http://hdl.handle.net/2122/242 Ricerca nel canale cerca http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/6064 Titolo: Earthquake focal mechanisms and stress inversion in the Irpinia Region (southern Italy)<br/><br/>Autori: Pasquale, G.; Dipartimento di Studi Geologici ed Ambientali,Università degli Studi del Sannio, Benevento, Italy; De Matteis, R.; Dipartimento di Studi Geologici ed Ambientali,Università degli Studi del Sannio, Benevento, Italy; Romeo, A.; AMRA Scarl, Napoli, Italy; Maresca, R.; Dipartimento di Studi Geologici ed Ambientali,Università degli Studi del Sannio, Benevento, Italy<br/><br/>Abstract: The goal of this study was to estimatethe stress field acting in the Irpinia Region, anarea of southern Italy that has been struck in thepast by destructive earthquakes and that is nowcharacterized by low to moderate seismicity. Thedataset are records of 2,352 aftershocks followingthe last strong event: the 23 November 1980 earthquake(M 6.9). The earthquakes were recorded atseven seismic stations, on average, and have beenlocated using a three-dimensional (3D) P-wavevelocity model and a probabilistic, non-linear,global search technique. The use of a 3D velocitymodel yielded amore stable estimation of take-offangles, a crucial parameter for focal mechanismcomputation. The earthquake focal mechanismswere computed from the P-wave first-motion polaritydata using the FPFIT algorithm. Fault planesolutions show mostly normal component faulting(pure normal fault and normal fault with a strikeslipcomponent). Only some fault plane solutionsshow strike-slip and reverse faulting. The stressfield is estimated using the method proposed by Michael (J Geophys Res 92:357–368, 1987a) byinverting selected focal mechanisms, and the resultsshow that the Irpinia Region is subjected to aNE–SW extension with horizontal σ3 (plunge 0◦,trend 230◦) and subvertical σ1 (plunge 80◦, trend320◦), in agreement with the results derived fromother stress indicators. http://hdl.handle.net/2122/6049 Titolo: A Local Magnitude Scale for Southern Italy<br/><br/>Autori: Bobbio, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Vassallo, M.; Analisi e Monitoraggio Ambientale (AMRA) Scarl Napoli; Festa, G.; Dipartimento di Scienze Fisiche Università di Napoli Federico II<br/><br/>Abstract: A local magnitude scale has been defined for southern Italy, in the areamonitored by the recently installed Irpinia Seismic Network.Waveforms recorded frommore than 100 events of small magnitude are processed to extract synthetic Wood–Anderson traces. Assuming a general description of peak-displacement scaling withthe distance, by means of linear and logarithmic contributions, a global explorationof the parameter space is performed by a grid-search method with the aim of investigatingthe correlation between the two decay contributions and seeking for a physical solutionof the problem. Assuming an L2 norm, we foundM log A 1:79 log R 0:58;yielding an error on the single estimation smaller than 0.2, at least when the hypocenterlocation is accurate. Station corrections are investigated through the station residuals,referring to the average value of the magnitude. Using a z test, we found that some stationsexhibit a correction term significantly different from 0. The use of the peak accelerationand peak velocity as indicators of the magnitude is also investigated. http://hdl.handle.net/2122/6046 Titolo: On the transient behavior of frictional melt during seismic slip<br/><br/>Autori: Nielsen, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Mosca, P.; Scienze Fisiche, Università di Napoli, Federico II; Giberti, G.; Scienze Fisiche, Università di Napoli, Federico II; Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Hirose, Takehiro; Kochi Institute for Core Sample Research, Japan Agency Marine Earth Science and Technology, Kochi, Japan.; Shimamoto, T.; Hiroshima University, Dpt. of Earth and Planetary Systems Science, Higashi-Hiroshima, Japan.<br/><br/>Abstract: In a recent work on the problem of sliding surfaces under the presenceof frictional melt (applying in particular to earthquake fault dynamics),we derived from first principles an expression for the steady statefriction compatible with experimental observations. Building on theexpressions of heat and mass balance obtained in the above study forthis particular case of Stefan problem (phase transition with a migratingboundary) we propose here an extension providing the full time-dependentsolution (including the weakening transient after pervasive meltinghas started, the effect of eventual steps in velocity and the finaldecelerating phase). A system of coupled equations is derived andsolved numerically. The resulting transient friction and wear evolutionyield a satisfactory fit (1) with experiments performed under variablesliding velocities (0.9-2 m/s) and different normal stresses (0.5-20MPa) for various rock types and (2) with estimates of slip weakeningobtained from observations on ancient seismogenic faults that hostpseudotachylite (solidified melt). The model allows to extrapolatethe experimentally observed frictional behavior to large normal stressesrepresentative of the seismogenic Earth crust (up to 200 MPa), highslip rates (up to 9 m/s) and cases where melt extrusion is negligible.Though weakening distance and peak stress vary widely, the net breakdownenergy appears to be essentially independent of either slip velocityand normal stress. In addition, the response to earthquake-like slipcan be simulated, showing a rapid friction recovery when slip ratedrops. We discuss the properties of energy dissipation, transientduration, velocity weakening, restrengthening in the deceleratingfinal slip phase and the implications for earthquake source dynamics. http://hdl.handle.net/2122/6044 Titolo: Energy radiation from intermediate to large magnitude earthquakes: implications