Attenuation relations of ground motion for rock and soil sites in eastern United States

This paper presents the attenuation relations of peak ground acceleration and spectral accelerations for rock and soil sites in the central and eastern United States (CEUS). For the bedrock site condition, 56 pairs of moment magnitude M and epicentral distance R are used to simulate ground motion, and for each pair of M and R, 550 samples of ground motion parameters are generated using a seismological model together with random vibration theory and distribution of extreme values. From the regression analyses of these data, the attenuation relations of ground motion parameters for the bedrock site are established. With the aid of appropriate site coefficients, these attenuation relations are modified for the site categories specified in the 1994 NEHRP Provisions. These attenuation relations are appropriate for the assessment of seismic hazards at far-field rock and soil sites in the CEUS.     

M L Determination for Local and Regional Events Using a Sparse Network in Southwestern Germany

A method for the determination of consistent local magnitude M _L values (Richter scale, or M _WA) for earthquakes with epicentral distances ranging from 10 km through 1000 km is demonstrated. The raw data consists of nearly 1300 amplitude readings from a network of six digital seismographs in Baden–Württemberg (Southwestern Germany) during 26 months starting in 1995, later extended by another 1000 amplitude readings until 1999. Relying on most of the basics introduced by C.F. Richter a three-parameter attenuation curve (distance correction, magnitude-distance relation) for Baden–Württemberg and adjacent areas is presented. Station corrections are evaluated and the attenuation curve is calibrated with respect to other agencies for distances greater than 650 km. Reasonable parametrisations are discussed and meaningful error bars are attributed. Finally, a seventh station is incorporated by means of its station correction alone, without needing to update the attenuation curve.     

Peak Horizontal-to-Vertical Acceleration Ratio and Local Amplification of Strong Ground Motion

Residuals of the peak horizontal acceleration for site-independent attenuation relations are shown to have weak positive correlation with the average observed peak horizontal/vertical acceleration ratio (q) at the recording site. This ratio systematically increases as the hardness of the soil decreases. Taking the average observed q at the recording station into account reduces the scatter of data slightly in fitting the assumed peak acceleration attenuation law. If the soil classification of the data is available, soil dependence is found to be weaker if the data are corrected for the effect of q prior to regression. This correction reduced the mean value of q = 1.85 for the Dinarides area to q = 1.52, which, on the average, is characteristic of rock sites.     

Probabilistic aftershock hazard assessment II: application of strong ground motion simulations

Probabilistic aftershock hazard assessment (PAHA) has been introduced by Wiemer (Geophys Res Lett 27:3405–3408, 2000). The method, in its original form, utilizes attenuation relations in evaluating peak ground velocity (PGV) exceedence probability. We substitute the attenuation relations together with their uncertainties by strong ground motion simulations for a set of scenarios. The main advantage of such an approach is that the simulations account for specific details of the aftershock source effects (faulting style, slip distribution, position of the nucleation point, etc.). Mean PGVs and their standard deviations are retrieved from the simulation results obtained by the new hybrid k-squared source model, and they are used for the PAHA analysis at a station under study. The model chosen for the testing purposes is inspired by the Izmit A25 aftershock (M _w  = 5.8) that occurred 26 days after the mainshock. The PAHA maps are compared with (1) those obtained by the use of attenuation relations and (2) the peak values of ten selected strong-motion recordings written by the aftershock at epicentral distances <50 km. We conclude that, although the overall hazard decay with increasing fault distance is similar, the PAHA maps obtained by the use of simulations exhibit remanent radiation pattern effect and prolongation in the strike direction due to the directivity effect pronounced for some of the scenarios. As regard the comparison with real data, we conclude that the PAHA maps agree with observed peak values due to appropriate attenuation model adopted in the analysis.     

