汶川等巨震前M≥5地震活动对比研究
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摘要
本文对汶川、昆仑山口西、察隅和海原等8级巨震前震中距半径15°范围内,震前10年M≥5地震活动的对比研究表明,地震频度和强度的异常表现形式可分为大范围活跃、平静和局部活跃三种,异常展布范围半径为(600±200)km,异常分布受青藏亚板块边界断裂控制,边界断裂外异常不明显。震前无论活动频度或强度的异常增强或减弱,均以未来震中所在和相邻地块(或省区)最明显,异常强度多以突破其历史极值为特征,向外则逐渐减弱。研究区或震中所在省区M≥5地震累计年频次异常,多数于震前1~2年出现高值,个别出现在震前4年。8级巨震震中区均为M≥5地震的弱活动或异常平静区,一般表现为围空区,少数为活动条带,空区大小总体上与震级成正相关。
Comparative study has been made for M≥5 Seismic Activities 10 years before some large earthquakes such as Wenchuan,Kunlunshan,Chayu and Haiyuan wintin an epicentral range of 15°.It is demonstrated that abnormal types of seismicity and magnitude can be calassified into three kinds,i.e.large area acitivity,quiescence and local acitivity,with abnormaly range about(600±200)km.Abnormaly distribution is controlled by boundary faults of Qinghai-Tebetan sub-plate.The increase or decrease of abnormal activity and strength is the most obvious around the future epicenter or nearby crust blocks,characterized by exceeding the historical maximum value and gradually decreasing outward.High values of annual cumulative frequency anomalies of M≥5 earthqukes mostly appeared 1 to 4 years before the mainshock in the study area.The epicentral regions of large M8 earthquakes are areas of weak or quiescent M≥5 activities,generally gap,some belts and the size of the gap positively related to magnitude.
Comparative study has been made for M≥5 Seismic Activities 10 years before some large earthquakes such as Wenchuan,Kunlunshan,Chayu and Haiyuan wintin an epicentral range of 15°.It is demonstrated that abnormal types of seismicity and magnitude can be calassified into three kinds,i.e.large area acitivity,quiescence and local acitivity,with abnormaly range about(600±200)km.Abnormaly distribution is controlled by boundary faults of Qinghai-Tebetan sub-plate.The increase or decrease of abnormal activity and strength is the most obvious around the future epicenter or nearby crust blocks,characterized by exceeding the historical maximum value and gradually decreasing outward.High values of annual cumulative frequency anomalies of M≥5 earthqukes mostly appeared 1 to 4 years before the mainshock in the study area.The epicentral regions of large M8 earthquakes are areas of weak or quiescent M≥5 activities,generally gap,some belts and the size of the gap positively related to magnitude.
引文
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[5]陈立德,付虹.地震预报基础与实践[M].北京:地震出版社,2003.
[6]马宗晋,汪一鹏,张燕平.青藏高原岩石圈现现今变动与动力学汪一鹏[A].中国地震局地质所,青藏高原活动构造基本特征[C].北京:地震出版社,2001.88-103.
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