The Ms 6.4 earthquake occurred on May 21,2021 in Yangbi County,Dali Prefecture,Yunnan Province,which was the largest earthquake after the 2014 Jinggu Ms 6.6 earthquake,in western Yunnan.After the earthquake,the rapid ...The Ms 6.4 earthquake occurred on May 21,2021 in Yangbi County,Dali Prefecture,Yunnan Province,which was the largest earthquake after the 2014 Jinggu Ms 6.6 earthquake,in western Yunnan.After the earthquake,the rapid field investigation and earthquake relocation reveal that there was no obvious surface rupture and the earthquake did not occur on pre-existing active fault,but on a buried fault on the west side of Weixi–Qiaohou–Weishan fault zone in the eastern boundary of Baoshan sub-block.Significant foreshocks appeared three days before the earthquake.These phenomena aroused scholars'intensive attention.What the physical process and seismogenic mechanism of the Yangbi Ms 6.4 earthquake are revealed by the foreshocks and aftershocks?These scientific questions need to be solved urgently.展开更多
Successive waveforms of the vertical component recorded by 888 broadband seismic stations in the China Seismography Network from January,2010 to June,2011 are used to investigate the temporal and spatial distribution ...Successive waveforms of the vertical component recorded by 888 broadband seismic stations in the China Seismography Network from January,2010 to June,2011 are used to investigate the temporal and spatial distribution of ambient noise intensity,and the images of ambient noise intensity at the period of 10 s in the Chinese Mainland are obtained. The temporal variation of ambient noise intensity shows some seasonal and periodic characteristics. The maximum ambient noise intensity occurred from January,2011 to March,2011. The spatial distribution images of ambient noise intensity show obvious zoning features,which doesnt correlate with surface geology,suggesting that the noise field is stronger than the site factors. The strength in southeastern coastal areas reaches its maximum and generally decreases toward to inland areas,and arrives at the minimum in the Qinghai-Tibetan Plateau. The zonal intensity distribution is probably correlated with ocean tides from the Philippine Ocean and the Pacific Ocean. It also shows that the influence from the Indian Ocean seems small. However, the ambient noise intensity increases to a certain degree in the Xinjiang area,indicating that the main source of ambient noise in the western area of the Chinese Mainland is not derived from the East and South China Sea,but rather from the deep interior of the Eurasian continent. The ambient noise intensity obtained in this study can supply reference for seismology research based on ambient noise correlation. Moreover,it can supply basic data for attenuation research based on ambient noise, and thus help achieve the object of retrieving the attenuation of Rayleigh waves from ambient noise.展开更多
The paper begins with a brief review of the research history of earthquake size measurement. On this basis, the author pointed out the following points： ① In recent decades, ML, mb （mH ）, Ms magnitude scales are w...The paper begins with a brief review of the research history of earthquake size measurement. On this basis, the author pointed out the following points： ① In recent decades, ML, mb （mH ）, Ms magnitude scales are widely used as measures of earthquake size. However, these magnitude scales have a deficiency of ＂overgeneralization＂ and ＂magnitude saturation＂. Moreover, since they do not fully take into account the regional difference of seismic attenuation, especially the difference of site effects on the amplification of ground motion, these magnitude scales are but inaccurate measures of earthquake size. ② Seismic moment M0 not only has clear physical meaning, but also overcomes the deficiencies existing in ML, mb （mB ） and Ms magnitude scales, so it is the most suitable physical quantity for measuring earthquake size scientifically. In order to continue to use the term ＂magnitude＂, Kanamori defined the moment magnitude scale Act. Although its prerequisite assumptions remain to be studied, it is still a reasonable scale used as a measure of the relative size of an earthquake. ③ For measuring the earthquake size more scientifically, we must make full use of a large amount of waveform data from modern regional digital seismograph networks, strengthen the research on seismic wave attenuation characteristics, site effect, calculation of source parameters and the related scaling relations. In improving the measurement methods for ML, mb （mB ） and Ms magnitude, we should focus on the improvement of Mw scale and carry forward the work as gradually taking Mw magnitude scale as the uniform physical quantity to measure the relative size of earthquakes, so as to lay a more solid foundation for research in earthquake science and earthquake prediction.展开更多
The source rupture process of the MS7.0 Lushan earthquake was here evaluated using 40 long-period P waveforms with even azimuth coverage of stations.Results reveal that the rupture process of the Lushan MS7.0 event to...The source rupture process of the MS7.0 Lushan earthquake was here evaluated using 40 long-period P waveforms with even azimuth coverage of stations.Results reveal that the rupture process of the Lushan MS7.0 event to be simpler than that of the Wenchuan earthquake and also showed significant differences between the two rupture processes.The whole rupture process lasted 36 s and most of the moment was released within the first 13 s.The total released moment is 1.9×1019N m with MW=6.8.Rupture propagated upwards and bilaterally to both sides from the initial point,resulting in a large slip region of 40 km×30 km,with the maximum slip of 1.8 m,located above the initial point.No surface displacement was estimated around the epicenter,but displacement was observed about 20 km NE and SW directions of the epicenter.Both showed slips of less than 40 cm.The rupture suddenly stopped at 20 km NE of the initial point.This was consistent with the aftershock activity.This phenomenon indicates the existence of significant variation of the medium or tectonic structure,which may prevent the propagation of the rupture and aftershock activity.The earthquake risk of the left segment of Qianshan fault is worthy of attention.展开更多
