Rock Site Conditions Research Articles

Site-specific probabilistic seismic hazard analysis in Nuweiba, Gulf of Aqaba, Egypt: Combining area source model and active faults

Gulf of Aqaba in Eastern Egypt is characterized by significant seismic activity and high deformation rate, making it a major source of destructive earthquakes in the region. While previous studies have produced probabilistic seismic hazard analysis (PSHA) maps for the region, they have not adequately accounted for active faults or site response in their calculations. This study introduces a newly developed seismic source model for the Gulf of Aqaba, considering area source, active fault source, and a combination of both models to improve seismic hazard assessment for the region. The study incorporates the previously measured average shear-wave velocity for the upper 30 m (Vs30), fundamental frequency (F0), and amplification factor (A0) at some selected sites in Nuweiba city. Accordingly, site-specific PSHA is carried out for the bedrock condition (Vs30 = 800 m/s, according to the Egyptian Building Code) and for the surface of soft sediments using F0, A0, and Vs30. Uncertainties in slip rate, maximum magnitude, and recurrence model are accounted during PSHA computation. Ground motion parameters such as peak ground acceleration (PGA) and spectral acceleration (SA) for various probabilities of exceedance in 50-year lifetime are calculated for both rock site conditions and soft sediments. The maximum calculated PGA and SA are 0.65 g and 1.25 g, respectively, for a 10% probability of exceedance over 50 years at bedrock conditions.

Site‐specific response spectra developed by considering near‐fault motion with finite‐fault simulation in Taiwan

AbstractA new methodology is proposed for developing a scenario‐based site‐specific response spectrum (RS) considering near‐fault effects in Taiwan. First, source parameters, together with reference rock site conditions, are defined according to the available geological and geophysical information at a target site close to a potential active fault in northern Taiwan. Secondly, the scenario‐based response spectrum for a reference rock site condition is developed theoretically through an empirical approach by using a ground motion prediction equation (GMPE). The effect of the pulse period and the occurrence probability of near‐fault pulse‐like ground motion on RS is evaluated by using the ground motion simulation (GMS) technique, in which the stochastic finite‐fault simulation method is validated and applied for evaluating velocity pulse. Third, site‐specific site amplification is incorporated into RS through a site transfer function calculated from the measured horizontal‐to‐vertical Fourier spectral ratio through the microtremor (MHVR) of the target site. Finally, the design spectrum of the target site is compared with the derived site‐specific RS to evaluate the impact of the neighbor fault on the structure of the target site.

Site effect influence on the seismic vulnerability of unreinforced masonry buildings in low to moderate seismic urban areas in Algeria

PurposeThis paper aims to develop preliminary damage scenarios for unreinforced masonry buildings located in low to moderate seismic hazard areas in Algeria, taking into account the specific site effects.Design/methodology/approachThree soil types were considered in this analysis according to the definition of the Algerian seismic code (RPA99/2003). Peak ground acceleration values were assigned to each soil type issued from a probabilistic seismic hazard analysis (PSHA). To highlight the effect of soil conditions on the seismic vulnerability analysis of masonry buildings, a site vulnerability increment is carried out, and the macroseismic Risk-UE method has been adopted and applied by developing two main seismic scenarios according to both return periods of the PSHA, 100 and 475 years, respectively.FindingsBased on the preliminary results of rock site condition, it can be outlined that the significant damage obtained for different earthquake scenarios discovered a substantial worldwide seismic risk to the building stock of the study area. Once the site effect is integrated into the analysis, more high values of vulnerability indexes and expected damages are obtained. Moreover, it can be concluded that soft soil (S3) is a little bit more influential than stiff soil (S2) on the final vulnerability index compared to (S1). However, the difference between the soil effect S2 and S3 on the vulnerability index can be neglected.Research limitations/implicationsResearchers are encouraged to test the mechanical approaches for more detailed outcomes of a specific building analysis.Practical implicationsThis research proves to the Algerian decision-makers that due to the site effects and the vulnerability of the masonry buildings, an urgent intervention program is required even for existing buildings located in low to moderate seismic hazard areas.Originality/valueSeveral seismic vulnerability types of research have been conducted in Algeria for the unreinforced masonry buildings in moderate to high seismic areas in which generally the soil effect is neglected. In this context, this research paper proves that due to the site effects and the vulnerability of the masonry buildings, special attention is required even for existing buildings located in low to moderate seismic hazard areas. With this conclusion, the requirement of taking into account the soli effect in the high seismic areas is even more pronounced and should be conducted.

