Seismic Hazard Mapping of the National
Capital Region Using Random Field Models
C. Guney Olgun
Department of Civil and Environmental Engineering, Virginia Tech
Thomas A. Barham, Morgan A. Eddy, Mark Tilashalski,
Martin C. Chapman, Adrian Rodriguez-Marek
GSA 2015
Baltimore, Maryland
3 November 2015
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
M.A. Eddy
National Park Service
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
1
Vs (m/s)
2
Vs (m/s)
0
500 1000 1500 2000
0
500 1000 1500 2000
0
0
Residual
10
20
20
Depth (m)
Depth (m)
1. Piedmont
Alluvial
10
30
40
Weathered
Rock
Residual
30
40
50
50
60
60
Weathered
Rock
Legend
3. Coastal Plain
Vertical
Alluvial Soil
3
400
800 1200 1600
0
Potomac Formation
0
Vs (m/s)
0
Alluvial
Residual Soil
20
50
Meters
Rock
Piedmont
Fall Line
Coastal Plain
Horizontal
0
2
4 km
Depth (m)
Weathered Rock
100
40
60
80
Idealized Subsurface Cross-section for Washington, D.C.
100
Potomac
Formation
Investigation of Subsurface Geology
39.00

38.96
38.92
Latitud
e


38.88
-77.13
-77.09
-77.05
Longitude
-77.01
38.84
-76.97
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
150
Ground Surface
100
Elevation (m)
50
0
-50
Potomac
Rock
-100
-150
-200
-1
0
W
1
2
3
4
5
6
7
8
9
Distance (km)
10
11
12
13
14
15
16
E
Geological Cross-Sections (W-E)
38.8880
150
100
Elevation (m)
Ground Surface
50
0
Rock
Potomac
-50
-100
-150
-1
0
W
1
2
3
4
5
6
7
8
9
Distance (km)
10
11 12 13
14
15
16
E
Geological Cross-Sections (W-E)
38.9015
38.9423
150
150
Ground Surface
Elevation (m)
Elevation (m)
100
100
50
050
Rock
Potomac
-50
0
-100
-150
-50
-1-1 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 1010 1111 1212 1313 1414 1515 1616
Distance
Distance(km)
(km)
W
E
Geological Cross-Sections (S-N)
-77.0051
150
Ground Surface
100
Elevation (m)
50
0
Rock
Potomac
-50
-100
-150
-200
-1 0
S
1
2
3
4
5
6
7
8 9 10 11 12 13 14 15 16 17 18 19 20
Distance (km)
N
Geological Cross-Sections (S-N)
-77.0936
150
Ground Surface
Elevation (m)
100
50
Rock
0
-50
-1 0
S
1
2
3
4
5
6
7
8 9 10 11 12 13 14 15 16 17 18 19 20
Distance (km)
N
Vs Measurements of Geological Units
Random Field Modeling
Piedmont Site : 2nd District Police Station
Spectral ratio (ground surface to rock)
12
Shear Wave Velocity (m/s)
0
400
800 1200 1600 2000
5
Depth (m)
Residual Soil
10
15
10

Stiff shallow site

Residual soils (~15 m thick)
underlain by rock

Spectral Ratio
0
Fundamental frequency 4.5 Hz
8
6
4
2
20
0
25
Weathered
Rock
0.1
1
10
Frequency (Hz)
30
7
2.0
Bedrock
Ground Surface
6
Spectral Ratio
Spectral Acceleration (g)
2.5
1.5
1.0
0.5
0.0
0.01
5
4
Fa =2.80
3
2
Fv =0.94
1
0.1
Period (sec)
1
10
0
0.01
0.1
Period (sec)
1
10
(courtesy T. Pratt and S. Hough)
100
Fall Line Site : 1328 14th St. NW
Spectral ratio (ground surface to rock)
12
Shear Wave Velocity (m/s)
0
200 400 600 800 10001200
5
Depth (m)
Alluvial Soil
10
10

Stiff site

Alluvial and residual soils (~19
m thick) underlain by rock
15

Spectral Ratio
0
Fundamental frequency 5.0 Hz
8
6
4
2
20
0
25
0.1
Weathered
Rock
1
10
Frequency (Hz)
30
66
Bedrock
Ground Surface
2.0
55
Spectral Ratio
Ratio
Spectral
Spectral Acceleration (g)
2.5
1.5
1.0
0.5
0.0
0.01
44
33
Fa =2.68
22
Fv =0.90
11
0.1
Period (sec)
1
10
00
0.01
0.01
Fv =2.65
Fa =2.45
0.1
0.1
11
Period
Period (sec)
(sec)
10
10
(courtesy T. Pratt and S. Hough)
100
Coastal Plain Site : Washington Monument
Spectral ratio (ground surface to rock)
Shear Wave Velocity (m/s)
12
200 400 600 800 10001200
10
Spectral Ratio
0
0
10
Depth (m)
20
30
Alluvial Soil
and Potomac
Formation

40
50

60
Weathered Rock
Deep alluvial and
Potomac formation
(~60 m thick)
underlain by rock
8
6
4
2
Fundamental
frequency 1.5 Hz
0
0.1
1
10
Frequency (Hz)
70
(courtesy R. Kayen)
2.0
6
Bedrock
Ground Surface
5
Spectral Ratio
Spectral Acceleration (g)
2.5
1.5
1.0
0.5
0.0
0.01
4
3
Fa =2.68
Fv =2.65
2
1
0.1
Period (sec)
1
10
0
0.01
0.1
Period (sec)
1
10
(courtesy T. Pratt and S. Hough)
100
7
Fa (0.1-0.5 sec)
6
5
Piedmont
Fall Line
Coastal Plain
4
3
IBC
2
1
D
C
B
0
200 300 400 500 600 700 800 900 1000 1100 1200
Vs30 (m/s)
Fv - Mid-to-Long Period Amplification Factor
Fa - Short Period Amplification Factor
Summary and Conclusions
5
Fv (0.4-2.0 sec)
4
3
2
IBC
1
0
D
B
C
200 300 400 500 600 700 800 900 1000 1100 1200
Vs30 (m/s)

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
Washington D.C. area geotechnical and shear wave velocity data provided by
Piedmont
Geotechnical, 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
NEHRP Earthquake Hazards Program award numbers
G10AP00035, G13AP00076, G15AP00047