Moment tensor solution, rupture process and rupture characteristics of the great Wenchuan M8.0 earthquake are studied by using 39 long-period P and SH waveforms with evenly azimuth coverage of stations. Our results re...Moment tensor solution, rupture process and rupture characteristics of the great Wenchuan M8.0 earthquake are studied by using 39 long-period P and SH waveforms with evenly azimuth coverage of stations. Our results reveal that the Wenchuan M8.0 event consisted of 5 sub-events of Mw≥7.3 occurring succesively in time and space. Rupture started with a Mw7.3 introductory strike-slip faulting in the first 12 s, then within 12?40 s, two sub-events with Mw7.6 and Mw7.4 occurred within 80 km northeast from the initial point with the dominant rupture type of thrust moving. From 40 to 62 s, a Mw7.5 and Mw7.4 right-lateral strike-slip type of sub-events occurred on the two sides of Beichuan, 120 km away northeast from the initial point. The whole rupture process lasted 105 s and unilaterally propagated from the initial point on the WS section of the Yingxiu-Beichuan fault to the NE direction, resulting in a 230-km-long surface rupture zone and the average surface dislocation is up to 4 m. Two asperities are identified and the whole rupture process is formed by WS and NE parts. In the WS part named Dujiangyang-Wenchuan, where the initial point is located, the rupture process showed reverse faulting with the maximum slip of 8.2 m. Around Mianzhu, rupture changed to right-lateral strike slip faulting and formed a Beichuan-Qingchuan large slip area. The rupture area on this part is about 10 km in depth, shallower than on the WS part. The maximum slip is 6.53 m. Consequently, there formed 2 segments with the surface dislocation larger than 6 m. One is the Dujiangyan-Wenchuan segment with the maximum surface displacement of 6.44 m, the other is the Beichuan-Qingchuan segment with the maximum surface displacement of 6.53 m. This segmentation may have its geological and tectonic background.展开更多
文摘The Ms 6.4 earthquake occurred on May 21,2021 in Yangbi County,Dali Prefecture,Yunnan Province,which was the largest earthquake after the 2014 Jinggu Ms 6.6 earthquake,in western Yunnan.After the earthquake,the rapid field investigation and earthquake relocation reveal that there was no obvious surface rupture and the earthquake did not occur on pre-existing active fault,but on a buried fault on the west side of Weixi–Qiaohou–Weishan fault zone in the eastern boundary of Baoshan sub-block.Significant foreshocks appeared three days before the earthquake.These phenomena aroused scholars'intensive attention.What the physical process and seismogenic mechanism of the Yangbi Ms 6.4 earthquake are revealed by the foreshocks and aftershocks?These scientific questions need to be solved urgently.
基金funded by the“Track Research on Strong Earthquake Risk along Southern Segment of the Longmenshan Fault Zone by Seismological Method(2014IES0100103)”“Dynamic Stress Response of Typical Faults in Reservoir Area to Reservoir Filling and Water Level Variation(2015IES010305)”special projects of basic scientific research of Institute of Earthquake Science,China Earthquake Administration and Joint Inversion of Crustal Upper Mantle Structure in the Taiwan Straits and Its Surrounding Area,Natural Science Foundation of China(NSFC4127405)
文摘Successive waveforms of the vertical component recorded by 888 broadband seismic stations in the China Seismography Network from January,2010 to June,2011 are used to investigate the temporal and spatial distribution of ambient noise intensity,and the images of ambient noise intensity at the period of 10 s in the Chinese Mainland are obtained. The temporal variation of ambient noise intensity shows some seasonal and periodic characteristics. The maximum ambient noise intensity occurred from January,2011 to March,2011. The spatial distribution images of ambient noise intensity show obvious zoning features,which doesnt correlate with surface geology,suggesting that the noise field is stronger than the site factors. The strength in southeastern coastal areas reaches its maximum and generally decreases toward to inland areas,and arrives at the minimum in the Qinghai-Tibetan Plateau. The zonal intensity distribution is probably correlated with ocean tides from the Philippine Ocean and the Pacific Ocean. It also shows that the influence from the Indian Ocean seems small. However, the ambient noise intensity increases to a certain degree in the Xinjiang area,indicating that the main source of ambient noise in the western area of the Chinese Mainland is not derived from the East and South China Sea,but rather from the deep interior of the Eurasian continent. The ambient noise intensity obtained in this study can supply reference for seismology research based on ambient noise correlation. Moreover,it can supply basic data for attenuation research based on ambient noise, and thus help achieve the object of retrieving the attenuation of Rayleigh waves from ambient noise.
