Seismic Microzonation Research Articles

Detailed seismic zoning of the East Kazakhstan region in the Republic of Kazakhstan

Kazakhstan is currently drafting new construction regulations that comply with the major provisions of the Eurocodes. Such regulations are created on the basis of seismic zoning maps of various degrees of detail, developed by our Institute of Seismology using a new methodological approach for Kazakhstan. The article is about creating the first normative map of the Detailed Seismic Zoning on a probabilistic foundation for the Republic of Kazakhstan's East Kazakhstan region. We carried out the probabilistic assessment of seismic hazard using a methodology consistent with the main provisions of Eurocode 8 and updated compared with that used in developing maps of Kazakhstan's General Seismic Zoning and seismic microzoning of Almaty. The most thorough and current data accessible for the area under consideration were combined with contemporary analytical techniques. Updates have been done to not only the databases being used but also the way seismic sources were shown, including active faults now. On a scale of 1:1000000, precise seismic zoning maps of the East Kazakhstan region were created for two probabilities of exceedance: 10 % and 2 % in 50 years in terms of peak ground accelerations and macroseismic intensities. The obtained seismic hazard distribution is generally consistent with the General Seismic Zoning of Kazakhstan's previous findings. However, because active faults were included and a thoroughly revised catalog was used, there are more pronounced zones of increased danger along the fault in the western part of the region. In the west of the territory, acceleration values also increased due to a more accurate consideration of seismotectonic conditions. Zoning maps are the basis for developing new state building regulations of the Republic of Kazakhstan.

Contribution of HVSR, MASW, and geotechnical investigations in seismic microzonation for safe urban extension: A case study in Ghabt Admin (Agadir), western Morocco

Ghabt Admin, located in western Morocco, is prone to seismic activity and site effects due to its position within an alluvial basin situated between two faulted mountain belts. The region has experienced several devastating earthquakes, including the 1960 Agadir earthquake that resulted in the loss of 12,000 lives and the destruction of over 75% of the city. Moreover, the area has recently undergone rapid urbanization, necessitating the implementation of seismic studies to make informed decisions regarding land use. This study aims to conduct the first seismic microzonation and site characterization studies by using HVSR, 1D-MASW, and geotechnical investigations. The datasets consist of 80 microtremors, 15 1D-MASW profiles, detailed geological observations, boreholes, and soil/rock identification tests. Due to challenges related to anthropogenic sources and soil heterogeneities, only 31 H/V measurements met the SESAME criteria. The HVSR results indicate the following: (i) the predominant peak frequency (f0) ranges from 1.4 to 15.7 Hz, with lower values (1.4–3 Hz) observed in the Oued Issen alluvial fans and the sand dune area, while moderate to high values (4–15.7 Hz) are found in the lacustrine limestone and Tagragra’s dome. (ii) The amplitude peak frequency (A0) ranges from 2 to 7.7, with higher values observed in the southwestern zone and certain parts of the glacis-fans zone, particularly in the Oued Issen zone. (iii) The seismic vulnerability index (Kg) ranges from 0.28 to 39.5. The Oued Issen area, which is composed of recent unconsolidated deposits and affected by the Oued Issen fault, exhibits high Kg values. Analysis of HVSR curve typology reveals complex geology. The VS30 map shows VS values ranging from 179 m/s to 830 m/s, classifying the study area into soil classes A, B, and C according to Eurocode 8. Furthermore, the 1D-MASW results are compatible with the HVSR results and the distribution of the geological units.

