Seismic Amplification Research Articles

An Empirical Correlation between the Residual Gravity Anomaly and the H/V Predominant Period in Urban Areas and Its Dependence on Geology in Andean Forearc Basins

The study of site amplification effects is crucial to assess earthquake hazards that can produce great damage in urban structures. In this context, the gravity and the ambient noise horizontal-to-vertical spectral ratio (H/V) are two of the most used geophysical methods to study the properties of the subsoil, which are essential to estimate seismic amplification. Even though these methods have been used complementarily, a correlation between them has not been thoroughly studied. Understanding this correlation and how it depends on geology could be important to use one method as an estimator of the other and to make a distinction between the seismic and gravimetric basement. In this research, a comparison between the residual gravity anomaly and the H/V predominant period is performed using a long dataset from different projects on sedimentary basins in a group of the most important cities in Chile. To simplify the geological information, a seismic classification is used for soils, which considers the Vs30 and the predominant period of vibration (T0). The results of this comparison show a direct correlation between both parameters, the higher the negative residual gravity anomaly the higher the H/V predominant period. This correlation improves when only soft soils are considered, increasing the R2 value in more than a 50% in all the individual cities with respect to the overall correlation. When all the cities are considered, the R2 value for soft soils increases up to 0.87. These results suggest that the ideal geological background for this correlation is when a soft soil layer overlies a homogeneous bedrock. Heterogeneities in the bedrock and in the soil column add dispersion to the correlation. Additionally, the comparison between the depth to basement inferred by both methods show differences of less than 15% in soft sites; in denser sites, the difference increases up to 30% and the definition of a clear H/V peak is more difficult. In general, the gravimetric basement is deeper than the seismic one. However, gravimetric depths to basement can be under/over-estimated in zones with a heterogeneous soil column.

Profiling the Quito basin (Ecuador) using seismic ambient noise

SUMMARY Quito, the capital of Ecuador, with more than 2.5 M inhabitants, is exposed to a high seismic hazard due to its proximity to the Pacific subduction zone and active crustal faults, both capable of generating significant earthquakes. Furthermore, the city is located in an intermontane piggy-back basin prone to seismic wave amplification. To understand the basin’s seismic response and characterize its geological structure, 20 broad and medium frequency band seismic stations were deployed in Quito’s urban area between May 2016 and July 2018 that continuously recorded ambient seismic noise. We first compute horizontal-to-vertical spectral ratios to determine the resonant frequency distribution in the entire basin. Secondly, we cross-correlate seismic stations operating simultaneously to retrieve interstations surface-wave Green’s functions in the frequency range of 0.1–2 Hz. We find that Love waves travelling in the basin’s longitudinal direction (NNE–SSW) show much clearer correlograms than those from Rayleigh waves. We then compute Love wave phase-velocity dispersion curves and invert them in conjunction with the HVSR curves to obtain shear-wave velocity profiles throughout the city. The inversions highlight a clear difference in the basin’s structure between its northern and southern parts. In the centre and northern areas, the estimated basin depth and mean shear-wave velocity are about 200 m and 1800 ms−1, respectively, showing resonance frequency values between 0.6 and 0.7 Hz. On the contrary, the basement’s depth and shear-wave velocity in the southern part are about 900 m and 2500 ms−1, having a low resonance frequency value of around 0.3 Hz. This difference in structure between the centre-north and the south of the basin explains the spatial distribution of low-frequency seismic amplifications observed during the Mw 7.8 Pedernales earthquake in April 2016 in Quito.

