Scaling relations of moment magnitude,local magnitude,and duration magnitude for earthquakes originated in northeast India

In this study, we aim to improve the scaling between the moment magnitude (M _W), local magnitude (M _L), and the duration magnitude (M _D) for 162 earthquakes in Shillong-Mikir plateau and its adjoining region of northeast India by extending the M _W estimates to lower magnitude earthquakes using spectral analysis of P-waves from vertical component seismograms. The M _W-M _L and M _W-M _D relationships are determined by linear regression analysis. It is found that, M _W values can be considered consistent with M _L and M _D, within 0.1 and 0.2 magnitude units respectively, in 90 % of the cases. The scaling relationships investigated comply well with similar relationships in other regions in the world and in other seismogenic areas in the northeast India region.     

Earthquake damage to earth dams in Japan—maximum epicentral distance to cause damage as a function of magnitude

Small scale agricultural earth dams have been damaged by several past earthquakes. Damage to earth dams occurred at distances from the epicentre that increased in proportion to the scale of the earthquakes. On studying the damage a constant relation between the magnitude of the earthquake and maximum epicentral distance where the damage occurred was obtained. This relationship is similar to that obtained between the magnitude and the maximum epicentral distance at which liquefaction occurs. This, and the fact that earth dams which have been damaged several times due to liquefaction were near the critical epicentral distance, suggests that liquefaction of the foundation ground is the main cause of damage to earth dams.     

Calibration of magnitude scales for earthquakes of the Mediterranean

In order to provide the tools for uniform size determination for Mediterranean earthquakes over the last 50-year period of instrumental seismology, we have regressed the magnitude determinations for 220 earthquakes of the European-Mediterranean region over the 1977–1991 period, reported by three international centres, 11 national and regional networks and 101 individual stations and observatories, using seismic moments from the Harvard CMTs. We calibrate M(M₀) regression curves for the magnitude scales commonly used for Mediterranean earthquakes (M_L, M_WA, m_b, M_S, M_LH, M_LV, M_D, M); we also calibrate static corrections or specific regressions for individual observatories and we verify the reliability of the reports of different organizations and observatories. Our analysis shows that the teleseismic magnitudes (m_b, M_S) computed by international centers (ISC, NEIC) provide good measures of earthquake size, with low standard deviations (0.17–0.23), allowing one to regress stable regional calibrations with respect to the seismic moment and to correct systematic biases such as the hypocentral depth for M_S and the radiation pattern for m_b; while m_b is commonly reputed to be an inadequate measure of earthquake size, we find that the ISC m_b is still today the most precise measure to use to regress M_W and M₀ for earthquakes of the European-Mediterranean region; few individual observatories report teleseismic magnitudes requiring specific dynamic calibrations (BJI, MOS). Regional surface-wave magnitudes (M_LV, M_LH) reported in Eastern Europe generally provide reliable measures of earthquake size, with standard deviations often in the 0.25–0.35 range; the introduction of a small (±0.1–0.2) static station correction is sometimes required. While the Richter magnitude M_L is the measure of earthquake size most commonly reported in the press whenever an earthquake strikes, we find that M_L has not been computed in the European-Mediterranean in the last 15 years; the reported local magnitudes M_WA and M_L do not conform to the Richter formula and are of poor quality and little use, with few exceptions requiring ad hoc calibrations similar to the M_S regression (EMSC, ATH). The duration magnitude M_D used by most seismic networks confirms that its use requires accurate station calibrations and should be restricted only to events with low seismic moments.     

吉林地震台网与中国地震台网测定东北地区深源地震震级偏差研究

选用吉林地震台网正式运行以来记录的18次东北地区mb (mB)≥4.0深源地震资料,以中国地震台网地震目录给出的震级为标准震级,进行震级偏差统计分析,得出震级校正值.分析震级差异形成的原因,为吉林地震台网测定东北深源地震震级偏差校正提供参考.     

Loss estimation: a powerful tool for risk assessment and mitigation

Earlier loss estimation studies were limited to investigating particular scenarios and were carried out by highly specialized experts. Today, loss estimation techniques are translated into efficient software applications that are accessible by a large constituency of end-users. These techniques offer a high level of analysis sophistication and enable users to perform various ‘if–then’ scenarios to study the sensitivity of the results, to develop a better understanding of the outcomes and to gain insight on the consequences of the findings and decisions. Functionality of loss estimation models has improved significantly due to advances in information technology such as the introduction of Geographical Information Systems (GIS). GIS allows for easy display of input and output (in standard reports and maps) providing a critical functionality for communication of outcomes to emergency planners and decision-makers.     

