Three-dimensional P-and S-wave velocities（vP,vS）,Poisson＇s ratio（σ）,crack-density（ε） and bulk-sound velocity（vφ） structures along the slab upper boundary beneath the fore-arc regions were determined using ...Three-dimensional P-and S-wave velocities（vP,vS）,Poisson＇s ratio（σ）,crack-density（ε） and bulk-sound velocity（vφ） structures along the slab upper boundary beneath the fore-arc regions were determined using a large number of high-quality P-wave and S-wave arrival times from both onshore and offshore earthquakes in Japan.The velocity and Poisson＇s ratio images provide a compelling evidence for a highly hydrated and serpentinized fore-arc mantle and fluid-bearing anomalous low velocity and high Poisson＇s ratio associated with slab dehydration under the fore-arc areas.Most great thrust earthquakes（M〉7.5） occurred at or close to the high-velocity areas along the slab interface under the fore-arc areas,suggesting strong interplate coupling（asperities） with slab subduction.On the other hand,prominent low-velocity anomalies were revealed along the slab upper boundary,which may reflect weak coupled or decoupled patches（aseismicity） of the plates due to serpentinization of the fore-arc mantle wedge.The crack-density and bulk-sound velocity images,calculated from the corresponding velocity models,indicate that the interplate coupling in northeastern Japan is different from that under central and southwestern Japan owing to differences between the tectonic backgrounds of the subduction system,such as the geological age,thermal regime and dipping angle of the oceanic plates.A comparison between fluid-related anomalies of Japan,Cascadia,Chile,and Costa Rica subduction zones suggests that seismic mantle may be common in fore-arc settings and these reflect similar 3-D seismic structures relatively to fluid liberating processes.We consider that the fluid-bearing anomalies along the interface of the subducting slab,attributing to processes such as slab dehydration and serpentinization of the fore-arc mantle,are mainly contributed to the interplate coupling and the repeated generation of the great thrust earthquakes under the fore-arc regions in Japan.展开更多
Master event location method was described in detail in this paper. Some problems in the application of master event method have been analyzed and some improvements of the method have been made. As compared the locat...Master event location method was described in detail in this paper. Some problems in the application of master event method have been analyzed and some improvements of the method have been made. As compared the location results of MS>=3.0 earthquakes of Jiashi swarm obtained by using this method with that by the traditional absolute method, the result obtained by using the master event method shows more reasonable and more consistent with that from the focal mechanism solutions. After relocation, we can see, the epicenters of M>=5.0 earthquakes show an echelon-type alignment along NNW-SSE direction, and all earthquakes concentrate nearly in a volume region about 30 km (N-S) × 15 km (E-W) × 15 km (U-D). Earthquake focal depths are mainly in the range of 15-28 km.展开更多
The high-resolution hypocenter locations of the mainshocks on July 21 (M6.2) and October 16, 2003 (M6.1) and their aftershock sequences are determined in Dayao, Yunnan by using a double-difference earthquake location ...The high-resolution hypocenter locations of the mainshocks on July 21 (M6.2) and October 16, 2003 (M6.1) and their aftershock sequences are determined in Dayao, Yunnan by using a double-difference earthquake location algorithm. The results show that the epicenters of the two mainshocks are very close to each other and the distribution of the aftershock sequence appears to be very linear. The distribution of the earthquake sequence is very consistent with the focal mechanism, and both mainshocks are of nearly vertical right-lateral fault. Unlike most other double earthquakes in the Yunnan area, the aftershock distribution of the M6.2 and M6.1 Dayao earthquakes does not appear to be a conjugated distribution but to be in a line, and there are some stacks in the two earthquake sequences. It can be inferred that they are all controlled by the same fault. The distribution of aftershocks is asymmetrical with respect to the mainshock location and appears to be unilateral. The aftershocks of the M6.2 mainshock centralize in the northwest of M6.2 earthquake and the aftershocks of the M6.1 earthquake are in the southeast of the mainshock, moreover, the M6.1 earthquake appears to be another rupture on the southeastern extension of the same fault as the M6.2 earthquake. The results of Coulomb failure static stress changes Δσ_f show that the earthquake on July 21 (M6.2) apparently triggered the earthquake on October 16 (M6.1), the two mainshocks have stress triggering to their off-fault aftershocks to different extents, and the M6.5 earthquake that occurred in Yao’an in 2000 also triggered the occurrence of the two Dayao earthquakes.展开更多
To better understand repeatability of strong earthquakes in previously ruptured zones during one seismogenic period, we studied the rupture zones of the doublet of M6 earthquakes in Zhongba region of southcentral Tibe...To better understand repeatability of strong earthquakes in previously ruptured zones during one seismogenic period, we studied the rupture zones of the doublet of M6 earthquakes in Zhongba region of southcentral Tibet, China, in 11 July 2004 and 7 April 2005, respectively. We focused on the overlapping degree of two strong quakes’ aftershock areas one week after the mainshocks by using the SQH station in China Seismic Network and a 68-stations temporary broadband seismic array, a part of the international HI-CLIMB project. About 115 local earthquakes were recorded in one week after the mainquakes, and we located these earthquakes by master event relative location （MERL） method. We also used this method to relocate 31 other M3.7 ＋ earthquakes from 1 July 2004 to 1 July 2005. Meanwhile, we studied two mainshocks’ coseismic ruptures with satellite interferometric synthetic aperture radar （InSAR）. Our results show that the ruptured zones of the two earthquakes do not overlapp substantially, either from early aftershock data or from InSAR inversions.展开更多