Seismic microzonation of a region with complex surficial geology based on different site classification approaches

A seismic microzonation study was conducted to refine the seismic hazard model for the city of Saguenay, Canada. The Quaternary geology underlying Saguenay shows complex glacial and post-glacial stratigraphy with a number of buried valleys filled with fluvioglacial and glaciomarine sediments. High impedance contrast between rock formations and surficial sediments is prone to seismic amplification. To evaluate their applicability, advantages and limitations in capturing the geological specificity of the study area, four site classification methods were applied: the current National Building Code of Canada (NBCC) and Eurocode 8, both mainly based on the average shear-wave velocity for the surficial sediments (VS,avg) and for the top 30 m (VS,30); a method based on the fundamental site period (T0); and a hybrid method based on the combination of VS,30, T0 and VS,avg. The study specifically aimed to evaluate the importance of the site classification parameters on the resulting microzonation maps. VS,30 is capable to present the geological and geotechnical site conditions, however, the results may be further improved by considering Vs,avg in shallow and T0 in thick layers of soil sediments as secondary parameters. The T0 method gives also satisfactory results with T0 showing a better correlation to Vs,30 than to Vs,avg. The versatile hybrid method may be challenging to apply in certain cases with its nine different site categories and parameters.

The Estimation of Seismic Site Amplification of Bukittinggi City, West Sumatera, Indonesia

Bukittinggi city area is exposed substantial risk of both, close to seismic source line and site amplification due to soft surface sediment / soil layer. The Great Sumateran Fault (GSF) which is crossing this area, notorious as a very active seismic source. Its responsible to some major earthquake in the vicinity of the fault line. Generally, Bukittinggi area is covered by volcanic product as pumiceous tuff. We applied combined array and single station microtremor measurement to characterize near surface sediment in this area. Based on analysis microtremor single station and array using spatial autocorrelation (SPAC) method, weathered surface layer thickness is in the range of 0-108 m with shear wave velocity in the range of 62-190 m/s, while the fresh pumiceous tuff is in the range of 375-629 m/s. The estimation of site amplification in this area which is indicated by mean amplification is in the range of 1-1.95. The high amplification zone is occupies the northernmost area and some area locally in the southern part of Bukittinggi city.

Study on seismic safety of Poshitougou flood intercepting dam

Poshitougou dam is located in Xichang City, Sichuan Province. The purpose of the dam is to divert the river section passing through the open-pit mining site to ensure the safe operation of the mining site. The dam is a concrete gravity dam with a length of 148.61m and a height of 34.0m, built on deep alluvium foundation with a depth of 160m. The nearest distance between the dam and the Anninghe fault is 10km, and the fault may have a magnitude 7.5 earthquake in the future, so the seismic safety of the dam is very important. In this paper, the finite element dynamic method is used to analyse the seismic response and dam safety under the design earthquake. According to the calculation results, there are serious potential safety hazards in the dam under strong earthquake, including: collision between adjacent dam sections may occur during the earthquake, causing local damage to the concrete near the joint; joint deformation may tear the water stop, leading to dam leakage; breakage of dam foundation curtain grouting may occur during the earthquake. This paper also discusses the possibility of constructing hardfill dam on deep alluvium foundation in strong earthquake area. The calculation results show that the seismic displacement of the hardfill dam is obviously reduced, the seismic amplification effect of the dam is significantly reduced, the dynamic stress of the dam is smaller and its seismic performance is good.

Sanxicun landslide: an investigation of progressive failure of a gentle bedding slope

A gentle bedding slope (16° dip angle) failure at Sanxicun (SXC) village in Dujiangyan city was triggered by heavy rainfall in 2013. The landslide has a sliding distance of up to 1200 m and caused 166 deaths. After this failure event, a detailed field survey and a series of laboratory tests were carried out to investigate the progressive failure mechanism of the slope. The results revealed that the slope deformation could be traced back to the Ming Dynasty in China (400 years before) at least. A sliding block with a width of 330 m and a length of 240 m detached its original position, resulting in a tension crack with 10 m in width and 25 m in depth at the rear of the sliding block. The field evidence reveals that the tension crack and cracked mudstone have provided convenience for water infiltration for a long time. The shake table test results show that these cracks can initiate and propagate in the slope during earthquakes. Especially, seismic stresses amplifications are induced in the mudstone to obviously degrade this layer. Besides, Direct shear tests of cracked mudstone with different immersion times were carried out. It is shown that the shear strength of mudstone decreased rapidly in the initial immersion and then tends to be stable gradually. Finally, numerical calculation indicates that the hydrostatic pressure in the tension crack and uplift pressure in the basal layer generated by the strongest rainwater in history (537.4 mm daily) cause the initiation of the block in 2013. We conclude that the catastrophic failure of the SXC landslide triggered by the rainwater in 2013 strongly depended on the pre-existing deformation and damage caused by historical earthquakes and rainwaters.

