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。     

Identification of Local Seismic Events Using the Mikhnevo Seismic Array

A large number of events with sources in the immediate vicinity of an array are usually detected during seismological observations with seismic arrays. These events should be detected and correctly interpreted during processing of seismic array records in order to avoid clogging up the event catalog. This problem can be solved by classifying records of local events by genetic features and creating a databank with the most representative samples. The present paper considers local events recorded using a unique scientific setup, the Mikhnevo small aperture seismic array. Epicenters of local seismic events are located less than 5 km from the center of the array. Seismic responses of acoustic shock waves are also examined. Seismic events caused by anthropogenic sources are identified and classified using cluster, cross-correlation, and wavelet analysis. Events accompanied only by the arrival of surface waves, as well as events represented by body, surface, and acoustic waves, are identified. Shock wave events are classified as a separate category. A small group of supposedly natural weak events is also found. As a result, a databank of waveforms of local seismic events for the Mikhnevo seismic array is established. In the future, this will make it possible to automate their identification when investigating the seismicity of the East European Platform.     

数字化台网中定位子台网选取对定位结果的影响

选取山西及邻区不同区域的33个地震事件,通过分析"定位子台网"分布对地震定位精度的影响,研究"定位子台网"的选取。分区域分别探讨两种台站分布情况下的定位偏差、水平误差、拟合残差随空隙角、近台距离、远台距离的变化,以及定位偏差与拟合残差的关系。结果显示,速报时选取9~12个台站,且台站分布相对合理的"定位子台网"参加定位结果比较好,使用水平误差估计定位结果的效果较理想。     

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.     

The CTBT and advances in earth science

David Booth and Peter Maguire report on a two-day meeting organized by the Royal Astronomical Society and the British Geophysical Association, that showed how scientific challenges generated by the Comprehensive Nuclear Test Ban Treaty have been addressed, and how they continue to stimulate advances in earth science.     

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。     

HYPOSAT – An Enhanced Routine to Locate Seismic Events

—?A program package, called HYPOSAT, has been under development that attempts to use the maximum information possible to estimate the hypocenter of a seismic source. The standard input parameters can be used: arrival times of first and later onsets with backazimuths and ray parameters (or apparent velocities). In addition, travel-time differences between different phases observed at the same station can be optionally used. The observed standard deviations are used to weight all input parameters and the inversion is done with a generalized matrix inversion code.¶A starting solution with a priori uncertainties can be calculated as the intersection of all backazimuth observations. If S observations are also available, a preliminary origin time is estimated using Wadati's approach to estimate a source time.¶Global earth models and user-defined horizontally layered local or regional models can be used alone or together to locate seismic events. To gain the best result from all input data, observations of all seismic phases as defined in the IASPEI91 tables can be inverted. Station corrections and corrections for phases with reflection points at the earth's surface can be applied by using local velocity structures.     

Stress Changes due to Recent Seismic Events in the Central Apennines (Italy)

The Central Apennines, Italy, are characterized by moderate seismic activity on normal faults, oriented in directions parallel to the Apenninic chain. The subject of this study is the Umbria-Marche Apennines, a segment approximately 200-km long, where three main seismic events occurred in the last three decades. The 1979 Norcia earthquake was a M_w = 5.8 event, taking place at the south end of the considered segment. The 1984 Gubbio earthquake was a M_w = 5.6 event which took place at the north end. The 1997-1998 Colfiorito sequence constituted 8 main shocks with magnitudes M_w between 5 and 6 and epicenters located between the Gubbio and the Norcia earthquake areas. A model made of an elastic half-space is considered, in which the seismic sources are represented by rectangular dislocations which have the appropriate values of source parameters, and in which the static stress field produced by each event is calculated. The analysis of the Coulomb stress change (ΔC) as a function of time shows that the coseismic stress transfer and fault interaction played an important role in the region during the past three decades: 7 earthquakes of the 9 considered took place where ΔC>0. Such an interaction has been confirmed by the analysis of the aftershocks in the Colfiorito zone post September 26, 1997: about the 61% of the aftershocks considered took place where ΔC>0. The comparison between the ΔC^s due to the coseismic stress transfer and the rate ΔĊ^t due to the tectonic stress allows us to quantify the time advance of the earthquakes. The ΔC^s pattern shows positive values in two areas that can be regarded as historical seismic gaps.     

一种自动扫描地震漏检事件方法的研究与实现

地震事件的自动处理过程中会发生遗漏.台站数量越多,地震分析员在手动扫描遗漏事件时所花费的时间就越长.本文讨论了一种自动扫描漏检事件的方法,该方法利用分析员的分析经验,结合台站分布状况和地球物理学规则,重新关联那些具有很可能来自特定震源区域而未被分析员关联的信号,以形成一个待验证的事件,供分析员审定.该方法大大减少了分析员的工作量,提高了地震公报的质量.     

