Complex Fault Geometry and Rupture Dynamics of the M_W 6.5, 30 October 2016, Central Italy Earthquake

Abstract

We study the 30 October 2016 Norcia earthquake (MW 6.5) to retrieve the rupture history by jointly inverting seismograms and coseismic Global Positioning System displacements obtained by dense local networks. The adopted fault geometry consists of a main normal fault striking N155° and dipping 47° belonging to the Mt. Vettore‐Mt. Bove fault system (VBFS) and a secondary fault plane striking N210° and dipping 36° to the NW. The coseismic rupture initiated on the VBFS and propagated with similar rupture velocity on both fault planes. Updip from the nucleation point, two main slip patches have been imaged on these fault segments, both characterized by similar peak‐slip values (~3 m) and rupture times (~3 s). After the breakage of the two main slip patches, coseismic rupture further propagated southeastward along the VBFS, rupturing again the same fault portion that slipped during the 24 August earthquake. The retrieved coseismic slip distribution is consistent with the observed surface breakages and the deformation pattern inferred from interferometric synthetic aperture radar measurements. Our results show that three different fault systems were activated during the 30 October earthquake. The composite rupture model inferred in this study provides evidences that also a deep portion of the NNE trending section of the Olevano‐Antrodoco‐Sibillini thrust broke coseismically, implying the kinematic inversion of a thrust ramp. The obtained rupture history indicates that in this sector of the Apennines, compressional structures inherited from past tectonics can alternatively segment boundaries of NW trending active normal faults or break coseismically during moderate‐to‐large magnitude earthquakes.

Shear Wave Splitting Evidence and Relations With Stress Field and Major Faults From the “Amatrice‐Visso‐Norcia Seismic Sequence”

“…Among the numerous models for the rupture geometry of the Norcia source on 30 October 2016, proposed in the literature (Cheloni et al, ; Pizzi et al, ; Liu et al, ; Walters et al, ; Xu et al, ), the observed anisotropic results seem to be according to seismogenic source solution proposed by Scognamiglio et al (). In fact, the strike of ϕ axes follows the boundaries of a source modeled on two separated fault planes; δtn peaks are located in correspondence of the south‐western and the northern edges on the second N210° fault (see supporting material for details)…”

“…In the first period (Figure a) the rectangle represents the Amatrice source (Tinti et al, ), in the second (Figure b) the Norcia and the Visso source projections (Chiaraluce et al, ; Scognamiglio et al, ), and in last period (Figure c) the Montereale activated plane (Buttinelli 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 ).…”

22‐kyr‐Long Record of Surface Faulting Along the Source of the 30 October 2016 Earthquake (Central Apennines, Italy), From Integrated Paleoseismic Data Sets

“…The largest mainshock of the 2016 sequence was the Mw 6.5 Norcia earthquake of 30 October, the largest event in Italy since the 1980 Mw 6.9 Irpinia earthquake. A wealth of coseismic geological data for the three events of the sequence was collected and analyzed (e.g., Civico et al, , and references therein; EMERGEO Working Group, , , ) along with seismological, geodetic, and geophysical observations (e.g., Cheloni et al, ; Chiaraluce et al, ; Scognamiglio et al, ). In general, those multidisciplinary works point out a substantial consistency in the description and understanding of the 2016 seismic sources.…”

“…Indeed, it is worth noting that the 2016 earthquake represents a rare surface faulting event in Italy and an unprecedented case of coseismic rupture trace mapped in detail and trenched with a total of nine excavations. Six out of nine trenches were dug after the Mw 6.5 event (maximum trench distance of 10 km) across three distinct splays of the system (Figure ; fault splays coded as PRA1, PRA2, VET1, and VET6 splays in Villani et al, ), where high values of coseismic slip at depth occurred (Scognamiglio et al, ).…”