Influence of local site effects on seismic risk maps and ranking of Italian municipalities

The latest studies concerning seismic risk assessment in Italy were developed without considering the site geo-lithological effects, thus limiting the assessment to rock soil type. In this study, for the evaluation of site amplification effects, we used the results of recent works based on the Italian seismic microzonation data. As this first study is performed for the entire Italian territory at the municipality scale, the site amplification factors (AFs) have been assigned to the chief town of each of the 7715 Italian municipalities, assuming that the building stock is concentrated in that small area. The AFs have been compared with those foreseen by the Italian building code (NTC2018). The PGA amplification with the new AFs ranges from 1 to 2.2 bringing to an average increase of 75% in the hazard, compared to 27% if using the NTC2018 amplification. The seismic risk has been evaluated using the probabilistic hazard assessment adopted in the NTC2018 and recent vulnerability/exposure models developed for Italy. The residential building stock was subdivided into 5 vulnerability classes (3 for masonry and 2 for concrete) derived from the national census data and further refined using the construction age and building height. The results show that, for a rock site condition, the loss estimates are comparable with those of previous works in terms of casualties, homeless, and economic damage. The introduction of the site effects brings to a significant increase in the expected losses resulting higher than the historical data retrieved from a careful analysis of the major Italian earthquakes. This suggests the importance of developing new fragility curves based on updated AFs. To support the implementation of risk reduction programs, a seismic risk index is introduced, allowing a municipality ranking by risk, a cost estimation of the seismic retrofitting in the highest risk municipalities, and an assessment of the consequent risk reduction.

Region Specific Ground-Motion Predictive Models for Shallow Active Regions

ABSTRACT Using a global dataset, we propose a series of ground-motion predictive models for acceleration response spectra. The proposed models include regional adjustments to source, path, and site terms with nonlinear soil behavior. The regression coefficients are computed using linear and nonlinear mixed-effect regression algorithms. Furthermore, we develop heteroscedastic variability models for between-event, site-to-site, and single-site standard deviations. The between-event sigma model depends solely on magnitude, but the single-site standard deviation model depends on both magnitude and distance. Finally, the site-to-site standard deviation model is given in terms of VS30 and spectral acceleration at rock site condition.

Simulation of strong ground motions onshore the southeastern coast of the Red Sea, Saudi Arabia

In the southernmost part of the Arabian Shield, southeastern onshore of the Red Sea, damage earthquakes were historically reported implying that the region may be susceptible to have a potential seismic hazard in future. To understand the potential seismic hazard in the region, we present an analysis to simulate the peak ground accelerations (PGA) from future large earthquakes of Mw 6.0, and 6.5 in the region using an empirical Green's function (EGF) summation technique. The waveform recordings for a small-sized earthquake of Mw 4.4, that occurred in 23rd of January 2014, were used as an element earthquake. The estimated PGA values are consistent with the corresponding values of ground motion prediction equations (GMPEs) that derived for California, Japan, and Western Saudi Arabia, indicating that these equations are applicable for rock site conditions in the region. The results of response spectra reveal periods vary from 0.2 s to 3.0 s, implying potential hazard impacts for short and tall buildings.

