Average Shear Wave Velocity Research Articles

Arias intensity attenuation relationship in Sichuan–Yunnan region, China

Arias intensity is an essential ground motion measure correlating with the potential for earthquake-induced landslides. The Sichuan–Yunnan region, which is primarily mountainous, is a high incidence region of earthquake-induced landslides in China. However, there is no available attenuation relationship for this intensity measure due to the backward construction of the stations. In this study, we developed a region-specific Arias intensity attenuation relationship using the China Strong-Motion Networks Center (CSMNC) database which was established in 2008. We recommend this relationship be applied in the Sichuan–Yunnan region for moment magnitudes ranging between 4.2 and 7.0, distances ranging between 0 and 300 km and with Vs30 (the average shear-wave velocity in the upper 30 m of a soil profile) ranging between 128 and 760 m/s. The current study finds that this relationship’s intra-event, inter-event, and total standard deviations are greater than for other regions. This is likely caused by the complicated seismotectonic activities, nonlinear site effects, error from inferring Vs30, basin effects, etc. However, this relationship has the best performance in fitting and predicting the data from the Sichuan–Yunnan region.

Relation of shear wave velocity variations with depth for different lithologies: A contribution towards mitigating the region's seismic risk

The state of Uttarakhand in India lies in a highly seismically active zone, therefore earthquake re- sistant design criteria have been followed for major construction practice in this region. One of the major inputs for earthquake-resistant design is average shear wave velocity (VS ) at 30 m depth. In the present work, at twenty-six different sites, the Horizontal to vertical spectral ratio (HVSR) technique and multichannel analysis of surface wave (MASW) is used for joint analysis to obtain a one-dimensional velocity model that supports both the HV spectrum and dispersion curve obtained from HVSR and MASW methods, respectively. Shear wave profiles obtained at various sites are compared with the bore log data obtained from drilling and it clearly shows that the (VS ) for the same formation have a strong dependence on the depth at which it occurred. Data from twenty- four shear wave profiles have been used to prepare a linear regression relation of (VS ) for different lithological formations with respect to their depth of occurrence. Root mean square error obtained from the developed relationship for various lithologies clearly shows that the results are fairly well within the range of acceptance. The developed relations have been further validated by calculating Vs profile from bore log data obtained at two new location sites that are not included in the data set used for the preparation of regression relations. A comparison of two velocity sections clearly shows that the velocity profile computed from regression relation matches closely with that obtained from the seismic survey and thereby establishing the efficacy of developed regression relationship for its practical implementation. This developed relation allows soil type classification for zoning purposes.

Characteristics of the foundation rocks using geophysical techniques: A case study for the Egyptian solar plant site, Aswan, Egypt

The main target of the present study is to investigate the foundation layers and the subsurface structures in an Egyptian solar plant site using geophysical techniques including the seismic refraction and Multichannel Analysis of Surface Waves (MASW). The studied solar park is situated at about 40 km to the north of Aswan city on the Aswan-Cairo highway road and is classified as the largest solar plant in Africa and worldwide. Due to its location in the vicinity of the most prone earthquake area in Egypt (Aswan seismic zone); it is imperative to mitigate the earthquake hazard in this region. The geophysical results show that the subsurface foundation in this site is primarily composed of two layers. The upper one is loose and incompetent soil sediments that extend down to about 10 m depth with P-wave velocity ranging from 400 to 1000 m/s and shear-wave velocity ranging from 260 to 550 m/s. The deeper section is considered the main foundation layer with velocities ranging between 650 and 1900 m/s and from 350 to 950 m/s for P-wave and shear-wave, respectively. The average shear-wave velocities calculated for the topmost 30 m (Vs30) vary almost between 319 and 834 m/s; thereby the studied site is primarily ranked into classes C&D (180-360 m/s & 360-760 m/s, respectively) according to the National Earthquake Hazards Reduction Program (NEHRP) soil classification. Additionally, the southwestern and southeastern zones of the site area are characterized by maximum velocity values, relative high values of rock densities, rigidity or shear modulus “μ”, Standard Penetration Test (N-Value), ultimate bearing capacity and allowable bearing capacity, while the low values are observed through the northern and middle sectors across the area. This study an integral part of many works being carried out delineating the subsurface foundation structures around the solar plant and allows the most appropriate sites for constructing the renewable energy plants to be sited away from the highly hazards prone areas.

