日本海—鄂霍次克海下俯冲带的应力状态及其深部形变

通过地震分布及地震机制解所反映的日本海—鄂霍次克海俯冲带的形态及应力状态,研究了俯冲带深部形变及650km间断面的穿透问题.日本海Benioff带较直,连续性较好;鄂霍次克海Benioff带弯度稍大,220—320km深度之间地震很少.两俯冲带在浅部及深部地震密集,100—200km深度之间有双地震层.应力状态随深度变化,200km深度以下P,T轴方向相对集中,P轴接近俯冲方向,在约100—200km深度附近,P,T轴均接近俯冲方向.观测和理论地震图拟合分析表明,地震断层面走向接近俯冲带走向,断裂的结果使俯冲带在深部倾角变小.

STRESS STATE AND DEEP DEFORMATION OF SUBDUCTION ZONE IN JAPAN SEA AND THE SEA OF OKHOTSK AND THE PROBLEM OF SLAB PENETRATION INTO THE LOWER MANTLE

The configuration and stress state of subtraction zone in Japan Sea and the Sea of Okhotsk were studied using the earthquake distribution and more than one hundred fault plane solutions for earthquakes from 1964 to 1985. The Benioff zone in Japan Sea is nearly continous and straight, with the maximum depth of about 560 km and the dip angle of about 29°. The one in Okhotsk Sea is slightly curved and from 220 to 320 km few earthquakes occured in it; the maximum depth is about 620 km, and the average dip angle is about 45°. There is a double seismic zone from about 100 to 200 km in both subduction zone. The stress state varies with the depth. In Japan Sea, from 100 to 200 km, most of P axes coincide with the subduction direction, a few of T axes are close to the direction of subduction. Below the depth of 200 km, the P axes are nearly close to the subducting direction. In he Sea of Okhotsk, above 114 km, the T axes coincide with subducting direction; from 114 to 175 km, the P axes for more than half of the fault plane solutions in this range are coincident with subduction direction, the T axes for the rest of fault plane solutions coincide with the subducting direction; from 320 to 440 km, the P and T axes are not as well in gathering as in other depths, but the P axes appear to close to the subducting direction; below 500km, the P axes coincide with the direction of subduction. The nodal planes were analysed, indicating that the strikes for one set of nodal planes for earthquake deeper than 500km are gathering and coincide with the strike of the subduction zone, but the events in Japan Sea show thrust type and in Okhotsk Sea show normal type. The source parameters obtained from synthetic seismograms show that these nodal planes are the rupture planes of the earthquake. The cause of the stress state and the deformation of the subduction zone were also studied.