Seismic hazard assessment of the Kathmandu Valley and its adjoining region using a segment of the main Himalayan Thrust as a source

An attempt has been made to evaluate seismic hazard in the Kathmandu Valley and its adjoining region. A segment of the Main Himalayan Thrust, which produced the 2015 Gorkha Earthquake is used as an earthquake source. Two rupture models of the source are utilized assigning unequal weight to estimate seismic hazard. The first model considers entire north-south rupture of the source that is similar to the rupture of the 1934 Bihar-Nepal Earthquake (Mw 8.2). The second model considers the northern-half rupture of the source, which is similar to that of the 2015 Gorkha Earthquake (Mw 7.8) and possibly the 1833 Nepal Earthquake (Mw 7.6).Seismic hazard maps are prepared for 500 and 200 year return periods at engineering rock site condition. A comparison is made between the peak ground acceleration (PGA) of Kathmandu and Nijgadh estimated for 200 year return period with the recorded PGA of the 2015 Gorkha Earthquake in Kathmandu (Kirtipur: a rock site) and empirically estimated PGA of that earthquake in Nijgadh respectively. Kathmandu and Nijgadh are selected for the comparison because Kathmandu falls within the rupture area of the 2015 Gorkha Earthquake and Nijgadh is in the Indogangetic Plain and away from the rupture area of that earthquake. The result shows that the PGA (0.23 g) estimated for Kathmandu for 200 year return period closely agrees with the instrumentally recorded PGA of the 2015 Gorkha Earthquake in Kathmandu (0.25 g). Instrumentally recorded PGA is not available in Nijgadh, which is at about 55 km in the south from Kathmandu. A seismic intensity survey was carried out in Nijgadh and its adjoining region to estimate the intensity of the 2015 Gorkha Earthquake in Nijgadh. The probabilistically estimated PGA (0.1 g) for Nijgadh for 200 year return period is in reasonable agreement with that of the 2015 Gorkha Earthquake (0.07 g) estimated from the seismic intensity (VI on MMI).

Probabilistic seismic hazard mapping of National Capital Region of India using a modified gridded seismicity model

This is the first comprehensive study for a seismic macro-zonation of the National Capital Region of India by using the probabilistic seismic hazard analysis approach. A modified gridded seismicity model is used for this purpose, in which the earthquake occurrence rates obtained using the Gutenberg-Richter's (G-R) relationships for conventional area type seismic sources are distributed non-uniformly among a grid of cells. This provides a more robust approach than the commonly used weighted sum of area sources of homogeneous seismicity and the zone-free smoothed gridded seismicity. Other distinguishing features of the present analysis include: detailed seismotectonic evaluation of the region to identify seven area type seismic sources, compilation of a comprehensive earthquake catalogue for the estimation of seismicity recurrence parameters, selection of the most appropriate ground motion prediction equation by using a database of 71 strong motion accelerograms recorded in the region, and estimation of the compatible distance parameters by associating a fictitious fault rupture plane to each grid cell with appropriate strike and dip angles. Hazards maps are prepared for the hard rock site condition in terms of the peak ground acceleration and the 5%-damping acceleration response spectrum amplitudes for several combinations of natural periods and return periods. A simple empirical approach is also developed to obtain amplification factors for modifying the uniform hazard response spectra for the rock sites to those for the soil sites with a given VS30 value. The hazard estimates from this study are found to be somewhat higher with greater site-to-site variations as compared to those from the earlier studies.

Natural Frequencies of Model Piers under Different Ground Support Conditions

The natural frequency is critical for evaluating the integrity of bridge piers. However, the natural frequency of bridge piers can vary with the support condition of the ground. The aim of this study is to investigate the natural frequency of bridge piers under different ground conditions and at different embedded depths using a small-scale concrete pier. The model piers were fixed to asphalt concrete pavement using epoxy to simulate the rock site condition. Furthermore, model piers of different embedded depths were installed in a soil chamber with dimensions of 1.0 m × 1.0 m × 0.5 m to simulate weathered soil conditions. The upper part of the model pier was hit with a hammer having a rubber tip, and the acceleration signals were measured using three accelerometers installed at the upper, middle, and bottom parts of the model pier. Fast Fourier transforms were performed to analyze the natural frequencies of the model piers. The experimental results showed that the natural frequency under the fixed condition using epoxy was significantly higher than that under the unfixed condition. In the case of weathered soil conditions, three peak points appeared in the frequency domain. The natural frequencies measured at these three points increased with the embedded depth. The increment ratio of the natural frequency with the largest amplitude was significant. This study demonstrates that ground support conditions should be considered when evaluating the integrity of bridge piers through natural frequency analysis.