Seismic microzonation for Lembang fault hazard area in West Bandung Regency based on microtremor measurement

Lembang district in Bandung Regency is prone to seismic risk because it is in the vicinity of a very well-known active fault called the Lembang Fault. The effort to reduce the seismic risk requires knowledge of the dynamic properties of the soils, mainly derived from young volcanic rocks. This paper presents the results of a seismic microzonation study based on microtremor measurements. In total 195 microtremor data from single-station measurements were processed using the HVSR method to estimate the dominant frequency and amplification factors. Furthermore, the Rayleigh wave ellipticity inversion has also been used to estimate the corresponding Vs profiles. The HVSR results show that the dominant frequency for the Lembang District is 0.2 Hz or higher, and the amplification factors are dominantly higher than 3. Some areas also have a lower dominant frequency than 2 Hz, especially the area with thick soft sediments. Results of the inversion show that the shear wave velocities of subsoil layers for the upper 30 m vary from 250 m/s to 300 m/s, indicating site class D. Meanwhile, the areas with Vs30 less than 250 m/s are especially located north of the Lembang Fault. Thus, the area is likely to have a stronger ground response to earthquake shaking than the other areas in Lembang District.

Futuristic study on seismic response analysis of North Indian soils– A sustainable approach

India's growing population and extensive unscientific structures put the country at risk of suffering major casualties during earthquakes. To make buildings more earthquake-resistant, and develop safe and durable structures for future, we need seismic sustainability. For this purpose, Cities should adopt ‘seismic microzonation’, which includes Site response analysis (SRA). In this paper, SRA for eight places in Varanasi (India) was performed using the equivalent linear technique subjected to four significantly different strong motions (Bhuj, Uttarkashi, Chamba, and Kobe motion). Geotechnical data from various government and private entities have been gathered for this purpose. Analysis has been conducted using equivalent linear approach in DEEPSOIL software. The results of the study have been formulated in terms of surface time histories, response spectra, Fourier spectra and PGA along the depth. These findings may be applied to dynamic analysis and structural design, as well as the preparation of advanced dynamic lab tests. Furthermore, sites in Varanasi have been found to considerably enhance ground motion, thus a site-specific design approach must be implemented for important constructions.

Seismic microzoning in Novi Sad, Serbia – A case study in a low-seismicity region that is exposed to large and distant earthquakes

Seismic microzoning in Novi Sad, Serbia – A case study in a low-seismicity region that is exposed to large and distant earthquakes

Editorial: Seismic microzonation and risk reduction

Editorial: Seismic microzonation and risk reduction

NC92Soil: A computer code for deterministic and stochastic 1D equivalent linear seismic site response analyses

The extensive evaluation of the impact of local seismo-stratigraphic configurations on seismic ground motion presents significant challenges due to the necessity of considering the combined effects of uncertainty and small-scale lateral variability of the relevant parameters. To effectively explore these sources of uncertainty, a new Python-based computer program is proposed for one-dimensional seismic site response simulations, adopting the equivalent linear viscoelastic approach in the frequency domain. With respect to existing software, the code introduces new pre- and post-processing features, which also meet the specific requirements of seismic microzonation studies. Within the code, the complete spectrum of uncertainties related to local seismo-stratigraphic configurations, including lithotype successions, layer thicknesses, and seismic and geotechnical properties for the considered lithotypes, is managed by considering user-defined constraints and statistical properties of the relevant parameters. Additionally, a batch approach is offered, enabling the application of the procedure to an unlimited number of different scenarios. To demonstrate the potentiality of the proposed code, a comprehensive set of 90,000 local seismic site response analyses was conducted, showing a clear correlation between the amplification factors, the mean shear wave velocity in the upper 30 m, the fundamental frequency of the deposit and the depth to the seismic bedrock.

Development and application of neural network technology in solving geodynamic problems

The present study is aimed at searching the most effective, easy-to-use method for seismic zoning, in order to consider the ongoing environmental change in real time. The study demonstrates the relevance and necessity of tackling this problem, provides characteristics and peculiarities of current microzonation methods, and discusses the problem of seismic microzoning. The paper highlights traditional and neural network approaches as two directions in solving the problem, and determines their advantages and disadvantages. In addition, the paper provides significant arguments for applying the neural network approach and defines the perspectives for the solution. An intermediate problem of geophysics is suggested to be solved using the neural network approach. The current study results involved searching networks able to provide sufficient accuracy for obtaining pictures of geological sections and conducting analysis of predicted results for a number of neural networks. Multilayer perceptron is considered to give the most reliable results. The future work is supposed to develop an algorithm for building a map of seismic microzonation by means of neural network technology.