Landslides triggered by the 2018 Lombok earthquake sequence, Indonesia

During July and August 2018, a series of four Mw > 6.0 earthquakes (Event I − 2018.07.28 Mw 6.4, Event II − 2018.08.05 Mw 6.9, Event III − 2018.08.19 Mw 6.3, and Event IV − 2018.08.19 Mw 6.9) struck Lombok Island, Indonesia. A detailed interpretation of satellite imagery reveals that the Lombok earthquake sequence triggered 10,521 landslides with a cumulative extent of 28.0 km2 over an affected area reaching approximately 1850 km2, which are divided into seismic earthflows, topography-based landslides and gully-based landslides. A total of 5621 and 2980 landslides were triggered by Event II and Events III-IV, respectively, and 1920 landslides were concentrated in the 2018.08.10 cloud-covered area. Event II caused most of the landslides. The landslide areas of all the events follow an exponential distribution. The cumulative landslide number (N) and landslide area (A) exhibit a linear logarithmic relationship of Log(N) = −1.341*Log(A) + 3.9. The western section of Mount (Mt.) Rinjani is clearly a landslide-prone area that contains mainly seismic earthflows. Rainfall is a dominant factor influencing the landslide distribution, and generally, higher rainfall corresponds to a higher landslide concentration. Seismic shaking is not a key factor in deposit failure, while in the lower gently sloping section (elevation < 1500 m), the peak ground acceleration (PGA) of landslides increases with a decrease in elevation. Moreover, the top section of the mountain with a steeper slope (Subzones II and V) caused a stronger seismic amplification effect, resulting in numerous landslides.

The dynamic response of coseismic liquefaction-induced ruptures associated with the 2019Mw5.8 Mirpur, Pakistan, earthquake using HVSR measurements

The Mirpur area of Pakistan was severely damaged by extensive coseismic liquefaction following an earthquake of Mw5.8 on 24 September 2019. Villages within 6 km of the epicenter were adversely affected due to extensive coseismic liquefaction-induced surface and shallow subsurface deformations. The earthquake affected all types of buildings and key infrastructure (e.g., the Upper Jhelum Canal and the main Jhelum–Jatlan road). Field observations and associated effects are presented, including horizontal-to-vertical spectral ratio (HVSR) data sets acquired from three sites to evaluate the site response characteristics of the liquefaction-affected soil profiles. As a result, rupture events strongly influenced spectral features (amplitude and frequency) and site-specific 1D shear-wave velocity profiles at sites S1 and S2. The dynamic behavior of HVSRs across ruptures at sites S1 and S2 corresponds to varied levels of seismic amplification, demonstrating the impact of liquefaction-induced ruptures of seismic origin on the site response that have not been reported previously in the literature. The consistent HVSR pattern of well-established high-frequency peaks at site S3 adjacent to partially damaged to completely collapsed buildings of different types further indicates the susceptibility of potential liquefaction hazard. These results agree with the surface liquefaction signatures in the field, revealed by inverted electrical resistivity tomography models in terms of liquified sand plugs, clay lenses and associated fractures, and increasing trends of radon concentration in the soil with decrease in the distance toward ruptures. Additionally, the successful application of HVSR as a cost-effective and speedy tool attests to the potential of the proposed approach in furnishing complementary information for better assessment of liquefaction hazards in the developing world, where financial constraints are a major issue. This can help with seismic hazard analysis and mitigation in the Mirpur area and may have applications in other seismically active regions of the world.