新疆喀什原场地地震动频谱特性研究

2020年1月19日和2020年2月21日在新疆喀什地区先后发生M_S6.4和M_S5.1地震,针对新疆强震动台网收集到的128条强震动记录进行统计分析,研究2次地震记录的幅值及反应谱特性,并与两个现行规范设计反应谱进行对比,结果表明：(1)震级相同时,震中距越小加速度反应谱越大,且加速度反应谱衰减速度越慢;震中距相同时,震级越大加速度反应谱越大,且加速度反应谱衰减速度越慢;(2)震级越大加速度谱值、速度谱值、位移谱值越大;(3)M_S6.4、M_S5.1地震波加速度反应谱及其平均值曲线相近,与我国现行规范加速度反应谱相比差别很大。建议在新疆喀什地区采用基于当地强震记录的加速度反应谱进行结构抗震设计。     

Site-specific response spectra from the combination of microzonation with probabilistic seismic hazard assessment—An example for the Cologne (Germany) area

Seismic noise was measured at some 20 sites in the Cologne area (Germany) aligned nearly perpendicular to a graben structure. The H/V spectral noise ratio for each site was used to derive realistic S-wave velocity profiles down to the bedrock by means of a genetic algorithm inversion. Numerical simulations were performed for different combinations of source and propagation path parameters: focal depth, epicentral distance, attenuation and fault mechanism. Synthetic seismograms were produced and converted to Fourier and response spectra. Finally, the site-specific values from response spectral ratios, with their uncertainties, were used to modify attenuation functions entering the logic-tree algorithm of the probabilistic seismic hazard assessment (PSHA). The site-specific response spectra show the significance of taking into account the local S-wave velocity structure in PSHA.     

Response of vertical deformation on faults to remote strong earthquakes

Vertical coseismic deformation on non-causative fault caused by remote strong earthquakes(epicentral distance≥1500 km,MS≥7.0)are observed by fault-monitoring instruments of new type during recent two years.The monitor-ing result shows,delay time,maximum amplitude and duration of vertical deformation on the non-causative faulthave remarkable close relationship with earthquakes magnitude and epicentral distance.The delay time of verticalcoseismic deformation have positive linear relationship with epicentral distance.The velocity of coseismic defor-mation is 5.5 km/s,close to the velocity of surface wave in granite.The logarithms of maximum amplitude of co-seismic deformation and epicentral distance have remarkable linear relationship with magnitude.The greater themagnitude and the closer the epicentral distance are,the bigger the maximum amplitude of coseismic deformationon non-causative fault will be.Relative to the epicentral distance,the magnitude is the most important factor to theduration of coseismic vertical deformation on the non-causative fault.Stronger earthquake causes longer vibrationduration of coseismic deformation.The experiential equation of co-seismic deformation faults obtained by thiswork is significant on the coseismic deformation research.     

四川地区地震动峰值衰减规律研究

基于四川省地震监测台网27个基岩台站,2008年5月12日——2008年6月10日105次地震（震级ML=4.0——6.4,震中距△=26——623km）的8505条宽频带速度记录,利用实时仿真方法得到了相应的加速度记录,进而对数据进行回归分析,获得了四川地区基岩场地中小地震峰值加速度和峰值速度的衰减关系,并用最近发生的一次4.8级地震对该规律进行了验证．通过四川台网的记录,提出了符合四川地质条件的衰减关系      

Seismic motion attenuation relations in Si-chuan and adjacent areas

The Sichuan and adjacent areas is divided into southwest China region (SWCR) and Sichuan Basin region (SCBR) according to tectonic backgrounds and seismic damage distribution features. 96 modern destructive earthquakes in SWCR and 40 in SCBR are gathered respectively. All their magnitude parameters are checked. Based on the statis-tic relations between epicentral intensity and magnitude as well as relation between sensible radius and magnitude, the near and far field seismic intensity attenuation features are represented and controlled. And then the seismic intensity attenuation relations along major axis, minor axis and mean axis are established separately. The system-atic deviations of surface wave magnitude between China seismograph network and U.S. seismograph network are considered in this paper. By making use of the new attenuation relations of bedrock horizontal ground acceleration response spectrum in west U.S., the attenuation relations of bedrock horizontal ground acceleration response spec-trum in SWCR and SCBR are digital transformed based on the attenuation model considering acceleration satura-tion of distance and magnitude in near field.     

