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1.
In 1991, a digital seismic monitoring network was installed in Iceland with a digital seismic system and automatic operation. After 20 years of operation, we explore for the first time its nationwide performance by analysing the spatiotemporal variations of the completeness magnitude. We use the Bayesian magnitude of completeness (BMC) method that combines local completeness magnitude observations with prior information based on the density of seismic stations. Additionally, we test the impact of earthquake location uncertainties on the BMC results, by filtering the catalogue using a multivariate analysis that identifies outliers in the hypocentre error distribution. We find that the entire North-to-South active rift zone shows a relatively low magnitude of completeness Mc in the range 0.5–1.0, highlighting the ability of the Icelandic network to detect small earthquakes. This work also demonstrates the influence of earthquake location uncertainties on the spatiotemporal magnitude of completeness analysis. 相似文献
2.
G. A. Sobolev D. G. Sobolev I. N. Migunov N. A. Zakrzhevskaya 《Izvestiya Physics of the Solid Earth》2014,50(4):474-483
The low-frequency seismic noise recorded by the broadband IRIS stations in 1994–2012 is studied in the period range of 40 to 360 s. It is shown that for samples of a few months in length, the power spectra of noise at stations spaced apart a few thousand kilometers and operating in different meteorological and seismotectonic conditions are overall similar, which indicates that the sources of the noise are global. At the same time, the slope of the spectra changes with the increase in the period in the subintervals of 40–90, 120–200, and 200–360 s, which points to the difference of the sources generating the seismic noise. The amplitude of the noise at the stations located a few thousand km apart from the Sumatra earthquake of December 26, 2004, M = 9.2, and from the Tohoku earthquake of March 11, 2011, M = 9.0, increased after these events. This indicates the global character of the aftermath of these seismic catastrophes. After the Kronotskoe earthquake of December 5, 1997, which was weaker (M = 7.9), the noise grew only at the PET station located within 300 km of the epicenter. According to the records at the PET station, this earthquake was preceded by the increased noise level observed in 1994–1997. After 1999, the seismic noise declined and remained low up to the end of the studied interval with a duration of 14 years. Our results show that the low-frequency seismic noise generated by the sources in the atmosphere of the Earth is contributed by the processes taking place in the lithosphere. 相似文献
3.
The diurnal periodicity of seismic events of different energy from the Greece earthquake catalog was studied. Earthquake samplings of different energy with a known level of magnitude of completeness were compiled. Parameters of the diurnal periodicity of earthquakes in different time and magnitude intervals were analyzed. Significant diurnal periodicity of earthquakes with M ≤ 4.1 was revealed. The most important result of the paper is the discovery of the diurnal periodicity of the representative earthquakes with M = 3.2–4.1. The diurnal periodicity of representative earthquakes cannot be explained at the base of the prevailing hypothesis considering the diurnal periodicity of earthquakes as an apparent phenomenon resulting from diurnal changes in the real sensitivity of the seismic network due to diurnal variations of seismic noise. 相似文献
4.
