Application of 3D empirical travel times to routine event location

The unmodeled effects of lateral heterogeneity are a primary cause of event mislocation in routine methods. Approaches that account for the effect of lateral heterogeneity on travel times are commonly used in specialized studies, but some methods have recently been developed that are suitable for routine location. A variety of changes to the routine procedures have been suggested by other authors. These proposed changes are shown to be compatible to with the use of 3D travel time predictions. 3D empirical travel times are discussed in a routine context. This one step approach, based on direct use of a database of the most reliable previous observations, is shown to be suitable as an additional final step in routine procedures to give a supplementary high accuracy location. The empirical travel time approach is tested on a reference dataset of 155 ground truth events and shown to reduce epicentral mislocation by 45%. The approach is found to be particularly effective at reducing large mislocations. Improvement is demonstrated for every region represented in the dataset but particularly large improvements are shown for events in Europe, USA and Japan.     

Results of locating the IASPEI GT(0-5) reference events using the standard ISC procedures

The International Seismological Centre (ISC) is charged with production of the definitive global bulletin of seismic events, based on the most comprehensive set of parametric data collected from all over the world. Almost every event in the bulletin retains the original hypocentral solutions reported to the ISC by contributing agencies. In addition, where possible, the ISC computes its own solution, which is intended to be the most accurate where the data from several networks are used. It is because of the requirement for consistency of the bulletin over the years that the procedures used at the centre to compute hypocentres have remained rather conservative despite considerable advances made in the field of earthquake location.The ISC has developed and put into operation a new data management system. As a result, it is now possible to review and subsequently introduce more up-to-date methods of locating seismic events into the operations. The ISC Governing Council called for a workshop dedicated to location procedures, which was held during the 2005 IASPEI General Assembly in Santiago, Chile.To compare the accuracy of different location algorithms, a list of 156 reference events (IWREF) was selected prior to the workshop. The list includes geographically well distributed earthquakes and explosions with positions known with an accuracy of up to 5 km. It covers the period of 1954-2001 and includes all station readings and hypocentral solutions of different agencies available for these events in the ISC bulletin. Although the original ISC solutions are included, these may be different from the solution obtainable now due to changes in the ISC procedures over the years. This paper presents the results of relocation of these events using standard ISC location procedures as of 2005. These new ISC locations and analysis of their shifts with respect to reference locations present a benchmark for further improvement.     

The Characteristic Analysis and Seismic Triggering Study of the M6.2 and M6.1 Dayao Earthquake Sequences in 2003

INTRODUCTIONTheM6·2 andM6·1 earthquakes occurred successivelyin Dayao,Yunnan Province on July 21and October 16 ,2003 and bothinduced human casualty and economic loss to some extent .Adequatehistorical information reveals that ,earthquakes bigger thanM6·0 in Yunnan are distributed mainlyalong some active tectonic faults and seismic belts . Dayao and Yao an are in the Dianzhong tectonicblock andthere are noapparentfaultsthere(Su Youjing,2004) .Seismic activitylevel inthisregioniswea…     

Grid-search event location with non-Gaussian error models

This study employs an event location algorithm based on grid search to investigate the possibility of improving seismic event location accuracy by using non-Gaussian error models. The primary departure from the Gaussian error model that is considered is the explicit use of non-Gaussian probability distributions in defining optimal estimates of location parameters. Specifically, the class of generalized Gaussian distributions is considered, which leads to the minimization of L_p norms of arrival time residuals for arbitrary p≥1. The generalized Gaussian error models are implemented both with fixed standard errors assigned to the data and with an iterative reweighting of the data on a station/phase basis. An implicit departure from a Gaussian model is also considered, namely, the use of a simple outlier rejection criterion for disassociating arrivals during the grid-search process. These various mechanisms were applied to the ISC phase picks for the IWREF reference events, and the resulting grid-search solutions were compared to the GT locations of the events as well as the ISC solutions. The results indicate that event mislocations resulting from the minimization of L_p residual norms, with p near 1, are generally better than those resulting from the conventional L₂ norm minimization (Gaussian error assumption). However, this result did not always hold for mislocations in event depth. Further, outlier rejection and iterative reweighting, applied with L₂ minimization, performed nearly as well as L₁ minimization in some cases. The results of this study suggest that ISC can potentially improve its location capability with the use of global search methods and non-Gaussian error models. However, given the limitations of this study, further research, including the investigation of other statistical and optimization techniques not addressed here, is needed to assess this potential more completely.     

2002年夏季长白山天池火山区的地震活动研究

2002年6月以来,长白山天池火山区的地震活动明显增加. 本文利用2002年夏季布设在长白山天池火山区15套宽频带流动地震台站的记录资料,对天池火山区的地震活动进行了研究. 地震观测结果表明,2002年夏季长白山天池火山日平均地震发生频次超过30次. 地震主要位于长白山天池西南部和东北部两个区域,震源深度较浅,离地表的深度一般小于5km. 天池西南部和东北部的地震,b值存在较大的差异. 火山区地震记录的频谱分析和时频分析结果表明,这些地震主要为火山构造型地震. HSZ和DZD等台站地震记录中丰富的低频成分,可能与台站附近的局部介质或断层带有关. 我们认为2002年夏季频繁发生的地震和小震震群活动是由火山深部活动诱发的局部断裂活动引起.     

