Seismic Hazard Zones Research Articles

Loss-Driven Rapid Warning Methodology for Seismic Risk Mitigation of a Target Railway Infrastructure

Due to historical, geographical and economic conditions, the population of the Italian peninsula live in zones of intermediate and high seismic hazard. Nevertheless, Italy has a railway network that is deployed throughout its national territory as customary in developed countries. This network plays a fundamental role in the Italian economy and contributes to the resilience of the big cities to seismic events. In this direction, an active strategy for seismic risk mitigation is achieved with the use of information systems, which alert the occurrence of a seismic event and, in some cases, estimate the state of damage, at local or territorial scale, and the economic loss (e.g. early earthquake warning, rapid response system, aftershock warning system). However, the seismic hazard scenario of the Italian country, with most of active faults along its central area of the peninsula, makes it difficult to implement a comprehensive seismic early warning system. In response to this situation, this study proposes a Railway Rapid Warning System (RRWS) for a railway viaduct of the Campania region of Italy. The case study viaduct is approximately 1 km long connecting Quarto Centro and Quarto stations of the Circumflegrea line. The decisional phase of the protocol is based on an economic loss minimization criterion in order to prevent both missing and false alarm states as a main requirement to the new generation of information systems. The minimization consists of a multi-cost analysis combining structural, environmental, urban context and other aspects associated with risk mitigation actions. From the point of view of structural vulnerability, the protocol uses dynamic analysis and kinematic analysis based on the viaduct elements. It is important to mention that the end user of the warning protocol is the institution in charge of the management of the viaduct, who receives the alarm from a web page, e-mail and SMS. Additionally, the alarm describes the intensity measure of the earthquake and, above all, immediately recommends a set of seismic risk mitigation actions specifically targeted on actual conditions of the reference structure.

Seismic Analysis of Soft Storey Building in Earthquake Zones

In this paper (G+8) building is modeled like a bare frame, a bare frame with the shear wall, and a bare frame with X bracing by changing the soft storey to different floors. The static analysis effect is determined for all three models with zone IV and zone V using Staad pro-V8i software. The main objective of the research was to assess the impact of a soft storey in various earthquake zones and by varying places of the soft storey from first to the top floor and for frames with different column shapes by seismic analyses in staad pro. The results of variable building models are obtained from the research regarding various parameters such as displacement, storey drift, and base shear. More significantly, comparing different structural systems revealed a reduction in lateral displacement and story drift. The shear wall reduced the Storey Displacement by 98.838% and storey drift by 99.86%. The Steel bracing reduced the Storey Displacement by 97.846 % and storey drift by 92.6%. Finally, it has been found that the Shear wall reduces lateral displacement and storey drift, thus significantly contributing to greater structural stiffness. The analysis results recommended that the shear wall use reinforced concrete frames for the seismic hazard zones and the Steel bracing recommended for the low seismic zones.

Wavelet level decomposition of the seismic response of a historic masonry bell tower with and without simulated structural damage

Historical buildings are of foremost importance due to their unique and irreplaceable value. However, their ageing structure and materials make them particularly vulnerable to structural damage. This may result in catastrophic failure under strong motions, which are unfortunately not uncommon in seismic areas such as Italy. This numerical study discusses the application of Wavelet Level Decomposition (WLD) to the seismic response of such historical structures. The simulated data are obtained from a calibrated Finite Element (FE) model of the Santa Maria and San Giovenale Cathedral bell tower in Fossano (Northern Italy). This structure suffered major structural damage during an earthquake in 1887; it then underwent several interventions, the last one being in 2012. It is also currently scheduled for further reinforcement works in the near future. The FE analyses consider a set of realistic earthquake inputs in accordance with the seismic hazard zone of Fossano, with and without damage (modelled as a stiffness reduction in the façades, considering several possible crack patterns). The results show the potential for WLD-based retrospective analysis after seismic events on recorded signals.

