基于SIO(Scripps Institute of Oceanography)最新全球重力和高程模型,计算了巴颜喀拉地块东部及邻区的布格重力异常、均衡重力异常、岩石圈有效弹性厚度及荷载比.结合大地热流、地震速度结构、地震活动和断裂构造分布等,分析了地壳均...基于SIO(Scripps Institute of Oceanography)最新全球重力和高程模型,计算了巴颜喀拉地块东部及邻区的布格重力异常、均衡重力异常、岩石圈有效弹性厚度及荷载比.结合大地热流、地震速度结构、地震活动和断裂构造分布等,分析了地壳均衡状态和岩石圈有效弹性厚度、地质构造单元间的差异及与地震活动的相关性特征.研究结果表明,该区域布格重力变化范围约为-500~0 mGal(1 mGal=10-5 m·s^-2,下同),在巴颜喀拉块体东部区域形成弧形重力梯度带,近年来的中强地震活动频发于该梯度带不同部位,应与其应力依次释放有关;均衡重力异常结果表明,其变化范围约为-80^+100 mGal,且大部分区域处于±20 mGal以内的被认为处于重力均衡的状态,重力非均衡(正或负)多出现于块体边界带附近,地震多发生在靠近块体边界的均衡重力异常(正或负,主要为正)区域内;巴颜喀拉地块东部及邻区岩石圈有效弹性厚度(Te)为10~65 km,不同构造单元之间Te空间分布差异明显,较低的T e值出现在龙门山构造带附近,T e值为20 km左右,岩石圈荷载加载比为0.5~0.8,表明现今的岩石圈挠曲状态主要由莫霍面加载形成.进一步分析表明,巴颜喀拉地块东部挤压增生与横向流动同时发生,是造成该区域地震发生与重力均衡异常高值重合、岩石圈有效弹性厚度和大地热流值较低的主要原因.本文获得的地壳均衡特征及岩石圈有效弹性强度结果,加深了对巴颜喀拉东部及邻区岩石圈构造演化过程的认识.展开更多
Based on the data of the repeated gravity observation network in Chinese mainland since 1998, we analyzed the temporal changes of regional gravity field before the 2008 Yutian Ms7.3 earthquake. The result shows some m...Based on the data of the repeated gravity observation network in Chinese mainland since 1998, we analyzed the temporal changes of regional gravity field before the 2008 Yutian Ms7.3 earthquake. The result shows some mid-to-long term （two to ten years） changes during the earthquake＇ s preparation. Notable fea- tures are a gravity increase lasting several years and a relatively large-scaled gradient zone of gravity change, the former indicating a continuous energy accumulation and the latter a possible location of seismic rupture. These gravity changes showed a trend of increase-accelerated increase-decelerated increase, similar to that of the Tangshan Ms7.8 earthquake in 1976. The maximum accumulated gravity change related to the earthquake reached 200 × 10 -8 ms -2.展开更多
Yushu Ms7.1 earthquake occurred on the Ganzi-Yushu fault zone, across which we carried out a joint relative-gravity and seismic-reflection survey, and then performed a gravity inversion constrained by the seismic-refl...Yushu Ms7.1 earthquake occurred on the Ganzi-Yushu fault zone, across which we carried out a joint relative-gravity and seismic-reflection survey, and then performed a gravity inversion constrained by the seismic-reflection result. Based on the data of complete Bouguer gravity anomaly and seismic reflection, we obtained a layered interface structure in deep crust down to Moho. Our study showed that the inversion could reveal the interfaces of strata along the survey profile and the directions of regional faults in two-dimension. From the characteristics of the observed topography of the Moho basement, we tentatively confirmed that the uplift of eastern edge of Qinghai-Tibet plateau was caused by the subduetion of the Indian plate.展开更多
The Northe South Seismic Belt(NSSB) is a Chinese tectonic boundary with a very complex structure, showing a sharp change in several geophysical field characteristics. To study these characteristics and their relations...The Northe South Seismic Belt(NSSB) is a Chinese tectonic boundary with a very complex structure, showing a sharp change in several geophysical field characteristics. To study these characteristics and their relationship with the distribution of earthquakes and faults in the study area, we first analyze the spatial gravity anomaly to achieve the Bouguer gravity anomaly(EGM2008 BGA) and the regional gravity survey Bouguer gravity anomaly.Next, we ascertain the Moho depth and crustal thickness of the study area using interface inversion with the control points derived from the seismic and magnetotelluric sounding profiles achieved in recent years. In this paper, we summarize the relief, trend, Moho gradient, and crustal nature, in addition to their relationship with the distribution of earthquakes and faults in the study area. The findings show that earthquakes with magnitudes greater than Ms7.0 are mainly distributed in the Moho Bouguer anomaly variation belt and faults. The results of the study are important for future research on tectonic characteristics, geological and geophysical surveys, and seismicity patterns.展开更多
By using GPS and gravity data before and after the Wenchuan Ms8.0 earthquake and combining data from geological surveys and geophysical inversion studies, an initial coseismic fault model is constructed. The dip angle...By using GPS and gravity data before and after the Wenchuan Ms8.0 earthquake and combining data from geological surveys and geophysical inversion studies, an initial coseismic fault model is constructed. The dip angle changes of the fault slip distribution on the fault plane are inversed, and the inversion results show that the shape of the fault resembles a double-shovel. The Yingxiue Beichuan Fault is approximately 330 km long, the surface fault dip angle is 65.1, which gradually reduces with increasing depth to 0 at the detachment layer at a depth of 19.62 km. The Guanxiane Jiangyou Fault is approximately90 km long, and its dip angle at the surface is 55.3, which gradually reduces with increasing depth; the fault joins the Yingxiue Beichuan Fault at 13.75 km. Coseismic slip mainly occurs above a depth of 19 km. There are five concentrated rupture areas, Yingxiu,Wenchuan, Hanwang, Beichuan, and Pingwu, which are consistent with geological survey results and analyses of the aftershock distribution. The rupture mainly has a thrust component with a small dextral strikeeslip component. The maximum slip was more than10 m, which occurred near Beichuan and Hanwang. The seismic moment is 7.84 1020 Nm(Mw7.9), which is consistent with the seismological results.展开更多
