c. guney olgun department of civil and environmental engineering, virginia tech thomas a. barham,...
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C. Guney OlgunDepartment of Civil and Environmental Engineering,
Virginia Tech
Thomas A. Barham, Morgan A. Eddy, Mark Tilashalski,
Martin C. Chapman, Adrian Rodriguez-Marek
GSA 2015Baltimore, Maryland3 November 2015
Seismic Hazard Mapping of the National Capital Region Using Random Field
Models
2011 Mineral Virginia Earthquake
M5.8 Earthquake occurred August 23, 2011 at 1:51pm
Light to moderate damage in DC area, about 130 km away
Regional geological conditions contributed to significant soil amplification
PGA for DC area estimated 0.02-0.03g on rock and 0.06g at soil sites
Structural Damage in the Area
National Park Service
M.A. Eddy
Atlantic Coastal Plain Geology
(Ator et al. 2005)
Regional geology along the Atlantic coastal plain area dominated by several physiographic provinces
Shallow soils over rock (Piedmont, Fall Line)
Deep tertiary and cretaceous marine deposits over rock (Coastal Plain)
Sharp impedance contrasts between different geologic units (residual, young alluvial, tertiary and cretaceous marine, rock)
Washington D.C. Geology
Idealized Subsurface Cross-section for Washington, D.C.0 2 4 km
Horizontal
Legend
Alluvial Soil
Potomac Formation
Residual Soil
Weathered Rock
Rock
Piedmont Fall Line Coastal Plain
Meters
Vertical0
50
100
0 500 1000 1500 20000
10
20
30
40
50
60 Vs (m/s)
Dep
th (
m)
Weathered Rock
Residual
1
0 400 800 1200 16000
20
40
60
80
100 Vs (m/s)
Dep
th (
m)
Alluvial
Potomac Formation
3
1. Piedmont 2. F
all L
ine
3. Coastal Plain
0 500 1000 1500 20000
10
20
30
40
50
60 Vs (m/s)
Dep
th (
m)
2
Alluvial
Residual
Weathered Rock
Investigation of Subsurface Geology
38.84
38.88
39.00
38.96
38.92
-76.97
-77.05
-77.13
-77.09
-77.01Longitud
e
Lati
tud
e
Subsurface profiles from about 600 geotechnical investigations
Shear wave velocity profiles from 122 investigations
Artificial neural network (ANN) analysis of the geological profile in the area
Geological Cross-Sections (W-E)
38.8559
Distance (km)
-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16E
leva
tion
(m)
-200
-150
-100
-50
0
50
100
150
RockPotomac
Ground Surface
W E
38.8880
Distance (km)
-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Ele
vatio
n (
m)
-150
-100
-50
0
50
100
150
Geological Cross-Sections (W-E)
RockPotomac
Ground Surface
W E
38.9015
Distance (km)
-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Ele
vatio
n (
m)
-150
-100
-50
0
50
100
150
Geological Cross-Sections (W-E)
Rock Potomac
Ground Surface
38.9423
Distance (km)
-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16E
leva
tion
(m)
-50
0
50
100
150
W E
-77.0051
Distance (km)
-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Ele
vatio
n (
m)
-200
-150
-100
-50
0
50
100
150
Geological Cross-Sections (S-N)
RockPotomac
Ground Surface
S N
-77.0936
Distance (km)
-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Ele
