Predictive model of Arias intensity and Newmark displacement for regional scale evaluation of earthquake-induced landslide hazard in Greece

Defining the possible scenario of earthquake-induced landslides, Arias intensity is frequently used as a shaking parameter, being considered the most suitable for characterising earthquake impact, while Newmark׳s sliding-block model is widely used to predict the performance of natural slopes during earthquake shaking. In the present study we aim at providing tools for the assessment of the hazard related to earthquake-induced landslides at regional scale, by means of new empirical equations for the prediction of Arias intensity along with an empirical estimator of coseismic landslide displacements based on Newmark׳s model. The regression data, consisting of 205 strong motion recordings relative to 98 earthquakes, were subdivided into a training dataset, used to calculate equation parameters, and a validation dataset, used to compare the prediction performance among different possible functional forms and with equations derived from previous studies carried out for other regions using global and/or regional datasets. Equations predicting Arias intensities expected in Greece at known distances from seismic sources of defined magnitude proved to provide more accurate estimates if site condition and focal mechanism influence can be taken into account. Concerning the empirical estimator of Newmark displacements, we conducted rigorous Newmark analysis on 267 one-component records yielding a dataset containing 507 Newmark displacements, with the aim of developing a regression equation that is more suitable and effective for the seismotectonic environment of Greece and could be used for regional-scale seismic landslide hazard mapping. The regression analysis showed a noticeable higher goodness of fit of the proposed relations compared to formulas derived from worldwide data, suggesting a significant improvement of the empirical relation effectiveness from the use of a regionally-specific strong-motion dataset.     

Attenuation relation of Arias intensity for Zagros Mountains region (Iran)

Arias intensity is considered as a shaking parameter suitable for characterizing earthquake impact on ground stability. Within the framework of a study aimed at providing tools for the assessment of hazards related to earthquake-induced slope failures, Arias intensity attenuation relations were determined for the Zagros Mountains region, an active tectonic belt elongated NW–SE in the western and south-western part of Iran. The calculation of relation coefficients was based on strong-motion data of earthquakes located in the Zagros area and recorded by Iranian stations managed by the Building and Housing Research Center of Iran (BHRC). Five models of attenuation relation were considered and their coefficients were estimated through a least-square regression analysis. The relations obtained were then applied to a data sample different from that used for regression and the root mean square (RMS) of residuals was examined in order to compare effectiveness of different relations in probabilistic estimates. Furthermore a comparison made with attenuation relations obtained for Alborz and the central part of Iran showed significant differences possibly related to structural differences.     

Volcaniclastic debris-flow occurrences in the Campania region (Southern Italy) and their relation to Holocene–Late Pleistocene pyroclastic fall deposits: implications for large-scale hazard mapping

The Campania Region (southern Italy) is characterized by the frequent occurrence of volcaniclastic debris flows that damage property and loss of life (more than 170 deaths between 1996 and 1999). Historical investigation allowed the identification of more than 500 events during the last four centuries; in particular, more than half of these occurred in the last 100 years, causing hundreds of deaths. The aim of this paper is to quantify debris-flow hazard potential in the Campania Region. To this end, we compared several elements such as the thickness distribution of pyroclastic fall deposits from the last 18 ka of the Vesuvius and Phlegrean Fields volcanoes, the slopes of relieves, and the historical record of volcaniclastic debris flows from A.D. 1500 to the present. Results show that flow occurrence is not only a function of the cumulative thickness of past pyroclastic fall deposits but also depends on the age of emplacement. Deposits younger than 10 ka (Holocene eruptions) apparently increase the risk of debris flows, while those older than 10 ka (Late Pleistocene eruptions) seem to play a less prominent role, which is probably due to different climatic conditions, and therefore different rates of erosion of pyroclastic falls between the Holocene and the Late Pleistocene. Based on the above considerations, we compiled a large-scale debris-flow hazard map of the study area in which five main hazard zones are identified: very low, low, moderate, high, and very high.     

