论文部分内容阅读
把一种粘弹性弯矩理论应用到菲律宾海板块的消减板块。该板块在相对于岛弧南部的九州-琉球消减带北端急剧弯曲。在安芸滩、伊予滩和丰后水道,即九州和四国岛之间海域之下,该板块剖面图上的板块边界表现为一个圆弧状的岛弧,这已由10余年的微震分布所证实。基于这种几何形状估算了弹性弯矩,应用麦克斯威尔粘弹理论折算了这里由于粘滞性引起的形变。抗弯强度太大,以致于不能把它仅仅归结于板块的反向浮力。这里我们假设,水平压力是由大地测量已检测到广延地面运动的九州北部火山地区伴随上涌岩浆的扩展地幔流所引起。我们估计的使板块弯曲的均匀压力σ为72MPa,估计时取如下模型常数作为标准:板块的厚度h为30km,板块的杨氏模量E为1.8×10~5MPa,泊松比ν=0.27,板块开始消减的平均消逝时间t=1.9×10~6a,粘弹性板块的时间常数τ为3.0×10~5a,与周围大气相比板块的超密度△ρ=0.06×10~3kg/m~3。在板块上部的闭锁部分附近地震活动性最高,这里毁灭性的地震频频发生。2001年芸予M6.4地震就是其中之一,且发生在这条活跃地震带的东端。该地震的震源机制结果显示为正断层型,和这个地震活动地区的大多数小震震源机制结果相似。我们认为这个大地震的主要原因是板块的弯曲力。
A viscoelastic bending moment theory is applied to the subplate of the Philippine Sea plate. The plate is sharply bent at the northern end of the Kyushu-Ryukyu subduction zone to the south of the island arc. The plate boundaries on the section of the plate show an arcuate island arc beneath An Yun Beach, Yihutan and Feng-Feng channels, the sea area between Kyushu and Shikoku, which has been confirmed by the microseismic distribution for more than 10 years . Based on this geometry, the elastic bending moment is estimated, and the deformation due to the viscosity is converted here using Maxwell’s viscoelastic theory. The flexural strength is so great that it can not be attributed only to the reverse buoyancy of the plate. Here we assume that the horizontal pressure is caused by the extended mantle flow associated with upwelling magma in volcanic northern Kyushu where geodesy has detected extensive ground motion. We estimate that the plate bending average pressure σ is 72MPa, the following model constants are taken as the standard estimation: plate thickness h is 30km, plate Young’s modulus E is 1.8 × 10 ~ 5MPa, Poisson’s ratio ν = 0.27, The mean time elapsed from the beginning of plate tearing down to 1.9 × 10 ~ 6a, the time constant τ of viscoelastic plate is 3.0 × 10 ~ 5 a, and the super density of plate ρ = 0.06 × 10 ~ 3kg / m ~ 3 compared with the surrounding atmosphere . Seismic activity is highest near the top of the plate, where devastating earthquakes occur frequently. One of them, the Yun M6.4 earthquake in 2001, occurred at the eastern end of this active seismic zone. The focal mechanism of the earthquake showed a positive fault type, similar to the focal mechanism of most small earthquakes in this seismic area. We think the main reason for this earthquake is the bending force of the plate.