基于粘弹性边界的三维土体地震响应分析

利用有限元软件ANSYS建立了三维成层土体模型,分别进行了在EL-Centro波作用下土体的线性、等效线性化和非线性地震响应分析,其中采用了Extended Drucker-Prager模型模拟土体的非线性特征。通过对不同模型在多遇地震、设防地震和罕遇地震作用下计算结果的对比分析,得到如下结论:(1)当土体埋深较大时土的非线性影响不够明显,线性、非线性及等效线性化计算结果相差较小。随着埋深变浅和地震动强度的增大,三者出现显著的差异。(2)考虑土体非线性后,随着埋深变浅和输入地震动强度的增加,加速度峰值表现为线性条件大于非线性条件,非线性条件大于等效线性化条件。(3)随着埋深变浅和输入地震动强度的增加,考虑土体非线性时模量衰减,刚度和频率降低。在地震动输入较大时,由于等效线性化过高估计了场地土的非线性特性导致其高频部分快速降低。

3-Dimensional Irradiance Imaging with a Single Camera System

The focusing tomography is presented to reconstruct 3 dimensional irradiance distribution. A 3 dimensional luminous body could be considered as the combination of many 2 dimensional parallel luminous sections. Focus on these discrete sections respectively by a single camera, a group of images would be captured to form governing equations of irradiance. After inversion procedure, the irradiance distribution of different sections could be decoded. In this experimentation two lightbulbs are used to simulate two luminous sections. Reasonable results demonstrate that this technique could be a useful method in irradiance reconstruction after further development.

Research on the 3-D Seismic Structures in Qinghai-Xizang Plateau

Based on the recording data from the analogue and broadband digital seismic stations in and around Qinghai-Xizang (Tibet) Plateau, the three dimensional (3-D) seismic velocity structures in Qinghai-Xizang Plateau were obtained by using the regional body wave tomography and surface wave tomography. The results from these two tomography methods have similar characteristics for P- and S-wave velocity structures in crust and upper mantle. They show that there are remarkable low velocity zones in the upper crust of Lhasa block in the southern Qinghai-Xizang Plateau and the lower crust and upper mantle of Qiangtang block in the northern Qinghai-Xizang Plateau. These phenomena may be related to the different steps of collision process in southern and northern Qinghai-Xizang Plateau.

A New Method for 3D Finite Element Modeling of Human Mandible Based on CT Data

This study presents a reliable method for the semi-automatic generation of an FE model, which determines both geometrical data and bone properties from patient CT scans.3D FE analysis is one of the best approaches to predict the stress and strain distribution in complex bone structures, but its accuracy strongly depends on the precision of input information. In geometric reconstruction, various methods of image processing, geometric modeling and finite element analysis are combined and extended. Emphasis is given to the assignment of the material properties based on the density values computed from CT data. Through this technique, the model with high geometric and material similarities were generated in an easy way. Consequently, the patient-specific FE model from mandible CT data is realized also.

Three-dimensional crustal velocity structure and activity characteristics of the Madoi Ms7.4 earthquake in 2021

In this paper,using natural earthquake P-wave arrival time data recorded by the seismic network in the surrounding area of Madoi,the three-dimensional fine P-wave crustal velocity structure at depths above 60 km in the epicenter of the Madoi Ms7.4 earthquake was inverted using the double-difference seismic tomography method.On the basis of the relocation of the source of the aftershock sequence,we summarized the strip-shaped distribution characteristics along the strike of the Jiangcuo fault,revealing the significant heterogeneity of the crustal velocity structure in the source area.Research has found that most of the Madoi Ms7.4 aftershocks were located in the weak area of the high-speed anomaly in the upper crust.The focal depth changed with the velocity structure,showing obvious fluctuation and segmentation characteristics.There was a good correspondence between the spatial distribution and the velocity structure.The high-velocity bodies of the upper crust in the hypocenter area provided a medium environment for earthquake rupture,the low-velocity bodies of the middle crust formed the deep material,and the migration channel and the undulating shape of the high-speed body in the lower crust corroborated the strong pushing action in the region.The results confirmed that under the continuous promotion of tectonic stress in the Madoi area,the high-speed body of the Jiangcuo fault blocked the migration of weak materials in the middle crust.When the stress accumulation exceeded the limit,the Madoi Ms7.4 earthquake occurred.Meanwhile,the nonuniform velocity structure near the fault plane determined the location of the main shock and the spatiotemporal distribution of the aftershock sequence.

Three-dimensional velocity structure and tectonic characteristics of earthquake area in Yibin

In this study,on the basis of absolute first-arrival times of 84756 P-and S-waves from 6085 earthquakes recorded at 56 fixed stations in Yibin and surrounding areas in China from January 2009 to January 2019,focal parameters and three-dimensional(3 D)body-wave high-resolution velocity structures at depths of 0–30 km were retrieved by double-difference tomography.Results show that there is a good correspondence between the spatial distribution of the relocated earthquakes and velocity structures,which were concentrated mainly in the high-velocity-anomaly region or edge of high-velocity region.Velocity structure of P-and S-waves in the Yibin area clearly shows lateral inhomogeneity.The distribution characteristics of the P-and S-waves near the surface are closely related to the geomorphology and geologic structure.The low-velocity anomaly appears at the depth of 15–25 km,which is affected by the lower crust current.The Junlian–Gongxian and Gongxian–Changning earthquake areas,which are the two most earthquake-prone areas in the Yibin region,clearly differ in earthquake distribution and tectonic characteristics.We analyzed the structural characteristics of the Junlian–Gongxian and Gongxian–Changning earthquake areas on the basis of the 3 D bodywave velocity structures in the Yibin region.We found that although most seismicity in the Yibin area is caused by fluid injection,the spatial position of seismicity is controlled by the velocity structures of the middle and upper crust and local geologic structure.Fine-scale 3 D velocity structures in the Yibin area provide important local reference information for further understanding the crustal medium,seismogenic structure,and seismicity.