Local magnitude,surface wave magnitude and seismic energy

Summary The local magnitude M_L at the seismological station Pruhonice (PRU) was converted into surface wave magnitude M_S using the formula M_S=–3.2+1.45 M_L and the seismic wave energy was estimated using the relation log E (Joule)=1.2+2.0 M_L. It was proposed to apply the same conversion formulae at seismological stations Kaperské Hory (KHC) and Berggiesshübel (BRG) where the calibrating functions for local magnitudes were determined for the same set of earthquakes with common reference magnitudes as in the case of the PRU station.     

A scheme to set preferred magnitudes in the ISC Bulletin

One of the main purposes of the International Seismological Centre (ISC) is to collect, integrate and reprocess seismic bulletins provided by agencies around the world in order to produce the ISC Bulletin. This is regarded as the most comprehensive bulletin of the Earth’s seismicity, and its production is based on a unique cooperation in the seismological community that allows the ISC to complement the work of seismological agencies operating at global and/or local-regional scale. In addition, by using the seismic wave measurements provided by reporting agencies, the ISC computes, where possible, its own event locations and magnitudes such as short-period body wave m _b and surface wave M _S . Therefore, the ISC Bulletin contains the results of the reporting agencies as well as the ISC own solutions. Among the most used seismic event parameters listed in seismological bulletins, the event magnitude is of particular importance for characterizing a seismic event. The selection of a magnitude value (or multiple ones) for various research purposes or practical applications is not always a straightforward task for users of the ISC Bulletin and related products since a multitude of magnitude types is currently computed by seismological agencies (sometimes using different standards for the same magnitude type). Here, we describe a scheme that we intend to implement in routine ISC operations to mark the preferred magnitudes in order to help ISC users in the selection of events with magnitudes of their interest.     

地震监测仪器综合管理系统的设计与应用

随着地震监测建设力度的增加,地震监测系统主要涵盖了测震、形变、流体、磁电等四大学科的地震观测仪器.分析现有的仪器运维管理工作状况,存在着仪器组成复杂、配套设备繁杂、观测项目众多、维修更新管理落后等问题,结合江苏省地震观测仪器管理运维的实际情况,采用PHP语言开发了基于MySQL关系型数据库的地震监测仪器综合管理系统,初步实现了对地震监测仪器的运维监控和维修管理的网络化和实时化,该综合管理系统已在江苏省地震监测中心服务器上运行2年,取得较好的效果.     

Detection capability of seismic network based on noise analysis and magnitude of completeness

Assessing the detection threshold of seismic networks becomes of increased importance namely in the context of monitoring induced seismicity due to underground operations. Achieving the maximum possible sensitivity of industrial seismic monitoring is a precondition for successful control of technological procedures. Similarly, the lowest detection threshold is desirable when monitoring the natural seismic activity aimed to imaging the fault structures in 3D and to understanding the ongoing processes in the crust. We compare the application of two different methods to the data of the seismic network WEBNET that monitors the earthquake swarm activity of the West-Bohemia/Vogtland region. First, we evaluate the absolute noise level and its possible non-stationary character that results in hampering the detectability of the seismic network by producing false alarms. This is realized by the statistical analysis of the noise amplitudes using the ratio of 99 and 95 percentiles. Second, the magnitude of completeness is determined for each of the nine stations by analysing the automatic detections of an intensive swarm period from August 2011. The magnitude–frequency distributions of all detected events and events detected at individual stations are compared to determine the magnitude of completeness at a selected completeness level. The resulting magnitude of completeness M _c of most of the stations varies between ?0.9 and ?0.5; an anomalous high M _c of 0.0 is found at the most distant station, which is probably due to inadequate correction for attenuation. We find that while the absolute noise level has no significant influence to the station sensitivity, the noise stationarity correlates with station sensitivity expressed in low magnitude of completeness and vice versa. This qualifies the method of analysing the stationary character of seismic noise as an effective tool for site surveying during the seismic station deployment.     

广西区域数字地震台网建设与发展

进入21世纪以来,广西地震观测系统得到了迅速的发展.回顾了广西数字地震台网建设的发展历史,重点介绍了“十五”期间广西各级地震台网的建设情况,阐述了广西区域数字测震台网实现与邻省、地方和企业不同属性和类别的台网联网和数据共享后,地震监测能力获得了极大的提高过程.     

