GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.1 39 ARCHITECTURE AND FAULT ROCKS OF THE SEISMOGENIC MONTE MARINE FAULT ZONE (CENTRAL APENNINES, ITALY) S. Cortinovis 1* , F. Balsamo 1 , F. Storti 1 , F. La Valle 2 , M. Fondriest 2 , G. Di Toro 2 1 Dipartimento di Scienze Chimiche, della Vita e della Sostenibilità Ambientale, Università di Parma, Parma, Italy 2 Dipartimento di Geoscienze, Università degli Studi di Padova, Padova, Italy * Corresponding author: silvia.cortinovis@studenti.unipr.it The Central Apennines of Italy are characterized by a unique seismotectonic framework formed by a complex array of active seismogenic faults responsible for Mw<=7 seismic sequences (e.g., L’Aquila Mw 6.2, 2009; Amatrice Mw 6.6, 2016). Because of these seismic sequences, many seismological, geological and experimental studies have been performed to investigate earthquakes nucleation and propagation and to constrain fault zone frictional properties during the seismic cycle (Collettini et al. , 2017; De Paola et al. , 2011; Di Toro et al. , 2011; Nielsen et al. , 2017). Nevertheless, detailed field mapping and quantitative fault zone rock characterization (e.g. Demurtas et al. , 2016) are still lacking for the majority of the seismogenic faults affecting the Central Apennines. Structural architecture and fault rock distribution in active faults is a fundamental information for understanding the formation and evolution of faults, strain partitioning during the seismic cycle and the factors controlling the propagation and arrest of seismic ruptures. Accordingly, additional work on this subject is of paramount importance. In this contribution, we present the results of a field and laboratory studies of the seismogenic Monte Marine Fault Zone (MMFZ), which outcrops along the Aterno Valley near L’Aquila town, in the Central Apennines. The fault zone cuts through the Jurassic Calcare Massiccio Fm. and the Corniola Fm. and has a very old and complex seismotectonic history. The Monte Marine fault, which consists of a ~14 km long active segment (Galli et al. , 2011) was activated during the 1703 destructive earthquake that caused hundreds of fatalities along the Aterno Valley and in the near town of L’Aquila. Thanks to the trench excavations performed by Galli et al. (2011) and Moro et al. (2016), it was possible to verify the occurrence of further seismic surface ruptures during historical times along the fault and map the main fault trace in the Quaternary deposits near the villages of Pizzoli and Arischia. To study the along-strike fault zone architecture and related fault rock properties, twelve key-sectors were mapped at 1:500 scale and two detailed geological cross sections were constructed in the Barete and Pizzoli areas. Near Barete, the master slip surface is very smooth and quasi-planar and crops out discontinuously with an average attitude of N204°/65° (dip dir/ dip). In this site, the fault core is about 5 m thick. Based on grain size and shape distributions (obtained combining field observations and laboratory analyses), the following three cataclastic facies were identified (Fig. 1): Facies 1 is localized along the master slip surface and has grains with diameter < 63 µm with sub-rounded shapes; Facies 2 consists of a coarser cataclasite with grains between 63 µm and 2 mm; Facies 3 is a coarse breccia with sub-angular, cm to dm-scale grains. The facies 2 and 3 are also cut by secondary synthetic and antithetic normal faults, some of them showing ultra-comminuted cataclasites localized along mm-thick slip zones. Additionally, in places Facies 2 hosts carbonate-cemented concretionary bodies, suggesting sin- to post-kinematic meteoric fluid circulation. Between Pizzoli and Arischia, the structural architecture of the fault is more complex than in the Barete area because the fault zone width increases due to the presence of an overlapping zone characterized by E-W trending, breaching oblique-slip faults. In this sector, we found evidences of NE-SW strike-slip faults and NW-SE trending reverse faults, which are systematically cross-cut by the extensional faults. Reverse faults are likely inherited from the Apenninic compressional tectonics (with a 20-30°N tectonic transport direction) and were partially reactivated during the extensional phase. In this complex sector, the fault core is about 30 m thick and consists of ultracataclasites localized along major fault surfaces (Facies1), coarser cataclasites (Facies2) and coarse loose