Abstract
A first-order seismic characterization of Northern Apulia (Southern Italy) has been provided by considering geological information and outcomes of a low-cost geophysical survey. In particular, 403 single-station ambient vibration measurements (HVSR techniques) distributed within the main settlements of the area have been considered to extract representative patterns deduced by Principal Component Analysis. The joint interpretation of these pieces of information allows the identification of three main domains (Gargano Promontory, Bradanic Through and Southern Apennines Fold and Thrust Belt), each characterized by specific seismic resonance phenomena. In particular, the Bradanic Through is homogeneously characterized by low frequency (<1 Hz) resonance effects associated with relatively deep (>100 m) seismic impedance, which is contrasting corresponding to the buried Apulian carbonate platform and/or sandy horizons located within the Plio-Pleistocene deposits. In the remaining ones, relatively high frequency (>1 Hz) resonance phenomena are ubiquitous due to the presence of shallower impedance contrasts (<100 m), which do not always correspond to the top of the geological bedrock. These general indications may be useful for a preliminary regional characterization of seismic response in the study area, which can be helpful for an effective planning of more detailed studies targeted to engineering purposes.
Highlights
It is well known that the seismostratigraphic configuration of the shallow subsoil may severely affect seismic ground motion due to constructive interference of seismic waves trapped within the surface and seismic impedance contrasts (e.g., [1])
The analysis shows that the first and most important Principal Component (PC) only accounts for 40% of the overall variance, and this suggests a rather heterogeneous subsoil configuration of the study area
The joint analysis of geological and geophysical data has been used for a first-order seismic characterization of Northern Apulia
Summary
It is well known that the seismostratigraphic configuration of the shallow subsoil (down to a depth of few hundreds of meters) may severely affect seismic ground motion due to constructive interference of seismic waves trapped within the surface and seismic impedance contrasts (e.g., [1]). The main efforts are devoted to fully exploiting the huge amount of data (drillings, geophysical surveys, geotechnical reports, etc.) collected by local authorities and practitioners operating in the study area. Where this information is lacking or insufficient, geophysical surveys are planned by using cost-effective procedures based on ambient vibration monitoring, surface wave prospecting, etc. In the lack of widespread direct geophysical observations (e.g., by borehole measurements) or where these contrasts are relatively deep (more than some tens of meters), their buried morphology must be inferred by geological and surface geophysical considerations (e.g., [8,9,10]) An example of this situation is Northern Apulia (Southern Italy). The collected data are jointly interpreted with geological information to constrain the main seismostratigrahical features of the area
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