A method for extracting the preseismic gravity anomalies over the Tibetan Plateau based on the maximum shear strain using GRACE data

The occurrence of earthquakes is closely related to the crustal geotectonic movement and the migration of mass,which consequently cause changes in gravity.The Gravity Recovery And Climate Experiment(GRACE)satellite data can be used to detect gravity changes associated with large earthquakes.However,previous GRACE satellite-based seismic gravity-change studies have focused more on coseismic gravity changes than on preseismic gravity changes.Moreover,the noise of the north–south stripe in GRACE data is difficult to eliminate,thereby resulting in the loss of some gravity information related to tectonic activities.To explore the preseismic gravity anomalies in a more refined way,we first propose a method of characterizing gravity variation based on the maximum shear strain of gravity,inspired by the concept of crustal strain.The offset index method is then adopted to describe the gravity anomalies,and the spatial and temporal characteristics of gravity anomalies before earthquakes are analyzed at the scales of the fault zone and plate,respectively.In this work,experiments are carried out on the Tibetan Plateau and its surrounding areas,and the following findings are obtained:First,from the observation scale of the fault zone,we detect the occurrence of large-area gravity anomalies near the epicenter,oftentimes about half a year before an earthquake,and these anomalies were distributed along the fault zone.Second,from the observation scale of the plate,we find that when an earthquake occurred on the Tibetan Plateau,a large number of gravity anomalies also occurred at the boundary of the Tibetan Plateau and the Indian Plate.Moreover,the aforementioned experiments confirm that the proposed method can successfully capture the preseismic gravity anomalies of large earthquakes with a magnitude of less than 8,which suggests a new idea for the application of gravity satellite data to earthquake research.

Evolution and analysis of gas sorption-induced coal fracture strain data

Although coal swelling/shrinking during coal seam gas extraction has been studied for decades,its impacts on the evolution of permeability are still not well understood.This has long been recognized,but no satisfactory solutions have been found.In previous studies,it is normally assumed that the matrix swelling/shrinking strain can be split between the fracture and the bulk coal and that the splitting coefficient remains unchanged during gas sorption.In this study,we defined the fracture strain as a function of permeability change ratio and back-calculated the fracture strains at different states.In the equilibrium state,the gas pressure is steady within the coal;in the non-equilibrium state,the gas pressure changes with time.For equilibrium states,the back-calculated fracture strains are extremely large and may be physically impossible in some case.For non-equilibrium states,two experiments were conducted:one for a natural coal sample and the other for a reconstructed one.For the fractured coal,the evolution of permeability is primarily controlled by the transition of coal fracture strain or permeability from local matrix swelling effect to global effect.For the reconstituted coal,the evolution of pore strain or permeability is primarily controlled by the global effect.

Strains Recorded Using a Seismometer Data Acquisition Unit

A seismometer data acquisition unit has been used in the Changping seismic station to record the output of a strainmeter. The output of a strainmeter was sampled at a rate of l00/sec by seismometer acquisition from the original rate of 1 per minute. Plenty of high frequency sampled data was recorded. The minute value curve calculated from the seismometer acquisition are consistent with that of the original data sampled by the strain acquisition system. More complete waveforms were recorded with a higher sampling rate, and seismic phase parameters calculated by using higher sampling rate strain seismic waves are also in consistency with the results of its predecessors. Spectra of the strain seismic waves are compared with that of seismic waves recorded by a seismometer in the Shisanling seismic station, and their trends are almost the same. Besides, some lower frequency components still exist in strain seismic waves.

Time-varying Reliability Analysis of Long-span Continuous Rigid Frame bridge under Cantilever Construction Stage based on the Monitored Strain Data

In general,the material properties,loads,resistance of the prestressed concrete continuous rigid frame bridge in different construction stages are time-varying.So,it is essential to monitor the internal force state when the bridge is in construction.Among them,how to assess the safety is one of the challenges.As the continuous monitoring over a long-term period can increase the reliability of the assessment,so,based on a large number of monitored strain data collected from the structural health monitoring system(SHMS)during construction,a calculation method of the punctiform time-varying reliability is proposed in this paper to evaluate the stress state of this type bridge in cantilever construction stage by using the basic reliability theory.At the same time,the optimal stress distribution function in the bridge mid-span base plate is determined when the bridge is closed.This method can provide basis and direction for the internal force control of this type bridge in construction process.So,it can reduce the bridge safety and quality accidents in construction stages.

