Uniform Hazard Spectra Research Articles

PSHA Study Using EZ-Frisk Software Case Study Baychebaq Dam Site

Awareness of seismicity, is the earliest requirement in seismic design of Dam constructions. This article is devoted to study on Seismotectonic and seismicity and also seismic risk analysis of the Baychebaq reservoir dam. These studies involve detecting seismic sources and assessing seismicity parameters. According to the studies, Peak Ground Acceleration (PGA) is 0.1 gal. This PHA may be related to there activation process of Takhte Soleiman which can produce an event around 6.8 Ms in the distance of 20 km from Baychebaq dam. According to the changes of Uniform Hazard Spectrum (UHS), Spectral acceleration parameter increases from period of 0 (0.03 gal) to a period of 0.175 (0.1 gal) and then reduced slightly. Based on the results, the controlling earthquake has a magnitude of 6.1 and 6.5 Mw at a period of 0 for return periods of 475 and 2475 years.

The 2015 Mw 7.8 Gorkha Earthquake in Nepal and its aftershocks: analysis of strong ground motion

Various aspects of the 2015 Gorkha Earthquake and its aftershocks are presented, and different hypotheses about the nature of long period pulses observed in ground motion record in Kathmandu Valley are critically discussed and reviewed. The frequency-size distribution of aftershocks, as well as the temporal distribution within one year of the mainshock is discussed. Some interesting features of the strong ground motion of the mainshock recorded at different places in Kathmandu Valley are discussed. Although the root-mean-square horizontal ground accelerations recorded at rock and soft sites were similar, the peak accelerations varied significantly. Elastic response spectra of the mainshock near the centre of the Valley (KATNP station operated by USGS) contained two very distinct peaks: a narrower and larger peak at ~0.4 s and a smaller, but very wide, peak at ~5 s. The peak of the spectra was significantly larger than what is commonly adopted in design codes. The latest published uniform hazard spectra for a 475-year return period were found to significantly over-estimate seismic demands on stiff structures (fundamental period less than ~0.5 s,) and underestimate the demands on more flexible structures. The resonant site frequencies computed from microseismic recordings, as reported in published literature, are found to be much larger than what was observed in the spectral ratio of ground motion recorded in soft sediments and exposed bedrock in Kathmandu. Response spectra of aftershock motions recorded at two stations lacked the peculiar peak at 5 s observed in the spectra of mainshock motion. The relatively high Fourier spectral amplitudes (at frequencies near 0.2–0.3 Hz) of ground acceleration recorded at the rock site indicate that the long-period pulse prominent at the soft site was not entirely due to site effects. The polarization pattern of the 5 s pulse at the rock site and at soft site KATNP were found to be very different. Comparison of polarization patterns of mainshock ground motion at rock and soft sites indicate that the 5 s pulse observed at some locations in Kathmandu Valley is a combination of shear waves (the amplitudes of which were amplified by the basin layers) and Love waves.

Safety assessment of the seismic resistance of nuclear power plant technology

This paper gives the methodology to get the floor response spectra of the buildings on the base of the results of the probabilistic assessment. On the base of the geophysical and seismological monitoring of locality the peak ground acceleration and the uniform hazard spectrum of the acceleration was defined for the return period 10 4 years. The methodology of the seismic resistance of the cable support structures is described.

Comparison of Response of Building Structures to Blast Loading and Seismic Excitations

Blast loading and earthquake excitations can be regarded as the most destructive events a building structure can experience during its life. Response of the structures to these two types of dynamic loading can be of comparable magnitude. Therefore, in this study, response of a benchmark 10-story building to moderate blast loading is compared to that produced by several different synthetic ground motions whose spectra are compatible with the uniform hazard spectra for selected sites in the eastern and western regions of Canada. The results show that the lateral story drifts produced by blast loading are significantly larger than the corresponding seismic drifts. The study concludes that consideration of the global response of a building to blast loads is important, and response parameters, such as the lateral drifts and floor responses, should be paid attention in the design and response assessment procedures for blast loading.

