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Task 4 - Earthquake Recurrence Investigations
A fundamental earthquake hazard parameter is earthquake recurrence, or how often earthquakes
occur along each fault/earthquake source. Few paleoearthquakes have been documented and
dated in Las Vegas Valley that can be used to view earthquake recurrence directly. We will
compile and evaluate what constraints on earthquake recurrence paleoseismic information
provides, and incorporate any additional new data that may become available with fault
trenching (to be proposed to the U.S. Geological Survey Earthquake Hazard Program). In some
cases, we will be able to get better constraints on existing recurrence estimates through the new
dating. We will monitor pipeline and other excavations occurring in Las Vegas Valley during the
project and will attempt to use any new exposures across faults to gain additional local
paleoseismic data.
An approach that will be used for estimating how often earthquakes occur will be determining
fault slip rates (how fast faults are moving) and considering the time it takes with these rates for
earthquake displacement to accumulate. This is a standard approach used in the National Seismic
Hazard Map where a detailed paleoearthquake record is not available. The dates collected in
Task 1 will be critical in making slip rate estimates for local faults (calculated by dividing the
offset measurement by the age of the offset). The displacement of the ground during a single
earthquake (co-seismic displacement) is determined by direct measurements made in trenches or
through correlation with estimated earthquake magnitudes (the larger the earthquake magnitude,
the larger the average offset). The co-seismic displacement is divided by the fault slip rate to get
the average time between earthquakes.
The earthquake recurrence analysis will synthesize all available data into determining how often
earthquakes occur along individual and connected faults. This will include using insights gained
from tectonic and deformation models developed in Task 2. Average earthquake recurrence
intervals will be determined along with uncertainties in those estimations.
Task 4 is divided into four subtasks:
Task 4.1 -Estimating Fault Slip Rates,
Task 4.2 -Paleoseismic Studies and Inferences,
Task 4.3 -Earthquake Recurrence Analysis,
Task 4.4 -Final Report.
Most of Task 4 will be conducted in the third year of the project.
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