Multi-axial strain-stiffening elastic potentials with energy bounds:explicit approach based on uniaxial data

According to the well-known models for rubberlike elasticity with strain- stii^ening effects, the unbounded strain energy is generated with the unlimitedly growing stress when the stretch approaches certain limits. Toward a solution to this issue, an explicit approach is proposed to derive the multi-axial elastic potentials directly from the uniaxial potentials. Then, a new multi-axial potential is presented to characterize the strain-stiffening effect by prescribing suitable forms of uniaxia] potentials so that the strain energy is always bounded as the stress grows to infinity. Numerical examples show good agreement with a number of test data.

Contemporary crustal tectonic movement in the southern Sichuan-Yunnan block based on dense GPS observation data

We analyzed 360 permanent and campaign GPS data from 1999 to 2017 in the southern Sichuan-Yunan block, and obtained crustal horizontal deformation in this region.Then, we derived the strain rate using a multi-scale spherical wavelet method.Results reveal a complex pattern of tectonic movement in the southern Sichuan-Yunnan block.Compared to the stable Eurasian plate, the maximum rate of the horizontal deformation in the southern Sichuan-Yunnan block is approximately 22 mm/a.The Xiaojiang fault shows a significantly lower deformation—a left-lateral strike-slip movement of 9.5 mm/a.The Honghe fault clearly shows a complex segmental deformation from the north to south.The northern Honghe fault shows 4.3 mm/a right strike-slip with 6.7 mm/a extension; the southern Honghe fault shows 1.9 mm/a right strike-slip with 1.9 mm/a extension; the junction zone in the Honghe and Lijiang–Xiaojinhe faults shows an obvious clockwise-rotation deformation.The strain calculation results reveal that the maximum shear-strain rate in this region reaches 70 nstrain/a, concentrated around the Xiaojiang fault and at the junction of the Honghe and Lijiang–Xiaojinhe faults.We note that most of the earthquakes with magnitudes of 4 and above that occurred in this region were within the high shear strain-rate zones and the strain rate gradient boundary zone, which indicates that the magnitude of strain accumulation is closely related to the seismic activities.Comparison of the fast shear-wave polarization direction of the upper-crust with the upper-mantle anisotropy and the direction of the surface principal compressive strain rate obtained from the inversion of the GPS data reveals that the direction of the surface principal compressive strain is basically consistent with the fast shear-wave polarization direction of the upper crust anisotropy, but different from the polarization direction of the upper mantle.Our results support the hypothesis that the principal elements of the deformation mechanism in the southern Sichuan-Yunnan block are decoupling between the upper and lower crust and ductile flow in the lower crust.

A Review of the Calculation Formula for the Four-component Borehole Strainmeter and Application to Earthquake Cases

Based on the principle formula for the four-component strainmeters, we can directly obtain the specific plane strain, shear strain and azimuthal angle of the principal strain, and the maximum and minimum principal strains calculated afterwards are the indirect result. The problems of practicality of the sensitivity coefficients A and B of plane strain and shear strain are then discussed. Based on this idea, we analyzed the observation data of several four-component borehole strainmeters near the epicenter of the Yiliang M_S5.7 earthquake in 2012 and the Ludian M_S6.5 earthquake in 2014 in the Zhaotong area, Yunnan Province. The results show that the analysis based on the perspective of plane strain and shear strain has an obviously better effect than that based on the component readings, and can directly peel off the respective abnormality of the plane strain and shear strain. In addition, the correlation coefficient curves between measured data of two plane strains show significant anomalies which often occur several days before and during the earthquake.

Displacement fields denoising and strains extraction by finite element method

Optical full-field measurement methods are now widely applied in various domains. In general,the displacement fields can be directly obtained from the measurement,however in mechanical analysis strain fields are preferred.To extract strain fields from noisy displacement fields is always a challenging topic.In this study,a finite element method for smoothing displacement fields and calculating strain fields is proposed.An experimental test case on a holed aluminum specimen under tension is applied to validate this method.The heterogeneous displacement fields are measured by digital image correlation(DIC).By this proposed method,the result shows that the measuring noise on experimental displacement fields can be successfully removed,and strain fields can be reconstructed in the arbitrary area.

