Ground Motion Amplification Research Articles

Insights into the conditions of application of noise-based spectral ratios in a highly industrialized area: a case study in the French Rhone Valley

SUMMARY The local ground motion amplification related to the geology at a specific site (i.e. the so-called site effects) may be classically quantified through the SSR (standard spectral ratio) technique applied on earthquake recordings. However, such a quantification might be challenging to carry out in low-to-moderate seismicity regions. Methods based on background ambient noise, such as noise-based standard spectral ratio (SSRn), might be of great interest in these areas. But noise-derived amplification is particularly sensitive to local anthropogenic sources, which may introduce biases in the evaluation of site effects by dominating the geological effects, especially for frequencies higher than 1 Hz. A hybrid approach (SSRh), developed to reduce biases in noise-based spectral ratios by combining classical earthquake-based spectral ratio (SSR) and SSRn, was recently introduced and relies on a site reference. We here investigate the applicability of SSRn and SSRh in a heavily industrialized environment in the Tricastin Valley (south-east France), where critical facilities are located. We continuously recorded ambient noise from 2020 February to March on a 400-sensor seismic array covering an area of about 10 km by 10 km. We demonstrate that SSRn and SSRh computed below 1 Hz are able to reproduce amplification factors provided by SSR. By contrast, at frequencies higher than 1 Hz, SSRn strongly deviates from SSR. SSRh shows closer results to SSR but presents a dependence to the choice of the local site reference, thereby questioning the possibility to use SSRh blindly to estimate the local amplification in our context. These discrepancies reflect the impact of local anthropogenic sources. We therefore introduced a two-step workflow to mitigate the influence of local sources. The first step is to define a characteristic time window to optimally isolate significant transient signals. The second step consists in selecting the time segments that do not contain these transients with a clustering-based approach. By applying this workflow, we were able to remove some strong anthropogenic transient signals likely to be generated by local sources at some sites and therefore to locally improve the amplification assessment through noise-based spectral ratios. However, stationary sources, whose impact cannot be removed through our procedure, remain a major issue. This study provides some insights into the application of SSRn and SSRh in noisy industrialized areas, especially regarding the impact of local noise sources. It illustrates the difficulty of having a procedure for mitigating the impact of these sources that is efficient everywhere inside such a complex anthropized environment, where different types of sources (including stationary sources) cohabit.

Spatial coherency and amplification effects of ground motion with tunnel site based on multidimensional autoregressive model

The traditional periodic diagram method is primarily used to solve ground motion coherence coefficients. However, in this method, power spectra need to be artificially smoothed, which will result in an abhorrent situation. To solve this key problem, this study uses the dynamic centrifuge model test results with a circular tunnel completed by Schofield Centre (University of Cambridge) as the basic data. The multidimensional autoregressive (AR) model is used to replace the periodic diagram method for computation, and its rationality is evaluated and verified from many perspectives. The difference between the results of the two methods under the condition of tunnel sites in multiple dimensions is discussed from the perspectives of the reconstruction effect, coherence coefficient, and the site amplification effect of records. The results are as follows: The multidimensional AR model can realize the accurate reconstruction of strong motion acceleration records. The coherence coefficient calculated by the AR model is generally smoother than that calculated by the periodic diagram method, which is conducive to fitting and inducing the parameters of empirical models in subsequent research. Under EQ1–EQ4, the ground motion amplification coefficient of each vibration mode first decreases and then increases from the base to the surface. The AR model is more effective than the periodic diagram method in reflecting the importance of the influence of higher-order modes on site amplification.

The Importance of Assessing the Geological Site Effects of Ancient Earthquakes from the Archaeoseismological Point of View