四川及邻区地震动衰减关系

根据地震构造环境和震害分布特点, 将四川及邻区划分为西南地区和四川盆地地区. 收集了西南地区96次、 四川盆地地区40次近代破坏性地震资料, 并对各次地震的震级参数进行了统一校核. 按照该地区震中烈度与震级、 有感半径与震级的统计关系, 对地震烈度衰减进行了近场与远场特征控制, 建立了地震烈度沿长轴、 短轴和平均轴的衰减关系. 统一了中国与美国面波震级的震级标度, 利用最新得出的美国西部基岩水平向地震加速度反应谱衰减关系, 采用考虑地震加速度的近场距离饱和与震级饱和特征的衰减模型, 转换得到了该地区的基岩水平向地震加速度反应谱衰减关系.      

A note on attenuation of earthquake intensity in Macedonia

The attenuation of intensity of strong shaking is related to the dissipation of earthquake energy. It varies with distance from the epicenter, and depends on the local geological conditions. The 1437 data points have been collected from the Atlas of Isoseismal Maps (Catalogue of Earthquakes) in the UNDP/UNESCO Survey of the Seismicity of the Balkan Region (1974) and from unpublished data on seismic intensities in the Balkan region up to 1989.

A regression analysis has been performed to describe the attenuation of earthquake intensity in Macedonia in terms of epicentral intensity, I₀, epicentral distance, R, and local geological conditions at the recording site, s (s = 0, 1 or 2 for soft, medium and hard geological site conditions).     

2021年5月22日玛多MS 7.4地震地震动特征

为了研究2021年5月22日玛多M_S 7.4地震地震动特征,收集16个强震台的峰值加速度和其中9个台的强震波形数据,利用峰值加速度衰减及反应谱等分析玛多M_S 7.4地震强震动特征。结果表明,多数台站的PGA值都随震中距的增大而平稳下降,PGA的衰减特征与青藏区衰减关系间有较好的一致性;土层台与基岩台的加速度反应谱明显不同,震中距越小,短周期高频成分越多,衰减越快,震中距越大,长周期高频成分越少,衰减越慢;加速度反应谱的水平向与竖向比值曲线在4 s内呈现两峰一谷的现象,初步认为,距发震断层较近的野马滩1号大桥所受到的破坏及水泥路面的明显错断受水平向地震动作用的影响更大。     

Seismicity and codaQ values in the eastern Pyrenees: First results from the La Cerdanya seismic network

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.     

Bracketed and normalized durations of earthquake ground acceleration

Multiple regression analyses of the duration of earthquake ground acceleration are presented. Two types of duration are considered, i.e. bracketed duration and normalized duration. The bracketed duration t_a is defined as the elapsed time between the first and last acceleration excursions greater than a [cm/s²], and the normalized duration Tα is defined as the elapsed time between the first and last acceleration excursions greater than α times (0 < α < 1) the peak acceleration. Employed are 394 components of horizontal strong motion acceleration records obtained at 67 free field sites in Japan. With the use of multiple regression analysis, the dependence of the bracketed and normalized durations on earthquake magnitude and epicentral distance is studied.     

