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.

摘要由于板块边界是倾斜收敛的，相对板块运动向量常常被划分为弧法向分量和弧线平行分量。正向分量和平行分量的完全分离导致了弧前弧形平行逆冲褶皱和火山弧弧形平行走滑断裂。因此，前弧相对于覆盖板的内部平移。然而，两个组分的部分分离更常见，特别是当耦合发生在板界面上时。此外，沿板块边界收敛倾角的变化会在剪切应力中产生平行于弧形的梯度，从而产生弧前的内部变形。既可能发生弧形平行拉伸，也可能发生压缩。加勒比海东北角提供了一个极好的机会，可以利用全球定位系统(GPS)大地测量来研究应变分配、沿板块界面的耦合以及缓慢俯冲带中的弧形平行伸展。加勒比海-北美板块的相对运动约为20毫米/年。板块边界的走向由小安的列斯群岛的NNW向东大安的列斯群岛的EW向变化。会聚向量的ENE方位预测在马提尼克岛接近正常俯冲，在波多黎各接近走滑运动。小安的列斯群岛以东的浅冲地震产生的水平滑动方向位于预测的会聚方向和俯冲轨迹的法线之间，表明存在一定的分割作用。关注小安的列斯群岛北部有四个原因。首先，自1994年以来，国际和平研究所收集了该区域的全球定位系统数据，并建立了加勒比参照框架。其次，全球定位系统得到的南小安的列斯群岛的速度与加勒比海相对于北美在这些位置的运动预测的速度在误差范围内一致，这意味着俯冲板块的变形很小或没有变形。相反，一个简单的弹性半空间模型表明，来自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，北部的小安的列斯岛弧由两个同心的岛链组成，这两个岛链提供了更接近海沟的空中曝光，并超过了比南部岛屿更大的弧形横向距离。第四，在小安的列斯群岛北部，横跨弧形的NE向构造容纳了弧形平行伸展的成分。此外，个别岛屿上的火山中心已经平行于弧线迁移，其迁移速度与弧线平行汇聚部分的速率相同。最后，通过GPS大地测量，测量了东大安的列斯群岛东西向伸展的东西向伸展。加勒比海东北部缓慢的相对板块运动需要很长的GPS时间序列才能产生稳健的速度，以评估潜在的弧形平行应变梯度。因此，这项为期五年的建议以自1994年以来在加勒比东北部收集的数据为基础，如果在十年或更长的时间尺度上不能探测到小安的列斯群岛北部岛屿相对于加勒比板块的运动，这种情况在我们的初步数据集看来是不太可能的，这些地点将被用来为加勒比参考框架的制定提供额外的限制。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，这在加勒比海等运动缓慢的地区尤为重要；以及结果建模。要解决的问题是：在缓慢俯冲带，即小安的列斯群岛北部，斜滑是否被划分为海沟平行和正常分量？如果发生分割，是否取决于收敛的倾斜度？小安的列斯群岛北部板块界面的耦合程度是多少？弧形平行延伸是否足够大小可供GPS大地测量探测？如果是这样，它会随着俯冲倾角的增加而增加吗？弧形平行滑移和/或弧形平行伸展的速率是否与小安的列斯群岛北部火山中心的迁移率一致？这对深部岩浆作用的动力学有何影响？确定大安的列斯群岛东部和小安的列斯群岛加勒比板块一角的前缘是否由相对于加勒比内陆移动的不同地块(S)组成，也将限制加勒比东北部的地震危险，该地区的研究很少，而且特别有可能发生孕震海啸。