Based on the borehole strainmeter recordings immediately before the strong earthquakes （Ms〉7.5） during the period from 2001 to 2005 observed at the Taian observation station, Shandong Province, the authors make a s...Based on the borehole strainmeter recordings immediately before the strong earthquakes （Ms〉7.5） during the period from 2001 to 2005 observed at the Taian observation station, Shandong Province, the authors make a systematic and objective examination of the precursor waves of the quakes. The effects of Earth tides with periods larger than 128 min are eliminated through high-pass filtering; and atmospheric-pressure inferences are removed by linear regression. The 2-128 min signals are then separated into six frequency bands by employing the wavelet method. Results indicate that the wavelet method is capable of picking out information of weak variations in the signals. According to the characteristics of the ＇precursor waves＇ obtained from wavelet transformation, the method of overrun ratio analysis is put forward for examination. All the detailed components of the wavelets have been analyzed. For the time series of the overrun rate in all these components, statisitical calculation has been made for the slopes of fit curves, and mean values and standard deviations were obtained and positive-negative slope ratios were analyzed. The three statistical data show that ＇precursor waves＇ are not widely recorded by borehole strainmeter within 15 days before remote strong earthquakes.展开更多
This study involved the construction and explosion of a large-scale(80-meter-long)underdrain and detailed investigations of the damaging impacts of a gas explosion to provide an experimental foundation for similarity ...This study involved the construction and explosion of a large-scale(80-meter-long)underdrain and detailed investigations of the damaging impacts of a gas explosion to provide an experimental foundation for similarity modeling and infrastructural designs.The experiment vividly recreated the scene and explosion damage of the"11.22″explosion accident in Qingdao,China,thus allowing for evaluations of the movements and destruction of the cover plates.The damage mechanism was determined by analyzing the overpressure curves inside and outside the underground canal.It was determined that the cover plates were first lifted by the precursor wave,which induced a maximum overpressure of 0.06 MPa and resulted in explosion venting.The pressure entered the deflagration stage at the end of the explosion.The combustion wave overpressure reached 3.115 MPa close to the initiation point,and had a significant influence on the projectile energy of the cover plates there.Overall,64%of the cover plates were only affected by the precursor wave,while 36%of the cover plates were subjected to both the precursor wave and the combustion wave;these cover plates were severely damaged.The results of this study provide fundamental insights relevant to the prevention and control of underdrain gas explosions.展开更多
基金supported by National Natural Science Foundation of China (40374011)Joint Seismological Science Foundation of China (1040037)
文摘Based on the borehole strainmeter recordings immediately before the strong earthquakes （Ms〉7.5） during the period from 2001 to 2005 observed at the Taian observation station, Shandong Province, the authors make a systematic and objective examination of the precursor waves of the quakes. The effects of Earth tides with periods larger than 128 min are eliminated through high-pass filtering; and atmospheric-pressure inferences are removed by linear regression. The 2-128 min signals are then separated into six frequency bands by employing the wavelet method. Results indicate that the wavelet method is capable of picking out information of weak variations in the signals. According to the characteristics of the ＇precursor waves＇ obtained from wavelet transformation, the method of overrun ratio analysis is put forward for examination. All the detailed components of the wavelets have been analyzed. For the time series of the overrun rate in all these components, statisitical calculation has been made for the slopes of fit curves, and mean values and standard deviations were obtained and positive-negative slope ratios were analyzed. The three statistical data show that ＇precursor waves＇ are not widely recorded by borehole strainmeter within 15 days before remote strong earthquakes.
基金The authors gratefully acknowledge financial support given by the National 135 Key R and D Projects(Grant Nos.2018YFF0301000)as well as from the National Science Foundation of China(Grant Nos.71861167002,51834007).
文摘This study involved the construction and explosion of a large-scale(80-meter-long)underdrain and detailed investigations of the damaging impacts of a gas explosion to provide an experimental foundation for similarity modeling and infrastructural designs.The experiment vividly recreated the scene and explosion damage of the"11.22″explosion accident in Qingdao,China,thus allowing for evaluations of the movements and destruction of the cover plates.The damage mechanism was determined by analyzing the overpressure curves inside and outside the underground canal.It was determined that the cover plates were first lifted by the precursor wave,which induced a maximum overpressure of 0.06 MPa and resulted in explosion venting.The pressure entered the deflagration stage at the end of the explosion.The combustion wave overpressure reached 3.115 MPa close to the initiation point,and had a significant influence on the projectile energy of the cover plates there.Overall,64%of the cover plates were only affected by the precursor wave,while 36%of the cover plates were subjected to both the precursor wave and the combustion wave;these cover plates were severely damaged.The results of this study provide fundamental insights relevant to the prevention and control of underdrain gas explosions.
