Correlation of JMA instrumental seismic intensity with strong motion parameters

The Japan Meteorological Agency (JMA) seismic intensity (I_JMA) has been used as a measure of strong shaking for many years in Japan, and it necessitates to know the correlation between the JMA seismic intensity and other strong motion indices, e.g. Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), and Spectrum Intensity (SI). In this study, two strong motion data sets were selected; in which, the first set consists of 879 three‐components non‐liquefied records selected from 13 major earthquake events that occurred in Japan, the United States, and Taiwan, and the second set consists of 17 liquefied records selected from 7 major earthquake events that occurred in Japan and the United States. The JMA seismic intensity and other ground motion indices were calculated using the selected data sets. The relationships between the JMA seismic intensity and PGA, PGV, and SI were then derived performing a two‐stage linear regression analysis. Results from the analysis show that the JMA instrumental seismic intensity shows higher correlation with SI than PGA or PGV, and it shows the highest correlation with the parameters such as the combination of PGA and SI or the product of PGA and SI. The obtained relationships are also compared with the ones obtained by other studies, which may be useful for the disaster management agencies in Japan and deployment of new SI‐sensors that monitor both PGA and SI. Copyright © 2002 John Wiley & Sons, Ltd.     

Correlations of peak acceleration,velocity and displacement with earthquake magnitude,distance and site conditions

A brief review of proposed correlations between peak accelerations and earthquake magnitude and distance has been presented. It has been found that most investigators agree favourably on what should be the amplitude of peak accelerations for the distance range between about 20 and 200 km. For distances less than 20 km, there is significant disagreement in the predicted peak amplitudes, reflecting the lack of data there and the uncertainties associated with the extrapolation. Correlations of peak accelerations, peak velocities and peak displacements with earthquake magnitude, epicentral distance and the geologic conditions of the recording sites have been presented for 187 accelerograms recorded during 57 earthquakes. This data set describes strong earthquake ground motion in the Western United States during the period from 1933 to 1971. For large earthquakes, dependence of peak acceleration, velocity and displacement amplitudes on earthquake magnitude seems to be lost. This suggests that the amplitudes of strong ground motion close to a fault are scaled primarily by the maximum dislocation amplitudes and the stress drop, rather than the overall ‘size’ of an earthquake as measured by magnitude. The influence of geologic conditions at the recording station seems to be of minor importance for scaling peak accelerations, but it becomes noticeable for the peaks of velocity and even more apparent for the peaks of displacement.     

Preliminary empirical model for scaling fourier amplitude spectra of strong ground acceleration in terms of modified mercalli intensity and recording site conditions

This paper presents an empirical model for scaling Fourier amplitude spectra of ground acceleration during strong earthquake shaking in terms of the reported Modified Mercalli Intensity (MMI) and the simplified characteristics of the geologic environment at the recording station. This analysis shows that (i) for the intermediate and high-frequency motions the spectral amplitudes approximately double for every level of the MMI; that (ii) the uncertainties associated with estimation of Fourier spectral amplitudes in terms of MMI are not greater than the uncertainties associated with similar estimation in terms of earthquake magnitude and epicentral distance; that (iii) the high frequency spectral amplitudes tend to be greater on basement rock sites relative to alluvium sites, with this trend being reversed for the low-frequency spectral amplitudes; and that (iv) the spectral amplitudes of very high-frequency vertical shaking are equal to or higher than the corresponding spectral amplitudes for horizontal shaking.     

Relationship between geomorphological land classification and site amplification ratio based on JMA strong motion records

The relationship between the amplification ratio of earthquake ground motion and geologic conditions at Japan Meteorological Agency (JMA) stations nationwide was examined to propose an estimation method of the amplification ratio that is applicable to entire Japan. The amplification ratios for the instrumental JMA intensity, as well as for the peak ground acceleration and velocity, were obtained from the station coefficients of the attenuation relationships using strong motion records measured at 77 JMA stations over a period of more than 8 years. A combined use of geomorphological land classification and subsurface geology was found to yield the best estimate of the site amplification ratio. This result suggests that these data, and hence the Digital National Land Information, which is a nationwide GIS database, may be conveniently used for the estimation of strong motion distribution over large areas in Japan.     

