JournalTOCs

[9 followers] Follow
Full-text available via subscription

Subscription journal
ISSN (Print) 1593-5213 - ISSN (Online) 2037416X
Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia

[1 journal]

Demagnetization Analysis in Excel (DAIE). An open source workbook in Excel for viewing and analyzing demagnetization data from paleomagnetic discrete samples and u-channels
- Authors: Leonardo Sagnotti
  Abstract: The Demagnetization Analysis in Excel (DAIE) software is a single Microsoft Excel file designed for viewing and analyzing stepwise demagnetization data of both discrete and u-channel samples in paleomagnetic studies. DAIE is an Excel workbook and has an open modular structure organized in 10 worksheets. It is designed for an easy use and an interactive operability; all the commands and choices can be entered by sliding menus associated to single cells. The standard demagnetization diagrams and various parameters of common use are shown on the same worksheet including selectable parameters and user's choices. The remanence characteristic components may be computed by principal component analysis (PCA) on a selected interval of demagnetization steps. Saving of the PCA data can be done both sample by sample, or in automatic by applying the selected choices to all the samples included in the file. The whole workbook is free both for use and editing and it is available for download on a dedicated website.
  PubDate: 2013-05-13
  Issue No: Vol. 56 (2013)
The use of non-invasive field techniques in the study of small topographically closed lakes: two case studies in Sicily (Italy)
- Authors: Paolo Madonia|Marianna Cangemi|Francesco Paolo Di Trapani
  Abstract: Small endhoreic (topografically closed) lakes represent a little percentage of continental waters but, in arid or sub-arid regions, they develop special ecosystems potentially prone to ecological involution due to climatic changes. The mandatory use of light, non-invasive field techniques is often required, especially in protected areas. In the present work the use of non-invasive techniques like GPS−based bathymetric and photographic surveys have been applied to the study of two lakes, Specchio di Venere and Sfondato (Sicily, southern Italy), both natural reserves. The comparison between historical surveys and modern GPS−based bathymetries highlighted the difficulty of using the former for the reconstruction of climatic-induced variations due to the low number of measurements (spatial aliasing). In particular, at the intracaldera Lake Specchio di Venere, a high resolution survey gave new insights into a peculiar geo-ecosystem whose evolution is driven by both volcanic phenomena and biomineralization processes. On the contrary, the morphology of Lake Sfondato floor is much more simple and driven only by the superimposition of a detrital sedimentation on the initial collapse that generated the lake. The comparison betweem direct measurements and estimated changes of lake level, carried out between February 2008 and October 2009 variations, allowed us to test different hypotheses of hydrological balances, leading to opposite conclusions with respect to previous studies and remarking the fundamental importance of direct measurements in the validation of theoretical hydrological models.
  PubDate: 2013-05-06
  Issue No: Vol. 56 (2013)
A GIS-based application for volume estimation and spatial distribution analysis of tephra fallout: a case study of the 122 BC Etna eruption
- Authors: Marina Bisson|Paola Del Carlo
  Abstract: In this study, we demonstrate the use of a geo-spatial information system for volume estimation of fallout deposits and for identification of syn-eruptive and post-eruptive depositional mechanisms. For the first time, we present thickness distribution maps, isopachs maps, and fallout deposit volumes for the single stratigraphic units (A-F) of the 122 BC Plinian eruption of Etna, the most powerful eruption of this volcano in historical times. Thickness data collected during the field survey were organized into a geo-referenced database, and several interpolation algorithms were used to calculate the volumes of the six fallout layers of eruption (units A-F). The results are compared with those obtained using the Pyle method, which bases volume calculations on the exponential thickness-decay law of the deposits. Differences in the two methods are analyzed through applying two-dimensional (2D) and 3D geo-statistical analysis to thickness data, with an 'ideal' fallout deposit used as reference. Our approach allowed both identification of stratigraphic sections where the deposits were affected by secondary erosional or accumulation phenomena, and assessment of whether the secondary processes were caused by local morphologic conditions or by variations in eruptive dynamics (e.g., rotation of dispersal axis direction).
  PubDate: 2013-04-19
  Issue No: Vol. 56 (2013)
A simple statistical procedure for the analysis of radon anomalies associated with seismic activity
- Authors: Hugo Gonçalves Silva|Mourad Bezzeghoud|Maria Manuela Oliveira|António Heitor Reis|Rui Namorado Rosa
  Abstract: This study presents an analysis of data from various radon anomalies that were compiled by Toutain and Baubron [1999], to investigate their relationships with the earthquake parameters of magnitude and distance from epicenter. The simple methodology applied here reveals significant and positive correlation between the duration of the radon anomalies and the ratio between the earthquake preparation radius and the distance between the sensor and the event epicenter. This shows an important relationship between seismic activity and duration of radon anomalies at a local scale. The consequences and implications of this relationship are discussed.
