西太平洋板块俯冲运动与中国东北深震带

中国东北地区有一条震源深度达600公里的深震带,从震源剖面投影可以明显地看出,它是西太平洋板块俯冲的结果,俯冲的角度约为26°。 根据板块学说,建立了一个板块俯冲模型,主要考虑地幔物质和岩石层板块的热传导,计算了板块俯冲到一定深度时的温度分布。结果表明,西太平洋板块俯冲到中国东北地区深度达600公里时,其中心温度约为1200℃,仍比周围地幔物质的温度低得多,因而能产生弹性断裂,发生地震。 震源机制的结果表明,中国东北地区深震的主压应力轴方位为93°-113°,正好迎着板块俯冲的方向,仰角为27°-28°,与板块俯冲的角度大体一致。以上结果说明中国东北深震是西太平洋板块俯冲到中国东北大陆之下造成的。

THE UNDERTHRUSTING MOVEMENT OF THE WESTERN PACIFIC PLATE AND THE DEEP FOCUS EARTHQUAKE ZONE OF NORTHEAST CHINA

In the Huichuen region of northeast China, there is a deep focus earthquake zone, the depth of which reaches as deep as 600 km. As seen from the projection of the focal profile, it is the result of underthru sting of the Western Pacific Plate. The angle of the thrusting plate with the horizontal is about 26°.We set up a plate underthrusting model to calculate the temperature distribution within the thrusting plate at various depths, taking the thermal conduction between the mantle material and the lithospherical plate into account. The calculation shows that when the plate reaches the Huichuen region, at the depth of 600 km the temperature at its center is about 1200℃, which is much lower than that of the mantle material around it. So it is possible to form elastic fractures and thus generate deep earthquakes.The focal mechanism solution gives evidence that the azimuths of the main compression stress axis of these earthquakes are 93°-114°: just facing the underthrusting direction of the. plate. Their angles of elevation is about 27°-28°, almost the same as the angle of the thrusting plate with the horizontal. All these indicate that these deep earthquakes are initiated by the Western Pacific Plate which is thrusting under the continent of northeast China.