Analysis of historical landslide time series in the Emilia‐Romagna region,northern Italy

A catalogue of historical landslides, 1951–2002, for three provinces in the Emilia‐Romagna region of northern Italy is presented and its statistical properties studied. The catalogue consists of 2255 reported landslides and is based on historical archives and chronicles. We use two measures for the intensity of landsliding over time: (i) the number of reported landslides in a day (D_L) and (ii) the number of reported landslides in an event (S_event), where an event is one or more consecutive days with landsliding. From 1951–2002 in our study area there were 1057 days with 1 ≤ D_L ≤?45 landslides per day, and 596 events with 1 ≤ S_event ≤ 129 landslides per event. In the first set of analyses, we find that the probability density of landslide intensities in the time series are power‐law distributed over at least two‐orders of magnitude, with exponent of about ?2·0. Although our data is a proxy for landsliding built from newspaper reports, it is the first tentative evidence that the frequency‐size of triggered landslide events over time (not just the landslides in a given triggered event), like earthquakes, scale as a power‐law or other heavy‐tailed distributions. If confirmed, this could have important implications for risk assessment and erosion modelling in a given area. In our second set of analyses, we find that for short antecedent rainfall periods, the minimum amount of rainfall necessary to trigger landslides varies considerably with the intensity of the landsliding (D_L and S_event); whereas for long antecedent periods the magnitude is largely independent of the cumulative amount of rainfall, and the largest values of landslide intensity are always preceded by abundant rainfall. Further, the analysis of the rainfall trend suggests that the trigger of landslides in the study area is related to seasonal rainfall. Copyright © 2010 John Wiley & Sons, Ltd.     

Areal Distribution of Ground Effects Induced by Strong Earthquakes in the Southern Apennines (Italy)

Moderate to strong crustal earthquakes are generally accompanied by a distinctivepattern of coseismic geological phenomena, ranging from surface faulting to groundcracks, landslides, liquefaction/compaction, which leave a permanent mark in thelandscape. Therefore, the repetition of surface faulting earthquakes over a geologictime interval determines a characteristic morphology closely related to seismic potential. To support this statement, the areal distribution and dimensions of effects of recent historical earthquakes in the Southern Apennines are being investigated in detail. This paper presents results concerning the 26 July 1805 earthquake in the Molise region, (I = X MCS, M = 6.8), and the 23 November 1980 earthquake in the Campania and Basilicata regions (I = X MSK, M_s = 6.9). Landslide data are also compared with two other historical earthquakes in the same region with similar macroseismic intensity. The number of significant effects (either ground deformation or hydrological anomalies) versus their minimum distance from the causative fault have been statistically analyzed, finding characteristic relationships. In particular, the decay of the number of landslides with distance from fault follows an exponential law, whereas it shows almost a rectilinear trend for liquefaction and hydrological anomalies. Most effects fall within the macroseismic area, landslides within intensity V to VI, liquefaction effects within VI and hydrologicalanomalies within IV MCS/MSK, hence at much larger distances. A possible correlation between maximum distance of effects and length of the reactivated fault zone is also noted. Maximum distances fit the envelope curves for Intensity and Magnitude based on worldwide data. These results suggest that a careful examination of coseismic geological effects can be important for a proper estimation of earthquake parameters and vulnerability of the natural environment for seismic hazard evaluation purposes.     