Earthquakes have and continue to, occur worldwide, though some places are affected more than others by earthquake-induced ground shaking and the same earthquake can cause more damage in one area than in nearby locations due to site-specific geological site conditions, also known as local site effects. Depending on the chronology of the earthquakes, various disciplines of seismology include instrumental and historical seismology, archaeoseismology, palaeoseismology and neotectonics, each focusing on using specific sources of information to evaluate recent or ancient earthquakes. Past earthquakes are investigated to expand the pre-instrumental and instrumental earthquake catalog and better evaluate a region’s seismic hazard. Archaeoseismology offers a way to achieve these goals because it links how ancient civilizations and their environment might have interacted and responded to past earthquake-induced ground motion and soil amplification. Hence, archaeoseismology explores pre-instrumental (past) earthquakes that might have affected sites of human occupation and their nearby settings, which have left their co-seismic marks in ancient manufactured constructions exhumed by archaeological excavations. However, archaeoseismological observations are often made on a limited epicentral area, poorly constrained dated earthquakes and occasionally on unclear evidence of earthquake damage. Archaeological excavations or field investigations often underestimate the critical role that an archaeological site’s ancient geological site conditions might have played in causing co-seismic structural damage to ancient anthropogenic structures. Nevertheless, the archaeological community might document and inaccurately diagnose structural damage by ancient earthquake shaking to structures and even estimate the size of past earthquakes giving little or no consideration to the role of geological site effects in addressing the causative earthquake. This mixture of factors frequently leads to imprecise estimates of the size of ancient earthquakes and unlikely earthquake environmental impacts, leaving unexplained the location and the moment magnitude of the causative earthquake. Hence, it is essential not to rely solely on earthquake intensities based on archaeologically documented co-seismic damage without assessing the nature of the observed structural damage and the contribution of the geological site effects. This paper explains the geological site effects concept to archaeologists unfamiliar with the notion. It clarifies its role in assessing ground shaking, soil amplification and earthquake intensity by past earthquakes and how and why the geological site effects can be estimated when a site is thought to have been struck by an earthquake. Hence, the geological site effects must be considered when archaeological excavations describe and interpret destruction layers. Conversely, engineers and seismologists dealing with seismic hazard risk assessment must pay close attention to archaeological investigations assessing earthquake intensities and locations based on field evidence of damage to structures attributed to past earthquakes, because the geological site effects might have been factored in inaccurately or not at all.

Shear wave velocity estimation in the Bengal Basin, Bangladesh by HVSR analysis: implications for engineering bedrock depth

The S-wave velocity (VS) in the Bengal Basin, Bangladesh has not been resolved from the ground surface to an intermediate depth in a regional context despite its importance for seismic hazard and risk evaluation. For this reason, we estimated VS profiles beneath 19 seismic stations in Bangladesh to a depth approximately 2800 m by employing full horizontal to vertical spectral ratio (HVSR) curve inversion under the diffuse field theory for the noise wavefield. The seismic stations are concentrated in three tectonic zones within the basin: the Surma basin (SB, Zone 1), Bengal Foredeep (BF, Zone 2), and Chittagong Tripura Fold Belt (CTFB, Zone 3). Full HVSR analysis (from 0.2 to 10 Hz) allowed us to obtain deep profiles with combined insights from shallow geotechnical boreholes and deep P-wave velocity (VP) information from active seismic surveys. From the resultant VS profiles, engineering bedrock (VS > 760 m/s) depths were also identified throughout the study area for the first time. The VS profiles within the Holocene to Miocene sedimentary sequences showed rapid variations from location to location. This is due to the highly variable near-surface geology caused by the dense and complex river network and tectonic deformation in Bangladesh. Except for three stations, the engineering bedrock depth exceeded 30 m at all stations. These results indicate the existence of deep soft soil in the study area, where VS30 based site characterization is inappropriate. Furthermore, seismic site response was estimated at a station (DHAK) by simulating a subduction zone earthquake. The resulting response spectrum (RS) exhibited ground motion amplification over a longer period, suggesting that multistory buildings at the site may be at risk if subjected to large earthquakes. The outcomes of this study can serve as useful guidelines for seismic risk reduction planning in Bangladesh.

