论文部分内容阅读
1885～1999年的115年间日本地壳中的大地震(震级5.7～8.0,深度0～20 km)发生在由地震层析成像揭示出的低速区及其周围。低速区可能代表孕震地壳的薄弱部分。地壳弱化被认为与该区内太平洋板块和菲律宾海板块的俯冲密切相关。沿火山前沿及弧后区的地壳弱化可能是由活火山及岩浆房造成的。在弧前区,在地震震源区探测到了流体,这种流体可能会促使地壳弱化和破裂成核。流体可能与俯冲的菲律宾海板块的脱水作用有关。这些结果表明,地壳中的大地震并非在什么地方都会发生,而仅发生在用地球物理方法可能会探测到的异常区内。
During the 115 years from 1885 to 1999, large earthquakes in Japan’s crust (magnitude 5.7-8.0 and depth 0-20 km) occurred at and around the low-velocity zone revealed by seismic tomography. The low speed zone may represent the weakest part of the crust. Crustal weakening is believed to be closely related to the subduction of the Pacific and Philippine Sea plates in the area. The weakening of the crust along the volcanic foreland and backarc may be caused by active volcanoes and magma chambers. In the pre-arcuate zone, fluids are detected in the seismic source area, which may cause crustal weakening and fracture nucleation. Fluid may be related to the dewatering of the subducted Philippine sea plate. These results show that large earthquakes in the crust do not occur anywhere but only in the anomalous areas that may be detected by geophysical methods.