for dynamic fault weakening<br/><br/>Autori: Malagnini, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Nielsen, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Mayeda, K.; Weston Geophysical Corporation, Lexington, MA, and University of California, Berkeley, CA; Boschi, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia<br/><br/>Abstract: The amount of energy radiated from an earthquake can be measured using recent methods based on earthquake coda signals and spectral ratios. Such methods are not altered by either site or directivity effects, with the advantage of a greatly improved accuracy. Several studies of earthquake sequences based on the above measurements showed evidence of a breakdown in self-similarity in the moment to energy relation. Radiated energy can be also used as a gauge to estimate the average dynamic stress drop on the fault. Here we compute the dynamic stress drop, infer the co-seismic friction and estimate the co-seismic heating resulting from the frictional work during events from different main shock-aftershock earthquake sequences. We relate the dynamic friction to the maximum temperature rise estimated on the faults for each earthquake. Our results are strongly indicative that a thermally triggered dynamic frictional weakening is present, responsible for the breakdown in self-similarity. These observations from seismic data are compatible with recent laboratory evidence of thermal weakening in rock friction under seismic slip-rates, associated to various physical processes such as melting, decarbonation or dehydration. http://hdl.handle.net/2122/6007 Titolo: How to promote earthquake ruptures: different nucleation strategies in a dynamic model with slip–weakening friction<br/><br/>Autori: Bizzarri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia<br/><br/>Abstract: The introduction of the linear slip–weakening friction law permits the solution of theelasto–dynamic equation for a rupture which develops on a fault, by removing the singularity in the components of stress tensor, thereby ensuring a finite energy flux at the crack tip. With this governing model, largely used by seismologists, it is possible to simulate a single earthquake event but, in absence of remote tectonic loading, it requires the introduction of an artificial procedure to initiate the rupture, i.e, to reach the failure stress point. In this paper, by studying the dynamic rupture propagation and the solutions on the fault and on the free surface, we systematically compare three conceptually and algorithmically different nucleation strategies widely adopted in the literature: the imposition of an initially constant rupture speed, the introduction of a shear stress asperity, and the perturbation to the initial particle velocity field. Our results show that, contrarily to supershear ruptures which tend to “forget” their origins, subshear ruptures are quite sensitive to the adopted nucleation procedure, which can bias the runaway rupture. We confirm that that the most gradual transition from imposed nucleation and spontaneous propagation is obtained by initially forcing the rupture to expand at a properly chosen, constant speed (0.75 times the Rayleigh speed). We also numerically demonstrate that a valid alternative to this strategy is an appropriately smoothed, elliptical shear stress asperity. Moreover, we evaluate the optimal size of the nucleation patch where the procedure is applied; our simulations indicate that its size has to equal the critical distance of Day (1982) in case of supershear ruptures and to exceed it in case of subshear ruptures. http://hdl.handle.net/2122/5973 Titolo: Do Strike-Slip Faults of Molise, Central-Southern Italy, Really Release a High Stress?<br/><br/>Autori: Calderoni, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Rovelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Milana, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Valensise, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: The 31 October and 1 November 2002, Molise earthquakes (both MW 5.7) were caused by right-lateral slip between 12 and 20 km depth. These earthquakes are the result of large-scale reactivation of pre-existing, left-lateral, regionally extended E-W structures of Mesozoic age. Although recorded ground motions were generally smaller than expected for typical Italian earthquakes, a recent paper attributes a stress drop as high as 180 bars to the Molise earthquakes.We remark that a high stress drop is in contrast both with the relatively long source duration inferred in previous investigations and with geodetic evidence for a significantly smaller fault slip compared with other Apennines earthquakes having similarly large rupture area (e.g. 1997 Umbria-Marche earthquakes).We analyzed both ground acceleration spectra of the mainshocks and single-station spectral ratios of broad-band seismograms in an extended magnitude range (2.7 ≤ MW ≤ 5.7). Our results show that neither the spectral amplitudes of recorded ground motions nor the spectral ratios can be fit by a high stress drop source. Instead we find that the observations are consistent with a low stress drop, our best estimates ranging between 6 and 25 bars, in agreement with the relatively long source duration and small coseismic slip. We interpret the low stress of the 2002 Molise earthquakes in terms of lower energy release mechanisms due to the reutilization of faults reactivated opposite to their original sense of slip. http://hdl.handle.net/2122/5936 Titolo: Estimating earthquake magnitude with early arrivals; a test using dynamic and kinematic models<br/><br/>Autori: Murphy, S.; Università di Napoli, Federico II; Nielsen, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: Recent studies on seismological data indicate that earthquake magnitudescales with either the dominant period or the peak