核试验监测的地震学研究综述

侦察探测核爆事件,评估核爆信息等核试验监测工作,对评估核爆威力、研究核爆炸现象以及各种破坏因素的变化规律有着重要意义.地震学提供了核试验监测中关键的研究手段.核试验地震学监测研究主要包括核试验识别、定位、埋深、震级和当量的估计等内容.根据近半个世纪以来核试验方式的变化和技术的发展,介绍和总结了核试验监测中相关研究进展状况,主要包括事件定位、判别、震级测定、当量和埋深估计等地震学观测、理论和方法.     

山西临汾地震台地电阻率异常分析与探讨

对山西临汾地震台地电阻率观测数据在临汾及其周边地区发生4．0级以上地震时的异常变化、异常形态进行了对比分析,认为,临汾中心地震台地电阻率对于捕捉该区地震前兆异常信息有积极的意义;对2008年4月以来临汾中心地震台地电阻率观测数据的变化情况、变化形态做了分析,其结果可为场源外区域地电异常的研究提供依据和参考。     

山西大同数字遥测地震台网技术系统的建设

叙述了山西大同数字遥测地震台网的结构及监测能力，台网的功能及技术指标和遥测台技术系统、供电系统、中心系统、避雷系统、中继站、信道等的建设情况，分析了山西大同数字遥测地震台网考核运行期间获得的资料，结果表明，大同数字遥测地震台网在检测地震能力、动态范围、地震处理精度和速度方面优于模拟台网，对网内大部分区域及东部网缘区域的地震监控能力可达1.5级，网内地震响应速度小于10min，得出该台风可为地学研究及地震预报提供更为丰富的数字地震资料的结论。     

Intermediate and deep earthquakes in Spain

Recent improvements in the seismological networks on the Ibero-Maghrebian region have permitted estimation of hypocentral location and focal mechanisms for earthquakes which occurred at South Spain, Alboran Sea and northern Morocco of deep and intermediate depth, with magnitudes between 3.5 and 4.5. Intermediate depth shocks, range from 60 to 100 km, with greater concentration located between Granada and Málaga. Fault-plane solutions of 5 intermediate shocks have been determined; they present a vertical plane in NE-SW or E-W direction. Seismic moments of about 10¹⁵ Nm and dimensions of about 1 km have been determined from digital records of Spanish stations.P-wave forms are complex. This may be explained by the crustal structure near the station, discontinuities in the upper mantle and inhomogeneities near the source. Deep activity at about 650 km has only 3 shocks since 1954 (1954, 1973, 1990). Shocks are located at a very small region. Fault-plane solutions show a consistent direction of the pressure axis dipping 45° in E direction. For the 1990 shock seismic moment is 10¹⁶ Nm and dimensions 2.6 km. TheP-waves are of simpler form with a single pulse. The intermediate and deep activities are not connected and no activity has been detected between 100 and 650 km. The intermediate shocks may be explained in terms of a recent subduction from Africa under Iberia in SE direction. The very deep activity must be related to a sunk detached block of lithospheric material still sufficiently cold and rigid to generate earthquakes.     

Results of seismological observations in the western Kaliningrad region and in the Baltic Sea water area

In 2006–2007, researchers of the IO RAS conducted seismological observations in the Baltic Sea and western Kaliningrad region with the use of ocean-bottom and land-based autonomous seismic stations. According to maps of general seismic zoning of the territory of Russia, the Kaliningrad region is aseismic. However, a series of seismic phenomena with magnitudes of about 5 and sources located near the Bay of Gdansk coast occurred here in September 2004. The total duration of the IO RAS seismological observations in five areas of the region under investigation was more than 200 days. The analysis of seismic records of the IO RAS network located sources of two local weak earthquakes with magnitudes M _L = 3.4–3.5, which indicates that the seismic process in the western part of the Kaliningrad region continues and the region is far from being seismically stable.     

