Earthquake shaking scenarios for the metropolitan area of Lisbon

In this study, we simulate and compare ground motion shaking in the city of Lisbon and surrounding counties (metropolitan area of Lisbon (MAL)), using two possible earthquake models: the onshore source area of Lower Tagus Valley, M5.7 and M4.7 and the offshore source area, Marques de Pombal Fault, M7.6, one of the possible source of the 1755 Lisbon earthquake. The stochastic and a new hybrid stochastic-deterministic approach (DSM) are used in order to evaluate the ground shaking and to characterize its spatial variability. Results are presented in terms of response acceleration spectra (PSA) and peak ground acceleration (PGA) with respect to bedrock and surface. Site effects are evaluated by means of equivalent stochastic non-linear one-dimensional ground responses analysis, performed for a set of stratified soil profile units properly designed to cope with the soil site conditions of MAL region. A sensitive study is carried out using different input parameters and different approaches in order to give the basic information to evaluate the range of uncertainty in seismic scenarios.     

Seismic hazard assessment and design spectra for the Kozani-Grevena region (Greece) after the earthquake of May 13, 1995

The Kozani-Grevena (Greece) destructive earthquake occurred in a region of low seismicity. A considerable amount of strong-motion data was acquired from the permanent strong motion network of the Institute of Engineering Scismology and Earthquake Engineering (ITSAK) as well as from a temporary one installed after the earthquake. On the basis of this data set as well as on the observed macroseismic intensities, local attenuation relations for peak ground acceleration and velocity are proposed. A posteriori seismic hazard analysis is attempted for the affected and surrounding areas in terms of peak ground acceleration, velocity, bracketed duration and spectral acceleration. The analysis shows that the event of May 13, 1995 can be characterized as one with a mean return period of 500 to 1000 years. Relying on the observed spectral-acceleration amplification factors and the expected peak ground acceleration for mean return period of 500 years, region-specific elastic design spectra for the buildings of the Kozani and Grevena prefectures are proposed.     

Comparison of seismic risk assessment based on macroseismic intensity and spectrum approaches using ‘SeisVARA’

A comparative study of risk assessment methodologies based on macroseismic intensity and response spectrum approaches is presented. To facilitate the comparative study, a spreadsheet-based software tool ‘SeisVARA’ is developed for the estimation of earthquake risk, in which the seismic hazard can be specified either in terms of macroseismic intensity, or peak ground acceleration in combination with the spectral shape and soil amplification model of various earthquake building codes, or in terms of inelastic response spectra using the ‘next generation attenuation relationships’. A comparison of these different approaches is conducted for a typical city in northern India. In addition, the effect of different parameters, e.g., level of PGA, spectral shape, source-site parameters, and soil amplification models, is studied. It is observed that not only the different approaches result in widely varying damage and loss estimates, but also the variation of parameters within a given approach can result in considerable differences.     

Complex Site Effects in Thessaloniki (Greece): II. 2D SH Modelling and Engineering Insights

This paper presents results of numerical modelling of site response for Thessaloniki, obtained with two different 2D methods; a finite difference and a finite element method. Ground motion across a 2D model of the subsoil of the city has been simulated for vertically incident SH waves. The predominance of locally generated surface waves is very clear in the synthetic seismograms of a weak event and of stronger ones. These results are then compared with the observations in time domain and frequency domain. The role of the soil formations with high attenuation in the lateral propagation and the effect of the differential motion close to the lateral variations are also pinpointed. The stronger events were finally used to compute strong ground motion in order to reveal and to discuss practical engineering aspects such as peak ground acceleration value, the most familiar indicator in seismic norms, the soil to rock spectral coefficients for the period bandwidth of interest, and the aggravation factor in terms of 2D to 1D response spectra as a useful ruler to account for complex site effects.     

