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研究了缅甸山弧附近的中源地震分布,发现h>70km的地震主要分布在20°N—27°N之间,形成明显的条带分布,24°N以南走向近南北,24°N以北走向逐渐接近NE;通过垂直剖面的研究,发现缅甸山弧下的Benioff带形态是变化的,在南北两端倾角较小,且较为平直,延伸深度浅,小于100km;在地震带的中间部分,Benioff带的倾角逐渐加大,且倾角随深度加深而增大,延伸深度可达180km。在一些剖面上出现双地震层,一般出现在45—100km的深度范围内,两层间的距离从10—25km不等;在同一剖面上,两层间在浅部间距大,在深部间距小。研究了沉降带上的应力状态,发现沉降带上P轴的优势方向位于NE—SW,T轴分布较分散;P、T轴随深度没有明显变化;在上地震层中,T轴明显接近于Benioff带的倾向;通过地壳内及沉降带上地震机制解的对比,发现前者的优势方向相对于后者逆时针旋转了一定角度。
The distribution of mid-source earthquakes near Burma’s mountain arc is studied. It is found that the earthquakes h> 70km distribute mainly between 20 ° N and 27 ° N, forming obvious banding distribution. The southward 24 ° N travels towards the north and south and the 24 ° N And the northward direction gradually approaches NE. From the vertical section study, it is found that the Benioff belt in Burma’s mountain arc changes in shape and has a smaller dip angle at both the north and south ends and a shallower extension depth less than 100 km. In the seismic belt In the middle part, the inclination of the Benioff belt gradually increases, and the inclination angle increases with the deepening of the depth with an extension depth of up to 180km. In some sections, the double seismic layer appears, which usually occurs in the depth range of 45-100km and the distance between the two layers varies from 10-25km. On the same section, the spacing between shallow layers in the two layers is large and the distance between the two layers is small . The stress state on the subsidence zone was studied. The dominant direction of the P axis on the subsidence zone is located at NE-SW, and the distribution of T axis is relatively scattered. The P and T axes have no significant change with depth. In the upper seismic layer, the T axis is obviously close to Benioff belt tendency. Comparing the seismic mechanism solutions in the crust and the subsidence zone, it is found that the dominant direction of the former rotates counterclockwise relative to the latter.