Seismic Risk Assessment of Nagpur City using the Geographic Information System

Earthquakes are the major threat to mankind accounting for almost half of the fatalities brought about by all of the natural hazards and desert their traces in societies for years. It is well known that seismic risk cannot be eliminated but minimized. Risk studies lay down the roadmap to prepare and minimize the aftermath of any disastrous event. Geographic Information System (GIS) has been proved as an effectual tool for seismic risk assessment study. This study presents the seismic risk assessment of Nagpur city using the GIS framework. Albeit per Indian Standard (IS) 1893-2016 [1] seismic zonation of Nagpur city comes under zone II (relatively low seismic hazard zone), the seismic risk being a combination of hazard, elements at risk and, vulnerability cannot be denied. Similar to other Indian cities the city of Nagpur had a heterogeneous development pattern. Even though Nagpur city is municipalized in well distributed wards, many intra wards distributions show housing clusters of different socioeconomic status. Therefore, using the satellite imagery different socioeconomic housing clusters were identified and mapped in the ArcGIS platform. Six socioeconomic clusters were identified using satellite imagery for Nagpur. From the field survey of randomly selected typical clusters, 14 prevailing Model Building Types (MBTs) were identified. Census data were used to find the population density and its distribution throughout the city. Seismic hazard has been estimated from IS 1893-2016 [1] as well as using the probabilistic hazard map of NDMA [2]. Selected MBTs were assessed for their seismic vulnerability, seismic risk in terms of casualties and damage is calculated. Finally, thematic maps showing damages arrived from the various approach are shown and discussed.

Quaternary deformation patterns in East–Central Iran, constrained by coseismic–postseismic displacements of the 2017 Hojedk triplet earthquake in the Kerman Province

The Central Iranian Microcontinent (CIM) in east-central Iran is located north of the active Arabia–Eurasia collision zone. Here, we report on the structure, deformation patterns, and earthquake occurrences along the dextral Lakar–Kuh and Godar fault systems in the CIM. The geometry of these fault systems marks a major restraining bend responsible for surface and rock uplift in the Plio–Pleistocene that produced the Mian Kuh mountain range. The 2017 Hojedk triplet earthquake (Mw = 5.8–6.0) occurred in the Mian Kuh Range. Sentinel–1 A Interferometer Synthetic Aperture Radar (InSAR) images (descending and ascending) were used to extract the coseismic displacements associated with the earthquake and its aftershocks. The results indicate a maximum displacement of ∼20 cm, corresponding to hanging wall uplift along the radar Line-of-Sight (LOS) direction. The Geodetic Bayesian Inversion (GBIS) of the coseismic deformation indicates that the causative faults of the Hojedk earthquakes were two reverse faults with NW–SE–strikes and SW–dips, with minor dextral slip components. Given the focal mechanism solutions and the epicenter locations of the triple earthquake sequence, we infer that these faults at the southern termination of the Lakar–Kuh Fault represent two segments (with different dip angles) of a previously unrecognized, blind reverse fault (a splay of the Godar Fault at depth). The Hojedk Earthquake and the geometry and kinematics of its causative faults highlight the strong potential of seismic hazard zones along the strike-slip fault systems in the CIM.

Seismic performance of prefabricated steel tube-confined concrete circular pier

In this study, a prefabricated steel tube-confined concrete (PSTC) circular pier with a bottom grouted sleeve connection was developed to correct some limitations in typical precast concrete (PC) piers, such as over-dense grouting sleeves and insufficient energy dissipation capacity, thus promoting their use in high seismic hazard zones. To validate the performance of the proposed design, four scale models of an actual circular bridge pier, including two PSTC, one PC, and one cast-in-place (CIP) specimens, were fabricated and their seismic response under cyclic loading was investigated via quasi-static experimental and numerical tests. The seismic performance indices, hysteretic energy dissipation characteristics, skeleton curve, flexural strength, stiffness degradation, residual displacement, and ductility of the different specimens were compared. The experimental and numerical results indicated that, compared with the CIP and PC circular piers, the flexural strength and energy dissipation capacity of the PSTC piers were significantly improved owing to the confinement provided by the steel tube to the concrete core, their ductility and initial stiffness effectively increased, and the pier body stiffness (pier body curvature) was more uniformly distributed. Moreover, parametric finite element analyses of the PSTC pier under low-cycle reciprocating load were used to determine the influence of the steel tube thickness and strength on the seismic performance of the pier. It was found that an increase in the thickness and strength of the steel tube also increases the flexural strength, yield load, yield displacement and initial tangent stiffness of the PSTC circular pier. Consequently, this study demonstrates that PSTC piers are reliable and suitable for prefabricated bridge construction in high seismic hazard areas.