Multi-attribute seismic data spectrum analysis of tunnel orthogonal underpass landslide shaking table test

To explore the spatial deformation characteristics and dynamic response law of the tunnel's orthogonal underpass landslide under potential seismic action, we carried out the shaking table test for the first time. We measured and obtained the seismic data with various attributes, such as the characteristic image of different probability horizontal seismic action, acceleration, dynamic soil pressure and dynamic strain. Based on the time-domain analysis of multi-attribute data such as deformation characteristics and acceleration, we revealed the spatial dynamic response characteristics of the lining structure at different positions in the annular particle. By Wavelet Transform, we obtained the time-frequency variation relationship between the multi-attribute data. In addition, we discussed in detail the relationship between the frequency and the specific period of acceleration, dynamic soil pressure and dynamic strain at different probabilities of horizontal vibration stages. We then proposed the damage level correlation quantitatively characterized by the spectrum characteristics of multi-attribute data through Fast Fourier Transform and statistical probability scatter-matrix operations. The sensitivity difference of multi-attribute seismic data was significant. The time-history effect of dynamic soil pressure was the most sensitive and the time-history effect of dynamic strain had obvious hysteresis compared with acceleration. In the frequency domain of multi-attribute seismic data signals, the predominant frequencies were mainly concentrated in 1–10 Hz, and their dominant frequencies were significantly different. The singular boundary between low-frequency and high-frequency was 10 Hz, and the structures with frequencies between 15 and 20 Hz were relatively safe. Multi-attribute data response variables were positively correlated, acceleration was highly correlated with dynamic soil pressure response, while acceleration was weakly correlated with dynamic strain response, showing a significant correlation. Due to the spatial location of the tunnel's orthogonal underpass landslide, and the effect of seismic wave amplification and bias effect of mountain tunnel, the lining was damaged in a regional difference, and the inverted arch uplift cracked into a weak area. The research results can provide a theoretical reference for the failure model prediction and engineering safety evaluation of the tunnel's orthogonal underpass landslide in high intensity earthquake area.

Effects of topography and basins on seismic wave amplification: the Northern Chile coastal cliff and intramountainous basins

SUMMARYDuring earthquakes, structural damage is often related to soil conditions. Following the 2014 April 1 Mw 8.1 Iquique earthquake in Northern Chile, damage to infrastructure was reported in the cities of Iquique and Alto Hospicio. In this study, we investigate the causes of site amplification in the region by numerically analysing the effects of topography and basins on observed waveforms in the frequency range 0.1–3.5 Hz using the spectral element method. We show that topography produces changes in the amplitude of the seismic waves (amplification factors up to 2.2 in the frequency range 0.1–3.5 Hz) recorded by stations located in steep areas such as the ca. 1-km-high coastal scarp, a remarkable geomorphological feature that runs north–south, that is parallel to the coast and the trench. The modelling also shows that secondary waves—probably related to reflections from the coastal scarp—propagate inland and offshore, augmenting the duration of the ground motion and the energy of the waveforms by up to a factor of three. Additionally, we find that, as expected, basins have a considerable effect on ground motion amplification at stations located within basins and in the surrounding areas. This can be attributed to the generation of multiple reflected waves in the basins, which increase both the amplitude and the duration of the ground motion, with an amplification factor of up to 3.9 for frequencies between 1.0 and 2.0 Hz. Comparisons between real and synthetic seismic waveforms accounting for the effects of topography and of basins show a good agreement in the frequency range between 0.1 and 0.5 Hz. However, for higher frequencies, the fit progressively deteriorates, especially for stations located in or near to areas of steep topography, basin areas, or sites with superficial soft sediments. The poor data misfit at high frequencies is most likely due to the effects of shallow, small-scale 3-D velocity heterogeneity, which is not yet resolved in seismic images of our study region.