Seismic response analysis on the stability of running vehicles

The seismometer network of the Japanese expressway system has been enhanced since the 1995 Kobe earthquake. Using earthquake information from the instruments, the expressways are closed if the peak ground acceleration (PGA) is larger than or equal to 80cm/s². The aim of this regulation is to avoid secondary disasters, e.g. cars running into the collapsed sections. However, recent studies on earthquake damage have revealed that expressway structures are not seriously damaged under such‐level of earthquake motion. Hence, we may think of relaxing the regulation of expressway closure. But before doing this, it is necessary to examine the effects of shaking to automobiles since the drivers may encounter difficulties in controlling their vehicles and traffic accidents may occur. In this study, a vehicle was modelled with a six‐degree‐of‐freedom system and its responses were investigated with respect to PGA, peak ground velocity (PGV) and Japan Meteorological Agency (JMA) seismic intensity using five ground motion records. It was observed that the response of the vehicle shows a larger amplitude for the record that has larger response spectrum in the long period range compared to other records. However, similar response amplitudes of the vehicle were observed for all the records with respect to the JMA seismic intensity. The response characteristics of the vehicle model may be very useful for decision‐making regarding the relaxation of the expressway closure under seismic motion. Copyright © 2002 John Wiley & Sons, Ltd.     

Geotechnical engineering aspects of the catastrophic Tohoku (Japan) earthquake of March 11, 2011: the review of first results

Geotechnical engineering aspects of the catastrophic earthquake, which occurred in Japan on March, 11, 2011 and called Tohoku earthquake are discussed. A review is presented of the first results obtained mainly by Japanese scientists based on records of seismic networks of Japan K-NET, Kik-net and on GPS data. The basic concepts of seismic zoning in Japan and the location of the Tohoku-oki earthquake on the seismic zoning maps are described, as well as models of the source process obtained by various authors based on teleseismic data, strong motion data, GPS data, and tsunami observations. The recorded peak accelerations and velocities and their correspondence to the current empirical attenuation curves are discussed. The records of the Tohoku earthquake made by Japanese seismic networks K-NET, Kik-net and some others represent unique seismological material and the most complete seismic database (including vertical array records) in the near-source zone of a strongest earthquake with magnitude M _w = 9. These data will be studied by seismologists all over the world for many years and, probably, they will answer many questions of geotechnical seismic engineering.     

An evaluation of strong motion records and a new parameter A95

From the past studies of acceleration records, it is generally recognised that peak acceleration is not a suitable measure of the ground motion for design purposes. Usually, peak accelerations are difficult to predict. They occur in high frequency pulses containing very little energy and therefore are of little consequence. On the other hand acceleration has direct and useful application in engineering design. A new parameter A₉₅ is introduced in this paper which is defined as that level of acceleration which contains up to 95 per cent of the Arias Intensity. From the study of 135 records, it is noticed that the variation of the fraction of Arias Intensity with acceleration level can be described by a very well defined relationship. It is also observed that A₉₅ and Arias Intensity bear a stable relationship. Furthermore, the Arias Intensity at a site correlates more closely with the earthquake magnitude and the distance of the site from the source in attenuation relationships. From the available data, relationships are derived which show that there is a difference between the near-field and the far-field attenuation laws. The following relationships are obtained: where E_s = Arias Intensity, E_x = fraction of Arias Intensity above an acceleration level A, M = surface wave magnitude, R = nearest distance to the energy source or focal distance in km.     