Seismic Hazard for Cuba: A New Approach

Abstract A new seismic hazard study for Cuba is presented in terms of maps and uniform hazard spectra (UHS). An earthquake catalog from 1502 to 2012 was prepared for the region 16°–24° N and 67°–86° W, and was homogenized to M w and cleaned for aftershocks and foreshocks. A 16‐arm logic‐tree computation corresponding to four source branches and four ground‐motion prediction equations (GMPEs) was conducted (using only published GMPE relations due to a lack of local strong‐motion data). For each source model, the seismicity parameters ( β , λ , and M max ) were developed. The results were obtained and are presented in terms of maps and UHS graphs for a 475‐year return period, but results for other return periods are easily obtained. The influence of different branch weighting in the logic tree was investigated with respect to the final results. Peak ground acceleration values for Cuba were found to vary from less than 75 to 230 cm/s 2 .

Uniform hazard floor acceleration spectra for linear structures

SummaryThis paper presents a practical method to compute uniform hazard floor acceleration spectra for linear oscillators attached to a linear structure. The method builds on a probabilistic seismic demand model that relates the acceleration response of the oscillator with that of the generic mode of vibration of the supporting structure. Interaction between oscillator and structure is ignored. Independency of the model on the specific characteristics of seismic hazard at the site is shown. By using the method floor spectra are determined through a closed‐form expression, given the mean annual frequency of interest, the damping ratio of the oscillators, the modal properties of the structure, and three uniform hazard spectra representing seismic hazard at the site. Copyright © 2016 John Wiley & Sons, Ltd.

Evaluation of Ground Motion Selection Techniques for Seismic Rigid Sliding Block Analyses

AbstractSeismic sliding block displacements provide a useful index for the seismic performance of a slope and are computed for a suite of acceleration-time histories selected to fit a target ground motion. This paper explores the effect of different ground motion selection techniques on computed rigid sliding block displacements. In particular, capturing the characteristics of ground shaking through the consideration of the additional ground motion parameters that influence sliding displacement [i.e., peak ground velocity (PGV) and Arias intensity (Ia)] is investigated. Rigid sliding block displacements are computed for ground motion suites scaled to a target peak ground acceleration (PGA) and selected using different approaches. Two suites are selected to fit target acceleration response spectra [i.e., uniform hazard spectra (UHS) and conditional mean spectra (CMS)], and three suites are selected to fit conditional probability distributions for PGV and Ia through the generalized conditional intensity mea...

Updated Probabilistic Seismic‐Hazard Values for Egypt

Seismic hazard in terms of mean peak ground acceleration (PGA) and spectral acceleration (SA) values has been computed for Egypt using both historical and instrumental earthquake data. For this purpose, an updated earthquake catalog, spanning the time period from 2200 B.C. to 2013, has been compiled for Egypt as well as its surrounding regions and is prepared to be used in a new probabilistic seismic‐hazard assessment of Egypt. The earthquakes sizes were unified in terms of the moment magnitude scale. A new seismic source model for the seismic activity in and around Egypt, consisting of a total of 88 seismic zones (for shallow‐ and intermediate‐depth seismicity), was considered in this new assessment. The seismicity parameters have been specifically computed for 35 seismic sources covering the Egyptian territory and the Eastern Mediterranean region. A logic‐tree design was set up to consider the epistemic uncertainty in the Gutenberg–Richter b ‐value, maximum possible magnitude ( M max), and the selected ground‐motion prediction equations. Seismic‐hazard computations for rock‐site conditions with 10% and 5% probability of exceedance in 50 years were carried out. In addition, uniform hazard spectra for twelve, among the most important and populated cities in Egypt, are computed and compared with the most recent Egyptian building code values. It is interesting to highlight that the maximum hazard values are observed at the Gulf of Aqaba region, specifically around the epicentral location of the biggest Egyptian recorded earthquake of 22 November 1995 ( M w 7.2) Aqaba earthquake. The obtained seismic‐hazard values for Nuweiba city (located in this region) for mean PGA and SA (0.1 s) are 0.29 g and 0.74 g , respectively, for a return period of 475 years.

