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School of GeoSciences, University of Edinburgh, Edinburgh, UK.
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- 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 - 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 - PublicationOpen AccessSpatial migration of temporal earthquake clusters driven by the transfer of differential stress between neighbouring fault/shear-zone structures(2024-04)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Uncertainty concerning the processes responsible for slip-rate fluctuations associated with temporal clustering of surface faulting earthquakes is a fundamental, unresolved issue in tectonics, because strain-rates accommodated by fault/shear-zone structures are the key to understanding the viscosity structure of the crust and seismic hazard. We constrain the timing and amplitude of slip-rate fluctuations that occurred on three active normal faults in central Italy over a time period of 20–30 kyrs, using in situ 36Cl cosmogenic dating of fault planes. We identify five periods of rapid slip on individual faults lasting a few millennia, separated time periods of up to 10 millennia with low or zero slip-rate. The rapid slip pulses migrated across the strike between the faults in two waves from SW to NE. We replicate this migration with a model where rapid slip induces changes in differential stress that drive changes in strain-rate on viscous shear zones that drive slip-rate variability on overlying brittle faults. Earthquakes increase the differential stress and strain-rate on underlying shear zones, which in turn accumulate strain, re-loading stress onto the overlying brittle fault. This positive feedback produces high strain-rate episodes containing several large magnitude surface faulting earthquakes (earthquake clusters), but also reduce the differential stress on the viscous portions of neighbouring fault/shear-zones slowing the occurrence of large-magnitude surface faulting earthquakes (earthquake anticlusters). Shear-zones on faults experiencing anticlusters continue to accumulate viscous strain at a lowered rate, and eventually this loads the overlying brittle fault to failure, initiating a period of rapid slip through the positive feedback process described above, and inducing lowered strain-rates onto neighbouring fault/shear-zones. We show that these patterns of differential stress change can replicate the measured earthquake clustering implied by the 36Cl data. The stress changes are related to the fault geometry in terms of distance and azimuth from the slipping structure, implying that (a) strain-rate and viscosity fluctuations for studies of continental rheology, and (b) slip-rates for seismic hazard purposes are to an extent predictable given knowledge of the fault system geometry.61 7