Probabilistic seismic microzonation for ground shaking intensity, a case study in Türkiye

Probabilistic seismic microzonation for ground shaking intensity, a case study in Türkiye

Shear modulus reduction and damping ratios curves joined with engineering geological units in Italy

Numerical simulations of seismic site response require the characterization of the nonlinear behaviour of shallow subsoil. When extensive evaluations are of concern, as in the case of seismic microzonation studies, funding problems prevent from the systematic use of laboratory tests to provide detailed evaluations. For this purpose, 485 shear modulus reduction, G\\G0(γ) and damping ratio, D(γ) curves were collected from multiple literature sources available in Italy. Each curve was associated with the related engineering geological units considered in seismic microzonation studies. A statistical analysis of the data was carried out with the aim of shedding light on the significant difference between the laboratory classification of samples and the macroscopic/engineering geological one, provided during seismic microzonation studies. Since the engineering geological classification plays a prominent role in extensive site response evaluations, the outcomes of the present work may be of help at least when preliminary seismic response estimates are of concern. The dataset provides reference information that can serve as key data for large-scale hazard assessments worldwide.

Preface

The 5th International Conference on Earthquake Engineering and Disaster Mitigation, ICEEDM 2022, was held on 28th-29th September 2022. The 5th ICEEDM in Gadjah Mada University was profoundly enjoying the collaboration with the joint-organizing committee with the Indonesian Earthquake Engineering Association (AARGI), International Association for Earthquake Engineering (IAEE), Japan Association for Earthquake Engineering (JAEE), Bandung Institute of Technology, Indonesian Islamic University, and Atmajaya University. The conference was supported by a scientific committee from four countries and twelve keynote speakers from five countries, i.e., Canada, Indonesia, Japan, Taiwan, and the USA.The 5th ICEEDM 2022 was held to provide an opportunity to share experiences and disseminate the latest research and development results related to earthquake engineering, which will be very useful for increasing knowledge and disaster mitigation policies. It is hoped that this conference will benefit all parties to minimize the risk of earthquake hazards in Indonesia and worldwide.The 5th ICEEDM 2022 proceeding contains papers written by academics, professionals, researchers, and students from Indonesia and Japan. Various research works related to the conference theme were presented during the conference. A total of 41 full papers accepted upon review for the proceeding publication are categorized into the following topics: A. Structural Engineering, including; Structural Earthquake Engineering, Structural Dynamics, Performance-Based Design and Evaluation, Structural Assessment and Retrofit, Seismic Devices and Applications, Non-engineered Buildings, Experimental & Numerical Modelling B. Geotechnical Engineering, including; Geotechnical Earthquake Engineering, Soil-Structure Interaction C. Seismological Engineering, including; Seismic Micro-zonation, Case Histories in Recent Earthquakes, D. Disaster Mitigation, including; Seismic Hazard and Tsunami Disaster Mitigation, Early Warning System, Post Disaster Recovery and Reconstruction, Community-Based Disaster Risk Reduction & Management

Determination of the contrast boundaries of the low velocity zone by analyzing the features of the dispersion curves of the Rayleigh wave velocities based on empirical dependencies

An important application of the multichannel surface wave (MASW) method is seismic safety assessment. The key parameters in the calculation of increments in the input of seismic microzoning are the thickness and average velocity of the soil mass lying on the base of more rigid rocks. To determine these parameters, we propose a new method for constructing horizontally layered models of the upper part of the geological section using the features (positions of extrema of the second derivative) of the dispersion curves of phase velocities of the Rayleigh surface wave, which, as shown by numerical experiments, are associated with the position of contrasting boundaries in the medium under study. (e.g., the boundary between soils and rocks). This approach is much simpler than the problem of recovering a horizontally layered model traditionally solved in the MASW method from a set of phase velocities for a sequence of frequencies and does not require an initial approximation and/or any restrictions on the possible values of the model parameters. In the case of two-layer and three-layer media, our approach is reduced to a simple and fast application of explicit formulas.

