Fault Segmentation as Constraint to the Occurrence of the Main Shocks of the 2016 Central Italy Seismic Sequence

Abstract

We perform the finite‐extent fault inversion of the three main events of the 2016 Central Italy seismic sequence using near‐source strong motion records. We demonstrate that both earthquake nucleation and rupture propagation were controlled by segmentation of the (N)NW‐(S)SE trending Quaternary normal faults. The first shock of the sequence (24 August, Mw 6.0) ruptured at the relay zone between the Laga Mts (LF) and the Cordone del Vettore (CVF) normal faults. The second shock (26 October, Mw 5.9) nucleated at a minor relay zone within the Mt. Vettore‐Mt. Bove fault (VBF), while the third and largest one (30 October, Mw 6.5) initiated at the relay zone between the VBF and CVF, triggering the multiple rupture of the VBF, CVF, and probably LF. We show that this latter relay zone corresponds to the deeper, high‐angle, fault zone of the Sibillini Mts cross structure, a thrust‐ramp inherited from the Miocene‐Pliocene contractional phase of the Apennines. This structure acted as a barrier to rupture propagation of the first two events thus defining an area of large stress concentration until it acted as the initiator of the rupture originating the largest Mw 6.5 event that crossed the barrier itself. We suggest that the “young” CVF have started to cut through the barrier acting as a soft‐linkage between the two long‐lived LF and VBF. The evidence that coseismic cumulative slip shows a maximum at the CVF, provided by both slip inversion and original surface rupture data, suggests that the CVF is growing faster than the adjacent faults.

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 relatively large paleothrows at the Hope trench location would imply a rupture involving the southern section of the VBFS (splays VET6 and VET7) together with a larger portion of the LMFS in the period between 5 and 22 kyr. The paleoseismic data collected along this southernmost portion of the fault system would also be concordant with the fault linkage hypothesis proposed by Pizzi et al (). Further data, including the timing and the size of paleoruptures along the northern portion of the Laga fault, are needed to corroborate this hypothesis.…”

Rupture Kinematics and Structural‐Rheological Control of the 2016 Mw6.1 Amatrice (Central Italy) Earthquake From Joint Inversion of Seismic and Geodetic Data

“…This interpretation is in agreement with the results obtained by Pizzi et al (2017). This interpretation is in agreement with the results obtained by Pizzi et al (2017).…”

Bayesian Self‐Adapting Fault Slip Inversion With Green's Functions Uncertainty and Application on the 2016Mw7.1 Kumamoto Earthquake

“…Approaches to the inference of fault slip models differ mainly in the chosen parameterization of the source model (e.g., Ide, , and references therein). The inverse problem can be linear when a dense spatial and temporal discretization of the slip rates over the assumed fault is considered (e.g., Gallovič & Zahradník, ; Hartzell & Heaton, ; Olson & Apsel, ; Sekiguchi et al, ), as commonly used to infer kinematic sources of large crustal earthquakes (e.g., Asano et al, ; Asano & Iwata, ; Gallovič et al, ; Pizzi et al, ; Wald & Heaton, ). Linear inversions are typically overparameterized and hence extremely unstable, which requires regularization by, for example, the positivity of slip rates and spatial‐temporal smoothing.…”