Local Seismic Amplification Research Articles

Stochastic Approach for 2D Superficial Seismic Amplification Based on Quad4M; City of L’Aquila (Italy) Test Case

The values of the physical–mechanical properties of any soil are affected by uncertainties both due to experimental measurements and the impossibility of knowing them, in detail, at every point of the spatial domain. Accordingly, this work focuses on uncertainty in shear wave velocity (Vs) and its impact on the seismic response. The Monte Carlo method, based on pseudo-random number generation, was selected. To understand which random distributions could identify the site’s real conditions, the Fourier spectrum frequencies were calculated for each realization and were compared with the predominant natural site frequency. The experimental range data were used to calculate the spectral average acceleration and the horizontal amplification factors. The simulations were performed and interpreted by a modified version of VisualQ4M software based on 2D Quad4M, including the generation of pseudo-random numbers and pre- and post-data processing. A site at a small scale, in the territory of the city of L’Aquila (Italy), was selected as the test case. This paper demonstrates, from a numerical point of view, that both a simple local topographic modification due to excavation and the uncertainties of the numerical values, even of the shear wave velocity alone, can have an important impact on the local seismic amplification.

Seismic response of landslides to natural and man-induced ground vibrations: Evidence from the Petacciato coastal slope (central Italy)

This study focuses on the vibrational response of a landslide mass to natural and man-induced vibrations. The landslide is located in the Molise region (Italy) and involves a coastal slope extending approximately 5 km2, from the Petacciato village to the coastline. The landslide activity is well documented since 1909 with historical reactivations and resulted in severe damage to infrastructure and to the ancient village. This activity is characterised by a roto-translational mechanism involving blue clays, sands, and conglomerates of Pleistocene age. A multitemporal geomorphological analysis of the landslide activity allowed us to detect a retrogressive style corresponding to the crown area as well as a prograding toe that reaches the submerged nearshore. Seismic ambient noise measurements revealed that the local seismic amplification is strictly concentrated in the back-crown area, i.e., the area affected by the most recent retrogressive effects of the landslide mass. Moreover, ground vibrations generated by train transits were analysed to identify possible amplification phenomena of dynamic external input, that can occur inside the landslide mass with respect to the surrounding area. Therefore, a Spectral Aggravation Index (SAI) was defined by the ratio between the Fourier spectrum during train transit and that obtained for an equal time window in the absence of train traffic sources. The SAI was applied to compare the response to man-induced vibrations inside the landslide mass with the one outside, by computing a ratio of the SAI at different measurement points inside/outside the landslide mass. The obtained results highlight the intense activity of the landslide both in space and time, revealing a joining between the ongoing retreat areas, surveyed by multitemporal geomorphological analysis, and local seismic response, by geophysical investigations. On the other hand, most of the landslide mass from the middle- to downslope position is not resonant and its higher damping causes a lower intensity of ground motion in response to man-induced vibrations with respect to the surrounding areas.

Seismic Microzonation of the Pompeii Archaeological Park (Southern Italy): Local Seismic Amplification Factors

Pompeii Archaeological Park is the best laboratory for the study of the seismic site effects on cultural heritage: the ancient site was destroyed and buried by the 79 AD Vesuvian eruption and, furthermore, it was also affected by the 62–63 AD strong earthquake. Large sectors of the city were reconstructed after this earthquake while other parts were still under reconstruction when the fall-out and pyroclastic density currents of the eruption buried the Roman city. In order to evaluate the distribution of the damage and reconstructions due to the earthquake, detailed mappings of the structures were carried out using multidisciplinary approaches. In addition, analyses of the topographical features, subsoil stratigraphies, and geophysical surveys, responsible for local seismic amplification (site effects), allow us to define the sectors of the ancient city where the Amplification Factors (AFs) were the main ones responsible for damage. Selected areas and examples of compromised and reconstructed buildings show that the ancient topography and subsoil features (both lithological and seismic) are the main AFs. In particular, the damages caused by the 62–63 AD earthquakes seem to be mainly due to topographical factors such as steep scarps and slopes, ridges, peaks, and terraces, as well as to the major thickness of the soft sediments (loose volcanoclastic layers, paleosols, weathered lavas, and anthropogenic infillings) located over the well-lithified lavas. It is not uncommon to also have the combination of these two factors. For the first time, this multidisciplinary approach allows us to draw a seismic microzonation map for one of the most important archaeological sites of the world.

