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1.
In this paper, we give a brief introduction to the proposal and development history of the earthquake magnitude concept. Moment magnitude MW is the best physical quantity for measuring earthquakes. Compared with other magnitude scales used traditionally, moment magnitude is not saturated for all earthquakes, regardless of big and small earthquakes, deep and shallow earthquakes, far field and near field seismic data, geodetic and geological data, moment magnitude can be measured, and can be connected with well-known magnitude scales such as surface wave magnitude MS. Moment magnitude is a uniform magnitude scale, which is suitable for statistics with wide magnitude range. Moment magnitude is the preferred magnitude selected by the International Seismological community, and it is preferred by the departments responsible for publishing seismic information to the public.Moment magnitude is a uniform magnitude scale, which is suitable for statistics with wide magnitude range. Moment magnitude is a preferred magnitude for international seismology, it is preferred by the agency responsible for providing information about earthquakes to the public. We provide all formulas used in the calculation of moment magnitude, and the calculation steps in detail. We also analyzed some problems and rules to solve these problems by using different formulas and numerical value calculation steps.  相似文献   

2.
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3.
This paper provides a generic equation for the evaluation of the maximum earthquake magnitude mmax for a given seismogenic zone or entire region. The equation is capable of generating solutions in different forms, depending on the assumptions of the statistical distribution model and/or the available information regarding past seismicity. It includes the cases (i) when earthquake magnitudes are distributed according to the doubly-truncated Gutenberg-Richter relation, (ii) when the empirical magnitude distribution deviates moderately from the Gutenberg-Richter relation, and (iii) when no specific type of magnitude distribution is assumed. Both synthetic, Monte-Carlo simulated seismic event catalogues, and actual data from Southern California, are used to demonstrate the procedures given for the evaluation of mmax.The three estimates of mmax for Southern California, obtained by the three procedures mentioned above, are respectively: 8.32 ± 0.43, 8.31 ± 0.42 and 8.34 ± 0.45. All three estimates are nearly identical, although higher than the value 7.99 obtained by Field et al. (1999). In general, since the third procedure is non-parametric and does not require specification of the functional form of the magnitude distribution, its estimate of the maximum earthquake magnitude mmax is considered more reliable than the other two which are based on the Gutenberg-Richter relation.  相似文献   

4.
Most of the present earthquake early warning systems are based on broadband or strong motion recordings. How-ever, the short-period instruments are still deployed. It is well-known that short-period recordings have saturation problems for large earthquakes when estimating the size of an earthquake. Thus, it is necessary to make clear the magnitude at which saturation starts to occur for the commonly used τc and Pd measurements, respectively. To investigate the possibility of using short-period seismic recordings for earthquake early warning, we conducted a simulated experiment using the strong motion data of the 1999 Chi-Chi earthquake sequence including its main shock and 31 aftershocks, with magnitude span from 4 to 7.6. The strong motion acceleration recordings were convolved with the instrument response of short-period seismographs in northern China to simulate short-period seismograms. Parameters τc and Pd from the first-three-second seismograms were calculated for the simulated short-period recordings and compared with that obtained by the original strong ground motion recordings. The result showed that to some extent, short-period recordings can be used for threshold earthquake early warning, while the magnitude saturation of Pd estimation can be up to 6.5, better than τc estimation.  相似文献   

5.
孙冬军  刘芳  毕波 《中国地震》2022,38(1):112-119
本文选取2013年芦山地震和2017年九寨沟地震波形,重新量取垂直向振幅,计算宽频带面波震级MS（BB）,分析各台站实测震级出现方向性差异的原因。其中,通过572个宽频带台站实测芦山地震震级MS（BB）7.1,通过603个宽频带台站实测九寨沟地震震级MS（BB）6.9。芦山地震实测震级大于MS（BB）7.3的台站呈现WN-ES向分布,与断层倾向一致;实测震级小于MS（BB）7.0的台站呈现NE-WS向分布,与其所在断层走向一致。九寨沟地震实测震级大于MS（BB）7.0的台站分布呈现NE向分布,与断层倾向一致;实测震级小于MS（BB）6.8的台站总体分布较为离散,大体呈现NW-SE向分布,与树正断裂走向一致。实测震级偏大的台站方向性分布与多普勒效应和P波辐射花样联系不明显。对比分析芦山地震和九寨沟地震,去除场地响应和仪器自身影响,台站实测震级差异性仍然存在,因此,台站实测震级差异性是由于受到了多普勒效应、辐射花样、仪器和场地响应之外的因素影响。综合考虑地震震级涉及的影响因素,芦山地震和九寨沟地震的台站实测震级差异性可能与地震波的传播路径有关。  相似文献   

