Damped Spectral Acceleration Research Articles

A probabilistic seismic hazard assessment for the Turkish territory: part II—fault source and background seismicity model

Over the years, several local and regional seismic hazard studies have been conducted for the estimation of the seismic hazard in Turkey using different statistical processing tools for instrumental and historical earthquake data and modeling the geologic and tectonic characteristics of the region. Recently developed techniques, increased knowledge and improved databases brought the necessity to review the national active fault database and the compiled earthquake catalogue for the development of a national earthquake hazard map. A national earthquake strategy and action plan were conceived and accordingly with the collaboration of the several institutions and expert researchers, the Revision of Turkish Seismic Hazard Map Project (UDAP-C-13-06) was initiated, and finalized at the end of 2014. The scope of the project was confined to the revision of current national seismic hazard map, using the state of the art technologies and knowledge of the active fault, earthquake database, and ground motion prediction equations. The following two seismic source zonation models are developed for the probabilistic earthquake hazard analysis: (1) Area source model, (2) Fault and spatial smoothing seismic source model (FSBCK). In this study, we focus on the development and the characterization of the Fault Source model, the background spatially smoothed seismicity model and intrinsic uncertainty on the earthquake occurrence-rates-estimation. Finally, PSHA results obtained from the fault and spatial smoothed seismic source model are presented for 43, 72, 475 and 2475 years return periods (corresponding to 69, 50, 10, and 2% probability of exceedance in 50 years) for PGA and 5% damped spectral accelerations at 0.2 and 1.0 s.

Regional Low‐Magnitude GMPE to Estimate Spectral Accelerations for Earthquake Early Warning Applications in Southern Italy

ABSTRACT A low‐magnitude regional ground‐motion prediction equation (GMPE) for peak ground acceleration and 5% damped spectral acceleration at 11 oscillator periods ranging from 0.1 to 3 s was developed for applications of the earthquake early warning system operating in southern Italy. The accelerometric dataset was built out of 2270 waveforms from 319 earthquakes with local magnitude ranging from 1.5 to 4.2, recorded from 60 stations located on soil type B, according to the Italian Building Code and Eurocode 8, with hypocentral distances ranging from 3 to about 100 km. The GMPE coefficients were computed through a nonlinear weighted damped least‐squares algorithm, attributing a higher weight to ground‐motion data recorded at stations for which soil category was established using geotechnical and geophysical measurements. Predictions of the proposed GMPE were tested against independent ground‐motion data recorded in southern Italy and compared with other regional and global GMPEs through the log‐likelihood method. The comparison shows that the proposed GMPE performs better than any other GMPE considered in this study.

A probabilistic seismic hazard assessment for the Turkish territory—part I: the area source model

The seismic zoning map of Turkey that is used in connection with the national seismic design code (versions issued both in 1997 and 2007) is based on a probabilistic seismic hazard assessment study conducted more than 20 years ago (Gulkan et al. in En son verilere gore hazirlanan Turkiye deprem bolgeleri haritasi, Report No: METU/EERC 93-1, 1993). In line with the efforts for the update of the seismic design code, the need aroused for an updated seismic hazard map, incorporating recent data and state-of-the-art methodologies and providing ground motion parameters required for the construction of the design spectra stipulated by the new Turkish Earthquake Design Code. Supported by AFAD (Disaster and Emergency Management Authority of Turkey), a project has been conducted for the country scale assessment of the seismic hazard by probabilistic methods. The present paper describes the probabilistic seismic hazard assessment study conducted in connection with this project, incorporating in an area source model, all recently compiled data on seismicity and active faulting, and using a set of recently developed ground motion prediction equations, for both active shallow crustal and subduction regimes, evaluated as adequately representing the ground motion characteristics in the region. The area sources delineated in the model are fully parameterized in terms of maximum magnitude, depth distribution, predominant strike and dip angles and mechanism of possible ruptures. Resulting ground motion distributions are quantified and presented for PGA and 5 % damped spectral accelerations at T = 0.2 and 1.0 s, associated with return periods of 475 and 2475 years. The full set of seismic hazard curves was also made available for the hazard computation sites. The second part of the study, which is based on a fault source and smoothed seismicity model is covered in Demircioglu et al. in Bull Earthq Eng, (2016).

