西太平洋岛弧地震分布的不均匀性及其成因问题探讨

SPATIAL DIFFERENCES OF THE EARTHQUAKE DISTRIBUTION ALONG THE ISLAND ARCS IN THE WESTERN PACIFIC AND THEIR CAUSES

西太平洋地震活动沿岛弧呈狭窄的带状分布，但在岛弧的延伸方向上及岛弧间存在明显的差异。岛弧两端或岛弧与海岭的交接地段震源密度较大，而岛弧中段密度较小；菲律宾海板块西侧（靠大陆）的岛弧地震活动性较强，其东侧（靠太平洋）的马里亚纳岛弧地震活动性较弱；马里亚纳弧的ＮＮＥ和ＮＥ方向段地震活动比其它的方向段弱。震源密度与地貌格局及弧前构造应力有密切联系，表明导致地震活动的构造应力可能来源于大陆向海洋的运动。

The seismic activity shows a distribution in narrow belt shape along the island arcs of the western Pacific, but the activity frequency differs greatly along island arc stretch or between island arcs. It is indicated that the activity frequency at both ends of island arcs or the cross points of island arcs and submarine ridges is more intense than in the middle, along the island arcs in the west (near the continent) of the Philippine Plate is more intense than the east (near the Pacific Ocean), along the parts in NNE and NE direction of Marianas arc is less intense than the other parts.These facts are closely related to the landform pattern, the forearc stress and island arc movement. It is suggested that these do not support that the Pacific plate moves and extrudes to the continent on its own initiative. The stress causing earthquakes may come from the movement of continent (or island arc) to the ocean.