地震活动期、幕最大地震M1的估计及中-长期地震趋势预测

提出一种地震活动期、幕最大地震M1的估计方法：利用中低震级累计频度∑N与震级近似的直线关系得到间隔地震频度N与震级的线性关系。用间隔度N与震级的线性关系估计最大地震M1。结果表明，以震级－间隔频率的线性关系估计的M1比震级－累计频度关系得到的M1更接近实际发生的最大地震震级，震级－累计频率关系得到M1通常被高估。基于震级－累计频度关系曲线的特征和震级－间隔频度的线性关系估计的最大地震M1，可为中－长期地震趋势预测提供新的信息。研究表明，中国大陆自1979年开始的地震幕即将结束，而帕米尔东北侧自1915年以来的地震平静期也将结束。     

基于MGR模型修正我国大陆中强以上地震的震级-频度关系和确定震级极限值div

从理论上推导了修正的古登堡-里克特模型的震级上限的确定方法, 应用常用的两种模型对我国分区域进行了震级-频度关系的修正和震级极限值的确定. 结果表明, 我国大陆存在非线性的震级-频度关系, 传统的NGR模型不能反映非线性的震级-频度关系, 而MGR模型能反映适合非线性和线性的震级-频度关系, 因此MGR模型适合我国各研究区中强以上地震的震级-频度关系. 当震级 频度关系为非线性时, 用MGR模型确定的震级极限值较准确．      

地震强度因子Mf值在华南和东北地区中强以上地震前的空间异常变化

将地震强度因子Ｍｆ值用于华南和东北地区地震的中期预报,以检验Ｍｆ值在上述地区对Ｍｓ≥５．０级以上地震的预报效果。结果表明,震前２￣３ａ开始震中周围区域一般都出现明显的Ｍｆ值中期异常区,表明Ｍｆ值对华南和东北地区中强以上地震具有较好的预报效能。     

分区量规函数在河北地震台网近震震级测定的适用性

选取河北地震台网2008—2016年记录的1 714个M_L≥0.1地震,采用分区量规函数（新量规函数）重新计算并对比分析M_L震级。实际结果表明,采用新旧量规函数计算得到的近震震级一致性较好,M_L震级偏差在±0.1的地震共1 556个,约91.8%,且抽样地震近震震级均值和标准方差更小。因此,使用分区量规函数,河北地震台网近震震级测定精度和适用性更好。     

Maximum likelihood estimation of Gutenberg-Richterb parameter for uncertain magnitude values

The maximum likelihood estimation of theb parameter in the Gutenberg-Richter relation is extended to the case of uncertain magnitude. An interval which contains the real unknown magnitude is used rather than the uncertain magnitude itself. The proposed approach is very flexible, it allows for the combination of the parts of a catalog of different quality into a single minimally biased set of recurrence parameters.On leave from the Institute of Geophysics, Polish Academy of Sciences, 00-973 Warsaw, Pasteura 3, Poland     

影响福建数字遥测地震台网震级测定的部分因素

通过对福建数字遥测台网1999年所监测到的“9.21”台湾南投大震群和“9.23”福州小震群中的一系列较大地震进行分析，利用地震的时间和空间相对集中这一特点，有效地避开震源、路径及随时间变化的地质背景等因素对测定震级的干扰，发现了对测定台网平均震级影响的主要因素，不仅仅来自于台站地质背景的影响、台网使用的起算函数的影响，而且还发现在一定距离内地震周期也会对台网平均震级测定产生明显的影响。通过计算地动位移随震中距衰减的系数和起算函数随震中距增幅的系数，求出起算函数引起震级偏差的大小，提出了改进和消除这些影响的方法。     

Revision of the amplitude-distance relation for local magnitude estimation in Italy

Maximum amplitude observations of local and regional seismic phases(S _g and L _g, with 800 km) recorded by stations of the I.N.G.National Seismological Network in the period 1994–1999 have beenused to investigate the attenuation of such phases in Italy. The propagationmodel adopted herein accounts for both geometrical spreading, with a termdepending on a given power of distance, and inelastic absorption of themedium, with a term depending exponentially on the distance. Fitting theparameters of the model with experimental data, we considered two cases:assuming a quality factor Q proportional to the frequency f orindependent of f. We compared our results with the values tabled byRichter in 1935, which are still used for the local magnitude estimate in theI.N.G. bulletins. The values found in this study are different than thosegiven by Richter. This suggests that these new values should be used insteadto compute the local magnitude in Italy.     

