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A MATLAB toolbox, also compatible with GNU Octave, was developed in order to allow a user not necessarily expert in programming to calculate the strain rate field of an area by means of a procedure with a high level of automation starting from coordinate time series. The results can be used to investigate the crustal tectonic deformations of the studied area. These steps are implemented:time series download from a data repository, e.g. the Nevada Geodetic Laboratory (NGL), or another similar database (the download function can be easily edited to allow the use of input time series having different format); calculation of the station velocities by means of the Maximum Likelihood Estimation (MLE) method, including modeling of offsets, outliers, noise and periodic components. The MLE modeling is carried out by using the external package Hector (Bos et al., 2013. J. Geod., 87, 351-360), automatically called by means of a specifically developed MATLAB function; estimation of Common Mode Error and, if necessary, its removal from time series of some stations and recalculation of the corresponding velocities. calculation of the strain rate field on a regular grid with the modified least squares method, in which a scale factor can be introduced to define the locality of the deformation analysis. Besides the strain rate field, the toolbox provides the corresponding uncertainty estimation and geometric evaluation of the significance of the results; visualization of the results for their interpretation for scientific purposes, including the map of principal strain and the contour plots of change in area (or dilatation), engineering shear normalized to the change in area, second invariant of the strain, prevailing eigenvalue, corresponding uncertainties and geometric significance. The toolbox, which is available free of charge to any interested user, is characterized by considerable flexibility, and can be easily adapted to different data sources.The toolbox was recently used in order to refine the rates of active crustal deformation in the upper plate of subduction zones in the specific case of the E-dipping West Crati fault (Calabria) and to evaluate the convergence rate in the Main Thrust Fault (also called Sicilian Basal Thrust) north to Hyblean Plateau (South-Eastern Sicily).

Terrestrial laser scanning (TLS) and drone-based structure-from-motion (SfM) photogrammetry allowed the study of soil deformations due to blast-induced liquefaction during an experiment carried out on 4 June 2018. The research aimed at both evaluating the measurement quality and estimating the rammed aggregate piers (RAPs) effectiveness in mitigating the effects of soil liquefaction. These effects mainly consist of subsidence and deposits of ejected and extruded materials. The comparison between multitemporal 3D models provided surface variation maps and volume changes. In addition, classical topographical leveling allowed the measurement of subsurface vertical displacement along a specific cross section. The results pointed out a significant reduction, higher than 50% of soil deformation in areas improved by RAPs installation; moreover, the corresponding volume variations were no more than about 37% of those occurred in the not improved area. Finally, a critical comparison between remote sensing and leveling suggested that surface variation maps could underestimate the area lowering up to 15% in this kind of terrain.

The standard setting of a camera used in Infrared thermography (IRT) is based on the choice of the same values of emissivity and distance for all pixels of a thermal image even if the emissivity depends on the relative position of camera and observed surface. Often this is not a problem. However, the resulting temperature pattern could be inadequate if a body having a complex shape is observed from strongly constrained positions. In order to face this issue, a procedure aimed at providing a correct temperature pattern by using 3D information related to a point cloud is proposed together with its MATLAB implementation (COMAP3 toolbox). For each pixel of a thermal image, the relative position of camera and observed surface is estimated, leading to pixel-specific values of emissivity and distance. The temperature obtained in this way is also mapped onto the point cloud. The effectiveness of the procedure in recognizing areas characterized by peculiar thermal behavior is shown in the case of a historic cylindrical masonry bell tower (Caorle’s bell tower, Venice, Italy).

Structure-from-motion (SfM) is currently used for geological-geomorphological purposes under the condition that the modeling is based either on several ground control points (GCPs) well distributed in the scene or on direct georeferencing (DG). In emergency conditions and in presence of active morphodynamic processes, it could be unfeasible to use GCPs or DG. A study aimed at evaluating the quality of the results achievable by means of completely free SfM modeling of images taken from a distance of some hundred meters is shown in this paper. It is based on an experiment with an artificial target and some surveys of a bedrock scarp, where resolution and precision are evaluated as empirical functions of distance and focal length, taking into account the issues related to the scale factor. The problems related to the recognition of localized surface changes by means of multitemporal surveys are also studied. The primary result is that the free approach can really be used in geomorphological and seismotectonical surveying carried out in emergency conditions.

In the engineering geology field increased attention has been posed in recent years to potential liquefaction mitigation interventions in susceptible sand formations. In silty sands this is a major challenge because, as the fines content increases, vibratory methods for densification become progressively less effective. An alternative mitigation technique can be the installation of Rammed Aggregate Pier® (RAP) columns that can increase the resistance of the soil, accounting for its lateral stress increase and for the stiffness increase from soil and RAP composite response. To investigate the influence of these factors on liquefaction resistance, full-scale blast tests were performed at a silty sand site in Bondeno (Ferrara, Italy) where liquefaction was observed after the 2012 Emilia-Romagna earthquake. A multidisciplinary team of forty researchers carried out devoted experimental activities aimed at better understanding the liquefaction process at the field scale and the effectiveness of the treatment using inter-related methods. Both natural and improved areas were investigated by in-situ tests and later subjected to controlled blasting. The blast tests were monitored with geotechnical and geophysical instrumentation, topographical surveying and geological analyses on the sand boils. Results showed the RAP effectiveness due to the improvement of soil properties within the liquefiable layer and a consequent reduction of the blast-induced liquefaction settlements, likely due to soil densification and increased lateral stress. The applied multidisciplinary approach adopted for the study allowed better understanding of the mechanism involved in the liquefaction mitigation intervention and provided a better overall evaluation of mitigation effectiveness.

