Seismic Site Classification Research Articles

Subsurface velocity structures at the Egyptian seismological network stations retrieved by diffuse field assumption for Earthquakes

Retrieving detailed subsurface velocity structures down to the seismic bedrock at any given site is a crucial step to delineate the site amplification factors accurately and precisely. The present research work contributes first new estimations for detailed velocity structures down to the seismic bedrock beneath the Egyptian National Seismological Network (ENSN) stations, which are distributed in Egypt nationwide. We used the diffuse field assumption for earthquakes to reproduce the horizontal to vertical spectral ratios (EHVSR) at these stations. We accepted waveform database of 424 earthquakes recorded at 75 ENSN stations. After achieving the inverted subsurface velocity structures, we establish site-specific frequency-depth regression and map the VS30 and seismic bedrock depth beneath Egypt. Because of comparability regarding the seismic site class of B and C, the regression coefficients of the newly established frequency-depth regression exhibit similarity with those achieved from previous regressions in Japan. Furthermore, we observe modest consistency between the seismic bedrock depths and the various geologic features, particularly agreement between basin-shape seismic bedrock depths and the existence of Cretaceous and Jurassic extensional basins. Our findings suggest that the Precambrian basement rocks can be interpreted as the seismic bedrock in Egypt. One of the most significant obstacles in the present work is the low-dense distribution of ENSN stations nationwide. However, the achieved results raise new questions and challenges regarding precise and accurate future estimations for site amplification calculations at different localities in Egypt, particularly for urban planning by engineers.

Seismic site classification based on H/V spectral ratio from strong ground motion records: the urban areas of Bursa province

Seismic site classification based on H/V spectral ratio from strong ground motion records: the urban areas of Bursa province

An Alternative Fast Seismic Site Classification Method Based on Geological Maps: A Case Study in Shandong Province, North China

An Alternative Fast Seismic Site Classification Method Based on Geological Maps: A Case Study in Shandong Province, North China

Seismic site classification of Samandag district, Hatay province, Turkey, based on the HVSR method and equivalent linear ground response analysis

Seismic site classification of Samandag district, Hatay province, Turkey, based on the HVSR method and equivalent linear ground response analysis

Seismic site characteristics for geotechnical engineering purposes: Case study, South of Ras Samadai, Red Sea, Egypt

Nowadays, geophysical techniques are widely employed in geotechnical research. Among the techniques that are frequently employed is the Multichannel Analysis of Surface Waves (MASW) technique, it aims to depict spatial differences in physical characteristics of the subsurface layers. The aim of the current research is to produce multiple maps for the seismic site classification (SSC) and dynamic characteristics along the study area located on the Red Sea shoreline of Egypt, south of Ras Samadai. In order to achieve this goal MASW surveys have been conducted in the current study, and corresponding 1D-shear wave velocity profiles have been generated. Consequently, to trace the stiffness change in the subsurface layers, the study provides a series of maps using the shear wave velocity (Vs) values at different depths to help the geotechnical engineers to identify and mitigate the geotechnical potential risk. Additionally, The Vs30 map for the study site is prepared and classified in accordance with the EC8 classification system. Referring to the obtained Vs30 map, the study region is mostly described as category B, with limited zones falling under classes A and C. Moreover, the soil's dynamic properties, including soil amplification and site natural period have already been taken in consideration. Approximately, the whole region exhibits low-to-moderate amplification values. However, two constrained zones are significantly more susceptible to amplification. Furthermore, the studied area is divided into six separate zones according to the obtained isoperiod map. The obtained results could be applied to engineering problems contribute to soil to avoid the probable obstacles during construction on soft soil.

Probabilistic Evaluation of a Seismic Site Class from Electrical Resistivity Test Data

Probabilistic Evaluation of a Seismic Site Class from Electrical Resistivity Test Data

Reliable assessment of seismic site class using stochastic approaches

Reliable assessment of seismic site class using stochastic approaches

U.S. National VS30 Models and Maps Informed by Remote Sensing and Machine Learning

