Predicting Earthquake Shaking and hazard John N. Louie, Nevada Seismological Lab. with UNR undergraduate interns: Will Savran, Brady Flinchum, Colton Dudley, Nick Prina and Geology B.S. graduate Janice Kukuk J. Louie, NMSLC 3/3/2011

Last Week’s Earthquake in Christchurch, New Zealand  Magnitude 6.3 aftershock of M 7.1 in Sept. J. Louie, NMSLC 3/3/2011

Unexpectedly Intense Ground Shaking  Horizontal accelerations >2 times gravity J. Louie, NMSLC 3/3/2011

What Happens with Such Intense Shaking?  >200 deaths, 1/3 of city’s buildings destroyed J. Louie, NMSLC 3/3/2011 Stuff.co.nz

Photos by Marilyn Newton, Reno Gazette-Journal Could It Happen Here?  It Already Did! Wells, Nevada, Feb. 2008

How Do We Protect Nevada’s People and Economy from Earthquakes?  Stiffen building codes to strengthen buildings everywhere? But, would make construction too costly But, would make construction too costly  Improve our understanding of earthquake shaking What areas have high hazard? Put resources there. What areas have high hazard? Put resources there. Don’t waste money reinforcing safer areas Don’t waste money reinforcing safer areas J. Louie, NMSLC 3/3/2011

Three Elements to Predicting Shaking (1) Where are the earthquake sources? Discover and locate faults with seismic monitoring and surveying Discover and locate faults with seismic monitoring and surveying Characterize faults with geology and seismic surveying Characterize faults with geology and seismic surveying (2) How will the waves propagate from the sources? Characterize basins with gravity and seismic surveying Characterize basins with gravity and seismic surveying (3) How will the soils under your property react? Seismic microzonation with Parcel Mapping Seismic microzonation with Parcel Mapping  Scenario predictions with “Next-Level ShakeZoning” Use physics and geology to get realistic shaking predictions for likely earthquakes Use physics and geology to get realistic shaking predictions for likely earthquakes Combine predictions with probability of each earthquake Combine predictions with probability of each earthquake  Nevada researchers are working on these challenges. J. Louie, NMSLC 3/3/2011

Adding Fault Geology Black Hills Fault in Google Earth with USGS Qfaults trace J. Louie, NMSLC 3/3/2011

Adding Geology & Geotechnical Data Black Hills Fault in Google Earth with USGS Qfaults trace Earthquake Magnitude from Fault Size  M 0 = μAd μ = 3x10 11 dyne/cm 2 A = Fault Area (cm 2 ) = (9 km length)(10 5 cm/km) (9 km width)(10 5 cm/km) d = fault displacement = 200 cm (from geologists) J. Louie, NMSLC 3/3/2011

Adding Geotechnical Data ShakeZoning Geotech Map Obtained by Clark Co. and City of Henderson 10,721 site measurements J. Louie, NMSLC 3/3/2011

Adding Physics  2 nd -order PDE controls P(x,y,z) wave’s evolution in time  Uses Laplacian to get spatial derivatives  Use definition of derivative to compute a Finite Difference (don’t take limit) J. Louie, NMSLC 3/3/2011

Wave Computation on a 3D Geological Grid  Fine grid gives accurate FD estimate of derivatives  Finer grid takes longer to compute, higher cost  Finer grid for higher shaking frequencies J. Louie, NMSLC 3/3/2011

Adding Physics  Black Hills M6.5 event Short trace but 4-m scarps noted Short trace but 4-m scarps noted  Viscoelastic finite- difference solution 0.5-Hz frequency 0.5-Hz frequency 0.20-km grid spacing 0.20-km grid spacing A few hours on our small cluster A few hours on our small cluster  Map view of waves  Mode conversion, rupture directivity, reverberation, trapping in basins J. Louie, NMSLC 3/3/2011

Showing 3-D Vector Motions  3 computed components of the ground particle velocity vector: (x, y, z) (x, y, z)  3 components of color on your computer screen: (R, G, B) (R, G, B) red, green, blue red, green, blue J. Louie, NMSLC 3/3/2011

Showing 3-D Vector Motions  3 computed components of the ground particle velocity vector: (x, y, z) (x, y, z)  3 components of color on your computer screen: (R, G, B) (R, G, B) red, green, blue red, green, blue J. Louie, NMSLC 3/3/2011 from MathWorks.com

Showing 3-D Vector Motions  3 computed components of the ground particle velocity vector: (x, y, z) (x, y, z)  3 components of color on your computer screen: (R, G, B) (R, G, B) red, green, blue red, green, blue J. Louie, NMSLC 3/3/2011

Showing 3-D Vector Motions  3 computed components of the ground particle velocity vector: (x, y, z) (x, y, z)  3 components of color on your computer screen: (R, G, B) (R, G, B) red, green, blue red, green, blue J. Louie, NMSLC 3/3/2011

Showing 3-D Vector Motions  3 computed components of the ground particle velocity vector: (x, y, z) (x, y, z)  3 components of color on your computer screen: (R, G, B) (R, G, B) red, green, blue red, green, blue J. Louie, NMSLC 3/3/2011

Showing 3-D Vector Motions  Add the color components to get a perceived color  Color depends on strength and direction of wave vibration J. Louie, NMSLC 3/3/2011

