The rupture process of the May 12, 2008 Ms8.0 Wenchuan earthquake was very complex. To study the rupture zones generated by this earthquake, four dense temporary seismic arrays across the two surface breaking traces o...The rupture process of the May 12, 2008 Ms8.0 Wenchuan earthquake was very complex. To study the rupture zones generated by this earthquake, four dense temporary seismic arrays across the two surface breaking traces of the main-shock were deployed in July and recorded a great amount of aftershocks. This paper focuses on the data interpretation of two arrays across the central main fault, the northern array line 1 and southern array line 3. The fault zone trapped waves recorded by the two arrays were used to study the structure of the central main fault and the difference between the northern and southern portions. The results show that the widths of the rupture zone are about 170-200 m and 200-230 m for northern and southern portions respectively. And the corresponding dip angles are 80° and 70°. The seismic velocity inside the fracture zone is about one half of the host rock. By comparison, the northern portion of the rupture zone is slightly narrower and steeper than the southern portion. Besides these differences, one more interesting and important difference is the positions of the rupture zone with respect to surface breaking traces. At the northern portion, the rupture zone is centered at the surface breaking trace, while at the southern portion it is not but is shifted to the northwest. This difference reflects the difference of rupture behaviors between two portions of the central main fault. The width of the rupture zone is smaller than that of MS.1 Kunlun earthquake though these two earthquakes have almost the same magnitudes. Multiple ruptures may be one factor to cause the narrower rupture zone.展开更多
The great M_S8.0 Wenchuan earthquake on May 12,2008 was generated by abrupt faulting in the Yingxiu-Beichuan fault along the Longmenshan fault zone. The earthquake not only produced surface ruptures along the Yingxiu-...The great M_S8.0 Wenchuan earthquake on May 12,2008 was generated by abrupt faulting in the Yingxiu-Beichuan fault along the Longmenshan fault zone. The earthquake not only produced surface ruptures along the Yingxiu-Beichuan and Guanxian-Jiangyou faults,but also surface ruptures,arching of highway pavement,sand-boils and waterspouts in various degrees in areas such as Shifang and Mianzhu on the Chengdu Plain. To understand the shallow geological structures under the surface rupture zone,a 6350m long high-resolution shallow seismic reflection profile in near-EW direction was performed. This profile is located at Shigu town,Shifang city,where a suspected earthquake surface rupture zone was discovered. In this study,a group interval of 3m,shotpoint interval of 18m,and a 300-channel 25-fold observation system were used. In consideration of both near-surface reflections and dipping interface imaging,we adopted the split-spread geometry and asymmetrical zero-offset receiving technique. To better suppress random-noise and raise the signal-to-noise ratio of seismic data,30 times vertical stacking of vibrator signals was made for each common-shot gather after correlation of individual records. By using the above work method and spread geometry,we obtained high-resolution images of structures in the depth range of 15m～800m after data processing. The result shows the existence of buried thrust faults thrusting to the plain area and back-thrust faults under the surface rupture zone. It also shows that the activity of the buried thrust faults may be the main cause for folding and deformation in near-surface strata and coseismic surface rupturing.展开更多
The data obtained from a high resolution seismic refraction profile, which was carded out in Jiashi, Xinjiang, strong earthquake swarm area, were processed with both finite difference inversion and Hagedoorn refractor...The data obtained from a high resolution seismic refraction profile, which was carded out in Jiashi, Xinjiang, strong earthquake swarm area, were processed with both finite difference inversion and Hagedoorn refractor wavefront imaging technique and the fine upper crustal structure was determined. The results show that the upper crustal structure is relatively well-distributed in laterally and obviously by layers vertically.From surface to 11.0 km depth, there are about four layers. The P wave velocity of top two layers range from 1.65 to 4.5 km/s and their bottom boundaries, the buried depths of which are 0.4, 2.96-3.0 km respectively, are almost horizontal; The third layer is comparatively complicated and its P wave velocity presents inhomogeneous in both laterally and vertically. The bottom boundary of third layer is crystalline basement and shows a little uplift, which seemly suggest that the upper crust had been resisted while the hard Tarim block inserting into Tianshan Mountain; The forth layer is relatively even and its P wave velocity is about 6.3 km/s. There are a lateral velocity variation at the depth of about 4.0 km, and suggest that it has something to do with the hidden Meigaiti fault and Meigaiti-Xiasuhong fault but there are no the structure features about these faults stretching to the surface and passing through the crystalline basement. The seismogenic tectonic of Jiashi strong earthquake swarm at least lies in middle or lower crust beneath 11.0 km depth.展开更多
