GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 1.1 131 Within the Grotta Cola, in central Italy, we found evidence of significant coseismic deformation represented by near similar-sized speleothemconcretions on collapsed speleothems. This deformation event, which is recorded in several rooms of the cave, is characterized by a consistent direction of stalagmite collapse toward N330°±10°. Such collapse direction is expected for seismic wave propagation along a NNW-SSE striking causative fault, consistent with the strike of either the Liri fault, mapped at the foot of the range hosting Grotta Cola (Roberts and Michetti, 2004), and of the Velino fault, located further northeast and having the Grotta Cola in its hanging-wall (Schlagenhauf et al. , 2011). We dated the deformation at between ~4.2-5.8 cal ka. Although we do not provide dates, observations are consistent with more than a single event recorded in the cave. Laboratory measurements were performed on Grotta Cola speleothem samples in order to characterize their mechanical properties. The obtained values of density, Young’s modulus and tensile failure stress, both from broken and unbroken speleothems, have been used as input data for theoretical calculations and numerical modelling of the main collapsed speleothem. The horizontal ground acceleration resulting in failure and the natural frequency of the speleothem were assessed by the FEM modelling. The results suggest either the Liri or the Velino fault as the most probable causative fault of the cave speleothem collapses recorded ~4-5 ka ago. Noteworthy, the time range bracketed for the speleothem deformation is well consistent with a period of clustered slip recorded by cosmogenic dating of the Velino-Magnola fault scarp (Schlagenhauf et al. , 2011). In summary, our research contributes to assess the existence or lack of past earthquakes within the axial seismogenic belt of the Apennines. As a matter of fact, the Grotta Cola lies just west of the Fucino plain, where historical and modern seismic deformation of the central Apennines seismic belt has concentrated. Definition of the upper threshold for seismic shaking, as in the case for the recent behaviour of the Pollino region, can help reducing overestimated risks and calls for a fault-based revision of seismic hazard maps. References Becker, A., M. Ferry, Monecke K.; 2005: Multiarchive paleoseismic record of late Pleistocene and Holocene strong earthquakes in Switzerland. Tectonophysics, 400, 153-177. Becker, A., C. A. Davenport, U. Eichenberger, E. Gilli, P.-Y. Jeannin, Lacave C.; 2006: Speleoseismology: A critical perspective. J Seismol., 10, 371-388. Delaby S.; 2001: Palaeoseismic investigations in Belgian caves . Netherlands J. Geosciences, 80(3-4), 323– 332. Ferranti L., S. Improta, L. Maschio, Vittori E.; 1997: Attività tettonica recente nel massiccio del Pollino suggerita dallo studio di speleotemi fratturati. Il Quaternario, 10 (2), 501-504. Ferranti L., Maschio L.; 2007: Ri cerche speleosismologiche nel massiccio del Pollino, Appennino Meridionale . Atti I Convegno Regionale di Speleologia “Campania Speleologica”, 1-3 Giugno, Oliveto Citra (SA), 201-215. Forti P.; 2001: Seismotectonic and paleoseismic studies from speleothems : The state of the art. Netherlands J Geosciences, 80(3-4), 175–185. Forti P., Postpischl D.; 1984: Seismotectonic and paleoseismic analyses using karst sediments . Mar. Geol., 55, 145- 161 . Kagan E. J., A. Agnon, M. Bar-Matthews, Ayalon A.; 2005: Dating large infrequent earthquakes by damaged cave deposits. Geology, 33(4), 261-264. Lacave, C., A. Levret, Koller M.; 2000: Measurements of natural frequencies and damping of speleothems . Proc. of the 12th World Conference on Earthquake Engineering, Auckland, New-Zealand, paper 2118. Lacave C., M.G. Koller, Egozcue J.J.; 2004: What can be concluded about seismic history from broken and unbroken speleothems? J. Earthquake Engineering, 8 (3), 431-455. Lacave C., B. Sadier, J.J. Delannoy, C. Nehme, J.J. Egozcue; 2012: The use of speleothems to better constrain long return period seismic hazard in Lebanon . Proc. of the 15th World Conference on Earthquake Engineering, Lisbon, Portugal. Roberts G.P., Michetti A.M.; 2004: Spatial and temporal variations in growth rates along active normal fault Systems: an example from Lazio-Abruzzo, central Italy . J. Struct. Geol., 26, 339–376. MPS Working Group; 2004: Redazione della mappa di pericolosità sismica prevista dall’Ordinanza PCM 3274 del 20 marzo 2003 . Rapporto Conclusivo per il Dipartimento della Protezione Civile, INGV, Milano- Roma, 2004 april. 65 p. Schlagenhauf, A., I. Manighetti, L. Benedetti, Y. Gaudemer, R. Finkel, J. Malavieille, Pou K.; 2011: Earthquake supercycles in Central Italy, inferred from 36Cl exposure dating. Earth Plan. Scie. Letters 307, 487–500.