Search results for "EOF"
showing 10 items of 354 documents
Assessment of the Reliability of the SPAC Method in Urban Areas
2015
We have carried out several long-term measures of seismic noise with triangular arrays of broad-band seismic sensors, to investigate the reliability of the SPAC method in urban areas. We investigate the stationary and anisotropy of the microtremor wave field. We have found that the anisotropy of the microtremor wave field can be evaluated analyzing the HVNSR as function the azimuth. Furthermore, we showed as strong anisotropies in the microtremors are often observable in particular at high frequencies (> 1 Hz). We have verified as microtremors can be difficult to considered as ergodic processes, and for this reason time averaging, also even over a long periods of time, cannot replace an app…
On the stationarity of the horizontal to vertical noise spectral ratio
2015
The Horizontal to Vertical Noise Spectral Ratio (HVNSR) method is nowadays widely used to estimate the resonance frequencies of geological structures. In the HVNSR method, seismic noise is considered as a stationary stochastic process. However, especially in industrialized/urbanized area, this is a very strict assumption seldom occurred. Several sources of noise can generate non stationary and anisotropic microtremor fields. To investigate the stationarity of microtremor, we have carried out several long-term measures of seismic noise with broad-band seismic sensors, in areas where the main source of anthropogenic noise is well known. The signals acquired have been analyzed both in frequenc…
Comparison of different acquisition patterns for 2D tomographic resistivity surveys
2015
A systematic comparison is presented between some 2D resistivity models and their images by the inversion of synthetic datasets relating to three different arrays, suitable for multichannel data acquisitions (dipole-dipole (DD), Wenner-Schlumberger (WS) and multiple gradient (MG)). The goal is to study how the measurement errors affects the resolution of the tomographic models and the ability to retrieve correct information on buried targets. We considered different data acquisition patterns, gradually increasing the complexity of the combinations of potential spacing and dipolar distance. To this end we increased the number of current dipoles to obtain approximately the same amount of meas…
Seismostratigraphic modeling using constrained HVSR Data
2017
An application of HVSR inversion is presented in order to verify the effectiveness of this technique for purposes of reconstruction of the buried geological setting where stratigraphic constraints are available. Specifically, the reconstruction of the stratigraphy in the studied area has been obtained by a seismic-stratigraphic three-dimensional modeling. This allowed for geophysical and geognostic data derived from surveys carried out during this study, as well as previously by the municipality of Palermo.
Centroid-based Cluster Analysis of HVSR Data for Seismic Microzonation
2014
Horizontal to Vertical Spectral Ratio (HVSR) datasets acquired for studies of seismic microzoning in various urban centers of Sicilian towns, have been used to test clustering analysis through a nonhierarchical centroid-based algorithm. In this context clustering techniques may be useful to identify areas with similar seismic behaviour through HVSR data. Centroid-based algorithms generally require the number of clusters, k, and the initial centroid coordinates to be specified in advance. This aspect is considered to be one of the biggest drawbacks of these algorithms. The proposed algorithm doesn’t limit the number of k clusters and choose the initial centroids automatically from the data s…
Seismic Characterization by Inversion of HVSR Data to Improve Geological Modelling
2014
SUMMARY An application of HVSR inversion is presented in order to verify the effectiveness of this technique for purposes of geological reconstruction of the subsoil finalized to studies of seismic microzonation of heavily urbanized areas, where few stratigraphic and geophysical constraints are available and most of the information are derived from the geological maps. In such cases the uncertainty of the results is is enhanced by doubts on the nature of the H/V peaks, not always caused by stratigraphic discontinuities, and to the subjective choices done especially in the step of signal preprocessing. The investigated area (Altavilla Milicia, Sicily) includes the town center and the adjacen…
Seismic investigation for the characterization of a gravity concrete dam
2016
Monitoring of large-scale infrastructures plays an important role for public safety and prevention. The control of the safety assessment of a dam is largely dependent on knowledge of the mechanical parameters of the actual construction, as well as its geological substratum. The application of geophysical methods can considerably contribute to the examination indicating the less consolidated material and the degradation of mechanical parameters. A seismic tomographic approach has been used in a typical gravity concrete dam without reinforcement to detect mechanical properties of the body of the dam and its geological setting. Three seismic travel time tomographies in the dam body as well as …
Remotely controlled aerial and underwater vehicles in support to magnetic surveys
2019
This article deals with the creation of a professional magnetometer, a flexible, light and compact instrument that can be installed on aerial and marine drones. The instrument can accurately measure the local magnetic field. Subsequently, it was installed on AUV and a micro ROV to test its effectiveness for archaeological purposes and magnetic surveys. Experimental data show that both systems can be used by filtering disturbances from vehicles.
Valutazione della performance di localizzazione della RSNC-INGV tramite simulazione numerica
2010
A properly organized seismic network is a valuable tool formonitoring seismic zones and seismic risk assessment. This paper proposes a method for evaluating the performance in hypocenter location of a seismic network by numerical simulation (SNES, SeismicNetwork Evaluation through Simulation). The SNESmethod needs as input: the location of the stations that make the network and their noisiness, the velocity model used in the location routine and a law that allows to estimate the variance in the time residuals. This method gives, as function of magnitude, hypocentral depth and confidence level, the spatial distribution of: number of active stations in the location procedure and relative azim…