The role of modelling of site conditions and amplification in seismic hazard and risk assessment at urban scale. The case of Thessaloniki, Greece

One of the main challenges of large-scale seismic hazard and risk applications is the characterization of the amplification of seismic ground motion due to the local site conditions, often described by Vs,30, i.e., the time- averaged shear wave velocity in the upper 30 meters of the soil deposit. In most of these applications, Vs,30 values are directly estimated from microzonation investigations, inferred from proxies such as the topographic slope, or obtained from seismic codes based on a simplified site categorization. The scope of this work is to investigate the effects of the method applied for modelling of site conditions and site amplification in urban risk assessment. For this we consider the application of the 2020 updates of the European Seismic Hazard (ESHM20) and Risk (ESRM20) Models and we focus on Thessaloniki, Greece, a city which is very well documented in terms of both local site conditions and exposure.To this end, we compare seismic hazard and risk results obtained using two different approaches for site conditions / site amplification modelling. In the first approach, which may be considered as more rigorous but also more demanding, two different appropriate site condition models are directly used in the ESHM20 hazard logic tree. In the second approach, which is more simplified and efficient in practice, two site amplification models were developed for the study area based on the soil classification according to two different code-oriented classification schemes. Eventually, four hazard models are obtained. Seismic risk results are presented in terms of expected damages and economic losses for a seismic hazard with a 475-year return period. Both hazard and risk assessment calculations are undertaken with the OpenQuake Engine (Pagani et al., 2014; Silva et al., 2014). The main conclusion for the case of Thessaloniki is that, for the given fragility and vulnerability models, the estimated aggregate damages and economic losses at city scale are not significantly affected by the way that local site conditions are taken into account, which indicates that simplified approaches for site modelling may be used for large scale applications when more rigorous approaches are not feasible. Significant discrepancies may occur, however, at local scale.

The value of multi-modes of ultrasound in evaluating segmental mucosal healing in patients with Crohn's disease.

Mucosal healing, the result of endoscopic remission, is associated with prolonged clinical remission and delayed deterioration of Crohn's disease, which is significant and accompanied by reduced hospitalizations and surgeries. Currently, the relationship between ultrasonic parameters and mucosal healing remains controversial. To establish an ultrasonic regression model to evaluate mucosal healing, we conducted this preliminary study using multiple parameters from B-mode ultrasonography, colour Doppler flow imaging and shear wave elastography systematically. This study consisted of two single-centre investigations based on development and validation populations who received endoscopies (as the gold standard) and ultrasound. The involved bowel segments were divided into mucosal healing (MH) and nonmucosal healing (NMH) groups according to endoscopic results. Eight ultrasonic parameters were observed, including bowel wall thickness (BWT), mesenteric fat thickness (MFT), median modulus of elasticity (Emean), average shear wave velocity (SWV), Limberg scoring (LG), bowel wall stratification (BWS), ascites (AS) and lymph node enlargement (LN). We developed an ultrasonic regression model in the development phase to evaluate segmental mucosal healing and undertook prospective validation of this model. A total of 124 patients with 380 involved bowel segments from the development and validation cohorts were evaluated. Eight ultrasonic parameters were significantly different between the two groups (P<0.05) in the development phase. Four significant parameters with better AUC performance were selected to establish an ultrasonic regression model to predict mucosal healing. The AUCs of this ultrasonic model were 0.975 and 0.942 in the development and validation cohorts, respectively. The multimodal ultrasonic model has the potential to evaluate segmental mucosal healing in Crohn's disease.