Seismic amplification effects induced by ancient shallow cavities underneath the urban area of the historical city center of Chieti, Italy

Anthropogenic cavities excavated just beneath the walkable floor (about 1–6 m depth) are present in many ancient urban centres, particularly in Europe and along the Mediterranean basin. The oldest caves are Roman constructions and have been used for different purposes over time (i.e., water storage, secret pathways, shelters against sieges, and wars). For this reason, Seismic Microzonation (SM) studies performed in urban areas must consider the presence of these holes in the subsoil, with their effects predicted through numerical simulations of local seismic response on the surface. In this study, we investigate the seismic effects of ancient anthropogenic cavities in Chieti city centre (Italy) through the cavity amplification factor (CAF). A parametric study was carried out on several different dynamic subsoil models. We define CAF as the ratio between the Acceleration Spectral Intensities on the surface and at the bedrock calculated in the period range of 0.1–0.5 s. The 2-dimensional parametric simulations were performed adopting the soil equivalent linear constitutive law by varying: (1) shear wave velocity values of subsoil, (2) cavity dimensions, (3) cavity depths, (4) cavity lining shear wave velocity values. The CAF plots were calculated on the surface for cavity sizes (width x height) varying from 4 × 5 m to 7 × 9 m. Our study demonstrates that CAF values are relevant only in the period range of 0.1–0.5 s. In particular, results show that: (1) CAF values vary from 1% to 15%; (2) the maximum CAF is felt away from the cavity axis at a distance equal to about 1.5 times the cavity width (L); (3) the maximum difference in CAF values at the surface is equal to 40% within a horizontal distance from the cavity axis ranging from 6 to 14 m. Finally, the case study of the city centre of Chieti (Abruzzo Region) is considered to show how to draw CAF maps for microzonation purposes.

Geophysical Subsoil Characterization and Modeling Using Cluster Analysis for Seismic Microzonation Purposes

In the municipality of Enna, 80 HVSR measurements were performed, and some of these were combined with MASW seismic measurements, which made it possible to constrain the data inversion and obtain significant shear wave velocity models. A reconstruction of the depth of the seismic bedrock was performed for the whole territory, showing different depths for the higher and lower areas, as evidenced also by the Vseq parameter map. The frequency peaks identified in the H/V curve were analyzed through a cluster analysis algorithm to evaluate similarities that allow these peaks to be divided according to their stratigraphic origin. A non-hierarchical analysis algorithm modified in such a way as to avoid any a priori choice that could influence the partition has been used. The cluster analysis made it possible to divide the frequency peaks into five groupings, each of which was then associated with a seismic discontinuity, according to the geological contacts expected in the subsoil. Finally, the inversion of the data made it possible to reconstruct the geometries of these geological contact surfaces and to reconstruct a 3D model of the subsoil, which agrees well with the surface geology of the area.

Seismic microzonation mapping of Greater Vancouver based on various site classification metrics

The goal of the multi-year seismic microzonation mapping project for Greater Vancouver, British Columbia, Canada, is to produce seismic hazard maps inclusive of local site effects, in particular seismic hazard specific to one-dimensional site response and three-dimensional Georgia sedimentary basin amplification, as well as liquefaction and landslide hazard potential. We explore the variability in key seismic site characterization measures most often used for seismic microzonation mapping to evaluate the impact on mapping and communication of seismic microzonation of Greater Vancouver. This study focuses on the comparison of seismic microzonation maps of Greater Vancouver based on up to three seismic site term parameters and their associated classification schemes: 1) the time-averaged shear-wave velocity (Vs) of the upper 30 m (Vs30) and associated Canadian National Building Code (NBC) site class; 2) Vs30-based site classification proposed for the updated Eurocode 8; 3) site period (T0) determined from microtremor site amplification spectra; and 4) a hybrid site classification based on T0 and the average Vs and thickness of soil. 810 Vs30 and 2,200 T0 values are determined to evaluate sub-regional differences in these important seismic site parameters in Greater Vancouver. We find that the seismic microzonation of Greater Vancouver depends on the chosen seismic site parameter (Vs30, T0, or a combination of parameters) and that classification schemes with greater class divisions are beneficial to communicating the great variability in seismic site conditions in Greater Vancouver. We recommend that either one hybrid classification map or two classification maps of Vs30 and T0 together are required for effective communication of the seismic microzonation of Greater Vancouver.

