Structure and rheology of lithosphere in Italy and surrounding

We define the structure and rheology of the lithosphere in Italy and surrounding, combining the cellular velocity models derived from nonlinear tomographic inversion with the distribution vs. depth of hypocentres to assess the brittle properties of the Earth’s crust. We average, over cells sized 1 × 1 degree, the mechanical properties of the uppermost 60 km of the Earth, along with seismicity, grouping hypocentral depths in 4‐km intervals. For most of the cells, the earthquake energy is concentrated in the upper crust (4–12 km). For some regions, where orogenic processes occur, the release of earthquake energy is shallower and limited to the uppermost 10 km of the crust. Ambiguities in the structural models are minimized considering the hypocentral distribution, mainly to define the location of the Moho boundary, when its identification, based on shear‐wave velocities, is not straightforward.     

Lithosphere structure and statistical properties of seismicity in Italy and surrounding regions

A detailed statistical analysis applied to the seismicity of Italy and surrounding areas allows us to identify some correlations between several statistical parameters and the thickness and the elastic parameters of the lithospheric part of the mantle, the lid. In particular, the intensity of the flow of seismic events, deprived of aftershocks, shows concentrations in relation to large gradients in the lithospheric thickness, due to abrupt variations of the lid thickness. When this variation is not very large the intensity of flow of seismic events is smaller than on the average, but in these areas (e.g., the Calabrian Arc) the strongest shocks tend to occur. The average depth of crustal shocks tends to be very shallow in relation to the thin and soft (low shear-wave velocities) lid. The positive influence, probably reflecting the thermal state in the lithosphere, is very large in relation to the thin and soft lid and where strong gradients in lid thickness are observed, and is small in relation to thick and hard lid (high shear-wave velocities). From the observed correlation between seismicity properties and lid characteristics, it may be concluded that aseismic slip below the Moho might be a key seismogenetic process.     

Modelling of Seismic Ground Motion in Santiago de Cuba City from Earthquakes in Oriente Fault Seismic Zone

— We present the results of complete P-SV and SH waves modelling, up to a maximum frequency of 1?Hz, along two profiles in Santiago de Cuba city. The seismic sources are located in the depth range from 10 to 40?km on the Oriente fault zone at distances of several tens of kilometres from the city. The calculation has been made by a hybrid method: Modal summation in the regional anelastic model (one-dimensional) where the source is buried, and finite differences in the local sedimentary anelastic models (two-dimensional). The analysis of the influence of the depth and of the distance of the source on the site effects shows that standard traditional methods, based on the deconvolution analysis of the rock outcrop motion, can lead to erroneous results.     

Comparison of the multimode surface wave response in structures with and without a low velocity channel (part I: Dip-slip sources on a vertical fault plane)

Summary A comparison is made between the multimode Rayleigh wave response to dip-slip motion along a vertical fault plane in structures with and without a low-velocity channel. The use of the higher mode amplitude spectra is proposed as a discriminant between the two types of structure.