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SAF (How stress state evolves along SAF (Stress state ∆ during…
SAF
How stress state evolves along SAF
Stress state ∆
during interseismic periods
Not during earthquakes
Stored elastic energy dissipated during interseismic periods
Dissipates i.e. translated to mvmt / damage / heat
Transverse Ranges
Peak ~ 15 km
Equakes distributed over range of crustal Z up to 20 km
Associated with transpressional bends in SAF near LA
Thrust faulting dominates
accomodate compression caused by bend in SAF
Parkfield Aftershock Distribution
1. Well defined clusters of aftershocks @ some depth
2. Distributed over wide depth range/interval
Why this disparity in aftershock distribution?
Varies between parts of segment
Slip patch ruptures
Slip patch/
surface
= tens km of fault which slips / ruptures
usually elliptical
Max displacement
= in centre of slip patch
Coseismic displacement tapers off
moving away from centre
∴ min displacement @ edge of slip patch
∴ STRESS IS TRANSFERRED IN SYSTEM
Creeping section stress state ∆
Max ∆ Mohr circle diameter
= 4 MPa / hundred years (peanuts)
n.b. tensile strength rock usually ~ 10MPa
Extremely low μ strength in creeping zone
∴ small stress change would cause deformation
Parkfield Section SAF
Bounded by
Creeping section
on NW
~150 km long
where numerous small equakes
Locked portion on SE
(hundreds km)
few equakes detected in past century
Central Cali (SAF proper)
Strike-slip dominantly
Equakes - not just shallow crustal z
more than 90% < 10 km
peak @ 5 km
none below 15 km
---> brittle ductile transition
When Mohr circle touches yield envelope
Failure / rupture occurs
i.e. seismic events
Many earthquakes nucleate @
greenschist facies metamorphic conditions
Equake Depth Distributions