6.
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   

7.
Following the theory and definition of the Corioli force in physics, the Corioli force at the site of the M=8.1 Kunlun Mountain Pass earthquake on November 14, 2001, is examined in this paper on the basis of a statistical research on relationship between the Corioli force effect and the maximum attershock magnitude of 20 earth-quakes with M≥7.5 in Chinese mainland, and then the variation tendency of attershock activity of the M=8.1 earthquake is discussed. The result shows: a) Analyzing the Corioli force effect is an effective method to predict maximum attershock magnitude of large earthquakes in Chinese mainland. For the sinistral slip fault and the reverse fault with its hanging wall moving toward the right side oftbe cross-focus meridian plane, their Corioli force pulls the two fault walls apart, decreasing frictional resistance on fault plane during the fault movement and releasing elastic energy of the mainshock fully, so the maximum magnitude of aftershocks would be low. For the dextral slip fault, its Corioli force presses the two walls against each other and increases the frictional resistance on fault plane, prohibiting energy release of the mainshock, so the maximum magnitude of attershocks would be high.b) The fault of the M--8. l Kunlun Mountain earthquake on Nov. 14, 2001 is essentially a sinistral strike-slip fault,and the Corioli force pulled the two fault walls apart. Magnitude of the induced stress is about 0.06 MPa. Alter a comparison analysis, we suggest that the attershock activity level will not be high in the late period of this earth-quake sequence, and the maximum magnitude of the whole aftershocks sequence is estimated to be about 6.0.  相似文献   

8.
Scaling relations for seismic events induced by mining   总被引：1，自引：0，他引：1  
The values of seismic moment andS-wave corner frequency from 1575 seismic events induced in South African, Canadian, Polish, and German underground mines were collected to study their scaling relations. The values ofP-wave corner frequency from 649 events were also available. Seismic moments of these events range from 5*103 to 2*1015 N·m (moment magnitude is from –3.6 to 4.1), theS-wave corner frequency ranges from 0.7 to 4438 Hz, and theP-wave corner frequency is between 5 and 4010 Hz. The slope of a regression line between the logarithm ofS- andP-wave corner frequencies is equal to one, and the corner frequencies ofP waves are higher than those ofS waves on the average by about 25 percent. In studies of large and moderate earthquakes it has been found that stress drop is approximately independent of the seismic moment, which means that seismic moment is inversely proportional to the third power of corner frequency. Such a behavior was confirmed for most of the data considered here. A breakdown in the similarity betwen large and small events seems to occur for the events with moment magnitude below –2.5. The average values of seismic moment referred to the same range of corner frequency, however, are vastly different in various mining areas.  相似文献   

9.
    
The earthquake size distribution is generally considered to obey the Gutenberg-Richter (GR) law. We have introduced the concept of the b value spectrum based on the moment method to investigate the deviation of the actual magnitude distribution of earthquakes from this law. This enables us to describe characteristic features of the magnitude frequency distribution of earthquakes. We found also a simple relation between the η value and the b value spectrum. Analysis using this scheme showed that the actual size distributions of earthquakes have large variations from case to case and sometimes deviate considerably from the widely assumed the GR formula.  相似文献   

10.
对2021年5月21日云南漾濞M5.6、M6.4及M5.2地震中获取的120条强震动观测记录进行处理及分析,给出获取记录的地震动参数,绘制峰值加速度等值线分布图,发现其长轴均成NW-SE方向展布。将3次地震实际PGA观测值与俞言祥~([1])、汪素云~([2])地震动衰减关系进行对比,发现实际观测值与俞言祥预测值更吻合。对比分析典型台站的加速度反应谱,发现震级愈大,长周期分量愈明显;震级愈小,幅值衰减愈快。  相似文献   

