Las Vegas Valley Seismic Response Project Catherine Snelson, Wanda Taylor, and Barbara Luke University of Nevada Las Vegas John Louie, John Anderson, and Raj Siddharthan University of Nevada Reno Dave McCallen, Artie Rodgers, Jeff Wagoner, Shawn Larsen, Mike Gerhard, Chuck Noble Lawrence Livermore National Laboratory

LVVSRP Motivations Strong Ground Motion –Future Nuclear Testing –Earthquakes in and around Las Vegas, NV Geologic Problems –Quaternary faults are active and capable of M6.5 to 7.0 earthquake –Basin thickness estimated up to 5 km in the northeastern portion of the Valley. Characterize Las Vegas Basin –Test basin thickness estimates –Determine amplification and correlation to lithology

Las Vegas basin fault map. Green lines are strike slip faults that are considered inactive. Brow lines are normal faults with Quaternary motion in the east dipping direction; these are the faults of concern in the basin. Yellow lines are normal and strike-slip faults with Quaternary motion in the west dipping direction. Black contour lines represent current basin thickness estimates in km from Langenheim et al. (2001). Las Vegas Blvd (LVB) is shown by the orange line. LVVSZ - Las Vegas Valley Shear Zone; EDF - Eglington-Decater Fault; VV - Valley View fault; FMF - Frenchman Mountain Fault; RMF - River Mountains Fault; WCF - West Charleston Fault.

Barnwell event ground motions (0.2-1 Hz)

Seismic Data in Las Vegas Valley Legacy Refraction/Reflection data –Prodehl 1979 –Industry acquired profiles Quarry Blast data –May 2002 Watusi –September 2002 Las Vegas Valley Broadband Array –Deployment 1 – September 2002 to January 2003 –Deployment 2 – August 2003 to September 2004 SILVVER –August 2003

Results From the Watusi Experiment Potential focusing effect from mid- crustal structure along the NTS to Las Vegas corridor. Interpretation of reflection data untied to surface geology; lack of wells in proximity and mapped exposures.

SILVVER ’03 (Seismic Investigations of the Las Vegas Valley: Evaluating Risks) 792 seismic stations at 100 m spacing Planned for 12 blasts Shot 9 chemical blasts ranging from 50 to 1000 lb only recorded Deployed 6 Broadband sensors Many volunteers for deployment as well as housing instrumentation Positive community response to the project!!

Basemap of the study area with various seismic stations. The stars are shot point locations, purple are the quarry blasts, orange is the Watusi blast, and red are the SILVVER ’03 shots. The green line are the station locations for the quarry blast project, the yellow line is the station location of the Watusi line, and the dark blue lines are the SILVVER ’03 station locations.

SILVVER ’03 Summary The basin velocities range from 2.5 to 4.5 km/s Basin/bedrock contact located at 4.5 km/s velocity contour with corresponds to 4 to 6 km depth Apparent deeper structures within the deep portion of the basin that may correspond to known faults.

Z = km Z = km Z = km

4.5 km/s 2.9 km/s Model Slice - 21 km km 4 -6 km km 6.0 km/s Fault ?

2.9 km/s Model Slice - 25 km 6.0 km/s 4.5 km/s km 4 -6 km km Fault ?

2.9 km/s Model Slice - 26 km 6.0 km/s 4.5 km/s km 4 -6 km km Fault ?

Map of the Las Vegas Valley showing the station locations of LVVBB1 as blue triangles (September 2002 – January 2003) and LVVBB2 as yellow triangles (July 2003 – September 2004). The Blume and Associates array is show as black triangles for reference. Also shown are the contours of depth to basement (contour interval = 1 km) from Langenheim et al. (2001a; b). The deepest portion of the basin is found northwest of Frenchman Mountain with depths up to 5 km.

Additional Questions Correlation to the Gravity field – re- running Langenheim model Mid-crustal structure – what is it? Does it really focus energy into Las Vegas? High resolution seismic profiles to further tie the surface to depth