化爆标定地震定位方法研究

定位仿真表明,若标定震源在网内,震中偏差和震源深度偏差等值线都是以标定震源为圆心的同心圆,网内大约30%的事件,震中偏差为5%;如果标定震源位于台网一侧,约10%事件的震中误差为10%。无论标定源在网内还是在网外,计算震中都向标定震源方向移动,距标定点愈远,定位偏差愈大。速度标定定位显示,规则地震台网中对称线上的震源定位是不可靠的。实际网内化爆标定定位表明,对于网内事件,爆炸邻域定位精度比速度标定定位精度高;对于网外事件,邻域标定定位精度比速度标定定位精度低。     

Hypocenter location of mixed events in real-time processing systems

Automatic pickings in earthquake real-time monitoring systems often contain noise bursts and/or phases of different event(s) occurring almost simultaneously. Typically, a locator uses these picks as P and S waves arrival times coming from a single event and, therefore, should be complemented by a distinctive phase association logic. The method we propose manages to automatically associate data related to different events and eliminates the influence of spoiled data from single events. The method is based on “network beamforming”, a robust and stable algorithm, which utilizes a hypocenter grid search for the stack maximum of a set of complex exponents applied to the P phase readings. The algorithm separates the residual outliers and then uses them for location. If successful, a hypocenter is established for the interfering event. The solutions obtained are overall robust and independent from the estimate of origin times. The preliminary epicenter for the grid search is provided by the intersection of perpendicular bisectors in the modified “arrival order algorithm” or by the modified “T^now” algorithm, which uses non-arrival information. We applied this method to automatic first arrival phase readings of 915 events registered by the Hi-net Japan seismic network and our results are statistically promising. Here, we present two interesting and complicated examples.     

福建数字地震台网测定中国台湾中深源地震研究

对比福建数字地震台网测定的中国台湾中深源地震目录与中国台湾中央气象局公布的相应中深源地震目录,分析震源位置和发震时刻的差别情况,基本认为:福建台网测定中国台湾中深源地震的结果,在震中位置上,纬度偏大,即偏北;经度偏小,即偏向台网方向;采用单纯型方法定位的结果,发震时刻略偏小,震源深度偏小较多;用Locsat方法定位的结...     

利用地震波形态选定公格尔山地区计算机定位的初定深度

分析认为公格尔山地区计算机测定地震参数精度不太明显的直接原因是使用ＢＬＯＣ８６定位程序时初定深度选取不当，根据地震活动图像显示，说明该地区不适合选取固定的初定深度，可以参考的地震波的不同形态来选定相应的初定深度。     

A proposal for comparing the reliabilities of alternative seismic hazard models

Differences between statistical unertainty and modeling uncertainty are briefly discussed. It is pointed out that, when different models are proposed for the interpretation of reality, the uncertainty cannot be described in terms of mean value and coefficient of variation. The important question is: which of the proposed models is more reliable than the others? The attention, then, is concentrated on the comparison between different models proposed for the estimate of the required quantity, looking for a criterion leading to the selection of the most reliable one. A criterion for comparison of different models is suggested. In the example of application considered in this paper, it proved to be effective, so that the continuation of numerical experiments, exploring different and more complex situations, seems promising.     

上海地震台阵对2004年12月26日印度洋地震的精确定位

通过对上海地震台网和上海地震台阵对2004年12月26日印度洋地震的定位结果与NEIC定位结果的比较，得出上海台阵定位结果比上海台网的定位结果更加精确。     

多事件联合与双差地震定位方法研究：以朝鲜核试验定位为例

双差定位法（Double-difference Earthquake Location,简称DD）和多事件联合定位法（Joint Hypocenter Determination,简称JHD）是精确多事件定位中常用的两种方法.对震源机制相近的相邻事件,DD方法利用事件之间的相对到时精准地反演它们之间的相对位置,到时差数据能够利用波形互相关等方法直接测量,但是却无法准确地确定绝对位置;相比之下,JHD方法能够同时反演事件的绝对位置和台站走时校正值.结合两种方法的优点,本文提出一种混合定位方法,同时利用绝对到时数据和到时差数据准确地反演事件绝对位置和台站走时校正.本文利用模拟数据对该方法进行了验证并将其应用于朝鲜核试验定位,结果表明该方法能够有效减小走时计算误差所导致的定位误差.对于朝鲜核试验,相比单次事件+DD定位方法和JHD方法,相对Myers的定位结果定位偏差分别减小45.67%和40.00%.

     

L_p范数方法在地震定位中的应用

本文根据最小二乘法在地震定位中存在的“抗干扰”能力的不足,介绍了自适应Ｌｐ范数方法。该方法可以自适应选取ｐ值。通过对陕西台网地震定位的结果检验表明,该方法实用可行,并具有较强的“抗干扰”能力,即稳健性。     

地震定位研究综述

综述了各种地震定位方法的基本原理,重点介绍了Geiger的经典方法以及在此基础上建立的各种线性方法：联合定位法,相对定位法,和最新的双重残差法;对每一种方法的应用情况,尤其是国内的工作做了总结;同时也指出了各种方法的特点,并进行了相应的比较,此外,还简要介绍了空间域的定位方法和各种非线性定位方法。     

CTBTO国际数据中心地震数据处理软件研究进展

全球台网地震震相有效关联与快速精确定位是地震监测和禁核试核查的核心问题之一。禁核试条约组织（CTBTO）筹备委员会临时技术秘书处（PTS）国际数据中心（IDC）自成立以来,一直致力于台网震相自动关联有效率及自动处理公报质量的提高,以减轻分析员的工作量。NET-VISA作为IDC下一代全球震相自动关联和事件检测定位软件,使用概率模型和贝叶斯方法找到解释检测观测结果的最佳事件集,进而从这些观测结果中生成自动处理地震公报。测试结果表明,NET-VISA产生的公报要比IDC目前使用的全球关联方法生成的自动处理公报SEL3更加完整和精准。本文介绍了NET-VISA方法的基本原理和测试进展,最后对CTBT北京国家数据中心参加NET-VISA测试中朝鲜6次核试验的NET-VISA关联结果作了分析对比。