Soil liquefaction due to an earthquake can lead to permanent soil deformation and reduction of load-bearing capacity that in turn could act on building stability. Since a quantitative evaluation of post-liquefaction settlements is often very difficult, field scale liquefaction tests, carried out under controlled conditions, such as blast tests, are used to perform a correct quantitative analysis of the liquefaction phenomena. Among the significant parameters related to a blast test, there are the geometric ones, i.e. the extension of the area affected by the blast-induced liquefaction and the corresponding vertical displacements. This article shows the results of a blast test carried out at a trial site located in Mirabello (Ferrara, Italy) from a remote-sensing perspective. Data provided by aerial Structure-from-Motion photogrammetry, supported by terrestrial laser scanning measurements, were used to evaluate the soil deformation that, in the specific case study, aided a geological/geotechnical interpretation of the blast test results. In general, the proposed method can be used to characterize areas affected by blast-induced liquefaction, including those cases where blasting is used as ground improvement technique aimed at mitigating the seismic hazard.

A historical building is often a vulnerable system exposed to multiple natural and/or anthropic hazards. It seems to be the case of the 1000-year-old leaning bell tower of Caorle (Venice), whose leaning angle increased during the XX century up to 1.4°. The main interactions between this building and its environment were studied by means of a cost-effective approach based on soil stratigraphy and geomorphological data, geophysical measurements, surveying and historical information on the bell tower and the landscape. The results suggest a probable connection between tilt and overexploitation of water resources in the mid-XX century for agricultural use. In order to exclude other factors, the soil-structure resonant coupling and the effects of the bell ringing were also studied. The results highlight the importance of geoenvironmental sciences in Cultural Heritage preservation. Moreover, the proposed approach can be easily used in every similar context and could be further developed.

A seismic sequence that included a moment magnitude M W = 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.

The romanesque-byzantine style, 1000 year old leaning bell tower of Caorle (Venice Province, Italy) is a unique masonry structure, characterized by single and double lancet windows harmonically distributed on a cylinder-shaped shaft surmounted by a conic cusp. A terrestrial laser scanning (TLS) survey was carried out in 2011 and some analyses were performed on the resulting point cloud to provide the following: bell tower leaning angle, wall inclination/tapering and radius, local deviation from circular shape, and local curvature. Emphasis was placed on the changes of these quantities with elevation. In order to perform these analyses, a MATLAB/Octave toolbox was developed and is available as supplementary material of this paper. In this way, a reliable picture of the current geometry of the bell tower was obtained. In particular, a correlation between leaning angle (average value 1.4° towards East-South-East) and some surface deformations and damage (bulges, brick displacements or also material loss) was found. These results are useful for cultural heritage preservation purposes.

In this paper we present the geological effects induced by the 2012 Emilia seismic sequence in the Po Plain. Extensive liquefaction phenomena were observed over an area of ~ 1200 km2 following the 20 May, ML 5.9 and 29 May, ML 5.8 mainshocks; both occurred on about E–W trending, S dipping blind thrust faults. We collected the coseismic geological evidence through field and aerial surveys, reports from local people and Web-based survey. On the basis of their morphologic and structural characteristics, we grouped the 1362 effects surveyed into three main categories: liquefaction (485), fractures with liquefaction (768), and fractures (109). We show that the quite uneven distribution of liquefaction effects, which appear concentrated and aligned, is mostly controlled by the presence of paleo-riverbeds, out-flow channels and fans of the main rivers crossing the area; these terrains are characterised by the pervasive presence of sandy layers in the uppermost 5 m, a local feature that, along with the presence of a high water table, greatly favours liquefaction. We also find that the maximum distance of observed liquefaction from the earthquake epicentre is ~ 30 km, in agreement with the regional empirical relations available for the Italian Peninsula. Finally, we observe that the contour of the liquefaction observations has an elongated shape almost coinciding with the aftershock area, the InSAR deformation area, and the I ≥ 6 EMS area. This observation confirms the control of the earthquake source on the liquefaction distribution, and provides useful hints in the characterisation of the seismogenic source responsible for historical and pre-historical liquefactions.

The study of the health of a building connects humanistic and scientific research, and a complete characterization can be achieved by integrating all the available historical documentation, architectural and metrological studies, as well as laboratory and in situ analyses of the materials. A contactless, non-invasive surveying technique such as terrestrial laser scanning (TLS) allows the acquisition of dense and accurate geometric and radiometric (electromagnetic measurements such as signal intensity) information about the observed surface of the building, which can be easily integrated with data provided by high-resolution digital imaging. The early Christian Cantalovo church was surveyed for the first time in April 2011, by means of the ILRIS-3D ER very long range scanner. The second and last survey was performed in June 2012, after the main shocks of the Emilia earthquake seismic sequence. A very long range instrument is suitable for fast, simple and independent measurements, due to its technical characteristics and, for this reason, is easily usable for accurate surveying in emergency conditions. The main results are obtained by applying a data analysis strategy based on the creation of TLS-based morphological maps computed as point-to-primitive differences, which allow the creation of a deformation map and its evolution in time.

