15 research outputs found
The Central Southern Alps (N. Italy) paleoseismic zone: a comparison between field observations and predictions of fault mechanics
The internal sectors of the Orobic Alps (Northern Italy) are characterised by Alpine age regional shortening showing a transition, through time, from plastic to brittle deformation. Thrust faults cut Alpine ductile folds and are marked by cataclasites and, locally, by pseudotachylytes, suggesting that motion was accommodated by seismic frictional slip. In the Eastern Orobic Alps the thrusting initiated at depths deeper than 10 km (the emplacement depth of the Adamello pluton) and possibly continued at shallower depths. This demonstrates that thrust motion occurred between 10 km depth and the brittle-ductile transition, i.e., at mid-crustal depths. The Orobic Alps exhumed paleoseismic zone shows different geometries along strike. In the central sectors of the Orobic Alps, thrust faults, associated with pseudotachylytes, have average dips around 40 degrees and show no pervasive veining. Much steeper thrusts (dips up to about 85 degrees) occur in the eastern Orobic Alps. In this area, faults are not associated with pervasive veining, i.e., fluid circulation was relatively scarce. This suggests that faulting did not occur with supralithostatic fluid pressure conditions. These reverse faults are severely misoriented (far too steep) for fault reactivation in a sublithostatic fluid pressure regime, We suggest that thrust motion likely started when the fault, were less steep and that the faults were progressively rotated up to the present day dips. Domino tilting is probably responsible for this subsequent fault steepening, as suggested by a decrease of the steepness of thrust faults from north to south and by systematic rotations of previous structures consistently with tilting of thrust blocks. When the faults became inclined beyond the fault lock-up angle, no further thrusting was accommodated along them. At later stages regional shortening was accommodated by newly formed lower angle shear planes (dipping around 30-40 degrees), consistently with predictions from fault mechanics. (c) 2005 Elsevier B.V. All rights reserved
The fluctuations of Italian glaciers during the last century : a contribution to knowledge about Alpine glacier changes
This paper describes the recent evolution
of Italian glaciers through an analysis of all
available terminus fluctuation data that the authors
have entered in a glaciers database (named
GLAD) containing 883 records collected on glaciers
from 1908 to 2002. Furthermore, a representative
subset of data (249 glaciers located in Lombardy)
was analysed regarding surface area
changes.
For the analysis of terminus fluctuations, the glaciers
were sorted by size classes according to
length. The data showed that during the 20th century
Italian Alpine glaciers underwent a generalized
retreat, with one distinct and well documented
readvance episode that occurred between the 1970s
and mid-1980s, and a poorly documented one
around the early 1920s. The rates of terminus advance
and retreat have changed without significant
delays for the larger glaciers with respect to the
smaller ones. However, the smaller the glacier, the
more limited the advance (if any) during the 1970s
and early 1980s. The behaviour of glaciers shorter
than 1 km appears to have changed in the last decade,
and between 1993 and 2002 they retreated at a
very high rate.
The analysis of the subset of data led to a quantification
of surface reduction of c. 10% from 1992 to
1999 for glaciers in Lombardy. Small glaciers
proved to contribute strongly to total area loss: in
1999, 232 glaciers (c. 90% of the total) were smaller
than 1 km2, covering 27.2 km2 (less than 30% of the
total area), but accounted for 58% of the total loss in
area (they had lost 7.4 km2)