Antonino D’Alessandro José Badal Giuseppe D’Anna Dimitris Papanastassiou Ioannis Baskoutas Nurcan M. Özel 《Pure and Applied Geophysics》2013,170(11):1859-1880
Spain is a low-to-moderate seismicity area with relatively low seismic hazard. However, several strong shallow earthquakes have shaken the country causing casualties and extensive damage. Regional seismicity is monitored and surveyed by means of the Spanish National Seismic Network, maintenance and control of which are entrusted to the Instituto Geográfico Nacional. This array currently comprises 120 seismic stations distributed throughout Spanish territory (mainland and islands). Basically, we are interested in checking the noise conditions, reliability, and seismic detection capability of the Spanish network by analyzing the background noise level affecting the array stations, errors in hypocentral location, and detection threshold, which provides knowledge about network performance. It also enables testing of the suitability of the velocity model used in the routine process of earthquake location. To perform this study we use a method that relies on P and S wave travel times, which are computed by simulation of seismic rays from virtual seismic sources placed at the nodes of a regular grid covering the study area. Given the characteristics of the seismicity of Spain, we drew maps for M L magnitudes 2.0, 2.5, and 3.0, at a focal depth of 10 km and a confidence level 95 %. The results relate to the number of stations involved in the hypocentral location process, how these stations are distributed spatially, and the uncertainties of focal data (errors in origin time, longitude, latitude, and depth). To assess the extent to which principal seismogenic areas are well monitored by the network, we estimated the average error in the location of a seismic source from the semiaxes of the ellipsoid of confidence by calculating the radius of the equivalent sphere. Finally, the detection threshold was determined as the magnitude of the smallest seismic event detected at least by four stations. The northwest of the peninsula, the Pyrenees, especially the westernmost segment, the Betic Cordillera, and Tenerife Island are the best-monitored zones. Origin time and focal depth are data that are far from being constrained by regional events. The two Iberian areas with moderate seismicity and the highest seismic hazard, the Pyrenees and Betic Cordillera, and the northwestern quadrant of the peninsula, are the areas wherein the focus of an earthquake is determined with an approximate error of 3 km. For M L 2.5 and M L 3.0 this error is common for almost the whole peninsula and the Canary Islands. In general, errors in epicenter latitude and longitude are small for near-surface earthquakes, increasing gradually as the depth increases, but remaining close to 5 km even at a depth of 60 km. The hypocentral depth seems to be well constrained to a depth of 40 km beneath the zones with the highest density of stations, with an error of less than 5 km. The M L magnitude detection threshold of the network is approximately 2.0 for most of Spain and still less, almost 1.0, for the western sector of the Pyrenean region and the Canary Islands. 相似文献
5.
天津测震台网地震监测能力分析 总被引：2，自引：2，他引：0
通过计算地震台站最小监控震级,得到天津测震台网地震监测能力。采用经典谱估计中的Welch算法,计算天津测震台网31个地震台站噪声水平。取噪声水平有效值的30倍作为能检测到最小地震S波的最大振幅,通过近震震级公式,计算各台站地震震级,取第4个能被检测到的台站地震震级作为最小监控震级。 相似文献
6.
Monitoring the West Bohemian earthquake swarm in 2008/2009 by a temporary small-aperture seismic array 总被引：1，自引：1，他引：0
The most recent intense earthquake swarm in West Bohemia lasted from 6 October 2008 to January 2009. Starting 12 days after
the onset, the University of Potsdam monitored the swarm by a temporary small-aperture seismic array at 10 km epicentral distance.
The purpose of the installation was a complete monitoring of the swarm including micro-earthquakes (M
L < 0). We identify earthquakes using a conventional short-term average/long-term average trigger combined with sliding-window
frequency-wavenumber and polarisation analyses. The resulting earthquake catalogue consists of 14,530 earthquakes between
19 October 2008 and 18 March 2009 with magnitudes in the range of − 1.2 ≤ M
L ≤ 2.7. The small-aperture seismic array substantially lowers the detection threshold to about M
c = − 0.4, when compared to the regional networks operating in West Bohemia (M
c > 0.0). In the course of this work, the main temporal features (frequency–magnitude distribution, propagation of back azimuth
and horizontal slowness, occurrence rate of aftershock sequences and interevent-time distribution) of the recent 2008/2009
earthquake swarm are presented and discussed. Temporal changes of the coefficient of variation (based on interevent times)
suggest that the swarm earthquake activity of the 2008/2009 swarm terminates by 12 January 2009. During the main phase in
our studied swarm period after 19 October, the b value of the Gutenberg–Richter relation decreases from 1.2 to 0.8. This trend is also reflected in the power-law behavior
of the seismic moment release. The corresponding total seismic moment release of 1.02×1017 Nm is equivalent to M
L,max = 5.4. 相似文献
7.