11.
Recent seismicity in the northeast India and its adjoining region exhibits different earthquake mechanisms – predominantly thrust faulting on the eastern boundary, normal faulting in the upper Himalaya, and strike slip in the remaining areas. A homogenized catalogue in moment magnitude, M W, covering a period from 1906 to 2006 is derived from International Seismological Center (ISC) catalogue, and Global Centroid Moment Tensor (GCMT) database. Owing to significant and stable earthquake recordings as seen from 1964 onwards, the seismicity in the region is analyzed for the period with spatial distribution of magnitude of completeness m t, b value, a value, and correlation fractal dimension D C. The estimated value of m t is found to vary between 4.0 and 4.8. The a value is seen to vary from 4.47 to 8.59 while b value ranges from 0.61 to 1.36. Thrust zones are seen to exhibit predominantly lower b value distribution while strike-slip and normal faulting regimes are associated with moderate to higher b value distribution. D C is found to vary from 0.70 to 1.66. Although the correlation between spatial distribution of b value and D C is seen predominantly negative, positive correlations can also be observed in some parts of this territory. A major observation is the strikingly negative correlation with low b value in the eastern boundary thrust region implying a possible case of extending asperity. Incidentally, application of box counting method on fault segments of the study region indicates comparatively higher fractal dimension, D, suggesting an inclination towards a planar geometrical coverage in the 2D spatial extent. Finally, four broad seismic source zones are demarcated based on the estimated spatial seismicity patterns in collaboration with the underlying active fault networks. The present work appraises the seismicity scenario in fulfillment of a basic groundwork for seismic hazard assessment in this earthquake province of the country.  相似文献   

12.
针对九寨沟MS7.0地震之后不同时间段的余震序列目录,利用推定最大余震震级,给出了实际最大余震震级的估计值。结果表明,推定最大余震震级随主震后时间尺度的延长而趋于稳定,且该值与实际发生的最大余震的震级一致。需要强调的是,就九寨沟地震序列而言,当余震数据较为完备时,采用主震后较短时间段内（1～2天）的余震目录就可以较准确地估算出主震区域内可能发生的最大余震震级。实际上,主震后12h（0.5天）的余震数据已完全可以给出最大余震震级的有效下限。此外,计算中我们采用了里氏震级ML和面波震级MS的余震目录,结果显示,2种震级类型目录的估算结果完全一致,表明利用推定最大余震震级估算实际最大余震震级的方法不受震级类型的影响。据此,该最大余震震级快速评估方法可进一步推广应用于我国大陆地区中强震后强余震灾害分析评估中。目前的拟合技术也显示出随着测震技术的不断进步以及余震识别能力的提高,快速评估方法可以在主震后短时间（<1天）内准确地预测可能发生的最大余震震级。  相似文献   

13.
Seismicity in the La Cerdanya region of the eastern Pyrenees has been accurately mapped for the first time using data from a local seismic network. The majority of earthquakes lies on or near the La Cerdanya fault or secondary faults to the south. Coda magnitudes determined for these earthquakes, using magnitude relations from other regions, range between –0.5 and 2.2. These are, however, presumed to be underdetermined values sinceQ values appear to be very low in the La Cerdanya region. CodaQ values at a frequency of 1.5 Hz range between 17 and 120, the lowest values being obtained for the most seismically active regions. CodaQ values also increase with increasing distance, a result which indicates decreasing seismic attenuation with increasing depth in the crust.  相似文献   

14.
A total of 1503 events for a 2-month period associated with am N 2.6 rockburst is investigated for possible space-time correlations between low magnitude (–1.1 to –0.4)b values and several estimates of stress (static stress drop, apparent stress, and dynamic stress). Spatial variations of decreasingb values were found to be well correlated with increasing stress release estimates for time intervals prior to the rockburst and following the aftershock sequence. The strongest correlation tob value was with the dynamic stress drop, having correlation coefficients of 0.87 and 0.79 for the two intervals, respectively. The rockburst was found to actually occur at the intersection of the spatial coordinates corresponding to the largest gradient inb value. Based on these correlations, we conclude that the low magnitude seismicity is an indicator of the stress state within the rock mass, and can be used to study and forecast stress patterns in the vicinity of an impending major event. Time variations, however, did not show the same clear correlations and these are discussed in terms of departure from steady state conditions. Regardless, our results favour the use ofb values in a spatial, context rather than in a time analysis approach, and we consider thatb values provide valuable information regarding the changing stress conditions within the seismogenic volume.  相似文献   

15.
利用模板匹配方法对2015年11月23日青海省祁连县M_S5.2地震进行遗漏地震检测研究,由于主震后短时间内目录中遗漏事件较多,故对主震后1天的连续波形进行检测。主震后1天内青海测震台网记录到的余震个数(包括单台)共62个,选取主震后M_L1.0以上余震30个作为模板事件,通过匹配滤波的方式扫描出遗漏地震31个,约为台网目录给出的0.5倍。基于包络差峰值振幅与震级的线性关系估测检测事件的震级参数,最后将检测后的余震目录与台网余震目录在主震后1天内的最小完备震级进行对比分析,结果发现检测后最小完备震级从M_L1.2降到了M_L0.7,得到青海测震台网在祁连地区最小完整性震级为M_L0.7。  相似文献   