Abstract The shear-wave velocity time averaged over the upper 30 m (VS30) is widely used as a proxy for site effects, forms the basis of seismic site class, and underpins site-amplification factors in empirical ground-motion models. Many earthquake simulations, therefore, require VS30. This presents a challenge at regional scale, given the infeasibility of subsurface testing over vast areas. Although various models for predicting VS30 have thus been proposed, the most popular U.S. national, or “background,” model is a regression equation based on just one variable. Given the growth of community data sets, satellite remote sensing, and algorithmic learning, more advanced and accurate solutions may be possible. Toward that end, we develop national VS30 models and maps using field data from over 7000 sites and machine learning (ML), wherein up to 17 geospatial parameters are used to predict subsurface conditions (i.e., VS30). Of the two models developed, that using geologic data performs marginally better, yet such data are not always available. Both models significantly outperform existing solutions in unbiased testing and are used to create new VS30 maps at ∼220 m resolution. These maps are updated in the vicinity of field measurements using regression kriging and cover the 50 U.S. states and Puerto Rico. Ultimately, and like any model, performance cannot be known where data is sparse. In this regard, alternative maps that use other models are proposed for steep slopes. More broadly, this study demonstrates the utility of ML for inferring below-ground conditions from geospatial data, a technique that could be applied to other data and objectives.

Seismic site classification of Nakhon Nayok City, central Thailand, using the MASW technique

Shear-wave velocity (Vs) of soils in Nakhon Nayok City, Central Thailand were determined using the Multi-Channel Analysis of Surface Wave technique. The Vs. of 35 tested sites were weighted average to 30 m depth based on the National Earthquake Hazards Reduction Program (NEHRP) criteria, which revealed NEHRP site classes C, D, and E within the study area. Soil class C was found in the north of the city. Moreover, most of the residential area of Nakhon Nayok City is positioned on soil classes D and E. The soil in the area of study has an amplification value ranging from 1.4 to 3.9. The central and southwestern parts of the city, which mainly consist of soft sediments, have a higher amplification value than that in the northern part, which mainly consists of coarse grain soils of colluvial deposits. Based on the NEHRP and amplification value, the Nakhon Nayok City area will experience some effect from ground shaking from nearby and far away earthquake seismic sources.

Field and laboratory measurements of shear wave velocity in unsaturated soils

Shear wave velocity measurements in soil are important for assigning site soil profiles to seismic site classes and for calculating other dynamic soil properties. The seismic cone penetration test (SCPT) is commonly used to determine shear wave velocity profiles in the field. In the laboratory, bender elements provide an easy means to measure shear wave velocity of soil specimens from discrete depths. In this study, shear wave velocity measurements obtained from unsaturated soil profiles in the field and on field samples in the laboratory under similar stress conditions were analyzed and compared. Additionally, the influence of seasonal changes on the behavior of shear wave velocity was investigated. Comparisons of shear wave velocities from the field and laboratory were favorable for similar moisture and stress conditions. However, results showed that as the degree of saturation increases and suction decreases the shear wave velocity can decrease significantly.

Site response and liquefaction hazard analysis of Hawassa town, Main Ethiopian Rift

The study area is located in one of the most earthquake prone regions in southern Ethiopia, which is characterized by small-to-intermediate earthquake occurrences causing damage to buildings. Predicting liquefaction hazard potential and local site effects are imperative to manage earthquake hazard and reduce the damage to buildings and loss of lives. The objectives of this work were to perform the equivalent linear response analysis (ELA) and shear wave velocity (Vs.)-based liquefaction hazard analysis and classify the site into different seismic site classes based on the European and American codes. The SPT-N and Vs.30 values showed the site falls in the C and D classes based on the NEHRP (2015) code but falls in the B and C classes based on the EC8 (2003) code. The susceptibility of liquefaction was evaluated using grain size analysis curves. Moreover, peak ground acceleration (PGA), spectral acceleration (SA), and maximum strain (%), which are very critical to understanding the local site effects, were estimated by the DeepsoilV.7 program. The cyclic stress ratio and cyclic resistance ratio were used to calculate the factor of safety (FS). A liquefaction potential index (LPI), probability of liquefaction (PL), and probability of liquefaction induced ground failure (PG) were used to assess the probability of liquefaction. The peak ground acceleration (g) values ranged from 0.166 to 0.281 g, whereas spectral acceleration (g) was found to be high at 0.1–1s. The liquefaction susceptibility screening criteria revealed that the study area is highly susceptible to liquefaction. FS is < 1 for a liquefied site, but FS is > 1 for non-liquefied sites. In comparison to non-liquefied sites, the liquefaction forecast site has a liquefaction potential index value of 0–54.16, very likely high PL, and high PG. The findings will be helpful in the design of structures and in solving practical challenges in earthquake engineering.

