HR: 1340h
AN: S43A-1060    [Abstracts]
TI: Large Earthquake Repeat on Normal Faults: Insights from dense in-situ 36Cl Exposure Dating of Limestone Fault Scarps, Central Apennines, Italy
AU: * SCHLAGENHAUF, A
EM: aloe.schlagenhauf@obs.ujf-grenoble.fr
AF: Laboratoire de Géophysique Interne et Tectonophysique, LGIT, CNRS, Université J. Fourier, BP 53, Grenoble, 38041, France
AU: BENEDETTI, L
EM: benedetti@cerege.fr
AF: CEREGE, CNRS, Université de Provence, BP 80, Aix-en-Provence, 13545, France
AU: MANIGHETTI, I
EM: imanighe@obs.ujf-grenoble.fr
AF: Laboratoire de Géophysique Interne et Tectonophysique, LGIT, CNRS, Université J. Fourier, BP 53, Grenoble, 38041, France
AB: The only chance to learn how major earthquakes have repeated in the past on major active faults is to analyze their surface geological record, if any. We analyze such a record on 11 active normal faults to seek identifying, dating and measuring the large earthquake ruptures that have broken these faults in the last 10-20 kyrs, and determine how these major ruptures have followed in space and time on each fault and from one fault to another. As large earthquakes repeat on a normal fault, the fault plane is progressively exhumed and exposed at the free air, forming an escarpment at the surface. Provided that this escarpment is preserved from erosion, its surface holds the complete record of the successive ruptures (and possible aseismic slip) as they have broken the ground surface. We have started to analyze such a record on 11 neighboring, likely interacting active faults in the Fucino area, Central Italy, where seismic activity can be devastating (1915, M7 Avezzano earthquake, 30 000 casualties). Faults offset limestone rocks and form several hundred meters high cumulative escarpments, whose youngest parts (10-20 kyrs) are well preserved in the form of 10-20 m high, steep scarps running along the fault lengths (10-20 km). The Holocene seismic slip history of the faults can be recovered from base-to-top continuous in-situ 36Cl exposure dating of the limestone scarps (Benedetti et al. 2002, 2003; Palumbo et al. 2004). To reach that objective, we have sampled the faults in two different ways: two faults (Magnola and Roccapreturo) were sampled at several, regularly spaced sites along their length, so that to recover the earthquake slip variability in both space and time. Nine other faults (Fiamigniano, Campo-Felice, Velino, Tre- Monti, Trasacco, Parasano, San Sebastiano, Castel di Ieri, Roccacasale) were sampled at one single spot along their length, so that to examine the possible earthquake interactions within the entire fault system. Doing so, we have collected one thousand samples (60-100 sample per site). We are now in the process of measuring the in situ 36Cl concentrations of these samples. Preliminary results will be shown, in comparison with previous data coming from paleoseismology and catalogues of historical earthquakes.
DE: 1150 Cosmogenic-nuclide exposure dating (4918)
DE: 7221 Paleoseismology (8036)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Seismology [S]
MN: 2007 Fall Meeting