唐山响堂三维场地影响观测台阵

１９９４年７月中国地震局工程力学研究所在唐山余震区响堂镇建成了我国第一个三维场地影响观测台阵。该台阵目前有四个测点,分别布设在基岩地表、土层地表、地下１７ｍ和地下３２ｍ处。它安装了分辨率为１６位的井下数字观测系统,主机和从机同步运行,系统时钟采用Ｏｍｅｇａ导航信号自动校对（精度１ｍｓ）,地震数据采用固态方式（ＣＭＯＳ）存储,每个测点均布设一组 量力平衡式加速度计。该台阵自投入运行至１９９７年１２月     

Assessment of liquefaction potential based on peak ground motion parameters

Conventionally, evaluation of liquefaction potential of loose saturated cohesionless deposits as specified in Japanese design codes employs peak ground acceleration (PGA). However, recent large-scale earthquakes in Japan revealed that liquefaction at some sites did not occur even though large PGAs were recorded at or near these sites. As an alternative approach, an evaluation procedure based on peak ground motion parameters, i.e. incorporating both PGA and the peak ground velocity (PGV), is proposed. By performing parametric studies using one-dimensional seismic response analysis and formulating regression models, seismic-induced shear stresses within the deposit are expressed in terms of peak ground motion parameters at the surface, and these are used to calculate the factor of safety against liquefaction. Application to case histories in Japan indicates that the proposed two-parameter equation can adequately account for the occurrence and non-occurrence of liquefaction at various sites as compared to the conventional PGA-based approach. Moreover, analyses of several strong motion records at various sites show that liquefaction may occur when PGA≥150 gal and PGV≥20 kine, indicating that these values can serve as thresholds in assessing the possible occurrence of liquefaction.     

甘肃地区三水准超越概率水平地震动峰值加速度关系与场地放大效应研究

通过对甘肃省158个场地安全性评价结果的分析,讨论了不同的超越概率下水平地震动峰值加速度之间的关系以及不同的场地条件对基岩峰值加速度的放大效应。结果对甘肃地区地震安全性评价中水平地震动峰值加速度的取值提供必要的参考。     

On the seismic regime of the Japan region before the Tohoku mega-earthquake (M w = 9)

The seismic regime taking place before the Tohoku mega-earthquake was studied using the catalog of the Japan Meteorological Agency (JMA). We show that the Tohoku earthquake was preceded by a 6–7-year period of regional reduction in the b-value and in the rate of main shocks. The space-time regions that involved precursory activation were nearly identical with the predictive phenomena that were previously detected by A.A. Lyubushin from an analysis of seismic noise based on data from the Japanese F-net. We discovered a previously unknown effect of correlation between the number of main shocks and the b-value. Both the ordinary foreshock activation and the longer weaker tendency, which consist in a precursory increase in the seismicity rate, were identified in the vicinities of M ≈ 7 Japanese earthquakes (similarly to the seismicity in the Generalized Vicinities of large earthquakes based on worldwide data).     

Estimation of Strong Ground Motions for 2001 Bhuj (M w 7.6), India Earthquake

The strong ground motions for the 2001 Bhuj (M _w 7.6) India earthquake have been estimated on hard rock and B/C boundary (NEHRP) levels using a recently modified version of stochastic finite fault modeling based on dynamic corner frequency (Motazedian and Atkinson in Bull Seismol Soc Am 95, 995–1010 2005). Incorporation of dynamic corner frequency removes the limitations of earlier stochastic methods. Simulations were carried out at 13 sites in Gujarat where structural response recorder (SRR) recordings are available. In addition, accelerograms were simulated at the B/C boundary at a large number of points distributed on a grid. The corresponding response spectra have also been estimated. The values of peak ground accelerations and spectral accelerations at three periods (0.4, 0.75 and 1.25 s) are presented in the form of contour maps. The maximum value of peak ground acceleration (PGA) in the center of meizoseismal zone is 550 cm/s². The response spectral acceleration in same zone is 900 cm/s² (T = 0.4 s), 600 cm/s² (T = 0.75 s) and 300 cm/s² (T = 1.25 s). The innermost PGA contour is on the fault plane. A comparison of the PGA values obtained at 13 sites in this study with those obtained in earlier studies on the same sites, but employing different methods, show that the present PGA values are comparable at most of the sites. The rate of decay of PGA values is fast at short distances as compared to that at longer distances. The PGA values obtained here put some constraints on the expected values from a similar earthquake in the region. A synthetic intensity map has been prepared from the estimated values of PGA using an empirical relation. A comparison with the reported intensity map of the earthquake shows the synthetic MMI values, as expected, are lower by 1 unit compared to reported intensity map. The contour map of PGA along with the contour maps of spectral acceleration at various periods permit the assessment of damage potential to various categories of houses and other structures. Such information will be quite important in planning of mitigation and disaster management programs in the region.     