Ground‐Motion Prediction Equations for Region‐Specific Probabilistic Seismic‐Hazard Analysis

Abstract The goal of this article is to investigate the possibility of reducing the uncertainty of the ground motion predicted for a specific target area (Po Plain and northeastern Italy), by calibrating a set of ad hoc ground‐motion prediction equations (GMPEs). The derived GMPEs account for peculiarities that are not generally considered by standard predictive models, such as (1) an attenuation rate dependent on distance ranges and geological domains; (2) enhancement of short‐period spectral ordinates, due to the reflection of S waves at the Moho discontinuity; and (3) generation of surface waves inside an alluvial basin. The analyzed strong‐motion dataset was compiled by selecting events in the 4.0–6.4 magnitude range, records with distances shorter than 200 km, and focal depths shallower than 30 km; the major contribution comes from the recent 2012 Emilia sequence (first mainshock, 20 May 2012 M w 6.1; second mainshock, 29 May 2015 M w 6.0). The GMPEs are derived for the geometrical mean of horizontal components of peak ground acceleration, peak ground velocity, and 5% damped spectral acceleration in the 0.04–4 s period range. The derived region‐specific models led to a reduction of the hazard levels for several intensity measures, with respect to the values obtained by considering the reference Italian attenuation model (Bindi et al. , 2011), as exemplified by the comparison of the hazard curves computed for two specific sites. Online Material: Database of Northern Italy (DBNI) flat-file and tables of northern Italy ground‐motion prediction equations (GMPEs) (NI15) regression coefficients and variability components for use with Joyner–Boore and hypocentral distances.

Prediction of ground motion parameters for the volcanic area of Mount Etna

Ground motion prediction equations (GMPEs) have been derived for peak ground acceleration (PGA), velocity (PGV), and 5 % damped spectral acceleration (PSA) at frequencies between 0.1 and 10 Hz for the volcanic area of Mt. Etna. The dataset consists of 91 earthquakes with epicentral distances between 0.5 and 100 km. Given the specific characteristics of the area, we divided our data set into two groups: shallow events (SE, focal depth 5 km). The range of magnitude covered by the SE and the DE is 3.0 ≤ M L ≤ 4.3 and 3.0 ≤ M L ≤ 4.8, respectively. Signals of DE typically have more high frequencies than those of SE. These differences are clearly reflected in the empirical GMPEs of the two event groups. Empirical GMPEs were estimated considering several functional forms: Sabetta and Pugliese (Bull Seism Soc Am 77:1491–1513, 1987) (SP87), Ambraseys et al. (Earth Eng Struct Dyn 25:371–400, 1996) (AMB96), and Boore and Atkinson (Earth Spectra 24:99–138, 2008) (BA2008). From ANOVA, we learn that most of the errors in our GMPEs can be attributed to unmodeled site effects, whereas errors related to event parameters are limited. For DE, BA2008 outperforms the simpler models SP87 or AMB96. For SE, the simple SP87 is preferable considering the Bayesian Information Criterion since it proves more stable with respect to confidence and gives very similar or even lower prediction errors during cross-validation than the BA2008 model. We compared our results to relationships derived for Italy (ITA10, Bindi et al. Bull Earth Eng 99:2471–2488, 2011). For SE, the main differences are observed for distances greater than about 5 km for both horizontal and vertical PGAs. Conversely, for DE the ITA10 heavily overestimates the peak ground parameters for short distances.