The 1627 Gargano earthquake (Southern Italy): Identification and characterization of the causative fault

We present the results of a study of the subsurface tectonic features of the Basso Molise, Western Gargano and Northern Capitanata regions (Southern Italy) aimed at the identification of the source of the disastrous 1627 Gargano earthquake. In the maximum-damage area of this earthquake we have recognised a normal fault, here called the Apricena Fault, which has been identified as the fault that caused the seismic event. The Apricena Fault, striking WNW-ESE and dipping towards SSW, extends in the subsurface for about 30 kilometres from Serracapriola to Santa Maria di Stignano cutting through the whole Quaternary sequence. Other important tectonic structures trending WNW-ESE recognized in the area belong to an inactive Pleistocene strike-slip-fault system that is linked to the Mattinata Fault and to its offshore continuation in the Gondola-Grifone structural high. The Mattinata Fault and the Gondola-Grifone High form a quite complex structural feature whose kinematic behaviour is still matter of debate in the regional geological literature. NW-SE structural features recognized in the area are extensional faults whose activity was probably related to the late flexure-hinge retreat of the Adria plate margin during the Late Pliocene-Early Pleistocene eastward migration of the thrust belt-foredeep-foreland system.     

An evaluation of seismic hazard parameters in southern Turkey

To investigate the characteristics of earthquake hazard parameters as a means of identifying different zones of seismicity, we have compiled a catalogue of about 1850 moderate to large-sized earthquakes with magnitudes m4.0 or greater in southern Turkey for the time period from 1900 to 1990. Several methods have been applied to the earthquake catalogue to assess seismic hazard. The study area is divided into 77 overlapping cells of 2° size. Theoretical calculations were made for the prediction of maximum magnitude, intensity, b-values, strain energy release and corresponding m3 and peak ground acceleration levels for a given period of time. The resultant seismic hazard for each parameter is depicted as a contour map to indicate lateral variations in areas of seismic source. A combination and evaluation of various hazard parameters resulted in more reasonable estimates of hazard. It is found that the most hazardous seismic zones are the Rhodes and Burdur zones where the level of peak ground acceleration reaches up to 280 cm s-2 for an average return period of 100 years.     

Attenuation tomography of the Southern Apennines (Italy)

The aim of this study is to improve our knowledge of the attenuation structure in the Southern Apennines using a new amplitude ratio tomography method (Phillips et al., Geophys Res Lett 32(21):L21301, 2005) applied on both direct and coda envelope measurements derived from 150 events recorded by 47 stations of the Istituto Nazionale di Geofisica e Vulcanologia National Seismic Network (Rete Sismica Nazionale Centralizzata). The two-dimensional (2-D) analysis allows us to take into account lateral crustal variations and heterogeneities of this region. Using the same event and station distribution, we also applied a simple 1-D methodology, and the performance of the 1-D and 2-D path assumptions is tested by comparing the average interstation variance for the path-corrected amplitudes using coda and direct waves. In general, coda measurement results are more stable than using direct waves when the same methodology is applied. Using the 2-D approach, we observe more stable results for both waves. However, the improvement is quite small, probably because the crustal heterogeneity is weak. This means that, for this region, the 1-D path assumption is a good approximation of the attenuation characteristics of the region. A comparison between Q tomography images obtained using direct and coda amplitudes shows similar results, consistent with the geology of the region. In fact, we observe low Q along the Apennine chain toward the Tyrrhenian Sea and higher values to the east, in correspondence with the Gargano zone that is related to the Apulia Carbonate Platform. Finally, we compared our results with the coda Q values proposed by Bianco et al. (Geophys J Int 150:10–22, 2002) for the same region. The good agreement validates our results as the authors used a completely independent methodology.     

Spatial and temporal variations in soil erosion and deposition due to land‐levelling in a semi‐arid area of Basilicata (Southern Italy)