Probabilistic seismic hazard analysis of Madhya Pradesh (Central India) using alternate source models: a logic tree approach

This study presents the macro-level probabilistic seismic hazard analysis (PSHA) of Madhya Pradesh using the classical Cornell-McGuire method. It investigates the seismic hazard of the region using two different source models—one covering seismogenic sources within 200 km (19–28° N and 72–84° E), and another within 300 km (16–32° N and 69–88° E) from the peripheral boundaries of Madhya Pradesh. It also proposes a new hybrid model that combines the above two models using a logic-tree approach and produces hazard maps and response spectra (bedrock level) for the seven smart cities proposed under the Smart City Mission of the Government of India. Finally, the study’s results are compared with the standard recommendations by IS 1893–2016 (Part-1) and National Disaster Management Authority (NDMA 2010). PSHA is performed using an updated earthquake catalog between 1800 and 2020 compiled from various national and international resources. Standardization of catalog is performed in terms of homogenization of magnitudes to moment magnitudes (Mw), zone-wise catalog division, and declustering using Gardner and Knopoff (1974) algorithm. It utilizes the logic tree approach to address the uncertainties associated with source modeling, source characterization, and selection of ground-motion prediction equations (GMPEs). Ground accelerations corresponding to different parts of the study region are calculated by dividing the region into a 0.2° rectangular grid in orthogonal directions. This study presents the PGA maps for the entire region for the return periods of 475 and 2475 years (equivalent to 10% and 2% probability of exceedance in 50 years, respectively) and first-hand response spectra (bedrock level) for the seven smart cities corresponding to spectral accelerations, SA (T), for periods of 0.1 s, 0.2 s, 0.5 s, 1 s and 2 s on stable firm rock site condition (Vs30 as 760 m/sec) based on the 200 km, 300 km, and hybrid source models. The study finds the 200 km source model's results in fair agreement with the national recommendations, whereas the 300 km source model's results higher than the national recommendations. The results from this study shall render a great help to city planners for designing new structures and also in retrofitting the existing structures.

A probabilistic seismic hazard assessment for Wylfa Newydd, a new nuclear site in the United Kingdom

This study presents the probabilistic seismic hazard assessment (PSHA) for a nuclear site in the UK, Wylfa Newydd. The PSHA was defined at a bedrock horizon with shear wave velocity of 3000 m/s and developed to capture the centre, body and range of the technical defensible interpretations. Although not a formal SSHAC (Senior Seismic Hazard Assessment Committee) process, the PSHA met all the SSHAC Level 2 requirements with some aspects of SSHAC Level 3 and 4. Two base source models were developed: SM1 mainly driven by the observed seismicity and SM2 guided by the geology and tectonics. To capture epistemic uncertainty, variations of boundaries were included in the logic tree, resulting in five different models. Based on the selection discussed by Villani et al. (Bull Seismol Soc Am 109(4):1378–1400, 2019), four empirical models adjusted to the hard rock site conditions of Wylfa Newydd and a site-specific stochastic GMPE, developed within this project, were adopted in the logic tree for the median prediction. For all GMPEs a logic tree for the single-station sigma model was adopted. The PSHA resulted in a mean peak ground acceleration value for annual probability of exceedance of 10−4 of 0.192 g. The comparison of the mean 10−4 uniform hazard spectrum with the traditional piecewise linear design spectrum showed significant conservatism up to 20 Hz and underestimation at higher frequencies. To overcome this limitation, a performance-based design spectrum, following US practice (ASCE/SEI 43-05), was therefore recommended; this marks a significant difference to the traditional UK design practice.