Estimation of the Local Seismic Amplification on an Industrialized Site in the French Rhône Valley

Estimation of the Local Seismic Amplification on an Industrialized Site in the French Rhône Valley

New insights on bedrock morphology and local seismic amplification of the Castelnuovo village (L'Aquila Basin, Central Italy)

The Castelnuovo village is placed on a small NW-SE trending ridge, approximately 60 m higher than the valley floor, occupying a portion of the larger continental L'Aquila Basin (Central Italy). During the April 6, 2009 L'Aquila earthquake (Mw 6.3), the village suffered heavy damage. Several studies investigated the local seismic amplification of the Castelnuovo area employing geotechnical, geophysical, and geological surveys, together with 1D, 2D and 3D numerical models. However, all these studies relied on shallow geotechnical and geophysical surveys, which do not reach the engineering bedrock and do not constrain the presence of an impedance contrast at depth. To date, no detailed study has been carried out to assess the depth of the engineering bedrock. In this work, we fill this gap by executing two deep boreholes reaching the engineering bedrock, tied with an extensive campaign of microtremor measurements all over the Castelnuovo ridge and the surrounding plain. The interpretation of such new data, together with analytical, numerical, and geostatistical techniques, demonstrates that local seismic amplification is linked to a strong impedance contrast at more than 200-m depth beneath the Castelnuovo village associated with the lithological transition between clayey silts and breccias. Such results differ from those provided by previous studies, where such impedance contrast was considered shallower, and represent a milestone for assessing the local seismic hazard of the area.

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.

Seismically Induced Soil Liquefaction and Geological Conditions in the City of Jama due to the M7.8 Pedernales Earthquake in 2016, NW Ecuador

Seismically induced soil liquefaction has been documented after the M7.8, 2016 Pedernales earthquake. In the city of Jama, the acceleration recorded by soil amplification yielded 1.05 g with an intensity of VIII to IXESI-07. The current study combines geological, geophysical, and geotechnical data in order to establish a geological characterization of the subsoil of the city of Jama in the Manabi province of Ecuador. Then, the liquefaction potential index (LPI) has been evaluated considering the PGA-rock values calculated from deterministic methods applied to nearby geological faults, as well as the soil acceleration records for the city of Jama since the Pedernales megathrust earthquake. The importance of conducting geotechnical evaluations of particular colluvial, alluvial, and floodplain deposits, for which the liquefaction probability profiles have been additionally obtained, may serve as a useful tool for edifices foundations or earthquake resistant designs. Finally, the site response analysis is presented using a linear equivalent analysis, where previously seismic records compatible with the target spectrum have been selected. Hereby, the results of ground surface effects have been compared with the spectra of the Ecuadorian Regulation of Construction (NEC) in the context of local seismic amplification.

Quantifying local seismic amplification from regional charts and site specific numerical analyses: a case study