This paper examines the changes from 1955 to 2002 in soil erosion and deposition due to changes in land‐use patterns in the semi‐arid territory of Craco, which is characterized by landsliding and badland erosion. The area underwent continuous degradation during the last century due not only to its lithological vulnerability but also to the anthropic pressure favoured by the introduction of Common Agricultural Policy (CAP) measures, which has led to the reclamation of scrub lands and badlands for durum wheat cultivation. Our analysis integrates the Unit Stream Power Erosion Deposition (USPED) model with a geographic information system (GIS) to quantify erosion risk and predict deposition patterns. Soil data, land use inventory, digital elevation data and climatic atlases were used as resource data sets to generate USPED factor values. The obtained results correlate well with field measured erosion data by other researchers. In the investigated 47 years, stable areas decreased by about 280 ha (3·8% of the total surface area), largely attributable to the increase of the low and moderate erosion intensity without significant change in sedimentation. Results from this study have implications related to understanding the geomorphic response of sites that were abandoned following remodelling due to the application of the F measure of Regulation CEE 2078/92. The average annual erosion rates estimated for abandoned and remodelled sites are respectively 15·99 and 10·64 t ha^?1, meaning that the total amount of erosion in 20 years could be estimated at around 100 t ha^?1. Copyright © 2007 John Wiley & Sons, Ltd.     

Simulation of syn-eruptive floods in the circumvesuvian plain (southern Italy)

During explosive eruptions the deposition of fine-grained volcanic ash fallout reduces soil permeability, favouring runoff of meteoric water and thus increasing the occurrence of catastrophic floods. A fully dynamic, two-dimensional model was used to simulate flooding scenarios in the Vesuvian area following an explosive volcanic eruption. The highest risk occurs in the catchment area of the Acerra-Nola Plain N and NE of Vesuvius. This plain has a population of 70,000 living in low-lying areas. This catchment area is vulnerable to ash fall because it lies downwind of the dominant synoptic circulation and it lacks a natural outflow toward the sea. Our numerical simulations predict dangerous scenarios, even in quiescent periods, during extreme rain events (return periods of 200 years have been considered), and a significant increase in the extent of the flooded areas due to renewed volcanic activity. Based on these simulations a hazard zonation has been proposed. Editorial responsibility: A Woods     

The earthquake of 6 September 2002 and the seismic history of Palermo (Northern Sicily,Italy): Implications for the seismic hazard assessment of the city

On September 6, 2002, a M_L = 5.6 earthquake, occurring some tens of kilometres offshore from the Northern Sicilian coast (Southern Tyrrhenian Sea), slightly damaged the city of Palermo and surroundings (degree 6 in the European Macroseismic Scale 1998). The macroseismic investigation of the shock and a detailed study of effects of the main earthquakes which affected Palermo in the past have been performed in order to evaluate the seismic response of the city. Moreover, the comparison of the recent event, which is instrumentally constrained, with historical earthquakes allows us to infer new insights on the seismogenic sources of the area, that seem located offshore in the Tyrrhenian sea.In the last 500 years, Palermo has never been completely destroyed but has suffered effects estimated between intensities 6 and 8 EMS-98 many times (1693, 1726, 1751, 1823, 1940, 1968, 2002). The damage scenarios of the analysed events have shown that damage distribution is strongly conditioned by soil response in the different parts of the city and by a high building vulnerability, mainly in the historical centre and in the south-eastern zone of the modern city. As a matter of fact, Palermo has always suffered greater effects than those reported for other nearby localities. The hazard assessment obtained using observed site intensities has shown that the probability of occurrence for intensity 8 (the strongest intensity observed in Palermo) exceeds 99% for 550 years, while the estimated mean return period is 152 ± 40 years. These results, in connection with building vulnerability due to the urban expansion before the introduction of seismic code, suggest that the city is exposed to a relatively high seismic risk.This paper has not been submitted elsewhere in identical or similar form, nor will it be during the first 3 months after its submission to Journal of Seismology.     

Lava-flow hazard on the SE flank of Mt. Etna (Southern Italy)

A method for mapping lava-flow hazard on the SE flank of Mt. Etna (Sicily, Southern Italy) by applying the Cellular Automata model SCIARA_-fv is described, together with employed techniques of calibration and validation through a parallel Genetic Algorithm. The study area is partly urbanised; it has repeatedly been affected by lava flows from flank eruptions in historical time, and shows evidence of a dominant SSE-trending fracture system. Moreover, a dormant deep-seated gravitational deformation, associated with a larger volcano-tectonic phenomenon, affects the whole south-eastern flank of the volcano.     

