Seismic Reflection Profiles and Subsurface Geology of the Area Interested by the 2016–2017 Earthquake Sequence (Central Italy)

Abstract

Starting from 24 August 2016, a long seismic sequence, including nine Mw > 5.0 earthquakes, struck a wide area of the Central Italy. A large amount of geological, geodetic, and seismological data envisages a complex system of NNW‐SSE trending, seismogenic normal faults. These active tectonic structures are well known at the surface and consistent with previous seismotectonic studies. In order to improve the comprehension of the seismotectonic framework of this seismic sequence, we provide a novel reconstruction of the subsurface geology of the area close to the Norcia Mw 6.5 mainshock (30 October 2016), based on previously unpublished seismic reflection profiles and available geological data. All the data have been synthesized along a 47 km long, WSW‐ENE trending geological cross section, interpreted down to a depth of 12 km. Comparing the subsurface geological model with the available seismological data, we find that the majority of seismicity is confined within the sedimentary sequence and does not penetrate the underlying basement. The basement has been constrained at depths of 8 to 11 km and coincides with the cutoff of the seismicity. We have also traced the trajectories of the seismogenic normal faults activated during this seismic sequence, reconciling the high‐angle (dip>65°) normal faults exposed at the surface, with their angle (dip < 50°) at hypocentral depths. The results of this study may be useful for better understanding the rheological properties of the seismogenic rock volume, as well as the coseismic deformations of the topographic surface observed by geodetic techniques and field mapping.

Gravity and Magnetic Modeling of Central Italy: Insights Into the Depth Extent of the Seismogenic Layer

“…In fact, both magnetic and gravity anomalies predicted along these sections fit the observed anomalies producing errors with magnitude similar to those obtained on the geologically constrained Section . In our opinion, this approach further validates the initial geological model proposed by Porreca et al (), which is consistently supported across the entire study area.…”

“…(c) Modelled blocks. The geological model after Porreca et al () is reported at the bottom of the figure. For densities ( ρ ) and magnetic susceptibilities ( k ) not provided for blocks in Figure c, please refer to the values at the bottom of the figure.…”

“…">Geological model. The geological constraints are provided by (i) surface geology (Carta Geologica Regionale 1:10,000—Regione Marche, ; Carta Geologica Regionale 1:10,000—Regione Umbria, ; Pierantoni et al, ); (ii) the geologic model recently proposed by Porreca et al () for the upper crust (0–12 km), constrained to surface data, boreholes, and seismic reflection profiles (hereafter called the Reference Geological Model); (iii) seismic refraction data to constrain middle and lower crust geometries (e.g., Ponziani et al, ) and densities (e.g., Gualtieri & Zappone, ); and (iv) Moho maps (e.g., Di Stefano et al, ; Piana Agostinetti & Amato, ; Pontevivo & Panza, ). In this work we define the basement as the central part of the crust, between the Triassic Evaporites and the lower crust, with a positive k , capable of producing detectable magnetic anomalies (i.e., magnetic basement, sensu Arisi Rota & Fichera, ; Speranza & Chiappini, ).…”

“…Geologic map of the study area with the location of the three model sections. The white dashed line across Section corresponds to the geologic cross‐section described by Porreca et al (). Events locations, magnitude, and focal mechanisms are from Chiaraluce et al ().…”

Coseismic Throw Variation Across Along‐Strike Bends on Active Normal Faults: Implications for Displacement Versus Length Scaling of Earthquake Ruptures

“…It is unclear because on the 30 October 2016, before field surveys of the 26 October earthquakes, a M w 6.5 earthquake ruptured the total length of the Mt. Vettore fault, rerupturing locations that slipped in the 24 August 2016 earthquake and perhaps those on the 26 October (see Figures , , and ; Calderoni et al, ; Cheloni et al, ; Chiaraluce et al, ; Civico et al, ; Falcucci et al, ; Ferrario & Livio, ; Lavecchia et al, ; Mildon et al, ; Pavlides et al, ; Perouse et al, ; Pizzi et al, ; Porreca et al, ; Scognamiglio et al, ; Verdecchia et al, ; Villani, Civico, et al, ; Villani, Pucci, et al, ; Walters et al, ). Meter‐scale offset across surface ruptures was measured with near‐field 1‐Hz global navigation satellite system for the 30 October ruptures, revealing that the ruptures formed within 2–4 s and, before peak ground acceleration, supporting the primary tectonic origin of the ruptures (Wilkinson et al, ; Figure ).…”