Probabilistic seismic safety assessment of a CANDU 6 nuclear power plant including ambient vibration tests: Case study

Following the 2011 Fukushima Daiichi nuclear accident in Japan there is a worldwide interest in reducing uncertainties in seismic safety assessment of existing nuclear power plant (NPP). Within the scope of a Canadian refurbishment project of a CANDU 6 (NPP) put in service in 1983, structures and equipment must sustain a new seismic demand characterised by the uniform hazard spectrum (UHS) obtained from a site specific study defined for a return period of 1/10,000years. This UHS exhibits larger spectral ordinates in the high-frequency range than those used in design. To reduce modeling uncertainties as part of a seismic probabilistic safety assessment (PSA), Hydro-Québec developed a procedure using ambient vibrations testing to calibrate a detailed 3D finite element model (FEM) of the containment and reactor building (RB). This calibrated FE model is then used for generating floor response spectra (FRS) based on ground motion time histories compatible with the UHS. Seismic fragility analyses of the reactor building (RB) and structural components are also performed in the context of a case study. Because the RB is founded on a large circular raft, it is possible to consider the effect of the seismic wave incoherency to filter out the high-frequency content, mainly above 10Hz, using the incoherency transfer function (ITF) method. This allows reducing significantly the non-necessary conservatism in resulting FRS, an important issue for an existing NPP. The proposed case study, and related methodology using ambient vibration testing, is particularly useful to engineers involved in seismic re-evaluation of existing NPP.

Exploring Risk-Targeted Hazard Maps for Europe

In Europe, the design of new structures according to modern regulations requires a uniform hazard spectrum for a given return period (e.g., 475 years). The assumption is that the resulting collapse probability is equally uniform for all structures, regardless of their structural properties or location. However, the uncertainty in the collapse capacity and hazard curves at different sites lead to an unequal level of risk. This discrepancy is undesirable given that some inhabitants will live in dwellings with a lower seismic safety than others living in structures designed according to the same regulation. The estimation of risk-targeted hazard maps allows for the definition of a design ground motion leading to a uniform level of risk. Using hundreds of fragility models developed for European buildings and hazard results from the SHARE project, we calculate risk-targeted hazard maps for a pre-established annual collapse probability.

Seismic hazard assessment in continental Ecuador

A seismic hazard assessment study of continental Ecuador is presented in this paper. The study begins with a revision of the available information on seismic events and the elaboration of a seismic catalog homogenized to magnitude Mw. Different seismic source definitions are revised and a new area-source model, based on geological and seismic data, is proposed. The available ground motion prediction equations for crustal and subduction sources are analyzed and selected for the tectonic environments observed in Ecuador. A probabilistic seismic hazard assessment approach is carried out to evaluate the exceedance probability of several levels of peak ground acceleration PGA and spectral accelerations SA (T) for periods (T) of 0.1, 0.2, 0.5, 1 and 2s. The resulting hazard maps for continental Ecuador are presented, together with the uniform hazard spectra of four province capital cities. Hazard disaggregation is carried out for target motions defined by the PGA values and SA (1s) expected for return periods of 475 and 2475 years, providing estimates for short-period and long-period controlling earthquakes.

Probabilistic earthquake hazard analysis for Cairo, Egypt

Cairo is the capital of Egypt and the largest city in the Arab world and Africa, and the sixteenth largest metropolitan area in the world. It was founded in the tenth century (969 ad) and is 1046 years old. It has long been a center of the region’s political and cultural life. Therefore, the earthquake risk assessment for Cairo has a great importance. The present work aims to analysis the earthquake hazard of Cairo as a key input’s element for the risk assessment. The regional seismotectonics setting shows that Cairo could be affected by both far- and near-field seismic sources. The seismic hazard of Cairo has been estimated using the probabilistic seismic hazard approach. The logic tree frame work was used during the calculations. Epistemic uncertainties were considered into account by using alternative seismotectonics models and alternative ground motion prediction equations. Seismic hazard values have been estimated within a grid of 0.1° × 0.1 ° spacing for all of Cairo’s districts at different spectral periods and four return periods (224, 615, 1230, and 4745 years). Moreover, the uniform hazard spectra have been calculated at the same return periods. The pattern of the contour maps show that the highest values of the peak ground acceleration is concentrated in the eastern zone’s districts (e.g., El Nozha) and the lowest values at the northern and western zone’s districts (e.g., El Sharabiya and El Khalifa).

Seismic hazard estimation: directly using observations versus applying seismic hazard model

Seismic hazard evaluation for a site can be carried out based on direct observations such as ground motion records at the site or based on an adopted seismic hazard model, including the distribution of earthquake intensity, the spatio-temporal occurrence model of earthquakes in a region, and the ground motion prediction equations. The former is adequate if sufficient records at the site are available, while the latter is capable to incorporate information from similar tectonic regions. This study compares the seismic hazard estimated using these two approaches for a recording site in Mexico City. The comparison is carried out in terms of uniform hazard spectra by considering interplate earthquakes alone, inslab earthquakes alone, and both interplate and inslab earthquakes. Up to date ground motion records obtained at the site are employed for the analysis. The results showed quantitatively the differences between the uniform hazard spectrum (UHS) obtained by the two approaches and the differences between the estimated UHS and the design spectrum, which is important for seismic risk assessment and design code making. The results are also used to identify the differences between the standard deviation of the residuals for GMPEs developed using records from a single station and that obtained considering a broad network of stations.

