Jan. 14, 2008Southern Great Basin & Las Vegas1 3D Models of the Southern Great Basin and Ground Motion in Las Vegas Arthur Rodgers Seismology Group Atmospheric, Earth and Energy Division Lawrence Livermore National Laboratory

Jan. 14, 2008Southern Great Basin & Las Vegas2 Outline Projects over the last five years –Las Vegas Ground Motion Supported by DOE/NNSA Test-Site Readiness Participation of: –UNR (Louie, Anderson) –UNLV (Luke, Snelson, Taylor) –Non-Proliferation Experiment Modeling Supported by DOE/NNSA BAA, led by Steve Myers (LLNL) Understand S-wave generation from explosions Participation of UNR (Smith, Preston) Future/Possible projects –EarthVision geologic models –WPP anelastic wave propagation code

Jan. 14, 2008Southern Great Basin & Las Vegas3 Study Area - Southern NV Southern NV, NTS & Las Vegas Seismic Stations in Las Vegas Valley Basin depth from Langenheim et al. (2001)Stations (triangles) Explosions (stars) & Earthquakes (circles)

Jan. 14, 2008Southern Great Basin & Las Vegas4 We have legacy ground motion recordings in Las Vegas from NTS explosions ~ 180 km Las Vegas Valley NTS Pahute Mesa Yucca Flat ~ 110 km 13 NTS explosions ( ) 33 Sites in Las Vegas Data was painstakingly converted from analog FM tapes to digital form

Jan. 14, 2008Southern Great Basin & Las Vegas5 Amplification where basin deepest, spatial coverage of data is limited. Basin depth from Langenheim et al. (2001 ) Barnwell ground motions Hz

Jan. 14, 2008Southern Great Basin & Las Vegas6 SSR amplifications are large BLUME-NTS Average SSR (solid) w/ error HVR (dotted)

Jan. 14, 2008Southern Great Basin & Las Vegas7 Site response shows strong variation within Las Vegas Valley Amplifications strongest Hz Amplifications strongest in the central basin Amplifications approach 10! Lowest Frequencies Highest Frequencies

Jan. 14, 2008Southern Great Basin & Las Vegas8 We want(ed) to predict ground motions of future events Empirical data is limited –Spatial coverage Covers downtown well But not recently developed areas Coverage poor in the north where amplification is high –Frequency content (band-width) Legacy NTS ground motion data valid Hz 3D modeling can address these limitations –Spatial coverage limited by model coverage –Low-frequencies can be easily modeled

Jan. 14, 2008Southern Great Basin & Las Vegas9 3D Model of Southern Nevada and Las Vegas Yucca Mtn Little Skull Mtn Las Vegas We built a 3D model of Las Vegas and southern NV, including NTS & Yucca Mountain. Basin structure (except Las Vegas) are taken from a regional compilation by the USGS.

Jan. 14, 2008Southern Great Basin & Las Vegas10 3D modeling using Model Assembler model and Shawn Larsen’s E3D code Using early version of MA model (presented at AGU, 2002) Note shaking in basins …

Jan. 14, 2008Southern Great Basin & Las Vegas11 3D Simulation of Explosion Using John Louie’s Model Assembler Las Vegas Valley Barnwell

Jan. 14, 2008Southern Great Basin & Las Vegas12 LLNL (Jeff Wagoner) has developed EarthVision geologic models NPE Project –Detailed model of NPE shot-point –Great Basin regional model Other projects could benefit from existing EarthVision models LLNL WPP code reads etree models in parallel –EarthVision-to-Etree tool makes models more accessible

Jan. 14, 2008Southern Great Basin & Las Vegas13 Geologic structure in Las Vegas from well-log interpretations Work of Wanda Taylor (UNLV) and Jeff Wagoner (LLNL). Need relationships between lithology and v P, v S and .

Jan. 14, 2008Southern Great Basin & Las Vegas14 NPE - Improved Phenomenology of Underground Nuclear Explosions Detailed model of NTS based on geology and high-resolution geophysical data. Modeling with E3D improves understanding of seismic waves generated by underground explosions in the presence of complex topography and geology. Non-Proliferation Experiment Sept. 22, 1993 provides excellent data set.

Jan. 14, 2008Southern Great Basin & Las Vegas15 Regional Great Basin model Covers regional observations of NPE. Target h=60 m.

Jan. 14, 2008Southern Great Basin & Las Vegas16 NTS shot-point model

Jan. 14, 2008Southern Great Basin & Las Vegas17 EarthVision to Etree Capability Lithologic index P-wave velocity

Jan. 14, 2008Southern Great Basin & Las Vegas18 USGS Model Represented As An Octant Tree Or “Etree” Allows variable and hierarchical resolution. For seismic velocity models fine resolution near surface, coarser with at depth. 2D example

Jan. 14, 2008Southern Great Basin & Las Vegas19 WPP - anelastic wave propagation code Elastic and anelastic finite difference code 2nd order, node centered formulation Written in C++/C –Runs on Linux workstations/clusters & Mac OSX –Born parallel (uses mpich) But can run on single processor –Available for download ~50 page user’s guide & example input files

Jan. 14, 2008Southern Great Basin & Las Vegas20 WPP Current Features (version 1.1) 3D P- and S-wave velocity and density models –Block, vfile (binary raster) and etree models Purely elastic (no attenuation) –Handles acoustic case, where  =0 –Absorbing (Clayton and Enquist) boundary conditions –Free surface boundary conditions Models arbitrary number of sources –Point moment tensor & force, many source-time (moment) functions Output –Writes time-series of motion as SAC files and 2D and 3D images Mesh refinement Coming soon –Free surface topography and embedded boundaries