Seismicity in the Southern
Appalachians and the Eastern
Kentucky Seismic Hazard
International Workshop on the Seismic Stability of
Tailings Dams
Nov. 10 – 11 2003
Edward W. Woolery
University of Kentucky
Department of Geological Sciences
CEUS Seismicity
>M4.5 Earthquake Locations
• Historical and modern
seismicity suggest a
significant hazard in
southern Appalachians.
• Several “seismic zones”
affect the region, but are
relatively poorly
understood.
1568 – 1989
NESZ
GCSZ
ETSZ
SCSZ
(Stover and Coffman, 1993)
Why?
• Generally, for each known
fault, the rate it slips, its
length, and how it is
broken up (segmented) is
determined to get the
distribution and size of
potential earthquakes.
• Lack of surface fault
exposure and low
recurrence rates make ID,
segmentation, and slip
rates difficult to determine
in CEUS.
(courtesy USGS)
How?
Magnitude vs. Frequency
historical
to modern
seismicity
• CEUS use concept
that the rate of
small earthquakes
predicts the rate of
large ones.
• Going from M 5’s to
M 7’s is a large
assumption
• Beginning to use
neotectonics/paleoseismology to
constrain
extrapolated
Cramer, 2001
Problems/Consequences
(FMSM, 2002)
(FMSM, 2002)
(REI, 1999)
• The “seismic source” boundaries
and maximum magnitude input
parameters for seismic hazard
assessment poorly defined
• Results in greater uncertainty and
ultimately in over- or underestimated seismic design values
State-of-Knowledge
Northeast Kentucky (NESZ)
(Street and Woolery, 2000)
1980 Sharpsburg, Ky.: mb=5.2
(Stover and Coffman, 1993)
log10Nc = 1.95- 0.9mb
(Street and Woolery, 2000)
(Drahovzal et al., 1992)
East Tennessee (ETSZ)
(Powell et al., 1992)
1973 Maryville, Tn.: mb=4.7
(Chapman et.al., 1997)
log10Nc = 2.75- 0.9mb
(Bollinger et al., 1992)
(Stover and Coffman, 1993)
Giles County, VA (GCSZ)
(Bollinger et al., 1992)
log10Nc = 1.065- 0.64mb
(Bollinger et al., 1989)
(Stover and Coffman, 1993)
1897 Giles Co, VA: mb=5.8
(Stover and Coffman, 1993)
Charleston, SC (SCSZ)
(Marple and Talwani, 1992)
log10Nc = 1.065- 0.64mb
(Bollinger et al., 1989)
1886 Charleston, SC: mb=6.7
(Stover and Coffman, 1993)
(Stover and Coffman, 1993)
Summary Source/Path Parameters
Seismic Zone
Local
NESZ
ETSZ
GCSZ
SCSZ
Max. magnitude
(mb)
5.5
5.5
6.4
6.4
6.7
log10 Mo
(dyne-cm)
23.8
23.8
25.8
25.8
26.5
fmax (Hz)
50
50
50
50
50
Stress Drop (bars)
100
100
180
180
205
Q
1291
1291
1291
1291
1291
γ
0.65
0.65
0.65
0.65
0.65
FS
2.0
2.0
2.0
2.0
2.0
RP
0.63
0.63
0.63
0.63
0.63
RF
0.71
0.71
0.71
0.71
0.71
β (km/s)
3.50
3.50
3.50
3.50
3.50
ρ (kg/m3)
2700
2700
2700
2700
2700
Future Efforts
Passive Seismic Observation
• Increase network
stations
•Gain accurate
location and focal
depth measurements;
ID seismogenic
structure.
• Low rates of
seismicity require
long-term study and
network financial
commitment.
Active Geophysical/Geological Field Studies
(Woolery et al., 2003)
– Geophysics
• Thick, mechanically weak,
overburden masks bedrock
structure (i.e., no surface
expression)
• SH-Wave Seismic Refraction/
Reflection
• GPR
• etc.
– Geological
• Drilling and Paleoseismological Trenching for more
precise age determination.
(courtesy of E. Schweig, USGS)
Summary/Conclusions
• Definition of seismic source zones and recurrence
relations remain poorly characterized.
• Uncertainty results in over- or underestimated
seismic design loads.
• Identification of discrete seismic sources are
critical for improving overall seismic hazard
assessment.
• Enhanced passive and active studies are
required.