Low CodaQcin the Epicentral Region of the 2001 Bhuj Earthquake ofMw7.7

On 26 January, 2001 (03:46:55,UT) a devastating intraplate earthquake of M_w 7.7 occurred in a region about 5 km NW of Bhachau, Gujarat (23.42°N, 70.23°E). The epicentral distribution of aftershocks defines a marked concentration along an E-W trending and southerly dipping (45°) zone covering an area of (60 × 40) km². The presence of high seismicity including two earthquakes of magnitudes exceeding 7.7 in the 200 years is presumed to have caused a higher level of shallow crustal heterogeneity in the Kutch area; a site lying in the seismic zone V (zone of the highest seismicity for potentially M8 earthquakes) on the seismic zoning map of India. Attenuation property of the medium around the epicentral area of the Bhuj earthquake covering a circular area of 61,500 km² with a radius of 140 km is studied by estimating the coda-Q_c from 200 local earthquakes of magnitudes varying from 3.0–4.6. The estimated Q₀ values at locations in the aftershock zone (high seismicity) are found to be low in comparison to areas at a distance from it. This can be attributed to the fact that seismic waves are highly scattered for paths through the seismically active and fractured zone but they are well behaved outside the aftershock zone. Distribution of Q₀ values suggests that the local variation in Q₀ values is probably controlled by local geology. The estimated Q₀ values at different stations suggest a low value of Q=(102 ± 0.80)^*f^{(0.98 ± 0.02)} indicating an attenuative crust beneath the entire region. The frequency-dependent relation indicates a relatively low Q_c at lower frequencies (1–3 Hz) that can be attributed to the loss of energy due to scattering attenuation associated with heterogeneities and/or intrinsic attenuation due to fluid movement in the fault zone and fluid-filled cracks. The large Q_c at higher frequencies may be related to the propagation of backscattered body waves through deeper parts of the lithosphere where less heterogeneity is expected. Based on the attenuation curve estimated for Q₀=102, the ground acceleration at 240 km distance is 13% of 1 g i.e., 0.13 g agreeing well with the ground acceleration recorded by an accelerograph at Ahmedabad (0.11 g). Hence, it is inferred that the Q₀ value obtained from this study seems to be apt for prediction of ground motion for the region.     

Intensity attenuation in the Campania region,Southern Italy

Ground motion prediction equations (GMPE) in terms of macroseismic intensity are a prerequisite for intensity-based shake maps and seismic hazard assessment and have the advantage of direct relation to earthquake damage and good data availability also for historical events. In this study, we derive GMPE for macroseismic intensity for the Campania region in southern Italy. This region is highly exposed to the seismic hazard related to the high seismicity with moderate- to large-magnitude earthquakes in the Appenninic belt. The relations are based on physical considerations and are easy to implement for the user. The uncertainties in earthquake source parameters are accounted for through a Monte Carlo approach and results are compared to those obtained through a standard regression scheme. One relation takes into account the finite dimensions of the fault plane and describes the site intensity as a function of Joyner–Boore distance. Additionally, a relation describing the intensity as a function of epicentral distance is derived for implementation in cases where the dimensions of the fault plane are unknown. The relations are based on an extensive dataset of macroseismic intensities for large earthquakes in the Campania region and are valid in the magnitude range M _w = 6.3–7.0 for shallow crustal earthquakes. Results indicate that the uncertainties in earthquake source parameters are negligible in comparison to the spread in the intensity data. The GMPE provide a good overall fit to historical earthquakes in the region and can provide the intensities for a future earthquake within 1 intensity unit.     

A regional near-surface high frequency spectral attenuation (kappa) model for northwestern Turkey

One approach to model the high-frequency attenuation of spectral amplitudes of S-waves is to express the observed exponential decay in terms of Kappa (κ) factor [1]. Kappa is a significant parameter used for identifying the high-frequency attenuation behavior of ground motions as well as one of the key parameters for stochastic strong ground motion simulation method. As of now, there is not a systematic investigation of the Kappa parameter based on the recently-compiled Turkish ground motions. In this study, we examine a strong ground motion dataset from Northwestern Turkey with varying source properties, site classes and epicentral distances. We manually compute κ from the S-wave portion of each record and study both horizontal and vertical kappa values. We use traditional regression techniques to describe the (potential) relationships between kappa and selected independent variables such as the site class, distance from the source or magnitude of the event. A linear effect of magnitude on kappa is not found statistically significant for the database studied herein. We express the initial findings of a regional κ model for Northwestern Turkey as a function of site class and epicentral distances. Single station analyses at selected sites confirm the regional model. Finally, we present stochastic strong motion simulations of past events in the region using the proposed kappa model. Regardless of the magnitude, source-to-site distance and local site conditions at the stations, the high-frequency spectral decay is simulated effectively at all stations considered.     

