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.

项目摘要沿着倾斜会聚的板块边界，相对板块运动矢量经常被划分为弧法向分量和弧平行分量。 法向分量和平行分量的完全分离导致弧前的弧平行逆冲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为常见，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倾角的变化会产生剪应力的弧平行梯度，从而产生弧前的内部变形。 可能发生圆弧平行延伸或压缩。加勒比东北角提供了使用全球定位系统（GPS）大地测量学来检查应变分配、沿板块界面的耦合以及缓慢俯冲带中的弧平行延伸的绝佳机会。 加勒比海-北美相对板块运动约为每年 20 毫米。 板块边界的走向由小安的列斯群岛的北北西向沿大安的列斯群岛东部变为东西向。 收敛矢量的 ENE 方位角预测马提尼克岛接近正常俯冲运动和波多黎各接近走滑运动。 小安的列斯群岛以东的浅冲断地震产生的水平滑移方向位于预测的汇聚方向和俯冲迹线的法线之间，表明发生了一些分离。 重点关注小安的列斯群岛北部有四个原因。 首先，PI 自 1994 年以来一直在该地区收集 GPS 数据，并开发了加勒比参考系。 其次，由 GPS 得出的小安的列斯群岛南部的速度与这些地点加勒比海相对于北美运动的预测速度在误差范围内一致，这意味着上覆板块几乎没有变形。 相比之下，简单的弹性半空间模型表明，小安的列斯群岛北部的初步 GPS 大地测量结果与沿板块界面的耦合一致。 第三，北部小安的列斯群岛弧由两个同心岛链组成，与南部岛屿相比，这些岛链更靠近海沟，弧形横向距离更大。 第四，小安的列斯群岛北部横向于弧的NE向结构容纳了弧平行延伸的组成部分。此外，各个岛屿上的火山中心已平行于弧线迁移，其迁移速度相当于收敛的弧平行分量的速率。 最后，通过 GPS 大地测量法测量了东西向大安的列斯群岛东部沿南北走向结构的东西向延伸。加勒比海东北部缓慢的相对板块运动需要较长的 GPS 时间序列才能产生强大的速度来评估潜在的弧平行应变梯度。 因此，这项五年提案建立在自 1994 年以来在加勒比东北部收集的数据的基础上。如果在十年或更长时间的时间范围内无法检测到小安的列斯群岛北部岛屿相对于加勒比板块的运动，那么就会出现以下情况：考虑到我们的初步数据集，这些站点不太可能被用来为加勒比参考系的制定提供额外的约束。 拟议的工作包括：GPS数据的收集和处理；噪声分析，这在加勒比海等运动缓慢的地方尤其重要；和结果建模。 需要解决的问题是：在慢俯冲带（即小安的列斯群岛北部），斜滑移是否分为海沟平行部分和法向部分？如果发生划分，它是否取决于收敛的倾斜度？小安的列斯群岛北部沿板块界面的耦合程度是多少？弧平行延伸的幅度是否足够用于 GPS 大地测量学的检测？如果是这样，它的大小是否会随着俯冲倾角的增加而增加？ 弧平行滑动和/或弧平行延伸的速率与小安的列斯群岛北部火山中心的迁移速率一致吗？ 这对深层岩浆过程的动力学有何影响？ 确定大安的列斯群岛东部和小安的列斯群岛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海东北部的地震灾害，这一地区的研究很少尤其面临引发地震海啸的风险。