Detecting young, slow‐slipping active faults by geologic and multidisciplinary high‐resolution geophysical investigations: A case study from the Apennine seismic belt, Italy

Abstract

[1] The Southern Apennines range of Italy presents significant challenges for active fault detection due to the complex structural setting inherited from previous contractional tectonics, coupled to very recent (Middle Pleistocene) onset and slow slip rates of active normal faults. As shown by the Irpinia Fault, source of a M6.9 earthquake in 1980, major faults might have small cumulative deformation and subtle geomorphic expression. A multidisciplinary study including morphological-tectonic, paleoseismological, and geophysical investigations has been carried out across the extensional Monte Aquila Fault, a poorly known structure that, similarly to the Irpinia Fault, runs across a ridge and is weakly expressed at the surface by small scarps/warps. The joint application of shallow reflection profiling, seismic and electrical resistivity tomography, and physical logging of cored sediments has proved crucial for proper fault detection because performance of each technique was markedly different and very dependent on local geologic conditions. Geophysical data clearly (1) image a fault zone beneath suspected warps, (2) constrain the cumulative vertical slip to only 25-30 m, (3) delineate colluvial packages suggesting coseismic surface faulting episodes. Paleoseismological investigations document at least three deformation events during the very Late Pleistocene (<20 ka) and Holocene. The clue to surface-rupturing episodes, together with the fault dimension inferred by geological mapping and microseismicity distribution, suggest a seismogenic potential of M6.3. Our study provides the second documentation of a major active fault in southern Italy that, as the Irpinia Fault, does not bound a large intermontane basin, but it is nested within the mountain range, weakly modifying the landscape. This demonstrates that standard geomorphological approaches are insufficient to define a proper framework of active faults in this region. More in general, our applications have wide methodological implications for shallow imaging in complex terrains because they clearly illustrate the benefits of combining electrical resistivity and seismic techniques. The proposed multidisciplinary methodology can be effective in regions characterized by young and/or slow slipping active faults.Citation: Improta, L., et al. (2010), Detecting young, slow-slipping active faults by geologic and multidisciplinary highresolution geophysical investigations: A case study from the Apennine seismic belt, Italy,

Geological and geophysical characterization of the southeastern side of the High Agri Valley (southern Apennines, Italy)

“…The HAV was hit by the M 7, 1857 Basilicata earthquake. A seismogenic structure capable of producing large events is alternatively associated with: (1) the Monti della Maddalena Fault System (MMFS) (Pantosti and Valensise, 1988;Maschio et al, 2005;Improta et al, 2010) and (2) the Eastern Agri Fault System (EAFS) (Benedetti et al, 1998;Cello et al, 2003;Giano et al, 2000). The MMFS bounds the HAV to the SW and runs for about 25 km between Pergola and Moliterno villages, whereas the EAFS, which is associated with mature fault-line scarps, bounds the HAV to the NE.…”

“…In situ non-invasive and low-cost geophysical techniques are widely employed in the subsurface investigations (Improta et al, 2010;Siniscalchi et al, 2010;Tropeano et al, 2013;Perrone et al, 2014). In particular, the electrical resistivity tomography (ERT) and the horizontal-to-vertical spectral ratio (HVSR) techniques have been widely applied in seismic microzonation (Boncio et al, 2011;Moscatelli et al, 2012), seismotectonic and geomorphological studies (Giocoli et al, 2008), to characterize the seismogenic fault systems (Galli et al, 2014;Giocoli et al, 2011), to reconstruct 316 A. Giocoli et al: Geological and geophysical characterization of the High Agri Valley the geometry and the mechanical properties of the superficial litho-stratigraphic units Albarello et al, 2011;Gallipoli et al, 2013), to delineate landslide body (Gallipoli et al, 2000;Perrone et al, 2004;Mainsant et al, 2012) and to study coseismic liquefaction phenomena .…”

Integrated Morphometric Analysis in GIS Environment Applied to Active Tectonic Areas

“…This earthquake has been localized along the narrow topographic culmination of the chain where the historical destructive seismicity, characterized by extensional focal mechanisms, is concentrated together with the active faults of this portion of the Southern Appenines. Different models have been suggested for the 1857 seismogenetic structure, based on: geological and structural surveys (Borraccini et al, 2002;Cello et al, 2003;Giano et al,1997Giano et al, , 2000; geomorphological analysis (Di Niro et al, 1992, Di Niro andGiano, 1995;Giano, 2011); seismotectonic analysis (Benedetti et al, 1998;Burrato & Valensise, 2008;Improta et al, 2010;Maschio et al 2005;Pantosti and Valensise, 1988;Valensise & Pantosti, 2001a), but there are still some open questions. Indeed in this region, contrasting with the events size, several tectonic and geomorphic factors concur to hide the active extensional seismogenetic faults.…”

Electrical resistivity tomography for studying liquefaction induced by the May 2012 Emilia-Romagna earthquake (Mw = 6.1, northern Italy)

“…In the last few years, the ERT has been increasingly applied to study active faults (Galli et al, 2006(Galli et al, , 2014Improta et al, 2010;Giocoli et al, 2011), volcanic areas (Finizzola et al, 2010Siniscalchi et al, 2010), landslides (Perrone et al, 2004), geological and structural setting of sedimentary basins (Giocoli et al, 2008), local seismic response (Boncio et al, 2011;Mucciarelli et al, 2011;Moscatelli et al, 2012), etc. Only in very few cases was the ERT method applied in laboratory experiments in order to study liquefaction phenomenon during and after the shaking (Jinguuji et al, 2007).…”