Terrestrial laser scanning (TLS) and structure-from-motion photogrammetry (SfM) can both provide dense and accurate point clouds. Therefore, they can be used to perform a morphological analysis of the façades of a masonry building, which relies on evaluation of the differences between the point cloud and a reference regular surface fitted to it. To compare TLS and SfM performance in morphological analysis, multimodal surveys were carried out on the square cross-section, 48-m-high Garisenda Tower in Bologna, Italy (reference surface: plane), and the circle crosssection, 42-m-high Caorle's leaning bell tower in Venice, Italy (reference surface:moving cylinder). The results show that the TLS- and SfM-based morphologies are qualitatively the same, and the relative differences are lower than 10%-20% under the condition that the viewpoint positions (VPs) are optimal. Also, the overall geometries are correctly described by both the techniques. The main conclusion is that, if no particular constraints exist (e.g., unavoidable suboptimal VPs, night surveys are needed, or trees hide the surface), TLS and SfM have similar performance in morphological analysis.

SUMMARY The monitoring of crustal motions in Northern Victoria Land (NVL) of Antarctica by means of episodic GPS stations (EGPSs) provides an accurate and dense (∼50-km spaced) velocity field. The data, gathered starting in Austral summer 1999, derive from a series of benchmarks belonging to the Victoria Land Network for DEFormation control (VLNDEF) geodetic network. The velocity uncertainties are checked on the basis of length and returning time of the episodic surveys, to obtain a meaningful strain rate field by means of a least-square computation where the contribution of a GPS station is weighted by the inverse square of its velocity error. The study shows that the NVL is characterized by a complex kinematics and that, although three subregions with different prevailing deformational behaviour can be recognized, the single blocks cannot be resolved because too few stations exist. Only features having 150–200 km size at least can be recognized. Moreover, it is demonstrated that an appropriate data processing of EGPS data can lead to an accurate evaluation of the strain rate field even in a harsh environment like Antarctica.

The Asinelli and Garisenda towers are the main symbols of the city of Bologna (Italy). These leaning towers, whose heights are about 97 and 48 m respectively, were built during the early 12 th century and are two of the few surviving ones from about 100 tall medieval buildings that once characterized the city. Therefore, they are part of the Italian cultural heritage and their safeguard is extremely important. In order to evaluate in detail the deformations of these towers, in particular the deviations from a regular inclination of their walls, the terrestrial laser scanning (TLS) has been used and an efficient direct analysis method has been developed. The towers have been scanned from six viewpoints, providing 19-point clouds with a complete coverage of the visible surfaces with large overlap areas. For each tower, after the registration of the partial point clouds into a common reference frame, an accurate morphological analysis of the acquired surfaces has been carried out. The results show several zones affected by significant deformations and inclination changes. In the case of the Asinelli tower, for which a finite element model is available, the results have also been interpreted on the basis of the static load and normal modes. The correspondence between the measured deformation and the theoretically expected deformation, caused by a seismic sequence, is clear. This fact suggests a high sensibility of the tower to dynamic loads. Although a direct evaluation of the risk cannot be carried out with the obtained results, they lead to the general indication that the structural health of these buildings must be frequently checked and that man-made loads (e.g. vibration due to vehicular traffic) should be avoided or at least reduced.

