Site-specific Seismic Hazard Analysis Research Articles

Alternate method to develop ground motion prediction equations: Calibration over Himalayan region

An alternative approach for constructing GMPEs, the Consistent Spectral Shape approach (CSS), is recently proposed to overcome the limitations of the conventional methods. The CSS framework is already implemented using the NGA-West2 database to develop a set of five GMPEs of 5 % damped spectral accelerations (RotD50, RotD100, Geo-mean, GMRotD50, and GMRotD100). In this paper, the performance of the CSS-GMPEs based on the NGA-West2 database is first assessed against those developed in the NGA-West2 project. Two different yardsticks are considered for the comparison: overall root mean square error (RMSE) and similitude of spectral shape. RMSE for CSS-GMPE and five NGA-West2 GMPEs are nearly consistent, but CSS utilizes a significantly smaller number of independent variables. CSS-GMPE also performs better while comparing the similitude of spectral shape. This paper next modifies the existing set of five CSS-GMPEs for the Himalayan region using a generic modification function contingent on intensity measure (RotD50, RotD100, Geo-mean, GMRotD50, and GMRotD100). All five CSS-GMPEs modified for the Himalayan region are observed to be performed satisfactorily for all practical purposes. These modified GMPEs are expected to be a valuable tool for site-specific seismic hazard analysis.

Site response analysis beneath the Kashmir basin (NW Himalaya) using ambient noise

Deep sedimentary valleys entrap and amplify seismic waves, which is further responsible for site-specific amplification over the allied region. Kashmir valley is a deep and active sedimentary basin in the northwest portion of the Himalayan lap. To characterize the site response for the intermountain Kashmir valley for the first time, we acquire single station microtremor measurements using Lennartz (three components/5s seismometer) at 141 sites with a grid of (5 km × 5 km) and two-dimensional (2D) array measurements using seven units of recording station of different geometry pattern at 38 sites across different lithological setup within the basin. We present here (1) a first-order predominant fundamental frequency (0.21–10.19 Hz) and subsequent sedimentary thickness maps for the entire valley, reflecting deep deposition with spatial heterogeneity in the area using the horizontal-to-vertical spectral ratio (HVSR) technique; (2) spatial classification of generated HVSR curves linking subsurface geomorphology and post strong ground-motion scenario in the valley; (3) extraction of the best dispersion characteristics of Rayleigh waves (fundamental mode) from all recorded vertical signals at each array site using frequency–wavenumber (F-K) method with an emphasis on signal synchronicity; and (4) retrieval of one-dimensional (1D) shear wave velocity ( VS) profiles across the valley from the inversion of dispersion curves using the neighborhood algorithm. Distinct model parameterizations were tested for the inversion to achieve the optimal inversion misfit. The collocated 1D VS profiles are consistent with newly drilled borehole logs information. Besides, the presented first-ever ambient noise survey–based site response study meets the objectives of site-specific seismic hazard and risk analysis of the Kashmir valley at the regional scale.

Site-specific seismic hazard analyses in the Izmit region (Marmara, Turkey) through passive seismic tests

Site-specific seismic hazard analyses in the Izmit region (Marmara, Turkey) through passive seismic tests

Amplification analysis at Nador city and surrounding area (NE of Morocco)