Probabilistic Seismic Hazard Assessment of Pakistan Territory Using an Areal Source Model

A seismic hazard map for the national seismic design code of Pakistan (i.e., Building Code of Pakistan) is derived using probabilistic seismic hazard assessment (PSHA) approach. In order to update the seismic code, an updated seismic zoning map is required that should be based on usage of the recent seismic hazard elements. PSHA of Pakistan is an essential and important milestone. For this purpose, the standard Cornell–McGuire (1968–1976) approach is employed, and the computations are made over a rectangular grid of 0.1°. The main features of this study include usage of a recently compiled earthquake catalogue, recent ground motion prediction equations and an updated seismic source model. The resulting ground motions are obtained as peak ground acceleration (PGA) and 5% damped spectral acceleration (SA) at T = 0.2 s and T = 1.0 s for 475-, 975- and 2475-year return periods (RPs) (evaluated for the flat rock site conditions). Results of the study show that seismic hazard in Pakistan is highest in its central and northern parts. In the central part near Quetta, severe seismic hazard (PGA 0.40 g) is observed. Among the important cities in Pakistan, Balakot city is likely to experience a PGA value of 0.36 g, while Islamabad, Peshawar and Chitral are likely to experience 0.33 g. The cities of Gilgit, Karachi and Gwadar experience ground motion values of 0.34, 0.26 and 0.29 g, respectively, for the 475-year return period (RP). It has also been observed that ground motion values show variation in the distribution and magnitude in contrast to the hazard map of national design code. The hazard map presented in this study is the improved seismic hazard zoning map of Pakistan that would be helpful in developing pre-disaster mitigation strategies and risk assessment studies in Pakistan. It is concluded that the seismic zoning map of the national seismic design code of Pakistan underestimates the ground motion values, and it should be updated or replaced.

Urban seismic risk model for resilient cities. The case of Thessaloniki

Seismic risk assessment and loss estimation are of major importance for decision-making with respect to the reduction of earthquake-induced losses at local, urban, national and even continental scale. In this study we present a preliminary model for the probabilistic seismic risk assessment at urban scale. The studied model will be applied to the residential building stock of Thessaloniki, Greece, for which detailed building inventory and very good knowledge of the soil conditions are available. The applied model comprises three main components, i.e., seismic hazard, building exposure model and physical - socioeconomic vulnerability models. Seismic hazard for rock site conditions is properly amplified to account for site effects of Thessaloniki city, considering the available detailed data of the soil conditions. Exposure model for residential buildings of Thessaloniki is developed based on the results from the 2011 Population and Housing Census. Both physical and socioeconomic losses were considered. For the assessment of the physical and socioeconomic losses we applied the fragility and vulnerability models developed for Greece by GEM. The work has been conducted in the framework of SERA European project (http://www.sera-eu.org/en/home/), which aims at developing a pan-European seismic risk model, applicable at both urban and national risk assessment. The model developed in this work will contribute to the efforts towards increasing the resilience of cities.

Seismic Hazard Analysis of Surface Level, Using Topographic Condition in the Northeast of Algeria

The aim of this study is to conduct a probabilistic seismic hazard analysis and spatial variation of seismic hazard at the surface level for Northeast of Algeria, covering 4°E–9°E, 33°N–38°N. The most recent peak ground acceleration (PGA) attenuation relationship, along with the updated seismic catalog and the best knowledge on the seismic activity in the study area have been used to estimate the seismic hazard and its uncertainty. Two types of seismic source models, linear sources and areal sources, were considered to model the seismic sources. Different sets of ground motion prediction equations were used for different tectonic provinces to characterize the attenuation properties. The hazard estimation at bedrock level was carried out using a probabilistic approach and the results obtained from various methodologies were combined into a logic tree framework. In this paper, we generate PGA maps with 10% probability of exceedance in 50 years, for a rock site condition. The seismic site characterization of Algeria was done using topographic slope map derived from Digital elevation model data. We estimate the seismic hazard from the seismicity catalog and not from faults with recurrence rates obtained from geologic data. The hazard estimation at surface level, is achieved through the use of appropriate site amplification factors corresponding to various site classes based on topographic gradient. Spatial variation of surface level PGA for return periods of 100, 475 years and 2000 years are presented as contour maps. The maps obtained in this study are based on the assumption that the process of earthquake occurrence is inherently Poissonian, so that the probabilistic ground motion is time-independent.