  PubDate: 2013-04-19
  Issue No: Vol. 56 (2013)
The new CAS-DIS digital ionosonde
- Authors: Wang Shun|Chen Ziwei|Zhang Feng|Fang Guangyou
  Abstract: A high quality digital ionosonde called the Chinese Academy of Sciences digital ionosonde (CAS-DIS) has been developed for investigations of the ionosphere. Two important features are used for the CAS-DIS; first, the technique of analog down-conversion has been replaced by the new approach of digital down-conversion technology. Secondly, to solve the problem of large instantaneous receiving bandwidth in digital receivers, an analog narrowband tracking filter is used for the CAS-DIS. The center frequency of the filter tracks the carrier frequency transmitted in real-time, to ensure that the frequency components are filtered out of the effective bandwidth. This report describes the system architecture of the CAS-DIS, its main features, and its test results for ionosphere detection.
  PubDate: 2013-04-19
  Issue No: Vol. 56 (2013)
Magnetic anomalies of steel drums: a review of the literature and research results of the INGV
- Authors: Marco Marchetti|Vincenzo Sapia|Alessandro Settimi
  Abstract: The detection and evaluation of the status of disposal sites that contain hazardous waste materials is becoming an increasingly important element in environmental investigations. Close cooperation between the Istituto Nazionale di Geofisica e Vulcanologia (INGV; National Institute of Volcanology and Geophysics) in Rome and the Italian environmental police has resulted in numerous underground investigations of different buried materials. Among the geophysical investigation tools, magnetometry is the most effective, rapid and precise of all of the geophysical methods for localizing buried steel drums. Analysis of magnetic map anomalies can provide a variety of information about buried materials, including extension, distribution and depth, with processing of the acquired magnetic data. This information is also very useful in case of excavations that are aimed at the recovery of hazardous waste. This study determines the most relevant analyses reported in the literature, with modeling of magnetometric methods for environmental applications both theoretically and experimentally. Some studies and research results achieved by the INGV in relation to magnetic anomalies produced by buried steel drums are also reported, as found in field operations and as achieved from test sites.
  PubDate: 2013-04-19
  Issue No: Vol. 56 (2013)
Full three-dimensional relocation and tomographic inversion of the 1977-2008 earthquakes in north-eastern Italy: a feasibility study
- Authors: Aldo Vesnaver|Luca Urpi
  Abstract: In a regional seismological network, the estimation of the epicenter is usually robust, especially for events inside or close to the network boundaries. In contrast, the hypocentral depth is very sensitive to the assumed velocity field. In this study, we compare the hypocenter estimates obtained by a classical algorithm in a simple one-dimensional (1D) model with a recently developed full 3D model that is based on shrinking grids. This study is preliminary, as the 3D Earth model is based on limited data from the literature; however, it demonstrates that different patterns show up when a more representative geological model is adopted. This encourages further studies, based on fully integrated 3D models from active surface seismic, well data and other geophysical measurements. Such an integrated approach has been successfully adopted by the oil and gas industries for decades, which has increased the exploration success rate and the production of hydrocarbon reservoirs.
  PubDate: 2013-04-19
  Issue No: Vol. 56 (2013)
Buried active faults in the Zafferana Etnea territory (south-eastern flank of Mt. Etna): geometry and kinematics by earthquake relocation and focal mechanisms
- Authors: Salvatore Alparone|Salvatore D'Amico|Salvatore Gambino|Vincenza Maiolino
  Abstract: We relocated seismicity that occurred from 2000 to 2005 inside a sector of Mt. Etna, comprising the town of Zafferana Etnea, using the double-difference technique. This approach revealed some spatial clusters of events at depths of 3.0 km to 5.5 km b.s.l., which suggested NE-SW-oriented and NNW-SSE-oriented active structures located west and north-west with respect to Zafferana Etnea. We also calculated 64 fault plane solutions, and azimuth and dip distributions of maximum compression P axes. The data include eight events with magnitudes between 3.1 and 3.7 that caused damage to Zafferana Etnea. This approach has allowed the definition of the geometry of structures that show no surface evidence, but are potentially hazardous for this territory. These faults might be linked to the regional tectonics, although they were activated by stress changes related to a general pressurizing of the Mt. Etna magma system between 2000 and 2005.