This study presents a ground response assessment performed at Nador city (Morocco) and surrounding areas. We carried out the one-dimensional equivalent linear approach using the known geotechnical parameters to derive amplification analysis at studied sites, using the shear wave velocity (VS(30)) derived from boreholes. Seismic hazard assessment is performed using two gridded seismicity models and four ground motions attenuation equations, in order to address the epistemic uncertainty in a logic-tree framework. Seismic hazard maps depicting the mean estimated hazard values and including the uncertainty are presented in terms of spectral acceleration at 0.0, 0.1 and 0.2 s, with 10% and 5% probabilities of exceedance in 50 years, and for B, B/C and C soil conditions, as defined by the National Earthquake Hazards Reduction Program classification and for local site conditions as well. Typical values of Peak Ground Acceleration (PGA) equal to 0.18g±0.03 and 0.26g±0.05 are obtained at the Nador city for 475 and 975 return period respectively and for B/C soil conditions. The deaggregation analysis for both returns periods (475 and 975 years) in terms of magnitude-distance (named 2D deaggregation) and in azimuth (longitude and latitude named 3D deaggregation) allows us to derive the contribution of the different couple of magnitude-distance (M,D) and the different sources, the controlling earthquake are also determined at the five considered cities, for both return periods. From the site-specific seismic hazard analysis performed at five main cities located in the studied area, the seismic hazard curves and the uniform hazard spectra (UHS) are obtained with their uncertainties for the considered return periods and soil conditions, as well as the design spectra proposed by Malhotra (2005). Real accelerogram time-history is used to generate compatible acceleration time-history with the design spectra proposed by Malhotra (2005) and the EC-8 type 2 (Eurocode 8.2004), for both return periods and for B/C soil conditions. The lower root mean square error value (RMSE) is archived by using the Malhotra design spectra for the considered return periods. The results display a clear amplification in silty and clayey soils, greater than in silt-gravely soils, as well as no significant amplification in volcanic soils. Moreover, the resulting fundamental frequency is in the range of 1.4–2.8 Hz, and the maximum amplification factor observed in Nador is about 3.5. These values are consistent with the results derived from ambient noise, seismic records using HVSR technique and with the values given by Moroccan Seismic Code in the 2000 and 2011 regulations.

Constraints on near-source saturation models for avoiding over-saturation of response spectral ordinates in RVT-based stochastic ground-motion simulations

Inversions of empirical data and ground-motion models to find Fourier spectral parameters can result in parameter combinations that produce over-saturation of short-period response spectral ordinates. While some evidence for over-saturation in empirical data exists, most ground-motion modellers do not permit this scaling within their models. Host-to-target adjustments that are made to published ground-motion models for use in site-specific seismic hazard analyses frequently require the identification of an equivalent set of Fourier spectral parameters. In this context, when inverting response spectral models that do not exhibit over-saturation effects, it is desirable to impose constraints upon the Fourier parameters to match the scaling of the host-region model. The key parameters that determine whether over-saturation arises are the geometric spreading rate (γ) and the exponential rate within near-source saturation models (hβ). The article presents the derivation of simple nonlinear constraints that can be imposed to prevent over-saturation when undertaking Fourier spectral inversions.

Impact of rupture-plane uncertainty on earthquake hazard: observations from the 30 october 2020 Samos earthquake

We assess the significance of rupture-plane uncertainty in the estimated ground-motion intensity measures (IMs) by using the centroid moment-tensor and fault-plane solutions as well as the ground-motion recordings of the 30 October 2020 Samos Earthquake. We sampled ground-motion fields using stochastically generated rupture planes by considering the uncertainties imposed from alternative fault-plane solutions to reach our objective. Our observations indicate that the compromise between rupture-plane uncertainty and variability in the predicted ground-motion IMs depends on the modeling complexity of the ground-motion predictive model (GMPM). It also depends on the spatial location of the site relative to the ruptured fault. This conclusive remark is important for modelers who perform regional or site-specific seismic hazard and risk analyses. The presented case studies are also useful for GMPM developers because the ground-motion models contain predictor parameters, the most ubiquitous one is source-to-site distance, that are affected from rupture-plane geometry. Depending on the level of model complexity, the number of predictor parameters affected from rupture-plane geometry can increase and therefore the estimated ground-motion IMs can become more prone to rupture-plane uncertainty. Confined to our case-specific observations, we intend to make some suggestions to hazard, risk, and GMPM modelers for the consideration of rupture-plane uncertainty at the end of the paper.

