Study of Local Seismic Events in Lithuania and Adjacent Areas Using Data from the PASSEQ Experiment

The territory of Lithuania and adjacent areas of the East European Craton have always been considered a region of low seismicity. Two recent earthquakes with magnitudes of more than 5 in the Kaliningrad District (Russian Federation) on 21 September 2004 motivated re-evaluation of the seismic hazard in Lithuania and adjacent territories. A new opportunity to study seismicity in the region is provided by the PASSEQ (Pasive Seismic Experiment) project that aimed to study the lithosphere–asthenosphere structure around the Trans-European Suture Zone. Twenty-six seismic stations of the PASSEQ temporary seismic array were installed in the territory of Lithuania. The stations recorded a number of local and regional seismic events originating from Lithuania and adjacent areas. This data can be used to answer the question of whether there exist seismically active tectonic zones in Lithuania that could be potentially hazardous for critical industrial facilities. Therefore, the aim of this paper is to find any natural tectonic seismic events in Lithuania and to obtain more general view of seismicity in the region. In order to do this, we make a manual review of the continuous data recorded by the PASSEQ seismic stations in Lithuania. From the good quality data, we select and relocate 45 local seismic events using the well-known LocSAT and VELEST location algortithms. In order to discriminate between possible natural events, underwater explosions and on-shore blasts, we analyse spatial distribution of epicenters and temporal distribution of origin times and perform both visual analysis of waveforms and spectral analysis of recordings. We show that the relocated seismic events can be grouped into five clusters (groups) according to their epicenter coordinates and origin and that several seismic events might be of tectonic origin. We also show that several events from the off-shore region in the Baltic Sea (at the coasts of the Kaliningrad District of the Russian Federation) are non-volcanic tremors, although the origin of these tremor-type events is not clear.     

Locating Small Aftershocks Using a Small-Aperture Temporary Seismic Array

In this paper, we developed a specialized method to locate small aftershocks using a small-aperture temporary seismic array. The array location technique uses the first P arrival times to determine the horizontal slowness vector of the incoming P wave, then combines it with S–P times to determine the event location. In order to reduce the influence of lateral velocity variation on the location determinations, we generated slowness corrections using events well-located by the permanent broadband network as calibration events, then we applied the corrections to the estimated slownesses. Applications of slowness corrections significantly improved event locations. This method can be a useful tool to locate events recorded by temporary fault-zone arrays in the near field but unlocated by the regional permanent seismic network. As a test, we first applied this method to 64 well-located aftershocks of the 1992 Landers, California, earthquake, recorded by both the Caltech/USGS Southern California Seismic Network and a small-aperture, temporary seismic array. The average horizontal and vertical separations between our locations and the well-determined catalogue locations are 1.35 and 1.75 km, respectively. We then applied this method to 132 unlocated aftershocks recorded only by the temporary seismic array. The locations show a clear tendency to follow the surface traces of the mainshock rupture.     

智能化地震事件识别和定位系统研究现状及展望

数字地震观测技术的发展为提高台网信息处理能力、地震应急能力和台网服务功能提供了先决条件。智能化地震事件识别和快速地震定位是发挥台网社会效益的一个重要方面。文章对国内外基于现代信号处理技术的智能化地震事件识别和定位方法的研究现状进行了综合分析，针对该项研究存在的问题，对其发展趋势进行了探讨，初步提出了未来需要深入研究的课题。     

基于“加速度台阵”的近震震相识别方法

本文提出了一种在近震条件下,确定台阵三分向记录图中Pg波震相的初至识别方法,并对美国UPSAR台阵记录到的2003年发生在圣西门(San Simeon)地区6.5级的地震数据进行了Pg波震相分析和识别.分析结果表明,本文提出的震相识别方法是有效的.     

地震事件自动识别技术及其在南岭流动台阵的应用?

地震事件识别是地震层析成像的重要组成部分。然而,在处理宽频带流动台阵天然地震记录中识别地震事件过程中,利用传统的人工识别方法耗时巨大,效率十分低。本文首先运用STA/LTA 对地震事件进行初步判断,并结合支持向量机信号检测算法和多台联合检验法来提高地震事件判别的准确度及抗干扰能力,达到天然地震事件的自动识别。南岭流动台阵数据的应用结果表明该综合识别算法可自动快速准确地判别地震事件,并可用于地震震相的拾取。     

Characteristics of Seismic Wave Propagation in the Binchuan Region of Yunnan Using a Dense Seismic Array and Large Volume Airgun Shots

The Binchuan region of Yunnan is a structurally complex region with mountains, basins, and active faults. In this situation,seismic wave propagation exhibits complex characteristics due to strong heterogeneity of underground media instead of following the great-circle path. In order to obtain a high-resolution shallow crustal structure, a dense seismic array was deployed during March 21 to May 30, 2017 in this area. To better understand the complexities of seismic wave propagation in this region, we perform array-based frequency-domain beamforming analysis and single-station based polarization analysis to investigate the characteristics of seismic wave propagation, using airgun-generated P-wave signals recorded by dense array stations in this experiment. The results from these two methods both reveal similar but complex characteristics of seismic wave propagation in the Binchuan basin. The azimuth anomalies off the great-circle path are quite large with values up to 30°, which is caused by strong structural heterogeneity in the very shallow crust. Our research provide a better understanding of the complex geologic structures in this area and provide guidance for detecting concealed faults and distribution of velocity anomalies.     

