Cap de Creus

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

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

= Exhumed strike slip fault

Strike slip fault from depth exhumed & exposed today at surface

Dynamics

= how strain energy is translated into permanent deformation

Kinematics

motions that occurred during this strain accomodation at depth

= analogue for strike slip faulting @ 15 km depth