Between‐Event Variance for Large Repeating Earthquakes

We estimate the variance in ground motions related to repeated large earthquakes occurring on the same fault segment with similar magnitudes. We find eight earthquake pairs for which suitable strong‐motion records exist. Two are crustal strike‐slip earthquakes from California and six are subduction zone earthquakes from Japan. We consider only large earthquakes and deal with frequencies greater than the earthquake corner frequency, so the variability that is considered here is related to smaller scale differences in the rupture process, particularly on the part of the fault nearest the station. We find that the variance of the 5% damped spectral accelerations of these pairs, termed ![Graphic][1] , averages to about 45% and 80% of τ 2 for the crustal and subduction zone earthquakes, respectively, in which τ 2 is the contribution of source variability to the total variability of ground motion estimated by some recent ground‐motion prediction equations. We suggest that ![Graphic][2] is lower than τ 2, for the frequencies at which ![Graphic][3] is estimated, because it depends primarily on only local physical properties of a fault that are the same in repeated earthquakes. We therefore suggest that at sites where the hazard is controlled by a single rerupturing source, one could potentially use a between‐event variance that is smaller than τ 2 in seismic‐hazard calculations. Thus, these results may help to resolve the inconsistencies that are now present between the national hazard maps and some precariously balanced rocks in southern California. [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif [3]: /embed/inline-graphic-3.gif

Empirical Spectral Acceleration Amplification in the Iwate-Miyagi and Niigata Regions, Japan, Inferred by a Spectral Ratio Method Using Ground-Motion Prediction Equations

Abstract Using the strong ground motion dataset of M w 4.0–6.0 earthquakes in Japan from K‐NET and KiK‐net, we studied empirically the 5% damped spectral acceleration amplification for periods from 0.05 to 5 s at 75 seismic stations located in the Iwate–Miyagi and Niigata regions. The method of study is based on estimating the empirical site effect from the spectral ratio of observed and predicted ground motions based on the ground‐motion prediction equations (GMPEs). Our results show a large amplification at most analyzed stations at periods of 0.1 s and shorter; at periods of 0.3 s and longer, large amplifications generally dominate at basin stations, but deamplifications generally dominate at mountain stations. Empirical amplification factors of spectral acceleration were used to correct the observed strong ground motion data of two crustal earthquakes: the 2008 Iwate–Miyagi Nairiku earthquake ( M w 6.9) and the 2004 Chuetsu earthquake ( M w 6.6). The site‐corrected data fit better with GMPEs inferred by less standard error. We took advantage of a large body of empirical data to develop a mean empirical site‐response model for each region. These empirical models are superior to models predicted from GMPEs using only V S 30 site corrections. Those relations have shown a low correlation at short periods such as 0.1 s. We also found the relations are different for the mountain and basin stations. The method is efficient for calculating site effects at observation stations where insufficient velocity structure information and a history of earthquake recordings are available.

Ground Motion Relations for Active Regions in India

In this article, a study on development of ground motion prediction equations (GMPEs) is undertaken for seismically active regions in India. To derive the equations, the seismically active regions are divided into four units based on seismotectonic setting and geology. Due to lack of strong motion data, a stochastic finite-fault simulation method is used for generating a complete synthetic database with respect to magnitude and distance. The input parameters in the stochastic seismological model, such as site amplification and stress drop, are first derived from the past strong-motion data. A total of 236 three-component records from 62 earthquakes with magnitudes ranging from M w 3.4 to 7.8 are used to calibrate the seismological model. The obtained stress drops of these 62 events lie in between 60 and 165 bars. With the help of a large synthetic database generated from the calibrated seismological model, ground motion relations for 5 % damped spectral acceleration are obtained by regression analysis. The developed ground motion relations are compared with the existing GMPEs of the other active regions in the world. Although the proposed equations have trends similar to those of the existing relations, there are some differences attributed to stress drop and the quality factor of active regions in India. These relations will be useful to prepare spectral acceleration hazard maps of India for a given annual probability of exceedance.