人工神经元网络方法对首都圈地区潜在震源区的划分

指标选取是人工神经元网络方法应用中最基础，最重要的五环，是判别工作成败的关键。但目前尚没有比较成熟的指标选取或指标显著性评价方法。因此，指标问题入往成了方法效果进一步提高的“瓶颈”问题。该问题在潜在震源区划分应用中也同样存在。     

台阵地震学、地震台阵与禁核试条约监测系统

本文介绍了台阵地震学的发展,国内外地震台阵的建设和工作进展以及地震台阵与全面禁止核试验条约(CTBT)国际监测系统(IMS)的关系。另外比较系统地论述了台阵地震学在地震精确定位和地球内部构造反演中的应用。     

上海地震台阵的地震定位方法

上海地震台阵数据处理软件系统的地震定位方法,采用台阵的聚束方法得到地震方位角和视慢度,根据统计得到的视慢度——震中距表推算震中距。并结合了地震台网的定位方法,由单台记录的各类主要震相从JB走时表得到震中距,然后进行地震定位。该定位方法可对近震、远震进行定位处理,并由深震相得到震源深度。     

上海地震台阵的设计方法

从台阵波数响应特性、子台选址与测试、场地背景噪声分析和记录信号评价等方面，综合对上海地震台阵进行设计，确定了台阵子台的布局点位。本文还介绍了规则台阵与不规则台阵中的几种不同子台布局的台阵波数响应图，并由此得出，采用不规则的子台布局同样可得到性能较好的地震台阵；台阵的子台越多，其响应特性的主峰就越尖锐。     

Locating Seismic Events in the CTBT Context

—?The verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) requires the determination of accurate location of seismic events from a fixed network of seismic stations across the globe. The requirements of possible on-site inspections mean that the goal is to place the location estimate in a zone smaller than 1000 km² that includes the true location. Because a defined set of stations will be used, corrections can be refined to represent the influence of departures from the global reference model IASPEI91. The primary stations in the International Monitoring Scheme (IMS) are mostly seismic arrays and therefore the present location scheme is based on minimisation of a misfit function built from arrival time, azimuth and array slowness residuals. The effective network will change markedly with the magnitude of the event and as a result regional information has to be integrated into the location process.     

Using Neural Networks to Discriminate between Genuine and Spurious Seismic Events in Mines

—Careful observation has shown that mining-induced seismicity follows a multimodal distribution, which we assume to arise from many distinct physical processes. The two major modes however, arise from those seismic events that are associated in some way with geological features on the one hand, and those that are associated, among other things, with fracturing in the volume of extreme stress concentrations ahead of the stope faces, on the other. We call the former "genuine" events and the latter "spurious" events.¶Untangling these modes has been a major problem for those researchers wishing to work with unimodal seismic catalogs. Partial separation of the genuine events from a catalog can be obtained by a careful selection from a scatter diagram of log (radiated seismic energy) against log (scalar seismic moment) or equivalently by selecting a threshold value of magnitude say, from an inspection of the Gutenberg-Richter diagram. This threshold is usually considerably greater than the threshold of completeness that can be achieved by modern seismic networks on mines.¶The main objective of this paper will be the demonstration that a simple neural network can improve this separation. In this study, for example, simple elimination below the threshold of log (scalar seismic moment) = 9.5 resulted in 206 genuine events remaining in the catalog. After running the eliminated events through a trained neural network, an additional 72 genuine events were found, representing an increase of nearly 35%.¶This has important consequences for statistical hazard analysis and for the identification of active geological structures in mines.     

Seismic Moment Tensor Resolution on a Local Scale: Simulated Rockburst and Mine-induced Seismic Events in the Kopanang Gold Mine, South Africa