Large property contrasts between materials in a fault zone and the surrounding rock are often produced by repeating earthquakes. Fault zones are usually characterized by fluid concentration, clay-rich fault gouge, inc...Large property contrasts between materials in a fault zone and the surrounding rock are often produced by repeating earthquakes. Fault zones are usually characterized by fluid concentration, clay-rich fault gouge, increased porosity, and dilatant cracks. Thus, fault zones are thought to have reduced seismic velocities than the surrounding rocks. In this article, we first investigated the synthetic waveforms at a linear array across a vertical fault zone by using 3D finite difference simulation. Synthetic waveforms show that when sources are close to, inside, or below the fault zone, both arrival times and waveforms of P-and S-waves vary systematically across the fault zone due to reflections and transmissions from boundaries of the low-velocity fault zone. The arrival-time patterns and waveform characteristics can be used to determine the fault zone structure. Then, we applied this method to the aftershock waveform data of the 1992 Landers M7.4 and the 2008 Wenchuan （汶川） M8.0 earthquakes. Landers waveform data reveal a low-velocity zone with a width of approximately 270-370 m, and P-and S-wave velocity reductions relative to the host rock of approximately 35%-60%; Wenchuan waveform data suggest a low-velocity zone with a width of approximately 220-300 m, and P-and S-wave velocities drop relative to the host rock of approximately 55%.展开更多
Baiyangdian lake as the kidney of north China plays a huge ecological function, bringing about environmental and economic benefits as well as aesthetics value. It takes the role of adjusting climate, slowing flood, st...Baiyangdian lake as the kidney of north China plays a huge ecological function, bringing about environmental and economic benefits as well as aesthetics value. It takes the role of adjusting climate, slowing flood, storing water, alleviating drought, maintaining the water body＇s purifying capacity, protecting biodiversity as well as vegetating fish and reed, developing eco-tourism etc.. Now it is degenerating under the pressure from both physical and human society. This paper studied the process, condition and root causes of the lake shrinking, pollution, biodiversity losing and disasters. Adaptation and integrative management strategies are also put forward for maintaining the ecological function and sustainable development.展开更多
A 2-D model of lithospheric velocity structures in the southern part of the North China Craton was obtained using data from the Zhucheng-Yichuan deep seismic sounding profile.Results show that there are great differen...A 2-D model of lithospheric velocity structures in the southern part of the North China Craton was obtained using data from the Zhucheng-Yichuan deep seismic sounding profile.Results show that there are great differences in lithospheric structures between two sides of Taihang Mountain.In the eastern region,the lithosphere is thinner,with a thickness of about 70-80 km,while in the western region,the thickness is 85-120 km.There is a jump of the lithospheric thickness across Taihang Mountain gravity anomaly belt with a magnitude of about 30 km.P wave velocities of the lithospheric mantle and lower crust are lower in the eastern region and higher in the western region.In the eastern region,there are low velocity bodies in the middle and lower crust,while none were found in the western region.These differences indicate that the Taihang Mountain gravity anomaly belt is a belt with a abrupt change of lithospheric thickness and lithological composition.According to the Pm waveform,it can be deduced that the Moho in the eastern region is not a sharp discontinuity,but a complex transitional zone.From a preliminary analysis,it is found that the geothermal mechanical-chemical erosion could be the main mechanism causing the thinning and destruction of the lithosphere beneath the eastern side of Taihang Mountain.In addition,subduction of the Pacific Plate is an important factor which changes the properties of the lithospheric mantle of the North China Craton.展开更多
The crustal structures of P velocity and density on the deep seismic sounding profile across the Dabieshan erogenic belt are presented. There is a 5-km-thick crustal "root" between the Yuexi and Xiaotian whe...The crustal structures of P velocity and density on the deep seismic sounding profile across the Dabieshan erogenic belt are presented. There is a 5-km-thick crustal "root" between the Yuexi and Xiaotian where the elevation is highest on the profile. An apparent Moho offset of 4.5 km beneath the Xiaotian-Mozitan fault marks the paleo-suture of the Triassic collision. A high-velocity anomaly zone at the depth below 3 km beneath the ultra-high pressure (UHP) zone may be correlated to the higher content of UHP metamorphic rocks.展开更多
