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Long-term expression of the Paganica Fault vs. 2009 L'Aquila Earthquake surface ruptures: looking for a better understanding of its seismic behavior

The Mw6.3, April 6, 2009 earthquake occurred on the previously identified Paganica normal fault and produced a 3 km-long co-seismic surface rupture along its northern section, with few centimeters of vertical displacement. Extensive 1:10,000-scale
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  Geophysical Research AbstractsVol. 12, EGU2010-12775-1, 2010EGU General Assembly 2010© Author(s) 2010 Long-term expression of the Paganica Fault vs. 2009 L’Aquila Earthquakesurface ruptures: looking for a better understanding of its seismicbehavior Riccardo Civico (1), Stefano Pucci (1), Paolo Marco De Martini (1), Daniela Pantosti (1), Francesca RomanaCinti (1), Simona Pierdominici (1), Luigi Cucci (1), Paola Del Carlo (2), Carlo Alberto Brunori (1), AntonioPatera (1), and Stefania Pinzi (1) (1) Istituto Nazionale di Geofisica e Vulcanologia, Seismology and Tectonophysics, Rome, Italy (riccardo.civico@ingv.it), (2)Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy The Mw6.3, April 6, 2009 earthquake occurred on the previously identified Paganica normal fault and produceda 3 km-long co-seismic surface rupture along its northern section, with few centimeters of vertical displacement.Extensive 1:10,000-scale geological and geomorphological mapping has been carried out, focusing on thecharacterization of the long-term expression of the Paganica Fault at the surface. The field mapping was integratedby observations, made on 1:33,000 scale aerial photographs (GAI), 5-m-resolution Digital Elevation Model andstandard morphometric derivatives (hill-shaded and slope angle maps, Spatial Analyst™). Particular attentionwas devoted to the study of the continental deposits and landforms affected by cumulative offset with the aim toreconstruct the Quaternary deformational history of the fault. The fault runs for a total length of 20 km and, alongwith antithetic faults on its hanging-wall, forms the graben of the Middle Aterno River Valley. The whole faultsystem and the variable setting of deformation affecting the continental deposits at the surface were identified.The Paganica long-term morphologic signature is represented by a set of prominent scarps formed by the tectonic juxtaposition of late Pliocene-middle Pleistocene and late Pleistocene alluvial deposits, and by lower scarps inlate Pleistocene-Holocene deposits. In addition, evident Quaternary erosional and depositional paleosurfaces wererecognized and sampled for 14C and OSL (Optically Stimulated Luminescence) and tephra chronology dating forlong-term slip-rate calculations.This study resulted helpful to locate four paleoseismological investigations (see Pantosti et al. talk) and to providethe appropriate context for correctly interpret the depositional bodies outcropping on the trench walls. Thesepaleoseismological investigations evidenced the presence of repeated late Pleistocene-Holocene activity andallowed for slip-rate estimation at a shorter time-scale. Such estimates were valuable for a comparison with thepreliminary estimates on late Pleistocene calculations carried out by geomorphological investigations.Moreover, we correlated co-seismic deformations with the long-term morphologies and structures. The 2009co-seismic ruptures show a general coherence with the long-term Paganica fault trace, both in terms of locationand style. However, the limited extent of the 2009 surface ruptures coincides with the portion of the faulttrace where deformation is more localized and few splays contribute to the extension. This is also testified bythe presence on its hanging-wall of a large late Pleistocene-Holocene alluvial fan that subsides over the basindepocenter. Conversely, where the Paganica fault system branches out, various splays accommodated the small2009 co-seismic throw, resulting in a distributed and not evident extensional strain.The preserved fault-related geomorphology is evidence for the persistence of the rupture complexities duringQuaternary. On this light, further studies on the style of fault activity are needed to estimate if the Paganica faultis capable of earthquakes with Magnitude larger than the 2009 event.
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