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New insights from seismic tomography on the complex geodynamic evolution of two adjacent domains: Gulf of Cadiz and Alboran Sea

2012-12-31T23:00:00Z

Title: New insights from seismic tomography on the complex geodynamic evolution of two adjacent domains: Gulf of Cadiz and Alboran Sea Authors: Monna, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cimini, G. B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Montuori, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Matias, L.; Centro de Geofísica, Universidade de Lisboa, Lisbon, Portugal.; Geissler, W. H.; Alfred-Wegener-Institut für Polar- und Meeresforschung, Bremerhaven, Germany.; Favali, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: In this study, we present a three-dimensional P wave upper-mantle tomography model of the southwest Iberian margin and Alboran Sea based on teleseismic arrival times recorded by Iberian and Moroccan land stations and by a seafloor network deployed for 1 year in the Gulf of Cadiz area during the European Commission Integrated observations from NEAR shore sourcES of Tsunamis: towards an early warning system (EC NEAREST) project. The three-dimensional model was computed down to 600 kmdepth. The tomographic images exhibit significant velocity contrasts, as large as 3%, confirming the complex evolution of this plate boundary region. Prominent high-velocity anomalies are found beneath Betics-Alboran Sea, off-shore southwest Portugal, and north Portugal, at sublithospheric depths. The transition zones between high- and low-velocity anomalies in southwest and south Iberia are associated to the contact of oceanic and continental lithosphere. The fast structure below the Alboran Sea-Granada area depicts an L-shaped body steeply dipping from the uppermost mantle to the transition zone where it becomes less curved. This anomaly is consistent with the results of previous tomographic investigations and recent geophysical data such as stress distribution, GPS measurements of plate motion, and anisotropy patterns. In the Atlantic domain, under the Horseshoe Abyssal Plain, the main feature is a high-velocity zone found at uppermost mantle depths. This feature appears laterally separated from the positive anomaly recovered in the Alboran domain by the interposition of low-velocity zones which characterize the lithosphere beneath the southwest Iberian peninsula margin, suggesting that there is no continuity between the high-velocity anomalies of the two domains west and east of the Gibraltar Strait.

The Volcano-Seismic Clock of the South American Pacific Margin - A Possible First Link Between Natural Disasters Prevention and Expanding Earth

2012-11-30T23:00:00Z

Title: The Volcano-Seismic Clock of the South American Pacific Margin - A Possible First Link Between Natural Disasters Prevention and Expanding Earth Authors: Scalera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Editors: Scalera, Giancarlo; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: A volcano-seismic correlation was for a long time suspected to occur on the Pacific margin of South America. Scalera (2008) using the data available in 2006 in the Smithsonian Institution Catalogue of the volcanic eruptions, has revealed evidence that earthquakes happened into the South-American Wadati-Benio zone – with magnitude greater than 8.4 –are associated to an enhanced rate of volcanic eruptions, but has been impossible to determine the causal chain between the two phenomena. After 2006, the effort of the Smithsonian Institution to improve our knowledge of this region has resulted in a greatly increased completeness of the catalogue, adding the new eruptions for the 2000- 2010 interval, but also an additional 50% of new entries in the list of the Andean volcanoes. The occurrence of the Chilean earthquake of Maule – 27 February 2010 (M=8.8); occurred at five decades from the 1960 quake – has been the occasion to rework all the data searching for additional clues able to indicate a preferred causal direction eruptions-earthquakes or earthquakes-eruptions – or from a third more general cause (e.g. a mantle movements) to both eruptions and earthquakes. This short note discusses the three above-said hypotheses and tries to establish if these results could be useful to the aims of the Civil Protection in the programs of prevention and/or forecasting of natural disasters.

The Earth Expansion Evidence – A Challenge for Geology, Geophysics and Astronomy

2012-11-30T23:00:00Z

Title: The Earth Expansion Evidence – A Challenge for Geology, Geophysics and Astronomy Authors: Scalera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Boschi, E.; University of Bologna; Cwojdzinski, S.; Polish Geological Survey Editors: Scalera, Giancarlo; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Boschi, Enzo; University of Bologna; Cwojdzinski, Stefan; Polish Geological Survey

Distensional Mediterranean and World Orogens - Their Possible Bearing to Mega-Dykes Active Rising