Foundation Design and Construction Challenges with Marsh Deposits in a High Seismic Risk Zone

Driven piles are ideal for supporting structures over very soft ground, especially in high seismic risk zones. Challenges include achieving sufficient vertical and lateral load capacities within the constraints of pile spacing and geologic conditions. Through a unique case study, the authors will describe the process of site exploration, foundation selection, pile design, and installation of over 3,000 concrete piles in a small 4.5-acre (1.8 hectare) site (average of one pile per 65 square feet). A state-of-the-art, $180 million plant for biosolids processing, biogas management and energy recovery was sited in marshland next to an existing sewage treatment plant. The new construction included a 70-foot (21 m) tall building and three closely spaced, 90-foot (27 m) high, 65-foot (20 m) diameter, egg-shaped steel digester tanks. The site, classified as class “F”, was underlain by up to 45 feet (14 m) of highly compressible peat and organic clays, below which was a dense sand and gravel layer. The groundwater was very shallow and site-specific seismic hazard analyses were required. Particularly challenging was achieving the needed lateral resistance to seismic loads in the very weak clay and peat deposits. The project was instructive of the importance of adequate characterization of geologic conditions even in small sites; the necessary iterative collaboration process between geotechnical and structural engineers; and the value of a well-designed indicator pile program. The test pile program allowed for refining (shortening) the design pile lengths for considerable cost savings and reduced installation time. Of interest to the reader will be the surprising depth to refusal for some areas of the site, despite the test pile program.

Near-surface shear wave velocity estimation and V s 30 mapping for Dhaka City, Bangladesh

Dhaka, the capital city of Bangladesh, is one of the seismically vulnerable cities in the world due to its location close to the convergent boundary between the Eurasian and Indian Plates, unplanned urbanization, non-engineered construction practice, high population density, and weak emergency response system. The city is developed on an elevated Pleistocene terrace with surrounding Holocene floodplains. The terrace consists of the Pleistocene clayey soils, and the floodplains are composed of alluvial sandy and clayey soils. The average shear wave velocity of the near-surface soils up to a depth of 30 m (V s 30 ) is required for Dhaka City to estimate the amplification factors of seismic waves for site-specific seismic hazard analysis. Therefore, the V s 30 has been estimated in the city using downhole seismic (DS), multichannel analysis of surface waves (MASW), and small-scale microtremor measurement (SSMM) methods, and empirical correlation between the shear wave velocity (Vs) and standard penetration test blow count (SPT-N). The V s 30 has also been predicted using the relationship between the V s 30 and Holocene soil thickness. The V s 30 results of the DS, MASW, SSMM, and SPT-N vary from 127 to 320 m/s. The V s 30 values that are predicted based on the Holocene soil thickness vary from 145 to 260 m/s. Then, a V s 30 map has been prepared for Dhaka City using the V s 30 values that are predicted from the Holocene soil thickness at a grid of 30 m. The near-surface soils of the city are classified based on the V s 30 as site classes D (stiff soils) and E (soft soils) according to the NEHRP (National Earthquake Hazards Reduction Program, the USA) and as subsoil classes C and D according to the Eurocode 8.

A continuous map of near-surface S-wave attenuation in New Zealand

Quantifying the near-surface attenuation of seismic waves at a given location can be important for seismic hazard analysis of high-frequency ground motion. This study calculates the site attenuation parameter, κ0, at 41 seismograph locations in New Zealand. Combined with results of a previous study, a total of 46 κ0 values are available across New Zealand. The results compare well with previous t* studies, revealing high attenuation in the volcanic arc and forearc ranges, and low attenuation in the South Island. However, for site-specific seismic hazard analyses, there is a need to calculate κ0 at locations away from a seismograph location. For these situations, it is common to infer κ0 from weak correlations with the shear wave velocity in the top 30 m, VS30, or to adopt an indicative regional value. This study attempts to improve on this practice. Geostatistical models of the station-specific κ0 data are developed, and continuous maps are derived using ordinary kriging. The obtained κ0 maps can provide a median κ0 and its uncertainty for any location in New Zealand, which may be useful for future site-specific seismic hazard analyses.

