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by CJ SIEBENECK
Erin Jensen studying the Courthouse Crack. | Credit: Dr. Jeff Moore GEOHAZARDS, DUE TO THE WAY
different mechanisms and influences
surface of an instability. They aren’t
THEY CONSTANTLY CHANGE, ARE
that are happening at a particular site.”
providing much information about the internal structure, or what’s going
A SOURCE OF USEFUL RESEARCH INTO L ANDSLIDES AND HOW
Seismic resonance is an emerging
THEY HAPPEN.
technique within the field of
on at depth.”
geohazards and has allowed Jensen to
Seismic monitoring not only bridges
When landslides and slope failures
collect more data on the Courthouse
the gap between surface and
occur in our built and natural
Mesa instability than can be obtained
subsurface techniques but does so
environments, damaging property
with traditional approaches.
without being structurally invasive,
and threatening life, there’s a scramble
though it can be costly. In the end,
to secure reliable assessments to
Perhaps surprising to the uninitiated,
Jensen used a combination of new
prevent further damage. But what
structures like buildings, bridges,
and traditional techniques to create
if there were ways to measure the
as well as natural rock formations
a clearer picture of the instability of
character and instability of rock
like arches have natural vibration
Courthouse Crack as a whole.
and soil beforehand and to predict
modes and are constantly in motion
potential disasters?
at their resonance frequencies. The
THE MOTHER OF INVENTION
new technique can help detect and
At sites like Courthouse Mesa,
Recently, PhD student Erin
characterize rock slope instabilities.
traditional methods include expensive
Jensen used seismic resonance
Using sensitive seismic instruments
means of drilling and field mapping
measurements to characterize the
has changed how researchers detect
which means measuring the cracks
Courthouse Crack, a potentially
changes in slope stability and what
you can see, plotting it out on a
hazardous rock slope near Moab, Utah
those changes look like.
map, and viewing the geometry of
that is part of the Courthouse Mesa.
instability. Alternatively, generating
“It’s important to be able to see a site
“Traditional techniques are easy to
field data with seismic resonance and
like this in person,” Jensen says, “and
implement, and fairly inexpensive,”
then coupling the data with numerical
really appreciate the size and scale.
Jensen says. “But the main limitation is
models result in an improved picture
I get to experience firsthand all the
that they’re really only measuring the
of crack conditions, which Jensen
D OWN TO EA RTH
| Department of Geology & Geophysics
