Geology Reference
In-Depth Information
Characteristic Earthquakes
repeated magnitude
of offset at any location
earthquake3
earthquake2
earthquake1
Trace of the fault
Random Earthquakes
variable magnitude
of offset at any location
Fig. 1.7
Scenario of characteristic
earthquake displacement versus
unpredictable, random
displacement.
Characteristic earthquakes
repeatedly rupture the same part of
a fault and show similar along-
strike variations in coseismic
displacements from one event to
the next. Random earthquakes vary
in both the location of the rupture
and patterns of displacement.
earth-
quake4
earthquake3
earth-
quake5
earth-
quake2
earthquake1
Trace of the fault
If paleoseismological studies were to indicate
that successive ruptures of a particular fault
occurred at regularly spaced intervals in time, it
would then be possible to define a “recurrence
interval.” If we also know when the last rupture
occurred, we could predict when the next
earthquake was likely to happen. But, do faults
display regularity in their rupture histories? The
known paleoseismological record commonly
extends back through only a few earthquakes,
making it difficult to define a statistically sig-
nificant recurrence interval.
One popular model among paleoseismologists
suggests that many faults can be said to
experience “characteristic earthquakes,” imply-
ing that each successive rupture mimics the
displacement of the previous event. If true, this
implies that, along any particular section of a
fault, the amount of displacement that results
from a single earthquake will be duplicated
in subsequent ruptures (Fig. 1.7). Imagine the
predictive power that would result if faults were
shown to generate both characteristic earth-
quakes and to have predictable recurrence
intervals! City planners and paleoseismologists
would all be delighted. For most faults, however,
this seductively attractive concept has yet to
be demonstrated. Consequently, much current
debate revolves around whether or not certain
faults display characteristic earthquakes and
predictable recurrence intervals. Or, could some
faults display a very irregular behavior in both
the time between ruptures and displacement
variations in successive events? Far from being
resolved, this debate lies at the core of paleo-
seismology, and has spawned much recent work
both in the field and in numerical models of the
faulting process.