基于《建筑抗震设计规范》强度包线函数参数取值研究

利用《中国地震动参数区划图》采用的地震动参数衰减关系,以及《中国地震动参数区划图》中地震动峰值加速度和地震动加速度反应谱特征周期反推不同设防烈度和设计地震分组对应的震级和震中距,再根据《建筑抗震设计规范》中各设防水准的峰值加速度确定对应的震级和震中距,进而根据地震动强度包线参数与震级和震中距关系计算地震动强度包线参数的取值,为基于强度包线函数生成人工地震动提供参考,并讨论强度包线参数的取值规律：(1)随着设防烈度的提高,加速度时程曲线上升段持续时间t₁和平稳段持续时间t_s减小,下降段衰减指数c增大;(2)随着地震水准和设计地震分组的提高,加速度时程曲线上升段持续时间t₁和平稳段持续时间t_s增加,下降段衰减指数c减小;(3)在生成人工地震动时,除考虑峰值加速度和设计地震分组影响外,还需要考虑设防烈度影响。     

Propagation and attenuation characteristics of the crustal phaseLg

TheLg wave consists of the superposition ofS waves supercritically reflected, and thus trapped, in the crust. This mode of propagation explains the strong amplitude of this phase and the large distance range in which it is observed. The numerical simulation leads to successful comparison between observed seismograms in stable continental areas and synthetics computed for simple standard crustal models. In regions with strong lateral variations, the influence of large-scale heterogeneities on theLg amplitude is not yet clearly established in terms of the geometrical characteristics of the crustal structure.The analysis of the decay of amplitude ofLg with epicentral distance allows the evaluation of the quality factor ofS waves in the crust. The results obtained show the same trends as codaQ: a clear correlation with the tectonic activity of the region considered, both for the value ofQ at 1 Hz and for its frequency dependence, suggesting that scattering plays a prominent part among the processes that cause the attenuation.The coda ofLg is made up of scatteredS waves. The study of the spatial attenuation of the coda indicated that a large part of the arrivals that compose the coda propagate asLg. The relative amplitude of the coda is larger at sites located on sediments because, in these conditions, a part ofLg energy can be converted locally into lower order surface modes.     

QLg tomography in Gujarat,Western India

We propose a novel Lg attenuation tomography model (Q_Lg tomography) for the state of Gujarat, Western India, using earthquake data recorded by the Gujarat Seismic Network, operated by the Institute of Seismological Research in Gandhinagar. The waveform dataset consist of 400 3-component recordings, produced by 60 earthquakes with magnitude (M_L) spanning from 3.6 to 5.1, recorded at 60 seismic stations having epicentral distances spanning between 200 and 500 km. Spectral amplitude decays for Lg wave displacement were obtained by generalized inversion at 17 frequencies spanning between 0.9 and 9 Hz. Lg wave propagation efficiency was measured by Lg/Pn spectral ratio categorizing as efficient ratio ≥6 for 86%, intermediate ratio of 3–6 for 10% and inefficient ratio <3 for 4% paths of total 400 ray paths. The earthquake size and quality of waveform recorded at dense network found sufficient to resolve lateral variation of Q_Lg in Gujarat.Average power-law attenuation relationship obtained for Gujarat as Q_Lg(f) = 234f^0.64, which corresponds to high attenuation in comparison to peninsular India shield region and other several regions around the world. Q_Lg tomography resolves the highly attenuating crust of extremely fractured Saurashtra region and tectonically active Kachchh region. The Gujarat average attenuation is also lying in between them. The low attenuation in Cambay and Narmada rift basins and extremely low attenuation in patch of Surendranagar area is identified. This study is the first attempt and can be utilized as pivotal criteria for scenario hazard assessment, as maximum hazard has been reported in highly attenuating tectonically active Kachchh region and in low attenuating Cambay, Narmada and Surendranagar regions. The site and source terms are also obtained along with the Q_Lg inversion. The estimated site responses are comparable with observed local geological condition and agree with the previously reported site amplifications at the same sites. The source terms are comparable with local magnitude estimated from Network. The M_w (Lg) is nearly equivalent to M_L (GSN) and the slight differences are noted for larger magnitude events.