Coseismic Slip Vectors of 24 August and 30 October 2016 Earthquakes in Central Italy: Oblique Slip and Regional Kinematic Implications

Abstract

After 24 August and 30 October 2016 central Italy earthquakes (Mw 6.0 and 6.5, respectively), photogrammetry and geodetic survey were performed at various sites along a 6-km-long portion of the rupturing Monte Vettore fault system, providing very high-resolution georeferenced 3-D point clouds and imagery of the 24 August rupture and a data set of bedrock fault scarp before/after the 30 October earthquake. The maximum coseismic displacement for both events occurs near Scoglio dell' Aquila with an average normal dip slip of 22 ± 4 and 184 ± 6 cm, respectively. Coseismic slip vectors and meter-scale corrugation axis are oriented N280 ± 10°on the~N140°striking main Vettore fault involving oblique normal slip with a right-lateral component and N205 ± 10°on~N170°fault strands implying oblique normal slip with a left-lateral component. We quantify the near-field coseismic displacements of the Monte Vettore fault for the 30 October event: the footwall has been translated horizontally by 42 ± 2 cm toward the ENE and uplifted by 11 ± 2 cm. The hangingwall has moved horizontally by 26 ± 2 cm, toward the NW, in a direction parallel to the fault plane and subsided by 116 ± 2 cm. The fault geometry and our determined surface coseismic slip vectors are mechanically compatible with a σ3 = N65 ± 15°. This stress regime is consistent with the 30 October 2016 focal mechanism and the relative motion between the Adriatic microplate and the Tyrrhenian coastal region. The 30 October surface rupture results from seismic slip at depth and thus has a tectonic origin. Plain Language SummaryAfter 24 August and 30 October 2016 central Italy earthquakes, we acquire a very high-resolution data set of the effect of the fault at the surface before and after the 30 October earthquake. Those data sets allow quantifying the motion of each compartment on both side of the fault during the earthquake and the direction of this motion. The footwall has been translated horizontally by 42 ± 2 cm toward the ENE and uplifted by 11 ± 2 cm. The hangingwall has moved horizontally by 26 ± 2 cm, toward the NW, and subsided by 116 ± 2 cm. These results are consistent with the seismic data and suggest that surface ruptures observed are resulting from seismic slip at depth.In 2016, Italy was struck by an earthquake sequence that lasted several months with three shocks on 24 August, Mw = 6.0; 26 October, Mw = 5.9; and 30 October, Mw = 6.5 (Figure 1). This sequence occurred in Central Apennines, where NW-SE striking normal fault systems are accommodating~4 mm/year of PEROUSE ET AL. 3760

Gravity Versus Tectonics: The Case of 2016 Amatrice and Norcia (Central Italy) Earthquakes Surface Coseismic Fractures

“…For the CVF, specifically investigated by Iezzi et al (), our analysis for the entire fracture zone results in an angular discrepancy of 10.3° and 18.2° between the aspect and fracture dip direction of each database entry, respectively, for the Amatrice and Norcia earthquakes. We also find a good correspondence between the few slip vector angles (Figure ) measured at selected sites at the contact limestone/SDCE materials (Perouse et al, ) and the maximum slope orientation. Perouse et al () attributed the displacement entirely to primary faulting with oblique kinematics, inferring a change from oblique dextral to pure normal to oblique sinistral slip along the concave fracture zone at midslope (Figures a and l).…”

“…We also find a good correspondence between the few slip vector angles (Figure ) measured at selected sites at the contact limestone/SDCE materials (Perouse et al, ) and the maximum slope orientation. Perouse et al () attributed the displacement entirely to primary faulting with oblique kinematics, inferring a change from oblique dextral to pure normal to oblique sinistral slip along the concave fracture zone at midslope (Figures a and l). Slip vector angles reported by Perouse et al (), however, are compatible with the direction of maximum slope (Figure ).…”

“…The spatial pattern of fractures, including their orientation, continuity, and coherence, was seen by many as the main evidence for interpreting them exclusively as resulting from surface faulting along Mount Vettore (Emergeo Working Group, ; Lavecchia et al, ; Perouse et al, , among others). Following our field work and our close inspection of all available photographic material (Figure and Emergeo Working Group, and Emergeo Working Group, ), however, we remark that the coseismic ground deformation responds to a strong structural and rheological control, with a loss of slope continuation in SDCE or a collapse of the same deposits where in contact with limestone.…”

“…Following the Amatrice earthquake, several newly formed fractures and rejuvenated bedrock fault scarps were reported at various heights along the western flank of Mount Vettore and in the underlying Piano Grande basin (Figures b and a–e; see also photographs of Emergeo Working Group, ). According to the prevailing opinion (Emergeo Working Group, ; Lavecchia et al, ; Perouse et al, ; Pizzi et al, , among others), all the observed surface deformation results from the propagation of the main earthquake rupture up to the surface, corresponding with the Cordone del Vettore fault (CVF), and should hence be interpreted as primary surface faulting. Other researchers (Bonini et al, ; Valensise et al, ) contended that the causative fault for the 2016 earthquake sequence is an inverted, shallow dipping thrust and that the steep CVF is a secondary feature.…”

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 ).…”