A Preliminary Result of Seismic Hazard Analysis in Eastern Part of Bali Island, Indonesia

Bali Island is one of the main tourist destinations in Indonesia. However, Bali Island is also prone to earthquakes, as evidenced by several historical destructive earthquakes, especially in the eastern part of Bali. A probabilistic seismic hazard modeling is undertaken to analyse the earthquake hazard, as well as studying the contribution of local geological conditions to earthquake ground motion. We use seismic waveforms retrieved from 23 temporary seismic stations across the eastern part of Bali Island from December 2018 to June 2019 and 5 permanent seismic stations around Mount Agung and Batur. The recording data were processed using the Horizontal to Vertical Spectral Ratio (HVSR) method. Our preliminary result shows local geological conditions for each station, represented by the value of the average shear-wave velocity on rocks to a depth of 30 meters (Vs30) and the total thickness of sediments above the bedrock (basin depth). These initial results will then be developed as site parameter input for probabilistic seismic hazard analysis in the eastern part of Bali.

Along‐strike variation in the shear wave crustal structure of the NE Himalayan and Indo‐Burmese arc: Evidence based on surface wave dispersion analysis

Surface wave dispersion data is used to infer the shear wave velocity structure variation in the north‐east Himalaya and Indo‐Burmese arc regions. We have used 25 earthquakes data from four groups with a magnitude range of 5.0–6.7, epicentral distance range 368–800 km, and focal depth less than 50 km. Ray paths from the earthquake location to the seismic station are transversely passing different geotectonic units of the Himalayas, Indo‐Gangetic plains, and Indo‐Burma collision zones. The weighted average dispersion curve and the path averaged shear wave velocity models are computed for the four groups located at different azimuths around Shillong seismic station. Non‐linear least‐square inversion is performed to obtain the shear wave velocity structure of the crust and uppermost mantle from joint inversion of Rayleigh and Love waves group velocities. Subsequently, Rayleigh and Love waves group velocities are inverted separately to obtain vertical and horizontal components of S‐wave velocity. Next, using these components anisotropy coefficient values at different depths for each path are also estimated. A high variation of dispersion curves and the shear wave velocity models from one group to another indicates that the region is geotectonically very complex. An approximately 80 km‐thick zone beneath the study region has shear wave velocity as low as 1.7 km/s in the uppermost crust in the southern part and ~4.7 km in the uppermost mantle beneath the Eastern Himalayan Syntaxis (EHS). Inferred velocity is also lower than that of PREM and AK135 global models with a much thicker crust beneath the study region. Radial anisotropy varies even within the northern part from the Indo‐Eurasian collision zone to EHS and northern to southern Indo‐Burma ranges. Anisotropy is comparatively stronger in the deeper part below ~40 km for the three paths, except for the EHS, where the result is contrary.

Deep shear wave velocity profiles in the Mississippi embayment from surface wave measurements

Local geology in the Mississippi embayment is a significant source of site effects due to the deep unconsolidated sediments and basin effects near the edge of the embayment. Proper characterization of the velocity structure of the embayment is crucial for site response and seismic hazard studies. In this paper, deep dynamic site characterization was conducted in the Mississippi embayment to develop shear wave velocity profiles down to bedrock at 24 sites using active and passive source surface wave methods. Study sites cover parts of Arkansas, Missouri, Kentucky, and Tennessee, with bedrock depths ranging from 250 to 1115 m. Multimodal joint inversion of surface wave data, which included both Rayleigh and Love wave dispersion and site fundamental frequency was utilized to develop the shear wave velocity profiles (VS profiles). The developed VS profiles provided reasonable site characterization solution and captured the site signature from experimental dispersion data and fundamental frequency. Average shear wave velocity down to bedrock ranges from 462 to 686 m/s and is proportionally related with the site period and depth to bedrock of the site. Average shear wave velocities estimated by previous studies using the resonance period-sediment thickness relationship tend to systematically overestimate the average shear wave velocity in the embayment by 25–40%. Formation velocities calculated for the commonly found geologic units in the embayment, Quaternary, Upper Tertiary, Memphis sand, Paleocene, Cretaceous, and Paleozoic bedrock are approximately 214, 418, 607, 665, 967, and 2211 m/s, respectively. Comparison of the developed VS profiles demonstrated better agreement with related VS profiles generated from direct measurements, but differences up to 30% are observed with the current velocity models of the Embayment.

