High-Resolution Earthquake Location in the New Madrid
Seismic Zone
T51D-0767
Meredith Dunn, Steve Horton, Heather DeShon, and Christine Powell
mmdunn@memphis.edu
Data Set and Analysis
Purpose
Provide improvement of fault plane resolution
through calculation of double difference
earthquake locations in the New Madrid Seismic
Zone (NMSZ).
• 1394 Earthquakes
• 313 Stations
• Events recorded between 2000-2006
• Double Difference Relocations found for 6 clusters using the
program hypoDD (Waldhauser, 2001).
Figure 1:
Locations and relocations
of clusters 1 and 2 (see
figure 3). Cluster 1 is
indicated by red circles,
cluster 2 is indicated by
blue circles. Cross
Section is oriented N45E.
This arm is thought to be
a vertical, right later
strike slip fault.
Figure 3:
Tectonic
setting of the
NMSZ.
Seismicity
occurs
primarily in the
Reelfoot Rift, a
possible failed
rift system.
Red circles
indicate
earthquakes.
4
3
5
6
1
2
Map showing
catalog
locations
with station
coverage, as
well as major
arms of
seismicity
and 6
clusters
relocated in
this study.
Figure 7:
Study Area
Results and Discussion
The NMSZ was divided into 6 clusters based on known tectonics and
natural breaks in seismicity. Waveform cross correlation was performed
on the entire data set. Results were examined for the NMSZ and for
individual clusters. Clustered relocations were more computationally
stable and provide more small scale improvements over relocation of the
whole NMSZ. Relocations provide a clear image of the fault plane, with
improvement over original catalog locations.
Cluster 5
Locations and relocations of
cluster 5 (see figure 3) the
northern portion of the
central thrust fault. Dip
estimated to be 30-32
degrees for relocations,
more shallow than southern
portion of fault (see figure
8). Cross section is oriented
N25W.
Figure 8:
• Most seismically active region east of the Rocky
Mountains.
• Region has history of damaging earthquakes
including three M7.0 events in 1811-1812.
• Seismicity occurs within Mississippi Embayment,
characterized by thick sediment layer at surface.
Figure 6:
Clusters 1 and 2
Cluster 6
Locations and relocations of
cluster 6 (see figure 3), the
southern portion of the
central thrust fault. Dip
estimated to be 35-40
degrees, slightly more
shallow than original
locations. Cross section is
oriented N25W.
Future Work
Figure 2:
Original
catalog
locations
contained in
the data set.
Color
indicates
depth of
events. The
same color
legend is used
in figures 4
and 5.
Figure 4:
Figure 5:
Results from relocation of entire data set
with no clustering performed. These are to
be compared with results in figure 5.
Results reconstructed from relocation of 6
clusters individually. The depths in several areas
such as the northeast and southwest arm are
different than those in figures 2 and 4.