Aerial digital photogrammetry and laser scanning (lidar) and marine multibeam bathymetry can play a fundamental role in the generation of digital terrain models (DTMs) of land and submarine areas, respectively. Integrating these survey techniques is crucial for providing accurate and homogeneous DTMs along narrow coastal zones that often cannot be adequately surveyed owing to logistical limitations on collecting bathymetric data in shallow water. In this project, three aerial photogrammetric surveys, two multibeam bathymetric surveys and a lidar survey were analysed and integrated in the same reference system in order to generate the first 3D high resolution “digital terrain and marine model” (DTMM) of the volcanic island of Panarea (Aeolian Islands, Italy). This is a volcanically active area that underwent a submarine gas eruption in November 2002, and produced impacts on the environment as well as potential hazards for the local population. The DTMM shows the morphological features of this volcanic area with an average grid resolution of 1 m and a maximum elevation error of 1 m. This model will significantly improve geophysical and geomorphological studies of this volcanic island and assist in reducing future hazards. Resume La photogrammetrie numerique aerienne, le laser aeroportea balayage et la bathymetrie multifaisceaux jouent un role fondamental dans la production de modeles numeriques de terrain (MNT) de zones emergees et sous-marines. L’integration de ces techniques de restitution fournit des modeles numeriques de terrain precis et homogenes sur d’etroites bandes cotieres qui sont souvent difficiles a cartographier en raison des difficultes pratiques liees a l’obtention de donnees bathymetriques en eaux peu profondes. Dans cet article, trois leves photogrammetriques aeriens, deux leves bathymetriques multifaisceaux et un leve lidar sont analyses et integres dans le meme systeme de reference afin de produire le premier modele numerique terrestre et marin de l’ile volcanique de Panarea (Iles Eoliennes, Italie). Il s’agit d’une zone volcanique active ou une eruption gazeuse sous-marine s’est produite en novembre 2002, entrainant des impacts environnementaux ainsi que des menaces potentielles pour la population locale. Ce modele montre les caracteristiques morphologiques de cette zone volcanique avec un pas d’echantillonnage moyen de 1 m et une erreur altimetrique maximale de 1 m. Ce modele permettra d’ameliorer de maniere significative les etudes geophysiques et geomorphologiques de cette ile volcanique et contribuera a la reduction des risques futurs. Zusammenfassung Digitale Luftbildphotogrammetrie, flugzeuggestutztes Laserscanning und Facherlote zur Meerestiefenmessung spielen eine zentrale Rolle bei der Generierung digitaler Gelandemodelle (DTM) von Land- und Meeresbodenflachen. Eine Integration dieser Vermessungstechniken tragt entscheidend zur Gewinnung genauer und homogener Digitaler Gelandemodelle entlang schmaler Kustenstreifen bei. Diese konnen oft nicht in adaquater Weise allein durch Bathymetrie im flachen Wasser wegen logistischer Begrenzungen erfasst werden. Dieser Beitrag stellt drei Bildfluge, zwei Tiefenmessungen mit Facherloten und einen Laserscanning Datensatz aus einer Befliegung vor, die analysiert und in das gleiche Referenzsystem integriert wurden, um das erste hochauflosende Digitale Gelande- und Marine Modell (DTMM) der Vulkaninsel Panarea (Aolische Inseln, Italien) zu erstellen. Dies ist ein vulkanisch aktives Gebiet, das im November 2002 einer Unterwassergaseruption ausgesetzt war, die die Umwelt beeinflusste und die lokale Bevolkerung potentiellen Gefahren aussetzte. Das DTMM zeigt morphologische Merkmale des vulkanischen Gebietes mit einer mittleren Gitterweite von 1 m und einem maximalen Hohenfehler von 1 m. Mit diesem Modell konnen geophysikalische und geomorphologische Studien dieser Vulkaninsel deutlich verbessert, und zukunftige Gefahrdungen reduziert werden. Resumen La fotogrametria aerea digital, el escaner laser aereo y la batimetria multihaz juegan un papel fundamental en la produccion de modelos digitales del terreno de areas subaereas y submarinas. La integracion de estas tecnicas de obtencion de datos es crucial para producir modelos homogeneos y exactos de bandas estrechas a lo largo de la costa, y que a menudo no pueden ser exploradas por las limitaciones logisticas para la toma de datos batimetricos en aguas someras. En este articulo se analizan tres vuelos fotogrametricos, dos barridos batimetricos multihaz y un vuelo lidar que se integran en un mismo sistema de referencia para calcular el primer modelo digital tridimensional de alta resolucion del terreno y marino (DTMM) de la isla volcanica de Panarea (Islas Eolias, Italia). Esta es un area volcanica activa que sufrio una erupcion submarina de gas en noviembre de 2002 que impacto el medio ambiente y que representa un peligro para la poblacion local. El modelo complejo obtenido muestra los rasgos morfologicos de esta area volcanica con una resolucion espacial media de 1 m y un error medio de elevacion de 1 m. Este modelo permitira mejorar significativamente los estudios geofisicos y geomorfologicos de esta isla volcanica y ayudara a la reduccion del peligro.

Artificial targets are generally used in terrestrial laser scanner (TLS) practice for data georeferencing. This is because they are well recognized and modelled from the point cloud and their positions can be contemporarily measured by topographical techniques. The accuracy of target identification directly influences the georeferencing quality. In particular, retro-reflective materials can cause anomalies in range measurement due to the too high amplitude of the returned pulse. If the received pulse intensity exceeds the limits of the sensor dynamic range, the receiver saturates, producing a truncated pulse preventing the correct time-of-flight computation. A series of experiments was performed in order to test the performances of a specific instrument (Optech ILRIS 3D) for the acquisition of artificial targets made of retro-reflective material, resulting in very high reflectance. Dealing with ranges lower than about 300 m, two cases were clearly observed: the wrong distance measurement of points over high reflecting surfaces and the presence of haloes around these surfaces. Neglecting these phenomena has serious implications and can lead to wrong georeferencing. Experiments were executed and data was analysed, providing a qualitative and semi-quantitative phenomenon description. Finally, the design of a target that can be easily recognized and correctly modelled was proposed.

