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Integrating geologic fault data into tsunami hazard studies

2013-04-18T22:00:00Z

Title: Integrating geologic fault data into tsunami hazard studies Authors: Basili, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Tiberti, M. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Kastelic, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Romano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Piatanesi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Selva, J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Lorito, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: We present the realization of a fault-source data set designed to become the starting point in regional-scale tsunami hazard studies. Our approach focuses on the parametric fault characterization in terms of geometry, kinematics, and assessment of activity rates, and includes a systematic classification in six justification levels of epistemic uncertainty related with the existence and behaviour of fault sources. We set up a case study in the central Mediterranean Sea, an area at the intersection of the European, African, and Aegean plates, characterized by a complex and debated tectonic structure and where several tsunamis occurred in the past. Using tsunami scenarios of maximum wave height due to crustal earthquakes (Mw=7) and subduction earthquakes (Mw=7 and Mw=8), we illustrate first-order consequences of critical choices in addressing the seismogenic and tsunamigenic potentials of fault sources. Although tsunamis generated by Mw=8 earthquakes predictably affect the entire basin, the impact of tsunamis generated by Mw=7 earthquakes on either crustal or subduction fault sources can still be strong at many locales. Such scenarios show how the relative location/orientation of faults with respect to target coastlines coupled with bathymetric features suggest avoiding the preselection of fault sources without addressing their possible impact onto hazard analysis results.

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.

Deriving thrust fault slip rates from geological modeling: examples from the Marche coastal and offshore contraction belt, Northern Apennines, Italy.

2012-12-31T23:00:00Z

Title: Deriving thrust fault slip rates from geological modeling: examples from the Marche coastal and offshore contraction belt, Northern Apennines, Italy. Authors: Maesano, F. E.; Toscani, G.; Dipartimento di Scienze della Terra e dell'Ambiente, Università di Pavia; Burrato, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Mirabella, F.; Dipartimento di Scienze della Terra, Università di Perugia; D'ambrogi, C.; ISPRA - Servizio Geologico d'Italia; Basili, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: We present a reconstruction of the central Marche thrust system in the central-northern Adriatic domain aimed at constraining the geometry of the active faults deemed to be potential sources of moderate to large earthquakes in this region and at evaluating their long-term slip rates. This system of contractional structures is associated with fault-propagation folds outcropping along the coast or buried in the offshore that have been active at least since about 3Myr. The ongoing deformation of the coastal and offshore Marche thrust system is associated with moderate historical and instrumental seismicity and recorded in sedimentary and geomorphic features. In this study, we use subsurface data coming from both published and original sources. These comprise cross-sections, seismic lines, subsurface maps and borehole data to constrain geometrically coherent local 3D geological models, with particular focus on the Pliocene and Pleistocene units. Two sections crossing five main faults and correlative anticlines are extracted to calculate slip rates on the driving thrust faults. Our slip rate calculation procedure includes a) the assessment of the onset time which is based on the sedimentary and structural architecture, b) the decompaction of clastic units where necessary, and c) the restoration of the slip on the fault planes. The assessment of the differential compaction history of clastic rocks eliminates the effects of compaction-induced subsidence which determine unwanted overestimation of slip rates. To restore the displacement along the analyzed structures, we use two different methods on the basis of the deformation style: the fault parallel flow algorithm for faulted horizons and the trishear algorithm for fault-propagation folds. The time of fault onset ranges between 5.3-2.2 Myr; overall the average slip rates of the various thrusts are in the range of 0.26-1.35 mm/yr.

Active faulting and transpression tectonics along the plate boundary in North Africa

2011-12-31T23:00:00Z

Title: Active faulting and transpression tectonics along the plate boundary in North Africa Authors: Meghraoui, M.; Institut de Physique du Globe de Strasbourg (UMR 7516) 16 5, rue René Descartes 17 67084 Strasbourg cedex, France; Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: We present a synthesis of the active tectonics of the northern Atlas Mountains and suggest a kinematic model of transpression and block rotation that illustrates the mechanics of this section of the Africa - Eurasia plate boundary. Neotectonic structures and significant shallow seismicity (with Mw > 5.0) indicate that coeval east-west trending right-lateral faulting and NE-SW thrust-related folding, result from the oblique convergence at the plate boundary, and form a transpressional system. The strain distribution obtained from fault - fold structures and P axes of focal mechanism solutions, and the geodetic (NUVEL1 and GPS) convergence shows that shortening and convergence directions are not coaxial. The transpressional strain is partitioned along strike and the quantitative description of displacement field yields a compression to transcurrence ratio varying from 33% near Gibraltar, to 50% along the Tunisian Atlas. Shortening directions oriented NNE to NNW for the Pliocene and Quaternary, respectively, and the S shape of Quaternary anticline axes are in agreement with the 2.24° - 3.9 °/Myr modeled clockwise rotation of small tectonic blocks and paleomagnetic results. The convergence between Africa and Eurasia is absorbed along the Atlas Mountains, at the upper crustal level, by means of thrusting above decollement systems, controlled by subdued transcurrent faults. The Tell Atlas of NW Algeria that experienced numerous large earthquakes with respect to other regions is interpreted as a restraining bend that localizes strain distribution along the plate boundary.

