Key seismological terminology Barriers = areas of smaller amount of slip in a single EQ Asperities = areas of larger amount of slip in a single EQ Ammon et al, 2005
The rupture process of great subduction earthquakes: the concept
of the barrier and asperity models Yoshihiro Kaneko (Presentation
based on Aki, 1984; Rundle and Kanamori, 1987; Park and Mori, 2007;
Das and Aki, 1977; Madariaga, 1983; Heaton, 1990; Dunham et al.,
2003) Ge 277 Fall, 2007 Two important seismological observations
1.Slip is heterogeneous over a fault plane with several patches of
relatively larger slip 2.Rise time at any point is shorter than the
duration of an EQ Rise Time: 15-30s Rupture velocity: 2.5-3kms
Duration: 80s Ozgun Kunca Key seismological terminology Barriers =
areas of smaller amount of slip in a single EQ Asperities = areas
of larger amount of slip in a single EQ Ammon et al, 2005 Barrier
vs. asperity models (interpretation by Aki, 1984) Barrier/asperity
= regions of higher shear strength Concept of barrier model Concept
of asperity model Summary: barrier vs. asperity models Barrier
model Barrier model Stress roughening process (homogenous ->
heterogeneous) Stable barrier is unbroken in repeated EQs, but
weaker ones break in different patterns (different amount of slip
in different EQs) Resulting in characteristic fault length but not
a characteristic amount of slip How do strong barriers behave over
time (the region needs to accommodate some slip eventually)?
Asperity model Asperity model Stress smoothening process
(heterogeneous -> homogenous) Consistent with many great
interplate earthquakes that show stable slip patches over EQ cycles
(both characteristic fault length and amount of slip) The stability
of asperity strength can explain "the time predictable model" Act
as a strong barrier during interseismic(?), or slipping seismically
An evidence for the barrier model: Maximum slip scales with barrier
interval barrier interval (km) maximum slip (m) Aki (1984)
Observational studies: Are asperities and barriers stable? Papua
New Guinea sequences (Park and Mori, 2007) Papua New Guinea
sequences (Park and Mori, 2007) Colombia-Ecuador sequences (Randle
and Kanamori, 1987) Colombia-Ecuador sequences (Randle and
Kanamori, 1987) Nankai trough sequences (Randle and Kanamori, 1987)
Nankai trough sequences (Randle and Kanamori, 1987) Sumatra
sequences (J.-P. Avouac, introduction) Sumatra sequences (J.-P.
Avouac, introduction) Tectonic setting Park and Mori (2007) 8 15
cm/year Studied Area Locations of the fault planes and focal
mechanisms Park and Mori (2007) Asperities do not overlap Park and
Mori (2007) Asperities may not be stable in some places The studied
area (Papua New Guinea subduction) may be tectonically complicated
region (?). Rundle and Kanamori (2007) Nankai Trough sequences 6.5
cm/year Rundle and Kanamori (2007) Remark: Slip at a given patch is
larger in the largest EQ than that those in individual small EQs
Colombia-Ecuador sequences Rundle and Kanamori (2007) Remark:
Moment is 2.7 7 times larger in the largest 1906 EQ than that the
sum of the other 3 EQs. Sumatra subduction zone (J.-P. Avouac, this
class) - Are asperities stable over many earthquake cycles? - Is
the time predictable model applicable for this region? - Is slip at
a given patch greater in the largest EQ than that those in
individual small EQs? Hiroos comments Alternative model (Yoshi,
Avouac, Nadia) Feature: - asperities are stable over EQ cycles -
time predictable (on average) - the slip at a given point is
comparable or greater in the largest EQ than those in small EQs -
explains the relation of seismic coupling and asperity