In this study, we analyzed the gravity and, magnetic characteristics, and the occurrence of a fault zone and discussed the relationships between the two locations. The results reveal that the subsurface structures str...In this study, we analyzed the gravity and, magnetic characteristics, and the occurrence of a fault zone and discussed the relationships between the two locations. The results reveal that the subsurface structures strikes are different compared with those in the research region. In other words, the geophysical advantageous directions from the gravity and magnetic anomalies are not the same as those caused by the surface structures. The local horizontal gradient results from the gravity and magnetic anomalies show that the majority of earthquakes occur along an intense fault zone, which is a zone of abrupt gravity and negative magnetic change, where the shapes match very well. From the distribution of earthquakes in this area, we find that it has experienced more than 11 earthquake events with magnitude larger than Ms7.0. In addition, water development sites such as Jinshajiang, Lancangjiang, and the Red River and Pearl River watersheds have been hit ten times by earthquakes of this magnitude. It is observed that strong earthquakes occur frequently in the Holocene active fault zone.展开更多
Using the PSGRN/PSCMP software and the fault model offered by USGS and on the basis of finite rectangular dislocation theory and the local layered wave velocity structures of the crust-upper-mantle, the in- fluences o...Using the PSGRN/PSCMP software and the fault model offered by USGS and on the basis of finite rectangular dislocation theory and the local layered wave velocity structures of the crust-upper-mantle, the in- fluences of crustal layering and thickness on co-seismic gravity changes and deformation of Wenchuan earthquake have been simulated. The results indicate that： the influences have a relationship with the attitude of faults and the relative position between calculated points and fault. The difference distribution form of simula- ted results between the two models is similar to that of co-seismic effect. For the per centum distribution, it＇ s restricted by the zero line of the co-seismic effects obviously. Its positive is far away from the zero line. For the crustal thickness, the effect is about 10% -20%. The negative and the effect over 30% focus around the zero line. The average influences of crustal layering and thickness for the E-W displacement, N-S displacement, vertical displacement and gravity changes are 18.4 % , 18.0% , 15.8 % and 16.2% respectively, When the crustal thickness is 40 km, they are 4.6% ,5.3% ,3.8% and 3.8%. Then the crustal thickness is 70 kin, the average influences are 3.5%, 4. 6% ,3.0% and 2.5% respectively.展开更多
基金supported by the National Natural Science Foundation of China(40574012)
文摘Based on the data of the repeated gravity observation network in Chinese mainland since 1998, we analyzed the temporal changes of regional gravity field before the 2008 Yutian Ms7.3 earthquake. The result shows some mid-to-long term （two to ten years） changes during the earthquake＇ s preparation. Notable fea- tures are a gravity increase lasting several years and a relatively large-scaled gradient zone of gravity change, the former indicating a continuous energy accumulation and the latter a possible location of seismic rupture. These gravity changes showed a trend of increase-accelerated increase-decelerated increase, similar to that of the Tangshan Ms7.8 earthquake in 1976. The maximum accumulated gravity change related to the earthquake reached 200 × 10 -8 ms -2.
基金supported by the Key Foundation of Institute of Seismology,China Earthquake Administration( IS200916004)
文摘Yushu Ms7.1 earthquake occurred on the Ganzi-Yushu fault zone, across which we carried out a joint relative-gravity and seismic-reflection survey, and then performed a gravity inversion constrained by the seismic-reflection result. Based on the data of complete Bouguer gravity anomaly and seismic reflection, we obtained a layered interface structure in deep crust down to Moho. Our study showed that the inversion could reveal the interfaces of strata along the survey profile and the directions of regional faults in two-dimension. From the characteristics of the observed topography of the Moho basement, we tentatively confirmed that the uplift of eastern edge of Qinghai-Tibet plateau was caused by the subduetion of the Indian plate.