An Alternative Analysis of the Probabilistic Seismic Hazard for Las Vegas Valley, Nevada

Abstract Probabilistic seismic‐hazard calculations relevant for rock‐site conditions in the Las Vegas Valley (LVV), Nevada, have been computed. These account for seismic sources not included in the current (2008) U.S. Geological Survey national seismic‐hazard model (NSHM) due to insufficient knowledge or documentation, using the commercial software package EZ‐FRISK. The LVV is underlain by a system of mapped, active normal faults that comprise the LVV fault system (LVVFS), with maximum potential earthquakes of M 6.8. The 2008 NSHM explicitly includes only one fault of the LVVFS. This analysis includes four more faults of the LVVFS plus four regional faults, in addition to those included in the 2008 NSHM, and modifies parameters of two others. As such, this study demonstrates the effect of a significant modification to expectations for seismic sources. These results can be considered as a “what if” scenario for seismic hazard of the LVV. Nominal peak ground acceleration (PGA) and 5% damped spectral acceleration (SA) were calculated for 0.2 s and 1.0 s periods using five ground‐motion prediction equations (GMPEs). A logic‐tree formulation accounted for uncertainty in the GMPEs and source parameters. Hazard values for PGA and SA, computed at ∼2.8 km spacing, are comparable with those of the 2008 NSHM on the margins of the LVV but are considerably higher in the north‐central parts of the LVV near downtown Las Vegas and the city of North Las Vegas. The study provides a rationale for the urgency to intensify investigations of faults in and around the LVV.

Probabilistic seismic response analysis of a 3-D reinforced concrete building

This paper presents the probabilistic seismic demand analysis with respect to seismic input uncertainty only of a 3-D reinforced concrete building model subjected to three-component earthquake ground motion excitation. Response history analyses are carried out on a nonlinear frame model. Probability distributions are assumed for the ground motion Intensity Measure (IM) taken as the linear 5% damped elastic spectral acceleration at the fundamental period of the structure. Part of the framework of the so-called Performance Based Earthquake Engineering (PBEE) methodology developed by the Pacific Earthquake Engineering Research (PEER) Center is used in this study. This paper has two main objectives. The first objective is to perform a probabilistic demand analysis of an existing building conditional on the ground motion IM. The second objective is to use the results obtained from this existing testbed, with real-world complexities, to demonstrate the deficiency of the PEER PBEE methodology when using a scalar ground motion IM for 3-D structural models. This last objective shows the need for improving the definition of the seismic IM in the PBEE methodology for the general case of 3-D structures subjected to multi-directional input ground motions. To this effect, an ensemble of natural ground motion records is used to represent the inherent randomness in ground motion time-histories (i.e., record-to-record variability). The statistical correlation of different Engineering Demand Parameters (EDPs) with a set of IMs, taken as the 5% damped spectral accelerations at different periods for two horizontal ground motion components, is investigated in order to assess the dispersion in the EDPs due to different ground motion records. Some statistical correlation coefficients are found to be high, indicating that the dispersion of the EDPs is heavily influenced by the spectral content at periods different from the fundamental period. This result points to the need for using vector-valued ground motion Intensity Measures in the PBEE methodology currently proposed by PEER.

Ground‐Motion Prediction Equations for The Geysers Geothermal Area based on Induced Seismicity Records

Abstract The Geysers geothermal field in Northern California, which has been actively exploited since the 1960s, is the world’s largest geothermal field. The continuous injection of fluids and the consequent stress perturbations induce seismicity that is clearly felt in the surrounding communities. In order to evaluate seismic hazard due to induced seismicity and the effects of seismicity rate level on the population and buildings in the area, reliable ground‐motion prediction equations (GMPEs) must be developed. This paper introduces the first GMPEs specific for The Geysers area in terms of peak ground velocity (PGV), peak ground acceleration (PGA), and 5% damped spectral acceleration SA( T ) at T =0.2 s, 0.5 s, and 1.0 s. The adopted non‐linear mixed‐effect regression technique to derive the GMPE includes both fixed and random effects, and it permits to account for both inter‐event and intra‐event dependencies in the data. Site‐specific effects are also estimated from the data and are corrected in the final ground‐motion model. We used data from earthquakes recorded at 29 stations of the Berkeley‐Geysers network during the period September 2007 through November 2010. The magnitude range is 1.3≤ M w ≤3.3, whereas the hypocentral distances range between 0.5 km and 20 km. The comparison of our new GMPE for The Geysers with a standard model derived in a different tectonic context shows that our model is more robust when predictions have to be made for induced earthquakes in this geothermal area.