Time-weighted average shear wave velocity profiles from surface wave tests through a wavelength-depth transformation

We investigate the possibility of obtaining time-weighted average shear wave velocity profiles through a wavelength-depth transformation of experimental dispersion curves from surface wave tests, without a formal solution of the inverse problem. We evaluate this approach on a wide flat-file database (Polito Surface Wave Database, PSWD) of experimental dispersion curves and related shear wave velocity profiles, both from dispersion curve inversion and invasive tests. The results show that the proposed wavelength-depth transformation can be valuable for seismic site evaluations offering an estimation of time-weighted average shear wave velocity profiles very similar to a state-of-the-art inversion of the experimental dispersion curves and with similar uncertainty with respect to invasive tests. This transformation has the advantage of avoiding time-consuming inversion processes, with related uncertainty sources, and any assumption on layer parameterization and a-priori information. Moreover, in conjunction with an experimental evaluation of the fundamental frequency of the site, from independent surveys, the wavelength-depth transformation can be used to get a direct and fast estimate of the position of the engineering bedrock.

Determination of Seismic Site Class and Potential Geologic Hazards using Multi-Channel Analysis of Surface Waves(MASW) at the Industrial City of Abu Dhabi, UAE

ABSTRACT Geophysical investigation activities were conducted at ICAD-II, Abu Dhabi, UAE using Multi-Channel Analysis of Surface Waves (MASW) to determine subsurface geology , material stiffness, potential weak zones down to ~35 m depth, and to propose the appropriate seismic site classification for a proper foundation design. A total of 20 MASW lines were carried out over a grid layout of 5 m spacing. Data acquisition, processing and inversion have been parameterised and selected to produce shear velocities that represent subsurface conditions. The estimated average shear-wavevelocity (Vs30 = 577.97 m/s) suggests that the investigated site can be classified as Class C (V.D. Soil & Soft Rock). The constructed geological model comprises sand, weak sandstone, weak mudstone, and hard mudstone. Analysing the shear wave velocities indicates the absence of apparent cavities/ hazardous zone . However, a relatively weak layer of sandstone/mudstone rocks intercalations was detected from ~7m to ~25m. Meanwhile, the uncorrelated part of 2D MASW data indicates potentially harder mudstone encountered at a depth starting from ~25 m to >35 m. Hence, the foundation layer may be placed on the upper surface of the sandstone bed (~7 m) depending on the height and load of the proposed building and following the construction standards and requirements of the structural engineer.

Seismic site characterization of a few Indian coal ash deposits using multichannel analysis of surface waves

This study presents the outcome of an extensive field experiment undertaken to characterize coal ash deposits in terms of dynamic properties. In-situ shear wave velocity ( V s ) was measured over three hydraulically deposited coal ash deposits (two active ponds and one abandoned pond) situated in the central and southern parts of India. Multichannel analysis of surface waves was performed at twenty-one different locations on the ash deposits and the dyke top to measure the V s profiles along the depth ( z ). V s profiles measured for the abandoned coal ash deposits were greater than those of the active deposits. Moreover, the empirical association of V s profiles from active and abandoned coal ash deposits in India, based on the present study and reported literature, yields a piecewise linear relationship between shear wave velocity and depth. • Shear wave velocity (V s ) values from MASW for three coal ash ponds in India. • Box and whisker plots for inter and intra-site variations in V s profiles. • Comprehensive data on the variation of V s vs. z for all Indian coal ash deposits. • Empirical association between in-situ average shear wave velocity, V s,a vs. z for Indian ashes.

