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From high temporal resolution to enhanced radiometric resolution: Night Thermal Gradient results
No full textAnomalous thermal infrared (TIR) emissions have been widely detected by satellite sensors prior to major earthquakes. A recent processing technique for data from geostationary satellites, here demonstrated for the case of the April 06, 2009 magnitude 6.3 L’Aquila earthquake, allows us to identify areas of enhanced TIR emission around the epicentral region within a distance of about 100 kilometres. The index, called Night Thermal Gradient (NTG) identifies TIR anomalies by following the temperature trend during the night, when the surface of the Earth normally cools. However, leading up to the earthquake, an anomalous warming trend was observed. We compare the anomalous NTG pattern to the expected normal trend, taking into account the overall tectonic setting, the seismogenic faults and lithological spatial features, the orography, and the world stress map for the epicentral region. While a certain lithological selectivity can be recognized, the main stress field and known seismogenic faults seem to be less important than topographic heights, which are to be classified as non-seismogenic. The strong correlation between topography and TIR anomalies agrees with the proposed physical mechanism for the generation of TIR anomalies, namely the role played by stress-activated positive hole charge carriers, which tend not to stay in the valleys but to spread to mountain tops. This relation is apparent in the association of two tectonic features with thrust, where strong – horizontal – compressive stresses seem to be provide favorable conditions for the generation of TIR anomalies. The modification of these stress fields prior to the L’Aquila event have triggered the failure of the Paganica Fault. It is important to note that the distances, over which the TIR anomalies occurred, are an order of magnitude larger than the estimated length of the main fault rupture. Pixel-by-pixel time series comparisons between the maximum TIR anomaly area and the epicentre of the main shock show that the increase in radiative emission was associated with the areas of highest TIR anomalies, not with the area immediately surrounding the epicenter
From high temporal resolution to synthetically enhanced radiometric resolution: insights from Night Thermal Gradient results.
Full text linkElectromagnetic emissions in thermal infrared bands are an important research topic on pre-earthquake studies.
Satellite thermal data have been investigated by many independent research groups looking for their anomalous behaviour before main earthquakes occurrences. Among them, geosynchronous satellite data are reported as less prone to artefacts during data processing. In this work, the Night Thermal Gradient (NTG) algorithm is presented, which has been specifically proposed for geostationary thermal infrared data processing. NTG method relies on the exploitation of high temporal resolution data to find coherent low frequency components of a hypothetical precursory signal of seismic activity. In this paper, the method is presented by giving details about the applied procedures, steps, theoretical assumptions and results obtained during the studies of L’Aquila 2009 earthquake and the seismic activity of Central Italy and Sardinia
GPR prospection at the San Leonardo de Siete Fuentes’ church, Santu Lussurgiu, Italy
No full textThis paper presents the results of a ground penetrating radar (GPR) prospection over the floor of the main room of the church of San Leonardo de Siete Fuentes, a rural medieval building in the countryside of Santu Lussurgiu, Sardinia, Italy. Thanks to the GPR survey, the original shape of the preexisting religious building was found and reconstructed: it was a single hall church with a semicircular apse on the side opposite to the present façade that include the more ancient one. Moreover, two more locations inside the main room are indicated as points of potential archaeological interests, for the possible presence of burials or anyway manmade features just below the floor
Thermal remote sensing applications to seismology and earthquake precursors: the case of L’Aquila 2009
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Simultaneous observations of radon concentrations in soil and thermal satellitar features in a seismically active area
No full textDynamic control of historical buildings through interferometric radar technique: an useful approach for Structural Health Monitoring on earthquake damaged structures
No full textFast dynamic control of damaged historical buildings: a new useful approach for Structural Health Monitoring after an earthquake
Full text linkThe structures damage conditions assessment requires numerous precautions to ensure the safety of people during site-visits and inspections. Among several methods providing useful information about the conservation status of the structures, dynamic monitoring techniques are suitable to retrieve global behaviour of the buildings. The anomalous features diagnosis of the structural dynamic response is an index of alterations of the material state and, in the worst cases, is related to the presence of damaged structural elements. This paper proposes the use of remote control systems for the structural evaluation of the damage state of buildings, and describes the results achieved in an interesting application: the experimental dynamic analysis carried out on the inaccessible damaged bell tower of the Church of Santi Giacomo and Filippo in Mirandola (Italy). The study is based on observations performed using the IBIS-S ground-based radar interferometer to remotely measure the displacements of several elements of the building above 0.01 mm amplitude. This totally non-invasive and non-destructive approach has proved to be reliably implemented as a useful method to Structural Health Monitoring procedures and especially for extensive and fast inspection analyses aiming at the first evaluation of the damage level and the soundness of slender buildings after earthquakes
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