Site specific seismic hazard analysis and determination of response spectra of Kolkata for maximum considered earthquake

This paper presents site specific seismic hazard analysis of Kolkata city, former capital of India and present capital of state West Bengal, situated on the world's largest delta island, Bengal basin. For this purpose, peak ground acceleration (PGA) for a maximum considered earthquake (MCE) at bedrock level has been estimated using an artificial neural network (ANN) based attenuation relationship developed on the basis of synthetic ground motion data for the region. Using the PGA corresponding to the MCE, a spectrum compatible acceleration time history at bedrock level has been generated by using a wavelet based computer program, WAVEGEN. This spectrum compatible time history at bedrock level has been converted to the same at surface level using SHAKE2000 for 144 borehole locations in the study region. Using the predicted values of PGA and PGV at the surface, corresponding contours for the region have been drawn. For the MCE, the PGA at bedrock level of Kolkata city has been obtained as 0.184 g, while that at the surface level varies from 0.22 g to 0.37 g. Finally, Kolkata has been subdivided into eight seismic subzones, and for each subzone a response spectrum equation has been derived using polynomial regression analysis. This will be very helpful for structural and geotechnical engineers to design safe and economical earthquake resistant structures.

Site-specific seismic hazard analysis for Calabrian dam site using regionally customized seismic source and ground motion models

Probabilistic seismic hazard analysis (PSHA) are performed for routine applications using source models and ground motion models (GMMs) recommended by a government agency (e.g., US Geological Survey) or an expert panel (e.g., SHARE project). For important projects, site-specific PSHA involves critical analysis of GMMs and sources for the application region. We adopt the latter approach for a dam site in Calabria (southern Italy), a high seismic hazard region. We consider area sources as well as fault sources coupled with background zones, tailoring a model developed in the SHARE project for the subject site. We identify several problems with assigned maximum magnitudes for fault and in-slab subduction sources. We also add two sources not previously considered – the crustal Lakes fault and the Calabrian arc subduction interface. We select GMMs that are better constrained in the hazard-controlling range of magnitudes and distances than those typically used in prior Italian applications. Short-period median spectral accelerations at the 2475-year return period exceed those from prior SHARE studies by about 10–15%, and those from the Italian building code by amounts ranging from 15% to 96%. Despite the site being located in a region with finite faults capable of generating large events, the 2475-year hazard is dominated by source zones that allow for earthquakes directly beneath the site.

Development of Seismic Demand for Chang-Bin Offshore Wind Farm in Taiwan Strait

Taiwan is located on the Pacific seismic belt, and the soil conditions of Taiwan’s offshore wind farms are softer than those in Europe. To ensure safety and stability of the offshore wind turbine supporting structures, it is important to assess the offshore wind farms seismic forces reasonably. In this paper, the relevant seismic and geological data are obtained for Chang-Bin offshore wind farm in Taiwan Strait, the probabilistic seismic hazard analysis (PSHA) is carried out, and the first uniform hazard response spectrum for Chang-Bin offshore wind farm is achieved. Compared with existing design response spectrum in the local regulation, this site-specific seismic hazard analysis has influence on the seismic force considered in the design of supporting structures and therefore affects the cost of the supporting structures. The results show that a site-specific seismic hazard analysis is required for high seismic area. The paper highlights the importance of seismic hazard analysis to assess the offshore wind farms seismic forces. The follow-up recommendations and research directions are given for Taiwan’s offshore wind turbine supporting structures under seismic force considerations.