Rating damage potential of ground motion records

In this study, a total of 115,246 ground motions recorded during earthquakes of Moment magnitudes ranging from M_w 5.0 to M_w 9.0 are analyzed statistically. A total of 21 ground motion parameters characterising the recorded acceleration time histories are used in the analysis. Classification of these parameters through statistical correlation is reported and a parameter called "distance from zero-amplitude axis," or d_Z-A, is formulated in the principal component space. The ability for d_Z-A to rate the damage potentials of strong motion records is evaluated through correlation of d_Z-A with Japan Meteorological Agency(JMA) instrumental seismic intensities. This parameter can be used to rate damage potential of any strong motion record irrespective of the magnitude and location of the earthquake. It can also be used in selecting ground motion records of appropriate damage potential in seismic design and probabilistic analysis.     

A ground motion prediction equation for JMA instrumental seismic intensity for shallow crustal earthquakes in active tectonic regimes

The JMA (Japan Meteorological Agency) seismic intensity scale has been used in Japan as a measure of earthquake ground shaking effects since 1949. It has traditionally been assessed after an earthquake based on the judgment of JMA officials. In 1996 the scale was revised as an instrumental seismic intensity measure (I_JMA) that could be used to rapidly assess the expected damage after an earthquake without having to conduct a survey. Since its revision, Japanese researchers have developed several ground motion prediction equations (GMPEs) for I_JMA using Japanese ground motion data. In this paper, we develop a new empirical GMPE for I_JMA based on the strong motion database and functional forms used to develop similar GMPEs for peak response parameters as part of the PEER (Pacific Earthquake Engineering Research Center) Next Generation Attenuation (NGA) project. We consider this relationship to be valid for shallow crustal earthquakes in active tectonic regimes for moment magnitudes ( M ) ranging from 5.0 up to 7.5–8.5 (depending on fault mechanism) and rupture distances ranging from 0 to 200 km. A comparison of this GMPE with relationships developed by Japanese researchers for crustal and shallow subduction earthquakes shows relatively good agreement among all of the relationships at M 7.0 but relatively poor agreement at small magnitudes. Our GMPE predicts the highest intensities at small magnitudes, which together with research on other ground motion parameters, indicates that it provides conservative or upwardly biased estimates of I_JMA for M <5.5. Copyright © 2010 John Wiley & Sons, Ltd.     

Prediction of the number of equivalent cycles for earthquake motion

This paper addresses new prediction models for computing the number of equivalent cycles in liquefaction analyses. Three models are presented for the Italian seismicity as a function of synthetic ground motion parameters that are often available from earthquake data web-sites immediately after events. In particular, it is observed that the number of earthquake cycles can be best estimated from the five following parameters: peak ground acceleration; epicentral distance; Arias Intensity; the mean period; and, the frequency of zero crossings. However, strong estimations can be obtained from the first three parameters only. We use statistical indicators to determine the goodness of the models and the usefulness of the selected independent variables, and we present a comparative analysis to validate our predictive equations. Moreover, this paper describes the existing correlation between magnitude and cycle numbers. The study is primarily based on Italian acceleration records, even if the database is also expanded to recorded European, Japanese and American events to amplify the magnitude values range. These simplified models are useful in addressing practical earthquake engineering problems which require the knowledge of number of equivalent cycles.     

