Comparison of two earthquake early warning location methods

According to earthquake catalog records of Fujian Seismic Network, the T _now method and the four-station continuous location method put forward by Jin Xing are inspected by using P-wave arrival information of the first four stations in each earthquake. It shows that the four-station continuous location method can locate more seismic events than the T _now method. By analyzing the results, it is concluded that the reason for this is that the T _now method makes use of information from stations without being triggered, while some stations failed to be reflected in earthquake catalog because of discontinuous records or unclear records of seismic phases. For seismic events whose location results can be given, there is no obvious difference in location results of the two methods and positioning deviation of most seismic events is also not significant. For earthquakes outside the network, the positioning deviation may amplify as the epicentral distance enlarges, which may relate to the situation that the seismic stations are centered on one side of epicenter and the opening angle between seismic stations used for location and epicenter is small.     

新创企业的时空分异与区位选择——基于中国汽车制造业的实证研究

新创企业区位选择不仅是企业重要的决策活动,也深刻影响中国制造业地理空间格局演变。在全球化、市场化、分权化背景下,基于“中国工业企业数据库（1998—2012）”和“中国城市统计年鉴（1999—2013）”中新创企业及城市属性数据,采用随机效应面板Tobit模型分析中国汽车制造业新创企业的时空分异与区位选择。研究发现：① 1998—2012年,中国汽车新创企业活跃地区由东部沿海地区向中西部地区转移,尤其是2010—2012年,新创企业呈现向中西部大规模扩散趋势,西部成渝地区逐渐成为新热点区域。② 从新创企业区位选择时空综合机制来看,全球化影响不显著,而市场化和分权化均存在显著影响,其中劳动力、集聚经济、市场潜力与区位商等因素能促使新创企业成立,而国有企业占比则会阻碍新创企业成立。③ 在时间特征差异上,全球化表现不显著,分权化则始终保持对新创企业的显著影响。市场化的劳动力因素影响作用变化说明新创企业区位选择正逐渐从关注劳动力成本转向于关注劳动力质量,而集聚经济和市场潜力在多样化和城市化经济的冲击下作用减弱。④ 在空间特征差异上,全球化的出口因素在东部地区影响显著,但在中西部地区表现不明显,市场化中劳动力因素和市场潜力在东部地区影响不显著,而在中西部地区劳动力因素则显著为正,除此之外,外商直接投资、集聚经济、区位商和国有企业占比对不同区域新创企业区位选择影响大体相同。在经济高质量发展情景下,揭示新创企业时空分异及区位选择机制,强调“区位机会窗口”对某些地区实现企业区位空间调整及其把握企业与政府关系的重要性,不仅能丰富演化经济地理学视角下的企业区位选择的研究,还能更好地理解中国典型区域正在发生的经济转型和空间重构。     

LOCATIONAL PROBLEMS AND PREFERENCES IN PRESCHOOL CHILD CARE*

With the increased use of formal child care, the number of child care alternatives has grown. The locational problems and preferences of University of Connecticut employees who use formal child care for children under age 6 are examined because an on-site program is available as one option. Difficulty finding care at a convenient location is related to residential location. Preference for worksite care decreases with increasing commuting distance. Variations in reported locational preferences by commuting zone are consistent with the notion of locating services within the activity spaces of the users. As commuting distance increases, worksite day care represents a greater displacement from the activity spaces of the child and possibly of other family members.     

A non-dominated sorting genetic algorithm for the location and districting planning of earthquake shelters

The improvement of emergency coping capacity is one of the most efficient measures for mitigating disaster impact. Shelter planning is an important strategy to reduce the number of casualties and injuries and facilitate disaster recovery. This study aims to address earthquake shelter location selection and the districting planning of service areas jointly. A bi-objective model is proposed to minimise the total evacuation distance and the total cost, subject to capacity and contiguity constraints. A non-dominated sorting genetic algorithm is developed to tackle the bi-objective model, which involves a multitude of decision variables. To fit the model, the chromosome structure, initialisation process and genetic operators in the algorithm are specifically designed to maintain the contiguity of the service area. And a hybrid strategy of bidirectional multi-point crossover and bidirectional single-point crossover helps promote the diversity of the solutions and accelerate the convergence. Moreover, the Pareto-optimal strategy and feasibility-based rule are combined to obtain trade-offs between objectives. The model and algorithm are validated in a case study of the earthquake shelter location and districting planning problem in Chaoyang District of Beijing, and the results confirm the effectiveness and efficiency of the method.     

