Geophysical surveys to study a landslide body (north-eastern Sicily)

Almost the entire Italian territory is prone to hydrogeological risk mostly due to landslides and flooding. The high frequency of extreme weather events in areas prone to geological–hydraulic hazards contributes significantly to increasing the risk for cities and its infrastructure, but above all for the people living there. Therefore, it is vital to research into rapid monitoring techniques to be applied following a disaster such as a landslide, so that important background information, useful for planning interventions aimed at hazard mitigation, can be obtained. This work seeks to identify the depth of the sliding surface of a landslide affecting the municipal area of Tripi (village in the Messina province, Sicily), through two geophysical field surveys (MASW and HVSR) undertaken in the same area at an interval of about 5 years. The MASW surveys have enabled to reconstruct the distribution of shear wave velocity with depth. The HVSR surveys have provided information on resonant frequency and directional effects. The data integration obtained by the two methods allowed to reconstruct impedance contrast sections indicating the depth of the sliding surface of the landslide.

     

Technique of phase-velocity change determination using continuous waves in a solid medium

Experiments involving phase-velocity change determination by means of continuous waves in a solid medium with boundaries can be designed and operated to avoid difficulties due to component non-stationarity or to presence of several wave modes. Site, gauge, and transmitter geometry have great effect on the radiation and propagation of body and surface waves and may be chosen to avoid unwanted modes within the gauge length. Technique for determination of velocities of the wave modes within the gauge length, which implies the ability to identify those wave modes which are present, is described.     

IRAC photometric analysis and the mid-IR photometric properties of Lyman-break galaxies

We present photometric analysis of deep mid-infrared (mid-IR) observations obtained by Spitzer /IRAC covering the fields Q1422+2309, Q2233+1341, DSF2237a,b, HDFN, SSA22a,b and B20902+34, giving the number counts and the depths for each field. In a sample of 751 Lyman-break galaxies (LBGs) lying in those fields, 443, 448, 137 and 152 are identified at 3.6-, 4.5-, 5.8-, 8.0-μm IRAC bands, respectively, expanding their spectral energy distribution to rest-near-IR and revealing that LBGs display a variety of colours. Their rest-near-IR properties are rather inhomogeneous, ranging from those that are bright in IRAC bands and exhibit  [ R ]−[3.6] > 1.5  colours to those that are faint or not detected at all in IRAC bands with  [ R ]−[3.6] < 1.5  colours and these two groups of LBGs are investigated. We compare the mid-IR colours of the LBGs with the colours of star-forming galaxies and we find that LBGs have colours consistent with star-forming galaxies at   z ∼ 3  . The properties of the LBGs detected in the 8-μm IRAC band (rest-frame K band) are examined separately, showing that they exhibit redder  [ R ]−[3.6]  colours than the rest of the population and that although in general, a multiwavelength study is needed to reach more secure results, IRAC 8-μm band can be used as a diagnostic tool, to separate high z , luminous AGN-dominated objects from normal star-forming galaxies at   z ∼ 3  .