Geology Reference
In-Depth Information
Water Loading
Great
Salt
Lake
Fig. 9.31
Climatic modulation
of fault slip rates.
A. Water loading. (Left) Areal
extent of glacial Lake
Bonneville in proximity to
the Wasatch Fault. (Right)
Numerical model of normalized
slip and slip-rate changes in
response to lake-loading
history that extends from 34
to 13 ka (dark trapezoid) in
comparison to observed slip
(see Fig. 6.30). Note that the
model predicts a prolonged
interval of suppressed slip
when the lake is present,
followed by brief, but
significantly accelerated, slip
rates when the lake load is
removed. B. Ice loading.
(Left) Reconstructed ice
thickness for the Yellowstone
ice cap and the Teton Range.
(Right) Modeled slip history
of the Teton Fault in response
to the waxing and waning ice
load compared to the fault's
observed slip history. Note
that the observed history only
extends to
∼
16 ka. Modified
after Hampel
et al.
(2007) and
Hetzel and Hampel (2006).
Lake-loading
history
1.0
Glacial
Lake
Bonneville
s
uppressed
slip
SLC
Model
0.5
Wasatch
Fault
0 0
Observed
0.0
0
10
20
30
40
A
Time (ka)
kilometers
0
50
kilometers
B
Ice Loading
1.0
N
Ice-loading
history
1100 m
Yellow-
stone ice
cap
0.5
s
uppressed
slip
900 m
Observed
Model
N
??
accelerated
slip
??
C
S
100 m
0.0
Teton Fault
300 m
0
10
20
30
Time (ka)
Teton Range
provide strong evidence for a fixed fault tip, at
least for the past 140 kyr.
case, climate change has induced the expansion
and subsequent contraction of either a large lake
or an ice cap during late Quaternary times.
Whereas the growing load of the lake or glacier
is predicted to have moved nearby normal faults
farther from failure and, thereby, to have reduced
their slip rates, waning ice or water loading
should have caused accelerated slip rates
(Fig. 9.2). For example, at its maximum extent
at
∼
18 ka, glacial Lake Bonneville covered more
than 50 000 km
2
(Fig. 9.31A) and was over 300 m
deep (Gilbert, 1890). During most of Lake
Bonneville's existence, numerical models predict
that slip rates on the nearby Wasatch Fault should
be suppressed (Hetzel and Hampel, 2006). As the
lake shrank at
∼
12.5 ka, slip rates are predicted to
have rapidly accelerated for several thousand
Climatically modulated fault slip
The observed temporal coincidence of summer-
time water loading in the Himalayan foreland
and suppression of both seismicity and conver-
gence rates in the hinterland suggest climate-
tectonic linkages at seasonal time scales
(Box 5.2). Uncertainty remains, however, about
whether variations in loads at intermediate time
scales also impact rates of deformation. From a
theoretical perspective, we expect that changing
water, ice, or rock loads could influence fault
behavior (Fig. 9.2), and several recent studies
provide data supportive of such linkages. In each