基金sponsored by National Natural Science Foundation of China (No.40674043, 90814001)China Earthquake Admini-stration (Wenchuan Earthquake Scientific Survey 03-05)The contribution No. of this paper is RCEG 0905 of Geophysical Prospecting Center,China Earthquake Administration
文摘The rupture process of the May 12, 2008 Ms8.0 Wenchuan earthquake was very complex. To study the rupture zones generated by this earthquake, four dense temporary seismic arrays across the two surface breaking traces of the main-shock were deployed in July and recorded a great amount of aftershocks. This paper focuses on the data interpretation of two arrays across the central main fault, the northern array line 1 and southern array line 3. The fault zone trapped waves recorded by the two arrays were used to study the structure of the central main fault and the difference between the northern and southern portions. The results show that the widths of the rupture zone are about 170-200 m and 200-230 m for northern and southern portions respectively. And the corresponding dip angles are 80° and 70°. The seismic velocity inside the fracture zone is about one half of the host rock. By comparison, the northern portion of the rupture zone is slightly narrower and steeper than the southern portion. Besides these differences, one more interesting and important difference is the positions of the rupture zone with respect to surface breaking traces. At the northern portion, the rupture zone is centered at the surface breaking trace, while at the southern portion it is not but is shifted to the northwest. This difference reflects the difference of rupture behaviors between two portions of the central main fault. The width of the rupture zone is smaller than that of MS.1 Kunlun earthquake though these two earthquakes have almost the same magnitudes. Multiple ruptures may be one factor to cause the narrower rupture zone.
基金Special R&D Project of Earthquake Trade ( No.200808041)the Project of Emergency Investigation of M_S8.0 Wenchuan Earthquake of CEA
文摘The great M_S8.0 Wenchuan earthquake on May 12,2008 was generated by abrupt faulting in the Yingxiu-Beichuan fault along the Longmenshan fault zone. The earthquake not only produced surface ruptures along the Yingxiu-Beichuan and Guanxian-Jiangyou faults,but also surface ruptures,arching of highway pavement,sand-boils and waterspouts in various degrees in areas such as Shifang and Mianzhu on the Chengdu Plain. To understand the shallow geological structures under the surface rupture zone,a 6350m long high-resolution shallow seismic reflection profile in near-EW direction was performed. This profile is located at Shigu town,Shifang city,where a suspected earthquake surface rupture zone was discovered. In this study,a group interval of 3m,shotpoint interval of 18m,and a 300-channel 25-fold observation system were used. In consideration of both near-surface reflections and dipping interface imaging,we adopted the split-spread geometry and asymmetrical zero-offset receiving technique. To better suppress random-noise and raise the signal-to-noise ratio of seismic data,30 times vertical stacking of vibrator signals was made for each common-shot gather after correlation of individual records. By using the above work method and spread geometry,we obtained high-resolution images of structures in the depth range of 15m～800m after data processing. The result shows the existence of buried thrust faults thrusting to the plain area and back-thrust faults under the surface rupture zone. It also shows that the activity of the buried thrust faults may be the main cause for folding and deformation in near-surface strata and coseismic surface rupturing.
基金National Natural Science Foundation of China (40334040) and Joint Seismological Foundation (106076).
文摘The data obtained from a high resolution seismic refraction profile, which was carded out in Jiashi, Xinjiang, strong earthquake swarm area, were processed with both finite difference inversion and Hagedoorn refractor wavefront imaging technique and the fine upper crustal structure was determined. The results show that the upper crustal structure is relatively well-distributed in laterally and obviously by layers vertically.From surface to 11.0 km depth, there are about four layers. The P wave velocity of top two layers range from 1.65 to 4.5 km/s and their bottom boundaries, the buried depths of which are 0.4, 2.96-3.0 km respectively, are almost horizontal; The third layer is comparatively complicated and its P wave velocity presents inhomogeneous in both laterally and vertically. The bottom boundary of third layer is crystalline basement and shows a little uplift, which seemly suggest that the upper crust had been resisted while the hard Tarim block inserting into Tianshan Mountain; The forth layer is relatively even and its P wave velocity is about 6.3 km/s. There are a lateral velocity variation at the depth of about 4.0 km, and suggest that it has something to do with the hidden Meigaiti fault and Meigaiti-Xiasuhong fault but there are no the structure features about these faults stretching to the surface and passing through the crystalline basement. The seismogenic tectonic of Jiashi strong earthquake swarm at least lies in middle or lower crust beneath 11.0 km depth.