Field survey around strong motion stations and its implications on the seismic intensity in the Lushan earthquake on April 20, 2013

The M _s7.0 Lushan earthquake on April 20, 2013 is another destructive event in China since the M _s8.0 Wenchuan earthquake in 2008 and M _s7.1 Yushu earthquake in 2010. A large number of strong motion recordings were accumulated by the National Strong Motion Observation Network System of China. The maximum peak ground acceleration (PGA) at Station 51BXD in Baoxing Country is recorded as ?1,005.3 cm/s², which is even larger than the maximum one in the Wenchuan earthquake. A field survey around three typical strong motion stations confirms that the earthquake damage is consistent with the issued map of macroseismic intensity. For the oscillation period 0.3–1.0 s which is the common natural period range of the Chinese civil building, a comparison shows that the observed response spectrums are considerably smaller than the designed values in the Chinese code and this could be one of the reasons that the macroseismic intensity is lower than what we expected despite the high amplitude of PGAs. The Housner spectral intensities from 16 stations are also basically correlated with their macroseismic intensities, and the empirical distribution of spectral intensities from Lushan and Wenchuan Earthquakes under the Chinese scale is almost identical with those under the European scale.     

Ground motion characteristics of the Chi‐Chi earthquake of 21 September 1999

The purpose of this paper is to investigate the ground motion characteristics of the Chi‐Chi earthquake (21 September 1999) as well as the interpretation of structural damage due to this earthquake. Over 300 strong motion records were collected from the strong motion network of Taiwan for this earthquake. A lot of near‐field ground motion data were collected. They provide valuable information on the study of ground motion characteristics of pulse‐like near‐field ground motions as well as fault displacement. This study includes: attenuation of ground motion both in PGA and spectral amplitude, principal direction, elastic and inelastic response analysis of a SDOF system subjected to near‐field ground motion collected from this event. The distribution of spectral acceleration and spectral velocity along the Chelungpu fault is discussed. Based on the mode decomposition method the intrinsic mode function of ground acceleration of this earthquake is examined. A long‐period wave with large amplitude was observed in most of the near‐source ground acceleration. The seismic demand from the recorded near‐field ground motion is also investigated with an evaluation of seismic design criteria of Taiwan Building Code. Copyright © 2000 John Wiley & Sons, Ltd.     

Probabilistic Microzonation of Urban Territories: A Case of Tashkent City

—?The problem of accounting for local soil effect on earthquake ground motion is especially urgent when assessing seismic hazard – recent needs of earthquake engineering require local site effects to be included into hazard maps. However, most recent works do not consider the variety of soil conditions or are performed for generalized site categories, such as “hard rock,”“soft soil” or “alluvium.” A technique of seismic hazard calculations on the basis of the Fourier Amplitude Spectra recently developed by the authors allows us to create hazard maps involving the influence of local soil conditions using soil/bedrock spectral ratios. Probabilistic microzoning maps may be constructed showing macroseismic intensity, peak ground acceleration, response and design spectra for various return periods (probability of exceedance), that allow optimization of engineering decisions. An application of this approach is presented which focused on the probabilistic microzoning of the Tashkent City.     

非发震断层的地震效应问题

本文采用二维动态有限元分析的方法，排除了影响宏观震害的其它因素，建立非发震断层的场地地震反应分析模型。计算中较全面地考虑了断层破碎带的尺度及带内岩土物理力学性能、断面产状、断层错距、覆盖层厚度、基岩起伏、输入波动力特性等一系列因素对地面峰值加速度及相对加速度反应谱的影响，并结合有关宏观震害资料从不同的角度对这些问题进行了初步的分析和探讨，认为非发震断层所表现出来的实际地震效应具有很大的随机性，其随机程度受控于断层自身要素的组合型式及各种外部条件。     

2010年4月14日玉树Ms7.1地震加速度场预测

基于有限断层震源、且使用动力学拐角频率的地震动随机模拟方法预测玉树地震近断层的加速度场.首先,基于有限断层震源建模方法建立该次地震的震源模型;然后,基于上述地震动模拟方法预测玉树地震近断层191个节点的加速度时程.在此基础上,取每个结点的加速度峰值绘制该次地震的近断层加速度场.结果表明:(1)近断层加速度场主要受震源破裂过程和断层面上滑动分布的影响.断层面上凹凸体投影到地表的区域附近,加速度峰值最大,也是震害最严重的区域;(2)对于走滑地震,断层沿线附近的场地并非均会发生破裂方向性效应;发生破裂方向性效应的场地与凹凸体在断层面上的位置有关.     