基金supported by the research grants of the National Natural Science Foundation of China(Nos.40872148 and 40974024)the New Century Excellent Talents in University,Ministry of Education(NCET2009)
文摘Three-dimensional P-and S-wave velocities（vP,vS）,Poisson＇s ratio（σ）,crack-density（ε） and bulk-sound velocity（vφ） structures along the slab upper boundary beneath the fore-arc regions were determined using a large number of high-quality P-wave and S-wave arrival times from both onshore and offshore earthquakes in Japan.The velocity and Poisson＇s ratio images provide a compelling evidence for a highly hydrated and serpentinized fore-arc mantle and fluid-bearing anomalous low velocity and high Poisson＇s ratio associated with slab dehydration under the fore-arc areas.Most great thrust earthquakes（M〉7.5） occurred at or close to the high-velocity areas along the slab interface under the fore-arc areas,suggesting strong interplate coupling（asperities） with slab subduction.On the other hand,prominent low-velocity anomalies were revealed along the slab upper boundary,which may reflect weak coupled or decoupled patches（aseismicity） of the plates due to serpentinization of the fore-arc mantle wedge.The crack-density and bulk-sound velocity images,calculated from the corresponding velocity models,indicate that the interplate coupling in northeastern Japan is different from that under central and southwestern Japan owing to differences between the tectonic backgrounds of the subduction system,such as the geological age,thermal regime and dipping angle of the oceanic plates.A comparison between fluid-related anomalies of Japan,Cascadia,Chile,and Costa Rica subduction zones suggests that seismic mantle may be common in fore-arc settings and these reflect similar 3-D seismic structures relatively to fluid liberating processes.We consider that the fluid-bearing anomalies along the interface of the subducting slab,attributing to processes such as slab dehydration and serpentinization of the fore-arc mantle,are mainly contributed to the interplate coupling and the repeated generation of the great thrust earthquakes under the fore-arc regions in Japan.
文摘Master event location method was described in detail in this paper. Some problems in the application of master event method have been analyzed and some improvements of the method have been made. As compared the location results of MS>=3.0 earthquakes of Jiashi swarm obtained by using this method with that by the traditional absolute method, the result obtained by using the master event method shows more reasonable and more consistent with that from the focal mechanism solutions. After relocation, we can see, the epicenters of M>=5.0 earthquakes show an echelon-type alignment along NNW-SSE direction, and all earthquakes concentrate nearly in a volume region about 30 km (N-S) × 15 km (E-W) × 15 km (U-D). Earthquake focal depths are mainly in the range of 15-28 km.
基金This project was sponsored by the National Programon KeyBasic Research Projects (2004CB418406) ,the Programfor the Tenth"Five-Year Plan"of China (2004BA601B01-04-03) andthe Joint Earthquake Science Foundation of China (606042) .
文摘The high-resolution hypocenter locations of the mainshocks on July 21 (M6.2) and October 16, 2003 (M6.1) and their aftershock sequences are determined in Dayao, Yunnan by using a double-difference earthquake location algorithm. The results show that the epicenters of the two mainshocks are very close to each other and the distribution of the aftershock sequence appears to be very linear. The distribution of the earthquake sequence is very consistent with the focal mechanism, and both mainshocks are of nearly vertical right-lateral fault. Unlike most other double earthquakes in the Yunnan area, the aftershock distribution of the M6.2 and M6.1 Dayao earthquakes does not appear to be a conjugated distribution but to be in a line, and there are some stacks in the two earthquake sequences. It can be inferred that they are all controlled by the same fault. The distribution of aftershocks is asymmetrical with respect to the mainshock location and appears to be unilateral. The aftershocks of the M6.2 mainshock centralize in the northwest of M6.2 earthquake and the aftershocks of the M6.1 earthquake are in the southeast of the mainshock, moreover, the M6.1 earthquake appears to be another rupture on the southeastern extension of the same fault as the M6.2 earthquake. The results of Coulomb failure static stress changes Δσ_f show that the earthquake on July 21 (M6.2) apparently triggered the earthquake on October 16 (M6.1), the two mainshocks have stress triggering to their off-fault aftershocks to different extents, and the M6.5 earthquake that occurred in Yao’an in 2000 also triggered the occurrence of the two Dayao earthquakes.
基金supported jointly by Joint Seismological Science Foundation of China (Nos.200808078 and 200708035)
文摘To better understand repeatability of strong earthquakes in previously ruptured zones during one seismogenic period, we studied the rupture zones of the doublet of M6 earthquakes in Zhongba region of southcentral Tibet, China, in 11 July 2004 and 7 April 2005, respectively. We focused on the overlapping degree of two strong quakes’ aftershock areas one week after the mainshocks by using the SQH station in China Seismic Network and a 68-stations temporary broadband seismic array, a part of the international HI-CLIMB project. About 115 local earthquakes were recorded in one week after the mainquakes, and we located these earthquakes by master event relative location （MERL） method. We also used this method to relocate 31 other M3.7 ＋ earthquakes from 1 July 2004 to 1 July 2005. Meanwhile, we studied two mainshocks’ coseismic ruptures with satellite interferometric synthetic aperture radar （InSAR）. Our results show that the ruptured zones of the two earthquakes do not overlapp substantially, either from early aftershock data or from InSAR inversions.
