非地震勘探在四川盆地的应用前景

Application of non-seismic exploration technologies to Sichuan Basin

目前地震勘探的资料品质和分辨率,在四川盆地火山岩的精细识别和山前带推覆体成像方面有一定困难。因此,尝试通过非地震勘探补充地震勘探的不足。根据四川盆地已有的非地震资料,结合现有地质认识分析盆地内地层的重磁电物性特征,设计不同的地质模型来进行正演计算,论证重磁电对深层地质体的探测精度。结果表明:①在地质体埋深大于6.0km情况下,地质体宽度大于2.0km、地质体沉积岩厚度大于1.0km时,引起的重力异常能被识别出来,当密度差大于0.05g/cm^3,在地质体同等宽度的情况下,可探测的地质体厚度可以更小;②天然场源电法勘探点距250m,地质体埋深大于6.0km,地质体宽度大于5.0km引起的电性异常均可探测,当地质体与围岩的电阻率差异大于5倍时,在地质体同等厚度的情况下,电法点距减小,可探测的地质体宽度可以更小。研究结果认为:①非地震勘探精度有能力解决基底断裂和山前带构造的展布格局和构造演化研究;②火山岩、深层裂陷以及古剥蚀面可以引起明显的重磁电异常,非地震勘探技术具有有效的识别能力。

At present,both seismic-data quality and resolution have certain difficulties to intensively identify volcanic rocks and to carry out an imaging of piedmont nappe in Sichuan Basin.In this study,we attempted to adopt non-seismic technologies to compensate some deficiencies occurring in seismic technologies,collected many existing non-seismic data,combined with achieved geological understandings, analyzed gravitational,magnetic,and electrical characteristics,established various geological models for forward calculation, and finally demonstrated an accuracy of gravity,magnetic,and electrical prospecting on deeper geological bodies.Results show that (1) some gravity-induced anomalies may be identified if geological bodies are over 6 000 m deep and 2 000 m wide and their sedimentary rock is more than 1000 m thick.Under geological bodies with same width,the thickness of detectable bodies can be smaller when density difference is greater than 0.05 g/cm^3;and (2) other electric-induced anomalies may also be detectable when the point spacing of electrical prospecting is 250 m for natural field source and geological bodies are more than 6 000 m deep and 5 000 m wide.Under geological bodies with same width,the width of detectable body can be smaller along with a decrease of point spacing when the resistivity difference between body and its surrounding rock is more than 5 times.In conclusion,from the point of accuracy,non-seismic exploration technologies can be used to study the distribution pattern and structural evolution of the basement faults and piedmont structures;volcanic rocks,deeper faulted depressions,and paleo-denudation planes can lead to obvious gravitational,magnetic and electrical anomalies,which also can be identified effectively by means of non-seismic technologies.