Generic-To-Reference Rock Scaling Factors for Seismic Ground Motion in Italy

ABSTRACT In this article, we apply the reference-rock identification method (RRIM; Lanzano et al., 2020) to the ITalian ACcelerometric Archive, which includes more than 1600 recording stations in Italy and in the neighboring countries, with different levels of site characterization. The RRIM is based on the identification and the evaluation of site parameters representing the reference site conditions (Steidl et al., 1996) and the construction of the scoring scheme to classify the candidate stations. Given the large number of sites, the preselection of candidates is performed via residual analysis, selecting those characterized by flat site response and amplitude similar or lower than the one for the generic rock (average shear-wave velocity in the uppermost 30 m, VS30=800 m/s). The main results of this study are: (1) a list of reference rock sites in Italy, with an associated score; (2) a scenario-independent generic-to-reference rock corrective factor for the ground-motion model for shallow active crustal events in Italy (ITA18; Lanzano, Luzi, et al., 2019); (3) a model for the generic-to-reference rock corrective factor, parametrized in terms of VS30 and κ0, that is, the high-frequency decay parameter (Anderson and Hough, 1984). A collateral product is a set of coefficients for the prediction of 81 ordinates of the Fourier amplitude spectra (FAS) in the frequency interval 0.1–30 Hz, calibrated with the same dataset and functional form of ITA18 for acceleration response spectra (SA). The application of RRIM allowed us to identify 116 stations with average measured VS30∼900 m/s. The corrective factor allows to scale both SA and FAS spectra, and has a significant effect at high frequencies, reducing the ground motion by up to a factor 1.7 at f = 10 Hz. The introduction of κ0 in the corrective term modeling is effective from 2 Hz onward and results in a reduction of variability at high frequencies (f &amp;gt; 10 Hz).

Vertical spectra consistent with horizontal seismic hazard

Construction of vertical spectra (V) for scenario- and intensity-based seismic performance assessment is proposed based on scaling of the associated horizontal spectral ordinates (H) through respective V/H spectral ratios. Geometric mean of the spectra along and normal to the principal plane components is considered as the intensity measure of the horizontal component. V/H spectral shape is constructed using a large database (PEER-NGA-WEST2) of strong motion records contingent on the magnitude of the event, epicentral distance and average shear wave velocity. The procedure is based on the ratio of median vertical-to median horizontal-spectral ordinates which are shown to be well representative of the median of V/H spectral ratio. The construction is based on median response of the scenario and also applies to the design level (of a particular facility located in a specific site, which is also governed by a scenario) under certain assumptions and involves two steps: construction of normalized V/H spectra with unity at zero period scaled by the ratio of median vertical-to median horizontal- PGA (beta). The normalized V/H spectrum is shown to be characterized by three control points. An empirical estimate is proposed for beta as a function of epicentral distance. Normalized V/H spectra are further idealized for use with the intensity-based assessment per seismic codes. Vertical spectra using the proposed framework are compared with the various recommendations reported in the prior art including seismic codes and recorded events. PESMOS and COSMOS databases of strong motion events recorded in the Indian subcontinent are also used during the assessment.

Site Amplifications from Earthquake Data and VS30 in the Fort Worth Basin, Texas

Abstract Following the development of unconventional oil and gas production in the Fort Worth Basin, Texas, a rapid increase in basin-wide seismicity began in 2008 that grew to include earthquakes affecting a substantial portion of the Dallas–Fort Worth metropolitan area. To assess and mitigate the seismic hazard, which in this region is impacted by the thickness of the sedimentary basin and accompanying soft soil layer, we estimate site effects at 22 seismic stations deployed to record these earthquakes. Site responses are derived using two different datasets and approaches: (1) a modified generalized inversion technique (GIT) based on the S-wave Fourier amplitude spectra from earthquakes; and (2) application of the quarter-wavelength approximation (QWA) using estimates of average shear-wave velocities in the upper 30 m, known as VS30. We find that site amplification estimates based on the two techniques are roughly consistent with one another (median of the amplification ratio = 0.92) over frequencies where a quarter-wavelength corresponds to ∼30 m depth. The site amplification factors from the two approaches are found on average to be about 3 at the quarter-wavelength frequency (QWF). These site amplification estimates are not well correlated with geologic characteristics including rock type and geologic age. Finally, QWA values at six sites do not match GIT site amplification at the QWF (outside of ± median absolute deviations boundary), which we attribute to a combination of the underlying assumptions of the QWA, uncertainty in VS30 estimates, and unmodeled site response complexity.