This study analyses the temporal clustering, spatial clustering, and statistics of the 2012–2013 Torreperogil-Sabiote (southern Spain) seismic swarm. During the swarm, more than 2200 events were located, mostly at depths of 2–5 km, with magnitude event up to mbLg 3.9 (Mw 3.7). On the basis of daily activity rate, three main temporal phases are identified and analysed. The analysis combines different seismological relationships to improve our understanding of the physical processes related to the swarm's occurrence. Each temporal phase is characterized by its cumulative seismic moment. Using several different approaches, we estimate a catalog completeness magnitude of mc≅ 1.5. The maximum likelihood b-value estimates for each swarm phase are 1.11 ± 0.09, 1.04 ± 0.04, and 0.90 ± 0.04, respectively. To test the hypothesis that a b-value decrease is a precursor to a large event, we study temporal variations in b-value using overlapping moving windows. A relationship can be inferred between change in b-value and the regime style of the rupture. b-values are indicators of the stress regime, and influence the size of ruptures. The fractal dimension D2 is used to perform spatial analysis. Cumulative gamma and beta functions are used to analyse the behaviour of inter-event distances during the earthquake sequence. 相似文献
8.
The paper addresses the collection and analysis of new data on aftershocks that occurred within 20 days of the main shock of the December 7, 1988, Spitak earthquake, Mw = 6.8. The data were used to improve the location of aftershock hypocenters and magnitudes. Available data concerning this 20-day period were the least reliable in terms of completeness, representativeness, and the accuracy of hypocenter location and, in particular, estimation of energy classes and magnitudes. New data were retrieved from the records and bulletins of the seismic stations of the regional and global networks. Hypocenter parameters were determined by means of the minimization of wave travel-time residuals and subsequent double-difference hypocenter relocation. Digital records of the Obninsk and Arti seismic stations (Δ = 15°–18°) and five more distant stations (Δ = 34°–53°) were used to more accurately estimate the surface-wave magnitude of the main shock and strongest aftershock. The aftershock catalog of the Spitak earthquake was substantially revised. First, the previous hypocenter locations (Aref’ev et al., 1991) were improved using the double-difference method; second, new data were retrieved from the bulletins of Caucasian seismic stations. The minimum magnitude of completeness (M c = 1.9) of the new catalog for the first 20 days after the main shock (when there were no epicentral observations) is the same as that for the period from December 7, 1988, to December 31, 1989. The new catalog contains information on 2090 aftershocks with magnitude M = 1.9 and more for the period from December 7, 1988, to December 31, 1989. The double-difference method allowed the location of the epicenters of clustered earthquakes to be reliably estimated with a longitude error of no more than 4.6 km, a latitude error of 4 km, and a depth error of 5 km. The new spatial distribution of the aftershock hypocenters is better correlated with the tectonic setting than the old data. The new catalog can be used to assess seismic hazard after strong earthquakes in the region. 相似文献
9.
针对2014年8月—2015年1月安徽金寨发生的M_L3.9震群,利用匹配滤波技术补充台网目录遗漏的地震事件,再利用波形互相关震相检测技术标定P波和S波到时,进一步采用双差定位方法对震群进行重定位,结合震源机制解等分析此次震群活动可能的发震构造。计算结果显示,通过互相关扫描检测到1376个地震台网常规分析遗漏的地震,数量约为台网目录给出的585个事件的2.35倍。检测到的遗漏地震震级估算为M_L0～2.3,通过震级-频次统计分析,加入遗漏地震后地震目录的完整性在M_L0～1.5范围内有较明显的改善。重定位后地震走时残差更小,水平位置更集中,沿NNE向断裂F和NW向青山-晓天断裂呈现近直立的条带状分布。结合地质构造、震源机制解和水库因素,推测2014年金寨M_L3.9震群可能是由周边水库水下渗引起NW向青山-晓天断裂与NNE向断裂F慢滑动而触发的。 相似文献
10.