Evaluation of Probabilistic Site‐Specific Seismic‐Hazard Methods and Associated Uncertainties, with Applications in the Po Plain, Northern Italy

Site‐specific ground‐motion hazard, as assessed by a probabilistic seismic‐hazard analysis one‐step approach that handles a single‐site sigma and its uncertainties and uses a simple logic tree, is compared with a two‐step approach that includes bedrock motion evaluation and wave propagation through a local soil profile with consideration of the main epistemic uncertainties. The one‐step analysis relies on accelerometer data from the Po Plain, a sedimentary basin in northern Italy where an earthquake sequence with two M w∼6.0 events was extensively recorded in 2012. Uniform hazard spectra (UHS) on soil and exposed bedrock are evaluated at three deep‐soil accelerometer sites (MRN, NVL, and T0821), using residual measures available from other studies, by which uncertainties in site terms ( δS 2 S ) and single‐site sigma ( σ ss , s ) are estimated. Despite similarity in geologic conditions, at least one out of three sites in the one‐step analysis displays substantial differences in mean level (T0821) or in the (84–16) percentile spread (NVL), depending on differences in site terms and single‐site sigma, possibly caused by source‐to‐site propagation effects. The two‐step approach was applied to the remaining site (MRN) using carefully selected and broadband‐matched acceleration signals and linear, equivalent‐linear, and nonlinear approaches as excitation in propagation analyses. We found that assumptions on soil degradation curves dominate the variability of results. The linear approach provided the best results, based on (1) the similarity of the one‐step nonergodic UHS with the two‐step result based on the linear approach; (2) the comparison with observed records at MRN during the 2012 sequence mainshocks, showing peak ground acceleration and short‐period spectral levels well beyond those predicted by different nonlinear assumptions; and (3) similar evidence from a set of 21 stations at deep soil sites of the Japanese KiK‐net.

Numerical Solution of the Total Probability Theorem in a Three Diensional Earthquake Source Domain for Developing Seismic Hazard Map and Hazard Spectrum

Probabilistic seismic hazard analysis is a method of assessing seismic threat on a region in the earth surface. Total probability theorem was utilized here has solved on earthquake source domain and employed it in seismic hazard analysis. Solution of the theorem is performed in a computer program and has been used to develop the Hazard Map and the Uniform Hazard Spectrum (UHS). The map is peak ground acceleration (PGA) of Sumatra Indonesia with hazard level 10% probability of exceedance in 50 years and the UHS is from a site in Surabaya Indonesia with hazard level 10% probability of exceedance in 50 years. The two result of the program are verified by the two previous study results. The result of the program is very similar to two other studies.

Hazard-consistent ground motions generated with a stochastic fault-rupture model

Conventional seismic probabilistic risk assessments (PRAs) of nuclear power plants consist of probabilistic seismic hazard and fragility curves. Even when earthquake ground-motion time histories are required, they are generated to fit specified response spectra, such as uniform hazard spectra at a specified exceedance probability. These ground motions, however, are not directly linked with seismic-source characteristics.In this context, the authors propose a method based on Monte Carlo simulations to generate a set of input ground-motion time histories to develop an advanced PRA scheme that can explain exceedance probability and the sequence of safety-functional loss in a nuclear power plant. These generated ground motions are consistent with seismic hazard at a reference site, and their seismic-source characteristics can be identified in detail.Ground-motion generation is conducted for a reference site, Oarai in Japan, the location of a hypothetical nuclear power plant. A total of 200 ground motions are generated, ranging from 700 to 1100cm/s2 peak acceleration, which corresponds to a 10−4 to 10−5 annual exceedance frequency. In the ground-motion generation, seismic sources are selected according to their hazard contribution at the site, and Monte Carlo simulations with stochastic parameters for the seismic-source characteristics are then conducted until ground motions with the target peak acceleration are obtained. These ground motions are selected so that they are consistent with the hazard. Approximately 110,000 simulations were required to generate 200 ground motions with these peak accelerations.Deviations of peak ground motion acceleration generated for 1000–1100cm/s2 range from 1.5 to 3.0, where the deviation is evaluated with peak ground motion accelerations generated from the same seismic source. Deviations of 1.0 to 3.0 for stress drops, one of the stochastic parameters of seismic-source characteristics, are required to obtain these acceleration deviations. A similar tendency can be found for some other seismic-source characteristics, meaning that ground motions obtained in this study cannot be generated by simulations of deterministic fault-rupture models with averaged seismic-source characteristics. Generated ground motions incorporate differences between each seismic-source characteristic, and they are effectively available for PRAs of structures.