Disaggregating UCERF3 for Site-Specific Applications

We present methods to simplify the use of the Uniform California Earthquake Rupture Forecast 3 (UCERF3) in site-specific seismic hazard analyses. UCERF3 defines the “state-of-practice” for hazard assessments in California and underlies the current USGS National Seismic Hazard Map (NSHM). UCERF3 contains many more ruptures than previous models and fault-to-fault connectivity in the model makes ruptures less readily incorporated into conventional hazard analyses. We demonstrate a decomposition of the UCERF3 model using site-specific subsection magnitude-frequency distributions (S3MFDs) that reduces computational demands while still including every rupture. The decomposed hazard can be used to evaluate site-specific fault source epistemic uncertainties. We illustrate using spectral acceleration at 1 Hz at three trial sites, one near a single dominant fault, one near Long Beach, where many low slip-rate faults contribute, and one in San Jose, where fault hazard is concentrated in a few high slip-rate faults.

Safety Aspects of Sustainable Storage Dams and Earthquake Safety of Existing Dams

Abstract The basic element in any sustainable dam project is safety, which includes the following safety elements: ① structural safety, ② dam safety monitoring, ③ operational safety and maintenance, and ④ emergency planning. Long-term safety primarily includes the analysis of all hazards affecting the project; that is, hazards from the natural environment, hazards from the man-made environment, and project-specific and site-specific hazards. The special features of the seismic safety of dams are discussed. Large dams were the first structures to be systematically designed against earthquakes, starting in the 1930s. However, the seismic safety of older dams is unknown, as most were designed using seismic design criteria and methods of dynamic analysis that are considered obsolete today. Therefore, we need to reevaluate the seismic safety of existing dams based on current state-of-the-art practices and rehabilitate deficient dams. For large dams, a site-specific seismic hazard analysis is usually recommended. Today, large dams and the safety-relevant elements used for controlling the reservoir after a strong earthquake must be able to withstand the ground motions of a safety evaluation earthquake. The ground motion parameters can be determined either by a probabilistic or a deterministic seismic hazard analysis. During strong earthquakes, inelastic deformations may occur in a dam; therefore, the seismic analysis has to be carried out in the time domain. Furthermore, earthquakes create multiple seismic hazards for dams such as ground shaking, fault movements, mass movements, and others. The ground motions needed by the dam engineer are not real earthquake ground motions but models of the ground motion, which allow the safe design of dams. It must also be kept in mind that dam safety evaluations must be carried out several times during the long life of large storage dams. These features are discussed in this paper.

Deterministic Seismic Hazard Analysis for the State of Haryana, India

The Indian state of Haryana is in a phase of rapid industrial development. In order to help engineers and town planners in designing earthquake resistant structures, it is necessary to carry out site specific seismic hazard analysis and plan mitigation measures. It is apprehended that Indian Code generalises the design peak ground acceleration values which may underestimate the seismic loading in high seismicity regions. Therefore, it is necessary to develop regional seismic hazard scenario in line with the local seismotectonic setting which is consistent with other seismic codes worldwide. In all, 12 seismogenic sources have been identified in the seismic study area. The maximum magnitude has been assigned to each seismogenic source considering regional rupture character. Ground motion prediction equation developed for Indo-Gangetic region by National Disaster Management Authority of India has been used. The peak ground acceleration along with response spectrum for A-type sites for the state have been estimated using state of the art in deterministic seismic hazard analysis methodology. These determined strong motion parameters have been compared with the values given in Indian Standard for criteria for earthquake resistant design of structures to validate them for further practical use. The prepared spectra can be further used to quantify seismic loading for designing earthquake resistant structures in Haryana.

Benefits of site-specific hazard analyses for seismic design in New Zealand

This paper summarizes the role site-specific seismic hazard analyses can play in seismic design and assessment in New Zealand. The additional insights and potential improvements in the seismic design and assessment process through a better understanding of the ground motion hazard are examined through a comparative examination with prescriptive design guidelines. Benefits include the utilization of state-of-the-art knowledge, improved representation of site response, reduced conservatism, and the determination of dominant seismic source properties, among others. The paper concludes with a discussion of these relative benefits so that the efficacy of site-specific hazard analysis for a particular project can be better judged by the engineer.