Rupture propagation on heterogeneous fault: Challenges for predicting earthquake magnitude

<p indent="0mm">Predicting magnitudes and ground motion of future strong earthquakes on seismogenic faults holds critical implications on seismic hazard zonation and mitigation. Although present approaches to seismic hazard assessment can effectively identify potential regions to host strong earthquakes, it remains extremely challenging to accurately predict future earthquake magnitudes because of various heterogeneities of fault zones, such as fault geometry, medium structure, and frictional properties. In this work, we review a few aspects that play important roles in earthquake rupture propagation and extent, so as to determine the final magnitude of earthquakes. Under the condition of heterogeneous stress distribution on faults, the final magnitude of earthquakes as well as shallow slip distribution depends on where the rupture initiates. As shown in recent numerical models of dynamic rupture simulations, different hypocenters with similar stress level can lead to completely different rupture scenarios, some of which may significantly break the ground whereas others may be buried underground. Such findings shed critical light on seismic hazard preparation, because surface-breaching ruptures can lead to severe damage as vividly evidenced by the 2022 Menyuan <italic>M</italic>_w 6.7 earthquake. To date, we cannot predict future hypocenter locations according to our knowledge of earthquake nucleation and therefore future relevant investigations are highly demanded. Furthermore, the size of seismogenic zone on strike-slip faults controls whether ruptures may become “break-away” to form large earthquakes or stop spontaneously as “self-arresting” of moderate magnitude events. Observations show that aspect ratios between rupture length and down-dip width of dip-slip earthquakes are usually no more than 8. In contrast, the length/width ratios of strike-slip earthquakes may rise to 40 and have a drastic change around the rupture width of <sc>~10 km.</sc> Intrinsic mechanism of such variation in strike-slip earthquakes is attributed to the energy release rate of rupture fronts, which is controlled by the down-dip width. As such, high-resolution constraints on down-dip seismogenic width can be used to estimate the magnitude of future earthquakes on strike-slip faults. Moreover, fault zone structure significantly affects rupture directivity and slip extents. For instance, low-velocity fault zones may promote rupture propagation and thus enlarge the earthquake magnitude. Given the rapid development of seismic observations and seismic imaging techniques, high-resolution fault zone structure can be obtained from data recorded by dense arrays, including nodal network and the newly developed distributed acoustic sensing (DAS) arrays. Integrating with laboratory results of rheology from samples representing crustal rocks, the near-fault high-resolution seismic structure can be converted into rheological properties on faults, which can then be used to outline asperities for future earthquakes. This may provide a critical step to link seismic structure to earthquake potential, as the outlined asperities can be further used to derive rupture scenarios and earthquake magnitudes. To advance our understanding on this front, future work may integrate multiple sources of observations and modeling. Conducting rupture simulations with constraints from geodetic and seismic measurements, as well as laboratory frictional experiments, can be helpful in exploring potential earthquake magnitudes. By considering heterogeneities on faults with reasonable constraints, the numerical models can be useful for investigating the probable hypocenter locations of large earthquakes. Thus, the numerical results may support future near-field observations to improve monitoring of nucleation and development of future large earthquakes. Furthermore, the ground motions generated from the numerical models can also fill the data gap of near-field observations of large earthquakes and provide critical support for physics-based seismic hazard assessment.

Seismic Hazard and Site Suitability Evaluation Based on Multicriteria Decision Analysis

Effective management and planning for sustainable urban regions&#x2019; development require up-to-date information. Natural hazard maps (NHMs) creation is critical for urban development. Urban areas along the western coast of Saudi Arabia are susceptible to natural disasters due to their hazard sources&#x2019; proximity, especially, with the lack of preparation. Yanbu&#x2019; Al-Bahr, a major Red Sea port, provides an excellent example. This research aims to combine NHMs into a single multi-hazard map, allowing acceptable site identification for urban development. To create a seismic hazard model of the rapidly growing Yanbu&#x2019; Al-Bahr region, spatial distributions of different hazard entities were assessed using the analytical hierarchy process (AHP). To create a multi-hazard map, six seismic hazard assessment maps were independently developed. Hazard attributes were assimilated into a geographic information system (GIS) platform to delineate seismic hazard zones and build a suitability map for urban development. Weight and rank values were determined during AHP and assigned to each layer and its corresponding classes. By overlaying all the weighted maps, a suitability map was created. This map depicts the research area&#x2019;s prospective appropriateness for urban growth. Accordingly, the study area was classified into five hazard categories, namely, very-low (VL), low (L), moderate (M), high (H), and very high (VH). Therefore, the limited regions, most appropriate locations, and least suitable areas were identified. Accordingly, stakeholders can use the produced seismic hazard map as a platform for future land-use planning and environmental hazard management. Furthermore, the AHP-GIS model would deliver more precise findings in urban development site selection studies.

