利用气枪重复震源研究祁连山北缘断裂带区域深部波速的时空演化

It is important for understanding the evolution of the Qinghai Tibet Plateau and earthquake mechanism by researching the temporal and spatial evolution of deep stress state in northern margin of the Qilian Mountains located on squeeze suture zone between Qinghai-Tibet Plateau and Alxa block，where have intense tectonic and frequent seismic activities and are particularly concerned to scientists. In recent years a large number of new research results show that using high precision velocity measurement can deduce the underground change of stress state, because it is difficult to measure deep stress state. In order to study the evolution of the regional deep medium in northern margin of the Qilian Mountain, we have built a large capacity repeat airgun source in Qilian mountainside. Preliminary results showed that, seismic signals generated by source can be recorded by station far from 300 km. In this study, we will carry out continuous high-precision velocity measurements by use of large capacity airgun source and dense seismic array which have been built in earthquake-prone fault zone of Northern Qilian Mountains. We intend to study the following scientific questions. (1)To achieve high precision velocity variation measurement through the analysis of the seismic signal inspired by repeated source. (2) Study on the temporal evolution of underground seismic wave velocity in Northern Qilian Mountains. (3) Study on the relationship between the temporal and spatial variation of seismic wave velocity and tectonic activity. In addition, this research will promote the development of new technology for observation, and has practical and theoretical significance to improve the understanding deep changes of the earth medium and reduce the regional disaster.

祁连山北缘地处青藏块体与阿拉善块体挤压缝合地带，该地区构造活动强烈、断裂发育、强震活动频繁，研究该区域深部应力状态的时空演化对于认识青藏高原的演化、地震发生机理具有重要的科学意义。但然而直接测量地震深度范围的应力状态是困难的，近年来大量研究新成果表明通过高精度波速测量能够推演出地下应力状态的变化。为研究祁连山北缘断裂带区域深部介质的演化，我们在祁连山腹地建成了一个大容量气枪重复震源。初步结果表明，该震源重复性好，震源产生的地震信号可以被300km的台站记录到。本研究将利用已建成的大容量气枪震源及周边的地震台阵开展如下研究工作：(1)分析重复震源激发的地震信号，实现高精度波速变化测量；(2)研究祁连山北缘断裂带地区地下波速的时空演化;(3)探讨波速时空变化与地震等构造活动的关系。本研究的开展将促进对于发展新型观测技术，提升对地球介质深部变化的认识和减轻区域灾害都具有实践和理论意义。

根据申请书的研究内容，应用祁连山主动源台网4年多的激发记录资料，开展了主动源激发信号与气枪沉放水深关系研究、主动源数据一致性分析、台网各个台站的多个震相走时变化研究、几次强震发生过程与波速变化的关系分析、固体潮实验及数据分析、气枪信号震相特征模拟和断裂带探测研究，获得了以下的重要结果：1）获得了主动源台网各台站气枪信号不同震相的走时变化特征，对个各个震相走时做了理论射线追踪模拟，确立了气枪最佳沉放深度范围，并建立波形数据库和震相走时特征数据库；2）对3次强震进行了分析研究，发现3次地震发生前后存在近似的走时变化特征，与理论推测结果吻合，为地震预测提供了识别依据或识别模型； 3）应用地震波方法，首次观测到了固体潮对地震波走时的影响，这一观测结果可以说明，应用主动源重复探测方法可适用于强烈地震孕育过程的监测；4）发表论文20篇，其中科技期刊论文13篇（SCI论文2篇），硕士研究生毕业论文5篇，2篇会议论文。获发明专利1项；5）在该课题的支撑下，对主动源研究团队加强了培养，团队被中国地震局评为2019年科技创新团队，一人被评为科技创新领军人才，1人被评为科技创新骨干人才。培养硕士研究生5人（已毕业）。