Hybrid testing of capacity designed RC structural walls for the determination of nonlinear seismic shear amplification

AbstractHybrid testing is an effective experimental method to study the dynamic behavior of structural elements under various types of loads. The hybrid testing method enables the seismic responses of large structural elements to be reproduced, such as the responses of reinforced concrete (RC) shear walls in a laboratory environment without needing to include the large masses typically encountered in multistory buildings. In this study, a test specimen corresponding to the base plastic hinge zone of an eight‐story RC structural wall was tested in a laboratory environment, whereas the remainder of the wall was modeled numerically to evaluate the seismic shear amplification due to nonlinear higher mode effects. A method is presented for controlling three degrees of freedom of a specimen with high axial stiffness and high lateral stiffness at the beginning of the test and the substantially reduced stiffness after cracking and yielding of the specimen. Because the duration of an uninterrupted test would have been very long, a method was used to stop and restart the test at will so that the whole test could be performed over several days. Seismic shear amplification due to nonlinear higher mode effects in a structural wall with yielding occurring at the base is measured for the first time in a hybrid test . The test results clearly present seismic shear amplification that is larger than building codes recommended values.

Resultant axial stresses in instrumented rockbolts induced by dynamic effects occurred due to multi-face blasting in the working areas

Multi-face blasting is one of the most frequently used active rockburst prevention methods in the Polish copper mines. Simultaneous firing of a group of faces generates vibrations which, propagating in the form of para-seismic waves, affect the condition of the rock mass structure and allow to trigger high-energy tremors during the production process. However, the simultaneous firing of explosives in several mining faces may have the negative impact on the condition of the rockbolt support system in the roof strata and stability of the roof rocks located in the vicinity of the mining front. Therefore, this impact under the conditions of selected mining panels of the Lubin mine was examined by measuring the axial stresses in instrumented rockbolts. The statistical correlation between the measured axial stresses and the estimated para-seismic peak particle velocity has been analysed to determine the potential dependence between these quantities. The obtained results have shown that in the geologic and mining conditions of the analysed mining panels, simultaneous firing of explosives in a number of mining faces did not induce significant permanent changes in values of the measured axial stresses within the instrumented resin anchored rockbolts. In result, further development of multi-face blasting in terms of seismic wave amplification may be proceeded without risk of significant damaging of the immediate roof strata.

Seismic Wave Propagation and Basin Amplification in the Wasatch Front, Utah

AbstractGround-motion analysis of more than 3000 records from 59 earthquakes, including records from the March 2020 Mw 5.7 Magna earthquake sequence, was carried out to investigate site response and basin amplification in the Wasatch Front, Utah. We compare ground motions with the Bayless and Abrahamson (2019; hereafter, BA18) ground-motion model (GMM) for Fourier amplitude spectra, which was developed on crustal earthquake records from California and other tectonically active regions. The Wasatch Front records show a significantly different near-source rate of distance attenuation than the BA18 model, which we attribute to differences in (apparent) geometric attenuation. Near-source residuals show a period dependence of this effect, with greater attenuation at shorter periods (T&amp;lt;0.5 s) and a correlation between period and the distance over which the discrepancy manifests (∼20–50 km). We adjusted the recorded ground motions for these regional path effects and solved for station site terms using linear mixed-effects regressions, with groupings for events and stations. We analyzed basin amplification by comparing the site terms with the basin geometry and basin depths from two seismic-velocity models for the region. Sites over the deeper parts of the sedimentary basins are amplified by factors of 3–10, relative to sites with thin sedimentary cover, with greater amplification at longer periods (T≳1 s). Average ground-motion variability increases with period, and long-period variability exhibits a slight increase at the basin edges. These results indicate regional seismic wave propagation effects requiring further study, and potentially a regionalized GMM, as well as highlight basin amplification complexities that may be incorporated into seismic hazard assessments.

New Insights into Long-Period (&amp;gt;1 s) Seismic Amplification Effects in Deep Sedimentary Basins: A Case of the Po Plain Basin of Northern Italy

