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Cap de Creus (Displacement Accommodation (Lower crust (High temperatures,…
Cap de Creus
Displacement Accommodation
Upper crust
Near cold surface, plate boundary = locked
∴ seismic events
accomodate relative plate motions
With increasing depth, temperature is increasingly important
Lower crust
High temperatures
∴ Rocks can creep continually
= Steady, slow viscous creep - no resistance
Frictional & Viscous Domains = Linked
Spatially - frictional-viscous transition
Temporally - Earthquake cycle
Seismic cycle describes how
elastic loading from below
affects seismic mvmts in upper crust
Deformation
at FVT
Dynamic region moderates btwn creeping lower & locked upper crust
Suite of processes exist between deep creep & earthquakes
Roughly half plate motions accomodated by
Intermediate dissipated phenomena btwn deep creep & earthquakes
e.g. slow slip, tremor
What depth majority of equakes?
Uppermost 50 km of crust
Nucleate at some depth i.e. not at surface
Relative plate motions
Generates stresses at plate boundaries
Two endmember mechanisms for accomodating this
1. Upper crust - frictional sliding
2. Lower crust - deep creep (ductile/viscous)
i.e. upper locked & lower keeps moving
= Exhumed strike slip fault
Strike slip fault from depth exhumed & exposed today at surface
= analogue for strike slip faulting @ 15 km depth
Dynamics
= how strain energy is translated into permanent deformation
Kinematics
motions that occurred during this strain accomodation at depth