Correlation between SPT-N and shear wave velocity (VS) and seismic site classification for Amaravati city, India

The present study proposes a set of correlations between standard penetration number (SPT-N) and shear wave velocity (VS) using nonlinear regression analysis. These correlations have been developed for different categories of soil for Amaravati city. This study area is the current de facto seat of government of the Indian state of Andhra Pradesh, India. For this study, SPT-N data has been obtained from 400 boreholes distributed across the city of area 217.23 km2. Most of the boreholes considered for this study have a boring depth of 25 m to 45 m below the recorded ground surface. A comparison between the proposed correlations with existing worldwide accepted correlations has been performed to check the authenticity of this study. In addition to this, Vs obtained from the recommended correlations have been validated with the Vs obtained from 30 microtremor tests as well as established graphical methods. Furthermore, the seismic site classification of the study area has been conducted using the developed correlation for all soils. It is observed that the major part of Amaravati city falls under class D as per the National Earthquake Hazard Reduction Program (NEHRP) provisions. The average SPT-N and VS distribution across the city has also been generated at depths of 5, 10, 15, 20, 25, and 30 m. The outcomes of the study can be further used for the design of earthquake-resistant structures, seismic hazard studies, estimation of ground movements, and generation of site-specific synthetic ground motions.

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.

Measurement uncertainty of shear wave velocity: A case study of thirteen alluvium test sites in Taipei Basin

Field seismic methods are widely applied to site investigations for seismic design. The most often used ones are cross-hole, down-hole, SCPT, suspension P–S logging, and surface wave methods. The choice of seismic methods has a variety of technical and cost considerations. However, the measurement uncertainty among resulting shear wave velocities by above methods are rarely statistically characterized with mathematical models and sound database in the literature, even though it is an important factor to consider before choosing a method. In this study, thirteen alluvium sites in Taipei Basin were chosen and carefully planned to simultaneously measure the velocity profiles using each of the five most common seismic methods with conventional shear wave triggering techniques. Using the data from the test and statistical models, the differences between seismic methods were quantified as the calibrated measurement uncertainty, which can be used as a reference for selecting an appropriate method for measuring shear wave velocity. Finally, the effect of measurement uncertainty on seismic site classification and simplified soil liquefaction potential evaluations based on shear wave velocity was investigated.

Shear wave velocities of prominent geologic formations in the Nelson-Tasman region

This paper presents the development of representative shear wave velocity profiles for the prominent geologic formations in the Nelson-Tasman region of New Zealand. Shear wave velocity (VS) profiles to depths of up to 100 m were developed at over 50 sites using a combination of active source and passive source surface wave testing. Using this data and regional geologic information, VS-depth functions were developed for six of the prominent geologic formations. Comparison with existing VS-depth functions from New Zealand and international studies highlighted the significantly higher shear wave velocities of the deposits in this region. VS exceeded 750 m/s for the Moutere Gravels and Port Hills Gravels at relatively shallow depths, representative of rock deposits. However, while the Port Hills Gravels transition to a conglomerate rock below depths of 30 m or less, the Moutere Gravel formation is an uncemented clay-bound gravel. The young gravel and sand deposits have VS higher than those from other regions. As the region is thought to have undergone cycles of geologic uplift, the resulting over-consolidation of these deposits could explain the high VS. Horizontal-to-vertical spectral ratio testing was not able to characterise the fundamental site period across the region, likely due to the weak impedance contrast that would exist at the gravel-rock interface at depth. These outcomes highlight the importance of regional geotechnical and geophysical characterisation to constrain the salient features that control potential seismic site amplification and site classification.

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.

HVSR-based Site Classification Approach Using General Regression Neural Network (GRNN): Case Study for China Strong Motion Stations

ABSTRACT Seismic site classification, which is fundamental for site-specific seismic hazard assessment, also plays an important role in accurate interpretation of ground motion data. However, detailed borehole information is not always available in many countries, e.g., China. Therefore, this study investigated application of the generalized regression neural network (GRNN) method to seismic site classification using China strong motion stations as example case. First, stations from KiK-net in Japan were classified based on their borehole information and individually assigned to I, II, III, and IV site classes as defined in Chinese seismic code. Then, mean horizontal-to-vertical spectral ratio (HVSR) curves for each site class were calculated as reference patterns. The overall recall rates for I, II, and III sites could reach 66.60%, 67.57%, and 68.42%, respectively, regarding use of KiK-net stations. The GRNN site classification scheme was validated using borehole information of K-NET stations, with recall rates for I and II site classes reaching 68% and 60%, respectively. Finally, based on HVSR curves calculated using strong ground motion data acquired during 2007–2015 in China, the site conditions of 167 National Strong Motion Observation Network System stations were estimated using the GRNN classification scheme. The results were partially validated using borehole information of 73 stations. The similarity between the mean HVSR curves and reference pattern curves indicated that the GRNN seismic site classification scheme is robust and could produce plausible results succinctly.