单台数字化地震监测系统在地方地震工作中的应用

广州市番禺区地层办公室在全国地方地层工作部门范围内，首先建成了一套单台数字化地层监测系统——TDS单台数字化地震监测处理系统，提高了番禺及其邻近地区的地层监测能力，为政府快速反应提供依据，并配合其他职能部门，在地震应急、解决因爆破引起的纠纷和地震科普宣传等方面得到了很好的应用。     

Anomalous CO2 content in the Gallicano thermo-mineral spring (Serchio Valley,Italy) before the 21 June 2013, Alpi Apuane earthquake (M = 5.2)

Since late 2002, a continuous automatic monitoring network is operating in Tuscany, Central Italy, to investigate the geochemical response of selected aquifers to local seismic activity. The monitoring is aimed at identifying possible earthquake geochemical precursors. The network is currently constituted by six stations, all equipped with sensors for the measurement of temperature, pH, redox potential, electrical conductivity, CO₂ and CH₄ dissolved concentration, that have been installed in the areas of highest seismic risk of the region. By combining geochemical data gathered from the automatic station of Gallicano (Garfagnana, Northern Tuscany), and obtained via chemical analyses of spring water samples collected during periodic field surveys in the area surrounding this station, the most significant aspects of the deep fluid circulation paths feeding the Gallicano thermo-mineral system have been investigated, and the geochemical baseline of the Gallicano spring defined. The CO₂ continuous signal recorded by the Gallicano automatic station has been then processed over the period 2003–2013 in the search for anomalies possibly related to local seismic activity. A substantial anomaly in CO₂ content has been observed at Gallicano in conjunction with the Alpi Apuane earthquake (M = 5.2) of 21 June 2013.     

2017年九寨沟7.0级地震前不同级别地震空区的演化过程分析

结合传统地震学方法与数字地震学方法,回顾总结了日常分析预报中针对九寨沟7.0级地震开展的相关工作,梳理总结了地震前提出的甘东南地震异常信息,进一步讨论了九寨沟地震前中期、短期及临震异常特征。通过分析九寨沟7.0级地震之前区域范围内不同震级活动图像,发现甘青川交界地区5级空区在震前向震中一侧收缩、4级地震超长平静458天、3级空区在震前4天被打破的现象,同时发现,震中附近区域震源机制一致性较高,反映了震源区的高应力水平。     

临夏地震台观测到的临震预滑和震颤震相

对临夏地震台的YRY-4分量应变仪、水位仪和地震仪记录数据分析后发现:2008年5月12日汶川MW 7.9地震前,在3种不同学科的观测记录上,在相近时间段内均记录到了预滑震相Xp和震颤震相Tp.总结Xp震相和Tp震相记录特征的基础上,试图用实验室做的小尺度黏滑实验结果来佐证和解释所记录到的临震预滑和震颤震相的物理机制....     

Vibration Effect of Near Earthquakes at Different Depths in a Shallow Medieval Mine

The shallow medieval Jeroným Mine is located at a distance of about 25 km southeast of the Nový Kostel focal zone where the most intensive seismic activity in West Bohemia (Czech Republic) has been documented. Permanent seismological monitoring has been carried out since 2004 in this mine. During the 2011 and 2014 seismic swarms, more than 1000 triggered records comprising almost 1500 earthquakes were recorded at the permanent station in the mine. Three short-term seismological experiments were accomplished during these swarms. Several temporary seismic stations were simultaneously placed in different parts of underground spaces which enabled comparison of vibration effect caused by near earthquakes in different parts of the mine. Although the depth of the lowest parts of mine is only about 60 m, a vibration effect generated by earthquakes from the Nový Kostel focal zone is not the same for the whole underground complex.     

Site characterizations for the Tehran network (TDMMO) in Tehran Region Using Micro-Earthquake,Microtremor and Quarry Blast Data

We did a Study of Horizontal-to-Vertical Component Spectral Ratio in the Tehran seismic zone. Micro-earthquakes, microtremors and quarry blasts data were used as an estimation of the site response in the Tehran zone. Site effects were studied based on horizontal to vertical ratios by the Nakamura׳s technique. Also, we used the spectra of signals for three components with the lowest noise levels for spectral slope studies. The analysis used seismic events from a network of 13 seismic stations by the permanent local seismological network of the Tehran Disaster Mitigation and Management Organization (TDMMO) from 2004 to 2007. The number of events used were different for each station. Quarry blast events were with 1.2≤M_L≤2.2 and micro-earthquakes were with 1.1≤M_L≤4.1.By comparing results for earthquake, microtremor and quarry blast, we could see that there is a significant difference between them. The data showed clear observations, especially in high-frequencies. The H/V spectral ratios indicate dominant frequency for rock/soft site with a higher ratio level for quarry blast ratios, which are comparable to the earthquake results due to their difference sources. The results derived by spectral H/V ratios and spectral analysis may be used to distinguish between local earthquakes and quarry blasts.     

