Discovering the characteristics of the surface faulting ancestors of the L’Aquila April 6, 2009 earthquake by paleoseismological investigations

The occurrence of the Mw 6.3, April 6, 2009 earthquake has highlighted how critical is the development of hazard models that incorporate all the information on the long-term seismic behavior of faults (i.e., individual events rupture length and slip, timing, etc.). Under this light we started a campaign of paleoseismological investigations in the epicentral area. The 2009 earthquake occurred on the Paganica normal fault (PF hereinafter) and produced a max 0.15 m high, 3 km-long continuous surface rupture along its central section, as well as several short, discontinuous cracks along the rest of the fault trace; secondary slip along nearby tectonic structures was observed too. The PF consists of a prominent NW-SE striking and SW dipping long-term morphologic scarp formed by the tectonic juxtaposition of Pliocene-middle Pleistocene and late Pleistocene alluvial deposits, and by smaller compound scarps in late Pleistocene-Holocene deposits. The fault runs for a total length of about 20 km along the NE side of the Aterno River valley, a graben-type basin bounded by marked antithetic faults. The limited extent and the small throw of the 2009 surface ruptures, when compared to the size of the Paganica long-term fault scarp, raise questions about the evolution and rupture history of this fault and suggest that the PF may have experienced larger Magnitude earthquakes than the 2009 seismic event. With the aim of defining the Max Magnitude expected for the PF by determining the size of the individual coseismic surface ruptures occurred in the past and their max extent, their frequency and the average rate of displacement we have been excavating new trenches and studied artificial exposures across the PF fault zone, in most of the cases intersecting the 2009 surface ruptures. Preliminary results show evidence for repeated decimetric surface faulting events during the past 3 millennia with the penultimate likely being the 1461 event (Me 6.4); evidence for possible previous larger slip events is found too. Whether the small ruptures are all related to slip at depth on the PF or would represent sympathetic slip triggered by earthquake occurred on nearby faults should be better investigated. Conversely, provided the “double size” slip behavior of the PF is confirmed, to characterize the seismic hazard of the area we should consider a more complex seismogenic model than that presently applied. In particular, we should include also the scenario that the PF produces relatively frequent (each 4-600 yr) 2009-type earthquakes and rare (each 3-4 millennia) larger events, likely in connection with other nearby active structures (i.e., San Demetrio Fault? Pettino Fault?)

HISTORICAL AND ARCHAEOSEISMIC STUDIES IN THE POLLINO AREA

Section 1. Reappraisal of the January 8, 1693 Pollino earthquake Section 2. Archaeoseismic field survey Section 3. Investigation of damaged speleothem

Subsidence induced by urbanisation in the city of Rome detected by advanced InSAR technique and geotechnical investigations

We applied the Interferometric Point Target Analysis (IPTA) technique to study the city of Rome (Italy) aiming to detect and measure the surface movements of buildings and urban structures. The available SAR dataset has been delivered by ESA CAT1 3258 and ranges the period 1992-2005. In particular ERS1-ERS2 data processed covers 1995-2000, while Envisat ASAR 2002-2005. The Point Target velocity map shows a general stability except for some very local areas affected by subsidence rate larger than 10 mm/year. The analysis of the time series, compared to a detailed geological and geotechnical investigation of the lithostratigraphy of the alluvial sediments of the Tiber River, and combined with a temporal reconstruction of the expansion of the city over the alluvial valleys, allowed us to depict the main factors controlling the observed subsidence. These are: the in situ effective stress conditions, the related compressibility and viscous characteristics of the loaded soils, the thickness of the compressible stratum, the time since loading instant, and the entity of loading. Furthermore the observed subsidence is time-dependent, even at a long time-scale, with respect to the age of the buildings being most of the buildings constructed since the '50s still affected by slow subsidence. We mainly focused on the Grottaperfetta stream valley that is characterized by an anomalous high and time-lasting subsidence. Original data on the lithostratigraphic setting of this alluvial valley indicate that the high subsidence rate measured up to 2005 is caused by a still active primary consolidation process. (C) 2008 Elsevier Inc. All rights reserved

Discovering the characteristics of the surface faulting ancestors of the L’Aquila April 6, 2009 earthquake by paleoseismological investigations