The Use of Stochastic Optimization in Ground Motion Prediction

In recent years stochastic optimization has become popular in modeling highly complex natural systems as opposed to traditional approaches, such as regression analysis. This paper tests the efficiency of regression analysis over mathematical optimization by evaluating the performance of stochastic (genetic algorithms, simulated annealing) and deterministic algorithms (nonlinear least squares, pattern search) in solving minimization problems. Qualitative and quantitative comparison of these solvers reveals that the implementation of genetic algorithms with initial population development, using Latin Hypercube sampling, outperformed other algorithms. Using the aforementioned solver, ground motion prediction equations are derived for the estimation of horizontal peak ground acceleration, velocity, and 5% damped spectral acceleration ordinates at discrete period estimators between 0.05 s and 2 s. Ground motion for stiff and soft soil sites is amplified by a constant factor with respect to rock site. These strong motion prediction equations are proposed for application in the range M4.5–M6.6 and for distances up to 150 km.

Deterministic seismic hazard assessment for Sultanate of Oman

The Sultanate of Oman forms the southeastern part of the Arabian plate, which is surrounded by relatively high active tectonic zones. Studies of seismic risk assessment in Oman have been an important on-going socioeconomic concern. Using the results of the seismic hazard assessment to improve building design and construction is an effective way to reduce the seismic risk. In the current study, seismic hazard assessment for the Sultanate of Oman is performed through the deterministic approach with particular attention on the uncertainty analysis applying a recently developed method. The input data set contains a defined seismotectonic model consisting of 26 seismic zones, maximum magnitudes, and 6 alternative ground motion prediction equations that were used in four different tectonic environments: obduction zone earthquake (Zagros fold thrust belt), subduction zone earthquakes (Makran subduction zones), normal and strike-slip transform earthquakes (Owen and Gulf of Aden zones), and stable craton seismicity (Arabian stable craton). This input data set yielded a total of 76 scenarios at each point of interest. A 10 % probability that any of the 76 scenarios may exceed the largest median ground acceleration is selected. The deterministic seismic hazards in terms of PGA, 5 % damped spectral acceleration at 0.1, 0.2, 1.0 and 2.0 s are performed at 254 selected points. The ground motion was calculated at the 50th and 84th percentile levels for selected probability of exceeding the median value. The largest ground motion in the Sultanate of Oman is observed in the northeastern part of the country.

Probabilistic seismic hazard maps for the sultanate of Oman

This study presents the results of the first probabilistic seismic hazard assessment (PSHA) in the framework of logic tree for Oman. The earthquake catalogue was homogenized, declustered, and used to define seismotectonic source model that characterizes the seismicity of Oman. Two seismic source models were used in the current study; the first consists of 26 seismic source zones, while the second is expressing the alternative view that seismicity is uniform along the entire Makran and Zagros zones. The recurrence parameters for all the seismogenic zones were determined using the doubly bounded exponential distribution except the zones of Makran, which were modelled using the characteristic distribution. Maximum earthquakes were determined and the horizontal ground accelerations in terms of geometric mean were calculated using ground-motion prediction relationships developed based upon seismic data obtained from active tectonic environments similar to those surrounding Oman. The alternative seismotectonic source models, maximum magnitude, and ground-motion prediction relationships were weighted and used to account for the epistemic uncertainty. Hazard maps at rock sites were produced for 5 % damped spectral acceleration (SA) values at 0.1, 0.2, 0.3, 1.0 and 2.0 s spectral periods as well as peak ground acceleration (PGA) for return periods of 475 and 2,475 years. The highest hazard is found in Khasab City with maximum SA at 0.2 s spectral period reaching 243 and 397 cm/s2 for return periods 475 and 2,475 years, respectively. The sensitivity analysis reveals that the choice of seismic source model and the ground-motion prediction equation influences the results most.