Assessing the Seismicity of Shillong Plateau Using 'b value'

The Shillong Plateau is a detached North-eastern portion of the Indian plate and is part of the Eastern Himalayan Syntaxial zone. It is one of the most seismically active plateaus in the world and falls under zone V of the Indian seismic hazard zonation map, the highest seismic hazard zone. During the period of study (2013-2017) numerous local earthquakes of varied magnitude were recorded by the installed broadband seismic stations.

Numerical analyses of embankment dams containing plastic concrete cut-off walls using finite difference method (A case study: The Karkheh Embankment Dam)

In this paper, numerical analyses have been performed on the Karkheh embankment dam with a clayey core and plastic concrete cut-off wall during construction, impounding, and permanent seepage stages. The dam has 127 meters height and is located in a high seismic hazard zone in Iran. Different stages of construction, water impounding, and steady state seepage were modelled and analyzed using the hyperbolic and Mohr-Coulomb models with the two dimensional finite difference method (FDM). So, nonlinear analyses were performed using FLAC 2D to investigate the settlements and the pore water pressure changes in different zones of the dam during above-mentioned stages and the results were compared to those of the other studies. The results show that at the end of the construction stage, the maximum settlement equal to 1.45m occurs inside the clay core at the height of 65m. Then, after impounding of the reservoir and steady state stage, the maximum magnitude of the horizontal deformations occurs in the downstream of the dam equal to 0.55m; however, these magnitudes reach to 0.17m at the crest of the dam. Moreover, it was shown that the maximum horizontal displacement of the plastic concrete cut-off wall has happened at the top of the wall in the clay core which is in a good agreement with the other studies’ result.

A form-finding method for membrane shells with radial basis functions

The equilibrium of a membrane shell is governed by Pucher’s equation that is described in terms of the relations among the external load, the shape of the shell, and the Airy stress function. Most of the existing funicular form-finding algorithms take a discretized stress network as the input and find the shape. When the resulting shape does not meet the user’s expectation, there is no direct clue on how to revise the input. The paper utilizes the method of radial basis functions, which is typically used to smoothly approximate arbitrary scalar functions, to represent C∞ smooth shapes and stress functions of shells. Thus, the boundary value problem of solving Pucher’s equation can be converted into a least-squares regression problem, without the need of discretizing the governing equation. When the provided shape or stress function admits no solution, the algorithm recommends users how to tweak the input in order to find an approximate solution. The external load in this method can easily incorporate vertical and horizontal components. The latter part might not always be negligible, especially for the seismic hazard zones. This paper identifies that the peripheral walls are preferable to allow the membrane shells to carry horizontal loads in various directions without deviating from their original shapes. When there are no sufficient supports, the algorithm can also suggest the potential stress eccentricities, which could inform the design of reinforcing beams.

Does the design according to the seismic zone affect the environment and the manufacturing cost of a 5-storey R/C building with a conventional plan?

The main scope of the present research is the analysis, dimensioning and estimation of the cost of a five-storey reinforced concrete building, which is similarly constructed in three different seismic hazard zones (ZI, ZII, ZIII). The ground plan of the building is a conventional floor plan with solid reinforced concrete slabs. The cross-sections of the structural members remain stable, except for the columns whose cross-sections are reduced in height. The aim of the present study is to analyze how the cost of manufacturing the load-bearing structure of a reinforced concrete building is affected by the seismic risk of the area, if that influence is significant and in what extent. Moreover, along with the construction cost, the possible influence to the environment is studied, too.