Evaluating the dynamic response and failure process of a rock slope under pulse-like ground motions

Earthquake-induced landslides represent a significant proportion of seismic hazards in mountainous areas. Numerous slope stability analysis methods exist; however, only a few consider the interactions between pulselike seismic waves and landslides. This study investigates the seismic response characteristics of a homogenous step-like slope to evaluate the acceleration ground motion amplification along the surface. Parametric analysis focusing on the effect of pulselike waves on the slope is conducted using the finite difference modeling code Flac 3 D. Based on the numerical simulation results, pulselike seismic waves greatly influence the acceleration and velocity amplification factor (MPGA & MPGV), with maximum amplification usually obtained at the slope’s crest, where sliding failure initiates. The MPGV of rock slope under pulselike seismic waves is 9.3% higher than near-fault non-pulselike and 16% higher than the far-fault. The displacement for pulselike seismic waves is 20% higher than non-pulselike waves. The dynamic failure analysis presented deep failure for the slope under pulselike seismic wave compared to the non-pulselike. The dynamic failure calculated using Flac 3 D agrees with the results of Newmark-type displacement, with a marginal error between 1 and 8%. The study’s findings can be factored into reinforcing seismic engineering design and probabilistic stability analysis.

A regional scale coseismic landslide analysis framework: Integrating physics-based simulation with flexible sliding analysis

This paper describes a framework for regional scale coseismic landslide evaluation that combines physics-based wave propagation simulation at a regional scale, with flexible sliding analysis at a site scale. The physics-based simulation incorporates fault rupture process, complex topography and dynamic site response. The sliding displacements of flexible masses are calculated by integrating seismic parameter k obtained from the physics-based simulation over seismic resistance.The framework is applied to the case study of coseismic landslides during the 2016 Mw 7.0 Kumamoto earthquake in Japan, which has well documented fault mechanism, geologic information and landslide inventory. The performance of the model prediction is evaluated by receiver operating characteristic (ROC) analysis. This study highlights the near-fault effect and soil nonlinear effect on landslide distribution, and it is demonstrated that the landslide prediction can be notably improved with the consideration of topographic amplification of ground motions. Empirical correlations between topographic amplification of key intensity measures and parameterized topographic features are developed. Overall, the simulation captures 58% of observed landslides in the inventory (using a displacement threshold of 15 cm), showing the proposed framework is a promising tool for regional coseismic landslide analysis.

Macroseismic analysis and the determination of a focal mechanism of the 31 October 2019, KwaZulu-Natal earthquake in South Africa

AbstractAn earthquake (magnitude, ML = 3.8) occurred on 31 October 2019 at 11:19 hours Greenwich Mean Time (GMT) in the Sunduza area of the KwaZulu-Natal (KZN) Province in South Africa. The earthquake was located near the broad fracture zone of the Ntlakwe-Bongwan fault and was felt along the eastern coast of South Africa. The effects of the event were assessed by conducting macroseismic investigations through interviewing members of the public and completing questionnaires. Analysis of all the collected macroseismic data showed that maximum shaking with Modified Mercalli Intensity of IV-V and V were experienced near the epicentral area as well as along the coast. Similar intensity values were also experienced in some parts of Durban about 100 km northeast of the epicentre. Shaking at such long distances was attributed to ground motion amplification due to site effects. A fault plane solution of the event obtained using both the first motion polarities and amplitude ratios showed normal faulting along a fault oriented in a strike of 185.0°, dipping at 68.0° with a rake of -52.0°. The strike of the focal mechanism solution aligns with the strike of the Ntlakwe-Bongwan fault zone and nearby faults suggesting that the event might have ruptured along one of the fracture segments of this fault mapped to the north. The obtained dip is also in line with a high angle fault comparable to that observed along the Ntlakwe-Bongwan fault. The epicentral region is highly faulted although the activity is not known.

Effect of Randomness of Parameters on Amplification of Ground Motion in Saturated Sedimentary Valley

Based on Biot’s theory and the indirect boundary element method (IBEM), the Monte Carlo method is utilized to generate random samples to calculate the displacement response of a saturated sedimentary valley under SV wave incidence. The purpose of this paper is to explore the effects of randomness of porosity, permeability coefficient, and geometric shape on the seismic amplification effect of saturated complex sites. It is shown that the change of media porosity in the saturated site with defined boundary has relatively little influence on the ground motion, and the influence of the permeability coefficient is slightly larger. While in the site with a random boundary, the influence of both the porosity and permeability coefficient are significant, which cannot be ignored. The conclusion plays an important guiding role in earthquake disaster prevention and mitigation, such as seismic risk analysis and earthquake microzonation in saturated sedimentary valleys.