Three levels of seismic microzonation are considered in the Italian guidelines: 1st level allows to qualitatively recognise those areas characterised by the same seismic performance, while 2nd and 3rd levels quantify the modification of the reference signal due to the specific site conditions. The paper summarises and compares the results of 2nd and 3rd level seismic microzonation studies for the Dovadola urban area (Emilia-Romagna, Italy). The site was selected due to the availability of in situ and laboratory investigations for the definition of a detailed geotechnical seismic model of the subsoil. The 2nd level study was conducted adopting the regional charts for the quantification of the stratigraphic amplification phenomena and the regional procedures for assessing the influence of topography. The 3rd level analysis was developed through mono- and two-dimensional seismic site response analyses adopting a numerical non-linear approach. Amplification factors for the peak ground acceleration and for the velocity spectrum intensity (i.e. the integral of the pseudo-spectral velocity of a ground motion from 0.1–0.5 to 0.5–0.1 s) were determined along two geotechnical sections of the site, both characterised by a central large and surficial valley bordered by irregular topography. The study indicates a general satisfactory match between the results of the simplified regional approach and the advanced numerical tool, especially when one-dimensional seismic site conditions prevail. Further comparative studies are encouraged to validate the 2nd level microzonation as a reliable tool for seismic risk mitigation.

New approaches to modelling of local seismic amplification susceptibility using direct characteristics of influencing criteria: case study of Bam City, Iran

Abstract. This paper proposes a new model in evaluating local seismic amplification susceptibility by considering direct characteristics of influencing criteria and it deals with uncertainty of modelling through production of fuzzy membership functions for each criterion. For this purpose, relevant criteria were identified by reviewing previous literature. These criteria include alluvial thickness, stiffness and strength of alluvial deposits, type of soil and particle size distribution of alluvial deposits, depth of groundwater, type of rock, topographic irregularities, slope, and type of bedrock. Two methods, analytic hierarchy process (AHP) and fuzzy logic (FL), were applied in order to define priority rank of each criterion and sub-criteria of each criterion through interview data of 10 experts. The criteria and sub-criteria were combined using the weighted linear combination method in GIS to develop a model for assessing local seismic amplification susceptibility in the study area of Bam City, Iran. The model's output demonstrated high to very high seismic amplification levels in central, eastern, northeastern, and northern parts of the study area. The validation results based on overall accuracy and kappa statistics showed 73.6 % accuracy, with 0.74 kappa indicating a good fit to the model's output. This model assists planners and decision makers in determining local seismic amplification susceptibility to be incorporated in designing new development plans of urban and rural areas and in making informed decisions regarding safety measures of existing buildings and infrastructures.

Combined Geophysical and Geotechnical Approaches for Microzonation Studies in Hispaniola Island

In this paper, we describe recent studies for the geophysical and geomechanical characterization of soils in Hispaniola (Greater Antilles), an island threatened by the eventual rupture of major seismogenic fault systems. The investigations were performed for four different cities settled on complex geological formations in Haiti (Cap-Haïtien, Port-au-Prince) and the Dominican Republic (Santo Domingo, Santiago de los Caballeros). We present the complete methodology we implemented for mapping zones of homogeneous seismic response and for microzonation studies, but each main stage of investigation is described as it was conducted in one or two cities. Therefore, first we present our site-characterization technique applied to Santo Domingo and Santiago de los Caballeros, which is based on geotechnical data, geophysical multichannel analysis of surface waves, and ambient-noise recordings. Then we present the site-response analysis through numerical analysis with nonlinear soil models that we performed for the city of Cap-Haïtien. Finally, we describe the amplification factors for site-specific response spectra that we derived for the microzonation of Port-au-Prince. We argue for the implementation of a multidisciplinary approach built upon complementary field geological, geophysical, and geotechnical data rather than solely depending on geophysical measures for the characterization of VS30. In addition, we explore the compatibility of the soil classes recommended by the International Building Code (IBC) in the context of local seismic amplification.