Assessment and mitigation of the risk induced by landslide activation need an appropriate phenomenon investigation, to obtain useful information about the failure processes. The first step is the complete kinematics characterization of the landslide ground surface, by evaluating the involved displacement and deformation patterns. A dense displacement field can be obtained from comparison of a series of multi-temporal observations performed by means of terrestrial laser scanning. Subsequently, the strain field can be computed from displacement vectors. In this paper, a modified least square technique is employed to compute the strain on the nodes of a regular grid (2D approach) or on the points of a digital terrain model (3D approach). Such a computation takes into account the displacements, their spatial distribution, as well as the measurement and modelling errors. A scale factor is introduced in order to emphasize the contributions of the experimental points on the basis of their distance from each computation point, and to recognize possible scale-depending behaviours. This method has been implemented in Matlab and applied on two landslides located in the northeastern Italian Alps (Lamosano and Perarolo di Cadore). The experiments show that different kinematics can be recognized, and the presence and influence of eventual discontinuities can be revealed. © 2007 Elsevier B.V. All rights reserved.

This work deals with the integration of different surveying methodologies for the definition of very accurate Digital Terrain Models (DTM) and/or Digital Surface Models (DSM): in particular, the aerial digital photogrammetry and the terrestrial laser scanning were used to survey the Vesuvio volcano, allowing the total coverage of the internal cone and surroundings (the whole surveyed area was about 3 km × 3 km). The possibility to reach a very high precision, especially from the laser scanner data set, allowed a detailed description of the morphology of the volcano. The comparisons of models obtained in repeated surveys allow a detailed map of residuals providing a data set that can be used for detailed studies of the morphological evolution. Moreover, the reflectivity information, highly correlated to materials properties, allows for the measurement and quantification of some morphological variations in areas where structural discontinuities and displacements are present.

This paper deals with terrestrial long-range laser scanner applications, gives an overview of topics related to this methodology, provides real and tested information about laser scanners, and analyses the reflectance of different materials. After positive results obtained during an experimental test executed in Bologna (Italy) on March 2005, the INGV (Bologna, Italy) and CODEVINTEC srl (Milan, Italy) planned a mission over the Mount Vesuvius volcano (Naples, Italy). For the first time, a wide crater area composed of low reflectivity materials was completely surveyed, creating a very accurate digital surface model. In this work, a long-range laser scanner was used to create high-precision surveys that demonstrated very low residual values in scan comparisons. The results lead to the conclusion that this methodology is suitable for surface monitoring proposals.

This paper describes a scientific approach aimed at studying the ancient part of Palazzo d’Accursio (Bologna, Italy), a masonry building which is part of the Italian cultural heritage. Laser scanning and the inspection of digital images are used to detect traces of restoration works and other interesting features related to both architectural marks and natural or anthropic events. One of the main elements of the method is the analysis of residual maps, obtained by computing the differences between the point coordinates of the facade and reference fit planes. The obtained results, based on both radiometric and geometrical analysis, are used to provide a reasonable hypothesis as to the original configuration of the studied building, while taking into account the available historical information about the constructive phases of the building.

In this study we analyse coseismic GPS displacements and DInSAR data to constrain a dislocation model for the three largest earthquakes of the 1997 Umbria-Marche seismic sequence. The first two events, which occurred on September 26 at 00:33 GMT (Mw 5.7) and 09:40 GMT (Mw 6.0) respectively, are investigated using both GPS displacements and DInSAR interferograms. We discuss and compare the results of previous studies which separately modeled a smaller subset of geodetic data. We provide a dislocation model for these two earthquakes which fits well both GPS and DInSAR data and agrees with the results of seismological and geological investigations. The first event consists of a unilateral rupture towards the southeast with a uniform dislocation. The strike, rake and dip angles are those resulting from the CMT solution. The second event consists of an unilateral rupture towards the northwest and a variable slip distribution on the fault plane. The strike and the rake are consistent with the CMT solution, but the dip angle has been slightly modified to improve the simultaneous fit of GPS and DInSAR data. While the second rupture (09:40 GMT) arrived very close to the surface, the fit to geodetic data shows that the first rupture (00:33 GMT) is deeper (2 km), despite the more evident surface geological effects. The analysis of new SAR interferograms allows the identification of a 5‐6 cm additional displacement caused by the October 3 (Mw 5.2) and 6 (Mw 5.4) seismic events. We use data from a new DInSAR interferogram to model the displacement field of the Sellano earthquake of October 14, 1997. For this event significant GPS measurements were not available. We tested two different fault plane geometries: a blind, planar fault (top depth = 2.4 km), and a curved (listric) fault reaching the surface. The two models provide a generally similar fit to the data, and show that most of the slip was released at depths greater than 2.4 km along a gently dipping (40‐45) fault surface. They also show that a unilateral rupture does not allow fitting the interferometric fringes since there is evident surface deformation to the northwest of the hypocenter. Moreover, we suggest that the concentration of high residuals in the southern part of our uniform slip model may in fact indicate a certain slip variability in this area. We conclude that, despite the moderate magnitudes and the lack of significant surface faulting, the space geodetic data allowed to constrain dislocation models giving new insights in the rupture process of the three largest events of the sequence.