川滇地震科学实验场地震目录最小完整性震级分析

地震目录是地震监测预报、地震活动性等研究的重要资料.川滇地震科学实验场地区近几十年来积累了大量的地震记录,为实验场的地震科学研究提供了宝贵的数据.地震台网密度和仪器观测精度是逐步提高的,不同时期地震目录的完整性存在差异,因此进行现代仪器观测记录的地震目录最小完整性震级（M_C,Magnitude of Completeness）分析,对正确研究和认识该地区地震活动规律及其影响因素等具有重要意义.本文采用震级—序号方法、最大曲率法（MAXC,Maximum Curvature）和拟合度检测法（GFT,Goodness-of-Fit Test）分析了川滇地震科学实验场地区1970—2018年地震目录的最小完整性震级M_C值,得到了实验场地区及其内部各地震区（带）M_C值的时间演化特征和空间分布特征.结果表明,实验场地区及其内部各地震区（带）M_C值变化趋势大致为1970—1986年M_L2.0~2.6,1987—1999年M_L2.5~2.6,2000—2008年后M_L1.4~2.1,2009—2018年M_L1.2~1.9;实验场地区M_C值的空间分布大致呈现东北部和西南部较低、西北部和东南部较高的特征,其中云南最南端的澜沧—耿马区和思普区、四川西北部的理塘—木里区以及川藏交界处的金沙江带M_C值普遍较高,云南北部和四川南部的松潘—龙门山带、安宁河带、元谋区、楚雄—建水带和大理—丽江—盐源区M_C值普遍较低;强震会使M_C值出现突然升高、之后逐渐恢复的现象,其中M_C值升高程度与震级有一定相关性,并且强震导致的M_C值升高是M_C值空间和时间分布不均匀的原因之一.

     

川滇地震科学实验场地震目录最小完整性震级分析

地震目录是地震监测预报、地震活动性等研究的重要资料.川滇地震科学实验场地区近几十年来积累了大量的地震记录,为实验场的地震科学研究提供了宝贵的数据.地震台网密度和仪器观测精度是逐步提高的,不同时期地震目录的完整性存在差异,因此进行现代仪器观测记录的地震目录最小完整性震级（M_C,Magnitude of Completeness）分析,对正确研究和认识该地区地震活动规律及其影响因素等具有重要意义.本文采用震级—序号方法、最大曲率法（MAXC,Maximum Curvature）和拟合度检测法（GFT,Goodness-of-Fit Test）分析了川滇地震科学实验场地区1970—2018年地震目录的最小完整性震级M_C值,得到了实验场地区及其内部各地震区（带）M_C值的时间演化特征和空间分布特征.结果表明,实验场地区及其内部各地震区（带）M_C值变化趋势大致为1970—1986年M_L2.0~2.6,1987—1999年M_L2.5~2.6,2000—2008年后M_L1.4~2.1,2009—2018年M_L1.2~1.9;实验场地区M_C值的空间分布大致呈现东北部和西南部较低、西北部和东南部较高的特征,其中云南最南端的澜沧—耿马区和思普区、四川西北部的理塘—木里区以及川藏交界处的金沙江带M_C值普遍较高,云南北部和四川南部的松潘—龙门山带、安宁河带、元谋区、楚雄—建水带和大理—丽江—盐源区M_C值普遍较低;强震会使M_C值出现突然升高、之后逐渐恢复的现象,其中M_C值升高程度与震级有一定相关性,并且强震导致的M_C值升高是M_C值空间和时间分布不均匀的原因之一.     

陕西数字地震台网子台测定近震震级的偏差

使用陕西数字地震台网数字地震记录资料，以台网平均震级为标准震级，分析各子台的震级偏差。结果表明，在150km震中距范围，子台测定震级偏差随震中距增大而减小，大于150km，震级偏差不明显。合阳、蒲城、华阴子台台基影响为正值，安康、汉中、彬县子台台基影响为负值，其他子台影响较小。震级偏差随方位角变化是明显的，且具有区域性相似特征。子台方位的震级偏差校正，台网震级标准误差显著改善样本数占81．7％，平均标准误差由0．243下降到0．168。     