Analysis on residual strain of Zipingpu Concrete Faced Rockfill Dam after Wenchuan earthquake

The Zipingpu Concrete Faced Rockfill Dam （CFRD） was subjected to significant local damage in the ＂5.12＂ Wenchuan earthquake. It is the first rockfill dam of more than one hundred meters high to encounter a strong earthquake anywhere in the world. Based on the finite element smoothing method, the residual strains at a typical cross-section and a downstream slope of the dam were obtained by processing the dam monitored displacement data. The position of and reason for the dam settlement and deformation ofrockfill dilatancy in the earthquake were analyzed according to the section residual strain. The results show that the maximum settlement ratio on the dam body approximately occurs at 2/3 of the dam height; dilatancy occurs from the dam crest to 25-30 m in the upstream and downstream slope; the immediate cause of the face slabs horizontal construction joint dislocation is excessive residual shear strain. Meanwhile, the position of and reason for the dam fissure in the earthquake were analyzed according to the dam slope residual strain.

Data processing and analysis of crustal deformation monitoring in the Fildes region,West Antarctica

In order to research contemporary crustal movement of Antarctica, China has constructed the deformation monitoring network in the Fildes Strait region,West Antarctica, monitored the network by using DI 20 geodimeter and GPS instruments, and participated the Antarctic GPS Campaign Observation organized by SCAR as well. During mathematics processing of crustal horizontal deformation observations,a method to bring deformation parameters into the error equations of observations is discussed in this paper. Several classical deformation models,such as rigid body displacement and strain,are introduced. By analyzing the reference datum of static and dynamic geodetic network,the method is developed to set up different additional weight matrix for every different kind of parameter. A series of programs are developed to implementing the method mentioned above and the analysis of West Antarctic Fildes Strait deformation monitoring network. Discussion is also made of GPS monitoring data by using the principle of monitoring network strain analysis in the paper. The research results indicate that the displacement did occur in Fildes rift region,but the displacement was not large,just a slight rift shear movement.

Damage Identification in Beam-Type Structures Using Pseudo Strain Energy Density and Grey Relation Coefficient

Based on pseudo strain energy density (PSED) and grey relation coefficient (GRC), an index is proposed to locate the damage of beam-type structures in time-domain. The genetic algorithm (GA) is utilized to identify the structural damage severity of confirmed damaged locations. Furthermore, a systematic damage identification program based on GA is developed on MATLAB platform. ANSYS is employed to conduct the finite element analysis of complicated civil engineering structures, which is embedded with interface technique. The two-step damage identification is verified by a finite element model of Xinxingtang Highway Bridge and a laboratory beam model based on polyvinylidens fluoride (PVDF). The bridge model was constructed with 57 girder segments, and simulated with 58 measurement points. The damaged segments were located accurately by GRC index regardless of damage extents and noise levels. With stiffness reduction factors of detected segments as variables, the GA program evolved for 150 generations in 6 h and identified the damage extent with the maximum errors of 1% and 3% corresponding to the noise to signal ratios of 0 and 5%, respectively. In contrast, the common GA-based method without using GRC index evolved for 600 generations in 24 h, but failed to obtain satisfactory results. In the laboratory test, PVDF patches were used as dynamic strain sensors, and the damage locations were identified due to the fact that GRC indexes of points near damaged elements were smaller than 0.6 while those of others were larger than 0.6. The GA-based damage quantification was also consistent with the value of crack depth in the beam model.

Formulation and procedure for in situ stress back-analysis from borehole strain changes measured during nearby underground excavation

Estimation of in situ stresses based on back-analysis of measured stress changes and displacements has become an alternative to the direct stress measurement methods.In order to help users conduct own measurement and analysis,this paper presents in detail a field stress back-analysis approach directly from borehole strain changes measured during nearby underground excavation.Essential formulations in major steps and the procedure for the entire analysis process are provided to allow users to follow.The instrument for borehole strain change measurement can be the CSIR or CSIRO stress cells and other borehole strain cells that can measure strains on borehole walls.Strain changes corresponding to the stress changes at a borehole location are calculated in borehole environment.The stress changes due to nearby excavation can be calculated by an analytical model for a single circular opening and simulated by a numerical model for non-circular and multiple openings.These models are based on isotropic,homogeneous and linear elastic assumptions.The analysis of borehole strain changes is accomplished by multiple linear regression based on error minimization and an integrated process provides the best-fit solution directly to the in situ stresses.A statistical technique is adopted for screening outliers in the measurement data,checking measurement compatibility and evaluating the reliability of analysis results.An application example is included to demonstrate the practical application and the analysis procedure.

