Geology Reference
In-Depth Information
Stress Drop (
Δτ
)
Seismic
Behavior
(-) (+)
Upper stability transition
50°
z p : depth of
maximum
stress drop
Typical
hypocenter
of large
earthquakes
300°
B. Difference between coeffi-
cients of dynamic and static
friction as a function of depth and
consequences for seismic
behavior. Modified after Zielke
and Arrowsmith (2008).
Lower stability transition
Max. rupture
depth (large
earthquakes)
Stress Drop &
Seismicity
B
2
1
Modeled Earthquakes
3
11
16
0
z p
max stress drop
2
M = 6.6
Stress
drop
2
1
C. Representative models
for slip during an M = 6.6
and an M
2
3
11
16
2
3
3
4
=
4
7.2 earthquake.
The smaller event does not
propagate through z p , but
both events show maximum
slip where
0
z p
5
5
5
M = 7.2
Stress
drop
0
50
100
150
t is largest on
the rupture surface.
Δ
C
Distance (km)
stresses are required to rupture toward, rather
than away from, the zone of maximum stress
drop. These small to moderate ruptures fol-
low a G-R distribution (see figure A). Third,
when coseismic stresses are large enough to
break through z p , the rupture tends to cas-
cade to the full width of the seismogenic
zone. Such behavior has two outcomes con-
sistent with observations: the frequency of
large, similarly sized (characteristic) earth-
quakes rupturing the entire fault width and
some distance along strike will be higher
than predicted by a G-R distribution of
smaller earthquakes; and relatively few earth-
quakes will fill the size gap between interme-
diate and large earthquakes (see figure A).
 
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