Evolution of Seismic Site Classification According to the Criteria in Chilean Design Codes

Design codes establish seismic site classifications to determine the seismic demand of a structure according to the response of the soil foundation under the action of earthquake ground motions; the site classification can even condition the feasibility of a project. The occurrence of great earthquakes in Chile has tested its design codes, generating much information and experience regarding the seismic design of structures that have allowed researchers to identify variations in seismic demands according to the kind of ground foundation and to propose seismic site classification methods in Chilean regulations since the 1930s; countries in the vanguard of seismic design, such as the USA, Japan, and New Zealand, proposed methods even earlier. In this document, the evolution of methodologies for seismic site classification according to the criteria in Chilean codes is analysed from their implementation in the 1930s to the most recently proposed design code NCh 433, 2018–2021. Although the distinctive features of each country shape the criteria in their design codes, clear knowledge of the evolution of established criteria from their origins is considered an important tool that contributes to the better understanding, interpretation and application of the seismic site classification methodologies contained in a design code with better criteria. Likewise, the review indicates a distinct need to conduct a continuous evaluation of the classification criteria supported by records of new earthquakes, as well as by physical and numerical models that allow incorporating variables which condition the response of the terrain such as topography, lateral heterogeneities, and basic effects.

Significant duration predictive models developed from strong‐motion data of thrust‐faulting earthquakes recorded in Mexico City

AbstractPredictive models for estimating strong‐motion duration in sites characterized by soft‐soil profiles are presented in this paper. The models were developed using a strong‐motion database that includes observations from subduction interface earthquakes that occurred from 1989 to 2020 and recorded in Mexico City, which is located at source‐to‐site distances up to 600 km. A linear mixed‐effects regression model, which is a statistical fitting procedure that allows to consider the correlation structure of grouped data, was used to develop the predictive models. Relative significant duration was selected to measure strong‐motion duration. This measure can be directly associated with the accumulation of energy of the ground movement. The proposed predictive models relate relative significant duration with moment magnitude, either hypocentral distance or closest distance to the rupture plane, and dominant period of the soil. Regression analyses were performed grouping the ground‐motion data by both seismic event and site class. Model assumptions, such as homoscedasticity, normality, and linearity of effects, were verified from residual analyses. From the results, the expected value of the natural logarithm of relative significant duration was found to be ∼1.2 times greater for an earthquake with a moment magnitude equal to 8.0 than for one of 6.0. An insightful discussion about the sources and character of the uncertainties detected in the proposed predictive models is also presented in this study. The predictive models proposed in this paper are of valuable application in seismic and structural engineering because they allow to circumscribe properly the dimension and randomness of strong‐motion duration.

Seismic site classification from HVSR data using the Rayleigh wave ellipticity inversion: A case study in Singapore

Shear wave velocity (Vs) profile is one of the critical geotechnical measurements of soil layers for seismic hazard assessment and liquefaction potential evaluation. Enhancing the effectiveness of in-situ Vs profiling by reducing time and cost is of great interest. For that reason, this study aims at assessing Vs profile generation from a single-station three-component geophone with additional borehole log data for constraining parameter space. Based on multichannel analysis of surface waves (MASW), and microtremor array Measurements (MAM) conducted previously at seven sites located in Bukit Timah Granite, Singapore, this study utilized HVSR signals for Rayleigh wave ellipticity (ellipticity curve) inversion with additional inversion constraint using borehole log data. The resulting Vs profiles and reference Vs profiles from MASW and MAM were quantitatively compared using average Vs of 30 m (Vs30). The profiles generated from ellipticity curve inversion revealed a good agreement with Vs reference profiles. Vs30 based site classification results also indicated a good fit of two test results. Therefore, HVSR measurements for further ellipticity curve inversion, with already available borehole log data for constraint, is considered as a promising cost and time-effective site classification approach.