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Structure and deformation processes active in seismogenic carbonate-hosted fault zones

Matteo Demurtas, University of Otago

Carbonate-built rocks are a widely recurrent lithology often involved in most of the present seismicity occurring in densely populated areas, such as the circum-Mediterranean area (e.g., L'Aquila 2009, MW 6.1; Amatrice 2016, MW 6.5).

The investigation of the structure and the deformation processes that control seismicity is essential for a more sound understanding of the seismic cycle.

The Vado di Corno Fault Zone (VCFZ) is located in the Central Apennines (Italy) and offers the chance of studying the internal structure of a beautifully exposed active fault zone.

The mapped fault network and damage distribution of the VCFZ strongly resemble the buried structures, highlighted by geophysical investigations, that are responsible for the present seismicity in that area of the Apennines. Motivated by their occurrence in the VCFZ, an experimental investigation of the friction and microstructural evolution of mixtures of calcite-dolomite gouges was carried out.

Microstructural analysis shows the formation of a foliation in the gouge only during coseismic sliding, suggesting this peculiar microstructure to be a potential indicator for seismic slip in the rock record. Electron backscatter diffraction analysis on the experimentally deformed gouges shows the development of a CPO in calcite in the bulk gouge during low-temperature deformation.

The CPO is interpreted as a result of grain rotation and preferential fracturing along the {101 ̅4} calcite cleavage planes during the early stages of cataclasis. Transmission Kikuchi diffraction analysis on the highly-localized principal slip zone of calcite-dolomite mixtures sheared at coseismic slip rates revealed a recrystallized nanograins aggregate, which likely accommodated coseismic sliding by grain-boundary sliding aided by diffusion creep.

All the observations from the field- to the nanoscale suggest that earthquakes occurring in the shallow crust made of carbonate-built rocks are likely the result of a combination of elasto-frictional ("brittle") but especially viscous-plastic ("ductile") micro-processes.

Date Wednesday, 11 April 2018
Time 1:00pm - 2:00pm
Audience Public
Event Category Sciences
Event Type Departmental Seminar
LocationBenson Common Room, (Gn9), Geology building, 360 Leith Street, Dunedin

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