程海断裂带挽近期活动性研究

NEOID ACTIVITY ON THE CHENGHAI FRACTURE

一、程海断裂带的一般特征程海断裂带位于“康滇古陆”西缘。北自宁蒗,南至弥渡,长逾200公里。断裂带南端与红河断裂带、北端与箐河-金河断裂带及鹤庆-小金河断裂带相交接。(图1) 程海断裂带东西影响宽度50公里左右。主干断裂分为东西两支;东支经大厂、平川一线,一般称之为大厂断裂;西支沿程海、期纳、宾川一线,即狭义的程海断裂带。西支远较东支挽近期活动明显,本文主要讨论西支。程海断裂带东侧是地台区,发育厚逾万米的中生代红色碎屑岩建造;西侧为地槽区。

The Chenghai fracture zone formed in Prepaleozoic Era is a multiple active crust one with evidently activity of tensilecounterclockwise shearing since the neoid period. The Chenghai fracture zone is mainly composed of three categories of faults: the first is a Prequaternary fault without obvious activity; the second is a Prequaternary fault with evident activity; the third is a new-born fault of Quaternary age. The second category of fault is the principal part of the Chenghai fracture zone characterized by large scale, intense activity in neoid period. Its planar shape converges in middle part and diverges at both ends with clear strike-slip in its convergent position and distinct dip-slip in divergent parts. The neoid activity of the Pianjiao—Binchuan segment of the said fracture zone commenced earlier being weaker(an average), and that of the other parts began later being relatively stronger. The mechanical property and arrangement pattern of the third category of fault indicate that the direction of the main compressive stress is northeast to north—northwesterly. The earthquake magnitudes for the Yongsheng earthquake occurred along the Chenghai fracture zone in 1515 ranged from 7.0 to 7.5 and its repeated cycle of strong earthquake would be about 800 years based on calculation.