A study of residuals for strong ground motions in Adapazari basin,NW Turkey,by ground motion prediction equations (GMPEs)

The city of Adapazarı — located in the Marmara Region of northwest Turkey — is situated on a deep sedimentary basin and was the city most heavily damaged by the strong ground motion of the 17 August 1999 Kocaeli earthquake (moment magnitude M_w = 7.4). This study determines site amplifications of the attenuation relationships for shallow earthquakes in the Adapazarı basin by using the previous ground motion prediction equations (GMPEs) and the traditional spectral ratio method. The site amplifications are determined empirically by averaging the residuals between the observed and predicted peak ground acceleration (PGA) and spectral acceleration (SA) values for various periods. Residuals are significantly correlated with the known characteristics of geological units. A new attenuation model has also been developed for 5% damped spectral acceleration to determine the dependence of strong ground motions on frequency.     

近断层强地震动场预测

以1997年4月11日新疆伽师地震（M_w6.1）为例,详细介绍了近断层强地震动场的预测方法.首先,用有限断层震源建模方法建立了该次地震的震源模型;然后,基于动力学拐角频率的地震动随机模拟方法,模拟了该次地震仅有主震加速度记录、且位于巨厚土层上的三个台站的加速度时程,并用实际地震记录进行了验证.在此基础上,基于预测的近断层77个节点的加速度时程的峰值绘制了该次地震的加速度场.结果表明,上述方法模拟的加速度时程在0.5 Hz以上的高频段是可行的、实用的;预测的近断层加速度场具有非常明显的上盘效应.地表最大加速度的范围与断层面上最大凹凸体位置相对应,说明与断层面上凹凸体相对应的地面上的建（构）筑物将会遭受到较为严重的震害.     

Stochastic ground motion simulation of the 12 October 1992 Dahshour earthquake

The stochastic method for finite faults is applied to simulate the ground motion of the 12 October 1992, m _b = 5.9, Dahshour earthquake. The method includes discritization of the fault plane into certain number of subfaults, and a ω-squared spectrum is assigned to each of them. Contributions from all subfaults are then empirically attenuated to the observation sites, where they are summed to produce the synthetic acceleration time-history. The method is first tested against its ability of reproducing the recording at Kottamya station. The calibrated model is then applied to calculate the synthetics at a large number of grid points covering the area around the fault plane. Simulated peak values are subsequently used to produce the synthetic peak horizontal acceleration map for the area. We compare the peak horizontal acceleration with the attenuation laws proposed for Egypt as well as the macroseismic intensity map of the 1992 Dahshour earthquake. The peak horizontal acceleration contours estimated using the calibrated model are mostly consistent with the observed intensity values and evidences of strong ground motions. Our results encourage the application of the approach as a supplementary tool for site-specific strong ground motion prediction.     

Investigating the role of source mechanism,surface topography,and attenuation on the observed PGA pattern in May 28, 2004, Mw 6.2 Baladeh earthquake (Iran)

In this paper, we use seismic waveform simulation to investigate the influence of source mechanism complexity, surface topography, and quality factor on the observed peak ground motions in May 28, 2004, moment magnitude (Mw) 6.2 Baladeh earthquake. The observed peak ground acceleration (PGA) pattern in this event, which is the biggest earthquake to hit the Central Alborz Mountains of Iran in modern instrumental era, is irregular in some respects. First, the observed PGA contours are elongated toward north-west and, second, the maximum observed PGA value of 1049 cm/s² on the horizontal component of Hasan Keyf station 50 km away from the epicenter is quite high and irregular for an earthquake of this magnitude, at such long distance. In this study, we employ the spectral element method, implemented in SPECFEM3D software package to simulate the 3D wave propagation from several source models in the area. Our results suggest directivity effect is the main cause of the anomalous observations in this earthquake and could account for the elongation of PGA contours and also the anomalous maximum PGA value observed at Hasan Keyf strong motion station. We show that the surface topography has minor effect on the observed peak ground acceleration and the resulting PGA maps. Also by finding the bounds of seismic quality factor effect on the peak ground acceleration values, we show that this factor could not account for the elongation of iso-acceleration contours in the north-west direction.     