Building geopolymers for CuHe part I: thermal properties of raw materials as precursors for geopolymers

This paper presents the results obtained from the thermal analysis of a set of geomaterials (clays, pyroclastic materials, and industrial recycled materials) to be used as raw materials for the synthesis of geopolymers, specifically designed for the conservation of Cultural Heritage (CH) buildings, particularly in seismic hazard zones such as Sicily. X-ray diffraction and gas volumetric analysis (calcimetry) were applied to this set of raw materials in order to characterize the materials from the chemical and structural point of view. Thermogravimetric analysis (TG), TG coupled to Fourier transform infrared spectroscopy (TG-FTIR), and differential scanning calorimetry were used to characterize their thermal behavior. The statistical treatment of the thermogravimetric data by principal component analysis and hierarchical clustering analysis highlights the direct relation between the thermal data and the material composition that will be exploited for the selection of the best materials to obtain geopolymers specifically designed for the conservation of CH buildings.

Distribution and characteristics of landslides in the 2018 Palu earthquake, Indonesia

The September 28, 2018 Mw7.5 earthquake of Palu earthquake, Sulawesi Island, Indonesia, has triggered a lot of landslides. We attempted to establish a detailed landslide inventory of this area, which is very important to understand the landslide distribution, geomorphic evolution and risk assessment of the earthquake. The purpose of this paper is to make a statistical analysis of the spatial distribution and influencing factors of landslides in the study area based on the landslide inventory of Palu earthquake. Combined with earthquake, topography, geology and other landslide influence factors, taking the percentage of landslide area (LAP) and landslide number density (LND) as indicators, the change trend of landslides in different factor intervals is analysed. The results show that the areas with elevation of 400-500 and 500 – 600m are prone to landslides. With the increase of elevation, LAD and landslide area showed a downward trend. LND first increased and then decreased, and reached the peak at the elevation of 1500-1600m. Large scale landslides are prone to occur in low altitude areas, while small scale landslides tend to occur in high altitude areas. LAD and LND increased with the increase of slope. The LAP decreases with the increase of the distance from the river, which is opposite to the LND, indicating that the small landslides often occur in the area far from the river. The results of this study are helpful to understand the causes of coseismic landslides. And provide a scientific reference for disaster prevention and mitigation of earthquake landslides in the seismic landslide hazard zoning.

In-plane behavior of clay blocks externally reinforced

The objective of this research work was to determine the resistance to cutting of clay block walls of size 1.20 m × 1.20 m without and with external reinforcement. Blocks of width equal to 0.10 m were used for four manufacturers, one located in Ocaña, Colombia, and three more established in San José de Cúcuta, Colombia. Reinforcement with electrowelded mesh is an alternative to reduce the seismic vulnerability of homes in areas of intermediate and high seismic risk. Ocaña, Colombia, is located in an intermediate seismic hazard zone and therefore the use of simple masonry in homes is not allowed. This made it necessary to determine the mechanical properties of the clay block pieces, such as compressive strength, compressive strength of the bonding mortar, compressive strength of clay block prisms, diagonal tensile strength, modulus of elasticity and shear modulus of reinforced and unreinforced walls. The tests were carried out on a universal machine with a compression capacity of 100 t, a tensile capacity of 60 t class B with a precision of 0.1% ± 0.05 mm. This research established the physical parameters of the clay block prisms and the physical behavior of shear deformation vs. Shear stress without and with exterior reinforcement, necessary to establish physical models of structural reinforcement of houses vulnerable to seismic movements, and with this avoid human losses.

Mesoscale seismic hazard zonation in the Central Seismic Gap of the Himalaya by GIS-based analysis of ground motion, site and earthquake-induced effects

Mesoscale seismic hazard zonation in the Central Seismic Gap of the Himalaya by GIS-based analysis of ground motion, site and earthquake-induced effects

A Preliminary Seismic Hazard Assessment of the Sakhalin–Mainland Area for a Critical Linear Structure