ABSTRACTThis study investigates and quantifies the influence of the shallower deposits (down to few hundreds of meters) of the Po Plain sedimentary basin (northern Italy) on the long-period component (i.e., 1 s&amp;lt;T&amp;lt;3 s) of seismic ground motion, in which amplification effects due to the soft sediments above seismic bedrock were observed.A new seismostratigraphic model of the shallow deposits of the entire basin is provided with an unprecedented detail by taking advantage of recently acquired geophysical data. The seismostratigraphic model is used to simulate the ground motion amplification in the Po Plain by means of extensive 1D ground response analysis. Results are compared with seismic observations available at a number of sites equipped with borehole seismic stations, where earthquakes have been recorded both at the surface and at the seismic bedrock depth. Despite the general agreement with observations concerning the seismic resonance frequencies, our model may fail in capturing the amplitude of the actual seismic amplification of the basin in the long-period range. We observe that 3D basin effects related to surface waves generated at the edge of the basin may play a significant role in those zones where seismic hazard is controlled by distant sources. In these cases, 1D modeling leads to average underestimations of 30%, up to a maximum of 60%. The amplification functions need to be corrected for a basin-effects correction term, which in this case is provided by the ground-motion prediction equation of the study area. The corrected amplification functions agree with the empirical observations, overcoming the uneven distribution of the recording stations in strong-motion datasets.These results should be taken into account in future seismic microzonation studies in the Po Plain area, where the 1D approach is commonly adopted in ground response analyses, and in site-specific seismic hazard assessments aimed at the design of structures that are sensitive to the long-period component of seismic ground motion (e.g., long-span bridges and tall buildings).

Seismic response characteristics and deformation evolution of the bedding rock slope using a large-scale shaking table

Qinghai-Tibet Plateau is one of the most seismically active aeras of China and rock mass structures or geological structure are also complex here. Earthquake-induced geological disasters are occurred frequently in this region. Among them, plane failure is often generated on bedding rock slope especially in destructive area of the Wenchuan earthquake which caused numerous casualties and serious economic loss. To reveal failure mechanism of bedding rock slope, this paper studied the seismic response and investigated progressive failure characteristics of the bedding rock slope through a large-scale shaking table test. A bedding rock slope of 45° contained an unfilled joint set with spacing of 0.1 m that dipped at an angle of 34° out of the surface, was conducted in a rigid model box, with a length of 3.47 m, width of 0.68 m, and height of 1.2 m, respectively. A series of tests results show that acceleration amplification factor in horizontal direction (AAF-X) increases with the increase of the slope elevation and acceleration amplification factor in vertical direction (AAF-Z) amplifies at lower part of the slope. When the shaking intensities are over 0.2 g, the slope crest and its vicinity start to show nonlinear dynamic response. Existence of bedding planes let the isoline morphology of AAF-X redistribute and dominate the seismic amplification at the crest. The progressive failure progress of the model under earthquake can be divided into four stages. This novel experiment offers some important insights to mechanism of bedding plane landslides triggered by earthquakes, evaluation stability of slopes under earthquake, and disaster prevention and mitigation.

Seismic amplification maps of Italy based on site-specific microzonation dataset and one-dimensional numerical approach

Prediction of surface ground motion based on advanced approaches is a non-trivial task at large area. In fact, advanced approaches require a detailed geological and geotechnical subsoil model based on geological, physical and mechanical properties retrieved from in situ investigations and laboratory data, and to perform time consuming numerical simulation of the seismic site response. Bearing in mind that there is a lack of available site investigations and laboratory data at large area, simplified methods based on “soft data” are often adopted. On this regard, a methodology to perform seismic site response analyses at national scale is proposed in this paper, based on the following assumptions: 1) homogeneous areas were identified at national scale based both on morpho-geological and lithological properties, in order to classify and analyse site-data archived in the Italian database of seismic microzonation studies; 2) geotechnical subsoil one-dimensional models of the Italian site conditions were defined according to site-data; 3) in accordance with the reference seismic hazard levels, pseudo-acceleration response spectra were selected as input motions for numerical simulations.About thirty million numerical simulations of seismic site response were performed, and national maps of seismic shaking amplification factors were produced in terms of ratio of response spectra referred to three intervals of period. This estimation of surface ground motion based on the proposed procedure is a supporting tool for large area territorial and emergency planning.