Design and validation of wireless strain test system for bridge based on the resistance strain sensor

In order to achieve an access to strain sensor data with wireless transmission in bridge engineering structure testing, a wireless strain test system is presented based on the resistance strain sensor of networks. The wireless bridge strain test system composed of master station and substation adopts the wireless method to realize the high accuracy data acquisition between the master station and the substation under a reliable communication protocol. The system has been tested in contrast with the present strain apparatus. Results show that the wireless system is high-reliable, and has many characteristics such as high efficiency, good precision, high stability with low cost, and good flexibility, without using the present communication network.

Fatigue Safety Assessment of Concrete Continuous Rigid Frame Bridge Based on Rain Flow Counting Method and Health Monitoring Data

The fatigue of concrete structures will gradually appear after being subjected to alternating loads for a long time,and the accidents caused by fatigue failure of bridge structures also appear from time to time.Aiming at the problem of degradation of long-span continuous rigid frame bridges due to fatigue and environmental effects,this paper suggests a method to analyze the fatigue degradation mechanism of this type of bridge,which combines long-term in-site monitoring data collected by the health monitoring system(HMS)and fatigue theory.In the paper,the authors mainly carry out the research work in the following aspects:First of all,a long-span continuous rigid frame bridge installed with HMS is used as an example,and a large amount of health monitoring data have been acquired,which can provide efficient information for fatigue in terms of equivalent stress range and cumulative number of stress cycles;next,for calculating the cumulative fatigue damage of the bridge structure,fatigue stress spectrum got by rain flow counting method,S-N curves and damage criteria are used for fatigue damage analysis.Moreover,it was considered a linear accumulation damage through the Palmgren-Miner rule for the counting of stress cycles.The health monitoring data are adopted to obtain fatigue stress data and the rain flow counting method is used to count the amplitude varying fatigue stress.The proposed fatigue reliability approach in the paper can estimate the fatigue damage degree and its evolution law of bridge structures well,and also can help bridge engineers do the assessment of future service duration.

基于MicroPython的结构应变采集系统设计

为了解决现有应变数据采集设备测量通道单一以及测量精度低的问题,结合MicroPython语言设计了基于振弦式传感器的应变采集系统。该系统能够同步获取4路应变和温度数据,并对4路应变与温度数据进行组间融合;通过宽度学习系统BLS拟合应变量与温度的线性关系对融合后的应变数据进行温度补偿,提高系统的监测精度,细化系统的场景分析。依托北京宣武门地铁基坑钢梁结构进行实地监测分析,结果表明,相较于实测应变数据和利用小波分解-最小二乘法补偿的应变数据,该系统提出的融合补偿算法得到应变数据的标准差分别降低了31.6%和25.4%,该系统能实时捕获更加准确的应变量,为结构应变高精度感知提供有效途径。

工程降水对钻孔应变的干扰特征及干扰机制研究

抽水干扰在钻孔应变观测中常见且影响显著,为了能真实捕捉到地震前兆信息,须对其干扰机制进行研究.随着城市化进程,基坑工程及其伴随的工程降水逐步增多,工程降水对钻孔应变的干扰比普通单井抽水干扰更为严重.工程降水对钻孔应变观测有何干扰特征、干扰机制如何、干扰数据能否修复等问题对地震异常的探测具有重要意义.本文基于莱阳体应变受到附近御龙湾项目工程降水干扰的观测案例,研究了工程降水的干扰特征,修复了干扰畸变,通过数值模拟确定了干扰机制.结果表明:(1)工程降水在干扰体应变趋势变化的基础上叠加了方向明确、量级稳定的固体潮畸变,可以通过一阶差分逆运算进行修复.修复固体潮畸变并扣除背景速率后,工程降水干扰量级达-15.65×10^(-9)/d;(2)通过建立基于集中载荷模型的网格算法,模拟出工程降水在体应变异常初期和后期分别产生6.61×10^(9) N和1.73×10^(10) N的集中力载荷,干扰量级明显大于常见的单井抽水干扰,压性干扰集中于体应变仪与抽水井连线的垂直方向;(3)通过固体潮畸变特征及力学机制分析确定了工程降水造成固体潮畸变的干扰机制为"抽水引起压性趋势下降—抽水暂停引起张性台阶上升—抽水引起压性趋势下降"周期行为,固体潮畸变时间间隔(频次)和钻孔水位之间呈显著同步特征,线性系数为0.737.