Probabilistic seismic hazard analyses and obtaining uniform hazard spectra of Tabriz, Iran

In this study Probabilistic Seismic Hazard Analysis is carried out for Tabriz region and results are presented by spectral isoacceleration maps and Uniform Hazard Spectra (UHS) for two levels of hazard. To achieve this goal, at first a catalog of all the historical and instrumentally recorded earthquakes covering timeline from 858 up to 2010, in a radius of 200 km around Tabriz city, has been gathered and processed for elimination of the aftershocks and foreshocks from main occurrences list and then seismicity parameters have been obtained by Kijko (2000) method. The seismic sources of the considered region have been studied and modeled. Probabilistic seismic hazard analysis is implemented for 22*17 grid points over Tabriz region and it's vicinity using SEISRISK III (1987) software by employing four attenuation relationships and two relationships between earthquake maximum magnitude and fault rupture length. The Results are combined using logic tree method and shown by spectral acceleration maps and Uniform Hazard Spectra with 2 and 10% probability of exceedence (PE) in 50 years for two types of soil.

Seismic Source Characterization for Greater Phoenix Area Earthquake Hazard

We have developed a model for active seismogenic faults for the greater Phoenix area. The Quaternary geologic record was used to delineate the local seismic sources, assess potential earthquake size, and estimate earthquake recurrence to support an integrated regional probabilistic evaluation of the seismic hazard. The probabilistic seismic hazard analysis is summarized as uniform hazard spectra and contour maps of peak ground acceleration and spectral acceleration at one second for weak rock site conditions at two percent probability of exceedance in 50 years. As building codes typically allow some level of reduction in design spectral accelerations from values obtained from the National Seismic Hazard Maps, we compared our results to values obtained from the National Seismic Hazard Maps. No reduction in building code seismic design requirements is justified in the areas addressed herein on the basis of our site specific analysis.

Microzonation of Banja Luka for performance-based earthquake-resistant design

New microzonation maps for the city of Banja Luka in the Republic of Srpska in Bosnia and Herzegovina are presented based on the uniform-hazard-spectrum (UHS) methodology. The results are compared with the previous generation of microzonation maps published in the early 1970s, which were determined for the largest expected levels of shaking and for the spatial variations based on the soil site properties and the observed damage during the 1969 earthquake. The old and new methods are compared with emphasis on their role in the long-term criteria for regional earthquake-resistant design guidelines and the associated consequences.

Multi-seismotectonic models, present-day seismicity and seismic hazard assessment for Suez Canal and its surrounding area, Egypt

Suez Canal is the most important navigational water stream in the world. It separates the eastern part of the Nile Delta from northern Sinai and controls 40 % of ship movement in the world. There is also the new Suez Canal project, which is one of the most important new projects in Egypt. The purpose of this study is to assess seismic hazards at and around Suez Canal. The technique used in hazard estimation is the probabilistic seismic hazard approach (PSHA). Alternative seismotectonic source models were included in the hazard assessment to account for the epistemic uncertainty. Contour maps were produced for ground motion on rock for spectral periods 0.2, 0.5, 1 and 2 s, as well as Peak Ground Acceleration (PGA) for return periods of 75, 475, 975 and 2475 years (equivalent to 20, 10, 5 and 2 % probability of exceeding ground motion in 50 years, respectively). The Uniform Hazard Spectra (UHS) was also estimated for some cities inside the study area on rock for return periods of 75, 475, 975 and 2475 years. The results show that the highest hazard level is at the southeastern part of the study area with maximum expected spectral acceleration of 280.3 cm/s2 (gal) at a spectral period of 0.2 s for a return period of 475 years. The results of this study can be used for seismic microzonation, seismic risk mitigation and for earthquake engineering purposes.