Multimodal Rayleigh and Love Wave Joint Inversion for S‐Wave Velocity Structures in Kanto Basin, Japan

AbstractPrevention of earthquake disaster is critical in the densely populated Kanto Basin, Japan, because of the presence of thick sediments that amplify strong ground motion. For this, a high‐resolution three‐dimensional S‐wave velocity model is essential to understand the complex amplification of strong ground motion. We constructed a three‐dimensional S‐wave velocity model using the joint inversion of multimodal dispersion curves of Rayleigh and Love waves. Inclusion of higher modes significantly improved the accuracy and precision of the surface‐wave inversion by more than 50% compared to using only fundamental mode. Our proposed model revealed a low‐velocity anomaly of sediments toward the east and a curved velocity contour of the basement rock, thereby better explaining the observed complex surface‐wave dispersion curves that have been unexplained in past homogeneous multilayered models. Estimated S‐wave velocity model better reflected subsurface heterogeneity, providing vital information for hazard assessment in a metropolitan area where huge earthquakes are expected.

A database of ground motion recordings, site profiles, and amplification factors from the Groningen gas field in the Netherlands

A comprehensive database that has been used to develop ground motion models for induced earthquakes in the Groningen gas field is provided in a freely accessible online repository. The database includes more than 8500 processed ground motion recordings from 87 earthquakes of local magnitude ML between 1.8 and 3.6, obtained from a large network of surface accelerographs and borehole geophones placed at 50 m depth intervals to a depth of 200 m. The 5%-damped pseudo-acceleration spectra and Fourier amplitude spectra of the records are also provided. Measured shear-wave velocity (VS) profiles, obtained primarily from seismic Cone Penetration Tests (CPTs), are provided for 80 of the ∼100 recording stations. A model representing the regional dynamic soil properties is presented for the entire gas field plus a 5 km onshore buffer zone, specifying lithology, VS, and damping for all layers above the reference baserock horizon located at about 800 m depth. Transfer functions and frequency-dependent amplification factors from the reference rock horizon to the surface for the locations of the recording stations are also included. The database provides a valuable resource for further refinement of induced seismic hazard and risk modeling in Groningen as well as for generic research in site response of thick, soft soil deposits and the characteristics of ground motions from small-magnitude, shallow-focus induced earthquakes.

Distinctive seismic reflections from the subducting Pacific slab for earthquakes in the Ryukyu arc

SUMMARY During moderate to deep (35–260 km) earthquakes within the Philippine-sea slab along the Ryukyu arc, distinctive later phases after S are observed across the Japanese archipelago for epicentral distances from 1500 to 2200 km, producing anomalous amplification of ground motion in central and northern Japan. Broad-band observations show that these later phases have a faster apparent wave speed (7–9.5 km s−1) than S, and are dominant at low frequencies (0.05–1 Hz), indicating S-wave reflections returned from the upper mantle with strong attenuation for high frequencies. Numerical simulation of seismic wave propagation in 3-D models including subduction of both the Pacific (PAC) and Philippine-sea (PHS) plates reveal the origin of these reflections. The triplicated S wave front from the 410 km discontinuity undergoes wide-angle reflection at the top of the Pacific slab bringing strong amplitudes in a narrow band of epicentral distance near 1500 km. Also, wide-angle S reflections at the 660 km discontinuity are reinforced by refraction when travelling through the high-wave speed Pacific slab; these arrive at the surface beyond 2000 km epicentral distance. The characteristics of the deep mantle reflections and the distribution of large ground motion across Japan due to the reflections are strongly dependent on the source depth and distance to the Ryukyu earthquakes. Tomographic imagery for western Japan indicates loss of the high-wave speed signal of the PAC slab below 200 km depth; the character of the large S reflections and pattern of enhanced ground motions favours a model in which the PAC slab is thinned rather than fully broken. The peculiar pattern of ground motion from Ryukyu earthquakes can be useful for constraining deep slab structures that are difficult to identify based on tomography.

