3 research outputs found
Liquefaction source layer for sand blows induced by the 2016 megathrust earthquake (Mw 7.8) in Ecuador (Boca de Briceño)
Numerous sand boils were generated in the alluvial plain at the mouth of the Rio Brice˜no valley (Ecuador) during
the Mw 7.8 earthquake of April 2016. The area is characterized by a series of raised marine terraces formed as a
consequence of the rapid tectonic coastal uplift during the Quaternary. Boreholes and geotechnical investigations
were carried during post-earthquake surveys and for the purpose of mitigating the liquefaction effects. Five
lithological units were identified at a site of embankment, which represented continental-marine and transitional
sedimentation since the Last Glacial Maximum. A comprehensive study of texture and petrographic composition
of sand boils has been performed and compared with sandy silts and silty sands of the buried sedimentary
sequence in order to identify the source levels for liquefaction. The petrographic components, in particular the
low content of bioclasts and carbonate fragments of the sand boils, allow to pinpoint a source layer made up of
fine-grained silty sands located between 2 and 4.5 m depth (Unit 2) whereas the deeper marine sands, richer in
bioclasts, were not involved. The results support the idea that earthquake-induced liquefaction phenomena are
not restricted to clean sands and well-sorted deposits, but may affect sand layers with significant amount of nonplastic
silt