Displacement-based seismic design of a shallow strip footing positioned near the edge of a rock slope

This paper presents a displacement-based dynamic design of shallow strip footings located close to the edge of homogeneous and isotropic rock slopes. The analysis is conducted using the “generalized tangential” technique in which the Hoek–Brown strength is replaced by an “optimal” tangential Mohr–Coulomb domain within the framework of the kinematic approach of limit analysis theory. In order to better understand the influence of these factors including geometrical features, rock strength parameters and seismic loading, a parametric study is carried out. An expression is derived and used to obtain a least upper bound solution for the bearing capacity of a footing on a rock slope considering a kinematically admissible log-spiral failure mechanism. In addition, a similar expression of the horizontal yield seismic coefficient is derived for a given load acting on the foundation.The assessment of earthquake-induced permanent displacement is performed by a simplified procedure. This requires the knowledge of a ground motion parameter that can be evaluated by site-specific seismic hazard analyses or ground motion prediction equations and that considers the actual sliding surface. The calculated displacement should not be greater than a selected limiting tolerable displacement for the specific case. An example is presented illustrating the application of the design procedure for the bridge foundations.

Site-Specific Seismic Ground Response Study for Nuclear Power Plants and Ports in Mumbai

AbstractThe importance of characterizing site-specific free-field surface motion of facilities of national and worldwide economic influence [like ports and nuclear power plants (NPPs)] is well-realized, especially in Mumbai, the most important commercial city in India, with 40% of its land reclaimed from the Arabian Sea. In the research reported in this paper, site-specific seismic hazard and one-dimensional (1D) equivalent linear ground response analysis (GRA) of important sites in Mumbai [Jawaharlal Nehru Port (JNPT), Mumbai Port, Bhabha Atomic Research Center (BARC), and Tarapur Atomic Power Station (TAPS)] are attempted. The seismicity of the research region is modeled through delineation of 31 fault sources with an earthquake database of the past 418 years (years 1594–2012). The epistemic uncertainty in hazard estimation is accounted by employing seven different ground motion prediction equations developed for worldwide shallow crustal intraplate environments. The probabilistic seismic hazard analysi...

Probability-based PGA estimations using the double-lognormal distribution: Including site-specific seismic hazard analysis for four sites in Taiwan

This study develops a probabilistic approach for examining site-specific seismic hazards using data from 438 Mw≥5.5 earthquakes and attenuation relationships local to the region around Taiwan. These are combined to generate semi-observed peak ground accelerations, in a form which can be modeled by a double-lognormal distribution. This model, which satisfies statistical goodness-of-fit, provides the relationship between the exceedance probability and a given ground motion level. The study includes site-specific seismic hazard analysis for four nuclear power plant sites in Taiwan. The results show that the seismic hazards at the four sites are not the same. While no seismic hazard analysis is without challenge, a troublesome trend appears that many applications of decision making are being influenced by the complexity of the calculation, instead of how well the fundamentals of the analysis are understood and can be verified. The study provides an analysis which is not overly complicated, is in good agreement with an empirical control, and offers transparency, traceability, and verifiability.

Site specific probabilistic seismic hazard analysis at Dubai Creek on the west coast of UAE

A probabilistic seismic hazard analysis (PSHA) was conducted to establish the hazard spectra for a site located at Dubai Creek on the west coast of the United Arab Emirates (UAE). The PSHA considered all the seismogenic sources that affect the site, including plate boundaries such as the Makran subduction zone, the Zagros fold-thrust region and the transition fault system between them; and local crustal faults in UAE. PSHA indicated that local faults dominate the hazard. The peak ground acceleration (PGA) for the 475-year return period spectrum is 0.17 g and 0.33 g for the 2,475-year return period spectrum. The hazard spectra are then employed to establish rock ground motions using the spectral matching technique.