Auxiliary material for
The 17 May 2012 M4.8 earthquake near Timpson, east Texas: An event
possibly triggered by fluid injection
Cliff Frohlich1, William Ellsworth2, Wesley A. Brown3, Michael Brunt4, Jim Luetgert2,
Tim MacDonald2 and Steve Walter2
Journal of Geophysical Research Solid Earth
Introduction
We provide a figure “fs01.eps” that shows producing oil and gas wells near the
Timpson sequence as well as injection disposal wells. We also provide three tables:
“ts01.txt” provides the coordinates of the temporary and permanent seismic
stations deployed in the Timpson area and used to locate earthquakes; “ts02.txt”
presents the preferred epicentral and hypocentral locations for earthquakes in the
Timpson sequence; and “ts03.txt” is the velocity model we determined from the data
and used to locate hypocenters and epicenters in this study.
1. fs01.eps For the region mapped in Figure 4, injection disposal wells (yellow squares
labeled “W”) and producing wells (blue squares labeled ‘P’) actively extracting oil or
water during the 2000-2011 interval. Larger blue squares are wells producing monthly
1
Institute for Geophysics, University of Texas at Austin, Austin TX 78758-4445
Earthquake Science Center, U.S. Geological Survey, Menlo Park CA 94025-3591
3 Department of Geology, Stephen F. Austin State University, Nacogdoches TX 75962
4 Eagle Pass High School, 2020 2nd Street, Eagle Pass TX 78852
2
Corresponding author: Cliff Frohlich, Institute for Geophysics, 10100 Burnet Rd.
(R2200), Austin, TX 78758-4445 (cliff@ig.utexas.edu)
volumes of water that exceeded 10,000 barrels (1600 m3) for one or more months
between 2000-2011. Note that producing wells are absent in the vicinity of the seismic
activity (circles). Other symbols are as in Figure 4.
2. ts01.txt Seismic stations providing data for this study.
2.1 Column “Station Code”, four-character identifier for seismic stations providing data
in this study.
2.2 Column “latitude”, latitude of seismic station
2.3 Column “longitude”, longitude of seismic station
2.4 Column “installed”, date of station installation
2.5 Column “removed”, date of station removal (when available)
2.6 Column “instrument”, instrument type or array identifier (when available)
3. ts02.txt Preferred locations for epicenters and hypocenters determined in this study.
Locations in Group 1 (white circles in Figure 4) epicenters were determined with focal
depths fixed at 2.5 km; epicenters are least reliable because of the absence of stations
within ~5 km. Stations recording events in Group 2 (green circles in Figure 4) were
situated along a southwest-northeast-trending line; epicenters were determined with fixed
focal depths. Temporary stations ETX01-ETX08 were in place to record events in Group
3 (red circles in Figure 4). Group 3 hypocenters were determined with free depths and are
considered relatively reliable.
3.1 Column “year”, origin time year of epicenter or hypocenter.
3.2 Column “date”, monty, day, hour, and minute of origin time
3.3 Column “lat”, latitude of epicenter or hypocenter (degrees)
3.4 Column “long”, longitude of epicenter or hypocenter (degrees)
3.5 Column “depth”, depth of epicenter (as fixed; see above) or hypocenter (km)
3.6 Column “res”, residual of epicenter or hypocenter as determined in this study (sec);
see text.
3.7 Column “gap”, largest azimuthal angle (degrees) between stations used to locate
epicenter or hypocenter.
3.8 Column “magnitude”, magnitude and source of magnitude for epicenter or
hypocenter (when available).
4. ts03.txt Velocity model used for location in this study.
4.1 Column “layer”, layer number, with “1” and surface and deeper layers “2”,”3”,
etc. at increasingly greater depths.
4.2 Column “P-velocity (km/sec)”, compressional velocity (km/sec)
4.3 Column “S-velocity (km/sec)”, shear velocity (km/sec)
4.4 Column “thickness (km)”, thickness of layer ( km)
4.5 Column “depth (km)”, depth range of top and bottom of layer (km), with surface
at 0 km.