Damage distribution and seismological model of the November 24, 2004, Salo' (Northern Italy) earthquake

The West side of lake of Garda, in Northern Italy, was struck by a ML=5.2 earthquake on November 24, 2004. The felt area is rather large (from Venice to Milan) and the damaged area consists of 66 municipalities, with a number of homeless of about 2200 and estimated direct damages of 215 millions of euros. Most of the damaged structures are old masonry buildings and churches, while there were almost no damage to reinforced concrete structures. The observed distribution of macroseismic intensity shows a strong azimuthal dependence, with high intensity level in a 10x10 km2 area located SW to the epicentre and rather large dispersion of values (ranging from V to VII-VIII) in the first 10 km epicentral distance. Taking into account the vulnerability level of the damaged structures and the features of the geological formations, we tried to explain the observed damage distribution in terms of finite fault properties of the source, despite the moderate magnitude of the event. Thus we hypothesised a fault geometry from seismotectonic considerations and we simulated the event by a high frequency simulation technique (Deterministic Stochastic Method, DSM). The synthetic ground motion parameters were converted into intensity values by empirical relationships and local geological conditions were considered to explain some discrepancies between simulated and observed intensities. It was possible to adequately reproduce both the observed distribution of macroseismic intensity and the ground motion recorded by an accelerometric station located at about 13 km epicentral distance

Testing Different Tectonic Models for the Source of the M w 6.5, 30 October 2016, Norcia Earthquake (Central Italy): A Youthful Normal Fault, or Negative Inversion of an Old Thrust?

We adopted a multidisciplinary approach to investigate the seismotectonic scenario of the 30 October 2016, Mw 6.5, Norcia earthquake, the largest shock of the 2016\u20132017 central Italy earthquake sequence. First, we used seismological and geodetic data to infer the dip of the main slip patch of the seismogenic fault that turned out to be rather low\u2010angle (~37\ub0). To evaluate whether this is an acceptable dip for the main seismogenic source, we modeled earthquake deformation using single\u2010 and multiple\u2010fault models deduced from aftershock pattern analyses. These models show that the coseismic deformation generated by the Norcia earthquake is coherent with slip along a rather shallow\u2010dipping plane. To understand the geological significance of this solution, we reconstructed the subsurface architecture of the epicentral area. As the available data are not robust enough to converge on a single fault model, we built three different models encompassing all major geological evidence and the associated uncertainties, including the tectonic style and the location of major d\ue9collement levels. In all models the structures derived from the contractional phase play a significant role: from controlling segmentation to partially reusing inherited faults, to fully reactivating in extension a regional thrust, geometrically compatible with the source of the Norcia earthquake. Based on our conclusions, some additional seismogenic sources falling in the eastern, external portions of the Apennines may coincide with inherited structures. This may be a common occurrence in this region of the chain, where the inception of extension is as recent as Middle\u2010Upper Pleistocene

Evidence for surface rupture associated with the Mw 6.3 L’Aquila earthquake sequence of April 2009 (central Italy)

An earthquake of Mw = 6.3 struck L Aquila town (central Italy) on 6 April 2009 rupturing an ~18-km-long SW-dipping normal fault. The aftershock area extended for a length of more than 35 km and included major aftershocks on 7 and 9 April and thousands of minor events. Surface faulting occurred along the SW-dipping Paganica fault with a continuous extent of ~2.5 km. Ruptures consist of open cracks and vertical dislocations or warps (0.1m maximum throw) with an orientation of N130°–140°. Small triggered slip and shaking effects also took place along nearby synthetic and antithetic normal faults. The observed limited extent and small surface displacement of the Paganica ruptures with respect to the height of the fault scarps and vertical throws of palaeo-earthquakes along faults in the area put the faulting associated with the L' Aquila earthquake in perspective with respect to the maximum expected magnitude and the regional seismic hazard.Published43-513.2. Tettonica attivaJCR Journalreserve

A photographic dataset of the coseismic geological effects induced on the environment by the 2012 Emilia (Northern Italy) earthquake sequence

We present a collection of pictures of the coseismic secondary geological effects produced on the environment by the 2012 Emilia seismic sequence in northern Italy. The May-June 2012 sequence struck a broad area located in the Po Plain region, causing 26 deaths and hundreds of injured, 15.000 homeless, severe damage of historical centres and industrial areas, and an estimated economic toll of ~2 billion of euros. The sequence included two mainshocks (Figure 1): the first one, with ML 5.9, occurred on May 20 between Finale Emilia, S. Felice sul Panaro and S. Martino Spino; the second one, with ML 5.8, occurred 12 km southwest of the previous mainshock on May 29. Both the mainshocks occurred on about E-W trending, S dipping blind thrust faults; the whole aftershocks area extends in an E-W direction for more than 50 km and includes five ML≥5.0 events and more than 1800 ML>1.5 events. Ground cracks and liquefactions were certainly the most relevant coseismic geological effects observed during the Emilia sequence. In particular, extensive liquefaction was observed over an area of ~1200 km2 following the May 20 and May 29 events. We collected all the coseismic geological evidence through field survey, helicopter and powered hang-glider trike survey, and reports from local people directly checked in the field. On the basis of their morphologic and structural characteristics the 1362 effects surveyed were grouped into three main categories: a) liquefactions related to overpressure of aquifers, occurring through several aligned vents forming coalescent flat cones (485 effects); b) liquefactions with huge amounts of liquefied sand and fine sand ejected from fractures tens of meters long (768); c) extensional fractures with small vertical throws, apparently organized in an en-echelon pattern, with no effects of liquefaction (109). The photographic dataset consists of 99 pictures of coseismic geological effects observed in 17 localities concentrated in the epicentral area. The pictures are sorted and presented by locality of observation; each photo reports several information such as the name of the site, the geographical coordinates and the type of effect observed. Figure 1 shows a map of the pictures sites along with the location of the two mainshocks; Figure 2 shows a detail of the distribution of the liquefactions in the area of S. Carlo. The complete description of the coseismic geological effects induced by the Emilia sequence, their relation with the aftershock area, the InSAR deformation area and the I>6 EMS felt area, along with the description of the technologies used for data sourcing and processing are shown in Emergeo Working Group [2012a and 2012b].Published1-703.2. Tettonica attivaN/A or not JCRope