Near-surface characterization using distributed acoustic sensing in an urban area: Granada, Spain

SUMMARY The Granada Basin in southeast Spain is an area of moderate seismicity. Yet, it hosts some of the highest seismic hazards in the Iberian Peninsula due to the presence of shallow soft sediments amplifying local ground motion. In urban areas, seismic measurements often suffer from sparse instrumentation. An enticing alternative to conventional seismometers is the distributed acoustic sensing (DAS) technology that can convert fibre-optic telecommunication cables into dense arrays of seismic sensors. In this study, we perform a shallow structure analysis using the ambient seismic field interferometry method. We conduct a DAS array field test in the city of Granada on the 26 and 27 August 2020, using a telecommunication fibre. In addition to the existing limitations of using DAS with unknown fibre-ground coupling conditions, the complex geometry of the fibre and limited data recording duration further challenge the extraction of surface-wave information from the ambient seismic field in such an urban environment. Therefore, we develop a processing scheme that incorporates a frequency–wavenumber (f−k) filter to enhance the quality of the virtual shot gathers and related multimode dispersion images. We are able to use this data set to generate several shear-wave velocity (VS) profiles for different sections of the cable. The shallow VS structure shows a good agreement with different geological conditions of soil deposits. This study demonstrates that DAS could provide insights into soil characterization and seismic microzonation in urban areas. In addition, the results contribute to a better understanding of local site response to ground motion.

Numerical investigation of influence of near-surface lateral heterogeneities on propagation of Rayleigh waves

Recent research on earthquake disasters has provided evidence that Rayleigh waves play a crucial role in causing damage to both underground and surface structures during earthquakes. In this study, we utilize the finite difference method to investigate the impact of the interaction between Rayleigh waves and near-surface heterogeneities on seismic ground response. Specifically, we analyze the effects of different types of cavities (vacuum cavity, water-filled cavity, and soft-soil-filled cavity) as well as granite boulders on the propagation of Rayleigh waves. Furthermore, we examine how the buried depth and size of the heterogeneous structure, as well as the distance from the center of the structure, influence the amplitude and frequency spectrum of Rayleigh waves. Our numerical results reveal that the presence of cavities leads to larger amplitudes of Rayleigh waves compared to the free field, with the amplification effects becoming more pronounced as the cavities become shallower. Although the amplitude of Rayleigh waves generally decreases with increasing offset, the complex interaction between Rayleigh waves and the heterogeneous structure causes significantly smaller amplitudes on the far offset side of the cavity, while the near offset side exhibits significant amplification phenomena. Moreover, the characteristics of the Rayleigh-waves field vary depending on the filling material inside the cavities. For instance, the wall of a water-filled cavity clearly shows the presence of Scholte waves, whereas a soft-soil-filled cavity exhibits an energy traps phenomenon. Additionally, the conversion phenomena of Rayleigh waves generated by these two types of cavities are characterized by strong energy and smooth continuity. On the other hand, granite boulders have a relatively minor influence on Rayleigh wave propagation at the far-source side, except for partial scattering of waves. However, at the near-source side, significant amplitude amplification occurs in the vicinity of granite boulders, particularly for the high-frequency radial component. Therefore, considering the intricate interaction between Rayleigh waves and near-surface lateral heterogeneities, the findings of this study can serve as valuable guidance for seismic micro-zonation and the design of observation systems using the high-frequency surface-wave method.