The results of seismic hazard zoning of the submerged crossing of the pipeline in the Nevelskoy Strait, between the village of Lazarev of the Nikolaevsky district, Khabarovsky krai, and Cape Pogibi near the village of Pogibi, Sakhalin oblast are presented. Along the water area, this section of the crossing is limited by a zone that is 500 m wide and 11 km long. It follows from the stock of geological documents of the Geophysical Service of the Russian Academy of Sciences and the general seismic zoning map (GSZ-2015) that the highest seismic activity in the Okhotsk region is observed in the area of the Kuril Islands, while the closest activity to the construction site manifests itself in the central zone of northern Sakhalin. Large earthquakes are recorded by a number of seismological stations in the immediate vicinity of the construction site. The foci of nearby earthquakes are displaced eastward of the construction site and are mostly confined to the systems of deep faults that result from the juncture between the West Sakhalin synclinorium and the Sikhote Alin volcanic belt. The main purpose of this research is related to the development of a procedure for forecasting seismic impacts for the areas that are prone to predicted strong earthquakes. In this context, an approach is proposed for the specific structure, which is based on the construction of a set of the most probable seismic models to reach the reference bedrock, setting of the pickup signal corresponding to initial seismicity of the area, calculating the main parameters of seismic impacts for them, and then, in the first approximation, the implementation of the technology for constructing an engineering–seismological cross-section along the pipeline construction site. The proposed approaches to forecasting seismic events for the section of the pipeline crossing in the Nevelskoy Strait are based on certain restrictions that made it possible to obtain a set of parameters of seismic impacts for predicted strong earthquakes that are necessary for design and construction of an earthquake-resistant linear structure. In improving the calculation methods and monitoring critically important objects, the advantage of this approach is the ability to recalculate seismic impacts on a structure using the constructed seismic ground-motion models.

Seismic behaviour of a mixed iron-masonry church: Santa Maria Maddalena, Ischia

The concept of vulnerability of the existing building stock is receiving increasing awareness and central importance in the scientific community working in earthquake risk mitigation. This assumes even more relevance when dealing with heritage structures located in relevant seismic hazard zones. This paper aims to identify and describe the earthquake-resistant features found in a unique masonry church in Ischia (Italy), and discuss their effectiveness on the impact of the post-seismic damage through the application of non-linear static analyses. The Santa Maria Maddalena Church represents one of the rare examples in which the technology of the Borbonic casa Baraccata (mixed timber−masonry construction), already well-known in the literature for its use in Italian seismic areas since the eighteenth century, is applied with the non-conventional combination of masonry and iron frames. The church was struck by the recent earthquake of 21 August 2017 with epicentre in Casamicciola Terme. The recorded post-seismic damage of the church evidenced non-relevant structural crack patterns, which are likely to be related to the efficacy of the construction system adopted.

A multi‐objective genetic algorithm strategy for robust optimal sensor placement

AbstractThe performance of a monitoring system for civil buildings and infrastructures or mechanical systems depends mainly on the position of the deployed sensors. At the current state, this arrangement is chosen through optimal sensor placement (OSP) techniques that consider only the initial conditions of the structure. The effects of the potential damage are usually completely neglected during its design. Consequently, this sensor pattern is not guaranteed to remain optimal during the whole lifetime of the structure, especially for complex masonry buildings in high seismic hazard zones. In this paper, a novel approach based on multi‐objective optimization (MO) and genetic algorithms (GAs) is proposed for a damage scenario driven OSP strategy. The aim is to improve the robustness of the sensor configuration for damage detection after a potentially catastrophic event. The performance of this strategy is tested on the case study of the bell tower of the Santa Maria and San Giovenale Cathedral in Fossano (Italy) and compared to other classic OSP strategies and a standard GA approach with a single objective function.

Evaluation of Key PSHA Assumptions—Case-Study for Romania

This case-study focuses on the analysis of several key assumptions necessary for the probabilistic seismic hazard assessment of Romania in the light of a future seismic hazard zonation of the territory. Among the aspects analyzed in this study are the appropriateness of the Poisson assumption which is tested on the earthquake catalogs of several seismic sources (crustal and the Vrancea intermediate-depth source), the azimuthal dependence of ground motion amplitudes from Vrancea intermediate-depth earthquakes and possible ground motion amplifications due to basin effects. The analyses performed in this study show that the Poisson distribution is able to model the observed earthquake frequency occurrence for the larger magnitude seismic events both for crustal and intermediate-depth seismic sources. Similar ground motion attenuation patterns irrespective of the azimuth with respect to the Vrancea intermediate-depth seismic source were observed only in the case of the 30 May 1990 earthquake, while in the case of the seismic events of 30 August 1986 and 31 May 1990 significant azimuthal ground-motion attenuation differences were observed. No significant differences in terms of ground motion amplitudes were observed at three seismic stations in Iasi area during the Vrancea intermediate-depth earthquakes of 30 May 1990 and 31 May 1990 possibly due to the limited elevation difference. Finally, significant long-period spectral amplifications were observed on the ground motions recorded at several sites from intramountainous depressions in Romania.