INFLUENCE OF PUMPING ON FOUR-COMPONENT BOREHOLE STRAIN AT TAI'AN SEISMIC STATION AND ITS INTERFERENCE MECHANISM

Four-component borehole strainmeter (FCBS) is one kind of high-precision borehole strain observation instruments invented in China. As a kind of near-surface deformation observation instrument, FCBS is also easily disturbed by the external environment factors. As a common factor, pumping has significant influence on FCBS observation. Existing studies mostly identify the pumping interference from the perspective of observation curve morphology, relatively few studies focus on its interference mechanism. In order to truly capture earthquake precursor information, it is necessary to study the interference mechanism. In recent years, RZB-3 type FCBS at Tai'an seismic station has been seriously affected by pumping, so it is necessary and also feasible to study the interference mechanism of pumping. Since the influence of pumping interference on borehole strainmeter is common, this work would be very practical and be used for reference by other borehole strain observation stations. We find that the original observation curves and observed surface strain, shear strain from RZB-3 type FCBS at Tai'an seismic station have the characteristics of synchronous change with the borehole water level, in which the linear correlation coefficient between the two observed shear strain curves and borehole water level reached 0.70 and 0.82 respectively. We further find that the principal strain direction of borehole and borehole water level after normalization meet the nonlinear function as y=1.217arctan(x)^0.224-0.284. The above phenomenon indicates that the observation of RZB-3 type FCBS at Tai'an seismic station is significantly affected by the borehole water level, and the influence is more obvious and the gradient is larger at the stage of low water level. Pumping interference often appears in low water level stage and changes the rock pore pressure state. Statistics show that pumping interference affects the borehole strain state. To investigate the interference mechanism of pumping to RZB-3 type FCBS at Tai'an seismic station, we take a known pumping as an example, in which we study the principal strain state of the borehole in three periods of normal pumping, interruption of pumping and resuming pumping respectively. During each period, we solve 3 parameters of the principal plane strain state, i.e. the maximum principal strain rate, the minimum principal strain rate and the maximum principal strain direction from four observation equations of FCBS by nonlinear iterative least squares algorithm. On the other hand, concentrated load model (CLM) is used to simulate the mechanical mechanism of pumping. Firstly, the depth of FCBS relative to pumping source and the concentrated load at pumping source are inversed, then, the strain state surrounding the pumping well, including the state at RZB-3 borehole, is simulated by forward modeling. By comparing these results, we find that: (1)The concentrated load at pumping source inversed by CLM during periods of normal pumping and resuming pumping are both located at or near the bottom of the pumping well, which is consistent with the actual situation, indicating that mechanism and degree of the influence of pumping on borehole strain are well simulated by CLM. (2)The observed strain state is consistent with the simulation result of pumping interference by forward modeling, indicating that the principal strain state of borehole calculated based on observation of FCBS reflects the true strain state of borehole under different pumping states.(3)The inversed concentrated load at pumping source during pumping periods is significant greater than the load of the pumped water, indicating that the pumping process has more significant influence on the pore pressure of rocks than the load of the pumped water. Even though CLM is an approximate simulation since it's based on some elastic assumptions, the interference mechanism of pumping on RZB-3 type FCBS at Tai'an seismic station is well explained, which is maybe very helpful for studying the influence of pumping interference on other deformation instruments, locating the unknown pumping source and studying the characteristics of pore pressure of rocks.     

基于PCA-GSM-SVM的地震伤亡人数预测

针对影响地震伤亡人数的评价指标数量较多且各指标之间存在着复杂的非线性关系,运用机器学习理论,提出了基于支持向量机(Support Vector Machine)的地震伤亡人数预测模型;首先利用主成分分析法(Principle Component Analysis)对7个地震死亡人数影响指标进行数据降维,然后对提取出的主成分进行归一化处理,将归一化的主成分数据作为预测模型的输入向量,将地震伤亡人数作为预测模型的输出向量;以27个地震伤亡实例作为学习样本进行训练,运用网格搜索法(Grid Search Method)寻优获得最优支持向量机参数,最终建立基于PCA-GSM-SVM的地震死亡人数预测模型,并对5组样本进行死亡人数预测。结果表明:PCA-GSM-SVM模型的最小误差、最大误差和平均误差分别为5.12%、15.7%和9.16%,其平均误差相比于GSM-SVM模型和SVM模型分别降低6.51%和7.11%,因此PCA-GSM-SVM模型预测精度较高,可在工程实际中推广。     

中强地震下建筑结构动力弹塑性损伤模型研究

抗震性能是建筑设计中的一项重要指标,需要对地震作用下的建筑结构动力弹塑性损伤情况进行分析。提出一种中强地震下建筑结构动力弹塑性损伤模型研究方法。从有效应力与Cauchy应力张量\,建筑材料损伤演化方程等方面对弹塑性损伤模型基本原理进行分析,以此为理论基础,分析建筑材料应变率与建筑结构损伤能释放率的相关关系,通过Bonora损伤模型获取失效建筑材料损伤指数,并计算整体建筑结构构件损伤指数,以建筑材料损伤指数和建筑结构构件损伤指数为依据,完成中强地震下的建筑结构动力弹塑性损伤模型构建。利用实例进行分析,地震加速度值为0.3g的情况下,该模型的建筑结构相对位移时程曲线与实际位移曲线拟合度较高,且具有较好的建筑结构动力弹塑性损伤模拟精度,表明该模型具有一定的可行性。     

Crustal structure study based on principal component analysis of receiver functions

