Summary: GEOLOGY, December 2008 995
INTRODUCTION
The main strength of the lithosphere is carried by upper mantle
peridotite and possibly also by dry granulites in the lowermost conti-
nental crust (e.g., Jackson et al., 2004). Rock-mechanical experiments
and numerical models based on results from such experiments, extrapo-
lated to subduction zone conditions, suggest that old (108
yr) and cold
(500 ± 50 °C) upper mantle rocks with olivine rheology are strong
(>1.5 GPa) at geological strain rates (10­14
s­1
). Strength is also grain-
size-dependent, and coarse-grained peridotite, as studied here, is par-
ticularly strong (e.g., Kelemen and Hirth, 2007; Stüwe, 2007). Byerlee's
(1978) friction data also indicate that faults are strong (~102
to 103
MPa
at confining pressures discussed here). The strong versus weak fault dis-
parity may be a result of most earthquakes being associated with vari-
ably efficient weakening processes (Rice, 2006), such as high pore fluid

Source: Andersen, Torgeir Bjørge - Centre for Physics of Geological Processes & Department of Geosciences, Universitetet i Oslo

Collections: Geosciences