TY  - JOUR
ID  - epos1378
UR  - http://dx.doi.org/10.1785/0120050190
IS  - 5
A1  - Eagar, K. C.
A1  - Pavlis, G. L.
A1  - Hamburger, M. W.
Y1  - 2006/10//
N2  - To evaluate the spatial structure of seismicity in the Wabash Valley of
southern Indiana and Illinois, we analyzed data from a temporary seismic network
that included 10 three-component, short-period seismometers and a 10-component
dense phased array. We produced the ?rst comprehensive catalog of local earthquakes recorded during the 211-day deployment, from November 1995 through June
1996. The results are dominated by a cluster of 534 microearthquakes, with magnitudes ranging from 0.6 to 1.8, near the town of New Harmony, Indiana, that were
detected and recorded only by the phased array. The remarkable similarity of the
cluster events in terms of waveform, magnitude, and temporal distribution suggests
a tightly spaced grouping from a single seismic source. We relocated the earthquakes
using improved relative arrival times of P and S waves computed by time-domain
cross-correlation of the vertical beam traces and by complex cross-correlation of the
horizontal beam traces, respectively. Additional constraints on absolute locations
were applied using a graphical method of arrival-time difference analysis for six
earthquakes recorded by two network stations outside the phased array. The resulting
locations de?ne a tight spatial grouping about a zone of post-Paleozoic faulting just
west of the Indiana-Illinois border, in White County, Illinois. Average source depths
from phased-array location methods and waveform modeling with synthetic seismograms indicate, in contrast to larger events in the region, that the earthquakes
occurred at depths less than 4 km, within the sedimentary section of the Illinois
Basin. We propose that these earthquakes are arti?cially induced events, likely related
to water injection for the purpose of secondary recovery of petroleum in the Illinois
Basin. The primary evidence for this includes: (1) tight spatial clustering of earthquakes; (2) unusually shallow earthquake depths; (3) good spatial correlation of the
relocated hypocenters to existing wells and oil ?elds; and (4) highly repetitive events
with only a small range in magnitude.
PB  - Seismological Society of America
JF  - Bulletin of the Seismological Society of America
VL  - 96
SN  - 0037-1106
TI  - Evidence of Possible Induced Seismicity in the Wabash Valley Seismic Zone from Improved Microearthquake Locations
SP  - 1718
AV  - none
EP  - 1728
ER  -