伊豆-小笠原-马里亚纳俯冲带地震成因

计算了伊豆-小笠原、马里亚纳弧段的浅源地震与俯冲速率的相关系数，证实了俯冲速率是一个重要的控制因素。地震统计结果展示马里亚纳中深度(60~300 km)地震存在较明显分段性，且与海底地形起伏度相对应，推断这种现象一方面因为海山俯冲引起的板块破裂程度高，导致更多的流体供应所致; 另一方面可能与海山俯冲机制导致板片局部变形有关。通过全球P波波速模型，提取马里亚纳之下大约8.0 km/s的等值面，揭示了俯冲板片的深部形态，在马里亚纳弧的南北两侧之下，存在两个明显的缺失，代表了板片深部的撕裂，且北部撕裂程度要比南部高，可能与北部小笠原高原与南部卡罗琳洋中脊俯冲有关。重力数据与地震数据揭示了相对于马里亚纳俯冲带北部，南部可能为强耦合，菲律宾海板块之下410~660 km不连续界面滞留为太平洋板片，西南部与马里亚纳俯冲带南部俯冲太平洋板片相连。初步推断这种结构与具有较大浮力的卡罗琳洋中脊可能共同决定了马里亚纳俯冲带南部8°N、137.3°E存在的旋转极。

TRIGGERING CAUSES OF EARTHQUAKES ALONG THE IZU-BONIN-MARIANA SUBDUCTION ZONE

The correlation coefficient between shallow earthquakes and plate subduction rates along the IBM is calculated in this paper. It suggests that the plate subduction rate is an important parameter to determine the spatial distribution of earthquakes. Statistic of earthquakes reveals that intermediate to deep (60~300 km) seated earthquakes along the Mariana Arc show an obvious feature of segmentation corresponding to the relief of sea floor. It is inferred to be caused by over supply of fluids during the seamount subduction, which leads to the break and local deformation of the subducting slab and change in coupling of thermal pattern. A counter surface of 8.0 km/s from the global P-wave model beneath the Mariana Arc is extracted and presented by the Paraview software. Two gaps are observed under the north and south ends of the Mariana Arc, owing to the tearing up of the subducting slab, which is stronger in the north and weaker in the south, and the difference in subduction rate in the northern Ogasawara Plateau and the southern Caroline Ridge respectively. The gravity and earthquake data also reveals that in the southern part of the Mariana Arc there may be strong interplate coupling, and 3D P-wave speed map shows that the 410~670 km remanent Pacific Plate beneath the Philippine Sea Plate extend to the southwest and there is an indirect contact with the subducting Pacific plate from the southern Mariana Arc. A preliminary deduction is that the deep structure and the buoyant Caroline Ridge may determine the existence of the rotation pole located at 8°N, 137.3°E in the southern Mariana.