Hi folks,
for my phd thesis, I am working in an intermontane basin in Central Italy, with
no known surface deformation-wise seismic record (> M 5/5.5), scarce/none
geological evidences of active normal faulting and a host of seemingly
contradicting geomorphic evidences. Active/present tectonics is known and
well documented in surrounding basins, so a seismic gap and an inactive fault
system in the area is/would be a puzzle.
Only very minor (traces less than 500 m) faulting (expressed by
diffusion-transport scarps) are to be found, and only in a very small area.
There is no surface rupture across Quaternary alluvium AND Mesozoic/Tertiary
bedrock. Which, in turn, is heavily tectonized by long-traced faults (of not
always clear geometry), predominantly trending WNW-ESE - the same as the minor
structures.
From what we know about the geology of Central Italy, active tectonics style in
the overall region and expected/known deformation rate, normal faulting of such
an extent and displacement is highly unlikely to be. Another possible solution,
in my opinion, could be a differential compaction response of the loose
alluvium onto the buried pre-existing faults, of considerable displacement and
extent. Notice that the alluvial cover here is considerably thin, likely a few
tenths of m.
Since the high-angle master fault lies well beneath the cover and a surface
rupture would thus require a deep-rooted fault splay of the border fault, I am
more and more inclined to believe that a surface response may have accomodated
for the underlying faulted topography.
Does anybody deal with similar scenarios and could please lend me a hint or
two..? Or a reference..? Notice that I am not very much a stability/geotechnics
expert..
Thank you in advance for any help and best regards.
Cordially,
Umberto Fracassi
Università di Firenze
Italy
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