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COMET, Department of Earth Sciences, University of Oxford, Oxford, UK.
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- PublicationRestrictedAn upper bound on the rate of strain in the Central Apennines, Italy, from triangulation measurements between 1869 and 1963(1999-06-15)
; ; ;Hunstad, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;England, P.; Department of Earth Sciences, University of Oxford, Oxford; Italy is covered by a first-order triangulation network that was established between 1869 and 1908 and re-measured in patches between 1936 and 1963. We analyse the measurements made in the central part of Italy to form an estimate of the rate of strain in the Central Apennines. We conclude that the rate of strain in this region is too small to detect from the repeated triangulation measurement. This result places an upper bound of about 10(exp-7)/yr on the strain rate of the Central Apennines, and implies that the maximum rate of extension across the region is no higher than about 3 mm/yr.199 20 - PublicationRestrictedCoseismic and post-seismic slip of the 2009 L'Aquila (central Italy) MW 6.3 earthquake and implications for seismic potential along the Campotosto fault from joint inversion of high-precision levelling, InSAR and GPS data(2014-03-15)
; ; ; ; ; ; ; ; ; ; ; ; ; ;Cheloni, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Giuliani, R.; Ufficio Rischio Sismico e Vulcanico, DPC, Roma ;D'Anastasio, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Atzori, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Walters, R. J.; COMET+, School of Earth and Environment, University of Leeds, Leeds ;Bonci, L.; ISPRA, Roma ;D'Agostino, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Mattone, M.; Ufficio Rischio Sismico e Vulcanico, DPC, Roma ;Calcaterra, S.; ISPRA, Roma ;Gambino, P.; ISPRA, Roma ;Deninno, F.; IGM, Firenze ;Maseroli, R.; IGM, Firenze ;Stefanelli, G.; IGM, Firenze; ; ; ; ; ; ; ; ; ; ; ; After the April 6th 2009 MW 6.3 (ML 5.9) L'Aquila earthquake (central Italy), we re-measured more than 100 km of high-precision levelling lines in the epicentral area. The joint inversion of the levelling measurements with InSAR and GPS measurements, allowed us to derive new coseismic and post-seismic slip distributions and to de- scribe, with high resolution details on surface displacements, the activation and the slip distribution of a second- ary fault during the aftershock sequence that struck the Campotosto area (major event MW 5.2). Coseismic slip on the Paganica fault occurred on one main asperity, while the afterslip distribution shows a more complex pattern, occurring on three main patches, including both slips on the shallow portions and on the deeper parts of the rup- ture plane. The comparison between coseismic and post-seismic slip distributions strongly suggests that afterslip was triggered at the edges of the coseismic asperity. The activation of a segment of the Campotosto fault during the aftershock sequence, with a good correlation between the estimated slipping area, moment release and distribution of aftershocks, raises the opportunity to discuss the local seismic hazard following the occurrence of the 2009 L'Aquila mainshock. The Campotosto fault appears capable of generating earthquakes as large as his- torical events in the region (M N 6.5) or as small as the ones associated with the 2009 sequence. In the case that the Campotosto fault is accumulating a significant portion of the current interseismic deformation, the 2009 MW N 5 events will have released only a small amount of the accumulated elastic strain, and then a significant hazard still remains in the area. Continuing geodetic monitoring and a densification of the GPS networks in the region are therefore needed to estimate the tectonic loading across the different recognized active fault systems in this part of the Apennines.589 118 - PublicationRestrictedThe 2009 L’Aquila earthquake (central Italy): A source mechanism and implications for seismic hazard(2009-09-05)
; ; ; ; ; ; ; ; ; ;Walters, R. J.; COMET, Department of Earth Sciences, University of Oxford, Oxford, UK. ;Elliott, J. R; COMET, Department of Earth Sciences, University of Oxford, Oxford, UK. ;D’Agostino, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;England, P. C.; COMET, Department of Earth Sciences, University of Oxford, Oxford, UK. ;Hunstad, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Jackson, J. A.; COMET, Department of Earth Sciences, University of Cambridge, Cambridge, UK. ;Parsons, B.; COMET, Department of Earth Sciences, University of Oxford, Oxford, UK. ;Phillips, R. J.; School of GeoSciences, University of Edinburgh, Edinburgh, UK. ;Roberts, G.; Research School of Earth Sciences, University College London, London, UK.; ; ; ; ; ; ; ; We use InSAR and body-wave seismology to determine independent source parameters for the 6th April 2009 Mw 6.3 L’Aquila earthquake and confirm that the earthquake ruptured a SW-dipping normal fault with 0.6–0.8 m slip. The causative Paganica fault had been neglected relative to other nearby range-frontal faults, partly because it has a subdued geomorphological expression in comparison with these faults. The L’Aquila earthquake occurred in an area with a marked seismic deficit relative to geodetically determined strain accumulation. We use our source model to calculate stress changes on nearby faults produced by the L’Aquila earthquake and we find that several of these faults have been brought closer to failure.288 32 - PublicationRestrictedGeodetic strain in peninsular Italy between 1875 and 2001(2003-02-25)
