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Abstract: The Mercure earthquake (Mw 5.6) of September 9, 1998 and the associated aftershocks occurred in a small Pleistocene–Holocene continental basin of the Southern Apennines, in a region of low instrumental and moderate historical seismicity. Seismological, photogeological and field survey data were analyzed and integrated in order to identify the likely seismogenic structure, to depict its 3-D geometry and kinematics and to provide further constraints to the seismogenic potential of the rupture processes in the study area. The mainshock occurred at the NW edge of the seismic sequence (40.03°N and 15.95°) at a depth of 10.5±1.5 km. The aftershocks volume was determined from the relocation of about 200 events (1.1= Ml =3.9) registered by local networks from September 10 to October 12, 1998. The relocation procedure was based on choosing P and S waves for all the events and the definition of ten 9-layers velocity models appropriate for the different stations. The kinematics of the seismogenic deformation was defined through the computation of 36 well-constrained focal mechanisms. The seismological and geological stress tensors were determined through inversion of focal mechanisms and fault slip data. Both of them resulted in the tensional type, with ENE–WSW and NE–SW trending σ 3 axis, respectively. The map and the section distribution of the aftershocks sequence depicts an average NW–SE striking and 60° SW-dipping seismogenic volume. Most of the events (80%) were located at depths between 3 and 8 km in the footwall of the Mercure basin (MBB) boundary fault but along the possible down-dip continuation of a previously unidentified, N120°E striking and WSW-dipping, Holocene normal fault alignment, which extends from Castello Seluci to Piana Perretti and Timpa della Manca (CPST fault). A small percentage of events (10%) were located at depths between 10 and 12 km where the CPST seismogenic fault may detach. The reconstructed rupture area (RA) of the Mercure 1998 earthquake has an along-strike length (L) of about 9 km and a down-dip width (W) of about 9 km, yielding a total area of approximately 81 km2. On the other hand, the L and W dimension of the entire individual seismogenic structure identified as responsible for the earthquake, e.g. the CPST fault, are about 19 and 12 km, respectively, with a consequent RA of about 230 km2. This may imply a maximum magnitude (Mw) equal to 6.3 which lead us to compare the Mercure area, in terms of seismogenic hazard, to the adjacent Pollino-Castrovillari area where strong paleoseismological events are documented. [Copyright &y& Elsevier]

Abstract: We present the results of a probabilistic seismic hazard assessment and disaggregation analysis aimed to understand the dominant magnitudes and source-to-site distances of earthquakes that control the hazard at the Celano site in the Abruzzo region of central Italy. Firstly, we calculated a peak ground acceleration map for the central Apennines area, by using a model of seismogenic sources defined on geological-structural basis. The source model definition and the probabilistic seismic hazard evaluation at the regional scale (central Apennines) were obtained using three different seismicity models (Gutenberg–Richter model; characteristic earthquake model; hybrid model), consistent with the available seismological information. Moreover, a simplified time-dependent hypothesis has been introduced, computing the conditional probability of earthquakes occurrence by Brownian passage time distributions. Subsequently, we carried out the disaggregation analysis, with a modified version of the SEISRISK III code, in order to separate the contribution of each source to the total hazard. The results show the percentage contribution to the Celano hazard of the various seismogenic sources, for different expected peak ground acceleration classes. The analysis was differentiated for close (distance from Celano <20km) and distant (distance from Celano >20km) seismogenic sources. We propose three different “scenario earthquakes”, useful for the site condition studies and for the seismic microzoning study: (1) large (M=6.6) local (Celano-epicentre distance ∼16km) earthquake, with mean recurrence time of ∼590 years; (2) moderate (M=5.5) local (Celano-epicentre distance ∼7.5km) earthquake, with mean recurrence time of ∼500 years; and (3) large (M=6.6) distant (Celano-epicentre distance ∼24km) earthquake, with mean recurrence time of ∼980 years. The probabilistic and time-dependent approach to the definition of the “scenario earthquakes” changes clearly the results in comparison to traditional deterministic analysis, with effects in terms of engineering design and seismic risk reduction. [Copyright &y& Elsevier]

We present the results of an interdisciplinary study aimed at defining the geometry of the fault segments activated by the Emilia 2012 thrust sequence (MW up to 6.1), which are located at the front of the Ferrara Arc (northern Italy) and partially overlap with an area undergoing hydrocarbon exploitation since 1980 (Cavone oil field). We relocate 40 well-recorded earthquakes with MW prevailingly ≥4.0 in the time interval from May 20 to June 12, 2012, plus an event that occurred in a nearby area on July 17, 2011 (MW 5.0). The geological and seismotectonic setting of the area is discussed, some interpretative geological sections across the hypocentral volumes are elaborated, and the shape of the identified individual seismogenic fault segments is schematically represented as depth contour lines. The resulting earthquake/fault association highlights a rather complex segmentation pattern, with four neighbouring sources involved, all belonging to the SSW-dipping Ferrara Thrust System. The two main events of the Emilia 2012 sequence did not activate the Mirandola thrust underlying the Cavone reservoir, although this thrust was illuminated by some subsidiary activity mainly concentrated close to the hydrocarbon field. The likelihood of triggered seismicity effects due to the extraction/ injection activities within the Cavone oil field are discussed. [ABSTRACT FROM AUTHOR]