Unravelling the complexity of the geometry and nucleation phase of Apennininc extensional systems: the case of the 2009 MW 6.1 L’Aquila normal fault system (Central Italy).

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• Lauro Chiaraluce, Istituto Nazionale di Geofisica e Vulcanologia, Rome
• Tuesday 15 November 2011, 16:30-17:30
• Harker 1 seminar room, Department of Earth Sciences.

If you have a question about this talk, please contact John Maclennan.

In 2009, a MW 6 .1 normal faulting earthquake struck the axial area of the Abruzzo region in Central Italy. We analysed the continuous recordings of the very dense seismic network composed by 60 stations that operated in the epicentral area for 9 months by integrating an accurate automatic picking procedure together with cross-correlation and double-difference relative location methods. The adopted procedure allowed us to recover an extraordinary set of data composed by high-precision locations for 64000 earthquakes. Events span in magnitude (ML) between -0.9 to 5.9, reaching a completeness magnitude of 0.7. For the first time the geometry of the faults at depth imaged by seismicity distribution (seismological faults) highly resemble from the kilometer to meter scale, the geometry of the outcropping faults mapped on the field (geological faults). These data will help us to improve our knowledge about: a) how faults behave at the surface; b) how crustal faults ‘end’ at depth; c) what the transition from brittle to ductile crust looks like and d) how stress gets distributed at the transition. We also inverted P‐ and S‐wave travel times to infer the velocity structure in the crustal volume where the April 6th main shock nucleated to image local variations of P‐wave velocity and Poisson ratio along the fault zone. The interpretation of the complex initial stages of the mainshock rupture and the spatial variations of VP and Poisson ratio once again points to a strong correlation between material properties and presence of fluids in the source volume. Finally, we focus on the analysis of about 300 clusters of repeating earthquakes characterising the mechanical behaviour of secondary fault segments structures often not optimally oriented with the crustal stress field.

References.

The anatomy of the 2009 L’Aquila normal fault system [Central Italy] imaged by high resolution foreshock and aftershock locations. L. Chiaraluce, L. Valoroso, D. Piccinini, R. Di Stefano and P. De Gori (In press on JGR ).

Di Stefano, R., C. Chiarabba, L. Chiaraluce, M. Cocco, P. De Gori, D. Piccinini, and L. Valoroso (2011), Fault zone properties affecting the rupture evolution of the 2009 (Mw 6.1) L’Aquila earthquake (central Italy): Insights from seismic tomography, Geophys. Res. Lett., 38, L10310 , doi:10.1029/2011GL047365.

This talk is part of the Department of Earth Sciences Seminars (downtown) series.

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