基金supported by the Open Fund of the Key Labo-ratory of Geo-detection (China University of Geosciences, Bei-jing),Ministry of Education (No. GDL0708)
文摘Large property contrasts between materials in a fault zone and the surrounding rock are often produced by repeating earthquakes. Fault zones are usually characterized by fluid concentration, clay-rich fault gouge, increased porosity, and dilatant cracks. Thus, fault zones are thought to have reduced seismic velocities than the surrounding rocks. In this article, we first investigated the synthetic waveforms at a linear array across a vertical fault zone by using 3D finite difference simulation. Synthetic waveforms show that when sources are close to, inside, or below the fault zone, both arrival times and waveforms of P-and S-waves vary systematically across the fault zone due to reflections and transmissions from boundaries of the low-velocity fault zone. The arrival-time patterns and waveform characteristics can be used to determine the fault zone structure. Then, we applied this method to the aftershock waveform data of the 1992 Landers M7.4 and the 2008 Wenchuan （汶川） M8.0 earthquakes. Landers waveform data reveal a low-velocity zone with a width of approximately 270-370 m, and P-and S-wave velocity reductions relative to the host rock of approximately 35%-60%; Wenchuan waveform data suggest a low-velocity zone with a width of approximately 220-300 m, and P-and S-wave velocities drop relative to the host rock of approximately 55%.
文摘Baiyangdian lake as the kidney of north China plays a huge ecological function, bringing about environmental and economic benefits as well as aesthetics value. It takes the role of adjusting climate, slowing flood, storing water, alleviating drought, maintaining the water body＇s purifying capacity, protecting biodiversity as well as vegetating fish and reed, developing eco-tourism etc.. Now it is degenerating under the pressure from both physical and human society. This paper studied the process, condition and root causes of the lake shrinking, pollution, biodiversity losing and disasters. Adaptation and integrative management strategies are also put forward for maintaining the ecological function and sustainable development.
基金supported by National Natural Science Foundation of China (Grant Nos. 90814001,40974053)Geophysical Prospecting Center,China Earth-quake Administration (Grant No. RCEG201004)
文摘A 2-D model of lithospheric velocity structures in the southern part of the North China Craton was obtained using data from the Zhucheng-Yichuan deep seismic sounding profile.Results show that there are great differences in lithospheric structures between two sides of Taihang Mountain.In the eastern region,the lithosphere is thinner,with a thickness of about 70-80 km,while in the western region,the thickness is 85-120 km.There is a jump of the lithospheric thickness across Taihang Mountain gravity anomaly belt with a magnitude of about 30 km.P wave velocities of the lithospheric mantle and lower crust are lower in the eastern region and higher in the western region.In the eastern region,there are low velocity bodies in the middle and lower crust,while none were found in the western region.These differences indicate that the Taihang Mountain gravity anomaly belt is a belt with a abrupt change of lithospheric thickness and lithological composition.According to the Pm waveform,it can be deduced that the Moho in the eastern region is not a sharp discontinuity,but a complex transitional zone.From a preliminary analysis,it is found that the geothermal mechanical-chemical erosion could be the main mechanism causing the thinning and destruction of the lithosphere beneath the eastern side of Taihang Mountain.In addition,subduction of the Pacific Plate is an important factor which changes the properties of the lithospheric mantle of the North China Craton.
基金Project supported by the National Natural Science Foundation of China and the Joint Earthquake Science Foundation
文摘The crustal structures of P velocity and density on the deep seismic sounding profile across the Dabieshan erogenic belt are presented. There is a 5-km-thick crustal "root" between the Yuexi and Xiaotian where the elevation is highest on the profile. An apparent Moho offset of 4.5 km beneath the Xiaotian-Mozitan fault marks the paleo-suture of the Triassic collision. A high-velocity anomaly zone at the depth below 3 km beneath the ultra-high pressure (UHP) zone may be correlated to the higher content of UHP metamorphic rocks.