Application of scaling-rule theory in crustal rock fracture to studying characteristics of seismological precursors associated with M=6.1 Shandan-Minle earthquake

In the paper, we introduce Allegre＇s scaling-rule theory of rock fracture and the probability to develop a method for predicting earthquake occurrence time on its basis. As an example, we study the characteristics of seismological precursors （seismic spatial correlation length and coda Qc） associated with the earthquake （M=6.1） occurred in Shandan-Minle, Gansu Province. The results show an increasing trend of seismic spatial correlation length and coda Qc before the earthquake. And a power exponent relation is used to fit the increasing variation form of these two parameters. The study has provided a basis for creating a method and finding indexes to predict the earthquake occurrence time by using the monitored seismic spatial correlation length and coda Qc.     

Designing and testing a network of passive seismic surveying and monitoring in Dehdasht (South Western Iran)

From August 2016 to July 2017, a passive seismic survey was conducted in South Western Iran as a part of a pilot project aimed to improve the imaging in geologically complex areas. Passive seismic methods have shown to be a useful tool to infer the physical properties of the underground geological structures where traditional hydrocarbon exploration methods are challenging. For this purpose, a dense passive seismic network consisting of 119 three-component borehole seismic stations was deployed over an area of 400 km² around the city of Dehdasht. This paper focuses on the details of the network design, which was devoted to high-resolution seismological applications, including local earthquake tomography and seismic attenuation imaging. In this regard, we describe the instrument types and the station installation procedures used to obtain high-quality data that were used to retrieve three-dimensional models of P- and S-wave velocity and P-wave attenuation in the area using tomographic inversion techniques. We also assess the network performance in terms of the seismic ambient noise levels recorded at each station site, and we revise the horizontal orientation of the sensors using surface waves from teleseismic earthquakes.     

Changes in earthquake energy class as a factor affecting the parameters of the recurrence relation: The Baikal region

The numerical modeling of actually observed events contained in the Baikal earthquake catalog allowed the production of synthetic catalogs. These catalogs reflect real situations that can give rise to heterogeneities in earthquake catalogs acquired by seismological monitoring. For each of the resulting 65 catalogs we calculated the slope γ and seismic activity (so-called in Russian; it is the seismicity rate or the constant term in the frequency-size relation) A ₁₀ in the recurrence relation. We also investigated the effects of changes in estimates of earthquake energy class on the parameters of the recurrence relation. It was shown that the slope γ is not very sensitive, but that the seismic activity A ₁₀ is sensitive, to changes in earthquake energy class and can be used to test an earthquake catalog for heterogeneity. Formulas were derived to relate the parameters of recurrence relations and the scaling factors of two energy scales, which can yield recurrence parameters for one of the scales, provided we know the ratio of the respective scaling factors and the recurrence parameters based on the other scale.     

Seismological model parameters for northeastern and its surrounding region of India

A point source seismological model is used in this study to model the available strong motion accelerograms recorded by 17 events and to calculate three seismological model parameters, the source, path, and quality factor. Due to the paucity of recorded events, this is the first time these model parameters have been obtained for the northeastern and its surrounding region of India. The quality factors of the horizontal and vertical components of recorded events with corresponding standard deviations are Q_H(f) = 188.55f^0.94, σ₁ value (25, 0.025) and Q_V(f) = 169.76f^0.93, σ₁ value (20, 0.03), respectively. The source parameter stress drop values (μσ) vary within 124–180 bars for the subduction region and 80–169 bars for the active region. The Kappa factors for the horizontal and vertical components of recorded events on the soft rock site are 0.06 and 0.05, respectively. These seismological model parameters obtained in this study will be useful for future work deriving a ground motion attenuation relation based on a spectral model. Finally, these results are useful for seismic hazard assessment of a region having sparsely recorded events.