Maximum Credible Earthquake Ground Motions with Focus on Site Amplification due to Deep Subsurface

Since an Earthquake Ground Motion (EGM) is amplified from the propagation through the ground, different models are required for each ground type in the seismic design of structures. While the shallow subsurface indicators are used for the classification of ground types, a deep subsurface has a significant impact on the amplification of the EGMs. This study discusses the maximum credible EGMs for seismic design reflecting seismic amplification due to deep subsurface. The design spectra, reflecting the site amplification factor of the target location, are presented by the calculation of the EGMs with the same source and path characteristics and different site amplification factors as recent major Japanese earthquake records have shown, from the perspective of establishing the maximum credible EGMs that may occur in the future at a target site. The present design spectra, which are based on the natural period of a shallow subsurface, are compared with those based on the site amplification factors, considering the effect of deep subsurfaces. Although there are almost no differences in the design spectra with the present design methods according to the surface ground type, the proposed method provides significantly different design spectra for each site amplification factor.

2-D Seismic Response Analysis of a Slope in the Tyrrhenian Area (Italy)

The Caronia area is located in the Tyrrhenian north-eastern sector of Sicily (Italy). Starting in 2010, attention focused on the study of landslides phenomena that occurred in this area, which caused significant economic damage to buildings and infrastructures and loss of productive activities. The site is characterized by geotechnical, geological and morphological heterogeneity, and for this reason the site is particularly prone to seismic topographic amplification effects. In this paper, the authors carried out numerical studies focused on the topographic seismic effect evaluation concerning the slope affected by the landslide phenomena. For this site, geotechnical characterization was available concerning both in-situ and laboratory tests; boreholes, piezometers, down-hole tests, multichannel analysis of surface waves tests, seismic tomographies and inclinometer measurements were carried out. Furthermore, 1-D and 2-D local seismic response analyses were carried out by using different synthetic seismograms related to the earthquake of Messina and Reggio Calabria on 28 December 1908. The results of the numerical analyses are presented in terms of response seismograms and response spectra at the surface.

Engineering-Geological Features Supporting a Seismic-Driven Multi-Hazard Scenario in the Lake Campotosto Area (L’Aquila, Italy)

This paper aims to describe the seismic-driven multi-hazard scenario of the Lake Campotosto artificial basin (Abruzzo Region, Central Italy), and it can represent a preparatory study for a quantitative multi-hazard analysis. A comprehensive multi-hazard scenario considers all the effects that can occur following the base ground shaking, providing a holistic approach to assessing the real hazard potential and helping to improve management of disaster mitigation. The study area might be affected by a complex earthquake-induced chain of geologic hazards, such as the seismic shaking, the surface faulting of the Gorzano Mt. Fault, which is very close to one of the three dams that form the Lake Campotosto, and by the earthquake-triggered landslides of different sizes and typologies. These hazards were individually and qualitatively analyzed, using data from an engineering-geological survey and a geomechanical classification of the rock mass. With regard to the seismic shaking, a quantitative evaluation of the seismic response of the Poggio Cancelli valley, in the northern part of Lake Campotosto, was performed, highlighting different seismic amplification phenomena due to morphologic and stratigraphic features. Some insights about the possible multi-hazard approaches are also discussed.

Understanding the Damages Caused by the 1999 Kocaeli Earthquake on One of the Towers of the Theodosian Walls of Constantinople

ABSTRACT The Theodosian walls of Constantinople have suffered many partial destructions in their long-lasting life, often because of strong seismic events, undergoing subsequent reconstructions. With reference to the 1999 Kocaeli earthquake, the article illustrates a procedure implemented to understand the damages suffered by one of the towers (tower 19) of this magnificent piece of heritage, that had just been partially reconstructed in the framework of a large manutention and preservation program of the whole historic defensive system. The seismic action on the tower was calculated considering local seismic site amplification, and the seismic behaviour of the masonry tower was analysed taking into account dynamic soil-structure interaction. Based on the available level of knowledge, the seismic demand of the tower is first evaluated by the classical modal response analysis and then by a linear time domain approach. Under both situations, the comparison between the compliant and the fixed base models allowed to recognize the detrimental effect of Soil Structure Interaction (SSI). Furthermore, the dynamic linear analysis allowed to detect the mechanism of earthquake induced triggering damage into the masonry panels.