Probabilistic seismic hazard assessment for Hanoi city

In this study, the methodology of probabilistic seismic hazard assessment proposed by Cornell and Esteva in 1968 was applied for Hanoi city, using an earthquake catalog updated until 2018 and a comprehensive seismotectonic model of the territory of Vietnam and adjacent sea areas. Statistical methods were applied for declustering the earthquake catalog, then the maximum likelihood method was used to estimate the parameters of the Gutenberg–Richter Law and the maximum magnitude for each seismic source zone. Two GMPEs proposed by Campbell & Bozorgnia (2008) and Akkar et al., (2014) were selected for use in hazard analysis. Results of PSHA for Hanoi city are presented in the form of probabilistic seismic hazard maps, depicting peak horizontal ground acceleration (PGA) as well as 5-hertz (0.2 sec period) and 1-hertz (1.0 sec. period) spectral accelerations (SA) with 5-percent damping on a uniform firm rock site condition, with 10%, 5%, 2% and 0,5% probability of exceedance in 50 years, corresponding to return times of 475; 975; 2,475 and 9,975 years, respectively. The results of PSHA show that, for the whole territory of Hanoi city, for all four return periods, the predicted PGA values correspond to the intensity of VII to IX degrees according to the MSK-64 scale. As for the SA maps, for all four return periods, the predicted SA values at 1.0 s period correspond to the intensity of VI to VII, while the predicted SA values at 0.2 s period correspond to the intensity of VIII to X according to the MSK-64 scale. This is the last updated version of the probabilistic seismic hazard maps of Hanoi city. The 2019 probabilistic seismic hazard maps of Hanoi city display earthquake ground motions for various probability levels and can be applied in seismic provisions of building codes, insurance rate structures, risk assessments, and other public policy.

Evaluation of Generic Reference Rock Site Conditions for Israel

Evaluation of Generic Reference Rock Site Conditions for Israel

Earthquake hazard potential of Indo-Gangetic Foredeep: its seismotectonism, hazard, and damage modeling for the cities of Patna, Lucknow, and Varanasi

The Indo-Gangetic Foredeep region lies in close proximity to the Himalayan collision tectonics and the Peninsular Shield thereby subjecting it to repeated strong ground shaking from large and great earthquakes from these active tectonic regimes. An attempt is, therefore, made to understand the seismotectonic regime of the Indo-Gangetic Foredeep region while performing probabilistic seismic hazard modeling of its important cities of Patna and Lucknow and the religious city of Varanasi based on consideration of seismogenic source characteristics, smoothened gridded seismicity zoning, and generation of next generation ground motion attenuation models appropriate for this region along with other existing region-specific ground motion prediction equations in a logic tree framework. In the hazard modeling, peak ground acceleration (PGA) and 5% damped pseudo-spectral acceleration (PSA) at different time periods for 10 and 2% probability of exceedance in 50 years with a return period of 475 and 2475 years have been estimated at firm rock site condition (site class B/C) with an average shear-wave velocity of about 760 m/s, of which, however, the results of only 475 years of return period have been presented here for urban development and earthquake engineering point of view. Surface-consistent probabilistic seismic hazard is modeled using the International Building Code-compliant short and long period site factors corresponding to topographic gradient-derived shear-wave velocity-based site classes. The estimated surface-consistent PGA is seen to vary in the range of 0.222–0.238 g in Patna City, while it varies in the range 0.257–0.295 g in Lucknow and 0.146–0.172 g in the city of Varanasi. The cumulative damage probabilities in terms of ‘none,’ ‘slight,’ ‘moderate,’ ‘extensive,’ and ‘complete’ have been assessed using the capacity spectrum method in the Seismic Loss Estimation Approach (SELENA) using both the fragility and capacity functions for six model building types in these cities. The discrete damage probability exhibits that the building types ‘IGW-RCF2IL (PAGER/FEMA:C1L),’ ‘IGW-RCF21M (PAGER/FEMA:C1M),’ and ‘IGW-RCF11L (PAGER/FEMA:C3L)’ will suffer minimum damage, while ‘IGW-RCF21H (PAGER/FEMA:C1H),’ ‘IGW-RCF11M (PAGER/FEMA:C3M),’ and ‘PAGER/FEMA:C3H’ will suffer extensive damage in the event of a maximum earthquake of Mw 7.2 impacting the terrain as predicted from median nodal maximum magnitudes in a heuristic search in the probabilistic protocol. The estimated probabilistic seismic hazard and damage scenario are expected to play vital roles in the earthquake-inflicted disaster mitigation and management of these cities for better predisaster prevention, preparedness, and postdisaster rescue, relief, and rehabilitation. The results may also be incorporated in the building codal provisions of these smart cities as intended by the Federal Government of India.

