摘要
位于南北地震带南段的云南地区是中国大陆内部地震活动最强的地区之一,近年来该区地震活动频繁,展开对该区的探测与研究对人们认识地震孕震背景及板块相互运动具有重要意义.在中国地震局＂中国地震科学台阵探测——南北地震带南段＂行业专项的支持下,2011年底中国地震局地球物理勘探中心在滇南沿镇康—泸西一线布设一条近东西向的深地震宽角反射/折射探测剖面.该探测剖面跨越三江褶皱系、扬子地台、华南地块等多个地质构造单元,同时穿越南汀河断裂、澜沧江断裂、红河断裂带、小江断裂带等多个重要断裂带.探测剖面长600km,沿线共布设11个炮点和400余台三分量地震数字仪进行爆破和接收.本文利用有限差分和时间项方法对沿线11炮初至波资料进行了计算处理,获取了探测剖面的基底速度结构.研究结果表明：沿线不同地质构造单元基底界面形态起伏变化剧烈,其深度在1.0~7.0km范围内变化,速度横向不均匀性明显.在测线西端地表速度约4.6km·s^-1,基底深度较浅,起伏变化不大;地表速度在三江褶皱系下降至4.3km·s^-1,而基底埋深达7.0km左右.在扬子地台基底埋深有一个缓慢的变浅,基底深度约5.0km,地表速度约4.5km·s^-1.测线在东端进入华南块体,基底深度迅速变浅,甚至出露于地表,地表速度增至约5.2km·s^-1.在速度等值线变化剧烈的地方与该区分布的断裂带有很好的对应关系,尤其是在红河断裂带两侧速度等值线及界面形态变化剧烈,该特征在首波的记录截面图上也能清晰的体现.本结果为进一步研究该区强震发生背景及深部动力学意义提供了重要的科学依据.
Yunnan province,located in the southern section of the North-South seismic（SSNSS）belt,is one of the areas with most active seismicity in China mainland,where frequentearthquakes have occurred in recent years.Observations and research in this region are of important significance to understand interaction of plates and geodynamic background.Under the support of the seismic industry special project of China Earthquake Administration（CEA）＂China Earthquake Scientific Array Detection-SSNSS＂,a nearly EW-trending deep seismic wide-angle reflection/refraction profile was deployed along Zhenkang-Luxi by Geophysical Exploration Center of CEA at the end of 2011.This profile crosses through a number of major tectonic units（such as the Sanjiang fold system,Yangzi platform and South China block）and a series of seismic belts（e.g.,the Nanting river fault,Lancangjiang fault,Red River fault and Xiaojiang fault etc.）.The length of this profile is 600 km,and the numbers of shots and three-component seismometers are 11 and 400,respectively.In this paper,the finite difference and time-terms methods are used to process the first arrival times for 11 shots of this profile,and the basement velocity structure in this area is obtained.The results show that the shape of basement interface of different tectonic units changes dramatically,with depths ranging from 1.0km to 7.0km.The deepest point of the basement is about 7.0km in the Sanjiang fold system,while the basement is as shallow as about 1.0km in the Zuogong-Gengma fold system.In the Yangzi block,the basement depth becomes shallow slowly,which is about 5.0km on average.The eastern segment of this profile is the South China block,where the basement depth shallows rapidly,even exposes on the surface.The lateral velocity heterogeneity is obvious along this profile,and the location of velocity contours with drastic change is consistent with the fault distribution in this area.The surface velocity is relatively high,about 5.2km·s^-1,in the South China block,and down to4.3km·s^-1 and 4.5km·s^-1 in the Sanjiang fold system and Yangzi platform,respectively,while increasing to 4.6km·s^-1 in the Zuogong-Gengma fold system.Normally,the velocity change is obvious in the vicinity of fault zones,especially showing obvious differences on the basement interfere and both sides of the Red River fault zone,which is clear in the record section of Pg waves.Generally,the stress is easy to accumulate and release at the place where basement interfere and velocity contours change dramatically,and active faults cross each other.Therefore,the frequent earthquakes in this area are closely related to the distribution of these faults.These results are consistent with previous work,and provide a scientific basis for the further research on the background of strong earthquakes and its deep dynamic significance in this region.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第11期3917-3927,共11页
Chinese Journal of Geophysics
基金
国家自然科学基金项目(41404049
41474077)
地震科技星火计划项目(XH13035)
中国地震科学台阵探测--南北地震带南段(201008001)
中国地震局地球物理勘探中心青年优秀科技人才项目(SFGEC2014004)联合资助
中国地震局地球物理勘探中心论著号RCEG201409
关键词
南北地震带南段
有限差分方法
时间项方法
红河断裂带
Southern section of North-South seismic belt
Finite difference method
Time-terms method
Red River fault zone
