predicting earthquake shaking and hazard
Post on 22-Feb-2016
40 Views
Preview:
DESCRIPTION
TRANSCRIPT
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 Earthquakein 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 3/3/2011Stuff.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
Improve our understanding of earthquake shaking What areas have high hazard? Put resources
there. 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 Characterize faults with geology and seismic surveying
(2) How will the waves propagate from the sources? Characterize basins with gravity and seismic surveying
(3) How will the soils under your property react? Seismic microzonation with Parcel Mapping
Scenario predictions with “Next-Level ShakeZoning” Use physics and geology to get realistic shaking predictions for
likely earthquakes Combine predictions with probability of each earthquake
Nevada researchers are working on these challenges.
J. Louie, NMSLC 3/3/2011
Adding Fault GeologyBlack Hills Fault in Google Earth with USGS Qfaults trace
J. Louie, NMSLC 3/3/2011
Adding Geology & Geotechnical DataBlack Hills Fault in Google Earth with USGS Qfaults trace
Earthquake Magnitude from Fault Size
M0 = μAdμ = 3x1011 dyne/cm2
A = Fault Area (cm2)= (9 km length)(105 cm/km)
(9 km width)(105 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
2nd-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 Viscoelastic finite-
difference solution 0.5-Hz frequency 0.20-km grid spacing 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-DVector Motions
3 computed components of the ground particle velocity vector: (x, y, z)
3 components of color on your computer screen:
(R, G, B) 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)
3 components of color on your computer screen:
(R, G, B) red, green, blue
J. Louie, NMSLC 3/3/2011
from MathWorks.com
Showing 3-DVector Motions
3 computed components of the ground particle velocity vector: (x, y, z)
3 components of color on your computer screen:
(R, G, B) red, green, blue
J. Louie, NMSLC 3/3/2011
Showing 3-DVector Motions
3 computed components of the ground particle velocity vector: (x, y, z)
3 components of color on your computer screen:
(R, G, B) red, green, blue
J. Louie, NMSLC 3/3/2011
Showing 3-DVector Motions
3 computed components of the ground particle velocity vector: (x, y, z)
3 components of color on your computer screen:
(R, G, B) red, green, blue
J. Louie, NMSLC 3/3/2011
Showing 3-DVector 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
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
LVH
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
LVH
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)
Intense surface waves funneling into Henderson
LVH
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)
Like ocean wave: vertical in between radial motions
LVH
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
Much energy left behind in soft geologic basins
LVH
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
Shaking trapped in basins, radiating out
LVH
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
Need to know how likely
J. Louie, NMSLC 3/3/2011
Frenchman Mountain Fault M6.7 ScenarioPossible Scarp in Neighborhood
Event Inside the LVV Basin
J. Louie, NESC 2/9/2011
Frenchman Mountain Fault M6.7 ScenarioEvent Inside the LVV Basin
Cue up and play:FMF_ClarkCo_0.5Hz_24fps.m4
v
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 u0
rate(M, sourcej) = annual rate of occurrence for an earthquake with magnitude M at source location j
P = probability of ground motions u ≥ u0 at site i, if an earthquake occurs at source location j with magnitude M
US Geological Survey
Hazard Maps On line at
http://earthquake.usgs.gov/hazards/
Mostly from past earthquakes
No wave physics
J. Louie, NMSLC 3/3/2011
Fault
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• Mw: 5.94 (Anderson et al., 1996)• Frequency: 0.1 Hz and 1.0 Hz
Physics-Based Wave Propagation0.1 Hz Model 1.0 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/s Max PGV: 46 cm/s
top related