Geology Reference
In-Depth Information
Time-Predictable Behavior
Year (AD)
Events
C
100
?
?
1
?
?
20 ± 5
0
80±12
110±16
2.3°S
-100
100
B
0
10±5
0
1
30±30
120±30
170±20
-100
2.6°S
A
100
110±21
0
150±25
73
-100
250±50
320±60
(cumulative)
3.1°S
-200
1300
1400
1500
1600
1700
18
00
1900
2000
3
2
4
1
Supercycles
130±30
emergence (event driven)
long-term emergence rate
supercycle failure sequence
submergence rate (mm/yr)
Fig. 6.28
Time-predictable rupture along the Sumatran subduction zone.
The coral-based chronology of subduction-zone earthquakes from the Mentawai Islands, Sumatra. A background
emergence rate of 1-2 mm/yr at each site indicates permanent strain in the forearc. Megathrust earthquakes occur each
time this long-term trend of local sea-level fall (dotted gray line) is reached. Four supercycles of megathrust earthquakes
with recurrence intervals of about 200 years are clearly delineated at each site. The sites at 2.3
°
S and 2.6
°
S commonly
show a sequence of smaller offsets in the decades preceding a very large earthquake. At 3.1
°
S, where 2.5 m of subsidence
occurred in the 1833 earthquake, the 2007
M
= 8.4 earthquake appears likely to be the first in a series of major
earthquakes that would be expected to affect all three sites in the coming decades. Modified after Sieh
et al.
(2008).
earthquakes tend to occur in the last few decades
of a cycle prior to a much larger event. If earth-
quakes cluster in time, not only does this behav-
ior provide some predictive power, but it also
provides some insight on seismic behavior. Such
clustering signifies a pulse of regional strain
release. Clustering might result from interac-
tions, such as stress transfer (Stein, 1999), among