2012-11-30T23:00:00Z

Title: Distensional Mediterranean and World Orogens - Their Possible Bearing to Mega-Dykes Active Rising Authors: Scalera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Editors: Scalera, Giancarlo; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Boschi, Enzo; University of Bologna; Cwojdzinski, Stefan; Polish Geological Survey Abstract: An overview of the modern progresses of the expanding Earth conceptions as they come out from new data and their possible interpretations is provided in this paper. The starting point of this review is the new detailed 3D distributions of relocated hypocenters laying under orogenic belts. The similarity of the hypocentral patterns under the Tethyan orogenic belts, and under the South American Pacific orogenic margin is considered to be a major font of information on which to build a more realistic global geodynamic model. Clusters and filaments of hypocenters are recognizable instead of regular patterns. These clusters taper downwards, leading to the idea of a deep origin in narrow regions of disturbance, besides other important facts that witness in favour of surfaceward movements of deep material along what can be called "mega-dykes". The outpouring of the material on the surface produces gravitational nappes and their overthrust on the sediments of the preexisting trough, forcing them on a burial path which emulate the subduction process, but without reaching depths greater than 50-70 km. Phenomenons like metamorphism, mixing, migmization, upward transport of fragments of the buried lithosphere etc. are possible at the boundary between uplifting material and down-pushed crust and lithosphere. Additional clues can be collected that confirm the new proposed framework. The astronomical indications of a coseismic displacement of the instantaneous Earth’s rotation axis in the occasion of the great Sumatra (Mw=9.3) and Honshu (Mw=9.0) earthquakes are especially significant because in complete disagreement with the plate tectonics modelled axis shift and in agreement with the shift expected in the new conception. Because of analogous opposite predictions of the length of day variation following the extreme magnitude earthquakes (ΔLOD<0 vs ΔLOD>0), future improvements of the time measurement techniques could allow a final choice between rival geodynamical models.

Gravity fluctuations induced by magma convection at Kılauea, Hawai‘i

2012-06-28T22:00:00Z

Title: Gravity fluctuations induced by magma convection at Kılauea, Hawai‘i Authors: Carbone, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Poland, M.; U.S. Geological Survey, Hawaiian Volcano Observatory, PO Box 51, Hawaii National Park, Hawaii 96718-0051, USA Abstract: Convection in magma chambers is thought to play a key role in the activity of persistently active volcanoes, but has only been inferred indirectly from geochemical observations or simulated numerically. Continuous microgravity measurements, which track changes in subsurface mass distribution over time, provide a potential method for characterizing convection in magma reservoirs. We recorded gravity oscillations with a period of ~150 s at two continuous gravity stations at the summit of Kīlauea Volcano, Hawai‘i. The oscillations are not related to inertial accelerations caused by seismic activity, but instead indicate variations in subsurface mass. Source modeling suggests that the oscillations are caused by density inversions in a magma reservoir located ~1 km beneath the east margin of Halema‘uma‘u Crater in Kīlauea Caldera—a location of known magma storage.

Distensional Mediterranean and World Orogens

2011-12-31T23:00:00Z

Title: Distensional Mediterranean and World Orogens Authors: Scalera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Editors: Scalera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Cwojdzinski, S. Abstract: An overview of the modern progresses of the expanding Earth conceptions as they come out from new data and their possible interpretations is provided in this paper. The starting point of this review is the new detailed 3D distributions of relocated hypocenters laying under orogenic belts. The similarity of the hypocentral patterns under the Tethyan orogenic belts, and under the South American Pacific orogenic margin is considered to be a major font of information on which to build a more realistic global geodynamic model. Clusters and filaments of hypocenters are recognizable instead of regular patterns. These clusters taper downwards, leading to the idea of a deep origin in narrow regions of disturbance, besides other important facts that witness in favour of surfaceward movements of deep material along what can be called "mega-dykes". The outpouring of the material on the surface produces gravitational nappes and their overthrust on the sediments of the preexisting trough, forcing them on a burial path which emulate the subduction process, but without reaching depths greater than 50-70 km. Phenomenons like metamorphism, mixing, migmization, upward transport of fragments of the buried lithosphere etc. are possible at the boundary between uplifting material and down-pushed crust and lithosphere. Additional clues can be collected that confirm the new proposed framework. The astronomical indications of a coseismic displacement of the instantaneous Earth’s rotation axis in the occasion of the great Sumatra (Mw=9.3) and Honshu (Mw=9.0) earthquakes are especially significant because in complete disagreement with the plate tectonics modelled axis shift and in agreement with the shift expected in the new conception. Because of analogous opposite predictions of the length of day variation following the extreme magnitude earthquakes (ΔLOD<0 vs ΔLOD>0), future improvements of the time measurement techniques could allow a final choice between rival geodynamical models.

Volcanic deformation and flank instability due to magmatic sources and frictional rheology: the case of Mount Etna

2011-12-31T23:00:00Z

Title: Volcanic deformation and flank instability due to magmatic sources and frictional rheology: the case of Mount Etna Authors: Cianetti, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Giunchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Casarotti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: The overall picture of Mount Etna deformation emerging since a couple of decades of geodetic surveys shows effects of magma accumulation, characterized by inflation/deflation cycle, accompanied by a sliding instability of the southeast flank, whose manifestation is an increase in the horizontal deformation away from the volcano summit. This is a very interesting case to test whether advanced models, taking into account topography, internal structure and frictional rheology, may contribute to a better understanding of the complex interplay among mechanical response, magmatic activity and gravitational load occurring in a volcanic system. Using finite element numerical models we make predictions of surface displacements associated with a simple expansion source and with a dike like vertical discontinuity. A new methodology is developed to initalize the lithostatic stress field according to the material and geometrical complexities of the models considered. Our results show that, while an amplification of the horizontal displacement can be easily obtained up to a maximum distance of 10 km from the source, we have not been able to find any onfiguration to extend further this signal. For the case of Mount Etna this suggests that the large horizontal displacements observed in the east flank along the coast cannot be directly related to magma accumulation below the volcano's summit.

