为查明蓬莱近海岸的地应力状态,开展了2个钻孔(深度小于200m)的水压致裂地应力测量工作,并与长岛附近海域3个钻孔的地应力状态进行了对比,采用回归分析方法,分析了该地区地应力随深度变化的特征,结合最大剪应力与平均主应力之比(μ m)...为查明蓬莱近海岸的地应力状态,开展了2个钻孔(深度小于200m)的水压致裂地应力测量工作,并与长岛附近海域3个钻孔的地应力状态进行了对比,采用回归分析方法,分析了该地区地应力随深度变化的特征,结合最大剪应力与平均主应力之比(μ m)和侧压力系数( K′)探讨了研究区的断层稳定性。结果表明:蓬莱近海岸和长岛海域的地应力状态基本一致,最大水平主应力方向主要表现为北东东至东西向,这与华北的区域应力场相一致;水平应力的梯度大于环渤海圈的平均地应力梯度;研究区浅部三向主应力相对大小以 S H >S h >S v 为主,这有利于逆断层的活动;研究区 K′值和μ m值均较高,分布区间分别为:2.76~3.98和0.47~0.59;陆区断层与区域应力方向均以较大角度相交,处于稳定的状态;海域的北西西向和北东向断层与区域应力场的方向夹角较小,如果区域应力持续增强,将有利于走滑断层的活动,这与震源机制以走滑型地震为主相符。研究结果对研究区内断层稳定性的评价和重大工程的设计及施工都具有重要参考意义。展开更多
In the Longmenshan thrust belt,the Dayi seismic gap,an area with few earthquakes,is located between the ruptures of the 2008 Wenchuan Earthquake and the 2013 Lushan Earthquake,with a length of approximately 40–60 km....In the Longmenshan thrust belt,the Dayi seismic gap,an area with few earthquakes,is located between the ruptures of the 2008 Wenchuan Earthquake and the 2013 Lushan Earthquake,with a length of approximately 40–60 km.To date,however,the extent of the seismic hazard of the Dayi seismic gap and whether this gap is under high stress are still hotly debated.To further evaluate the seismic hazard of the Dayi seismic gap with regard to stress,two boreholes(1,000 and 500 m deep)were arranged to carry out hydraulic fracturing in situ stress measurement on either side of the Shuangshi-Dachuan fault zone.This zone has a high seismic hazard and the capacity to undergo surface rupture.Through the analogy of this new data with stability analysis using Byerlee’s Law and existing stress measurement data collected before strong earthquakes,the results show that the area surrounding the Shuangshi-Dachuan fault zone in the Dayi seismic gap(Dachuan Town)is in a state of high in situ stress,and has the conditions necessary for friction slip,with the potential hazard of moderate to strong earthquakes.Our results are the first to reveal the in situ stress profile at a depth of 1,000 m in the Dayi seismic gap,and provide new data for comprehensive evaluation of the seismic hazard in this seismic gap,which is of great significance to explore the mechanism of earthquake occurrence and to help mitigate future disaster.展开更多
文摘为查明蓬莱近海岸的地应力状态,开展了2个钻孔(深度小于200m)的水压致裂地应力测量工作,并与长岛附近海域3个钻孔的地应力状态进行了对比,采用回归分析方法,分析了该地区地应力随深度变化的特征,结合最大剪应力与平均主应力之比(μ m)和侧压力系数( K′)探讨了研究区的断层稳定性。结果表明:蓬莱近海岸和长岛海域的地应力状态基本一致,最大水平主应力方向主要表现为北东东至东西向,这与华北的区域应力场相一致;水平应力的梯度大于环渤海圈的平均地应力梯度;研究区浅部三向主应力相对大小以 S H >S h >S v 为主,这有利于逆断层的活动;研究区 K′值和μ m值均较高,分布区间分别为:2.76~3.98和0.47~0.59;陆区断层与区域应力方向均以较大角度相交,处于稳定的状态;海域的北西西向和北东向断层与区域应力场的方向夹角较小,如果区域应力持续增强,将有利于走滑断层的活动,这与震源机制以走滑型地震为主相符。研究结果对研究区内断层稳定性的评价和重大工程的设计及施工都具有重要参考意义。
基金supported by the National Natural Science Foundation of China(Grant Nos.41941016,U1839204,42074105)the National Key R&D Program of China(Grant No.2018YFC1504104)the special project for Basic Scientific Research Business of the National Institute of Natural Hazards,Ministry of Emergency Management(Grant No.ZDJ2019-20)。
文摘In the Longmenshan thrust belt,the Dayi seismic gap,an area with few earthquakes,is located between the ruptures of the 2008 Wenchuan Earthquake and the 2013 Lushan Earthquake,with a length of approximately 40–60 km.To date,however,the extent of the seismic hazard of the Dayi seismic gap and whether this gap is under high stress are still hotly debated.To further evaluate the seismic hazard of the Dayi seismic gap with regard to stress,two boreholes(1,000 and 500 m deep)were arranged to carry out hydraulic fracturing in situ stress measurement on either side of the Shuangshi-Dachuan fault zone.This zone has a high seismic hazard and the capacity to undergo surface rupture.Through the analogy of this new data with stability analysis using Byerlee’s Law and existing stress measurement data collected before strong earthquakes,the results show that the area surrounding the Shuangshi-Dachuan fault zone in the Dayi seismic gap(Dachuan Town)is in a state of high in situ stress,and has the conditions necessary for friction slip,with the potential hazard of moderate to strong earthquakes.Our results are the first to reveal the in situ stress profile at a depth of 1,000 m in the Dayi seismic gap,and provide new data for comprehensive evaluation of the seismic hazard in this seismic gap,which is of great significance to explore the mechanism of earthquake occurrence and to help mitigate future disaster.
