Geology Reference
In-Depth Information
Why is that? A simple flexural model (see figure B) predicts that downward flexure of the
foreland due to seasonal water loading will cause extensional stresses at seismogenic depths
(2-15 km) within the Himalaya. Such extension would partially counterbalance the overall con-
tractional regime, thereby both slowing down the rate of contraction (as shown by the GPS)
and inhibiting seismicity. With the end of the monsoon, water loading diminishes, the crust
beneath the foreland rebounds elastically, contractional stresses are increased within
the Himalaya, and seismicity accelerates. This stunning correlation suggests that faults are
surprisingly sensitive to very small stress changes (2-4 kPa) and are most sensitive to changes
in the rate of stress change. The success of this study highlights the insights that have emerged
from nearly continuous and carefully coordinated measurements of geodesy, gravity, altimetry,
and seismicity.
South
North
Horizontal
displacement
_
_
Vertical
displacement
Flexural Model
for Water Load
North
flexed plate
load-induced
extension
water loading
Summer
Moho
South
unloading
Winter
North
Moho
B
unloading-induced
compression
B. Modeled changes in displacement and crustal stress due to seasonal water loads.
GeoEarthscope, which, between them, have
acquired thousands of square kilometers of
lidar imagery over major faults in the western
United States. Shortly after processing, most
NSF-supported lidar acquisitions are available
to the public (www.opentopography.org; www.
calm.geo.berkeley.edu) and can be readily
explored using *.kmz files in conjunction
with Google Earth (see Fig. 4.21 for some
examples).
Ground-based lidar is just beginning to be
extensively used. This approach promises to
provide tremendously detailed topographic
imagery of geomorphic features that will enable
