生强大的速度来评估潜在的弧平行应变梯度。 因此，这个五年的建议，建立在自1994年以来在加勒比东北部收集的数据。如果没有运动的北方小安的列斯群岛相对于加勒比板块可以检测到超过十年或更长的时间尺度的情况下，是不太可能给我们的初步数据集，这些网站将被用来提供额外的约束加勒比参考框架的制定。 拟议的工作包括：全球定位系统数据的收集和处理;噪声分析，这在加勒比等运动缓慢的地方特别重要;以及结果建模。 要解决的问题是：斜滑划分为沟平行和正常的组成部分，在缓慢俯冲带，即小安的列斯群岛北方？如果发生分割，它是否依赖于收敛的一致性？小安的列斯群岛北方板块界面沿着的耦合程度如何？弧平行延伸的大小是否足以用GPS大地测量法进行探测？如果是的话，它的大小是否随着俯冲速度的增加而增加？ 弧平行滑动和/或弧平行延伸的速率是否与小安的列斯群岛北方火山中心的迁移速率一致？ 这对深部岩浆过程的动力学有什么影响？ 确定大安的列斯群岛和小安的列斯群岛东部的加勒比板块角的前缘是否由相对于加勒比内陆移动的不同块体组成，也将限制加勒比东北部的地震危险性，这一地区很少被研究，特别是有地震海啸的风险。