SUMMARY We propose a dislocation model for the two normal faulting earthquakes that struckthe central Apennines (Umbria^Marche, Italy) on 1997 September 26 at 00:33 (Mw 5.7) and 09:40 GMT (Mw 6.0). We ¢t coseismic horizontal and vertical displacements resulting from GPS measurements at several monuments of the IGMI (Istituto Geogra¢co Militare Italiano) by means of a dislocation model in an elastic, homogeneous, isotropic half-space. Our best-¢tting model consists of two normal faults whose mechanisms and seismic moments have been taken from CMT solutions; it is consistent with other seismological and geophysical observations. The ¢rst fault, which is 6 km long and 7 km wide, ruptured during the 00:33 event with a unilateral rupture towards the SE and an average slip of 27 cm. The second fault is 12 km long and 10 km wide, and ruptured during the 09:40 event with a nearly unilateral rupture towards the NW. Slip distribution on this second fault is non-uniform and is concentrated in its SE portion (maximum slip is 65 cm), where rupture initiated. The 00:33 fault is deeper than the 09:40 one: the top of the ¢rst rupture is deeper than 1.7 km; the top of the second is 0.6 km deep. In order to interpret the observed epicentral subsidence we have also considered the contributions of two further moderate-magnitude earthquakes that occurred on 1997 October 3 (Mw 5.2) and 6 (Mw 5.4), immediately before the GPS survey, and were located very close to the 09:40 event of September 26. We compare the pattern of vertical displacements resulting from our forward modelling of GPS data with that derived from SAR interferograms: the ¢t to SAR data is very good, con¢rming the reliability of the proposed dislocation model.

Monitoring damaged buildings in an area where an earthquake has occurred requires the use of techniques which provide rapid and safe measurements even in emergency conditions. In particular, remote sensing techniques like terrestrial laser scanning (TLS) can satisfy these requirements, since they produce very dense point clouds in little time and also allow an accurate geometric modeling of observed buildings. Nevertheless, strong constraints on TLS data acquisition geometry, such as acquisition distance and incidence angles, typically characterize an area in seismic emergency conditions. In order to correctly interpret the data, it is necessary to estimate errors affecting TLS measurements in these critical conditions. A reliable estimation can be achieved by means of experiments and numerical simulations aimed at quantifying a realistic noise level, with emphasis on reduction of artifacts due to data acquisition, registration and modeling. This paper proposes a data analysis strategy in which TLS-based morphological maps computed as point-to-primitive differences are created. The method can be easily used for accurate surveying in emergency conditions. In order to demonstrate the proposed method in very diverse situations, it was applied to rapidly detect deformation traces in the San Giacomo Roncole Campanile (Modena), the Asinelli tower (Bologna) and the Cantalovo Church (Verona), three buildings damaged by the Mw 5.9 Emilia Romagna 2012 earthquake (Italy). © 2013 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS).

On May 20, 2012, a Ml 5.9 seismic event hit the Emilia Po Plain, triggering intense earthquake activity along a broad area of the Po Plain across the provinces of Modena, Ferrara, Rovigo and Mantova (Figure 1). Nine days later, on May 29, 2012, a Ml 5.8 event occurred roughly 10 km to the SW of the first main shock. These events caused widespread damage and resulted in 26 victims. The aftershock area extended over more than 50 km and was elongated in the WNW-ESE direction, and it included five major aftershocks with 5.1 ≤Ml ≤5.3, and more than 2000 minor events (Figure 1). In general, the seismic sequence was confined to the upper 10 km of the crust. Minor seismicity with depths ranging from 10 km to 30 km extended towards the southern sector of the epicentral area (ISIDe, http://iside.rm.ingv.it/). […]

A continuous global positioning system station (CGPS) provides accurate coordinate time series, while episodic GPS stations (EGPSs), which operate throughout short measurement sessions, are generally used to improve the monitoring spatial density. In an urban environment, EGPSs are typically equipped with removable mounts (topographical tripod or bipod). In this paper, a method is proposed to evaluate vertical surface motions by means of differential measurements of removable mount EGPSs with respect to a nearby reference CGPS. For each day, the correct position of this CGPS is used as reference for the quick differential EGPS measurements to allow the correction of their positions. The method is applied to evaluate subsidence in the centre of Bologna, which is characterized by significant vertical movements, probably related to seasonal climatic effects, and where these movements differ significantly even among closely spaced locations. © 2012 Nanjing Geophysical Research Institute.

Results of observations of the Mt. Vesuvius caldera, carried out by means of terrestrial laser scanning (TLS) in May 2005, October 2006 and June 2009, are reported here. In each survey the whole crater was acquired with 17/20 scans from 6 different viewpoints and the corresponding digital surface models were generated and registered into the UTM-WGS84 reference frame. In this way, a comparison between the multitemporal models leads to an evaluation of the occurred changes. The deformation maps, i.e. the contouring plots of the differences between the models along the direction of maximum variations, showed a progressive mass loss due to rock-falls from the NE vertical crater wall whose area was about 5000m2. The TLS data also showed the accumulation at the bottom. The volume loss which occurred from 2005 to 2009, was computed by subtraction of volumes defined with respect to reference planes parallel to the caldera walls and was estimated to be 20300m3. The volume uncertainties due to registration errors, subsampling noise effects, and effects due to choice of the reference plane, were also estimated. Some results were also interpreted on the basis of micro-seismic and meteorological data in order to plan a monitoring technique where seismic signals related to rock-fall and/or signals of intense rainfalls are used as alarms for fast TLS surveys able to characterize the corresponding changes of the caldera walls. The proposed methodology, in particular the simple but effective approach used in the estimation of volume uncertainties, can be applied to each rock slope instability phenomenon, regardless of the particular environment. © 2011 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS).