Adding Physics  Cue up and play: BH-ClarkCo-0.5Hz.m4v  Timelapse animation 60 seconds wave propagation compressed to 16.6 sec video 60 seconds wave propagation compressed to 16.6 sec video Time compression factor of 3.6 Time compression factor of 3.6 J. Louie, NMSLC 3/3/2011

Adding Physics  Cue up and play: BH-ClarkCo-0.5Hz.m4v  0 seconds after rupture begins on the Black Hills fault (9 km down)  Las Vegas basin in shaded relief LV H H FM BH J. Louie, NMSLC 3/3/2011

Adding Physics  Cue up and play: BH-ClarkCo-0.5Hz.m4v  2.2 seconds after rupture begins on the Black Hills fault  Seismic waves reach the surface in Eldorado Valley LV H H FM BH J. Louie, NMSLC 3/3/2011

Adding Physics  Cue up and play: BH-ClarkCo-0.5Hz.m4v  6.9 seconds after rupture begins on the Black Hills fault P wave in Las Vegas, small (dark yellow) P wave in Las Vegas, small (dark yellow) Intense surface waves funneling into Henderson Intense surface waves funneling into Henderson LV H H FM BH J. Louie, NMSLC 3/3/2011

Adding Physics  Cue up and play: BH-ClarkCo-0.5Hz.m4v  13.4 seconds after rupture begins on the Black Hills fault Rayleigh wave in W. Las Vegas, large (red- blue) Rayleigh wave in W. Las Vegas, large (red- blue) Like ocean wave: vertical in between radial motions Like ocean wave: vertical in between radial motions LV H H FM BH J. Louie, NMSLC 3/3/2011

Adding Physics  Cue up and play: BH-ClarkCo-0.5Hz.m4v  23.9 seconds after rupture begins on the Black Hills fault Rayleigh wave carrying energy to Pahrump Rayleigh wave carrying energy to Pahrump Much energy left behind in soft geologic basins Much energy left behind in soft geologic basins LV H H FM BH J. Louie, NMSLC 3/3/2011

Adding Physics  Cue up and play: BH-ClarkCo-0.5Hz.m4v  45.2 seconds after rupture begins on the Black Hills fault Rock areas like FM insulated from shaking Rock areas like FM insulated from shaking Shaking trapped in basins, radiating out Shaking trapped in basins, radiating out LV H H FM BH J. Louie, NMSLC 3/3/2011

Black Hills M6.5 Scenario Results  Max Peak Ground Velocity (PGV) >140 cm/sec  PGV over 60 cm/sec (yellow) bleeds into LVV by Railroad Pass  Large event for a short fault Geologists are divided on likelihood Geologists are divided on likelihood  Need to know how likely J. Louie, NMSLC 3/3/2011

Frenchman Mountain Fault M6.7 Scenario Possible Scarp in Neighborhood Event Inside the LVV Basin J. Louie, NESC 2/9/2011

Frenchman Mountain Fault M6.7 Scenario Event Inside the LVV Basin  Cue up and play: FMF_ClarkCo_0.5Hz_24fps.m4v  Timelapse animation 60 seconds wave propagation compressed to 24 sec video Time compression factor of 2.5 J. Louie, NMSLC 3/3/2011

2-Segment Frenchman Mtn. Fault M6.7 J. Louie, NESC 2/9/2011

2-Segment Frenchman Mtn. Fault M6.7  All of Las Vegas Valley shakes as hard as Wells in 2008 (20 cm/s)  Higher shaking in areas of refraction and focusing  Less shaking in west Valley: stiffer soil J. Louie, NMSLC 3/3/2011

We Are Computing Dozens of Scenarios J. Louie, NESC 2/9/2011

J. Louie, NMSLC 3/3/2011 Combine the Scenarios Probabilistically  λ = annual frequency of exceeding ground motion u 0  rate(M, source j ) = annual rate of occurrence for an earthquake with magnitude M at source location j  P = probability of ground motions u ≥ u 0 at site i, if an earthquake occurs at source location j with magnitude M

US Geological Survey Hazard Maps  On line at usgs.gov/hazards / usgs.gov/hazards / usgs.gov/hazards /  Mostly from past earthquakes  No wave physics J. Louie, NMSLC 3/3/2011

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Model Setup Two Basin-Thickness Datasets: Widmer et al., 2007 Washoe Co. gravity model Saltus and Jachens 1995 gravity model Two Geotech Datasets: Pancha 2007 ANSS station measurements Scott et al., 2004 shallow shear-velocity transect Scenario Fault (like 2008 Wells): Strike: N-S Motion: Normal- down to the west Length: 7.58 km M w : 5.94 (Anderson et al., 1996) Frequency: 0.1 Hz and 1.0 Hz

Physics-Based Wave Propagation 0.1 Hz Model1.0 Hz Model Cue up and play DowntownReno-1Hz-5.04M.m4v The basin amplifies and traps seismic shaking Wave propagation unaffected by basin dataset boundaries in the 0.1 Hz Model Wave propagation is affected by basin dataset boundaries in the 1.0 Hz Model- but not in basin

Peak Ground Velocities (PGV) Max PGV: 22 cm/sMax PGV: 46 cm/s