Mapping Depth to Bedrock, Shear Stiffness, and Fundamental Site Period at CentrePort, Wellington, Using Surface‐Wave Methods: Implications for Local Seismic Site Amplification

Wellington's port (CentrePort) experienced significant damage from the $M_w$ 7.8 Kaik\=oura earthquake as a result of soil liquefaction, lateral spreading, and shaking-induced damage to structures. To investigate these ill effects, and propose mitigation measures to prevent similar damage in future earthquakes, there was a need to quantify the variations in the depth to bedrock, shear stiffness, and fundamental site period ($T_0$) across the port. In order to characterize $T_0$ and develop shear wave velocity (Vs) profiles for use in seismic site response analyses, horizontal-to-vertical (H/V) spectral ratio measurements and active-source and passive-wavefield surface wave testing (i.e., MASW and MAM, respectively) were performed across the port. A site period map developed from 114 H/V spectral ratio measurements indicates several areas of rapidly changing, complex subsurface structure. Deep (200-plus meters) Vs profiles developed at six reference locations across the port were used to estimate the depth to soft (Vs $>$ 760 m/s) and hard (Vs $>$ 1500 m/s) rock. $T_0$ estimates from H/V spectral ratio measurements ($T_{0,H/V}$) at the six reference locations are shown to be related to the depth of hard rock based on linear viscoelastic transfer functions calculated from Vs profiles truncated at several depths. $T_{0,H/V}$ measurements at two ground motion stations near the port are also shown to be in reasonably good agreement with predominant periods of maximum spectral amplification recorded during both the 2016 Kaik\=oura and 2013 Cook Strait earthquakes, despite these sites also being effected by soil nonlinearity and potential 3D basin edge effects.

First assessment of the local seismic amplification susceptibility of the Isernia Province (Molise Region, Southern Italy) by the integration of geological and geomorphological studies related to the first level seismic microzonation project

This paper presents the results of the geological and geomorphological investigation carried out during the first level seismic microzonation project in the Isernia Province territory. The study area falls in one of the most seismically active areas of the Apennine chain and it has been struck, in historical times, by destructive earthquakes that caused several causalities and diffuse damages to the buildings. The analysis points out the occurrence of geological features that can determine possible site amplification phenomena related to areas with extensive outcrops of thick continental deposits or to unstable areas (both covering about 48% of the investigated areas). The latter are sometimes combined with geomorphological features such as scarps, isolated peaks, and ridges that are also responsible for possible site amplification. In addition, a susceptibility to local seismic amplification index has been introduced which highlights that more than 64% of the investigated area, along with a significant percentage of buildings, fall within the highest categories of susceptibility to local seismic amplification.

Local seismic site amplification: effects of obliquely incident antiplane motions

Seismic site amplification studies are generally used to assess the effects of local geology and soil conditions on ground motion characteristics. Although extensive reviews on site amplification phenomena associated with stratigraphic effects can be found in the specialized literature, it should be pointed out that most of the practical applications have been limited to the study of vertically propagating shear horizontal (SH) waves, i.e., to the 1-D soil amplification problem. Furthermore, little attention, if any, has been devoted to the study of the effects of non-vertically incident SH waves on surface accelerograms and on the earthquake response of structures. In the present work, the study is extended to an investigation of 2-D site amplification of non-vertically propagating seismic shear waves in multilayered viscoelastic soil deposits. Sensitivity analyses of the effects of non-vertical incidence on site amplification functions are performed based on site geotechnical data collected from post-seismic investigations of the 1980 El-Asnam earthquake. Analytical results are discussed in terms of seismic site transfer functions, spectral ratios, surface acceleration time histories, and structural response spectra for different values of wave incidence angle. Both bedrock and rock outcropping cases are examined.

Site classification map of Italy based on surface geology

Abstract In this article a method developed for the creation of a site classification map at a territorial scale, starting from the geological mapping available at 1:100 000 scale, is described. This map has been used to embed amplification factors as provided by the Italian seismic code in seismic hazard studies, in order to consider the contribution of the surface geology on the expected ground motion values. The Italian territory has been divided into polygons classified on the basis of lithologies that the seismic code considers homogeneous in their average seismic response. The data processing has been conducted in a GIS environment, starting from the digital format of the lithological map of Italy at 1:100 000 scale. Our results can be used in seismic risk analyses that take into account the local seismic amplification due to the geological characteristics of an area, and in studies on ground motion prediction equations (GMPE).