A GPS-based geodetic study at a regional scale requires the availability of a dense network that is characterized by 10 km to 30 km spacing, typically followed in a few continuous GPS stations (CGPSs) and several non-permanent GPS stations (NPSs). As short observation times do not allow adequate noise modeling, NPS data need specific processing where the main differences between NPSs and CGPSs are taken into account: primarily time-series length and antenna repositioning error. The GPS data collected in the 1999-2007 time-span from non-permanent measurement campaigns in the central Apennine area (Italy) that was recently hit by the Mw 6.3 L'Aquila earthquake (April 6, 2009) are here further analyzed to compute a reliable strain-rate field at a regional scale. Moreover, areas characterized by different kinematics are recognized, and a complete characterization of the regional-scale kinematics is attempted. These new data can be interpreted as indicators from the viewpoint of seismic risk assessment.

SURMODERR is a MATLAB toolbox intended for the estimation of reliable velocity uncertainties of a non-permanent GPS station (NPS), i.e. a GPS receiver used in campaign-style measurements. The implemented method is based on the subsampling of daily coordinate time series of one or more continuous GPS stations located inside or close to the area where the NPSs are installed. The continuous time series are subsampled according to real or planned occupation tables and random errors occurring in antenna replacement on different surveys are taken into account. In order to overcome the uncertainty underestimation that typically characterizes short duration GPS time series, statistical analysis of the simulated data is performed to estimate the velocity uncertainties of this real NPS. The basic hypotheses required are: (i) the signal must be a long-term linear trend plus seasonal and colored noise for each coordinate; (ii) the standard data processing should have already been performed to provide daily data series; and (iii) if the method is applied to survey planning, the future behavior should not be significantly different from the past behavior. In order to show the strength of the approach, two case studies with real data are presented and discussed (Central Apennine and Panarea Island, Italy). © 2010 Elsevier Ltd.

We computed the horizontal strain rate field for a sector of tbc Central-Southern Apennines (Italy) from GPS data collected during yearly repeated campaigns performed from 1994 to 2000 on tbc GeoModAp (Geodynamic Modeling of the Apennines) geodetic network. Site velocities were obtained starting from tbc daily coordinates and covariance solutions, using a Kalman filter approach. The residual velocity field with respect to a Eurasian 6xed reference frame shows two different prevalent motion trends, NE-ward for tbc eastern sector of the network and NW-ward for tbc western one. The mean strain rate tensor, obtained from a least square inversion method, shows a signifcant extensional deformation (1.2 x 10 ' strain/yr) normal to tbc Apennine chain, in agreement with seismological and neotectonic data. On the basis of tbc network dimension, of about 250 km, this value gives a well constrained estimate of about 3.0 ± 0.2 mm/yr of the extensional velocity oriented N55E, normal to the chain axis. Our results show a transition of the strain rate field from about N-S compression in tbc Tyrrbenian sfide to about NE-SW extension toward tbc Adriatic, which depicts a more complex deformation pattern.

During the time span 1999-2003 was set up and repeatedly surveyed a not permanent GPS network located across one of the highest seismic areas of the central Apennines (Italy). The Central Apennine Geodetic Network (CA-GeoNet), extends across Umbria, Abruzzo, Marche and Lazio regions, in an area of ?180x130 km, from Tyrrhenian to the Adriatic sea. It consists in 125 GPS stations distributed at 3-5 km average grid and includes 7 permanent GPS stations operated by the Italian Space Agency (ASI) and the Istituto Nazionale di Geofisica and Vulcanologia (INGV). With the aim to estimate the active strain rate across this part of the chain, the GPS sites have been located on the main geological units of the area and across the typical basin and range structures, related with the main seismogenic faults. In this paper we show the network and the first results obtained for a subset of 23 stations that have been occupied at least during three repeated campaigns, in the time span 1999-2003. Data analysis, performed by Bernese 4.2 software, shows an extensional rate normal to the chain, in agreement with geological and seismic data. The strain rates in the inner chain are ranging from 12x10-9±11yr-1 to 16x10-9±11yr-1 and from -14x10-9±11yr-1 to -3x10-9±11yr-1. This result provides an improved estimation of the ongoing deformation of this area with respect to previous studies and is in agreement with the style of deformation inferred from seismicity and with the features of the main seismogenic sources from recent geological and seismological investigations.

