Evaluation of liquefaction potential in an intermountain Quaternary lacustrine basin (Fucino basin, central Italy)

In this study, we analyse the susceptibility to liquefaction of the Pozzone site,
which is located on the northern side of the Fucino lacustrine basin in central Italy. In 1915,
this region was struck by a M 7.0 earthquake, which produced widespread coseismic
surface effects that were interpreted to be liquefaction-related. However, the interpretation
of these phenomena at the Pozzone site is not straightforward. Furthermore, the site is
characterized by an abundance of fine-grained sediments, which are not typically found in
liquefiable soils. Therefore, in this study, we perform a number of detailed stratigraphic
and geotechnical investigations (including continuous-coring borehole, CPTu, SDMT,
SPT, and geotechnical laboratory tests) to better interpret these 1915 phenomena and to
evaluate the liquefaction potential of a lacustrine environment dominated by fine-grained
sedimentation. The upper 18.5 m of the stratigraphic succession comprises fine-grained
sediments, including four strata of coarser sediments formed by interbedded layers of sand,
silty sand and sandy silt. These strata, which are interpreted to represent the frontal lobes of
an alluvial fan system within a lacustrine succession, are highly susceptible to liquefaction.
We also find evidence of paleo-liquefaction, dated between 12.1–10.8 and 9.43–9.13 kyrs
ago, occurring at depths of 2.1–2.3 m. These data, along with the aforementioned
geotechnical analyses, indicate that this site would indeed be liquefiable in a 1915-like
earthquake. Although we found a broad agreement among CPTu, DMT and shear wave
velocity ‘‘simplified procedures’’ in detecting the liquefaction potential of the Pozzone soil,
our results suggest that the use and comparison of different in situ techniques are highly recommended for reliable estimates of the cyclic liquefaction resistance in lacustrine sites
characterized by high content of fine-grained soils. In geologic environments similar to the
one analysed in this work, where it is difficult to detect liquefiable layers, one can identify
sites that are susceptible to liquefaction only by using detailed stratigraphic reconstructions,
in situ characterization, and laboratory analyses. This has implications for basic
(Level 1) seismic microzonation mapping, which typically relies on the use of empirical
evaluations based on geologic maps and pre-existing sub-surface data (i.e., age and type of
deposits, prevailing grain size, with particular attention paid to clean sands, and depth of
the water table).