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首页> 外文期刊>Geochemistry, geophysics, geosystems >Horizontal principal stress orientation in the Costa Rica Seismogenesis Project (CRISP) transect from borehole breakouts
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Horizontal principal stress orientation in the Costa Rica Seismogenesis Project (CRISP) transect from borehole breakouts

机译：哥斯达黎加地震发生项目（CRISP）断层横断面的水平主应力方向

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The Costa Rica Seismogenesis Project (CRISP) drilled the Pacific margin of the Middle America Trench just north of where the Cocos Ridge enters the subduction zone, resulting in basal erosion of the upper plate. Here we report the orientations of the maximum horizontal principal stress (S-Hmax) from borehole breakouts detected by logging-while-drilling and wireline downhole measurements. All S-Hmax directions were estimated in the sediment cover of the margin, above the deeper rocks of the deformed margin wedge. We observe three overall S-Hmax orientations: NNE-SSW (25 degrees azimuth) in the deepest interval drilled at the upper slope Site U1379; ENE-WSW (82 degrees) in the rest of Site U1379 and in Site U1413, also drilled in the upper slope; and NNW-SSE (157 degrees) in the mid-slope Site U1378. Our preferred interpretation is that the deepest interval of Site U1379 records the stress conditions in the underlying margin wedge, as S-Hmax is parallel to the direction of the Cocos-Caribbean plate convergence and of the compressional axes of plate boundary fault earthquakes. The variable S-Hmax directions observed elsewhere are likely due to the effect of a network of normal faults that subdivide the sediment cover into a number of independently deforming blocks. In addition, the observed S-Hmax directions may be influenced by the subducting Cocos Ridge, which acts as an indenter causing oblique deformation, and by the transition to seismogenic subduction along the plate boundary fault.
机译：哥斯达黎加地震发生项目（CRISP）在科科斯山脊进入俯冲带的北部钻了中美洲海沟的太平洋边缘，导致了上板的基底侵蚀。在这里，我们报告了随钻测井和电缆井下测量所检测到的井眼突围的最大水平主应力（S-Hmax）的方向。所有S-Hmax方向都在边缘的沉积物覆盖层中估算，在变形边缘楔的深层岩石上方。我们观察到了三个总体S-Hmax方向：在上斜坡站点U1379钻出的最深间隔中的NNE-SSW（方位角25度）;在U1379的其余部分和U1413的ENE-WSW（82度）中也钻探了上坡;中坡站点U1378的NNW-SSE（157度）。我们的首选解释是，U1379站点的最深间隔记录了下伏边缘楔形中的应力条件，因为S-Hmax平行于科科斯-加勒比板块收敛的方向和板块边界断裂地震的压轴。在其他地方观测到的可变S-Hmax方向可能是由于正常断层网络的作用，该断层将沉积物覆盖层细分为多个独立变形的块体。此外，观测到的S-Hmax方向可能会受到俯冲的科科斯山脊（其作用为导致倾斜变形的压头）以及沿板块边界断层向地震成生的俯冲转变的影响。

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