Birth of an ocean in the Red Sea: Initial pangs

2012-08-17T22:00:00Z

Title: Birth of an ocean in the Red Sea: Initial pangs Authors: Ligi, M.; CNR-ISMAR Bologna; Bonatti, E.; CNR-ISMAR Bologna; Bortoluzzi, G.; CNR-ISMAR Bologna; Cipriani, A.; CNR-ISMAR Bologna; Cocchi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Caratori Tontini, F.; GNS Science; Carminati, E.; Università di Roma "La Sapienza"; Ottolini, L.; CNR -Pavia; Schettino, A.; Università di Camerino Abstract: We obtained areal variations of crustal thickness, magnetic intensity, and degree of melting of the sub- axial upwelling mantle at Thetis and Nereus Deeps, the two northernmost axial segments of initial oceanic crustal accretion in the Red Sea, where Arabia is separating from Africa. The initial emplacement of oceanic crust occurred at South Thetis and Central Nereus roughly $2.2 and $2 Ma, respectively, and is taking place today in the northern Thetis and southern Nereus tips. Basaltic glasses major and trace element com- position suggests a rift-to-drift transition marked by magmatic activity with typical MORB signature, with no contamination by continental lithosphere, but with slight differences in mantle source composition and/or potential temperature between Thetis and Nereus. Eruption rate, spreading rate, magnetic intensity, crustal thickness and degree of mantle melting were highest at both Thetis and Nereus in the very initial phases of oceanic crust accretion, immediately after continental breakup, probably due to fast mantle upwelling enhanced by an initially strong horizontal thermal gradient. This is consistent with a rift model where the lower continental lithosphere has been replaced by upwelling asthenosphere before continental rupturing, implying depth-dependent extension due to decoupling between the upper and lower lithosphere with man- tle-lithosphere-necking breakup before crustal-necking breakup. Independent along-axis centers of upwell- ing form at the rifting stage just before oceanic crust accretion, with buoyancy-driven convection within a hot, low viscosity asthenosphere. Each initial axial cell taps a different asthenospheric source and serves as nucleus for axial propagation of oceanic accretion, resulting in linear segments of spreading.

Seismic attenuation tomography beneath the retreating Southern Tyrrhenian Sea subduction system

2011-04-02T22:00:00Z

Title: Seismic attenuation tomography beneath the retreating Southern Tyrrhenian Sea subduction system Authors: Baccheschi, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; De Gori, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Chiarabba, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia Abstract: We investigate the seismic attenuation structure of the Ionian slab and surrounding mantle beneath the Southern Tyrrhenian subduction system. We present a high-resolution Vp, Vp/Vs, Qp and Qs models obtained by the inversion of high quality P- and S-waves t* from slab earthquakes. In our analysis we first located 304 earthquakes with M>= 2.8 , depth >= 30 km and azimuthal gap <= 200 and we used a 3D a priori Vp and Vp/Vs model. Then, t* values were measured from spectra of P and S waves. For computing t* we have determined the corner frequency (fc) which has been estimated using a grid search over the frequency range 1 - 10 Hz using all the recordings for each event. The obtained t* values are then used in the inversion for the 3-D attenuation structure using, and kept fixed, the 3-D velocity model. Tomographic inversion show high-attenuation regions corresponding to the crustal layers with low values of Qs (values down to 200) but high values of Qp. The subducting slab is identified as a body of low attenuation, but heterogeneous in the Qs and Qp structure (Qs values up to 1100; Qp values up to 1200), surrounded by high-attenuation regions beneath the Aeolian magmatic arc. At 100 km depth the high Qp and Qs body is well reconstructed beneath the Calabrian arc and at 200 km depth it is extended offshore the Southern Tyrrhenian Basin beneath the Aeolian Islands. Between 100 and 200 km depth, the Ionian slab is characterized by intermediate depth seismicity, but Qp and Qs models clearly show the existence of high-attenuation region, with low values of Qs and high Qp/Qs structure. The observed low Qp and Qs anomalies could likely due to the fluids released from dehydrating minerals associated to the slab metamorphism. The observed low Qs anomalies regions between the slab and the Aeolian volcanic arc could be indicative of melting processes in the mantle and also of the large-scale serpentinization.