基金supported by the China Earthquake Administration, Institute of Seismology Foundation (201326126)Institute of Seismology Foundation (201326128)Chinese earthquake scientific array exploration e northern section of North South seismic belt gravity profile Foundation (201308011)
文摘The Northe South Seismic Belt(NSSB) is a Chinese tectonic boundary with a very complex structure, showing a sharp change in several geophysical field characteristics. To study these characteristics and their relationship with the distribution of earthquakes and faults in the study area, we first analyze the spatial gravity anomaly to achieve the Bouguer gravity anomaly(EGM2008 BGA) and the regional gravity survey Bouguer gravity anomaly.Next, we ascertain the Moho depth and crustal thickness of the study area using interface inversion with the control points derived from the seismic and magnetotelluric sounding profiles achieved in recent years. In this paper, we summarize the relief, trend, Moho gradient, and crustal nature, in addition to their relationship with the distribution of earthquakes and faults in the study area. The findings show that earthquakes with magnitudes greater than Ms7.0 are mainly distributed in the Moho Bouguer anomaly variation belt and faults. The results of the study are important for future research on tectonic characteristics, geological and geophysical surveys, and seismicity patterns.
基金supported by the China Earthquake Administration, Institute of Seismology Foundation (IS201226003, IS201326128)the National Natural Science Foundation of China (41104049)the National Basic Research Program of China (2013CB733304-2)
文摘By using GPS and gravity data before and after the Wenchuan Ms8.0 earthquake and combining data from geological surveys and geophysical inversion studies, an initial coseismic fault model is constructed. The dip angle changes of the fault slip distribution on the fault plane are inversed, and the inversion results show that the shape of the fault resembles a double-shovel. The Yingxiue Beichuan Fault is approximately 330 km long, the surface fault dip angle is 65.1, which gradually reduces with increasing depth to 0 at the detachment layer at a depth of 19.62 km. The Guanxiane Jiangyou Fault is approximately90 km long, and its dip angle at the surface is 55.3, which gradually reduces with increasing depth; the fault joins the Yingxiue Beichuan Fault at 13.75 km. Coseismic slip mainly occurs above a depth of 19 km. There are five concentrated rupture areas, Yingxiu,Wenchuan, Hanwang, Beichuan, and Pingwu, which are consistent with geological survey results and analyses of the aftershock distribution. The rupture mainly has a thrust component with a small dextral strikeeslip component. The maximum slip was more than10 m, which occurred near Beichuan and Hanwang. The seismic moment is 7.84 1020 Nm(Mw7.9), which is consistent with the seismological results.
基金supported by the Chinese Earthquake Administration,Institute of Seismology Foundation(IS201326126)Chinese earthquake scientific array exploration northern section of North South Seismic Belt gravity profile Foundation(201308011)
文摘In this study, we analyzed the gravity and, magnetic characteristics, and the occurrence of a fault zone and discussed the relationships between the two locations. The results reveal that the subsurface structures strikes are different compared with those in the research region. In other words, the geophysical advantageous directions from the gravity and magnetic anomalies are not the same as those caused by the surface structures. The local horizontal gradient results from the gravity and magnetic anomalies show that the majority of earthquakes occur along an intense fault zone, which is a zone of abrupt gravity and negative magnetic change, where the shapes match very well. From the distribution of earthquakes in this area, we find that it has experienced more than 11 earthquake events with magnitude larger than Ms7.0. In addition, water development sites such as Jinshajiang, Lancangjiang, and the Red River and Pearl River watersheds have been hit ten times by earthquakes of this magnitude. It is observed that strong earthquakes occur frequently in the Holocene active fault zone.
基金supported by the National Natural Science Foundation of China(40574012)the Earthquake Science Joint Foundation(A07030)
文摘Using the PSGRN/PSCMP software and the fault model offered by USGS and on the basis of finite rectangular dislocation theory and the local layered wave velocity structures of the crust-upper-mantle, the in- fluences of crustal layering and thickness on co-seismic gravity changes and deformation of Wenchuan earthquake have been simulated. The results indicate that： the influences have a relationship with the attitude of faults and the relative position between calculated points and fault. The difference distribution form of simula- ted results between the two models is similar to that of co-seismic effect. For the per centum distribution, it＇ s restricted by the zero line of the co-seismic effects obviously. Its positive is far away from the zero line. For the crustal thickness, the effect is about 10% -20%. The negative and the effect over 30% focus around the zero line. The average influences of crustal layering and thickness for the E-W displacement, N-S displacement, vertical displacement and gravity changes are 18.4 % , 18.0% , 15.8 % and 16.2% respectively, When the crustal thickness is 40 km, they are 4.6% ,5.3% ,3.8% and 3.8%. Then the crustal thickness is 70 kin, the average influences are 3.5%, 4. 6% ,3.0% and 2.5% respectively.
