Mature Diffuse Tectonic Block Boundary Revealed by the 2020 Southwestern Puerto Rico Seismic Sequence
Mature Diffuse Tectonic Block Boundary Revealed by the 2020 Southwestern Puerto Rico Seismic Sequence
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2020年波多黎各西南部地震序列揭示的成熟弥漫构造块边界
DOI：
10.1029/2021tc006896
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发表时间：
2021
期刊：
影响因子：
4.2
通讯作者：
B. Andrews
中科院分区：
文献类型：
--
作者：
U. T. ten Brink;E. Vanacore;E. Fielding;J. Chaytor;A. López;W. Baldwin;D. Foster;B. Andrews
分布的断层通常倾向于合并成一个或几个重复变形的断层。波多黎各西南部（SWPR）2020年地震序列期间聚集的中型（≥Mw4.5）地震的进展、通过干涉合成孔径雷达对海岸线沉降进行建模以及通过高分辨率地震反射剖面进行海底测绘，表明2020年SWPR地震序列分布在瓜亚尼拉海底峡谷岛架和上斜坡下方的几个短的交叉走滑和正断层上。海底多波束测深图显示，地震活动区大陆架边缘受到严重侵蚀和后退，以及通常在地质时期形成的斜坡平行线性构造和海底峡谷曲流。中等地震的T轴进一步匹配先前在上新世早期后（>3 Ma）断层上测量的延伸方向。我们的结论是，虽然类似的变形可能发生在这个地区在最近的地质时期，它似乎并没有在这段时间合并。该变形可能代表扩散边界的最南端，即西波多黎各变形边界，该边界可容纳波多黎各和伊斯帕尼奥拉弧形块体之间的差异运动。这种差异运动可能是由沿波多黎各-伊斯帕尼奥拉俯冲带的差异地震耦合沿着驱动的。我们认为，整个岛弧成分的不均匀性延缓了集中变形成一个单一的故障的过程。鉴于这里提出的证据，我们不应该期望在这个地区发生一个单一的大型事件，而是在未来发生类似的扩散序列。
Distributed faulting typically tends to coalesce into one or a few faults with repeated deformation. The progression of clustered medium‐sized (≥Mw4.5) earthquakes during the 2020 seismic sequence in southwestern Puerto Rico (SWPR), modeling shoreline subsidence from InSAR, and sub‐seafloor mapping by high‐resolution seismic reflection profiles, suggest that the 2020 SWPR seismic sequence was distributed across several short intersecting strike‐slip and normal faults beneath the insular shelf and upper slope of Guayanilla submarine canyon. Multibeam bathymetry map of the seafloor shows significant erosion and retreat of the shelf edge in the area of seismic activity as well as slope‐parallel lineaments and submarine canyon meanders that typically develop over geological time. The T‐axis of the moderate earthquakes further matches the extension direction previously measured on post early Pliocene (∼>3 Ma) faults. We conclude that although similar deformation has likely taken place in this area during recent geologic time, it does not appear to have coalesced during this time. The deformation may represent the southernmost part of a diffuse boundary, the Western Puerto Rico Deformation Boundary, which accommodates differential movement between the Puerto Rico and Hispaniola arc blocks. This differential movement is possibly driven by the differential seismic coupling along the Puerto Rico—Hispaniola subduction zone. We propose that the compositional heterogeneity across the island arc retards the process of focusing the deformation into a single fault. Given the evidence presented here, we should not expect a single large event in this area but similar diffuse sequences in the future.