针对仪器运行状况和外界环境等影响观测质量的因素,以及台站所处地质构造不同对台站影响的问题,采用位于鄂尔多斯块体北缘的乌加河台、包头台、乌海台2015～2017年DSQ水管倾斜仪的观测资料,对比分析3个台站的年零漂、相对噪声水平M_1、M2波潮汐因子γ值均方差等特征参数,并进行同震响应分析。研究表明,包头台水管仪的观测质量优于其它台站,主要是体现在零漂小、精度高、稳定性好,研究结果为评定水管仪观测质量提供了科学依据。同震响应的延迟时间与震中距相关,最大振幅与震级间呈正相关,与震中距间呈负相关。 相似文献
11.
The potential and limits of monitoring induced seismicity by surface-based mini arrays was evaluated for the hydraulic stimulation of the Basel Deep Heat Mining Project. This project aimed at the exploitation of geothermal heat from a depth of about 4,630?m. As reference for our results, a network of borehole stations by Geothermal Explorers Ltd. provided ground truth information. We utilized array processing, sonogram event detection and outlier-resistant, graphical jackknife location procedures to compensate for the decrease in signal-to-noise ratio at the surface. We could correctly resolve the NNW?CSSE striking fault plane by relative master event locations. Statistical analysis of our catalog data resulted in M L 0.36 as completeness magnitude, but with significant day-to-night dependency. To compare to the performance of borehole data with M W 0.9 as completeness magnitude, we applied two methods for converting M L to M W which raised our M C to M W in the range of 0.99?C1.13. Further, the b value for the duration of our measurement was calculated to 1.14 (related to M L), respectively 1.66 (related to M W), but changes over time could not be resolved from the error bars. 相似文献
12.
内蒙古地区地方性震级的量规函数研究 总被引：2，自引：1，他引：1
选取2008年1月~2015年11月内蒙古测震台网81个台站所记录的6342次地震事件,基于震级残差统计方法,计算了81个台站单台震级与台网平均震级的偏差、平均偏差和标准偏差。分析认为,BHS等6个台站震级偏差较大的原因可能是台站场地响应放大、台基风化等。台基校正前、后单台震级平均偏差值ΔMLi随震中距的变化曲线显示,曲线形态基本未有大的改变,台基校正后较之前震级平均偏差绝对值降低0.01,表明台基对地方性震级偏差的影响不大。同时,进行了81个台站的台基校正获得了内蒙古新量规函数,结果表明,全国量规函数除了震中距为0~120km时适合于内蒙古地区以外,其余情况下均偏高,不符合内蒙古地区的特征。因此,本文修定了全国量规函数,得到了校正后的内蒙古地区量规函数。 相似文献
13.
利用山东台网记录的长岛震群2017年2月14日—9月1日期间的波形与震相资料研究长岛地区非弹性衰减系数,得到该地区介质平均Q值与频率f的关系式为Q(f)=363.9f1.374 1。采用Moya等[1]提出的利用遗传算法联合反演得到长岛周边台站的场地响应,根据Brune模型震源参数计算公式求解长岛震群序列地震震源参数。结果显示,各个震源参数之间均存在一定的相关关系,地震矩随ML震级的增大而增加,地震矩与破裂半径R之间存在半对数关系,拐角频率fc随地震矩的增大而减少;长岛地震序列的应力降数值普遍偏小,最大不超过0.9MPa,这意味着长岛震源区整体构造应力较低,也可能指示长岛震群为低摩擦应力的断层作用;震源参数随时间的变化方面,整体而言,长岛震群地震应力降变化起伏很大,在M4.1地震发生前,拐角频率与应力降均发生快速下降后随即翻转上升的现象,证明在M4.1地震发生前震源区整体应力的挤压逐渐增强。 相似文献
14.