Bayesian probabilistic seismic hazard analysis with respect to near-fault effects

Uniform hazard spectrum (UHS) provides a set of spectral accelerations at various periods which have the same probability of exceedance. In this research, UHS for Bojnord region was determined based on the Bayesian concept as a powerful approach in considering and combining randomness and uncertainties. Source-to-site geometry parameters were included in the seismic hazard analysis to consider the near-fault directivity effects. Results show that near-fault hazard spectra for rock and soil site conditions are 20% larger than ordinary ones at periods longer than 1 s, on average. It was shown that near-fault pulse effects can be approximately included by systemically multiplying ordinary UHS by a near-fault amplification factor. Two-point method modified with the near-fault amplification factor was used to construct design response spectra having the highest similarity with the calculated uniform hazard spectra on different soil site conditions. The parameters of the two-point spectrum found here are close to those of ASCE7, except that the long-period site coefficient for soft soil is 1.21 and 1.10 times those of ASCE7-10 and ASCE7-16, respectively.

Wavelet analysis of soil-structure interaction effects on seismic responses of base-isolated nuclear power plants

Seismic base isolation has been accepted as one of the most popular design procedures to protect important structures against earthquakes. However, due to lack of information and experimental data the application of base isolation is quite limited to nuclear power plant (NPP) industry. Moreover, the effects of inelastic behavior of soil beneath base-isolated NPP have raised questions to the effectiveness of isolation device. This study applies the wavelet analysis to investigate the effects of soil-structure interaction (SSI) on the seismic response of a base-isolated NPP structure. To evaluate the SSI effects, the NPP structure is modelled as a lumped mass stick model and combined with a soil model using the concept of cone models. The lead rubber bearing (LRB) base isolator is used to adopt the base isolation system. The shear wave velocity of soil is varied to reflect the real rock site conditions of structure. The comparison between seismic performance of isolated structure and non-isolated structure has drawn. The results show that the wavelet analysis proves to be an efficient tool to evaluate the SSI effects on the seismic response of base-isolated structure and the seismic performance of base-isolated NPP is not sensitive to the effects in this case.

A Site Amplification Model for Crustal Earthquakes

A global dataset which is composed of more than 20,000 records is used to develop an empirical nonlinear soil amplification model for crustal earthquakes. The model also includes the deep soil effect. The soil nonlinearity is formulated in terms of input rock motion and soil stiffness. The input rock motion is defined by the pseudo-spectral acceleration at rock site condition (PSArock) which is also modified with between-event residual. Application of PSArock simplifies the usage of the site model by diminishing the need of using the period-dependent correlation coefficients in hazard studies. The soil stiffness is expressed by a Gompertz sigmoid function which restricts the nonlinear effects at both of the very soft soil sites and very stiff soil sites. In order to surpass the effect of low magnitude and long-distant recordings on soil nonlinearity, the nonlinear site coefficients are constrained by using a limited dataset. The coefficients of linear site scaling and deep soil effect are obtained with the full database. The period average of site-variability is found to be 0.43. The sigma decreases with decreasing the soil stiffness or increasing input rock motion. After employing residual analysis, the region-dependent correction coefficients for linear site scaling are also obtained.