  PubDate: 2013-04-19
  Issue No: Vol. 56 (2013)
Sicily and southern Calabria focal mechanism database: a valuable tool for local and regional stress-field determination
- Authors: Luciano Scarfì|Alfio Messina|Carmelo Cassisi
  Abstract: In this work, we present a new catalog of focal mechanisms calculated for earthquakes recorded in Sicily and southern Calabria. It comprises about 300 solutions, for events with magnitudes ranging from 2.7 to 4.8 that occurred from 1999 to 2011. We used P-wave polarities to compute the fault-plane solutions. Two main goals are achieved. For the first, the catalog allows the stress regime and kinematics characterizing the studied area to be depicted at a regional and more local scale. In particular, moving along the tectonic lineament that extends from the Aeolian Islands to the Ionian Sea, there is a change from a regime characterized by sub-horizontal P-axes, ca. NW-SE directed, to an extensive one in the Calabro-Peloritan Arc, where T-axes striking in a NW-SE direction prevail. Our results also show that part of the seismicity is clustered along the main active seismogenic structures, of which the focal mechanisms indicate the kinematics. Finally, in the Etna volcano area, different stress fields act at different depths due to the combination of the regional tectonics, the strong pressurization of the deep magmatic system, and the dynamics of the shallower portion of the volcano. As a second goal, we highlight that the catalog also represents a valuable tool, through the data distribution on the internet, for further studies directed towards improving our understanding of the geodynamic complexity of the region, and for a better characterization of the seismogenic sources.
  PubDate: 2013-04-19
  Issue No: Vol. 56 (2013)
Repeat-station surveys: implications from chaos and ergodicity of the recent geomagnetic field
- Authors: Angelo De Santis|Enkelejda Qamili|Gianfranco Cianchini
  Abstract: The present geomagnetic field is chaotic and ergodic: chaotic because it can no longer be predicted beyond around 6 years; and ergodic in the sense that time averages correspond to phase-space averages. These properties have already been deduced from complex analyses of observatory time series in a reconstructed phase space and from global predicted and definitive models of differences in the time domain. These results imply that there is a strong necessity to make repeat-station magnetic surveys more frequently than every 5 years. This, in turn, will also improve the geomagnetic field secular variation models. This report provides practical examples and case studies.
  PubDate: 2013-04-18
  Issue No: Vol. 56 (2013)
Tectonic blocks and suture zones of eastern Thailand: evidence from enhanced airborne geophysical analysis
- Authors: Arak Sangsomphong|Dhiti Tulyatid|Thanop Thitimakorn|Punya Charusiri
  Abstract: Airborne geophysical data were used to analyze the complex structures of eastern Thailand. For visual interpretation, the magnetic data were enhanced by the analytical signal, and we used reduction to the pole (RTP) and vertical derivative (VD) grid methods, while the radiometric data were enhanced by false-colored composites and rectification. The main regional structure of this area trends roughly in northwest-southeast direction, with sinistral faulting movements. These are the result of compression tectonics (sigma_1 in an east-west direction) that generated strike-slip movement during the pre Indian-Asian collision. These faults are cross-cut by the northeast-southwest-running sinistral fault and the northwest-southeast dextral fault, which occurred following the Indian-Asian collision, from the transpession sinistral shear in the northwest-southeast direction. Three distinct geophysical domains are discernible; the Northern, Central and Southern Domains. These three domains correspond very well with the established geotectonic units, as the Northern Domain with the Indochina block, the Central Domain with the Nakhonthai block, the Upper Southern Sub-domain with the Lampang-Chaing Rai block, and the Lower Southern Sub-domain with the Shan Thai block. The Indochina block is a single unit with moderate radiometric intensities and a high magnetic signature. The direction of the east-west lineament pattern is underlain by Mesozoic non-marine sedimentary rock, with mafic igneous bodies beneath this. The Nakhonthai block has a strong magnetic signature and a very weak radiometric intensity, with Late Paleozoic-Early Mesozoic volcanic rock and mélange zones that are largely covered by Cenozoic sediments. The boundaries of this block are the southern extension of the Mae Ping Faults and are oriented in the northwest-southeast direction. The Lampang-Chaing Rai and Shan Thai blocks, with very weak to moderate magnetic signatures and moderate to very strong radiometric intensities are dominated by marine clastic and igneous rocks or a northwest-southeast trending deformation zone of inferred Precambrian complexes, respectively. It is suggested that these tectonic plates collided against one another in a west-east direction.
