Gambling in Las Vegas: Understanding Seismic Hazards in Southern Nevada

by Catherine Snelson
University of Nevada, Las Vegas

3-4pm
Friday April 18, 2003
Refreshments served at 2:45pm
Munk Conference Room
Cecil and Ida M. Green Institute of Geophysics and Planetary Physics
Scripps Institution of Oceanography
University of California, San Diego
http://mahi.ucsd.edu/seminar/

Abstract

Located in the southern Basin and Range province, the cities of Las
Vegas, North Las Vegas, and Henderson sit atop a fault-bounded basin
with a depth of up to 5 km and basin dimensions of roughly 60 km wide
(east-west) by 50 km in length (north-south).  Previous isostatic gravity,
seismic reflection, and aeromagnetic studies indicate that a series of
sub-basins exist beneath the unconsolidated basin fill, with the deepest
sub-basin occurring 5 km west of the fault block bounding the eastern edge
of the basin (Frenchman Mountain).  The basin is significantly deeper
along its northern extremity, following the path of the fault block
bounding the northern edge of the basin (Las Vegas Valley Shear Zone),
and along the western edge of Frenchman Mountain.  Recent, paleoseismic
studies have indicated that faults in the Las Vegas basin have the
potential to produce an earthquake of M6.5 to 7.0.  It is estimated
that a M6.9 earthquake in the basin could produce about 11 billion
dollars in damage and a significant number of deaths and/or injuries.
In addition, an equivalent or larger event within 150 km distance of the
basin would also be devastating to the metropolitan area of approximately
1.5 million residents.

As a result, there is an increased effort to characterize the valley
for seismic hazards.  A multidisciplinary group of seismologists and
engineers from UNLV, UNR, and LLNL have formed to study the valley
and its potential response to strong ground motion.  As part of this
project, 12 broadband stations were installed in the northern portion
of the valley and were recording continuously from August 2002 till
January 2003. In addition, two refraction surveys were acquired in
2002 using quarry blasts around the valley and a chemical blast from
NTS as sources. Preliminary analyses of the refraction data indicate
that the basin is consistent in depth with previous calculations.
P-wave velocities range from 3.5-4.5 km/s in the basin. Also, preliminary
analyses of the broadband data indicate that there is a significant
amount of amplification in the valley. Additionally, an ongoing project
involves the installation of seismographs in the local schools to help
determine the micro-seismicity within the valley and supplement ground
motion studies. There are currently 9 of these stations in the valley
and 3 of these stations are contributing data directly to the regional
Nevada seismic network in real-time.