A fusion approach for evaluating ground conditions for seismic microzoning at the Egyptian Solar Park in Benban, Aswan

Seismic microzoning is the process of mapping out and comprehending the differences in ground motion due to earthquakes in a certain location. Accurate seismic microzoning is vital for the development and safety of buildings and infrastructure in earthquake-prone locations. In this work, we present the application of microtremors, multichannel analysis of surface and machine learning approaches for seismic microzoning at Benban Solar Park in Aswan, Egypt. The findings of the investigation indicated that the ground at Benban Solar Park was generally stiff, with certain regions having stronger stiffness and damping qualities than others. The data also indicated variances in the ground conditions at various sites inside the solar park, with certain regions having a greater risk of ground motion due to earthquakes. Overall, the combination of microtremors, multichannel analysis, and machine learning has shown to be an excellent strategy for correctly and effectively mapping out the ground conditions at Benban Solar Park and assuring the safety and structural integrity of the solar power plants at the park. Moreover, the results of the research could be used to guide the design and construction of the future solar power plants at the park and to examine the safety and structural integrity of the solar park. Furthermore, the application of these techniques not only ensures the safety and structural integrity of the solar power plants at Benban Solar Park, but also promotes sustainable development by providing valuable information for the design and construction of future solar power plants at the park, in line with the principles of environmentally-conscious and responsible development.

Contribution to the seismic microzonation of Lisbon based on the integration of geological, geophysical, and geotechnical data

Lisbon has been affected by several moderate to strong earthquakes that caused considerable damage and produced significant economic and social impacts (e.g., the November 1st, 1755, earthquake). Studies on the potential damage due to a seismic event have been done considering Lisbon's moderate to high seismic hazard, but the seismic site effects have not yet been investigated at the city scale. The local ground conditions can locally modify the characteristics of surface seismic motion.Based on a multidisciplinary dataset composed of surface geology, a geotechnical database, and a geophysical database that compiles all the available geophysical tests carried out in Lisbon, an integrated approach to seismic ground characterisation was performed.A regression analysis of the shear-wave velocity values compiled in the geophysical database was done for each geological unit. The peak frequency distribution in the city, assessed from the ambient vibration measurements, showed a pattern in peak frequency variation. It decreases from the oldest to the most recent geological formations that outcrop in the SW-NE direction. Three zones based on peak frequency value distribution were proposed.An estimation of the impedance contrast depths was computed through two processes, considering the previous results: (i) the shallower contrast depth was assessed through a sharp variation of NSPT values available in the geotechnical database, and (ii) the deeper contrast depth was estimated based on geology data and deep borehole information. The results showed that for the upper ∼100 m of depth, a consistent relationship between the contrasts identified through different data was obtained, even if uncertainty increased with depth.

Investigating the effects of structural parameters on seismic aggravation of two-dimensional sedimentary valleys

The valley-induced ground motion amplification has been well-documented and validated in previous studies, however, it remains challenging to fully integrate them into ground motion models, seismic hazard assessment, and engineering practice. In this paper, we first investigate the 2D seismic response in the Mygdonian basin, Greece, and compare the numerical results with comparable studies to validate the feasibility of our numerical toolbox in quantifying ground motion aggravation. In order to orientate towards more generally applicable conclusions rather than a site-specific, 32 idealized three-layered sediment-filled trapezoidal valleys are constructed with reference to the geological structure of the Mygdonian basin, aiming to explore the sensitivity of their additional effects attributes to the subsurface structure parameters of the valley. The half-width of the valley surface is divided into three subregions according to the wave propagation path, similar to the concept of seismic microzonation. The multivariate analysis reveals that the seismic response of each sub-region has differential or even diametrically opposite sensitivity to these structural parameters. The aggravation factor of the valley edge region shows a significant tendency to decrease with increasing edge angle, but poor sensitivity to the shape factor. On the contrary, the aggravation factor of the central region is positively correlated with the shape factor, but largely independent of the valley edge angle. Furthermore, we performed a quantitative statistical analysis and gave a simple correspondence between the seismic aggravation factor and structural parameters for different period intervals, which is an acceptable quantitative scheme from an engineering point of view.