针对中国地震台网"十五"项目建成后的地震监测能力科学评估的需求,为进一步优化台网布局、提升边疆海域等重点地区监测能力,本研究利用"基于概率的完整性震级"（PMC）方法,对中国地震台网1001个台站以及2008-10-01-2015-09-17期间实际产出的地震观测资料进行了研究,分析了指定震级档下的检测概率PE和最小完整性震级MP的分布.除台网整体监测能力分布外,为直观地用单分值表述逐个台站的地震检测能力,本文发展了基于等振幅曲线的"地震检测能力评分表",给出了国家台和区域台每个台站的地震检测能力评分统计特征和空间分布特征.此外,研究中还采用设定"最佳"地震监测能力目标函数的方式,模拟了通过改进观测条件可获得的地震台网监测能力提升的理论结果.研究结果表明,我国华北和东南沿海等东部地区地震监测能力较高,西部尤其是青藏高原南部地区Mp仅约为4.5,近海海域Mp仅约为3.5;从单个地震台站的运行效益角度,台网运行水平和地震观测资料的分析程度对台站的实际的地震检测能力影响显著,新疆等部分台站稀疏地区地震检测能力较高,而中等台站密度的贵州等部分区域相对较低;国家台的地震检测能力评分Dscore系统优于区域台,新疆等西部边疆地区,以及福建等东南沿海地区的Dscore明显高于台站密集的东部地区;模拟结果显示,在现有台站布局条件下,通过台站优化改造和提升运维管理水平,可显著提升对内蒙古西部、四川西部、甘肃-青海的北部交界地区、鄂尔多斯地块内部、贵州大部分地区,以及我国近海海域、朝鲜半岛北部和中南半岛北部地区的地震监测能力. 相似文献
15.
Romania is an earthquake prone area with a few destructive earthquakes per century. The National Institute for Earth Physics carries out the seismic survey of Romania through the Romanian National Seismic Network (RNSN) consisting of 65 real-time seismic stations. Daily reports and monthly bulletins are delivered after routinely analyzing and processing the recorded data. In the present paper we applied the Seismic Network Evaluation through Simulation method for the RNSN configuration as it was in August 2011 to estimate the background noise level, assess the appropriateness of the velocity model adopted in routine location procedure, evaluate the hypocenter location uncertainty and determine the detection magnitude threshold. Areas of greater (southern Romania) and lower (Carpathians and Apuseni Mountains) background noise within the RNSN are identified by mapping the average power of noise in 1–12?Hz frequency range. The statistical study of the P and S phases residual times allow us to assess the appropriateness of the velocity model used in routine location. Both P- and S-wave velocity models can be optimized to improve the quality of the hypocenter location. As shown by our analysis, the RNSN is able to detect and locate earthquakes with M L magnitude above 2.5 anywhere on the Romanian territory, except the border areas, such as the Crisana–Maramures seismic source zone. Merging data from both sides of the border significantly improves the quality of hypocenter location in these areas. 相似文献
16.
Probabilistic seismic hazard analysis (PSHA) has been carried out for Iraq. The earthquake catalogue used in the present study covers an area between latitude 29°–38.5° N and longitude 39°–50° E containing more than a thousand events for the period 1905–2000. The entire Iraq region has been divided into thirteen seismogenic sources based on their seismic characteristics, geological setting and tectonic framework. The completeness of the seismicity catalogue has been checked using the method proposed by Stepp (1972). The analysis of completeness shows that the earthquake catalogue is not complete below Ms=4.8 for all of Iraq and seismic source zones S1, S4, S5, and S8, while it varies for the other seismic zones. A statistical treatment of completeness of the data file was carried out in each of the magnitude classes. The Frequency Magnitude Distributions (FMD) for the study area including all seismic source zones were established and the minimum magnitude of complete reporting (Mc) were then estimated. For the entire Iraq the Mc was estimated to be about Ms=4.0 while S11 shows the lowest Mc to be about Ms=3.5 and the highest Mc of about Ms=4.2 was observed for S4. The earthquake activity parameters (activity rate , b value, maximum regional magnitude mmax) as well as the mean return period (R) with a certain lower magnitude mmin m along with their probability of occurrence have been determined for all thirteen seismic source zones of Iraq. The maximum regional magnitude mmax was estimated as 7.87 ± 0.86 for entire Iraq. The return period for magnitude 6.0 is largest for source zone S3 which is estimated to be 705 years while the smallest value is estimated as 9.9 years for all of Iraq.The large variation of the b parameter and the hazard level from zone to zone reflects crustal heterogeneity and the high seismotectonic complexity. The seismic hazard near the source boundaries is directly and strongly affected by the change in the delineation of these boundaries. The forces, through which the geological structure along the plate boundary in Eastern and Northeastern Iraq are evolved, are still active causing stress-strain accumulation, deformation and in turn producing higher probabilities of earthquake activity. Thus, relatively large destructive earthquakes are expected in this region. The study is intended to serve as a reference for more advanced approaches and to pave the path for the probabilistic assessment of seismic hazard in this region. 相似文献
17.