Characteristics of the low energy seismicity of central Apulia (southern Italy) and hazard implications

The central part of the Apulia region, in southern Italy, has been generally considered practically free from significant level of seismicity, but historical documentation, geological indicators and recent instrumental observations suggest that the activity of local minor tectonic structures could have been masked (and partly also induced) by that of major seismogenic structures located in the neighbouring regions. A revision of the central Apulia seismicity characteristics was conducted considering its space and time distribution, energy release rate and focal mechanisms, in view of possible hazard implications. To better constrain the seismicity rates inferable from the set of available historical data, special attention was paid to the declustering of a catalogue of low energy events (magnitude < 3.5) instrumentally detected in about 20 years: a new declustering procedure, useful for cases like to the one at hand, was purposely devised taking into account the peculiarity of local seismicity characteristics and the limitations of the available database. The results obtained by combining instrumental and historical data show that this area is affected by a rather sporadic seismicity, likely associated to a general tensional regime and possibly stimulated by the interaction with Apenninic and northern Apulia seismogenic activity. Even though less energetic, the local seismicity contributes to increase the moderately damaging shaking probability due to the activity of seismic sources located in the near areas, so to justify the adoption of at least a minimum level of caution in relation to the local definition of seismic protection measures.     

Late Quaternary deformation on the island on Pantelleria: New constraints for the recent tectonic evolution of the Sicily Channel Rift (southern Italy)

Structural observations carried out on the volcanic Island of Pantelleria show that the tectonic setting is dominated by NNE trending normal faults and by NW-striking right-lateral strike-slip faults with normal component of motion controlled by a ≈N 100°E oriented extension. This mode of deformation also controls the development of the eruptive fissures, dykes and eruptive centres along NNE–SSW belts that may thus represent the surface response to crustal cracking with associated magma intrusions. Magmatic intrusions are also responsible for the impressive vertical deformations that affect during the Late Quaternary the south-eastern segment of the island and producing a large dome within the Pantelleria caldera complex. The results of the structural analysis carried out on the Island of Pantelleria also improves the general knowledge on the Late Quaternary tectonics of the entire Sicily Channel. ESE–WNW directed extension, responsible for both the tectonic and volcano-tectonic features of the Pantelleria Island, also characterizes, at a greater scale, the entire channel as shown by available geodetic and seismological data. This mode of extension reactivates the older NW–SE trending fault segments bounding the tectonic troughs of the Channel as right-lateral strike-slip faults and produces new NNE trending pure extensional features (normal faulting and cracking) that preferentially develop at the tip of the major strike-slip fault zones. We thus relate the Late Quaternary volcanism of the Pelagian Block magmatism to dilatational strain on the NNE-striking extensional features that develop on the pre-existing stretched area and propagate throughout the entire continental crust linking the already up-welled mantle with the surface.     

Geomorphic response to late Quaternary tectonics in the axial portion of the Southern Apennines (Italy): A case study from the Calore River valley

