南北地震带北段上地幔速度结构成象(Ⅲ)—应用和结果

IMAGING OF VELOCITY STRUCTURE OF THE UPPER MANTLE FOR THE NORTHERN PORTION OF NORTH-SOUTH SEISMIC BELT(Ⅲ)—APPLICATION AND RESULTS

根据地震波走时资料反演得出南北地震带北段地壳和上地幔速度结构,发现在该区上地壳存在三个近东西向的低速条带,其空间展布与该区内现今活动构速基本一致;上地幔速度分布显示在该区似有平行的北东和北西向低速条带相互穿插,总体呈现网状;海原—古浪断裂带在上下地壳及上地幔的速度结构中均表现出相应的低速带,表明它是切穿地壳的深大断裂。通过反演还发现青藏块体的东北部边界大致在天祝—兰州—静宁—千阳—略阳—江油一带。

Based on[1][2], imaging of seismic velocity structure of crust and upper mantle for the northern portion of N-S Seismic Belt is made. The velocity distribution of upper crust exists three low-velocity belts oriented near EW trend, which agrees with recent active fracturing zones, while in upper mante there are a lot of low velocity belts trend NE and NW, which appear network structures across each other. It is pointed out that the Haiyuan-Guyuan fracturing zone may be a great deep fault, being low velocity belts in upper-, lower-crust and uppermantle. Finally, it is suggested that the northeastern boundary of the Qinghai-Xizhang Block may locate along Tianzhu-Lanzhou-Jingning-Qianyang-Lueyang-Jiangyou, by using inversion.