Soil Liquefaction Effects in the Central Business District during the February 2011 Christchurch Earthquake

During the period between September 2010 and June 2011, the city of Christchurch was strongly shaken by a series of earthquakes that included the 4 September 2010 ( Mw = 7.1), 26 December 2010 ( Mw = 4.8), 22 February 2011 ( Mw = 6.2), and 13 June 2011 ( Mw = 5.3 and Mw = 6.0) earthquakes. The moment magnitude ( Mw ) values adopted in this paper are taken from GNS Science, New Zealand (http://www.geonet.org.nz); they are 0.1 units higher than the corresponding Mw values reported by the U.S. Geological Survey (http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usb0001igm/). These earthquakes produced strong ground motions within the central business district (CBD) of Christchurch, which is the central heart of the city just east of Hagley Park and encompasses approximately 200 ha. Some of the recorded ground motions had 5% damped spectral accelerations that surpassed the 475-year return-period design motions by a factor of two. Ground shaking caused substantial damage to a large number of buildings and significant ground failure in areas with liquefiable soils. The 22 February earthquake was the most devastating. It caused 181 fatalities and widespread liquefaction and lateral spreading in the suburbs to the east of the CBD and in areas within the CBD, particularly along the stretch of the Avon River that runs through the city. There were pockets of heavy damage in the CBD, including the collapse of two multistory reinforced concrete buildings, as well as the collapse and partial collapse of many unreinforced masonry structures including the historic Christchurch Cathedral in the center of the CBD. Soil liquefaction in a substantial part of the CBD adversely affected the performance of many multistory buildings, resulting in global and differential settlements, lateral movement of foundations, tilt of buildings, and bearing failures. The Mw = 6.2, 22 February 2011 earthquake …

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

The city of Adapazari — 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 Mw = 7.4). This study determines site amplifications of the attenuation relationships for shallow earthquakes in the Adapazari 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.

Influence of the 3D Distribution of Q and Crustal Structure on Ground Motions from the 2003 Mw 7.2 Fiordland, New Zealand, Earthquake

The M w 7.2 earthquake of 21 August 2003 provides an unprecedented opportunity to evaluate the applicability of the New Zealand acceleration response spectrum attenuation model (McVerry et al. , 2006) in the Fiordland region and to consider effects from 3D Q heterogeneity. This was the largest shallow earthquake in New Zealand in the past 40 yrs. It was well recorded by the GeoNet seismograph and strong-motion network. We compare the observed 5% damped response spectral accelerations (SAs) to the New Zealand model values, for both crustal reverse and subduction interface earthquakes. On average, both models underpredict the observed SAs, by approximately 0.4 in lnSA, for 0–400 km distance; however, the data show great variability. Using the South Island 3D Q model, we compute the path-averaged attenuation rate, CQ for synthetic Fiordland hypocenters to distributed sites. Compared to the standard model, the relatively high Q in South Island produces lower attenuation rates, although the low- Q crustal root of the Southern Alps produces a 10 times greater attenuation rate for certain paths. The average attenuation rate estimated from the SA data is similar to CQ for frequencies <5 Hz and constant above 5 Hz. For an acceleration model for Fiordland earthquakes, 0–60 km depth, an applicable anelastic attenuation rate is the mean CQ from the synthetic hypocenters, which is 0.006 km-1 at 2.5 Hz. For the observed SAs, the most significant regional effect is high relative SAs at some sites that may be due to postcritical Moho reflections from the Southern Alps crustal root.