Recorded ground motion and site effects evaluation for the April 6, 2009 L��Aquila earthquake

On April 6, 2009 a M_L = 5.8 earthquake hit the city of L’Aquila on the Apennine chain in central Italy. Notwithstanding the moderate-size event the L’Aquila city and several small villages along the Aterno river valley suffered severe damage, because of the unusual strong motions, mainly due to proximity to the fault (estimated hypocentral depth of about 10 km). In this paper the main features of the recorded motion are discussed. Four accelerometric stations were located within the surface projection of the fault and recorded peak values ranging from 0.4 to 0.6 g. The recorded motions were characterised by short durations and high peak accelerations both in the horizontal and vertical directions. The strong portions of vertical and horizontal motions occurred almost simultaneously due to the short travel paths of P and S waves from the fault to the ground surface near the fault area. Hence site response analyses were performed for the sites where recording stations were located. The geotechnical subsoil model was derived by boreholes, in situ dynamic tests (D-H and SDMT) and by laboratory tests (RCT). One-dimensional numerical analyses were carried out employing the well known computer code EERA. The numerical model was calibrated, in the linear equivalent range, by comparing numerical results with the horizontal acceleration recorded components.     

地震动加速度反应谱场地条件影响调整系数研究

场地条件对地震动特性影响显著,在抗震设计反应谱的确定过程中,需根据场地条件对加速度反应谱予以相应的调整。已有场地条件影响调整方案研究成果,均基于数值模拟或局部地区强震动记录统计,多数仅给出了峰值加速度PGA场地条件影响调整系数,对非线性的考虑缺乏观测数据依据。为此在全球强震动记录统计获得的PGA归一化加速度反应谱和日本钻井台阵记录获得的加速度反应谱平台值非线性衰减指数的基础上,结合钻孔模型数值模拟和近期研究成果,建立了考虑场地条件影响非线性的地震动加速度反应谱场地条件影响调整系数方案。     

A note on scaling peak acceleration, velocity and displacement of strong earthquake shaking by Modified Mercalli Intensity (MMI) and site soil and geologic conditions

It is shown that the overall trends of peak amplitudes of strong motion acceleration, velocity and displacement versus site intensity in the Western United States are consistent with our previous inferences, ¹⁸ but the larger present data base allows us to begin with identification of the additional changes of average peak amplitudes also in terms of the local soil and local geologic site conditions. These trends display a reversal of peak amplitude trends in going from small to large intensities, making it difficult to reconcile the simple scaling of design spectra in terms of peak ground acceleration.     

Modelling of rupture planes for peak ground accelerations and its application to the isoseismal map of MMI scale in Indian region

The rupture plane for an earthquake has been modelledby using the semi empirical technique of Midorikawa(1993). This technique estimates ground accelerationby modelling the rupture process during an earthquake.Modifications in this technique have been made for itsapplication to the Indian region. This has been tested forthe Uttarkashi earthquake of 20th Oct, 1991, India, whichwas well recorded at thirteen stations of installedstrong motion array in this region. After testingseveral possible rupture models, a final model has beenselected and peak ground acceleration due to thismodel is simulated at thirteen different stations.Dependency of methodology on model parameters, e.g.dip and mode of rupture propagation have also beenstudied in detail.Using this technique synthetic isoseismal maps wereprepared by converting peak ground acceleration intoMMI scale. Dependency of rupture models on syntheticisoseismals has also been studied in detail. Usingthis method, peak ground acceleration for the Laturearthquake of Sept 30, 1993 has been obtained atvarious places within meisoseismal area. Synthetic andfield intensity was compared at various well-knownsites. Since the region was not covered by anyinstrumental array during Latur earthquake, thesimulated peak ground accelerations are expected toserve basis of design criteria in this region.