amplitude in the seismogram’s firstfew seconds. At first sight, this may indicate that the earthquake’s final size is somehowrelated to the way rupture starts. One working hypothesis is that strong radiationfrom the initial phase of rupture is indicative of a triggering asperity releasing a consistentamount of elastic energy, with the potential to drive the fracture to large extents.We tested this concept with a number of numerical simulations, but within the modelsinvestigated, scaling was found only for ruptures extending up to about four times thesize of the initial asperity; at larger distances the correlation was lost. Alternatively, acareful kinematic analysis of the earthquake source radiation shows that the initialsignal recorded at any station does not necessarily correspond to the rupture initiationbut may represent an extended portion of the radiating source. Using the concept ofisochrones, we show that the apparent scaling may be explained by a simple kinematicmodel respecting causality, up to a given magnitude threshold where the scaling relationsaturates. The saturation level is in agreement with that observed in some, butnot all, of the real seismicity catalogs. http://hdl.handle.net/2122/5933 Titolo: RU03 | WP 2.1-2.2: Deployment of an on-land, off-shore seismic network to builD up an integrated seismic data archive<br/><br/>Autori: Moretti, Milena; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Govoni, Aladino; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Mangano, Giorgio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; D'Anna, Giuseppe; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Mandiello, Alfonso Giovanni; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Margheriti, Lucia; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Mazza, Salvatore; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Patanè, Domenico; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Selvaggi, Giulio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; "Messina 1908-2008" Working Group<br/><br/>Abstract: A passive seismic experiment to monitor the Messina Strait and the whole Calabrian arc began in October 2007 and it is still in progress. Overall about 16 temporary seismic stations were installed on land around the the Strait of Messina and 5 ocean bottom seismometers (OBS) to better monitor the area largely covered by the sea. The network incorporates and upgrades existing seismic stations (more than 20) of the permanent networks located in area.All the data gathered in the Messina 1908-2008 project together with all metadata will be archived in the same SEED data bank and will be accessible by the whole scientific community trough an ArcLink server.'s assemblage of a database and integration of innovative technologies could transform our understanding of the crust and mantle structure of the active tectonics and seismic hazards of the Strait of Messina. http://hdl.handle.net/2122/5932 Titolo: "Messina 1908-2008" Progetto di ricerca integrato sull'area Calabro-Peloritana: la campagna sismica<br/><br/>Autori: Moretti, Milena; Land Experiment working group; Archive working group<br/><br/>Abstract: Nell’ambito del Progetto Messina 1908-2008, il Centro Nazionale Terremoti (CNT) in collaborazione con la Sezione di Catania, ha progettato e realizzato un esperimento di sismica passiva con l’obiettivo di raccogliere nuovi dati sismologici nell’area colpita dal terremoto del 1908.Disporre di una rete sismica più densa permette l’abbassamento della soglia di detezione dei terremoti e il miglioramento delle localizzazioni consentendo così di associare la micro-sismicità alle strutture sismo-genetiche. I nuovi dati, di alta qualità e dettaglio, forniranno una migliore definizione dell'attività sismica locale aiutando in questo modo a comprendere come il processo di subduzione e le dinamiche superficiali interagiscono. http://hdl.handle.net/2122/5929 Titolo: Messina 1908-2008: understanding crust dynamics and subduction in Southern Italy<br/><br/>Autori: Govoni, Aladino; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Margheriti, Lucia; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; D'Anna, Giuseppe; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Selvaggi, Giulio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Patanè, Domenico; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Moretti, Milena; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Zuccarello, Luciano; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia<br/><br/>Abstract: To mark the centennial anniversary of the 1908 earthquake that shook Messina, Italy, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) has begun the "Messina 1908- 2008" research project. The aim is to clarify the extension deformation processes that occur in the Messina Strait and to understand relationships between subduction and crustal deformation there by merging existing data and studies, and by collecting new and more detailed seismological, geodetic, historical, and satellite observations. More than 20 permanent seismic stations and about 15 temporary stations are located in the study region. A dense permanent geodetic network also operates in the region, several campaign surveys are newly available, and new geodetic campaign measurements were performed in March 2008. In addition, during July 2008, five ocean bottom seismometers (OBS) were deployed to better monitor the area largely covered by the sea. Records of historical earthquakes that struck the Strait of Messina will be analyzed, and synthetic aperture radar images will help define surface deformation of the region. The Messina 1908-2008 project's assemblage of a database and integration of innovative technologies could transform our understanding of the crust and mantle structure of the active tectonics and seismic hazards of the Strait of Messina.