S041-06
Illuminating the complex fault zone structure of the 2016-2017 Amatrice, Central Italy, earthquake sequence with a high-resolution, high-density earthquake catalog
Friday, 11 December 2020: 10:52
Virtual
Felix Waldhauser1, Maddalena Michele2, Lauro Chiaraluce2, Raffaele Di Stefano2, David Paul Schaff1, William L Ellsworth3, Yen Joe Tan4, Gregory C Beroza3, Men-Andrin Meier5, Pasquale De Gori6 and Claudio Chiarabba6, (1)Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, United States, (2)Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy, (3)Stanford University, Department of Geophysics, Stanford, CA, United States, (4)Chinese University of Hong Kong, Hong Kong, Hong Kong, (5)California Institute of Technology, Seismological Laboratory, Pasadena, CA, United States, (6)Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy
Abstract:
We developed a high-resolution and high-density catalog of close to 400,000 earthquakes that occurred during the devastating Amatrice, Central Italy, earthquake sequence of 2016-2017. The new catalog, with magnitudes between -1 and 6.5, is based on a double-difference analysis of automatic phase picks from 130 stations with 6-8 km inter-station distances, and cross-correlation delay time measurements for events with correlated seismograms. It illuminates new fine-scale details of the normal faulting sequence that ruptured in three M > 5.9 mainshocks and activated several west-dipping normal faults, antithetic faults and near-surface splays. A prominent sub-horizontal shear zone truncates the normal faults at 8-10 km depth and connects to the inherited Sibillini thrust-structure formed prior to the extensional tectonic phase that today controls the central Apennines.
We reconstruct fault planes that ruptured during M>5 events using principal component analysis and measure fault damage zone width from the distribution of aftershocks normal to the fault plane. Damage zone widths vary between 1.0 and 1.7 km, with wider zones dominating the central part of the sequence. In comparison, damage zones as narrow as 0.5 km were found for the 2009 L’Aquila earthquake located to the south of the Amatrice sequence (Valoroso et al.., 2014). The wider damage zones north of the Sibillini thrust suggest complex faulting processes, which is also supported by a surprisingly low number of correlated events compared to earthquakes recorded south of the thrust. Strike and dip from focal mechanisms also show a greater variation near faults with wider damage zones. Damage zones are wider on the hanging wall side of the fault than the footwall side. The fragmented, sub-horizontal shear zone is about 1.5 km thick in areas undisturbed from abutting normal faults or adjacent, overlapping shear zone fragments. The normal faults terminate just above the basal shear zone, with no indication of listric behavior. The Sibillini thrust, on the other hand, turns listric where it connects to the shear zone at depth.
