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It is known that local geology can alter the ground motion characteristics at a particular site. Whereas some sites are characterised by outcropping low-velocity layers, others might have buried ones of considerable thickness which might still be a cause of ground motion amplification. The Maltese islands (Central Mediterranean) provide a good case study for profiles with a buried low-velocity layer. Parts of the islands are characterised by Upper Coralline Limestone covering a soft Blue Clay layer of considerable thickness (up to 75 m). This gives rise to a velocity inversion and makes the travel-time average shear-wave velocity (VS) in the upper 30 m not suitable for seismic microzonation purposes. This study presents a comprehensive site response analysis for such areas. Previously obtained shear-wave velocity (VS) profiles were used as an input to the equivalent linear programme SHAKE2000. Maps of amplification factors and 5% damped elastic response spectra confirm that the clay, even when buried under a hard outcropping layer, can still produce significant amplifications at frequencies which are of engineering interest when considering the recent urbanisation patterns. Moreover, the suitability of the VS30 and the travel-time average shear-wave velocity till bedrock parameters as proxies for site response was investigated, with the results highlighting the inadequacy of these parameters for sites characterised by buried low-velocity layers and the necessity for site-specific response studies. [ABSTRACT FROM AUTHOR]

The main goal of this study is to provide moment tensor solutions for small and moderate earthquakes of the Matese seismic sequence in southern Italy for the period of December 2013–January 2014. We estimate the focal mechanisms of 31 earthquakes with local magnitudes related to the Matese earthquake seismic sequence (December 2013–January 2014) in Southern-Central Italy which are recorded by the broadband stations of the Italian National Seismic Network and the Mediterranean Very Broadband Seismographic Network (MedNet) run by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The solutions show that normal faulting is the prevailing style of seismic deformation in agreement with the local faults mapped out in the area. Comparisons with already published solutions and with seismological and geological information available allowed us to properly interpret the moment tensor solutions in the frame of the seismic sequence evolution and also to furnish additional information about less energetic seismic phases. Focal data were inverted to obtain the seismogenic stress in the study area. The results are compatible with the major tectonic domain of the area. [ABSTRACT FROM AUTHOR]

Highlights: [•] A complete description of the characteristic of the ground-motion in the region. [•] Estimating the Peak Ground Acceleration and Velocity quantities (PGA, PGV). [•] Predicting the absolute level of ground shaking, comparing with strong-motion data. [•] Main features of the seismic ground motions caused by moderate earthquakes. [•] It may be useful for the seismic hazard assessment studies in the region. [Copyright &y& Elsevier]

Highlights: [•] A database of 312 moment tensor solutions for the 2009 L’Aquila seismic sequence (central Italy) is presented. [•] Stress tensors for the study region and selected sub-volumes are computed. [•] A relation between M w and M l properly calibrated for the study area is furnished. [Copyright &y& Elsevier]

Abstract: We report the first application of the Cut and Paste (CAP) method to compute earthquake focal mechanisms in the Messina Straits area by waveform inversion of Pnl and surface wave segments. This application of CAP has furnished new knowledge about low-magnitude earthquake mechanics that will be useful for improved understanding of the local geodynamics. This is possible because the CAP inversion technique can be applied to small earthquakes, for which traditional moment tensor inversion methods are not appropriate and P-onset focal mechanisms in the study area fail because of a lack of sufficient observations. We estimate the focal mechanisms of 23 earthquakes with local magnitudes in the range of 3–4 occurring in the 2004–2008 time period, and recorded by the broadband stations of the Italian National Seismic Network and the Mediterranean Very Broadband Seismographic Network (MedNet) run by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The solutions show that normal faulting is the prevailing style of seismic deformation in the northern part of the study area while co-existence of normal faulting and strike-slip has been detected in the southern part. In the whole area of investigation the T-axes of focal mechanisms display a preferential northwest-southeast direction of extension. Combined with the findings of previous investigations, this improved database of focal mechanisms allows us to better detail the transitional area between the extensional domain related to subduction trench retreat (southern Calabria) and the compressional one associated with continental collision (western-central Sicily). The observed spatial change of seismic deformation regime offers new data to current seismotectonic and seismic hazard investigations in the area of Messina Straits where a magnitude 7.2 earthquake caused more than 60,000 casualties on 28 December 1908. [Copyright &y& Elsevier]

On October 12, 2013, an earthquake with M w = 6.5 occurred in the southern Hellenic Arc, approximately 20 km off the west coast of Crete. The main shock, the focal depth of which is on the order of 40 km, was followed by aftershocks felt in the nearby cities and villages, although the aftershock sequence was poor. The epicentre was located at approximately 60 km from a radio receiver in Crete (CRE), which belongs to the European VLF/LF Radio Network. Several days before the earthquake, a clear disturbance occurred in one of the ten radio signals that the CRE receiver sampled. The disturbance, which can be considered an anomaly, appeared in the 216 kHz radio signal radiated by the Radio Monte Carlo (MCO) transmitter. The radio path MCO-CRE crossed directly over the epicentre area of the aforementioned earthquake. In this work, we present a detailed analysis of the MCO signal anomaly using spectral tools. We also investigate the behaviour of other radio signals sampled by the CRE receiver and consider other possible causes of disturbances on the MCO radio signal. We conclude that the disturbance in the MCO radio signal is a convincingly possible precursor of the earthquake in Crete. Emission of electromagnetic waves with a frequency band that includes 216 kHz from the focal zone of the earthquake can provide a satisfactory explanation of the radio anomaly. [ABSTRACT FROM AUTHOR]

• We show the existence of a transient tectonic regime imposed by megathurust earthquakes on volcanic arc. • The transient regime is extensional in a broadly compressive environment. • The transient regime may be able to explain the development of NW-striking volcanic complexes in the Southern Andes. Geophysical data show that megathrust earthquakes can promote transient tectonic regimes lasting up to several decades. However, such variations are not trivial to be recognises in the geological records of volcanic arcs. To better understand the occurrence of transient tectonic regimes we study the inter- and post-seismic deformation in the upper crust of the Andean volcanic arc affected by the M8.8 2010 Maule earthquake. We focus on the region around the Nevados de Chillán Volcanic Complex, Southern Central Chile, where we compare geological and earthquakes data. This NW-oriented Andean-transverse volcanic complex faces one of the regions that slipped the most during the 2010 M8.8 Maule earthquake. Field fault-slip data from lithostratigraphic units forming the basement of Nevados de Chillan Volcanic Complex point out three tectonic regimes. The principal is driven by a sub-horizontal and NE-oriented σ 1 (transpressional kinematics). This regime is compatible with today's GPS data recorded during inter-seismic periods. The second and third tectonic regimes are less abundant and indicate transpression (σ 1 sub-horizontal and NW-oriented) and normal (σ 1 sub-vertical and E-W-oriented) faulting, respectively. The geological record was also compared with seismic data acquired from 2010 to 2015 in the investigated region. The moderate-magnitude seismic activity occurred beneath the volcanic arc after the Maule earthquake points out an enhanced crustal deformation if compared to inter-seismic periods. The inversion of focal mechanisms suggests that intra-arc regions may experience a short-lived post-seismic transtensional regime with an E-W oriented σ 1 with a dip of about 45°. Our work suggests that megathrust earthquakes impose transient stress variations in the volcanic arc, possibly reactivating Oligo-Miocene NW-striking inherited crustal structures, upon which volcanic edifices develop. This may help explaining the occurrence of Andean-transverse volcanic complexes oriented sub-perpendicular to the NE-oriented σ 1 driving convergence in the Southern Andes. [ABSTRACT FROM AUTHOR]