Application of a time-magnitude prediction model for earthquakes

In this paper we discuss the physical meaning of the magnitude-time model parameters for earthquake prediction. The gestation process for strong earthquake in all eleven seismic zones in China can be described by the magnitude-time prediction model using the computations of the parameters of the model. The average model parameter values for China are： b = 0.383, c=0.154, d = 0.035, B = 0.844, C = -0.209, and D = 0.188. The robustness of the model parameters is estimated from the variation in the minimum magnitude of the transformed data, the spatial extent, and the temporal period. Analysis of the spatial and temporal suitability of the model indicates that the computation unit size should be at least 4°× 4°for seismic zones in North China, at least 3° × 3° in Southwest and Northwest China, and the time period should be as long as possible.     

地震预报中震级-时间模型的应用

本文从震级-时间模型的表达式出发,讨论了模型参数所含的物理意义,通过计算中国大陆各地震带的震级-时间模型参数,认为只有其中11条地震带的强震孕震过程可以用该模型来表达,其平均参数为b=0.383,c=0.154,d=0.035,B=0.844,C=-0.209,D=0.188。通过变换资料的震级下限、时间域和空间域的计算结果,讨论了模型参数的鲁棒性。通过对模型应用空间范围的分析,在华北地震区,在利用震级—时间模型对未来的地震危险进行预测时,计算单元应不小于4°×4°,而在西北和西南地区,计算单元不要小于3°×3°。而通过对模型应用时间范围的分析,在应用模型进行预测时,资料时间域要尽量长一些。     

DK-1面波震级偏差在二维空间的变化研究

提出了对震级二维空间的校正方法，对北京地震台1989～2001年的大震速报地震做了分析。由于全国各地震速报台均为DK—1仪器，故仪器的幅频特性不存在很大的差异性。通过本次研究，我们发现了我台速报震级在不同的震中距和不同的震中方位上存在明显的系统偏差，对我台的震级校正具有实质的作用。本次分析以《中国地震速报台网观测报告》的最终数据为准，利用四层地球模型下的震中距和震中方位角的计算公式，分别计算出每个地震的震中距和方位角，保证了分析结果的可靠性。     

Synthesis of magnitude and focal mechanism computations for the M ≥ 4.5 earthquakes in France for the period 1995–2000

This paper proposes a synthesis of thestudies made in terms of source parametersevaluation for the last earthquakes oflocal magnitude greater than 4.5 whichoccurred in or nearby France during thelast five years. Focal mechanisms andseismic moments have been computed for thethree most important events, largely feltby the population: St Paul de Fenouillet(February 18^th 1996, M_L 5.6),Annecy-Epagny (July 15^th 1996, M_L5.2) and St-Béat (October 4^th1999, M_L 4.8). These focal mechanismshave been obtained either by regionalmoment tensor inversion or from firstmotion polarities and are compared withcomplementary studies made on theseearthquakes. In addition, for the otherearthquakes of local magnitude greater than4.5 which occurred nearby French borderssince the beginning of the recording ofbroadband data by the RéNaSS(Réseau National de SurveillanceSismique, French Seismological Survey) inmid–1995, several magnitude calculationsconcerning the following earthquakes arepresented: Pamplona (25/2/1996, M_L4.7), Aoste (31/03/1996, M_L 4.6),Imperia (24/2/1997, M_L 4.5),Barcelonette (31/10/1997, M_L 4.8),Pamplona (27/10/1998, M_L 4.9), andBonifacio (26/4/2000, M_L 4.5). Localmagnitudes are usually higher thanthe M_b magnitudes reported by the PDE(Preliminary Determination of Epicenters),while the extension of the Msz scale toregional magnitudes and the Mw magnitudesderived from seismic moments give smallervalues. The relative importance of thevarious earthquakes in terms of surfacewave magnitude or seismic moment does notalways agree with that implied by localmagnitudes.     

Kernel estimation as a basic tool for geomorphological data analysis

Kernel estimation, based on the convolution of a probability density function with a set of magnitudes or event dates, provides tuneable smooth pictures of probability density functions and event intensity functions. Such pictures are in several respects superior to those provided by histograms, box plots, cumulative distributions or raw plots. They permit examination of broad features and fine structure, are readily produced with modest computational effort and are essentially free of artefacts arising from binning. Examples are given using data on cirque lengths, limestone pavements, glacier areas and dated flood deposits. The technique deserves widespread use in geomorphology and allied sciences. Copyright © 2007 John Wiley & Sons, Ltd.