; ; ; ; ; ; ;Hunstad, I.; Istituto Nazionale Geofisica Vulcanologia ;Selvaggi, G.; Istituto Nazionale Geofisica Vulcanologia ;D'Agostino, N.; Istituto Nazionale Geofisica Vulcanologia ;England, P.; Istituto Nazionale Geofisica Vulcanologia ;Clarke, P.; Istituto Nazionale Geofisica Vulcanologia ;Pierozzi, M.; Istituto Nazionale Geofisica Vulcanologia; ; ; ; ; We determine geodetic strain in peninsular Italy by the GPS reoccupation of the first order triangulation network of Italy installed from 1860. The uncertainties in the original measurements (about 3 ppm), and the time span between the two observations, imply that tectonic signals larger than about 0.03 ppm/yr are resolvable. Along the Apenninic belt, where the largest earthquakes are concentrated, the geodetic deformation has a clear and consistent strain pattern between adjacent regions, well above the uncertainties, and shows a pervasive NE-SW extension. Along the Tyrrhenian and Adriatic coasts the geodetic signal is not homogeneous and is comparable with the uncertainty in the original measurements. Seismic deformation, calculated over the same time interval, agrees well with estimated extensional direction, but the magnitudes of geodetic and seismic strain differ suggesting that, in part of the Apennines, significant strain accumulation over the past 130 years may not have been released in earthquakes.238 32 - PublicationRestrictedGravitational potential energy and active deformation in the Apennines(2014-05-09)
; ; ; ; ;D'Agostino, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;England, P.; University of Oxford ;Hunstad, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Selvaggi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; ; ; We use velocity measurements from a network of continuous GPS sites spanning the Apennines of peninsular Italy to test the hypothesis that the active deformation of the region is explained by variations in gravitational potential energy of the lithosphere. The simple geometry of the mountain chain allows us to treat the deformation as two-dimensional, neglecting gradients of velocity along the strike of the chain. Under this assumption, the integral of gravitational potential energy per unit area of the lithosphere (GPE) in the direction perpendicular to the chain is related by a simple expression to the velocity in the same direction. We show that the observed velocities match this expression with an RMS misfit of 0.5 mm/yr. This agreement suggests that deformation of the Apennines reflects a balance, within the mountain chain itself, between lateral variations in GPE and the stresses required to deform the lithosphere. Forces arising from processes external to the belt are not required to explain the observations.361 23 - PublicationOpen AccessShallow subsurface structure of the 2009 April 6Mw 6.3 L’Aquila earthquake surface rupture at Paganica, investigated with ground-penetrating radar(2010-06-22)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Roberts, G.; Research School of Earth Sciences, Birkbeck/UCL, University of London ;Raithatha, B.; Research School of Earth Sciences, Birkbeck/UCL, University of London ;Sileo, G.; Universit`a degli Studi dell’Insubria–Sede di Como, Italy ;Pizzi, A.; Dipartimento di Scienze della Terra Universit`a ‘G. d’Annunzio’ Chieti, Italy ;Pucci, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Walker, J. F.; Research School of Earth Sciences, Birkbeck/UCL, University of London ;Wilkinson, M.; Department of Earth Sciences, Durham University, Science Labs, Durham ;McCaffrey, K.; Department of Earth Sciences, Durham University, Science Labs, Durham ;Phillips, R.; Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, ;Michetti, A.; Universit`a degli Studi dell’Insubria–Sede di Como, Italy ;Guerrieri, L.; Geological Survey of Italy, ISPRA–High Institute for the Environmental Protection and Research, Italy ;Blumetti, A. M.; Geological Survey of Italy, ISPRA–High Institute for the Environmental Protection and Research, Italy ;Vittori, E.; Geological Survey of Italy, ISPRA–High Institute for the Environmental Protection and Research, Italy ;Cowie, P.; Institute of Geography, School of GeoSciences, University of Edinburgh, UK ;Sammonds, P.; Research School of Earth Sciences, Birkbeck/UCL, University of London ;Galli, P.; Dipartimento della Protezione Civile Nazionale, Rome, Italy ;Boncio, P.; Dipartimento di Scienze della Terra Universit`a ‘G. d’Annunzio’ Chieti, Italy ;Bristow, C.; Research School of Earth Sciences, Birkbeck/UCL, University of London ;Walters, R.; COMET, Department of Earth Sciences, University of Oxford, Oxford, UK; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The shallow subsurface structure of the 2009 April 6 Mw 6.3 L’Aquila earthquake surface rupture at Paganica has been investigated with ground penetrating radar to study how the surface rupture relates spatially to previous surface displacements during the Holocene and Pleistocene. The discontinuous surface rupture stepped between en-echelon/parallel faults within the overall fault zone that show clear Holocene/Pleistocene offsets in the top 10 m of the subsurface. Some portions of the fault zone that show clear Holocene offsets were not ruptured in 2009, having been bypassed as the rupture stepped across a relay zone onto a fault across strike. The slip vectors, defined by opening directions across surface cracks, indicate dip-slip normal movement, whose azimuth remained constant between 210◦ and 228◦ across the zone where the rupture stepped between faults. We interpret maximum vertical offsets of the base of the Holocene summed across strike to be 4.5 m, which if averaged over 15 kyr, gives a maximum throw-rate of 0.23–0.30 mm yr–1, consistent with throw-rates implied by vertical offsets of a layer whose age we assume to be ∼33 ka. This compares with published values of 0.4 mm yr–1 for a minimum slip rate implied by offsets of Middle Pleistocene tephras, and 0.24 mm yr–1 since 24.8 kyr from palaeoseismology. The Paganica Fault, although clearly an important active structure, is not slipping fast enough to accommodate all of the 3–5 mm yr–1 of extension across this sector of the Apennines; other neighbouring range-bounding active normal faults also have a role to play in the seismic hazard.210 270