Many highway bridges were severely damaged or completely collapsed during the 2008 Wenchuan earthquake. A field investigation was carried out in the strongly affected areas and over 320 bridges were examined. Damage t...Many highway bridges were severely damaged or completely collapsed during the 2008 Wenchuan earthquake. A field investigation was carried out in the strongly affected areas and over 320 bridges were examined. Damage to some representative highway bridges is briefly described and a preliminary analysis of the probable causes of the damage is presented in this paper. The most common damage included shear-flexural failure of the pier columns, expansion joint failure, shear key failure, and girder sliding in the transversal or longitudinal directions due to weak connections between girder and bearings. Lessons learned from this earthquake are described and recommendations related to the design of curved and skewed bridges, design of bearings and devices to prevent girder collapse, and ductility of bridge piers are presented. Suggestions for future seismic design and retrofitting techniques for bridges in moderate to severe earthquake areas are also proposed.展开更多
On July 4,2006,a MS5.1 earthquake occurred in Wen'an county of Hebei Province of which the epicenter is near the Beijing city.The six geoelectric field monitoring stations have been in operation for several years ...On July 4,2006,a MS5.1 earthquake occurred in Wen'an county of Hebei Province of which the epicenter is near the Beijing city.The six geoelectric field monitoring stations have been in operation for several years around the Beijing area to examine the relationship between electric field changes and earthquake.This paper firstly explains the principle of the eliminating noise method by using multi-dipole observation system of the geoelectric field.Then the data observed at the stations are studied and a lot of abnormal signals preceding the Wen'an earthquake are selected,of which five abnormal signals of the geoelectric field are finally recognized as the precursory signals.The result shows that 1 there probably exists the precursory signals of the geoelectric field preceding the Wen'an earthquake;2 there are sensitive sites in the spatial distribution of the abnormal variation of the geoelectric field before the quack;3 the anomalous signals do not appear synchronously,and their durations are not same at dif-ferent stations;4 the amplitudes of the abnormal signals recorded at Baodi station are small,but large at Changli station,while the latter is farther from the epicentral area than the former.展开更多
The May 12, 2008 Great Wenchuan Earthquake has resulted in more than 68,858 deaths and losses in the hundreds of billions RMB as of May 30, 2008, and these numbers will undoubtedly increase as more information becomes...The May 12, 2008 Great Wenchuan Earthquake has resulted in more than 68,858 deaths and losses in the hundreds of billions RMB as of May 30, 2008, and these numbers will undoubtedly increase as more information becomes available on the extent of the event. Immediately after the earthquake, the China Earthquake Administration （CEA） responded quickly by sending teams of experts to the affected region, eventually including over 60 staff members from the Institute of Engineering Mechanics （IEM）. This paper reports preliminary information that has been gathered in the first 18 days after the event, covering seismicity, search and rescue efforts, observed ground motions, and damage and loss estimates. The extensive field investigation has revealed a number of valuable findings that could be useful in improving research in earthquake engineering in the future. Once again, this earthquake has shown that the vertical component of ground motion is as significant as horizontal ground motions in the near-source area. Finally, note that as more information is gathered, the numbers reported in this paper will need to be adjusted accordingly.展开更多
Identification of the meta-instable stress state and study of its mechanism and evolution of relevant physical fields would be of great significance for determination of potential seismic risks and estimation of criti...Identification of the meta-instable stress state and study of its mechanism and evolution of relevant physical fields would be of great significance for determination of potential seismic risks and estimation of critical times. In laboratory experiments, that the specimen enters the meta-instable is marked by accelerated stress release. Could we use the experimental result to identify the earthquake in natural conditions? Because the observational data from one station can only reflect the stress state beneath this station, the key problem for identification of the meta-instability is how to recognize regional stress state through observational data from many stations. In this work, we choose the evolution of the temperature field over varied deformation stages during a stick-slip event on a 5 bending fault as an example, and attempt to find the response features of the physical quantity when the fault enters the meta-instable state. We discuss the characteristics of stages for the stress build-up, stress-time process deviating from linearity before instability, meta-instability, instability, and post-instability, respectively. The result shows that the fault instability slide is a conversion process from independent activities of each fault segment to synergism activity. The instability implies completion of the synergism. The stage deviating from linearity is the onset of stress release, and it is also the onset of the synergism. At the meta-instability stages, stress release becomes dominant, while the synergism tends to finish. Therefore, the analysis of the regional overall stress state should not start from individual stations, and instead it should begin with the evolution of the whole deformation field.展开更多
