SEISMIC HAZARDS IN SOUTHERN NEVADA: THE GAP BETWEEN THE PRESENT AND A STATE-OF-THE-ART EVALUATION

Of the major US cities with a significant seismic hazard, Las Vegas is arguably farthest behind in understanding the scope of the problem.

Seismic network coverage in southern Nevada has been project-driven, and not optimized for a comprehensive understanding of the urban seismic risks. Projects have included monitoring earthquakes triggered by Lake Mead, understanding the effects of underground nuclear testing, evaluating earthquake hazards at Yucca Mountain, and ANSS strong motion instruments in Las Vegas Valley. The historical rate of earthquakes within 100 km of Las Vegas is about one earthquake with MW> 5.0 every 100 years. Geodetic measurements predict that the long-term average rate might be substantially larger. The rates of earthquakes on Quaternary faults within and near Las Vegas Valley are very uncertain.

An understanding of the urban southern Nevada earthquake hazard adequate for public policy and safety should include monitoring and directed study to address the following:

1) Geological studies of relevant active faults, including trenching to determine the repeat times of large earthquakes

2) Geophysical investigation to determine velocity structure necessary for modeling of ground motions and reliable earthquake locations

3) Borehole seismometers (5 or more) to determine if microearthquakes occur on faults within the Las Vegas valley

4) An expanded network of broadband seismometers that measures noise and basin response in Las Vegas

5) A network of broadband seismometers meeting ANSS standards throughout the I-15 corridor

6) A permanent network of precision GPS stations, possibly collocated with the regional seismic network stations

7) Complete the strong motion network envisioned by ANSS planning documents

8) Data analysis aimed towards development of “early warning”—providing a few seconds of notice before a strong earthquake strikes Las Vegas

9) Proving a capability to model the ground motions that result from local and regional earthquakes

10) Testing probabilistic seismic hazard estimates using geological indicators

11) Aggressive public outreach so that these results will be used for the safety and general benefit of residents and visitors.

Focused effort and funding could yield results that would significantly improve public policy in five to ten years.