Multisensor surveys of tall historical buildings in high seismic hazard areas before and during a seismic sequence

A seismic sequence that included a moment magnitude MW=5.9 earthquake struck three regions of Northern Italy (Emilia Romagna, Veneto and Lombardy) in May–June 2012. The sequence caused significant damage to several historical buildings and in some cases caused complete structural collapse. Cracks appeared in the belfry and cusp of the 69 m high, ∼3° leaning bell tower of Ficarolo (Rovigo). A project aimed at studying the geometry of the tower, possible local seismic amplification and soil-structure interaction began in early 2013 before the earthquake. The data were provided by terrestrial laser scanning, low-cost operational modal analysis and geophysical measurements. The repetition of the surveys during and after the seismic sequence, which was augmented by thermal imaging measurements, allowed an evaluation of the changes caused by the earthquake. In addition to an evaluation of the damage, the data allowed the development of a method based on fast and relatively low-cost measurements that provide useful information for cultural heritage management purposes. The results highlighted that the surveys can be carried out during a seismic emergency and that preventive measures can be carried out under reasonable time and budget constraints in high seismic hazard areas.

Integrated geological and geophysical investigations to characterize the anthropic layer of the Palatine hill and Roman Forum (Rome, Italy)

The anthropic layer of Palatine hill (Rome, Italy) and surrounding areas was modeled with the aim of providing a valuable input for assessing local seismic hazard; results are presented in this paper. More than 200 boreholes, twenty-four Electrical Resistivity Tomography (ERT), and several Ground Penetrating Radar (GPR) surveys were integrated in order to (i) characterize the archaeological layer susceptible to seismic amplification, and (ii) map the basal surface of the anthropic cover. In terms of composition, the anthropic layer was distinguished in zones with dominant masonry remains, and zones with dominant infill. Zones with dominant masonry consist predominantly of building remains, typically alternate with sandy-pebbly fill materials with a silty-clay or pozzolan matrix. Zones with dominant infill are generally subordinate and consist of sandy-pebbles with a silty-clay or pozzolan matrix. The morphology buried below the anthropic layer was reconstructed through the integration of ERT and GPR surveys, that were calibrated and constrained using geological cross-sections, borehole and archaeological stratigraphies. The basal surface of the anthropic layer was interpolated by means of multicollocated cokriging, using buried escarpments as break lines. Thickness of the anthropic layer was than calculated starting from DTM and basal surface of the anthropic layer. Finally, the possible conditioning of the anthropic layer on local seismic amplification was discussed.

The role of near-field interaction between seismic waves and slope on the triggering of a rockslide at Lorca (SE Spain)

Abstract. A ~1000 m3 rockslide occurred close to Lorca (SE Spain) during the main shock (Mw = 5.1) of the May 2011 seismic sequence. The location of the rockslide, within 10 km of the earthquake epicenter and along the southern slope of a valley in which similar geological conditions occur on both slopes of the valley, suggests a significant near-field effect due to local seismic response. This could be related to the specific interaction between the topography and the obliquely propagating seismic waves. A dynamic stress strain numerical model was constructed using the FLAC 7.0 finite difference code to back analyze the Lorca rockslide event and relate its occurrence to both the local seismic amplification and the interaction between seismic waves and local topography. The results indicate that only for seismic waves with incidence angles in the range 0°–50° are the occurred slope instabilities expected. These results do not significantly change when varying the values for either stiffness or strength parameters within the range of the experimental data.