A Local Magnitude Scale from Borehole Recordings with Site Correction of the Surface to Downhole

Abstract The Central Weather Bureau of Taiwan deployed 62 borehole seismic stations equipped with accelerometers and broadband seismometers by the end of 2018. Currently, a large number of earthquake records has been accumulated because of the high seismicity rate of Taiwan. These records can be used to detect microseismicity because the background seismic noise level is lower at downhole stations than surface stations. However, the magnitudes of the waveforms recorded by the downhole stations are lower than those of surface stations because of near-surface site effects. In Taiwan, local magnitude (ML) determinations use an attenuation function derived from surface stations, and ML will be underestimated if this attenuation function is used for downhole stations. Records of 14,653 earthquakes were used to determine site amplifications corresponding to site corrections of the surface to downhole. For all available earthquake–station pairs, a total of 5470 amplification factors satisfied condition of the incident angle less than 35°, which are used for further discussion in this work. The results reveal that amplification factors ranging from 1.11 to 6.07 can be used to describe site effects. These amplification factors are strongly correlated with VS30 (average shear-wave velocity for the top 30 m of strata). The amplification factor was used to revise station ML for downhole accelerometer (denoted MLB), and revised MLB (MLBNEW) was compared with ML from the surface accelerometer (denoted MLS). Results show that MLBNEW and MLS are similar. Using the derived site corrections of surface to downhole, the downhole seismograms can be used to directly determine ML, especially for the borehole broadband waveforms, enhancing detection capabilities for microearthquakes and improving the Taiwanese earthquake catalog.

Machine-Learning-Based Surface Ground-Motion Prediction Models for South Korea with Low-to-Moderate Seismicity

ABSTRACT Ground-motion prediction models (GMPMs) have been developed to estimate seismic intensity considering earthquake magnitude, source-to-site distance, site condition, and so on. This study proposes GMPMs to predict 5% damped pseudospectral acceleration (PSA) for 27 periods ranging from 0.01 to 10 s in Korea, based on three machine-learning techniques (i.e., artificial neural network [ANN], random forest [RF], and gradient boosting [GB]). We use 1189 ground motions recorded at 50 surface stations during the 77 earthquakes with a local magnitude (ML) greater than 3.0, including the Gyeongju and Pohang earthquakes with ML of 5.8 and 5.4, respectively. We compare the performances of the three machine-learning-based models and the classical regression-based model in terms of the coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE), standard deviation of residuals, and between-event and within-event residuals. The GB-based model shows the best performance. In addition, we analyze the working process of the GB-based model using variable importance and partial dependence (PD) plots. Among the five independent variables (ML, epicentral distance [Repi], average shear-wave velocity of the upper 30 m [VS30], focal depth, and slope angle) used in this study, ML and Repi are the most influential variables and show strong correlations with PSAs. We apply the GB-based model to three recent earthquakes larger than ML 3.0, and the model accurately predicts the PSAs at various stations. We also generate maps of estimated PSA (PSAest) values for the four periods (T = 0.01, 0.1, 1, and 3 s) for the scenario earthquake with an ML of 5.0. We provide a method for training the GB-based model using the Python library, which can enhance the ground-motion prediction not only in Korea but also worldwide, and an executable version of the validated GB-based model.