Seismic Hazard Maps of Bengkulu City, Indonesia, Considering Probabilistic Spectral Response for Medium and Stiff Soils

Background: This paper presents the extended work of a seismic hazard map for Bengkulu City, Indonesia. In this current study, seismic hazard maps are generated by considering site variations in Bengkulu City, Indonesia. Methods: First, site investigation data is collected. Furthermore, the probabilistic spectral response for Bengkulu City is analysed. The spectral matching method is implemented to obtain appropriate ground motion considering the most dominant earthquake scenario that occurred. A seismic ground response analysis is conducted to obtain several ground motion parameters, such as peak ground acceleration, spectral acceleration values at 0.2 s and 1 s, and ground motion amplification. Results: The results show that peak ground acceleration in the study area is generally within the range of 0.5 to 0.6g. It indicates that most sites in Bengkulu city could undergo strong motion. Spectral accelerations at 0.2 s and 1 s are also dominantly found in the range of 0.9 to 1.2g and the range of 0.5 to 0.7g. Generally, ground motion in the study area could amplify up to 1.1 to 1.5. Conclusion: Spectral acceleration curve for site classes in Bengkulu City shows a similar trend to other spectral accelerations. It indicates that the spectral acceleration proposed in this study could be implemented in the study area.

Amplification effect of near-field ground motion around deep tunnels based on finite fracturing seismic source model

Dynamic failure of rock masses around deep tunnels, such as fault-slip rockburst and seismic-induced collapse, can pose a significant threat to tunnel construction safety. One of the most significant factors that control the accuracy of its risk assessment is the estimation of the ground motion around a tunnel caused by seismicity events. In general, the characteristic parameters of ground motion are estimated in terms of empirical scaling laws. However, these scaling laws make it difficult to accurately estimate the near-field ground motion parameters because the roles of control factors, such as tunnel geometry, damage zone distribution, and seismic source parameters, are not considered. For this, the finite fracturing seismic source model (FFSSM) proposed in this study is used to simulate the near-field ground motion characteristics around deep tunnels. Then, the amplification effects of ground motion caused by the interaction between seismic waves and deep tunnels and corresponding control factors are studied. The control effects of four factors on the near-field ground motion amplification effect are analyzed, including the main seismic source wavelength, tunnel span, tunnel shape, and range of damage zones. An empirical formula for the maximum amplification factor ( α m ) of the near-field ground motion around deep tunnels is proposed, which consists of four control factors, i.e. the wavelength control factor ( F λ ), tunnel span factor ( F D ), tunnel shape factor ( F s ) and excavation damage factor ( F d ). This empirical formula provides an easy approach for accurately estimating the ground motion parameters in seismicity-prone regimes and the rock support design of deep tunnels under dynamic loads.

Effect of Spacing and Slenderness Ratio of Piles on the Seismic Behavior of Building Frames

The general assumption of a rigid base at the bottom of building structures during analysis and design underestimates the seismic response. Building structures resting on loose sand and soft clayey soil are vulnerable to earthquake forces. The amplification of ground motion occurs due to the presence of this loose and soft soil deposit. Moreover, the spacing and slenderness ratio of piles play a vital role in altering the behavior of the overall soil-foundation-superstructure system. This study aimed at investigating the effect of soil-pile-structure interaction using 1-g shake-table testing. Free and forced vibration tests were performed on scaled building frames with either a rigid base or a flexible base, supported on sandy soil with 50% relative density. A laminar shear box container is used for an experimental study of soil-pile-structure interaction. The design parameters, such as the spacing (S = 3D, 5D, 7D, and 9D) and slenderness ratio (L/D = 15, 30, 45, and 60) of the piles, where S, D and L are spacing, diameter and length of the piles respectively, are considered in the analysis. The results, in terms of natural frequency, damping, pile-bending moment, story lateral displacement, and inter-story drift are estimated. From the findings, it is clear that the effects due to pile spacing are more considerable than the effects due to the slenderness ratio of the piles. The bending moment in the piles spaced at 3D is increased by 102% compared to the large-spacing (S = 9D) piles. This subsequently amplifies the story lateral displacement by 180% and amplifies the inter-story drift by 167%.

