Search results for "Geophysics"
showing 10 items of 2645 documents
In situ micro-Raman and X-ray diffraction study of diamonds and petrology of the new ureilite UAE 001 from the United Arab Emirates
2008
International audience; A new olivine-pigeonite ureilite containing abundant diamonds and graphite was found in the United Arab Emirates. This is the first report of a meteorite in this country. The sample is heavily altered, of medium shock level, and has a total weight of 155 g. Bulk rock, olivine (Fo79.8-81.8) and pyroxene (En73.9-75.2, Fs15.5-16.9, Wo8.8-9.5) compositions are typical of ureilites. Olivine rims are reduced with Fo increasing up to Fo96.1-96.8. Metal in these rims is completely altered to Fehydroxide during terrestrial weathering. We studied diamond and graphite using micro-Raman and in situ synchrotron X-ray diffraction. The main diamond Raman band (LO=TO mode at ~1332 c…
Geophysical study of an landslide in northern Sicily
2002
The San Fratello area in the Nebrodi Mountains (northern Sicily) is a region of high instability. It has suffered many devastating occurrences, which have hit and destroyed the village of San Fratello. At present the area is still subject to a high landslide risk. A series of geophysical surveys have been carried out with the aim of determining the thickness and dimensions of the landslide body as well as some tectonic features, in order to gain insight into the evolution of the landslide. The following geophysical techniques have been used: borehole seismic tomography, i.e. down-hole tomographic seismic soundings (DH TSS), time-domain electromagnetic (TDEM) soundings and georadar profiling…
Recognition of earthquake-induced damage in the Abakainon necropolis (NE Sicily): results from geo-morphological, geophysical and numerical analyses
2017
Seismotectonic activity and slope instability are a permanent threat in the archaeological site of Abakainon and in the nearby village of Tripi in NE Sicily. In recent times, signs of an ancient earthquake have been identified in the necropolis of Abakainon which dating was ascertained to the first century AD earthquake. The site is located on a slope of Peloritani Mts. along the Tindari Fault Line and contains evidence for earthquake-induced landslide, including fallen columns and blocks, horizontal shift and counter slope tilting of the tomb basements. In this paper, we used an integrated geomorphological and geophysical analysis to constrain the landslide. The research was directed to th…
Recurrence time distribution and temporal clustering properties of a cellular automaton modelling landslide events
2018
Abstract. Reasonable prediction of landslide occurrences in a given area requires the choice of an appropriate probability distribution of recurrence time intervals. Although landslides are widespread and frequent in many parts of the world, complete databases of landslide occurrences over large periods are missing and often such natural disasters are treated as processes uncorrelated in time and, therefore, Poisson distributed. In this paper, we examine the recurrence time statistics of landslide events simulated by a cellular automaton model that reproduces well the actual frequency-size statistics of landslide catalogues. The complex time series are analysed by varying both the threshold…
Integration of constrained electrical and seismic tomographies to study the landslide affecting the cathedral of Agrigento
2014
The Cathedral of Saint Gerland, located on the top of the hill of Agrigento, is an important historical church, which dates back to the Arab–Norman period (XI century). Unfortunately throughout its history the Cathedral and the adjacent famous Archaeological Park of the 'Valley of the Temples' have been affected by landslides. In this area the interleaving of calcarenites, silt, sand and clay is complicated by the presence of dislocated rock blocks and cavities and by a system of fractures partly filled with clay or water. Integrated geophysical surveys were carried out on the north side of the hill, on which the Cathedral of Agrigento is founded, to define lithological structures involved …
Geomorphological and geophysical investigations to study the landslide affecting the archaeological site of abakainon
2016
In recent years, a detailed archeoseismological investigation has been carried out in the necropolis of Abakainon in order to identify traces of an ancient earthquake. Although the identification of seismic damage was undoubtedly attributed to the 1st century AD earthquake, it was hypothesised that the level of damaging observed in the necropolis, as well as the counter slope tilting of the tomb basements may have also caused by a seismo-induced landslide, which produced locally an amplification of the seismic shaking. In order to identify the landslide, on which the Greek site lies, detailed geomorphological and geophysical surveys have been carried out. The research was directed to the ac…
BIFOCAL PAIRS OF IMAGES FOR LOW-COST SURVEY IN CLOSE RANGE PHOTOGRAMMETRY
2019
Abstract. This paper present a method for close range photogrammetry based on an camera positioning scheme in which two cameras capture an equal portion of an object at the same scale, but have different focal lengths and camera-to-object distances. This scheme is alternative to the stereoscopic scheme and is associated with a system of equations which permits one to calculate first the relief displacement of points on a photograph and then their relief relative to a reference plane. The obtained relief and relief displacement values can be used to produce low-cost orthophotographs by using software for image processing, which doesn’t need to be dedicated, but has to provide measurement and…
Time evolution of medium and long-period ground tilting at Campi Flegrei caldera
2020
Abstract. We analyse tiltmeter time series recorded from April 2015 to March 2019 at three borehole instruments installed at Campi Flegrei caldera (Italy). We evaluate the crustal response in terms of ground tilting to external excitations of medium/long-period tidal constituents by applying a polarization analysis. The azimuths of the tilt vectors show well-defined polarization directions and the ground tilting planes oscillate with the periodicity of the corresponding tidal constituents. For two of the three tiltmeters, the average ground oscillation pattern related to the monthly Mm and fortnightly Mf constituents show seasonal variations, which can be ascribed to rainfall-induced tiltin…
Morphodynamics of river bed variation with variable bedload step length
2013
Abstract. Here we consider the 1-D morphodynamics of an erodible bed subject to bedload transport. Fluvial bed elevation variation is typically modeled by the Exner equation, which, in its classical form, expresses mass conservation in terms of the divergence of the bedload sediment flux. An entrainment form of the Exner equation can be written as an alternative description of the same bedload processes, by introducing the notions of an entrainment rate into bedload and of a particle step length, and assuming a certain probability distribution for the step length. This entrainment form implies some degree of nonlocality, which is absent from the standard flux form, so that these two express…
Temperature variability in the Iberian Range since 1602 inferred from tree-ring records
2017
Abstract. Tree rings are an important proxy to understand the natural drivers of climate variability in the Mediterranean Basin and hence to improve future climate scenarios in a vulnerable region. Here, we compile 316 tree-ring width series from 11 conifer sites in the western Iberian Range. We apply a new standardization method based on the trunk basal area instead of the tree cambial age to develop a regional chronology which preserves high- to low-frequency variability. A new reconstruction for the 1602–2012 period correlates at −0.78 with observational September temperatures with a cumulative mean of the 21 previous months over the 1945–2012 calibration period. The new IR2Tmax reconstr…