Using broadband seismic records from regional networks, we determined the focal mechanisms and depths of 37 earthquakes in the 2013 M7.0 Lushan earthquake sequence(3.4≤Mw≤5.1) by fitting the three-component waveform...Using broadband seismic records from regional networks, we determined the focal mechanisms and depths of 37 earthquakes in the 2013 M7.0 Lushan earthquake sequence(3.4≤Mw≤5.1) by fitting the three-component waveform data. The results show that the earthquakes are predominantly thrust events, with occasional strike-slip mechanisms. Most earthquakes occurred at depths of 10–20 km. We derived the regional distribution of the average stress field in this area using the damped linear inversion method and the focal mechanisms obtained in this study. The inversion results suggest that the Lushan region and the adjacent area are mostly under compression. The orientations of the maximum principal axes trend NW-SE, with some local differences in the stress distribution at different depths. Compared with the distribution of the stress field in the Wenchuan earthquake area, the stress field in the southwest section of the Longmenshan Fault zone(LFZ) share similar characteristics, predominantly thrust faulting with a few strike-slip events and the maximum compression axes being perpendicular to the LFZ.展开更多
Moment tensor solutions of 88 earthquakes were determined by using the broadband waveform data recorded in six stations within 450 km around the Wenchuan Earthquake sequence by means of the time domain moment tensor i...Moment tensor solutions of 88 earthquakes were determined by using the broadband waveform data recorded in six stations within 450 km around the Wenchuan Earthquake sequence by means of the time domain moment tensor inversion method.It was found that the type of the focal mechanism solution is characteristic of obvious spatial segmentation.There are six segments along the main rupture zone from southwest to northeast,where initially the focal mechanism is of main thrust type,finally of main right-lateral strike-slip type and between these two areas there is a transition zone characterized in multiple types of focal mechanisms appearing in turn.Earthquakes of left-lateral strike-slip type perpendicular to the main rupture zone occurred near Xiaoyudong Town.The stress field of each segment is inversed by means of the FMSI program,and it was found that,along the main rupture zone from southwest to northeast,the direction of the maximum principal stress is gradually changing from near EW to NW-SE,and finally changing back to near EW.展开更多
基金National Natural Science Foundation of China Under Grant No. 90715032 and 50808105National Basic Research Program of China Under Grant No. 2007CB714203
文摘Many highway bridges were severely damaged or completely collapsed during the 2008 Wenchuan earthquake. A field investigation was carried out in the strongly affected areas and over 320 bridges were examined. Damage to some representative highway bridges is briefly described and a preliminary analysis of the probable causes of the damage is presented in this paper. The most common damage included shear-flexural failure of the pier columns, expansion joint failure, shear key failure, and girder sliding in the transversal or longitudinal directions due to weak connections between girder and bearings. Lessons learned from this earthquake are described and recommendations related to the design of curved and skewed bridges, design of bearings and devices to prevent girder collapse, and ductility of bridge piers are presented. Suggestions for future seismic design and retrofitting techniques for bridges in moderate to severe earthquake areas are also proposed.
基金Joint Seismological Science Foundation of China (106079).
文摘On July 4,2006,a MS5.1 earthquake occurred in Wen'an county of Hebei Province of which the epicenter is near the Beijing city.The six geoelectric field monitoring stations have been in operation for several years around the Beijing area to examine the relationship between electric field changes and earthquake.This paper firstly explains the principle of the eliminating noise method by using multi-dipole observation system of the geoelectric field.Then the data observed at the stations are studied and a lot of abnormal signals preceding the Wen'an earthquake are selected,of which five abnormal signals of the geoelectric field are finally recognized as the precursory signals.The result shows that 1 there probably exists the precursory signals of the geoelectric field preceding the Wen'an earthquake;2 there are sensitive sites in the spatial distribution of the abnormal variation of the geoelectric field before the quack;3 the anomalous signals do not appear synchronously,and their durations are not same at dif-ferent stations;4 the amplitudes of the abnormal signals recorded at Baodi station are small,but large at Changli station,while the latter is farther from the epicentral area than the former.