Seismic site classification of the Costa Rican Strong-Motion Network based on VS30 measurements and site fundamental period

In this paper, a new seismic site classification for the Costa Rican Strong-Motion Network (CRSMN) is proposed. The soil profile classification of the Costa Rican Seismic Code based on the average shear-wave velocity of the top 30 m (VS30) is used as a reference. The site fundamental period (Tf) is included as a parameter to complement the existing characterization. For this, the VS30 measurements from 52 accelerometric stations are related to the site fundamental period obtained through horizontal-to-vertical spectral ratios (HVSR) using ground motion records from the Costa Rican Strong-Motion Database. The H/V ratios are estimated with 5% damped acceleration response spectra and with traditional Fourier amplitude spectra from the S-wave window. From the relation between VS30 and Tf, different ranges of Tf are assigned to the existing soil profile classification and a graph with three-lines and four-areas is proposed to classify the stations of the CRSMN.

Velocity gradients choice affecting seismic site response in deep alluvial basins: Application to the Venetian Plain (Northern Italy)

Abstract The average shear-wave velocity of the first 30 metres of subsoil and the depth of the engineering bedrock are considered the key parameters for simplified seismic site response modelling. However, a reliable estimate of the site amplification should consider the entire shear-wave velocity profile from the ground surface down to the engineering bedrock. In deep alluvial basins, a typical geological context where the soil–bedrock interface may lie below the penetration depth of most common prospecting methods, only the shallow velocity profile can be defined in detail, while the deeper structures are commonly extrapolated with linear equations. The choice of a realistic interpolation between the shallow and deep soil still remains an open issue. We compute the 1D seismic site response of two sectors of the Venetian Plain (Northern Italy) characterised by gravelly and sandy deep formations. We model the 1D soil columns using theoretical non-linear gradients proposed in literature for deep alluvial basins. The numerical modelling results, in terms of strong motion parameters, show variations in the seismic site response up to 20%. The effect of the velocity gradients is also evaluated comparing the numerical simulations with real accelerometers recorded by a deep borehole seismometer and a seismic station located at the top of the borehole. These results demonstrate that the selection of the velocity gradient is crucial for seismic site characterisation of deep alluvial basins. In particular, the study suggests which is the most conservative gradient among the ones tested in terms of ground motion hazard estimation.

Characterisation of design spectra for vertical ground motion

Design recommendation on vertical ground motion offers dual challenges, namely the spectral shape and conditional peak-ground-acceleration. One way of recommending the vertical spectra is through V/H spectrum that can be multiplied with design horizontal spectrum. Seismic code recommendations do not explicitly account for the possible effects of magnitude (except EC8 Part-1) and epicentral distance. This paper is aimed to assess the possible effects of magnitude, epicentral distance and average shear wave velocity (representing the soil sites) on resulting V/H spectra. About 6,000 strong motion events are considered for this purpose. Resulting V/H and vertical spectra conditioned to the horizontal spectra are compared with the seismic code recommendations and prior-art. Also explored is the feasibility of possible recommendations on V/H spectra contingent on magnitude, epicentral distance and average shear wave velocity. Finally, the framework is assessed with respect to a strong motion event which was not included in the developmental database.

Peak Ground Acceleration Models Predictions Utilizing Two Metaheuristic Optimization Techniques

Peak ground acceleration (PGA) is frequently used to describe ground motions accurately to defined the zone is critical for structural engineering design. This study developed a novel models for predicting the PGA using Artificial Neural Networks-Gravitational Search Algorithm (ANN-GSA) and Response Surface Methodology (RSM). This paper grants the prediction of PGA for the seismotectonic of Iraq, which is considered the earlier attempt in Iraqi region. The magnitude of the earthquake, the average shear-wave velocity, the focal depth, the distance between the station, and the earthquake source were used in this study. The proposed models are constructed using a database of 187 previous ground motion records, this dataset is also utilized to evaluate the effect of PGA’s parameters. In general, the results demonstrate that the newly proposed models exhibit a high degree of correlation, perfect mean values, a low coefficient of variance, fewer errors, and an acceptable performance index value compared to actual PGA values. However, the composite ANN-GSA model performs better than the RSM model.