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Numerical models play a primary role in Cultural Heritage preservation. Nevertheless, the design of a realistic model remains challenging due not only to the complex behavior of masonry but also to the asynchronous building phases, the damage induced by natural and anthropic aggression, and the associated repairs. This paper discusses the impact of the information provided by an in-depth analysis of the construction history on the updating process of a Finite Element building model. The case study is the church of Sant'Agata del Mugello (Italy); for this building, a previous historical–archaeological study identified and recorded the asynchronous construction phases, the repair techniques, and the damage induced by three historical earthquakes (1542, 1611, and 1919) – moreover, a dense ambient vibration survey allowed to identify the modal parameters. The information from previous works is summarized in five Finite Element models with increasing complexity. A vibration-based model updating methodology based on a Particle Swarm Algorithm is developed. This work shows that the best minimization of the difference between the numerical and experimental modal parameters is obtained with the numerical model considering the identified construction techniques, repair phases, and connection relations between the bell tower and the nave. [ABSTRACT FROM AUTHOR] more...

The menhir of Locmariaquer lays in four fragments 200 m north of Locmariaquer (Morbihan, Brittany, France). Several hypotheses have been raised over time to explain its fall. This study discusses a potential earthquake origin and investigates the associated ground motion features. The historical seismicity and the current instrumental seismicity support the concept of an active seismic area. Soil and subsurface characterization highlights a complex site response. Several models of the menhir based on archaeological observations are proposed to simulate the dynamic response of the menhir. A ground motion selection from the European Strong Motion database is used as inputs. An earthquake scenario is compatible with the fall of the menhir. The associated Intensity Measures are discussed. [ABSTRACT FROM AUTHOR] more...

As the first large subduction thrust earthquake off the coast of western Guatemala in the past several decades, the 2012 November 7 Mw = 7.4 earthquake offers the first opportunity to study coseismic and postseismic behaviour along a segment of the Middle America trench where frictional coupling makes a transition from weak coupling off the coast of El Salvador to strong coupling in southern Mexico. We use measurements at 19 continuous GPS sites in Guatemala, El Salvador andMexico to estimate the coseismic slip and postseismic deformation of the November 2012 Champerico (Guatemala) earthquake. An inversion of the coseismic offsets, which range up to ~47mm at the surface near the epicentre, indicates that up to ~2m of coseismic slip occurred on a ~30 × 30 km rupture area between ~10 and 30 km depth, which is near the global CMT centroid. The geodetic moment of 13 × 1019 Nm and corresponding magnitude of 7.4 both agree well with independent seismological estimates. Transient postseismic deformation that was recorded at 11 GPS sites is attributable to a combination of fault afterslip and viscoelastic flow in the lower crust and/or mantle. Modelling of the viscoelastic deformation suggests that it constituted no more than ~30 per cent of the short-term postseismic deformation. GPS observations that extend six months after the earthquake are well fit by amodel in whichmost afterslip occurred at the same depth or directly downdip from the rupture zone and released energy equivalent to no more than ~20 per cent of the coseismic moment. An independent seismological slip solution that features more highly concentrated coseismic slip than our own fits the GPS offsets well if its slip centroid is translated ~50 km to the west to a position close to our slip centroid. The geodetic and seismologic slip solutions thus suggest bounds of 2-7m for the peak slip along a region of the interface no larger than 30 × 30 km. [ABSTRACT FROM AUTHOR] more...

The composite fault plane solutions for 24 large multiplets recorded in the western part of the Corinth Rift between 2000 and 2007 are computed by jointly inverting P polarities and Sv/P, Sh/P, Sv/Sh amplitude ratios of the direct waves. The fault plane solutions are determined using 1-D and 3-D velocity models. Solutions computed with the 3-D velocity model are preferred to the ones computed with the 1-D model because overall, 3-D solutions have a better score function. They correspond essentially to E–NE/W–SW and W–NW/E–SE striking normal faults, which is consistent with the N–S extensional/vertical shortening tectonic regime of the area. For 15 multiplets, one of the nodal planes is similar to the plane delineated by the earthquakes. It is then possible to determine which nodal plane is the fault plane. The analysis of the fault plane solutions highlights a clear decrease of their dip with depth and towards the north. Several multiplets with steeply dipping fault planes (50°–60°) located at depths of 7–8 km are clearly located at the base of onshore and offshore faults that crop out close to the south border of the Corinth Gulf, indicating that these faults are steep down to 7–8 km depth. To the north, multiplets underline a low angle north-dipping structure (20°–30°) on which steep north-dipping faults could take root. [ABSTRACT FROM PUBLISHER] more...

