La Valle, Fabio (2019) Factors controlling the thickness of fault damage zones in carbonates (Central Apennines, Italy). [Magistrali biennali]
Full text disponibile come:
The Italian Central Apennines are one of the most seismically active areas in the Mediterranean (e.g., L’Aquila-Pizzoli Mw 6.7, 1703; Avezzano Mw 7.1, 1915; L’Aquila Mw 6.1, 2009). Most of this continuous seismicity is produced by earthquake ruptures propagating along normal faults hosted in carbonate rocks (dolostones and limestones). Some of these active fault zones are well-exposed in the mountain belt within badlands exposures. The most impressive structural feature of these exposed fault zones is the occurrence of up to hundreds of meters thick in-situ shattered rocks (fault rocks reduced in fragments < 1 cm in size on average and affected by negligible shear strain, i.e. they may preserve original sedimentary fabrics such as bedding, laminations etc.). However, both the geometry of these shattered rock bodies and how they have been produced (during seismic rupture propagation or other stages of the seismic cycle) remain largely unknown, also because of the lack of quantitative fault zone structural data (e.g., how shattered fault rocks are distributed along fault strike, how their thickness varies with fault length, displacement, geometry, etc.). A deep understanding of how in-situ shattered carbonate rocks are produced may impact our understanding of earthquake mechanics in carbonates and seismic hazard studies. Given the lack of quantitative data about in-situ shattered fault rocks in active fault zones in carbonates, the main goals of this thesis are: 1. the detailed field structural survey to quantify the distribution and thickness of in-situ shattered rocks and, 2. the remote-sensing analysis coupled with literature data review to determine, if any, scale relations between fault zone length, displacement, geometry and thickness of in-situ shattered fault rocks in carbonates. Indeed, such dataset is at the base of any model about the formation of the in-situ shattered rocks. To achieve these goals: 1. I conducted detailed field structural geology survey of the Monte Marine fault zone (Central Apennines), whose damage zone is characterized by in-situ shattered dolostones, 2. I conducted Optical and Scanning Electron Microscopy microstructural investigations of both in-situ shattered fault rocks and fault slipping zones, 3. I produced a catalogue which includes six main active normal fault zones of the Central Apennines characterized by up to 100s m thick damage zones with in-situ shattered carbonates. In particular, I mapped at 1:500 scale the Monte Marine fault zone (between thevillages of Pizzoli and Arischia, 10 km NE of the town of L’Aquila, Italy) where two fault strands overlap and collected data in 26 structural stations. Here, the fault core is ~ 30 m thick while the damage zone reaches ~ 1000 m in thickness and hosts in-situ shattered rocks, plus hundreds of minor synthetic and antithetic extensional faults, strike-slip and thrust faults. The latter are interpreted as Miocene to Pliocene structures reactivated during the Quaternary extensional phase and that interfered with newly formed post-orogenic normal faults, thus increasing the cataclastic rock volume in the intersection areas. The geological cross sections provided in this study underlie structural complexities due to the linkage of different fault segments and to the inherited compressional-to-extensional tectonic inversion. Based on the field observations, I propose that the extraordinary volumes of damage zone in the studied area of the Monte Marine Fault zone result from a combination of 1. geometrical complexities associated to the overstep sector, 2. presence of inherited compressional structures (thrust faults) and 3. seismogenic behaviour of the Master and minor faults. Cataclasites and in-situ shattered rocks are inferred to be the result of shattering up to hundreds of meters far from the Master Fault due to the stress perturbations and the near-field elastic waves induced and released by the propagation of seismic ruptures both along the Master Fault (main shocks) and minor faults cutting the damage zone (aftershocks). To produce the fault catalogue I used satellite images coupled with published geological maps to recognize where badland-type exposures could be related to the presence of in-situ shattered rocks. The Middle-Aterno Valley, the Morrone, the Venere, the Campo Imperatore and the Pescasseroli fault zones were also selected for less detailed structural geology survey to determine the fault damage zone thickness. The main results of the thesis include: 1. the first description of fault zone rocks distribution of the Monte Marine Fault and the reconstruction of the fault architecture in the overstep sector, 2. the first description of inherited compressional structures within the Monte Marine Fault zone, 3. exploiting the still limited fault catalogue, I find power-law relations between fault damage zone thickness, fault displacement and fault length. In particular, the thickness of the damage zone increases with fault displacement and slightly decreases with fault length suggesting that first order geometrical complexities (e.g., presence of step-overs) control the thickness of damage zones.
BibliografiaI riferimenti della bibliografia possono essere cercati con Cerca la citazione di AIRE, copiando il titolo dell'articolo (o del libro) e la rivista (se presente) nei campi appositi di "Cerca la Citazione di AIRE".
Le url contenute in alcuni riferimenti sono raggiungibili cliccando sul link alla fine della citazione (Vai!) e tramite Google (Ricerca con Google). Il risultato dipende dalla formattazione della citazione e non da noi.
Solo per lo Staff dell Archivio: Modifica questo record