The present study focuses on the morphotectonic evolution of the axial portion of the Southern Apennine chain between the lower Calore River valley and the northern Camposauro mountain front (Campania Region). A multidisciplinary approach was used, including geomorphological, field‐geology, stratigraphical, morphotectonic, structural, ⁴⁰Ar/³⁹Ar and tephrostratigraphical data. Results indicate that, from the Lower Pleistocene onwards, this sector of the chain was affected by extensional tectonics responsible for the onset of the sedimentation of Quaternary fluvial, alluvial fan and slope deposits. Fault systems are mainly composed of NW‐SE, NE–SW and W‐E trending strike‐slip and normal faults, associated to NW‐SE and NE–SW oriented extensions. Fault scarps, stratigraphical and structural data and morphotectonic indicators suggest that these faults affected the wide piedmont area of the northern Camposauro mountain front in the Lower Pleistocene–Upper Pleistocene time span. Faults affected both the oldest Quaternary slope deposits (Laiano Synthem, Lower Pleistocene) and the overlying alluvial fan system deposits constrained between the late Middle Pleistocene and the Holocene. The latter are geomorphologically and chrono‐stratigraphically grouped into four generations, I generation: late Middle Pleistocene–early Upper Pleistocene, with tephra layers ⁴⁰Ar/³⁹Ar dated to 158±6 and 113±7 ka; II generation: Upper Pleistocene, with tephra layers correlated with the Campanian Ignimbrite (39 ka) and with the slightly older Campi Flegrei activity (⁴⁰Ar/³⁹Ar age 48±7 ka); III generation: late Upper Pleistocene–Lower Holocene, with tephra layers correlated with the Neapolitan Yellow Tuff (~15 ka); IV generation: Holocene in age. The evolution of the first three generations was controlled by Middle Pleistocene extensional tectonics, while Holocene fans do not show evidence of tectonic activity. Nevertheless, considering the moderate to high magnitude historical seismicity of the study area, we cannot rule out that some of the recognized faults may still be active. Copyright © 2018 John Wiley & Sons, Ltd.     

Rate of soil erosion processes on vineyards in central Piedmont (NW Italy)

The ‘Tertiary Basin of Piedmont’ is a hilly region, mainly composed of marine sediments, such as marls, silts and sands. The slopes, largely devoted to grape production, are usually kept bare of vegetation and are thus prone to soil erosion processes. For two years we have measured soil loss in relation to rainfall on experimental plots located in vineyards. In all the plots considered erosion started with low rainfall intensities (0·07 mm/min), and above 0·4 mm/min the amount of soil loss dramatically increased (to over 1800 g/m in one event). Most of the erosion occurs during summer rainstorms, but the behaviour of the soil under erosive rainfalls is very different from one site to another, depending only in part upon the various rainfall rates, soil and geometrical characteristics of the plots. It can be seen that soil loss varies from nearly negligible values (20 g/m/yr) to unacceptably high levels (to over 4·7 kg/m/yr), according to the different types of land cultivation. Deep ploughing and heavy herbicide treatment give rise to accelerated erosion processes leading to soil losses much higher than in other vineyard plots in Europe.     

Geochemistry of Quaternary travertines in the region north of Rome (Italy): structural, hydrologic and paleoclimatic implications

In the Tyrrhenian region of central Italy, late Quaternary fossil travertines are widespread along two major regional structures: the Tiber Valley and the Ancona-Anzio line. The origin and transport of spring waters from which travertines precipitate are elucidated by chemical and isotopic studies of the travertines and associated thermal springs and gas vents. There are consistent differences in the geochemical and isotopic signatures of thermal spring waters, gas vents and present and fossil travertines between east and west of the Tiber Valley. West of the Tiber Valley, δ¹³C of CO₂ discharged from gas vents and δ¹³C of fossil travertines are higher than those to the east. To the west the travertines have higher strontium contents, and gases emitted from vents have higher ³He/⁴He ratios and lower N₂ contents, than to the east. Fossil travertines to the west have characteristics typical of thermogene (thermal spring) origin, whereas those to the east have meteogene (low-temperature) characteristics (including abundant plant casts and organic impurities). The regional geochemical differences in travertines and fluid compositions across the Tiber Valley are interpreted with a model of regional fluid flow. The regional Mesozoic limestone aquifer is recharged in the main axis of the Apennine chain, and the groundwater flows westward and is discharged at springs. The travertine-precipitating waters east of the Tiber Valley have shallower flow paths than those to the west. Because of the comparatively short fluid flow paths and low (normal) heat flow, the groundwaters to the east of the Tiber Valley are cold and have CO₂ isotopic signatures, indicating a significant biogenic contribution acquired from soils in the recharge area and limited deeply derived CO₂. In contrast, spring waters west of the Tiber Valley have been conductively heated during transit in these high heat-flow areas and have incorporated a comparatively large quantity of CO₂ derived from decarbonation of limestone. The elevated strontium content of the thermal spring water west of the Tiber Valley is attributed to deep circulation and dissolution of a Triassic evaporite unit that is stratigraphically beneath the Mesozoic limestone. U-series age dates of fossil travertines indicate three main periods of travertine formation (ka): 220-240, 120-140 and 60-70. Based on the regional flow model correlating travertine deposition at thermal springs and precipitation in the recharge area, we suggest that pluvial activity was enhanced during these periods. Our study suggests that travertines preserve a valuable record of paleofluid composition and paleoprecipitation and are thus useful for reconstructing paleohydrology and paleoclimate.     

