1. AN ALTERNATIVE ANALYSIS OF THE PROBABILISTIC SEISMIC HAZARD FOR LAS VEGAS VALLEY, NEVADA Barbara Luke Wanda J. Taylor

2. ACTIVE FAULTS IN AND NEAR LAS VEGAS VALLEY sources of M>6 earthquakes since 1.6 Ma distant sources Sources within Las Vegas Valley Las Vegas Valley fault system and Frenchman Mtn fault 100 km radius

3. LAS VEGAS VALLEY FAULT SYSTEM EF splay - MRE 2245 BCE VVF splay – MRE 14,500 14 C BP (dePolo et al., 2006)

4. 1400+ well logs Sediment ranges from fine to coarse Alluvial fans around basin Interfingered grain sizes near LVVFS LAS VEGAS VALLEY WELL DATA

5. LAS VEGAS VALLEY BASIN FILL AT DEPTH Well data show that ~2/3 of the basin-fill is > ~5 Ma <5 Ma basin has less paleorelief along its base, is broader and more symmetric Shape difference and depocenter shift caused by E- dipping LVFS bedrock >~5 Ma < ~5 Ma

6. SUPERIMPOSED BASINS Non-planar faults Upper basin controlled by LVVFS and FMF

7. Probabilistic seismic hazard analysis (PSHA): Combined hazard due to multiple earthquake sources -3 ground shaking parameters -Peak Ground Acceleration (PGA) -0.2-s spectral acceleration -1.0-s spectral acceleration -10%, 5%, 2% probability of exceedance (PE) in 50 years -Uses logic tree formalism -Fault parameters -Fault recurrence -Ground motion relations http://earthquake.usgs.gov/hazards/products/conterminous/2008/maps/ 0.35 – 0.65 g OUR SEISMIC HAZARD ACCORDING TO USGS (2008) Hypothetical bedrock outcrop * 0.2-s spectral acceleration 2% PE in 50 years ~ 2500 year return period Acceleration, g Model does not explicitly consider most of Las Vegas Valley Fault System (LVVFS) * Does not address effects of basin-fill sediments

8. USGS FAULT CLASS “B” Not considered explicitly as fault source in PSHA

9. NEW PSHA - SUCHAN LAMICHHANE, PH.D. All known sources within 200 km 29 Latest Quaternary 1 Late Quaternary (Frenchman Mountain) What is different from USGS (2008)? Faults added: Cashman, Decatur, Valley View, Whitney Mesa, Rock Valley, West Specter Range, Pahrump Valley, Yucca Mountain – up to M7.2 Faults characteristics modified: Eglington: slip rate Black Hills: magnitude and slip rate Added USGS 2008 Heavy outlines: strike-slip; otherwise normal Lamichhane, S., Luke, B. Taylor, W. 2014. An alternative analysis of the probabilistic seismic hazard for Las Vegas Valley, Nevada. Bulletin of the Seismological Society of America 104:741-768.

10. FAULTS USGS quaternary fault and fold database http://earthquake.usgs.gov/hazards/qfaults/google.phphttp://earthquake.usgs.gov/hazards/qfaults/google.php October 2011 WMF: Whitney Mesa Fault VVF: Valley View Fault CF: Cashman Fault DF: Decatur Fault Added 200 km

12. PSHA USES LOGIC TREE Weight Addresses uncertainties due to lack of knowledge and understanding (“epistemic”) Different with this analysis Ground motion prediction equation

13. 10% PE in 50 years 2% PE in 50 years Reference location EZ-FRISK v. 7.62 2% PE in 50 years: ~70% increase 72 % 69 % 71 % Total hazard curves Uniform hazard spectra PSHA OUTCOME Period (s) 5% damping

14. PSHA OUTCOME 441 locations, ~ 3 km grid Peak ground acceleration Background & gridded sources 4 seconds period Distant faults 0.15 – 0.55 g Reference location LVVFS Deaggregations 2% PE in 50 years Long period (4 s) PGA

15. 5% PE in 50 years2% PE in 50 years10% PE in 50 years ~ 0.2 - 0.6 g~ 0.1 - 0.3 g~ 0.07 - 0.1 g Compare to USGS 2008 PGA is: Consistently higher Maximum increase ~150% Greatest impact in north-central, least in south News: USGS next iteration maps (2014 preliminary): Hazard increases by ~ 30% PGA

16. PRELIMINARY http://earthquake.usgs.gov/hazards/2014prelim/ We acknowledge Suchan Lamichhane Technical contributions from Woody Savage, Jeff Wagoner, Alex Goya Funding from DOE, UNLV