The occurrence of the Mw 6.3, April 6, 2009 earthquake has highlighted how critical is the development of hazard models that incorporate all the information on the long-term seismic behavior of faults (i.e., individual events rupture length and slip, timing, etc.). Under this light we started a campaign of paleoseismological investigations in the epicentral area. The 2009 earthquake occurred on the Paganica normal fault (PF hereinafter) and produced a max 0.15 m high, 3 km-long continuous surface rupture along its central section, as well as several short, discontinuous cracks along the rest of the fault trace; secondary slip along nearby tectonic structures was observed too. The PF consists of a prominent NW-SE striking and SW dipping long-term morphologic scarp formed by the tectonic juxtaposition of Pliocene-middle Pleistocene and late Pleistocene alluvial deposits, and by smaller compound scarps in late Pleistocene-Holocene deposits. The fault runs for a total length of about 20 km along the NE side of the Aterno River valley, a graben-type basin bounded by marked antithetic faults. The limited extent and the small throw of the 2009 surface ruptures, when compared to the size of the Paganica long-term fault scarp, raise questions about the evolution and rupture history of this fault and suggest that the PF may have experienced larger Magnitude earthquakes than the 2009 seismic event. With the aim of defining the Max Magnitude expected for the PF by determining the size of the individual coseismic surface ruptures occurred in the past and their max extent, their frequency and the average rate of displacement we have been excavating new trenches and studied artificial exposures across the PF fault zone, in most of the cases intersecting the 2009 surface ruptures. Preliminary results show evidence for repeated decimetric surface faulting events during the past 3 millennia with the penultimate likely being the 1461 event (Me 6.4); evidence for possible previous larger slip events is found too. Whether the small ruptures are all related to slip at depth on the PF or would represent sympathetic slip triggered by earthquake occurred on nearby faults should be better investigated. Conversely, provided the “double size” slip behavior of the PF is confirmed, to characterize the seismic hazard of the area we should consider a more complex seismogenic model than that presently applied. In particular, we should include also the scenario that the PF produces relatively frequent (each 4-600 yr) 2009-type earthquakes and rare (each 3-4 millennia) larger events, likely in connection with other nearby active structures (i.e., San Demetrio Fault? Pettino Fault?).UnpublishedWien (Austria)3.2. Tettonica attivaope

HISTORICAL AND ARCHAEOSEISMIC STUDIES IN THE POLLINO AREA

Section 1. Reappraisal of the January 8, 1693 Pollino earthquake Section 2. Archaeoseismic field survey Section 3. Investigation of damaged speleothemsUnpublishedRome3.10. Storia ed archeologia applicate alle Scienze della Terraope

22‐kyr‐Long Record of Surface Faulting Along the Source of the 30 October 2016 Earthquake (Central Apennines, Italy), From Integrated Paleoseismic Data Sets

International audienceWe integrate paleoseismic data sets along the Mt. Vettore‐Mt. Bove normal fault system rupturing at the surface in the 30 October 2016 Norcia earthquake. Through the analysis of new trenches from this work and a review of the preexisting data, we correlate events among trench sites along antithetic and synthetic fault splays. We recognize seven M 6.5, 2016 Norcia‐type (or larger) surface‐faulting events in the last ~22 kyr, including 2016. Before 2016, one event occurred in the past two millennia (260–575 CE) and possibly corresponds to the event damaging Rome in 443 or 484/508 CE. Three previous events occurred between 10590 and 415 BCE, whereas the two oldest ones date between 19820 and 16540 BCE. The average recurrence time is 3,360–3,640 years for the last ~22 kyr and 1,220–1,970 years for the last ~4 kyr. We infer a minimum dip‐slip rate of 0.26–0.38 mm/year on the master fault in the central portion of the Mt. Vettore–Mt. Bove normal fault system and a dip‐slip rate of at least 0.10 mm/year on the southernmost portion. We infer a Middle–Late Pleistocene inception of the long‐term scarp of the investigated splays. The along‐strike variation of slip rates well reproduces the trend of the 2016 surface slip; thus, the time window exposed in the trenches is representative for the present fault activity. Based on trenching data, different earthquake rupture scenarios should be also considered for local hazard assessment

Integrating multidisciplinary, multiscale geological and geophysical data to image the Castrovillari fault (Northern Calabria, Italy)

The Castrovillari scarps (Cfs) are located in northern Calabria (Italy) and consist of three main WSW-dipping fault scarps resulting from multiple rupture events. At the surface, these scarps are defined by multiple breaks in slope. Despite its near-surface complexity, the faults likely merge to form a single normal fault at about 200 m depth, which we refer to as the Castrovillari fault. We present the results of a multidisciplinary and multiscale study at a selected site of the Cfs with the aim to (i) characterize the geometry at the surface and at depth and (ii) obtain constraints on the fault slip history. We investigate the site by merging data from quantitative geomorphological analyses, electrical resistivity and ground penetrating radar surveys, and palaeoseismological trenching along a 3c40 m high scarp. The closely spaced investigations allow us to reconstruct the shallow stratigraphy, define the fault locations, and measure the faulted stratigraphic offsets down to 20 m depth. Despite the varying resolutions, each of the adopted approaches suggests the presence of sub-parallel fault planes below the scarps at approximately the same location. The merged datasets permit the evaluation of the fault array (along strike for 220 m within a 370-m-wide zone). The main fault zone consists of two closely spaced NW\u2013SE striking fault planes in the upper portion of the scarp slope and another fault at the scarp foot. The 3-D image of the fault surfaces shows west to southwest dipping planes with values between 70\u25e6 and 80\u25e6; the two closely spaced planes join at about 200 m below the surface. The 8-to-12-m-high upper fault, which shows the higher vertical displacements, accommodated most of the deformation during the Holocene. Results from the trenching analysis indicate a minimum slip per event of 0.6 m and a maximum short-term slip rate of 0.6 mm yr\u20131 for the Cf. The shallow subsurface imaging techniques are particularly helpful in evaluating the possible field uncertainties related to postfaulting modification by erosional/depositional/human processes, such as within stream valleys and urbanized zones