Seismic records contain information about the effect of the source as well as the effect of wave propagation through the rock mass. The effect of wave propagation is usually not well known as only simplified models of geological structures are available. Therefore, the information about the source retrieved by inverting seismograms may include errors due to incomplete knowledge of the rock mass along the propagation path, which in turn cause a distortion in the calculated moment tensor (MT). The distortion of the MT on a local scale was observed by inverting records of a simulated rockburst conducted at the Kopanang gold mine in South Africa. A dominant isotropic component of the explosive characteristics was found from the inversion. The deviatoric components retrieved from the blast are spurious. A test of their stability indicated that they are not significant, assuming an uncertainty above 5% for velocities and 10% for attenuation within the homogeneous model available for the mine. Thus, the retrieval of the MT from records of local networks in mines using a homogeneous model of the rock mass seems to be feasible. However, the homogeneous model of the rock mass can only be applied to close stations, within a few kilometers of the source. The seismic records from distant stations were too complex to be modelled by a homogeneous rock mass. Records of six mine-induced seismic events recorded at the Kopanang gold mine were also inverted. A vertical linear dipole along the pressure (P) axis was found for three of the events, suggesting a pillar burst. The mechanism of two events contains an isotropic implosion together with a nearly vertical dip-slip, and seems to indicate a combination of a cavity collapse with a down dip-slip along a nearly vertical fault. One event corresponds to a dipole along the tensional (T) axis. However, it is vertical, thus its association with tensile faulting of the hangingwall is uncertain.     

上海地震台阵观测系统的建立

介绍了上海地震台阵观测系统，该观测系统是由地震台阵、佘山数据中心、上海信息中心等部分组成，对各部分的功能及设备系统结构作了较为翔实的分析，并简要描述了台阵数据处理软件系统。上海地震台阵投入并网运行后表明，从根本上改善了地震波形、特别是远震波形的记录，并从总体下提出了上海地震台网的地震综合监测能力。     

上海地震台阵电缆的铺设

前言一般来说 ,台阵各子台地震计所检测的地震信号是通过有线或无线的方式传输汇集到位于台阵附近的数据中心。如德国格兰芬堡台阵分为 3个子台阵 ,采用有线的方式先将各子台阵每一子台的地震信号传输到子台阵中心 ,然后再将汇集到各子台阵的地震信号再分别传输到埃尔兰根的台阵中心。又如加拿大黄刀台阵的初期 ,各子台的地震信号输出采用悬挂在木制三角架上的电缆传输到附近的控制中心。 1 986年加拿大政府对黄刀台阵进行了重大更新 ,除了在台阵安装不同频带的地震计外 ,还采用高分辨的数字化输出 ,并将地震数据通过 UHF数字无线遥测传输…     

上海地震台阵的数据传输

上海地震台阵采用了多种数据传输方法。台阵子台采用直埋电缆、基带调制解调器MODEM的传输方式将各子台信号传送到余山数据中心。而佘山数据中心到上海信息中心的数据传输则采用复接复分技术 ,将台阵 1 6个子台的实时信号和一路快速以太网信号合用一条带宽为 2 56K的 DDN数字传输专线进行传输。1　台阵子台到佘山数据中心的数据传输上海地震台阵按计划在佘山地区建造 1 6个子台。 1 6个子台分布在约 3 km范围内的山脚下 ,地震计输出的信号全部在台站经数字采集器转换成每秒 2 0 0个采样点 ,每个采样点为 2 4位二进制字长的数字信号。全…     

格尔木地震台阵勘址数据分析与台阵布局设计

为了增强西部地区的地震监测能力, 中国拟在格尔木地区建立一个小孔径地震台阵。 本文对台阵勘址数据进行了噪声与信号的相关性分析, 得到地震监测的最佳台间距。 结果表明, 对于近震和区域震的监测, 该台阵子台间距最好小于500 m, 对于远震的监测, 台站组合间距应为1500～2000 m。 最后将勘址布设的台阵作为初选台阵进行了台阵响应计算, 计算显示, 台阵响应的主瓣在NW-ES方向较窄, 表明对来自该方向事件的慢度分辨率较高; 由于呈“L”型分布, 该初选台阵确定某些方向地震的方位角较好, 但检测其他方向事件的方位角精度不高, 这可以通过台阵校正进行改善; 台阵响应中出现的多处侧瓣是由于子台间距较大造成的。     

上海地震台阵的F-K分析

频率－波数（F－K）谱分析是地震台阵数据处理基本方法之一。采用该分析方法，可以从地脉动背景中提取有用的地震信号，提高地震的定位精度。本文列举了F－K功率谱的不同计算方法，并将该方法应用于上海地震台阵所记录的地震事件。对地震和地脉动的F－K分析结果得出，地震的方位角和慢度值分别对记录长度的分布呈线性特征，而地脉动的方位角和慢度值则呈不规则分布。     

上海地震台阵的子台建设

地震台阵观测系统的基础 ,除了台阵子台的合理布局外 ,就是对台阵子台的建设。子台的建设主要包括子台台室的基建和台室内地震计等设备的安装与调试。由于上海台阵的子台分布位于佘山的国家森林公园所在区域 ,为了不影响周围的景观 ,同时也考虑到台室内具有较小的温差 ,将台室建在地表以下约 2 .5m处 ,并采用伪装竹杆或树杆架设 GPS天线。上海台阵的子台基建工作是相当艰巨的 ,由于所有子台位于坚硬的安山岩上 ,可以说是一场对顽石的攻坚战。子台基建大致经过了场地开挖、台室浇铸、台室门盖制作、仪器墩磨光、室内装修、地网施工、GPS天…