Seismic surveys integrated with geological data for in-depth investigation of Mt. Pettino active Fault area (Western L’Aquila Basin)

Following the April 6 2009 L'Aquila earthquake, a great effort has been carried out by numerous research institutions for seismic microzonation purposes of urban areas in order to evaluate the seismic potential of the main active faults of the epicentral area. This is the case of the active Mt. Pettino master extensional fault (hereafter PEF) which controls the tectono-sedimentary evolution of western L'Aquila Basin. PEF is near to a strongly urbanized area which coincides with its pediment. This condition shows a high seismic exposition, so that specifically devoted multidisciplinary investigations, organised in subsequent in-depth steps and whose results are presented here, permitted to fine-tune its seismic hazard evaluation.The investigations were mainly based on a seismic reflection profile orthogonal to the fault strike in its hangingwall. The seismic profile was interpreted by comparison with the geological outcropping data and the stratigraphic analysis of numerous boreholes, several of which reached the pre-Quaternary substratum. The main goals were double: (i) to improve the integrated geological-geophysical subsurface model for the evaluation of the local seismic amplification and (ii) to estimate the PEF seismic hazard through the study of the sedimentary infill evolution and the tectonic subsidence of the PEF hangingwall which were strictly interrelated with the PEF seismic history.

The use of Rayleigh-wave ellipticity for site-specific hazard assessment and microzonation: application to the city of Lucerne, Switzerland

SUMMARY The sediments underlying the city of Lucerne (Switzerland) consisting of fluvio-lacustrine deposits of Quaternary age have the potential to produce strong amplification of the seismic wavefield. To obtain a reliable estimation of the deep soil structure, we combine different methodologies based on ambient noise recordings, such as single station horizontal to vertical ratios and three-component array analysis. Two novel techniques to estimate Rayleigh-wave ellipticity from ambient noise recordings are tested. These are based on a single- and a multistation approach, respectively. The first utilizes the continuous wavelet transform to perform a decomposition of the noise wavefield and to isolate and extract the Rayleigh-wave contribution. The second, conversely, relies on a high-resolution f–k method to achieve the same result. We compare the results from the two techniques to provide an evaluation of their capabilities and limitations. A two-step inversion scheme is then presented to improve resolution on the bedrock depth. In particular, the surface wave dispersion information is initially used to constrain the soft sediment part, while the Rayleigh-wave ellipticity peak is subsequently used for constraining the bedrock depth. It is shown that such an approach is beneficial to map the bedrock geometry over dense urban areas. The output velocity model is then used to compute the local seismic amplification by means of gridded 1-D approximation.

Heavier Damages without Site Effects and Site Effects with Lighter Damages: Boumerdes City (Algeria) after the May 2003 Earthquake

The ambient vibration H/V method (Nakamura 1989) is now widely used to determine the fundamental soil frequency and has proven to be a good tool for site effect evaluation ( e.g. , Bonnefoy-Claudet, Cornou et al. 2006). More particularly, it has been used for the zoning of a number of cities around the world, such as Basel, Switzerland (Fah et al. 1997); Quito, Ecuador (Gueguen et al. 2000); Barcelona, Spain (Alfaro et al. 2001); Caracas, Venezuela (Duval et al. 2001); Almeria, Spain (Navarro et al. 2001); and Thessaloniki, Greece (Panou et al. 2005). This method has also been used to find a correlation between damages from an earthquake and the frequency of ambient vibration H/V peaks ( e.g. Gueguen et al. 1998; Panou et al. 2005; Teves Costa et al. 2007; Cara et al. 2008). Other studies show that this correlation is not always clear or even does not exist (Fallahi 2003; Gonzales et al. 2004; Chatelain, Guillier, and Parvez 2008; Theodulis et al. 2008). The 21 May 2003 Algerian ( Mw = 6.8) earthquake produced severe damages in the city of Boumerdes, among others (see Figure 1 for locations). These damages were not uniformly distributed throughout the city, with a destruction level varying from 0 up to 5%, except in two neighborhoods where it reached 30% (Hamane et al. 2007). These observations led us to try to link the destruction pattern to variations of local seismic wave amplification. One of the most widely used methods for studying this type of site effect is based on recording ambient vibrations (noise) in both the vertical and horizontal directions and computing their spectral ratio (a comprehensive review of ambient vibration studies may be found in Bonnefoy-Claudet, Bard, and Cotton 2006). The physical meanings of the ambient …