一种低频地震事件的检测方法---在汶川地震和芦山地震前的初步应用

本文发展了一种单台检测低频地震事件的方法,并用其检测2008年汶川I Ms8．0地震、2013年芦山M。7．0地震震前的低频事件。使用汶JiI地震、芦山地震前周边的宽频带台站数月的垂直向连续波形,经过2～8 Hz带通滤波、窗长为10 S的包络平滑、窗长为20 rain的中值滤波,去除近场天然地震及远场大震与低频噪声的影响后,发现这两个大地震前有少数台站在连续数天的时间内,出现持续时间长(数十分钟到数小时)、包络中值明显大于背景噪声的现象,其波形记录及包络特征与非火山震颤(NVT)的波形记录及包络特征具有较好的相似性,我们认为这是汶川地震和芦山地震前的疑似慢地震事件。初步应用表明,本文所用的方法对于从宽频带连续波形资料中提取NVT信号是可行的。     

基于倾斜仪记录的地震事件自动判别初探

以垂直摆倾斜仪数据为资料,通过自编的软件对原始数据进行EMD分解,将低频固体潮和高频地震信号分开,分别对地震信号和固体潮在时间域中用长短时平均能量比(STA/LTA)的方法,实时监测到中国台湾5.4级和中缅边境地区4.9级地震事件,并区分了仪器故障。     

CTBT国际监测系统水声监测网络概况

介绍全面禁止核试验条约（CTBT）国际监测系统（IMS）水声监测网络的组成、类型、分布及其监测能力,从台站的地理位置选择、勘址条件及台站构成、性能指标等方面,详细阐述H-相和T-相水声台站的建设和发展,并分析新一代水听器台站的设计理念及研发测试进展,以期为相关技术研究和我国水声台站建设提供参考。     

Analysis of Temporal Structures of Seismic Events on Different Scale Levels

A statistical model for describing the energy scaling of the distribution of inter-event times is described. By considering the diverse region seismicity (natural and induced) on different scale (energy/magnitude) levels the self-similarity of the distribution has been determined. A comparison between the distribution of inter-event times on different scale levels and the most popular distributions of reliability theory has been carried out. The distribution of inter-event times for different scale levels is well approximated by the Weibull distribution. The Weibull distribution, with parameters which obey the scaling model and the Gutenberg-Richter law, has been tested.     

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.     

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.     

Source Time Function of Seismic Events at Rudna Copper Mine, Poland

—?The empirical Green's function deconvolution technique is used to retrieve the source time functions from the records of P waves of seven seismic events that occurred at the Rudna copper mine in 1996 and were located in the middle of the underground network. Their moment magnitudes ranged from 2.1 to 2.9. The records of smaller events from the same area and with similar source mechanism, with moment magnitudes ranging from 1.5 to 2.0, were accepted as empirical Green's functions. The relative source time functions were successfully retrieved at a number of stations for six events. Directivity effects, implying unilateral rupture propagation, were observed in five cases. The azimuth of rupture propagation direction and the rupture velocity were estimated from the distribution of pulse widths and pulse maximum amplitudes as a function of the cosine of station azimuths. The rupture propagated approximately either from south to north or from north to south. The rupture velocity was low, ranging from 0.25 to 0.54 of the shear-wave velocity. The source dimensions, represented by the fault length, were also small in comparison with those estimated in the frequency domain and ranged from 80 to 250?m.     

Satellite Earth Observations Support CTBT Monitoring: A Case Study of the Nuclear Test in North Korea of Oct. 9, 2006 and Comparison with Seismic Results

The Comprehensive Nuclear-Test-Ban Treaty prescribes the use of seismic stations and arrays as the main measure for verification of Treaty compliance. Since the inception of the Treaty, a vast amount of open source earth observation satellite data has become available. This paper investigates the potential for combining seismic and satellite data for more effective monitoring and response. With data acquired before, during and after the alleged North Korean underground nuclear test on October 9, 2006, wide area change detection techniques using medium resolution optical/infrared satellite sensors are combined with localized high-resolution imagery to attempt to pinpoint the test location within the area identified by the seismic measurements. Problems associated with the timeliness, degree of coverage and ambiguity of the remote sensing data are pointed out, however it is generally concluded that their integration into the CTBT regime would valuably complement the existing seismic observation network.     

The Rise of Earthquake Correlation Range and the Chains of Earthquakes before Large Seismic Events

Izvestiya, Physics of the Solid Earth - The paper summarizes the results of the experiment on advance earthquake forecasting using the Reverse Tracing of Precursors (RTP) algorithm based on the...     

Architecture and critical technologies of seismic information system in CTBT verification

Introduction Seismic monitoring is one of the most important approaches for ground-based nuclear explo-sion monitoring (CTBTO, 1998). The trend in this research field is to improve the monitoring ca-pability for low magnitude seismic events in regional scales. Seismic monitoring mainly includes detection, location, identification and characterization of seismic events. The correctness and accuracy of all of them depend on the quality of seismic re-cords and the degrees of uncertainties of ge…