Rock mass large deformation in underground powerhouse caverns has been a severe hazard in hydropower engineering in Southwest China.During the development of rock mass large deformation,a sequence of fractures was gen...Rock mass large deformation in underground powerhouse caverns has been a severe hazard in hydropower engineering in Southwest China.During the development of rock mass large deformation,a sequence of fractures was generated that can be monitored using microseismic(MS)monitoring techniques.Two MS monitoring systems were established in two typical underground powerhouse caverns featuring distinct geostress levels.The MS b-values associated with rock mass large deformation and their temporal variation are analysed.The results showed that the MS bvalue in course of rock mass deformation was less than 1.0 in the underground powerhouse caverns at a high stress level while larger than 1.5 at a low stress level.Prior to the rock mass deformation,the MS b-values derived from both the high-stress and low-stress underground powerhouse caverns show an incremental decrease over 10%within 10 d.The results contribute to understanding the fracturing characteristics of MS sources associated with rock mass large deformation and provide a reference for early warning of rock mass large deformation in underground powerhouse caverns.展开更多
The parameter b(commonly referred to as the b-value)is one of the most significant seismic parameters to describe the seismicity of an investigated region.In this study,the structural framework of the Sar?g?l-Buldan r...The parameter b(commonly referred to as the b-value)is one of the most significant seismic parameters to describe the seismicity of an investigated region.In this study,the structural framework of the Sar?g?l-Buldan region located in the intersection area of the western Anatolian graben system in Turkey was investigated by using seismicity and gravity data.As known,western Anatolia is one of the most seismically active regions of the Anatolian plate.Therefore,seismic activity in this region is very high.Analysis of the Bouguer gravity data enabled to define the shallow subsurface structure of the study area.Results from the gravity analysis indicated that the sediment basement depth varied from 0.1 km and 2.1 km.We also detected many NW-SE,E-W,and NESW trending lineaments that may be faults or fractures,and the NW-SE trending the Denizli basin lies to the east of the Ala?ehir basin.We observed that the findings from this analysis seem compatible with the regional geological trend.In addition to this,the seismicity of the region was analyzed by using the frequency-magnitude distribution to find out the seismic hazard risk.The most useful way in the analysis of the seismic hazard studies is to reveal the location of the earthquake boundary,which produces devastating big seismic events because such studies make it possible to forecast the location of possible future earthquakes and improve seismic hazard maps.The b-value for this study region was estimated by using the maximum likelihood method.Variations in the b-value were observed,which range from≈0.2 to 2.A higher b-value was detected in the Buldan horst and surrounding area.In contrast to this,lower bvalues were observed in the northeast part of the interaction region between the Denizli and the Ala?ehir grabens.The positive Bouguer anomaly values as high as+10 m Gal and low b-values in the north-eastern part of the study region were interpreted as indicating a thinner crustal root.In comparison,negative Bouguer anomaly values were observed in the Alasehir and the Denizli grabens.Also,in these grabens,intermediate to high b-values were found.This suggests that there is a relation between gravity anomaly and b-value.This relation is strongly related to the normal faulting mechanism existing in the region.展开更多
基金Projects(51809221,51679158)supported by the National Natural Science Foundation of ChinaProject(KFJJ20-06M)supported by the State Key Laboratory of Explosion Science and Technology(Beijing Institute of Technology),China。
文摘Rock mass large deformation in underground powerhouse caverns has been a severe hazard in hydropower engineering in Southwest China.During the development of rock mass large deformation,a sequence of fractures was generated that can be monitored using microseismic(MS)monitoring techniques.Two MS monitoring systems were established in two typical underground powerhouse caverns featuring distinct geostress levels.The MS b-values associated with rock mass large deformation and their temporal variation are analysed.The results showed that the MS bvalue in course of rock mass deformation was less than 1.0 in the underground powerhouse caverns at a high stress level while larger than 1.5 at a low stress level.Prior to the rock mass deformation,the MS b-values derived from both the high-stress and low-stress underground powerhouse caverns show an incremental decrease over 10%within 10 d.The results contribute to understanding the fracturing characteristics of MS sources associated with rock mass large deformation and provide a reference for early warning of rock mass large deformation in underground powerhouse caverns.
文摘The parameter b(commonly referred to as the b-value)is one of the most significant seismic parameters to describe the seismicity of an investigated region.In this study,the structural framework of the Sar?g?l-Buldan region located in the intersection area of the western Anatolian graben system in Turkey was investigated by using seismicity and gravity data.As known,western Anatolia is one of the most seismically active regions of the Anatolian plate.Therefore,seismic activity in this region is very high.Analysis of the Bouguer gravity data enabled to define the shallow subsurface structure of the study area.Results from the gravity analysis indicated that the sediment basement depth varied from 0.1 km and 2.1 km.We also detected many NW-SE,E-W,and NESW trending lineaments that may be faults or fractures,and the NW-SE trending the Denizli basin lies to the east of the Ala?ehir basin.We observed that the findings from this analysis seem compatible with the regional geological trend.In addition to this,the seismicity of the region was analyzed by using the frequency-magnitude distribution to find out the seismic hazard risk.The most useful way in the analysis of the seismic hazard studies is to reveal the location of the earthquake boundary,which produces devastating big seismic events because such studies make it possible to forecast the location of possible future earthquakes and improve seismic hazard maps.The b-value for this study region was estimated by using the maximum likelihood method.Variations in the b-value were observed,which range from≈0.2 to 2.A higher b-value was detected in the Buldan horst and surrounding area.In contrast to this,lower bvalues were observed in the northeast part of the interaction region between the Denizli and the Ala?ehir grabens.The positive Bouguer anomaly values as high as+10 m Gal and low b-values in the north-eastern part of the study region were interpreted as indicating a thinner crustal root.In comparison,negative Bouguer anomaly values were observed in the Alasehir and the Denizli grabens.Also,in these grabens,intermediate to high b-values were found.This suggests that there is a relation between gravity anomaly and b-value.This relation is strongly related to the normal faulting mechanism existing in the region.
