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David, Schaff
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- PublicationOpen AccessA comprehensive suite of earthquake catalogues for the 2016-2017 Central Italy seismic sequence(2022-11-18)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ;; ; ; ; ;The protracted nature of the 2016-2017 central Italy seismic sequence, with multiple damaging earthquakes spaced over months, presented serious challenges for the duty seismologists and emergency managers as they assimilated the growing sequence to advise the local population. Uncertainty concerning where and when it was safe to occupy vulnerable structures highlighted the need for timely delivery of scientifically based understanding of the evolving hazard and risk. Seismic hazard assessment during complex sequences depends critically on up-to-date earthquake catalogues-i.e., data on locations, magnitudes, and activity of earthquakes-to characterize the ongoing seismicity and fuel earthquake forecasting models. Here we document six earthquake catalogues of this sequence that were developed using a variety of methods. The catalogues possess different levels of resolution and completeness resulting from progressive enhancements in the data availability, detection sensitivity, and hypocentral location accuracy. The catalogues range from real-time to advanced machine-learning procedures and highlight both the promises as well as the challenges of implementing advanced workflows in an operational environment.381 13 - PublicationOpen AccessThe complex architecture of the 2009 MW 6.1 L’Aquila normal fault system (Central Italy) as imaged by 64,000 high-resolution aftershock locations.(2011-12-05)
; ; ; ; ; ;Valoroso, Luisa; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Chiaraluce, Lauro; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Di Stefano, Raffaele; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Piccinini, Davide; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;David, Schaff; LDEO-Columbia University NY ;Waldhauser, Felix; LDEO-Columbia University NY; ; ; ; ; AGUOn April 6th 2009, a MW 6.1 normal faulting earthquake struck the axial area of the Abruzzo region in Central Italy. We present high-precision hypocenter locations of an extraordinary dataset composed by 64,000 earthquakes recorded at a very dense seismic network of 60 stations operating for 9 months after the main event. Events span in magnitude (ML) between -0.9 to 5.9, reaching a completeness magnitude of 0.7. The dataset has been processed by integrating an accurate automatic picking procedure together with cross-correlation and double-difference relative location methods. The combined use of these procedures results in earthquake relative location uncertainties in the range of a few meters to tens of meters, comparable/lower than the spatial dimension of the earthquakes themselves). This data set allows us to image the complex inner geometry of individual faults from the kilometre to meter scale. The aftershock distribution illuminates the anatomy of the en-echelon fault system composed of two major faults. The mainshock breaks the entire upper crust from 10 km depth to the surface along a 14-km long normal fault. A second segment, located north of the normal fault and activated by two Mw>5 events, shows a striking listric geometry completely blind. We focus on the analysis of about 300 clusters of co-located events to characterize the mechanical behavior of the different portions of the fault system. The number of events in each cluster ranges from 4 to 24 events and they exhibit strongly correlated seismograms at common stations. They mostly occur where secondary structures join the main fault planes and along unfavorably oriented segments. Moreover, larger clusters nucleate on secondary faults located in the overlapping area between the two main segments, where the rate of earthquake production is very high with a long-lasting seismic decay.134 59 - PublicationOpen AccessRadiography of a normal fault system by 64,000 high-precision earthquake locations: The 2009 L’Aquila (central Italy) case study(2013)
; ; ; ; ; ; ;Valoroso, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Chiaraluce, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Piccinini, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Di Stefano, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Schaff, D. ;Waldhauser, F.; ; ; ; ;We studied the anatomy of the fault system where the 2009 L’Aquila earthquake (MW 6.1) nucleated by means of ~64 k high-precision earthquake locations spanning 1 year. Data were analyzed by combining an automatic picking procedure for P and S waves, together with cross-correlation and double-difference location methods reaching a completeness magnitude for the catalogue equal to 0.7 including 425 clusters of similar earthquakes. The fault system is composed by two major faults: the high-angle L’Aquila fault and the listric Campotosto fault, both located in the first 10 km of the upper crust. We detect an extraordinary degree of detail in the anatomy of the single fault segments resembling the degree of complexity observed by field geologists on fault outcrops. We observe multiple antithetic and synthetic fault segments tens of meters long in both the hanging wall and footwall along with bends and cross fault intersections along the main fault and fault splays. The width of the L’Aquila fault zone varies along strike from 0.3 km where the fault exhibits the simplest geometry and experienced peaks in the slip distribution, up to 1.5 km at the fault tips with an increase in the geometrical complexity. These characteristics, similar to damage zone properties of natural faults, underline the key role of aftershocks in fault growth and co-seismic rupture propagation processes. Additionally, we interpret the persistent nucleation of similar events at the seismicity cutoff depth as the presence of a rheological (i.e., creeping) discontinuity explaining how normal faults detach at depth.334 291 - PublicationOpen AccessFault Planes, Fault Zone Structure and Detachment Fragmentation Resolved With High‐Precision Aftershock Locations of the 2016–2017 Central Italy Sequence(2021)
; ; ; ; ; ;; ; ; Three devastating earthquakes of MW ≥ 5.9 activated a complex system of high-angle normal, antithetic, and sub-horizontal detachment faults during the 2016–2017 central Italy seismic sequence. Waveform cross-correlation based double-difference location of nearly 400,000 aftershocks illuminate complex, fine-scale structures of interacting fault zones. The Mt. Vettore–Mt. Bove (VB) normal fault exhibits wide and complex damage zones, including a system of bookshelf faults that intersects the detachment zone. In the Laga domain, a comparatively narrow, shallow dipping segment of the deep Mt. Gorzano fault progressively ruptures through the detachment zone in four subsequent MW ∼ 5.4 events. Reconstructed fault planes show that the detachment zone is fragmented in four sub-horizontal, partly overlaying shear planes that correlated with the extent of the mainshock ruptures. We find a new, deep reaching seismic barrier that coincides with a bend in the VB fault and may play a role in controlling rupture evolution.206 9