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SUMMARY We captured post-seismic deformation close to the surface rupture of the 2009 L'Aquila earthquake ( M6.3, central Italy) using repeat terrestrial laser scan (TLS) methods. From 8 to 126 d after the earthquake, we repeatedly laser scanned four road surfaces that intersected the earthquake surface rupture. We modelled vertical near-field deformation, at millimetre-level precision, by comparing subsequent laser scan data sets to the first acquired at each site. The horizontal post-seismic deformation at each site was measured between reflectors paired across the rupture. The TLS data were supplemented by total station data from a fifth site which measured the vertical and horizontal components of post-seismic deformation between two points spanning the rupture. We find post-seismic deformation increased between 44 and 126 d at the southeastern end of the rupture, beneath which a significant gradient in coseismic slip exists within the fault zone. The location, rate of decay and spatially-localized nature of the post-seismic deformation, within tens of metres of the surface rupture suggests it is due to afterslip in the fault zone, driven by increased shear stresses at the edges of regions which slipped coseismically. We note that the magnitude of post-seismic deformation in the far field obtained from InSAR and GPS is not significantly greater than the deformations we have measured close to the rupture. We suggest that shallow, localized afterslip within the fault zone is responsible for the majority of the regional post-seismic deformation field. [ABSTRACT FROM AUTHOR]

Abstract Large continental earthquakes necessarily involve failure of multiple faults or segments. But these same critically-stressed systems sometimes fail in drawn-out sequences of smaller earthquakes over days or years instead. These two modes of failure have vastly different implications for seismic hazard and it is not known why fault systems sometimes fail in one mode or the other, or what controls the termination and reinitiation of slip in protracted seismic sequences. A paucity of modern observations of seismic sequences has hampered our understanding to-date, but a series of three M w > 6 earthquakes from August to November 2016 in Central Italy represents a uniquely well-observed example. Here we exploit a wealth of geodetic, seismological and field data to understand the spatio-temporal evolution of the sequence. Our results suggest that intersections between major and subsidiary faults controlled the extent and termination of rupture in each event in the sequence, and that fluid diffusion, channelled along these same fault intersections, may have also determined the timing of rupture reinitiation. This dual control of subsurface structure on the stop-start rupture in seismic sequences may be common; future efforts should focus on investigating its prevalence. Graphical abstract Highlights • 3 M > 6 earthquakes in Central Italy are a uniquely well-observed seismic sequence. • Pre-existing fault structures controlled the extent of rupture in each event. • Fluid diffusion along these structures may have determined timing of sequence. • Dual control of structure on stop-start rupture in seismic sequences may be common. [ABSTRACT FROM AUTHOR]

Abstract: To investigate the mechanism driving active extension in the central and southern Italian Apennines and the geography of seismic hazard, we compare spatial variations in upper crustal strain-rate measured across exposed fault scarps since 15±3ka with data on cumulative upper-crustal strain and topographic elevation, and free-air gravity, P-wave tomography and SKS splitting delay times that are a proxy for strain in the mantle. High extensional strain-rates across the Apennines since 15±3ka (0.4–3.1mm/yr along 90km transects) occur in two areas (Lazio-Abruzzo; SE Campania and Basilicata) where values for finite extensional strains that have developed since 2–3Ma are highest (2–7km cumulative throw), and where mean elevation in 5×90km NE–SW boxes is >600m; the intervening area (NW Campania and Molise) with<600m mean elevation in 5×90km boxes has extension-rates<0.4mm/yr and lower values for finite extensional strains (<2km cumulative throw). These two areas with high upper-crustal strain-rates overlie mantle that has relatively-long spatially-interpolated SKS delay times (1.2–1.8s) indicating relatively-high mantle strains and free-air gravity values (140–160mGals); the intervening area of lower extension-rate has shorter spatially-interpolated SKS delay times (0.8–1.2s) and lower free-air gravity values (120mGals). The two areas with high upper crustal strain-rates and strain, mean elevation, and mantle strain, coincide with the northern and southern edges of a slab window in the Tyrrhenian–Apennines subducting plate that has been inferred from published P-wave tomography. Together these correlations suggest that dynamic support of the topography by mantle flow through the slab window may control the present day upper crustal strain-rate field in the Apennines and the geography of seismic hazard in the region. [Copyright &y& Elsevier]