深厚软土场地基岩地震动反演——以天津波为例

根据天津波地表加速度记录和相应实测场地钻孔资料,采用等效线性化方法模拟土体非线性,进行了深厚软土场地基岩地震动反演,研究了频率截断对深厚软土场地基岩地震动反演的影响,为天津波地表加速度记录提供了相应的基岩地震动输入。研究表明:不同截断频率情况下,反演得到的基岩地震动峰值和反应谱曲线形状均相差悬殊,但反演后再正演所得到的地面运动与原地表记录相比,加速度时程曲线形状和峰值大小、反应谱曲线形状和峰值大小均非常接近;可根据工程需要对地表加速度记录进行不同频率的截断,反演得到所需强度的基岩地震动。     

2013年四川芦山MS7.0地震近断层强地面运动模拟及烈度分布估计

2013年4月20日在我国四川省发生了芦山M_S7.0地震,地震给当地群众的生命财产安全带来了巨大的损失,其中最严重的破坏发生在震中附近的芦山、宝兴等地区.根据地震发生的快速反演结果,及发震断层面上滑动位移的分布情况,构建有限断层模型,对近断层区域的强地面运动进行初步计算,并基于强地面运动的模拟结果给出震区烈度分布的初步估计.模拟结果显示：模拟烈度图显示极震区的烈度在IX级左右,VI级烈度影响范围大致为16000 km²,该结果与中国地震局于4月27日给出的震区实测烈度图一致程度较高.强烈地震发生后,基于近断层强地面运动模拟计算的结果,可以给出相对合理的地震烈度分布情况估计,对震区震情判定及救灾工作具备较高的现实意义.     

Characteristics of the strong ground motions from the 6 April 2009 L’Aquila earthquake,Italy

An M_w 6.25 earthquake occurred on April 6, 2009 at 03:33 a.m. local time, in the Abruzzo region (Central Italy), close to the city of L’Aquila. The earthquake ruptured a North-West (NW)–South-East (SE) oriented normal fault dipping toward the South-West (SW), with the city of L’Aquila lying a few kilometers away on the hanging wall.The main shock has been recorded by fifty-eight accelerometric stations: the highest number of digital recordings ever obtained in Italy for a single earthquake, one of the best-recorded earthquakes with a normal fault mechanism. Very high values of peak ground acceleration (0.3–0.65 g) were observed close to the center of L’Aquila (6 stations at zero JB distance from the fault). The earthquake caused severe loss of lives (299 victims and 1500 injured) and damage (about 18000 unusable buildings) in the epicentral area.In this study we analyze the ground motion characteristics of both the main shock in terms of peak ground acceleration (PGA), peak ground velocity (PGV), and pseudo-acceleration response spectra (5% of damping ratio). In particular, we compare the pseudo-acceleration response spectra for horizontal directions with the EC8 design spectrum and the new Italian building code (NTC08). In order to understand the characteristics of the ground motions induced by L’Aquila earthquake, we also study the source-related effects and site response of the strong motion stations that recorded the seismic sequence. A novel method is used for the analysis of inter-station and site-specific H/V spectral ratios for the main event and for 12 aftershocks.     

典型土层场地随机地震反应规律分析

针对硬、中、软3种土层场地,选取历史上实测到的Ⅰ类和Ⅱ类场地的地震动记录各100条,分别调整地震动记录加速度峰值至0.1g、0.2g和0.3g,并采用一维等效线性化方法开展了场地随机地震反应研究,系统分析了地震动峰值加速度、速度和位移反应的变异性规律。主要结论为,位移和速度峰值的变异性随场地土变软而增大;位移和速度峰值变异性较加速度峰值的变异性更为突出;利用50条左右的地震动记录即可获得场地地震反应均值和标准差较为稳定的结果。     

Simulation of strong earthquake characteristics of a scenario earthquake (MS7.5) based on the enlightenment of 2022 MS6.9 earthquake in Menyuan

