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
Could It Happen Here?
 It
Already Did! Wells, Nevada, Feb. 2008
Photos by Marilyn Newton, Reno Gazette-Journal
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?


Scenario predictions with “Next-Level ShakeZoning”



Seismic microzonation with Parcel Mapping
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 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

J. Louie, NMSLC 3/3/2011
M0 = μAd
μ = 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)
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 finitedifference 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-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
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-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
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
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
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
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
J. Louie, NMSLC 3/3/2011
FM
LV
H
BH
Adding Physics

Cue up and play:
BH-ClarkCo-0.5Hz.m4v

2.2 seconds after
rupture begins on the
Black Hills fault
FM
LV
H
BH

Seismic waves reach
the surface in
Eldorado Valley
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
J. Louie, NMSLC 3/3/2011
FM
LV
H
BH
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 (redblue)
Like ocean wave:
vertical in between
radial motions
J. Louie, NMSLC 3/3/2011
FM
LV
H
BH
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
J. Louie, NMSLC 3/3/2011
FM
LV
H
BH
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
J. Louie, NMSLC 3/3/2011
FM
LV
H
BH
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 Scenario
Possible Scarp in
Neighborhood
J. Louie, NESC 2/9/2011
Event Inside the LVV Basin
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
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
J. Louie, NMSLC 3/3/2011
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
Faul
t
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 Propagation
0.1 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