The receiver function(RF) technique is an effective method for studying crustal structure. For a single station, the average 1-D crustal structure is usually derived by stacking the radial RFs from all back-azimuths, whereas structural variations(such as dipping discontinuities or anisotropy) can be constrained through analysis of waveform dependence on the backazimuth of both the radial and tangential RFs. However, it is often difficult to directly extract information about structural variations from the waveform of RF, due to the common presence of noise in real data. In this study, we proposed a new method to derive structural variation information for individual stations by applying principal component analysis(PCA) to RFs sorted by back-azimuth. In this method(termed as RF-PCA), a set of principal components(PCs), which are uncorrelated with each other and reflect different characteristics of the RF data, were extracted and utilized separately to reconstruct new RFs. Synthetic tests show that the first PC of the radial RFs contains the average structural information of the crust beneath the corresponding station, and the second PC of the radial RFs and the first PC of the tangential RFs both reflect the variations of the crustal structure. Our synthetic modeling results indicate that the new RF-PCA method is valid for a variety of synthetic models with intra-crustal dipping discontinuities and/or anisotropy. We applied this method to the real data from a broadband temporary seismic station(s233) in the central part of the Sichuan Basin. The results suggest that the RF data can be best explained by the presence of two nearly parallel dipping discontinuities within the crust. Combining with previous logging data, seismic exploration and deep sounding observations, we interpret the shallow dipping discontinuity as the top boundary of the Precambrian crystalline basement of the Sichuan Basin and the deep one corresponding to the Conrad interface between the upper and lower crust, consistent with the geological feature of the study area. In this work, both synthetic tests and real data application results demonstrate the effectiveness of the RF-PCA method for studying crustal structures.     

应力主轴往返旋转条件下砂土变形规律试验研究

在已有空心圆柱扭剪仪上开发新的控制模块,实现应力主轴以任意初始方向角开始并以任意角度幅值进行往返旋转。在此基础上,对丰浦砂开展系列应力主轴往返旋转试验。试验结果表明:1应力主轴往返旋转角度幅值和初始主应力方向角均对砂土变形有不可忽视的影响;2不同于应力主轴连续循环旋转的情形,应力主轴往返旋转时砂土由于"楔入效应"可能出现体胀。     

Strength-reduction factors for the design of light nonstructural elements in buildings

Strength-reduction factors that reduce ordinates of floor spectra acceleration due to nonlinearity in the secondary system are investigated. In exchange for permitting some inelastic deformation to occur in the secondary system or its supports, these strength reduction factors allow to design the nonstructural elements or their supports for lateral forces that are smaller than those that would be required to maintain them elastically during earthquakes. This paper presents the results of a statistical analysis on component strength-reduction factors that were computed considering floor motions recorded on instrumented buildings in California during various earthquakes. The effect of yielding in the component or its anchorage/bracing in offering protection against excessive component acceleration demands is investigated. It is shown that strength-reduction factors computed from floor motions are significantly different from those computed from ground motions recorded on rock or on firm soils. In particular, they exhibit much larger reductions for periods tuned or nearly tuned to the dominant modal periods of the building response. This is due to the large differences in frequency content of ground motions and floor motions, with the former typically characterized by wide-band spectra whereas the latter are characterized by narrow-band spectra near periods of dominant modes in the response of the building. Finally, the study provides approximate equations to estimate component strength-reduction factors computed through nonlinear regression analyses.     

基于PCA方法的GPS台站时间序列分析

基于10 a以上的全球GPS台站数据,利用主成分分析法及其他数据处理方法,对台站时间序列进行预处理和结果分析,研究其中的非线性周期规律,探讨时间序列的主要影响机制。结果表明,主成分分析法可以将台站残差时空矩阵分解成若干正交成分,GPS台站时间序列的东西方向具有线性漂移趋势,全球大部分GPS台站都存在非线性周期规律,周年项和半周年周期占据主导地位。     

A regression model-based method for indoor positioning with compound location fingerprints

ABSTRACT

This paper proposed and evaluated an estimation method for indoor positioning. The method combines location fingerprinting and dead reckoning differently from the conventional combinations. It uses compound location fingerprints, which are composed of radio fingerprints at multiple points of time, that is, at multiple positions, and displacements between them estimated by dead reckoning. To avoid errors accumulated from dead reckoning, the method uses short-range dead reckoning. The method was evaluated using 16 Bluetooth beacons installed in a student room with the dimensions of 11 × 5 m with furniture inside. The Received Signal Strength Indicator (RSSI) values of the beacons were collected at 30 measuring points, which were points at the intersections on a 1 × 1 m grid with no obstacles. A compound location fingerprint is composed of RSSI vectors at two points and a displacement vector between them. Random Forests (RF) was used to build regression models to estimate positions from location fingerprints. The root mean square error of position estimation was 0.87 m using 16 Bluetooth beacons. This error is lower than that received with a single-point baseline model, where a feature vector is composed of only RSSI values at one location. The results suggest that the proposed method is effective for indoor positioning.     

基于改进的主成分分析法提取GRACE时变重力场信号

针对主成分分析法提取时变重力场模型信号中存在信号泄漏和去条带噪声不明显的问题,提出对球谐位系数主成分分析的改进方法。首先对球谐位系数进行主成分分析,提取主要的模态,再对不同模态根据其自身噪声特点选择合适的滤波方法和参数,最后在此基础上进行信号提取。以CSR发布的2005-01~2013-12(108个月)GRACE时变地球重力场模型进行实验,提取2006-06和2006-12等效水高数据和改进前的主成分分析进行比较,表明此方法在有效地剔除条带误差的同时又使得信号泄漏减小。