川滇实验场地区活动地块边界新划分参考方案

A NEW REFERENCE SCHEME FOR THE DELINEATION OF ACTIVE BLOCK BOUNDARIES IN THE SICHUAN-YUNNAN EXPERIMENTAL SITE

活动地块边界带是现今地壳应力高度积累和构造变形显著集中的区域,地震频发,是研究中国大陆强震活动规律的重要对象。中国地震科学实验场所在的川滇地区位于印度大陆与欧亚板块碰撞和持续会聚引起的强烈变形区,是中国大陆西部与周边板块动力传递的关键部位。根据前人划分活动地块边界带的方案和依据,文中综合分析了地块的整体性、立体性、层次性和活动性,将川滇地区的主要活动断裂带划分为3条一级活动地块边界带和16条次级活动块体边界带。通过川滇地区有记录以来的强震分布特征、地震数量和震级的分带分级性、GNSS揭示的现今变形分区性、速度结构和重力资料反映的地壳深部构造差异性等结果,新的参考方案将金沙江-红河断裂带、甘孜-玉树-鲜水河-安宁河-则木河-小江断裂带、龙门山断裂带归为一级活动地块边界带;丽江-小金河断裂、南汀河断裂、龙日坝断裂等研究区内其他主要活动断裂归为次级活动块体边界带。基于对研究区强震活动、现今变形特征、活动断裂规模、地壳深部结构及古地震等研究成果的综合分析,研究认为一级边界带具备发生M≥7.5大地震的潜力,次级边界带有发生M≥6.5强震的能力。川滇地区活动地块边界新划分的参考方案,可为后续川滇实验场区活动地块之间相互作用的力学数值模拟、强震概率预测分析及大地震危险性评估等提供科学依据。

Active block boundaries represent areas where significant crustal stress accumulates,leading to concentrated tectonic deformation and frequent seismic activity.These boundaries are crucial for understanding the patterns of strong earthquakes within China's Mainland.The China Seismic Experimental Site,located in the Sichuan-Yunnan region,is a key area of tectonic deformation caused by the collision and convergence of the Indian and Eurasian plates.This region plays a vital role in transferring tectonic stress between western China and adjacent plates.This comprehensive study analyzes the integrity,three-dimensional characteristics,hierarchy,and tectonic activity of blocks within the Sichuan-Yunnan region,following established schemes and criteria for defining active block boundaries.After detailed research,the major active fault zones in the region have been divided into three primary active block boundary zones and sixteen secondary boundary zones.A new reference scheme was developed by considering several factors,including the historical distribution of strong earthquakes,the hierarchical patterns of earthquake frequency and magnitude,spatial variations in present-day deformation as revealed by GNSS data,and deep crustal differences indicated by gravity data and velocity structures.The Jinshajiang-Honghe Fault,Ganzi-Yushu-Xianshuihe-Anninghe-Zemuhe-Xiaojiang Fault,and Longmenshan Fault are identified as the primary active block boundary zones,while faults such as the Lijiang-Xiaojinhe,Nantinghe,and Longriba faults are classified as secondary boundary zones.Through an integrated analysis of seismic activity,current deformation patterns,fault sizes,deep crustal structures,and paleoseismic data,the study estimates that the primary boundary zones have the potential to generate earthquakes of magnitude 7.5 or greater,while the secondary boundary zones could produce earthquakes of magnitude 6.5 or greater.The expansion of geophysical exploration,including shallow and deep earth data,has allowed for a transition in the study of active tectonics from surface-focused to depth-focused,from qualitative to quantitative,and from two-dimensional to three-dimensional analysis.By integrating multiple data sources,i.e.regional geology,geophysics,seismicity,and large-scale deformation measurements,this study presents a more refined delineation of active blocks in the Sichuan-Yunnan region.The new delineation scheme provides a scientific basis for future mechanical simulations of interactions between active blocks in the Sichuan-Yunnan Experimental Site.It also offers a framework for assessing the probability of strong earthquakes and evaluating seismic hazards.The purpose of this study is to re-analyze and refine the delineation of active block boundaries using high-resolution,coordinated data while building on previous research.In summary,the Sichuan-Yunnan region’s primary fault zones are divided into three primary and sixteen secondary active block boundary zones.The study concludes that primary boundary zones are capable of generating magnitude 7.5 or greater earthquakes,while secondary zones can produce magnitude 6.5 or greater earthquakes.While the current block delineation scheme offers a valuable foundation,further discussion and refinement of certain secondary boundary zones are needed as detection and observational data improve.This study provides an essential framework for analyzing the dynamic interactions between active blocks,identifying seismogenic environments,and assessing seismic risks in the Sichuan-Yunnan region.