Interevent and Interstation Variability Computed for the Italian Accelerometric Archive (ITACA)

Abstract The interevent and interstation ground-motion variability of the updated Italian strong-motion database (Italian Accelerometric Archive [ITACA]) has been explored through the development of new empirical ground-motion prediction equations (GMPEs) for Italy. The regressions have been performed on 241 three-component waveforms from 27 earthquakes with moment magnitudes ranging from 4.8 to 6.9, recorded by 146 stations at distances up to 200 km. The site classification follows the schemes previously proposed for Italy, in which two soil classes are defined, considering both shear-wave velocity and deposit thickness. The regression analysis uses the values of the explanatory variables (magnitude, fault distance, site class, and style of faulting) recently revised in the framework of a project funded by the Italian Department of Civil Protection. The equations have been derived for peak ground acceleration, peak ground velocity, and 5% damped spectral accelerations at 18 periods from 0.03 to 2 sec. The residual variance has been decomposed into interevent, interstation, and record-to-record components by applying a random effect regression scheme. The interevent and interstation error distributions have been analyzed as function of periods to detect sites and events for which predicted values significantly deviate from observations. For periods up to 0.35 sec, the interstation is the dominant component of variance, indicating that an improvement in the site classification could lead to a refinement of the GMPEs. For longer periods, the three components of variance provide similar contributions, indicating that a reduction of the uncertainty can be achieved by reducing the epistemic uncertainty affecting the physical model. The interevent error highlights the peculiarity of few earthquakes, suggesting that the evaluation of regional GMPEs can be important when specific scenario studies should be carried out. The interstation variability allows us to detect stations with peculiar site response and to assess the goodness of the considered site classification scheme.

Probabilistic seismic hazard maps for Sinai Peninsula, Egypt

Sinai experienced the largest Egyptian earthquake with moment magnitude (Mw) 7.2 in 1995 in the Gulf of Aqaba, 350 km from Cairo. It is characterized by the presence of many tourist projects in addition to different natural resources. The aim of the current study is to present, for the first time, the probabilistic spectral hazard maps for Sinai. Revised earthquake catalogues for Sinai and its surroundings, from 112 BC to 2006 AD with magnitude equal or greater than 3.0, are used to calculate seismic hazard in the region of interest between 27°N and 31.5°N and 32°E and 36°E. We declustered these catalogues to include only independent events. The catalogues were tested for the completeness of different magnitude ranges. 28 seismic source zones are used to define the seismicity. The recurrence rates and the maximum earthquakes across these zones were also determined from these modified catalogues. Strong ground motion relations for rock are used to produce 5% damped spectral acceleration values for four different periods (0.2, 0.5, 1.0 and 2.0 s) to define the uniform response spectra at each site (grid of 0.2° × 0.2° all over the area). Maps showing spectral acceleration values at 0.2, 0.5, 1.0 and 2.0 s periods as well as peak ground acceleration (PGA) for the return period of 475 years (equivalent to 90% probability on non-exceedence in 50 years) are presented. In addition, Uniform Hazard Spectra (UHS) at 25 different periods for the four main cities (Hurghda, Sharm El-Sheikh, Nuweibaa and Suez) are graphed. The highest hazard is found in the Gulf of Aqaba with maximum spectral accelerations 356 cm s−2 at a period of 0.22 s for a return period of 475 years.

An empirical attenuation relationship for Northwestern Turkey ground motion using a random effects approach

Using a random effects model that takes into consideration the correlation of data recorded by a single seismic event, a database consisting of 195 recordings from 17 recent events is employed to develop empirical attenuation relationships for the geometric mean of horizontal peak ground acceleration and 5-percent damped spectral acceleration ( S a). The recordings employed are obtained from strong motion stations operating in Northwestern Turkey and resulted from events that include the Kocaeli ( M w=7.4) and the Düzce ( M w=7.1) earthquakes and their aftershocks as well as other events. By studying differences in standard errors, the random effects model is compared with a fixed effects model that does not account for distinctions between intra- and inter-event variability. Effects of local site conditions are included in the empirical relationships developed. The dependence on frequency of the various model parameters is also studied. Frequency-dependent attenuation coefficients for the proposed random effects models developed are summarized in tables to facilitate their use.