Seismic Response Analysis of Uplift Terrain under Oblique Incidence of SV Waves

In order to analyze the impact of seismic waves on the venue earthquake, based on the display finite element method, the viscoelastic artificial boundary is used to analyze the variation of the ground motion amplification coefficient and the Fourier spectrum of the raised terrain under different incident angles with SV wave oblique incidence on different slopes. This verification model analysis solution and numerical solution are better. The numerical simulation results show that as the degree of the slope increases, the seismic amplification coefficient increases, and its slope amplification coefficient changes significantly. The X direction coefficient is greater than Y’s magnification coefficient. The Fourier curve with a frequency of 0.2~1 Hz increases with the slope of the raised terrain; when the El Centro is incorporated at 30°, the Fourier spectrum amplitude decreases as the incident angle increases in the low-frequency band. The amplitude of the Fourier spectrum at the high-frequency band monitoring point changes with the incident angle. In the high-frequency band from 1 to 10 Hz, the rate of amplitude change is the largest. When the incident angle is at 0°, the amplification coefficient in the Y direction is basically symmetric.

Effects of Lunar Near‐Surface Geology on Moonquakes Ground Motion Amplification

AbstractLunar seismology has focused on exploring the Moon's seismic activity and its internal structure. However, less attention has been given to site specific, near‐surface geology‐related amplification of seismic waves on the Moon. Here, we quantified ground‐motion amplifications of seismic waves due to local site conditions at the Apollo landing sites. We analyzed Apollo Passive Seismic Experiments seismometer recordings of 30 artificial and natural impacts and estimated the mid‐period (0.1–3 Hz) ground‐motion amplification at each site. We applied techniques commonly used in engineering seismology to understand the local site effects, such as the Horizontal over Vertical Spectral Ratio (HVSR) and the Reference Site Method (RSM) on lunar seismic data. The HVSR and the RSM show convergent spectral ratios specific for each landing site. To correlate these empirical results estimated from lunar artificial and meteoroid impact events with the local site geology, we simulated ground motion amplification using 2D finite difference modeling of lunar geological models and estimated the best geological setting capable of producing a similar frequency response to those observed at each Apollo landing site. Correlation results from the empirical methods and the simulated models show similarities ranging between 79% and 92%, a correlation more than 90% between the RSM and the HVSR results, and similarity exceeding 96% between RSM estimations using different reference sites. These results demonstrate the prominence of a local site geology dependent amplification for frequencies between 0.1 and 3 Hz.

Analysis of slope fracturing under transient earthquake loading by random discrete element method

Earthquake can cause significant rock fracturing in either the short or long terms. A comprehensive analysis of the fracturing mechanism is critical for assessing the risks of potential slope failures, landslides and rock avalanches in seismic prone areas. This study employed 2D discrete element method (DEM) to investigate the fracturing of an intact rock slope of 600 m in base length and 300 m in height, with explicit considerations of material heterogeneity by random field theory. A total of 5400 DEM simulations were performed, and the characteristics of slope fracturing were statistically analysed. The dynamic loading by earthquake has triggered significant amplifications of ground motion and slope damage at the slope crest, resulting in densely spaced and interconnect fractures. These fractures split the slope into a collection of rock fragments with varied shapes, and the fragment size followed the Weibull's cumulative distribution. More than 70% of generated fragments were finer than 0.1 times the initial slope size, while only few large fragments existed at the slope base. The fragment size distribution pattern could quantitatively agree with field observations. The distributions of final slope damage index and cumulated fragmentation energy all followed the normal distribution pattern. The overall bulk seismic energy input into the slope was dissipated mainly at discontinuities and decreased with the increase of slope inclination. • Differential ground displacements exist widely within the slope, which is critical for earthquake induced fractures. • The sizes of the generated rock fragments follow well the Weibull's cumulative distribution. • Statistically, the slope damage index and fragmentation energy all follow the normal distribution pattern. • The slope damage intensity decreases with the increase of slope inclination angle.

