松潘—甘孜造山带地壳速度结构  

CRUSTAL STRUCTURE BENEATH THE SONGPAN-GARZE OROGENIC BELT

作　　者：王椿镛[1] 韩渭宾[2] 吴建平[1] 楼海[1] 白志明[1] 

机构地区：[1]中国地震局地球物理研究所,中国北京100081 [2]四川省地震局,中国成都610041

出　　处：《地震学报》2003年第3期229-241,共13页Acta Seismologica Sinica

基　　金：国家基础研究发展规划项目 (编号G19980 4 0 70 0 /子课题 95 13 0 2 0 3)资助

摘　　要：位于川西地区的奔子栏—唐克深地震测深剖面以NNE走向穿越松潘—甘孜造山带 .根据人工地震记录分析得到的震相走时和相关的振幅信息 ,确定了该剖面二维P波地壳速度结构 .剖面的地壳结构可分为 5层 ,其中第 1,2 ,3层为上地壳 ;第 4 ,5层为下地壳 .上地壳中部普遍存在低速异常带 ,但龙日坝以北 ,这一低速带与其上覆的低速基底合为一体 .同时 ,沿剖面的地壳速度结构具有较强的横向变化 .据此 ,可将剖面分为 4段 ,即甘孜—理塘断裂以南、甘孜—理塘断裂至鲜水河断裂、鲜水河断裂至龙日坝断裂和龙日坝断裂以北 .这与区域构造划分基本一致 .地壳厚度沿测线从南西向北东逐渐减薄 ,即从金沙江畔的 6 2km减小到黄河附近的 5 2km .根据PmP震相分析 ,莫霍界面深度在鲜水河断裂两侧没有明显变化 .全剖面的地壳平均速度较低 ,为 6 .30km/s.奔子栏—唐克剖面揭示了该地区的“造山带”型地壳上地幔结构特征 .鲜水河断裂带位于剖面的中部 ,该地区的上地壳速度为正异常 ,而下地壳和上地幔顶部存在负异常 .笔者认为 ,这是一类有利于强震孕育和发生的深部构造环境 .The Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Songpan-Garze orogenic belt with trend of NNE. Based on the travel times and the related amplitudes of phases in the record sections, the 2-D P-wave crustal structure was ascertained in this paper. The velocity structure has quite strong lateral variation along the profile. The crust is divided into 5 layers, where the first, second and third layer belong to the upper crust, the forth and fifth layer belong to the lower crust. The low velocity anomaly zone generally exists in the central part of the upper crust on the profile, and it integrates into the overlying low velocity basement in the area to the north of Ma′erkang. The crustal structure in the section can be divided into 4 parts: in the south of Garze-Litang fault, between Garze-Litang fault and Xianshuihe fault, between Xianshuihe fault and Longerba fault and in the north of Longerba fault, which are basically coincided with the regional tectonics division. The crustal thickness decreases from southwest to northeast along the profile, that is, from 62 km in the region of the Jinshajiang River to 52 km in the region of the Yellow River. The Moho discontinuity does not obviously change across the Xianshuihe fault based on the PmP phase analysis. The crustal average velocity along the profile is lower, about 6.30 km/s. The Benzilan-Tangke profile reveals that the crust in the study area is orogenic. The Xianshuihe Fault belt is located in the central part of the profile, and the velocity is positive anomaly on the upper crust, and negative anomaly on the lower crust and upper mantle. It is considered as a deep tectonic setting in favor of strong earthquake′s accumulation and occurrence.

关 键 词：松潘-甘孜造山带 地壳速度结构 地震测深剖面 人工地震记录 震相走时 振幅信息 PmP震相分析 青藏高原 地壳上地幔结构 降升机制 

分 类 号：P542.1[天文地球—构造地质学] P631.4[天文地球—地质学]