  PubDate: 2013-04-18
  Issue No: Vol. 56 (2013)
Evaluation of soil thermal diffusivity algorithms at two equatorial sites in West Africa
- Authors: Taofeek Abiodun Otunla|Ezekiel Oluyemi Oladiran
  Abstract: This study presents comparisons between six algorithms used in the calculation of apparent thermal diffusivity (Kh) of the topsoil during measurement campaigns conducted at two equatorial sites. It further investigates the effects of transient and seasonal variations in soil moisture content (theta) on the estimation of Kh. The data used comprise soil temperatures (T) measured at depths of 0.05 m and 0.10 m, and theta within the period of transition from the dry season to the wet season at Ile Ife (7.55˚ N, 4.55˚ E), and for the peak of the wet season at Ibadan (7.44˚ N, 3.90˚ E). The thermal diffusivity, Kh, was calculated from six algorithms, of: harmonic, arctangent, logarithmic, amplitude, phase, and conduction-convection. The reliability of these algorithms was tested using their values to model T at a depth of 0.10 m, where direct measurements were available. The algorithms were further evaluated with statistical indices, including the empirical probability distribution function of the differences between the measured and modeled temperatures ([delta capitalized]T). The maximum absolute values of [delta capitalized]T for the six algorithms investigated were: 0.5˚C, 0.5˚C, 0.5˚C, 1˚C, 1˚C and 1˚C, respectively. Kh showed an increasing trend as theta increased from the dry season to the peak of the wet season, with R2 = 0.70 for the harmonic algorithm. The accuracy of all of the algorithms in modeling T reduced with transient variations of theta. The harmonic, arctangent and logarithmic algorithms were the most appropriate for calculating Kh for the region of study. The empirical relation between theta and Kh and the values of Kh obtained in this study can be used to improve the accuracy of meteorological and hydrological models.
  PubDate: 2013-04-18
  Issue No: Vol. 56 (2013)
Re-evaluation of the macroseismic effects produced by the March 4, 1977, strong Vrancea earthquake in Romanian territory
- Authors: Aurelian Pantea|Angela Petruta Constantin
  Abstract: In this paper, the macroseismic effects of the subcrustal earthquake in Vrancea (Romania) that occurred on March 4, 1977, have been re-evaluated. This was the second strongest seismic event that occurred in this area during the twentieth century, following the event that happened on November 10, 1940. It is thus of importance for our understanding of the seismicity of the Vrancea zone. The earthquake was felt over a large area, which included the territories of the neighboring states, and it produced major damage. Due to its effects, macroseismic studies were developed by Romanian researchers soon after its occurrence, with foreign scientists also involved, such as Medvedev, the founder of the Medvedev-Sponheuer-Karnik (MSK) seismic intensity scale. The original macroseismic questionnaires were re-examined, to take into account the recommendations for intensity assessments according to the MSK-64 macroseismic scale used in Romania. After the re-evaluation of the macroseismic field of this earthquake, the intensity dataset was obtained for 1,620 sites in Romanian territory. The re-evaluation was necessary as it has confirmed that the previous macroseismic map was underestimated. On this new map, only the intensity data points are plotted, without tracing the isoseismals.
  PubDate: 2013-04-18
  Issue No: Vol. 56 (2013)
The role of radiation damping in the modeling of repeated earthquake events
- Authors: Paola Crupi|Andrea Bizzarri
  Abstract: We have investigated the role of the radiation damping term (RDT) on repeated earthquake ruptures by modeling the faulting process through a single one-dimensional analog fault system governed by different constitutive laws. The RDT expresses the energy lost by the seismic waves. The RDT is inherently accounted for in more elaborated, fully dynamic models of extended fault, whereas it is neglected in one-dimensional fault models. In this study, we adopt various formulations of the laboratory-derived rate-dependent and state-dependent friction constitutive laws: the Dieterich-Ruina law, the Ruina-Dieterich law and the Chester and Higgs law. Our numerical results clearly indicate that the RDT significantly affects the system dynamics. More specifically, the more the RDT is effective, the more frequent the slip failures are (with a cycle-time reduction of ca. 30%). We also show that inclusion of the RDT tends to promote smaller but more frequent earthquake instabilities, irrespective of the choice of the governing law. Our data shed light on the limitations implied by the conventional formulation of the equation of motion for the spring system, in which the energy radiation is ignored.
  PubDate: 2013-04-18
  Issue No: Vol. 56 (2013)