16.
Using simulated data, it is demonstrated that one may estimate the body wave velocity in the crust by measuring the angle of incidence ofP-waves provided only the very first part of the signal is used. This angle has been measured for a set ofP-waves at the NORSAR long period instrument sites. Combining these observations with measurements of apparent velocities, we find that the data indicates a crust velocity of 6.1±0.4 km/sec. While it is somewhat uncertain to what depth the value is representative, the observations are in obvious disagreement with previous authors who concluded that long periodP-waves were not affected by the earth's crust. Because of difficulties in separating the effects of real velocity variations from measurement errors, the details of the observedP-wave variation across the array are difficult to interpret. The consistent behavior of the data does, however, indicate that variations of approximately 3% must exist in the crustalP-wave velocity across the array.  相似文献   

17.
A series of Hokkaido events, recorded by the FBV Broadband Seismograph System at the KHC Seismic Station, is used to study the structure of the earthquake magnitude scale on the basis of maximum velocity amplitudesA vmax of teleseismicPwaves in different period bands. Amplitude-periodband (APB) diagrams are constructed for each event. According to the shape of the APB diagrams the events investigated can be divided into three types: (a) events with largestA vmax values in the intermediate period range (periods ofA vmax from 2.2 to 23 sec), (b) events with largestA vmax values in the short-period range (periods ofA vmax from 1 to 2 sec), (c) events exhibiting anomalous APB diagrams. Type (a) events seem to represent the process of wave generation that prevails for shallow earthquakes. Type (b) events approach to explosive-like generation of seismic waves. The nature of the exceptionally occurring type (c) events must be clarified in further investigations. The influence of the type of earthquake on the magnitude values estimated on the basis of standard class A and B (short-period and intermediate-band) seismograms is demonstrated. It appears that for estimating correct values of earthquake magnitudes complementary information on the process of seismic wave generation in the focus is necessary. At teleseismic distances this information can be obtained from either APB diagrams or amplitude spectra ofP waves recorded, e.g., by broadband velocity sensing instruments.  相似文献   

18.
The borehole strain meter at Wushi station recorded obvious anomaly before Jiashi M s=6.8 earthquake occurred on February 24, 2003. Its features are as follows. (1) Anomaly types are complete. The trend anomaly, short-term anomaly, short-imminent anomaly and exponential anomaly appeared 19 months, 56 days, 4 days, and more than 1 month before the event, respectively; (2) Anomaly is large in magnitude. The maximal magnitude of strain anomaly is 1.7×10−5, which is rare in the past 20-year observation records at Wushi station; (3) Strain rate fluctuates sharply with obvious alternation of tension and compression. According to the magnitude of strain anomaly, time of exponential anomaly appearance and regional features of recorded anomaly, we could predict the magnitude, occurrence time and potential region to a certain degree.  相似文献   

19.
The G-R relation lgN=a-bM (1954) is an empirical formula used widely in the seismicity research. But the linearity of b curves has great difference in different time and space domains. An interested question in this paper is that in how large a space-time-strength domain the b value has certain physical connotation. This study told us that we can get optimal statistical results of b value in those space-time domains which can develop correspondent strong shocks with magnitude interval (M s≥8.5, 8.0≤M s<8.5, 7.0≤M s<8.0). Thus, the possible seismogenic areas in which strong shocks with different magnitude intervals develop can be inferred in different regions of the mainland of China. Finally, some new problems are proposed, such as the delimitation of seismic province, the seismicity parameter determination in seismic hazard analysis and in earthquake predictions by using b value. Contribution No. 96A-0074, Institute of Geophysics, SSB, China.  相似文献   

20.
Using 116 earthquakes over M_L3.8 in the Inner Mongolia region from 2008 to 2015, the local earthquake magnitude M_L and surface wave magnitude M_S are remeasured. Based on norm linear regression(SR1 and SR2) and norm(OR) orthogonal regression method, we established the conversion relationship between M_L and M_S. The results were tested with Gaussian disturbance. The result shows that the orthogonal regression method(OR) result has the best fitting curve, and the conversion relation is M_S=0.96 M_L-0.10. The difference between our result and Guo Lücan's(M_S=1.13 M_L-1.08) may be caused by regional tectonic characteristics. M_(S Inner Mongolia) value is significantly higher than the M_(S empirical) value, with an average difference of 0.23, the difference distribution of empirical relation and the rectified relation is in the range of 0.2-0.3.  相似文献   

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