Multivariate time series clustering on geophysical data recorded at Mt. Etna from 1996 to 2003

2012-12-31T23:00:00Z

Title: Multivariate time series clustering on geophysical data recorded at Mt. Etna from 1996 to 2003 Authors: Di Salvo, R.; Dipartimento di Ingegneria Elettrica, Elettronica e Informatica, Università degli Studi di Catania, Facoltà di Ingegneria, Italy; Montalto, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Nunnari, G.; Dipartimento di Ingegneria Elettrica, Elettronica e Informatica, Università degli Studi di Catania, Facoltà di Ingegneria, Italy; Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Puglisi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia Abstract: Time series clustering is an important task in data analysis issues in order to extract implicit, previously unknown, and potentially useful information froma large collection of data. Finding useful similar trends inmultivariate time series represents a challenge in several areas including geophysics environment research. While traditional time series analysis methods deal only with univariate time series, multivariate time series analysis is a more suitable approach in the field of researchwhere different kinds of data are available. Moreover, the conventional time series clustering techniques do not provide desired results for geophysical datasets due to the huge amount of data whose sampling rate is different according to the nature of signal. In this paper, a novel approach concerning geophysical multivariate time series clustering is proposed using dynamic time series segmentation and Self Organizing Maps techniques. This method allows finding coupling among trends of different geophysical data recorded from monitoring networks at Mt. Etna spanning from 1996 to 2003, when the transition from summit eruptions to flank eruptions occurred. This information can be used to carry out a more careful evaluation of the state of volcano and to define potential hazard assessment at Mt. Etna.

Parallel ‘large’ dense matrix problems: application to 3D joint inversion of seismological and gravity data

2012-10-31T23:00:00Z

Title: Parallel ‘large’ dense matrix problems: application to 3D joint inversion of seismological and gravity data Authors: Tondi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Cavazzoni, C.; CINECA, Interuniversity Computing Centre, Via Magnanelli 6/3, 40033 Casalecchio di Reno (BO), Italy; Danecek, P.; Univ Granada, Inst Andaluz Geofis, E-18071 Granada, Spain; Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: To obtain accurate and reliable estimations of the major lithological properties of the rock within a studied volume, geophysics uses the joint information provided by different geophysical datasets (e.g. gravimetric, magnetic, seismic). Representation of the different types of information entering the problem using probability density functions can provide the mathematical framework to formulate their combination. The maximum likelihood estimator of the resulting joint posterior probability density functions leads to the solution of the problem. However, one key problem appears to limit the use of this solver to an extensive range of real applications: information coming from potential fields that implies the presence of dense matrices in the resolving estimator. It is well known that dense matrix systems rapidly challenge both the algorithms and the computing platforms, and are not suited to high-resolution 3D geophysical analysis. In this study, we propose a procedure that allows us to obtain fast and reliable solutions of the joint posterior probability density functions in the presence of large gravity datasets and using sophisticated model parametrization. As it is particularly CPUconsuming, this 3D problem makes use of parallel computing to improve the performance and the accuracy of the simulations. Analysis of the correctness of the results, and the performance on different parallel environments, shows the portability and the efficiency of the code. This code is applied to a real experiment, where we succeed in recovering a 3D shear-wave velocity and density distribution within the upper mantle of the European continent, satisfying both the seismological and gravity data. On a multiprocessor machine, we have been able to handle forward and inverse calculations with a dense matrix of 215.66 Gb in 18 min, 20 s and 20 min, 54 s, respectively.

Is plate tectonics a Tychonian compromise?

2011-12-31T23:00:00Z

Title: Is plate tectonics a Tychonian compromise? Authors: Scalera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: The Danish astronomer Tycho Brahe (1546–1601) developed a model of the universe – the Tychonic system – by combining the Ptolemaic system with the Copernican system. In the Tychonic (geocentric) system the Moon and the Sun were considered to revolve around the Earth, while the planets (Mercury, Venus, Mars, Jupiter and Saturn) revolve around the Sun. In this paper the theory of the plate tectonics is interpreted as a Tychonic conception because – making several compromises – fixism and mobilism are mixed in a unique pattern, in which the compression and the extension are unified in a compressional interpretation (see the coexistence of trenches and orogenic chains on the active continental margins), while, conversely, the fold-belts and the mid-oceanic ridges are separated into two different geodynamic domains. For all these cases, the extensional description could be more appropriate. Description: In this paper the theory of the plate tectonics is interpreted as a Tychonic conception. The expanding Earth is the more complete description of the geologic reality.