基金Partially the Project 2007CB714205 of the National Basic Research Program of China
文摘The May 12, 2008 Great Wenchuan Earthquake has resulted in more than 68,858 deaths and losses in the hundreds of billions RMB as of May 30, 2008, and these numbers will undoubtedly increase as more information becomes available on the extent of the event. Immediately after the earthquake, the China Earthquake Administration （CEA） responded quickly by sending teams of experts to the affected region, eventually including over 60 staff members from the Institute of Engineering Mechanics （IEM）. This paper reports preliminary information that has been gathered in the first 18 days after the event, covering seismicity, search and rescue efforts, observed ground motions, and damage and loss estimates. The extensive field investigation has revealed a number of valuable findings that could be useful in improving research in earthquake engineering in the future. Once again, this earthquake has shown that the vertical component of ground motion is as significant as horizontal ground motions in the near-source area. Finally, note that as more information is gathered, the numbers reported in this paper will need to be adjusted accordingly.
基金supported by the National Natural Science Foundation of China(Grant Nos. 40872129, 41172180)
文摘Identification of the meta-instable stress state and study of its mechanism and evolution of relevant physical fields would be of great significance for determination of potential seismic risks and estimation of critical times. In laboratory experiments, that the specimen enters the meta-instable is marked by accelerated stress release. Could we use the experimental result to identify the earthquake in natural conditions? Because the observational data from one station can only reflect the stress state beneath this station, the key problem for identification of the meta-instability is how to recognize regional stress state through observational data from many stations. In this work, we choose the evolution of the temperature field over varied deformation stages during a stick-slip event on a 5 bending fault as an example, and attempt to find the response features of the physical quantity when the fault enters the meta-instable state. We discuss the characteristics of stages for the stress build-up, stress-time process deviating from linearity before instability, meta-instability, instability, and post-instability, respectively. The result shows that the fault instability slide is a conversion process from independent activities of each fault segment to synergism activity. The instability implies completion of the synergism. The stage deviating from linearity is the onset of stress release, and it is also the onset of the synergism. At the meta-instability stages, stress release becomes dominant, while the synergism tends to finish. Therefore, the analysis of the regional overall stress state should not start from individual stations, and instead it should begin with the evolution of the whole deformation field.
基金supported by the National Natural Science Foundation of China(Grant No.41104032)the Special Project Seismic Commonwealth Research(Grant No.201308013)
文摘Using broadband seismic records from regional networks, we determined the focal mechanisms and depths of 37 earthquakes in the 2013 M7.0 Lushan earthquake sequence(3.4≤Mw≤5.1) by fitting the three-component waveform data. The results show that the earthquakes are predominantly thrust events, with occasional strike-slip mechanisms. Most earthquakes occurred at depths of 10–20 km. We derived the regional distribution of the average stress field in this area using the damped linear inversion method and the focal mechanisms obtained in this study. The inversion results suggest that the Lushan region and the adjacent area are mostly under compression. The orientations of the maximum principal axes trend NW-SE, with some local differences in the stress distribution at different depths. Compared with the distribution of the stress field in the Wenchuan earthquake area, the stress field in the southwest section of the Longmenshan Fault zone(LFZ) share similar characteristics, predominantly thrust faulting with a few strike-slip events and the maximum compression axes being perpendicular to the LFZ.
基金Supported by the National Key Project of Scientific and Technical Supporting Programs Funded by Ministry of Science & Technology of China (Grant No.2008BAC38B02 and 2006BAC01B02)National Department Public Benefit Research Foundation (Grant No.200708026)
文摘Moment tensor solutions of 88 earthquakes were determined by using the broadband waveform data recorded in six stations within 450 km around the Wenchuan Earthquake sequence by means of the time domain moment tensor inversion method.It was found that the type of the focal mechanism solution is characteristic of obvious spatial segmentation.There are six segments along the main rupture zone from southwest to northeast,where initially the focal mechanism is of main thrust type,finally of main right-lateral strike-slip type and between these two areas there is a transition zone characterized in multiple types of focal mechanisms appearing in turn.Earthquakes of left-lateral strike-slip type perpendicular to the main rupture zone occurred near Xiaoyudong Town.The stress field of each segment is inversed by means of the FMSI program,and it was found that,along the main rupture zone from southwest to northeast,the direction of the maximum principal stress is gradually changing from near EW to NW-SE,and finally changing back to near EW.