We have employed 10 digital records and computed the spectral magnitude and the seismic radiated energy for 18 large earthquakes
(M
s≥6) occurred in Eur-asian belt during 1986–1989. The nine digital stations (CD-SN) distribute all over China and one in Germany.
The spectral magnitudes of various period have different stability among stations. The stability is better for maximum spectral
magnitudemi and seismic radiated energyE, their differences among stations are smaller, especially for the stations where the ray path main penetrates the low mantle.
But the stability of corner period is usually not good. The relation between seismic radiated energy and seismic moment magnitudeM
w is lg (E)=1.5Mw+c, wherec is a constant. The maximum spectral magnitudemi=M
w+0.1, it is consistant with theoretical prediction.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 418–426, 1993.
This work supported by the Deutsche Forschungsgemeinschaft, Bonn, F. R. Germany. The support is grateful acknowledge. 相似文献
18.
利用基于GPU加速的匹配定位法和双差定位法,对江苏盐城及邻区18个台站记录的2009~2018年共10年的连续地震资料进行分析。首先从台网目录中挑选211个地震事件作为模板事件,使用匹配定位技术对江苏盐城附近连续10年的地震进行检测和识别,共识别出1349个地震事件,约为台网目录地震事件的3倍,最小完备震级由台网目录的ML1.9降为ML1.2。然后利用双差定位法对检测到的地震事件进行精定位,精定位的结果揭示：建湖地区的地震密集带与洪泽-沟墩断裂有关,震源深度优势分布为5~20km,断裂两侧震源深度有显著差异,断裂带倾向NW;射阳震群震源深度比建湖震群有所加深,优势分布为10~25km,震源深度由南东向西北逐渐变浅;宝应地区地震丛集分布;东台地区由于模板事件相对较少,扫描定位后,地震事件在陈家堡-小海断裂带附近零星分布。研究结果为研究盐城地区的地震活动性、发震断层的深部构造提供了基础数据支撑。 相似文献
19.
使用2022年1月8日青海门源MS6.9地震前3天及后7天甘肃地震台网固定台站和邻省共享台站记录到的连续波形数据,利用RISP系统自动检测余震序列,并将检测结果与人工编目结果进行对比分析.结果表明:自动编目与人工编目定位结果基本一致,震中位置差(3.9±1.51)km,震级差值ML(0.17±0.22);自动编目结果的发震时刻普遍略早于人工目录,但两种目录中大部分余震发生时刻的差值在2s内.自动编目产出速度快,且能检测人工无法识别的微小余震,提高了目录完备性.综合来看,自动编目系统产出结果符合预期目标,可为震群趋势判断、破裂过程快速反演等相关科学研究提供数据支撑. 相似文献
20.
识别显著影响重点监视区地震检测能力的“敏感台站”, 对有针对性地开展地震台网运行维护和加强相关区域天然地震与非天然地震的监视跟踪工作有重要意义。 利用基于概率的最小完整性震级(PMC)方法, 通过对研究区地震台站进行“检测能力评分”(Dscore)和“缺失评分”(Missing Score)方式进行识别研究, 以龙门山断裂南段强震危险区为例的重点监视区“敏感台站”识别结果表明, 研究区内51个台站的“检测能力评分”及“缺失评分”, 可识别对重点监视区地震检测能力影响最大的台站, 给出台站停止运行引起的最小完整性震级的变化, 并探讨了多台站停止运行等造成影响的极限情况。 上述“敏感台站”的识别方式, 可为地震台网运行维护、 针对特定目标区的地震监视跟踪和进一步的台网优化改造提供参考。 相似文献