Crustal structure and seismotectonics of central Sicily (southern Italy): new constraints from instrumental seismicity

2012-05-31T22:00:00Z

Title: Crustal structure and seismotectonics of central Sicily (southern Italy): new constraints from instrumental seismicity Authors: Sgroi, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; de Nardis, R.; Dipartimento della Protezione Civile, Via Vitorchiano, Rome, Italy; Lavecchia, G.; Dipartimento di Scienze Umanistiche e della Terra, Università ‘G. D’Annunzio’, Campus Universitario, 66013 Chieti Scalo, Italy Abstract: In this paper, we propose a new model of the crustal structure and seismotectonics for central Sicily (southern Italy) through the analysis of the depth distribution and kinematics of the instrumental seismicity, occurring during the period from 1983 to 2010, and its comparison with individual geological structures that may be active in the area. The analysed data set consists of 392 earthquakes with local magnitudes ranging from 1.0 to 4.7. We defined a new, detailed 1-D velocity model to relocate the earthquakes that occurred in central Sicily, and we calculated a Moho depth of 37 km and a mean VP/VS ratio of 1.73. The relocated seismic events are clustered mainly in the area north of Caltanissetta (e.g. Mainland Sicily) and in the northeastern sector (Madonie Mountains) of the study area; only minor and greatly dispersed seismicity is located in the western sector, near Belice, and along the southern coast, between Gela and Sciacca. The relocated hypocentral distribution depicts a bimodal pattern: 50 per cent of the events occur within the upper crust at depths less than ~16 km, 40 per cent of the events occur within the middle and depth crust, at depths between 16 and 32 km, and the remaining 10 per cent occur at subcrustal depths. The energy release pattern shows a similar depth distribution. On the basis of the kinematic analysis of 38 newly computed focal plane solutions, two major geographically distinct seismotectonic domains are distinguished: the Madonie Mountain domain, with prevalent extensional and extensional-oblique kinematics associated with upper crust Late Pliocene–Quaternary faulting, and the Mainland Sicily domain, with prevalent compressional and compressional-oblique kinematics associated with thrust faulting, at mid to deep crust depth, along the north-dipping Sicilian Basal Thrust (SBT). The stress inversion of the Mainland Sicily focal solutions integrated with neighbouring mechanisms available in the literature highlights a regional homogeneous compressional tensor, with a subhorizontal NNW–SSE-striking σ1 axis. In addition, on the basis of geodetic data, the Mainland Sicily domain may be attributed to the SSE-ward thrusting of the Mainland Sicily block along the SBT plane. Seismogenic shearing along the SBT at mid-crustal depths was responsible for the unexpected Belice 1968 earthquake (Mw 6.1), with evident implications in terms of hazard assessment.

RECENT TECTONIC STRESS FIELD STATE IN ITALY FROM NUMERICAL MODELLING ANALYSIS

2009-12-31T23:00:00Z

Title: RECENT TECTONIC STRESS FIELD STATE IN ITALY FROM NUMERICAL MODELLING ANALYSIS Authors: Pierdominici, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Heidbach, O.; Helmholtz Zentrum Potsdam, Deutsches GeoForschungsZentrum GFZ, Germany Editors: Pierdominici, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Heibach, O.; Helmholtz Zentrum Potsdam, Deutsches GeoForschungsZentrum GFZ, Germany Abstract: We examine the contemporary stress in Italy studying the present-day maximum horizontal stress orientation to characterize the relationship between active stress, past tectonic setting and the seismicity. The geodynamic setting of Italy is particularly complex. Italy is involved in the N-S convergence of Africa and Eurasian plates and currently undergoing NE-SW extension perpendicular to the Apenninic fold and thrust belt and with the opening of the Tyrrhenian basin (Late Tortonian). This process happens in the presence of still active subduction system extending from Sicily to northern Apennines, as confirmed by recently seismicity. This tectonic setting with highly variable plate boundary events and body forces induced by topography results in an inhomogeneous stress pattern. Here we quantify the spatial changes of the wavelength of the stress pattern by a statistical analysis. As input data we use 600 data of SH records from the World Stress Map database release 2008 and about 100 new data records. The result of this statistical analysis is a mean orientation of the maximum horizontal compressional stress SH on a 0.1° grid and the maximum smoothing radius for which the standard deviation of the mean SH orientation is less than 25°. This latter is the wave-length of the stress pattern and reveals for Italy that the entire region has wave-length less than 200 km for Italy.