Seismic hazard assessment in the volcanic region of Mt. Etna (Italy): a probabilistic approach based on macroseismic data applied to volcano-tectonic seismicity

In the framework of the UPStrat-MAFA project, a seismic hazard assessment has been undertaken in the volcanic region of Mt. Etna as a first step in studies aimed at evaluating the risk on an urban scale. The analysis has been carried out with the SASHA code which uses macroseismic data in order to calculate, starting from the site seismic history, the maximum intensity value expected in a given site with a probability of exceedance of 10 % (I_ref), for a fixed exposure time. Depending on the aims of the project, hazard is estimated for local volcano-tectonic seismicity and short exposure times (10 and 30 years), without taking into account the contribution of “regional” events characterized by much longer recurrence times. Results from tasks A, B and D of the project have produced an updated macroseismic dataset, better performing attenuation models and new tools for SASHA, respectively. The maps obtained indicate that the eastern flank of Etna, the most urbanized sector of the volcano, is characterized by a high level of hazard with I_ref values up to degree VIII EMS, and even IX EMS locally. The disaggregated data analysis allows recognizing the “design earthquake” and the seismogenic fault which most contribute to the hazard at a site-scale. The latter analysis is the starting point to select the scenario earthquake to be used in the analyses of tasks C and F of the project dealing with, respectively, synthetic ground motion simulations and the evaluation of the Disruption Index.     

2-D spectral element simulations of destructive ground shaking in Catania (Italy)

This study wants to estimate the strong ground motion in the municipal area of Catania (Italy) for a catastrophic earthquake scenario. It is part of a larger research program funded by the National Research Council – National Group for the Defence Against Earthquakes (CNR-GNDT), The Catania Project, devoted to evaluating the seismic risk of a highly urbanised area, such as that of Catania, located in a seismically active region. The reference earthquake simulates the catastrophic event (M 7.2) of 1693. The ground shaking is computed solving the 2-D full-wave equation by the Chebyshev spectral element method (SPEM). Particular emphasis is given to the construction of realistic structural models, also including the finest local detail, obtained from the geophysical, geological and geotechnical data available. Simulations are performed for several sources, to account for both a change in source position and orientation, and the finite extension of the fault along its dip. Synthetic seismograms and peak ground acceleration (PGA) envelopes, calculated at the surface for four transects across the Catania area, constitute the main result of this study which can be used for practical purposes. Simulations show that ground motion is strongly influenced by both source characteristics and crustal structure. We have found that PGA values range between 0.1 g and 0.5 g, although particular site conditions strongly affect these values locally. For example, the frequencies of maximum interest in civil engineering (1.5–4 Hz) are enhanced selectively by a thick portion of surface sediments (i.e., 30–100 m for an average shear wave velocity of 500–600 m/s). An unexpected feature is the appreciable increase of PGA at large epicentral distances, which contradicts classical attenuation relations. All the results are examined through an analysis of the propagating wavefield.