HR: 17:45h
AN: V14A-08 INVITED     [Abstracts]
TI: Earthquakes and Strength of the Continental Lithosphere
AU: * Handy, M R
EM: mhandy@zedat.fu-berlin.de
AF: Dept. Earth Sciences Freie Universitaet Berlin, Malteserstrasse 74-100, Berlin, D-12267 Germany
AB: Deep-focus earthquakes are often considered to reflect brittle failure of strong parts of the lithosphere, whereas aseismicity is taken as a manifestation of ductile yield and creep. This contribution outlines why some earthquakes are more reasonably interpreted as manifestations of transient mechanical behaviour within shear zones. This renders seismicity an ambiguous indicator of lithospheric strength, but a potentially useful indicator of decoupling deep within the lithosphere. A conceptual model is presented in which lithospheric strength varies with depth and time during the earthquake cycle. Shear zones are domains of long-term weakness in which viscous creep is punctuated by high-stress, seismic events involving fracture, frictional melting and temporary loss of cohesion. Causes of instability include asperities, phase transformations, and sudden ingress of fluids and/or melt. The frictional-to-viscous transition (FVT) is regarded as a domain of variable width and fluctuating depth, whose location and extent depend on temperature, effective pressure, strain rate, grain size and fluid activity, as well as on the orientation of existing ansotropies. Maximum and minimum strengths at the FVT are attained, respectively, just prior to and after earthquake rupture. Fluid-induced effects can modify strength-depth curves significantly and are predicted to vary significantly with tectonic setting.
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8034 Rheology and friction of fault zones (8163)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8164 Stresses: crust and lithosphere
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005