Site-specific seismic hazard and risk potential of Bengal Basin with emphasis on holistic seismic hazard microzonation and its structural impact assessment in the cities of Dhanbad and Mymensingh

The Bengal Basin located in the eastern part of the Indian subcontinent at the conjunction of the Eurasian, Indian, and Indo-Burma plates with two progressing deformation fronts viz. the Himalayas and the Indo-Burmese orogenic belts is one of the largest fluvio-deltaic to shallow marine sedimentary basin covered by alluvial plains of Holocene deposits extending from the Himalayas to the Bay of Bengal over thick younger alluvium comprising shallow layers of silt, clay, and sand that can have disastrous consequences due to site-specific ground motion amplification and liquefaction effects. The basin surrounded by Shillong and Assam plateaus in the Northeast is in the active tectonofabric of major active faults and lineaments triggering many devastating earthquakes in the past implicating the MM Intensity of VIII–XI in the near-source region causing widespread damage and destruction in the basin, thus bringing in the essence of assessing surface level seismic hazard and the risk imposed on the basin. Consideration of seismicity patterns, fault networks, and similarity in focal mechanisms yielded 49 areal seismogenic sources and additional active tectonic features in the 0–25 km, 25–70 km, and 70–180 km hypocentral depth ranges, which along with 14 ground motion prediction equations that include site-specific next generation spectral attenuation models pertaining to Northeast India, East-Central Himalaya, and Bengal Basin tectonic provinces yielded probabilistic peak ground acceleration (PGA) at engineering bedrock in the range of 0.08–0.58 g. Both the geophysical and geotechnical investigations at 6,000 sites provided effective shear wave velocity distribution in the range of 113–948 m/s on the geographical information system, thus classifying the basin into 11 site classes with “None” to “Severe” liquefaction hazard potential. A systematic non-linear/equivalent linear site response analysis and its spectral convolution with firm rock peak ground acceleration yielded surface-consistent hazard in the range of 0.09–1.17 g, thus opening up the issue of risk assessment and holistic seismic hazard microzonation of all the cities in the basin and their structural impact assessment using the SELENA-based capacity spectrum method on FEMA and BMTPC-regulated 11 model building types in the damage states of “none,” “slight,” “moderate,” “extensive,” and “complete” for all of those, however, in-depth studies carried out for Mymensingh and Dhanbad have been presented.

The study of ground motion amplification based on an SMASS array site

There is a consensus in earthquake engineering that different soil structures have significant effects on ground motion. Three main methods can be used to study this issue: theoretical analysis, numerical simulation, and earthquake records analysis. Notably, the combined analysis of strong-motion records and station site information appears to be the most effective and reliable approach. In this study, we used site information from the Seismic Monitoring Array of Site and Structure (SMASS) of the Institute of Disaster Prevention and a record of the earthquake that occurred in Guye, China: a point on the bedrock was considered as reference for studying the amplification effect of the soil structure on ground motion through traditional spectral ratio analysis. Our main conclusions are the following. (1) The SMASS array data indicated that the shallow soil had an amplifying effect on ground motion: the frequency bands amplifying the horizontal ground motion were mainly those between 3.4 and 6.8, 11.3–13, and 15–20.8 Hz, while the frequency bands amplifying the vertical ground vibration were mainly those between 5 and 9.9, 13.5–15.9, and 18.5–21.9 Hz (2) The SMASS array data indicated that the influence of the deep soil on the horizontal ground motion frequency component was more significant than that of vertical ground motion. (3) Overall, the SMASS array site amplified the effects of both the high (3.4–20.8 Hz) and low (0.4–2.2 Hz) frequency components of ground motion with the depth decreases of buried depth; notably, the amplification effect of the high-frequency components grew much faster than that of the low-frequency components. (4) The groundwater table had an amplification effect on the vertical ground motion; therefore, its influence is also important to consider.

Italian seismic amplification factors for peak ground acceleration and peak ground velocity

ABSTRACT Ground motion modification over large areas is generally evaluated by focusing on source effects disregarding local lithostratigraphic site conditions. Hence, amplification maps of peak ground acceleration and peak ground velocity are proposed to improve the forecast of ground motion on a national scale. Topological information about litho-type successions and soil mechanical behaviour were retrieved from the Italian database of seismic microzonation and more than 30 million of seismic site response analyses were performed to quantify the amplification factors (i.e. the ratio between expected ground motion at the site of interest and that at the outcropping engineering bedrock). The maximum value of the amplified peak ground acceleration on the Italian territory results in about twice as much as the value expected at the outcropping of the engineering bedrock. Finally, damage scenario maps based on the amplified ground motion could be produced as a supporting tool for urban planning and emergency system management.