Terrestrial Laser Scanner (TLS) is an active instrument widely used for physical surface acquisition and data modeling. TLS provides both the geometry and the intensity information of scanned objects depending on their physical and chemical properties. The intensity data can be used to discriminate different materials, since intensity is proportional, among other parameters, to the reflectance of the target at the specific wavelength of the laser beam. This article focuses on the TLS-based recognition of rocks in simple sedimentary successions mainly constituted by limestones and marls. In particular, a series of experiments with an Optech ILRIS 3D TLS was carried out to verify the feasibility of this application, as well as to solve problems in data acquisition protocol and data processing. Results indicate that a TLS intensity-based discrimination can provide reliable information about the clay content of rocks in clean outcrop conditions if the geometrical aspects of the acquisition (i.e.distance) are taken into account. Reflectance values of limestones, marls and clays show, both in controlled conditions and in the field, clear differences due to the interaction of the laser beam (having a 1535 nm wavelength) with H2O-bearing minerals and materials. Information about lithology can be therefore obtained also from real outcrops, at least if simple alternation of limestones and marls are considered. Comparison between reflectance values derived from TLS acquisition of an outcrop and the clay abundance curves obtained by gas chromatography on rock samples taken from the same stratigraphic section shows that reflectance is linked by an inverse linear relationship (correlation coefficient r = - 0.85) to the abundance of clay minerals in the rocks. Reflectance series obtained from TLS data are proposed as a tool to evaluate the variation of clay content along a stratigraphic section. The possibility of linking reflectance values to lithological parameters (i.e.clay content) could provide a tool for lithological mapping of outcrops, with possible applications in various fields, ranging from petroleum geology to environmental engineering, stratigraphy and sedimentology. © 2009 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS).

We use regional and local networks of continuously-operating GPS stations (CGPS) distributed in the northern–central part of the Italian peninsula to investigate the subsidence phenomenon of the Po plain sedimentary basin and vertical movements of the surrounding areas. The observations of 146 scientific and commercial stations are analyzed and compared, adopting analytical techniques widely used to study GPS coordinate time series. The use of simple antenna supports in commercial installations, instead of a more rigorous geodetic monument, does not seem to induce significant differences in the noise characteristics and in the amplitudes of annual and semi-annual periodic signals. The vertical velocity field deduced from 129 sites with observation time spans greater than one year, located in the Central–Northern Italian Peninsula, indicates the presence of two mainly subsidence areas: the Po Plain and the Arno Plain, while the sites located in the Alps and Apennine domains show relatively low uplift. The areas of the Po Plain monitored by GPS seem to indicate that the subsidence rate is constant or, in some cases, decreasing with respect to the values obtained from the last measurements, performed up to 2006 by means of both SAR and levelling techniques. Only the central part of the eastern Po Plain close to the Apennine border (Modena city area) is characterized by a peak in subsidence consisting in a velocity of about 15 mm/yr.

An efficient procedure is proposed to define realistic lower limits of velocity errors of a non-permanent GPS station (NPS), i. e., a station where the antenna is installed and operates for short time periods, typically 10-20 days per year. Moreover, the proposed method is aimed at being independent of standard GPS data processing. The key is to subsample appropriately the coordinate time series of several continuous GPS stations situated nearby or inside the considered NPS network, in order to simulate the NPS behavior and to estimate the velocity errors associated with the subsampling procedure. The obtained data are used as lower limits to accept or correct the error estimates provided by standard data processing. The proposed approach is applied to data from the dense, non-permanent network in the Central Apennine of Italy based on a sequence of solutions for the overlapping time spans 1999-2003, 1999-2004, 1999-2005 and 1999-2007. Both the original and error-corrected velocity patterns are used to compute the strain rate fields. The comparison between the corresponding results reveals large differences that could lead to divergent interpretations about the kinematics of the study area. © 2009 Springer-Verlag.

The availability of a GPS network of 10-20 km mean size, provides good topographical support for the measurement of ground displacements, even at a local scale such as a landslide. In particular, a series of multitemporal kinematic or rapid-static GPS acquisitions of a landslide allows a good characterization of its displacements if the measurements are referred to a GPS reference network. Nevertheless, a wider network formed by stations located at long distances, for example at several tens of kilometers, characterized by large spacing, can lead to results affected by high noise, degrading the accuracy of final point positions. In order to obtain an adequate GPS reference network, some virtual reference stations (VRSs) can be introduced, even if a network refinement based on VRS cannot reach the same accuracy of a real local network. Some experiments, including measurements on a real landslide, have been performed in order to evaluate the performance of this technique. The results point out that the standard deviation of the obtained solutions is about two or three times larger than those which can be reached using a real local network.

Two Matlab™ software packages for strain field computation, starting from displacements of experimental points (EPs), are here presented. In particular, grid_strain estimates the strain on the nodes of a regular planar grid, whereas grid_strain3 operates on the points of a digital terrain model (DTM). In both cases, the computations are performed in a modified least-square approach, emphasizing the effects of nearest points. This approach allows users to operate at different scales of analysis by introducing a scale factor to reduce or also exclude points too far from grid nodes. The input data are displacements (or velocities) that can be provided by several techniques (e.g. GPS, total topographical station, terrestrial laser scanner). The analysis can be applied to both regional- and local-scale phenomena, to study tectonic crustal deformations (strain ≈10-8-10-6) or rapid landslide collapses (10-4-102), and to characterize the kinematics of the studied system. Errors on strains and geometric significance of the results are also provided. © 2008 Elsevier Ltd. All rights reserved.