安徽气枪实验固定台层析成像初步结果

Preliminary result of tomography from permanent stations in the Anhui air-gun experiment

为探索气枪震源在探测区域性地壳结构中的应用,2015年10月10～ 20日在长江马鞍山-安庆段开展了气枪流动激发实验（安徽实验）,在20个固定点激发2973炮,中间流动激发1872炮,由周边109个固定台、700个流动台（包括11条测线）进行接收.为获取郯庐断裂带南端较为精细的地壳速度结构,本文利用安徽气枪实验中采集到的固定台数据进行初至P波震相拾取,对20个气枪源、52个台站、335个震相进行体波层析成像,验证了利用气枪震源激发进行体波层析成像的可行性,并得到了P波速度结构的初步研究结果：①利用大容量气枪震源激发可进行三维体波层析成像;②15km深度的成像结果显示出大区域高、低速异常区的清晰轮廓,即从研究区中心向外整体呈现出低-超低-低-高的分布特征,该特征与地质构造背景相关,具有显著的横向不均匀性;③秦岭-大别造山带显示出高速异常,与其深部超高压变质岩相对应,而长江中下游地区整体呈现低速异常,与其特殊的成矿背景相对应.

The Air-gun source has many advantages：economical and environmental protection andexcellent repetition.The method has been used to study changes of the subsurface structure in recent years,and there are a lot of achievements.In order to explore the ability on imaging crust structure using active air-gun source,we conducted an experiment along the Yangzte River from Ma＇anshan to Anqing segment using offshore air-gun source （the Anhui experiment）.2973 shots and 1872air-gun shots were excited at twenty fixed points and were received by 109 permanent stations and 700 mobile stations（11 lines）.Air-gun source can form motivating and observational network densely with the accurate origin time and position.Compare with explosive source,air-gun has a very clear S phase.Thus,air-gun source can reduce the source location error in tomography,and can take full advantage of direct and later phases.To get the crust velocity structure in the southern tip of Tan-Lu fault,we used the data received by permanent stations in the Anhui air-gun experiment to pick P phase,and make tomography by 20air-gun sources,52 permanent stations,and 335 phases.We got a very good preliminary result of P wave velocity and verified the possibility to make tomography using air-gun source：（1） The use of high-capacity air-gun can make 3D body wave tomography.（2）Image of 15km depth shows the clear velocity anomaly outline,which is related to the geological tectonic background with prominent heterogeneity in transverse.（3）The Qinling-Dabie orogenic belt shows high velocity,which is associated with the ultrahigh-pressure metamorphic rocks in depth region,while the Yangtze River region presents low velocity anomaly,corresponding to the special background of mineralization.