LBS中基于轨迹的用户行为特征分析

LBS的发展趋势是向用户提供智能化、个性化的位置服务。以用户行为轨迹数据为基础,进行轨迹简化、POI匹配、时空融合、习惯分析等处理,建立起用户行为特征模型,从而实现向不同用户提供个性化位置服务。     

基于频率衰减补偿的微地震定位方法

本文分析了不同频率的震源子波在传播过程中频率衰减与传播距离的关系,提出了地震波频率衰减补偿的微地震定位方法.该方法通过对地震波频率衰减的补偿,间接获取微地震事件的道间时差,避免了微地震事件的信号识别与走时拾取,实现了对微地震事件的定位.本文提出了方法的基本原理和计算方法,并通过理论计算和误差分析表明该方法是合理的和有效的.

     

基于正八面体的四孔六边形球面格网编码及索引

将正八面体上下相邻的两个三角形面片合并成一个四分体,建立二维坐标系,在此基础上采用六边形格网单元的层次编码方案,分析了不同位置格网单元的编码特征,提出了一种“孔4双轴查找算法”,实现了相应的邻接单元及父、子单元查找,并进行了相关实验及对比分析。结果表明,该算法和传统的Vince算法相比较,邻接单元查找速度提高了约900倍,父单元和子单元的查找速度均提高了约120倍。     

Improvements in mining induced microseismic source locations at the Lucky Friday mine using an automated whole-waveform analysis system

For years, severe rockburst problems at the Lucky Friday mine in northern Idaho have been a persistent safety hazard and an impediment to production. An MP250 based microseismic monitoring system, which uses simple voltage threshold picking of first arrivals, has been used in this mine since 1973 to provide source locations and energy estimates of seismic events. Recently, interest has been expressed in developing a whole waveform microseismic monitoring system for the mine to provide more accurate source locations and information about source characteristics. For this study, we have developed a prototype whole-waveform microseismic monitoring system based on a 80386 computer equipped with a 50 kHz analog-digital convertor board. The software developed includes a data collection program, a data analysis program, and an event detection program. Whole-waveform data collected and analyzed using this system during a three-day test have been employed to investigate sources of error in the hypocenter location process and to develop an automatic phase picker appropriate for microseismic events.Comparison of hypocenter estimates produced by the MP250 system to those produced by the whole-waveform system shows that significant timing errors are common in the MP250 system and that these errors caused a large part of the scatter evident in the daily activity plots produced at the mine. Simulations and analysis of blast data show that analytical control over the solutions is strongly influenced by the array geometry. Within the geophone array, large errors in the velocity model or moderate timing errors may result in small changes in the solution, but outside the array, the solution is very sensitive to small changes in the data.Our whole-waveform detection program picks event onset times and determines event durations by analysis of a segmented envelope function (SEF) derived from the microseismic signal. The detection program has been tested by comparing its arrival time picks to those generated by human analysis of the data set. The program picked 87% of the channels that were picked by hand with a standard error of 0.75 milliseconds. Source locations calculated using times provided by our entire waveform detection program were similar to those calculated using hand-picked arrival times. In particular, they show far less scatter than source locations calculated using arrival times based on simple voltage threshold picking of first arrivals.     

S波影区地震精确定位的研究

长期的地震观测发现,北京地震台记录到的S波影区地震存在定位误差大的现象.由于来自震中距9°～36°的地震经过了低速层,造成了S波不发育.所以S波影区地震多用LG波来确定震中距.造成影区地震定位偏差大的现象有两个原因:①长期以来多是用短周期记录来区分LG1和LG2,定位偏差较大;②有的影区地震,S波也少许发育,但用S波来定位也存在定位偏差大的现象.为此搜集了北京地震台记录到的影区地震,通过NCDSN仿真成SK记录,通过理论震中距的比较,找到了准确定位影区地震的LG2识别位置.