vatio
n (m
)-50
0
50
100
150
Geological Cross-Sections (S-N)
Rock
Ground Surface
S N
Vs Measurements of Geological Units
Random Field Modeling
Period (sec)
0.01 0.1 1 10
Spe
ctra
l Rat
io
0
1
2
3
4
5
6
7
Period (sec)0.01 0.1 1 10
Spe
ctra
l Acc
ele
ratio
n (g
)
0.0
0.5
1.0
1.5
2.0
2.5BedrockGround Surface
Piedmont Site : 2nd District Police Station
(courtesy T. Pratt and S. Hough)
Spectral ratio (ground surface to rock)
Fa =2.80
Fv =0.94
Shear Wave Velocity (m/s)0 400 800 1200 1600 2000
De
pth
(m)
0
5
10
15
20
25
30
Frequency (Hz)0.1 1 10 100
Spe
ctra
l Rat
io
0
2
4
6
8
10
12
Stiff shallow site Residual soils (~15 m thick)
underlain by rock Fundamental frequency 4.5
Hz
Residual Soil
Weathered Rock
Period (sec)0.01 0.1 1 10
Spe
ctra
l Acc
eler
atio
n (g
)
0.0
0.5
1.0
1.5
2.0
2.5
BedrockGround Surface
Fall Line Site : 1328 14th St. NW
(courtesy T. Pratt and S. Hough)Period (sec)
0.01 0.1 1 10
Spe
ctra
l Rat
io
0
1
2
3
4
5
6
Fa =2.68 Fv =2.65
Shear Wave Velocity (m/s)0 200 400 600 800 10001200
De
pth
(m)
0
5
10
15
20
25
30
Spectral ratio (ground surface to rock)
Period (sec)
0.01 0.1 1 10
Spe
ctra
l Rat
io
0
1
2
3
4
5
6
Fa =2.45
Fv =0.90
Frequency (Hz)0.1 1 10 100
Spe
ctra
l Rat
io
0
2
4
6
8
10
12
Stiff site Alluvial and residual soils (~19
m thick) underlain by rock Fundamental frequency 5.0
Hz
Alluvial Soil
Weathered Rock
Coastal Plain Site : Washington Monument
Frequency (Hz)0.1 1 10 100
Spe
ctra
l Rat
io
0
2
4
6
8
10
12
(courtesy T. Pratt and S. Hough)
Shear Wave Velocity (m/s)0 200 400 600 800 10001200
Dep
th (
m)
0
10
20
30
40
50
60
70
(courtesy R. Kayen)
Period (sec)
0.01 0.1 1 10
Spe
ctra
l Rat
io
0
1
2
3
4
5
6
Fa =2.68 Fv =2.65
Period (sec)0.01 0.1 1 10
Spe
ctra
l Acc
eler
atio
n (g
)
0.0
0.5
1.0
1.5
2.0
2.5BedrockGround Surface
Spectral ratio (ground surface to rock)
Alluvial Soil and Potomac
Formation
Weathered Rock
Deep alluvial and Potomac formation (~60 m thick) underlain by rock
Fundamental frequency 1.5 Hz
Summary and Conclusions
Vs30 (m/s)
200 300 400 500 600 700 800 900 1000 1100 1200
Fa
- S
hort
Per
iod
Am
plifi
catio
n F
acto
r
0
1
2
3
4
5
6
7
PiedmontFall LineCoastal Plain
IBC
DC B
Fa (0.1-0.5 sec)
Vs30 (m/s)
200 300 400 500 600 700 800 900 1000 1100 1200Fv
- M
id-t
o-Lo
ng P
erio
d A
mpl
ifica
tion
Fac
tor
0
1
2
3
4
5
IBC
D C B
Fv (0.4-2.0 sec)
D.C. area geology exhibits sharp impedance contrasts that can significantly amplify ground motions
Subsurface profile mapped from extensive field data and ANN Limited information on regional velocity structure and relevant
properties (Q, k) (Hashash et al. 2013)
Acknowledgements
NEHRP Earthquake Hazards Program award numbers G10AP00035, G13AP00076, G15AP00047
PiedmontGeotechnical, Inc.
Seismometer measurements from D.C. area provided by Dr. Tom Pratt and Dr. Susan Hough (Poster Session 293, Exhibits Hall, 4 November 2015)
Washington Monument seismic profile provided by Dr. Robert Kayen, USGS
Washington D.C. area geotechnical and shear wave velocity data provided by