The Agios Ioanis earthquake swarm occurred below the southern edge of the Corinth Rift (Greece). The swarm is of interest due to its location and especially because the activated structure is oriented at a high angle to the rift's major active normal faults. We present a detailed study of the swarm including a high-resolution relocation of multiplets, accompanied by an analysis of their geometry and of their spatio-temporal evolution. P- and S-wave traveltime delays, calculated in the spectral domain to within subsampling precision, are inverted considering all pairs of events. In a second step, the large-scale structure of the swarm is refined by inverting traveltime delays calculated from absolute wave arrival-times. The relocation image, in combination with the results of the multiplet geometrical analysis, reveals a complex structure suggesting seismic activity on parallel planes that strike southwest and dip to the northwest. We propose that this fault zone connects to the Kerinitis Valley, where geological observations suggest the presence of a transverse fault linking normal faults striking . The spatio-temporal evolution of the relocated seismicity provides evidence of a ∼20 m day−1 migration of seismic activity towards the surface. Assuming fluid-driven seismicity, we model the spatio-temporal evolution as the diffusion of a pore-pressure perturbation. The preferred model indicates a hydraulic diffusivity equal to , suggesting that the spatio-temporal evolution of the seismicity is related to fluid flow at depth. Moreover, we estimate the hydraulic conductivity ( m s−1) and the rock permeability ( ), which compare well to available local observations. [ABSTRACT FROM AUTHOR] more...

Bouguer gravity anomalies along four profiles across the Western Himalaya and Ganga Basin show large deviations from local isostatic equilibrium. A deficit of mass characterizes the Ganga Basin, and an excess underlies the Lesser Himalaya. Both can be understood if the Indian plate is flexed down by the distributed load of part of the mountains. The cross sectional shape of the Ganga Basin seems to be controlled by the deflection of the Indian plate, which we compute assuming the Indian plate to overlie an inviscid fluid. From the shapes of both Bouguer anomaly profiles and the basement topography we place bounds on the flexural rigidity of such a plate. If the Ganga Basin is a steady state feature, then the age of the basal sediments in a given locality should be proportional to the distance of that locality from the southern edge of the basin. If the rate of convergence of India and the Himalaya were constant, that rate should equal the distance divided by the corresponding age. We find a rate of 10 to 15 mm/a for the last 15 to 20 Ma, which is consistent with a large part of the 50 mm/a rate of convergence between India and Eurasia being absorbed by the eastward extrusion of parts of Tibet. Profiles of Bouguer gravity anomalies show only a small peak or plateau over the southern edge of the Lesser Himalaya, implying that the boundary between the light sediments of the Ganga Basin and the heavier crustal rocks of the Lesser Himalaya is not sharp and that there exists some light material beneath the range. We infer that some sediment deposited in the Ganga Basin has been underthrust beneath the Lesser Himalaya, but the quantity is small; most of this sediment probably is scraped off the Indian plate to make the foothills of the range. We find that the load of the High Himalaya is too large to be supported solely by elastic stress in the Indian plate if the flexural rigidity of the plate is constant and if no other external forces act on the plate. The observed gradient in Bouguer gravity anomalies increases from an average of about 1 mGal/km over the Ganga Basin and Lesser Himalaya to about 2 mGal/km over the High Himalaya. This increase in the gravity gradient implies that the Moho dips more steeply (10°-15°) beneath the High Himalaya than beneath the Lesser Himalaya (2°-3°). We interpret this steepening of the Moho to be due to a weakening of the plate, which allows it to bend more sharply beneath the High Himalaya than farther south. With the inclusion of a weak segment of Indian plate beneath the High Himalaya, calculated anomalies show a somewhat increased gradient beneath the High Himalaya, but when the weight of the entire Himalaya is used as a load on the plate, calculated anomalies are more negative than observed. Therefore an external force system is needed to support much of the weight of the High Himalaya, as well as to bend the plate sufficiently beneath the High Himalaya. The magnitudes of the bending moment and the force per unit length that must be applied to the end of the plate are compatible with their sources being gravity acting on a part of India's mantle lithosphere, stripped of its crust and underthrust beneath southern Tibet. [ABSTRACT FROM AUTHOR] more...

Unusually high compressional (P) to shear (S) wave velocity ratios (Vp/Vs) were measured at different subduction zones and interpreted as fluid‐pressurized regions. Because no laboratory data reported such high values in isotropic rocks, mineralogical or anisotropic constrains were assumed. However, fluid‐saturated rocks' Vp/Vs is a frequency‐dependent property so that standard laboratory measurements cannot be directly upscaled to the field. Using a new methodology, we measured the property in the elastic regime relevant to field measurements for diverse lithologies. We obtained extreme Vp/Vs values, consistent with those reported at seismic frequency in the field. Consistently with a model, it shows that if high fluid pressure is a key factor, anomalous Vp/Vs values could evidence intense degrees of microfracturation in isotropic rocks, whichever its mineralogical content. The permeability of these regions could be larger than 10−16 m2. Plain Language Summary: Anomalous seismic properties measured at subduction zones across the globe have been linked to the occurrence of earthquakes or tremors. However, different physical causes were postulated to interpret such seismic properties, and none of the laboratory measurements quantitatively fitted with those anomalous values. From laboratory measurements dedicated to link with field ones, we report the first data set that fits with field measurements observed at subduction zones. We show that such values might evidence a large degree of microfracturing, opened by high pore fluid pressure, in isotropic rocks of any mineralogy. Key Points: First measurements of Vp/Vs in isotropic crustal rocks that quantitatively fit with the anomalously high values at subduction zonesAnomalous Vp/Vs might evidence large degree of damage, opened by quasi‐lithostatic fluid pressure, in isotropic rocks of any mineralogyPermeability ranges directly inferred from the reported Vp/Vs values could be very large [ABSTRACT FROM AUTHOR] more...