基金funded by the Basic R&D Special Fund of Institute of Earthquake Science,CEA(2012IES0204)
文摘The paper begins with a brief review of the research history of earthquake size measurement. On this basis, the author pointed out the following points： ① In recent decades, ML, mb （mH ）, Ms magnitude scales are widely used as measures of earthquake size. However, these magnitude scales have a deficiency of ＂overgeneralization＂ and ＂magnitude saturation＂. Moreover, since they do not fully take into account the regional difference of seismic attenuation, especially the difference of site effects on the amplification of ground motion, these magnitude scales are but inaccurate measures of earthquake size. ② Seismic moment M0 not only has clear physical meaning, but also overcomes the deficiencies existing in ML, mb （mB ） and Ms magnitude scales, so it is the most suitable physical quantity for measuring earthquake size scientifically. In order to continue to use the term ＂magnitude＂, Kanamori defined the moment magnitude scale Act. Although its prerequisite assumptions remain to be studied, it is still a reasonable scale used as a measure of the relative size of an earthquake. ③ For measuring the earthquake size more scientifically, we must make full use of a large amount of waveform data from modern regional digital seismograph networks, strengthen the research on seismic wave attenuation characteristics, site effect, calculation of source parameters and the related scaling relations. In improving the measurement methods for ML, mb （mB ） and Ms magnitude, we should focus on the improvement of Mw scale and carry forward the work as gradually taking Mw magnitude scale as the uniform physical quantity to measure the relative size of earthquakes, so as to lay a more solid foundation for research in earthquake science and earthquake prediction.
基金supported by the National Natural Science Foundation of China(41104033)the Basic Research Project of Institute of Earthquake Science,CEA(2011IES010104)
文摘The source rupture process of the MS7.0 Lushan earthquake was here evaluated using 40 long-period P waveforms with even azimuth coverage of stations.Results reveal that the rupture process of the Lushan MS7.0 event to be simpler than that of the Wenchuan earthquake and also showed significant differences between the two rupture processes.The whole rupture process lasted 36 s and most of the moment was released within the first 13 s.The total released moment is 1.9×1019N m with MW=6.8.Rupture propagated upwards and bilaterally to both sides from the initial point,resulting in a large slip region of 40 km×30 km,with the maximum slip of 1.8 m,located above the initial point.No surface displacement was estimated around the epicenter,but displacement was observed about 20 km NE and SW directions of the epicenter.Both showed slips of less than 40 cm.The rupture suddenly stopped at 20 km NE of the initial point.This was consistent with the aftershock activity.This phenomenon indicates the existence of significant variation of the medium or tectonic structure,which may prevent the propagation of the rupture and aftershock activity.The earthquake risk of the left segment of Qianshan fault is worthy of attention.
基金supported by the Special Program of Earthquake Profession, China Earthquake Administration (Grant No. 200708026)Basic R&D Project of Institute of Earthquake Science, China Earthquake Administration
文摘Moment tensor solution, rupture process and rupture characteristics of the great Wenchuan M8.0 earthquake are studied by using 39 long-period P and SH waveforms with evenly azimuth coverage of stations. Our results reveal that the Wenchuan M8.0 event consisted of 5 sub-events of Mw≥7.3 occurring succesively in time and space. Rupture started with a Mw7.3 introductory strike-slip faulting in the first 12 s, then within 12?40 s, two sub-events with Mw7.6 and Mw7.4 occurred within 80 km northeast from the initial point with the dominant rupture type of thrust moving. From 40 to 62 s, a Mw7.5 and Mw7.4 right-lateral strike-slip type of sub-events occurred on the two sides of Beichuan, 120 km away northeast from the initial point. The whole rupture process lasted 105 s and unilaterally propagated from the initial point on the WS section of the Yingxiu-Beichuan fault to the NE direction, resulting in a 230-km-long surface rupture zone and the average surface dislocation is up to 4 m. Two asperities are identified and the whole rupture process is formed by WS and NE parts. In the WS part named Dujiangyang-Wenchuan, where the initial point is located, the rupture process showed reverse faulting with the maximum slip of 8.2 m. Around Mianzhu, rupture changed to right-lateral strike slip faulting and formed a Beichuan-Qingchuan large slip area. The rupture area on this part is about 10 km in depth, shallower than on the WS part. The maximum slip is 6.53 m. Consequently, there formed 2 segments with the surface dislocation larger than 6 m. One is the Dujiangyan-Wenchuan segment with the maximum surface displacement of 6.44 m, the other is the Beichuan-Qingchuan segment with the maximum surface displacement of 6.53 m. This segmentation may have its geological and tectonic background.