甲状腺结节射频消融术后复发预测模型的构建与应用

目的探讨甲状腺结节射频消融术后复发的影响因素,构建列线图预测模型,以期指导临床诊治。方法选取2019年1月至2021年1月郑州大学第二附属医院收治的398例甲状腺结节作为研究对象,其中16例于生化复发前接受内分泌治疗,12例无术后2年随访信息,均予以剔除,经筛选后259例纳入训练集用于建立模型,111例纳入验证集用于验证模型,采用COX比例风险回归方程确定甲状腺结节射频消融术后复发影响因素,采用R软件可视化处理获得列线图预测模型,行内外部验证。结果术后2年,甲状腺结节射频消融术后复发率为15.14%(56/370);COX比例风险回归方程显示,体质量指数(BMI)(OR:6.873)、热休克蛋白70(HSP70)(OR:5.380)、弹性应变率比值(SR)(OR:3.872)、结节成分(OR:5.880)、结节内部血流(OR:6.944)、结节钙化(OR:3.764)是甲状腺结节射频消融术后复发影响因素(P<0.05);基于COX比例风险回归方程结果构建甲状腺结节射频消融术后复发列线图预测模型,该模型在训练集、验证集中曲线下面积(AUC)分别为0.856、0.874,且其预测效能与实际吻合较理想。结论基于SR、BMI、HSP70、结节成分、结节内部血流、结节钙化构建列线图预测模型对甲状腺结节射频消融术后复发具有良好区分度、精准度,有助于实现个体化预测,帮助临床医师识别高风险人群,确定合理防治措施。

左心房应变特征与慢性心力衰竭患者运动耐力的相关性

目的探讨左心房应变特征与慢性心力衰竭(CHF)患者运动耐力的相关性。方法前瞻性选取2021年11月至2023年1月聊城市人民医院收治的212例CHF患者为研究对象,根据最大摄氧量(VO2max)将患者分为2组,VO_(2max)≥16 ml/(kg·min)为高耐力组(125例),VO2max<16 ml/(kg·min)为低耐力组(87例)。分析2组患者的一般资料和实验室检查结果。采用多因素logistic回归分析影响患者运动耐力的相关因素。结果2组N末端B型钠尿肽前体(NT-proBNP)、二尖瓣舒张早期血流峰值速度(E)/二尖瓣环舒张早期血流峰值速度(e′)比值、E、左心室舒张末期容积指数(LVEDVI)、左心室收缩末期容积指数、左心室每搏量指数、左心室射血分数(LVEF)、左心室整体纵向应变、左心房最大容积指数、左心房最小容积指数、左心房存储应变(LASr)、左心房管道应变(LAScd)、左心房收缩应变(LASct)比较,差异有统计学意义(P<0.05);多因素logistic回归分析显示,LASr(OR=0.987,95%CI:1.003~1.029)、LAScd(OR=1.177,95%CI:0.688~0.955)、LASct(OR=1.341,95%CI:0.507~0.884)、NT-proBNP(OR=1.002,95%CI:0.995~1.000)、E/e′(OR=1.086,95%CI:1.000~1.183)、LVEDVI(OR=1.127,95%CI:0.805~0.936)、LVEF(OR=0.909,95%CI:0.824~1.000)是影响CHF患者运动耐力的相关因素(P<0.05);限制性立方条图显示,LASr、LAScd、LASct与CHF患者运动耐力呈显著非线性关系(χ^(2)分别为9.830、16.820、9.080,P<0.05)。结论左心房应变特征相关指标与CHF患者运动耐力具有相关性。

单点式应变量校准器电路设计方案分析

校准器输出电路是应变量校准器的最核心技术。本文介绍了两种常规的单点式应变量校准器电路设计方案,并通过理论计算和测试试验对其优缺点及可行性进行分析,提出最优方案。

基于LabVIEW的大型起重机应变监测系统的设计

在使用中的大型起重机的应变值的波动是判断大型起重机是否可靠的重要指标,针对如何监测在用大型起重机危险点的应变值,设计了大型起重机专用应变数据采集系统,给出了系统硬件总体设计方案,软件系统采用广泛应用于虚拟仪器开发的工具LabVIEW,开发出一种应变传感器数据采集系统,能够远程高效采集多个应变传感器传输的数据。该应变数据系统的主要模块包括传感器以及采集系统WiFi通信模块的参数设置、对传感器所传输的采集数据的显示以及对所采集数据的保存和记录等。该数据采集系统可以对多个应变传感器传输的数据同时进行采集和传输,也可应用于不同工况下应变传感器传输的实时数据,该系统具有显示信息多样、数据准确、操作简单便捷等优点。