The Menyuan area is an important transportation hub in the Hexi Corridor. The Menyuan M_S6.9 earthquake that occurred on January 8, 2022 had a major impact on the local infrastructure and transportation of this region. Due to the high possibility of similar strong earthquakes occurring in this area in the future, preliminary assessment of the seismic intensity characteristics of destructive earthquakes in this region is essential for effective disaster control. This paper uses the empirical Green′s function (EGF) method as a numerical simulation tool to predict the ground motion intensity of Datong Autonomous County under the action of the scenario earthquake (M_S7.5). Seismic records of aftershocks of the 2016 Menyuan M_S6.4 earthquake were used as Green’s functions for this simulation. The uncertainties associated with various source parameters were considered, and 36 possible earthquake scenarios were simulated to obtain 72 sets of horizontal ground motions in Datong County. The obtained peak ground acceleration (PGA) vs. time histories of the horizontal ground motion were screened using the attenuation relationships provided by the fifth-edition of China's Seismic Ground Motion Parameter Zoning Map and the NGA-West2 dataset. Ultimately, 32 possible acceleration-time histories were selected for further analysis. The screened PGA values ranged from 78.8 to 153 cm/s². The uncertainty associated with the initial rupture point was found to greatly affect the results of the earthquake simulation. The average acceleration spectrum of the selected acceleration-time history exceeded the expected spectrum of a intermediate earthquake, which means that buildings in Datong County might sustain some damage should the scenario earthquake occur. This research can provide reliable ground motion input for urban earthquake damage simulation and seismic design in Datong County. Growing the dataset of small earthquakes recorded in this region will facilitate the large-scale simulation of ground motions under different earthquake scenarios.     

The 1895 Ljubljana earthquake: can the intensity data points discriminate which one of the nearby faults was the causative one?

The earthquake (Mw 6 from the SHEEC defined by the MDPs) that occurred in the central part of Slovenia on 14 April, 1895, affected a broad region, causing deaths, injuries, and destruction. This event was much studied but not fully explained; in particular, its causative source model is still debated. The aim of this work is to contribute to the identification of the seismogenic source of this destructive event, calculating peak ground velocity values through the use of different ground motion prediction equations (GMPEs) and computing a series of ground motion scenarios based on the result of an inversion work proposed by Juki? in 2009 and on various fault models in the surroundings of Ljubljana: Vi?, ?elimlje, Borovnica, Vodice, Ortnek, Mi?jedolski, and Dobrepolje faults. The synthetic seismograms, at the basis of our computations, are calculated using the multi-modal summation technique and a kinematic approach for extended sources, with a maximum peak ground velocity value of 1 Hz. The qualitative and quantitative comparison of these simulations with the macroseismic intensity database allows us to discriminate between various sources and configurations. The quantitative validation of the seismic source is done using ad hoc ground motion to intensity conversion equations (GMICEs), expressly calculated for this study. This study allows us to identify the most probable causative source model of this event, contributing to the improvement of the seismotectonic knowledge of this region. The candidate fault that has the lowest values of average differences between observed and calculated intensities and chi-squared is a strike slip fault with a toward-north rupture as the Ortnek fault.     

基于数学建模的潜在地震破裂面源检测方法研究

大多数地震破裂面源检测方法都是通过简化地震震源,将地震震源表示成线源或者点源,无法有效描述地震带地震破裂面源产状和大小,不适用地震震级较大的情况下地震危险性检测。因此提出基于数学建模的潜在地震破裂面源检测方法,在地震震级较大时仍能检测出地震危险性概率。选取适宜的地震基岩水平峰值加速度衰减关系,分析地震震级、破裂长度、破裂宽度相互关系,确定地震引起的潜在地震破裂面源大小,计算给定地震动小于在场点处产生地震动的概率,将该概率同地震动加速度衰减关系结合,得到地震动年超越概率,分析地震危险性。经过实验检测发现,所提方法检测出的年超越概率与峰值加速度、最大震级有关,该概率能精准表示地震带地震破裂面源产状和大小,说明该方法检测地震危险性是合理的。