Evidence for surface rupture associated with the Mw 6.3 L’Aquila earthquake sequence of April 2009 (central Italy)

An earthquake of Mw=6.3 struck L’Aquila town (central Italy) on April 6, 2009 rupturing an approximately 18 km long SW-dipping normal fault. The aftershock area extended for a length of more than 35 km and included major aftershocks on April 7 and 9, and thousands of minor events. Surface faulting occurred along the SW-dipping Paganica fault with a continuous extent of ~2.5 km. Ruptures consist of open cracks and vertical dislocations or warps (0.1 maximum throw) with an orientation of N130°-N140°. Small triggered slip and shaking effects also took place along nearby synthetic and antithetic normal faults. The observed limited extent, and small surface displacement, of the Paganica ruptures with respect to the height of the fault scarps and vertical throws of paleoearthquakes along faults in the area, puts the faulting associated with the L’Aquila earthquake in perspective with respect to the maximum expected magnitude, and the regional seismic hazard

Evidence for surface rupture associated with the Mw 6.3 L’Aquila earthquake sequence of April 2009 (central Italy)

An earthquake of Mw = 6.3 struck L Aquila town (central Italy) on 6 April 2009 rupturing an ~18-km-long SW-dipping normal fault. The aftershock area extended for a length of more than 35 km and included major aftershocks on 7 and 9 April and thousands of minor events. Surface faulting occurred along the SW-dipping Paganica fault with a continuous extent of ~2.5 km. Ruptures consist of open cracks and vertical dislocations or warps (0.1m maximum throw) with an orientation of N130°–140°. Small triggered slip and shaking effects also took place along nearby synthetic and antithetic normal faults. The observed limited extent and small surface displacement of the Paganica ruptures with respect to the height of the fault scarps and vertical throws of palaeo-earthquakes along faults in the area put the faulting associated with the L' Aquila earthquake in perspective with respect to the maximum expected magnitude and the regional seismic hazard

Technologies and new approaches used by the INGV EMERGEO Working Group for real-time data sourcing and processing during the Emilia Romagna (northern Italy) 2012 earthquake sequence

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Rilievi geologici nell’area epicentrale della sequenza sismica dell’Aquilano del 6 aprile 2009

Il 6 Aprile 2009 un terremoto di Ml=5.8 (Mw=6.2) ha colpito L’Aquila e la media valle dell’Aterno in Abruzzo. In questo lavoro presentiamo in maniera sintetica i rilievi geologici effettuati in campagna dal gruppo di lavoro EmerGeo a seguito della sequenza sismica aquilana. Le attività di rilevamento condotte sono consistite principalmente nella verifica, definizione e caratterizzazione delle deformazioni cosismiche superficiali osservate lungo le strutture tettoniche note in letteratura; sono stati inoltre rilevati e riportati altri effetti cosismici locali (fratture su asfalto, frane e scivolamenti) non direttamente collegati alla presenza di strutture tettoniche. In totale sono stati rilevati oltre 300 punti di osservazione su una porzione di territorio estesa circa 900 km2. L’analisi preliminare dei rilievi effettuati indica che le rotture osservate lungo la faglia di Paganica, per la continuità e le caratteristiche, rappresentano l’espressione superficiale della faglia responsabile dell’evento del 6 aprile 2009, e che le rotture lungo le faglie di Bazzano e di Monticchio-Fossa possono rappresentare l’espressione in superficie di una struttura antitetica riattivata durante l’evento

Earthquake rupture forecasts for the mps19 seismic hazard model of Italy

In recent years, new approaches for developing earthquake rupture forecasts (ERFs) have been proposed to be used as an input for probabilistic seismic hazard assessment (PSHA). Zone-based approaches with seismicity rates derived from earthquake catalogs are commonly used in many countries as the standard for national seismic hazard models. In Italy, a single zone-based ERF is currently the basis for the official seismic hazard model. In this contribution, we present eleven new ERFs, including five zone-based, two smoothed seismicity-based, two fault-based, and two geodetic-based, used for a new PSH model in Italy. The ERFs were tested against observed seismicity and were subject to an elicitation procedure by a panel of PSHA experts to verify the scientific robustness and consistency of the forecasts with respect to the observations. Tests and elicitation were finalized to weight the ERFs. The results show a good response to the new inputs to observed seismicity in the last few centuries. The entire approach was a first attempt to build a community-based set of ERFs for an Italian PSHA model. The project involved a large number of seismic hazard practitioners, with their knowledge and experience, and the development of different models to capture and explore a large range of epistemic uncertainties in building ERFs, and represents an important step forward for the new national seismic hazard model