Geophysical Survey of the Barton Springs Pool

Mustafa Saribudak, founder of Environmental Geophysics Associates (EGA), is a prominent figure in the geophysical realm. In 1989, Dr. Saribudak joined the University of Houston Geoscience Department as a visiting geoscientist from Istanbul Technical University, Turkey. Following his time at the university, Dr. Saribudak dove into the industry and in 1994, ventured out on his own with EGA, a global geophysical and geological consulting firm. Dr. Saribudak is an active member of the Austin Geological Society, and is a well-known individual in the Austin geophysical community.

Dr. Saribudak’s company, EGA, offers a broad range of geophysical surveys that aid in geotechnical and environmental problems. Geophysical surveys are a cost effective, nonintrusive technique that images subsurface areas. EGA performs surveys to locate buried utilities, underground storage tanks, and other infrastructure, but their specialty is locating and delineating caves, voids, fractures, and sinkholes over the Edwards Aquifer.

The Edwards Aquifer is located in the central region of Texas, USA. This underground layer of water-bearing rock is between 300 and 700 feet thick and covers a total overlying surface area of approximately 3,600 square miles. The structural framework of the Edwards Aquifer is controlled by the Balcones Fault Zone. This aquifer serves a wide range of agricultural, industrial, domestic, and recreational needs for the surrounding areas.

The Barton Springs Pool is one such recreational entity benefitting from the Edwards Aquifer. Measuring three acres in size, the pool is fed from underground springs and is a popular destination for many Austin residents and visitors. The pool’s water source was originally believed to stem from one of the normal faults within the Balcones Fault Zone, the Barton Springs fault. This story outlines how EGA used Surfer during a geophysical survey to prove this was not correct and actually located a new fault.

Edwards Aquifer groundwater map

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Map detailing the Edwards Aquifer Region. Image courtesy of

Geophysical survey profiles of Barton Springs

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Map detailing geophysical profiles conducted within the survey area.

EGA’s findings resulted from a variety of surveys conducted across the Barton Springs Pool area including west of the pool across the Barton Springs fault, the southern and northern banks of the pool, and south of the pool in Zilker Park. EGA performed resistivity, induced polarization, self-potential, seismic refraction, ground penetrating radar, and conductivity surveys.

Resistivity and induced polarization surveys image the subsurface by measuring voltage differences between electrodes. Resistivity values are highly affected by the presence of water or moister, the amount of and distribution of pore space in the material, and temperature. Self-potential surveys help locate caves and sinkholes by measuring natural electrical currents which are detected by using a pair of non-polarizing copper sulfate electrodes and a sensitive measuring device. Seismic refraction works best in layered geology and identifies lateral and vertical seismic velocity and layer thickness changes. This method works only with layers that increase in velocity with depth. Ground penetrating radar employs radio waves to map near-surface geology and man-made features. Conductivity surveys correspond to geological variations, groundwater contaminants, and any subsurface feature associated with changes in ground conductivity.

By gathering all of this data, EGA was able to create a full picture of the subsurface elements of the Barton Springs Pool. The results were analyzed using a variety of software tools including Surfer

Seismic refraction data across the Barton Springs fault mapped in Surfer

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Seismic refraction data across the Barton Springs fault.

 Self-potential data across the Barton Springs fault

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 Self-potential data across the Barton Springs fault along the southern and northern banks of the swimming pool.

The survey data collected across the Barton Springs fault and southern and northern bank of the swimming pool resulted in few anomalies; however, to the south of the Barton Springs Pool, the data showed significant anomalies. The anomaly findings suggest the presence of a large conduit and a previously unknown fault. The new fault appears to obliquely cut the Barton Springs fault and has a western side upthrow.

Map of geophysical anomalies located along Barton Springs Fault created in Surfer

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Map displaying the location of the geophysical anomalies. Anomalies include a fault trending in the NW-SE direction from the south in Zilker Park towards the Barton Springs fault, as shown by the bold dashed line. 

Seismic Refraction Tomography Profile of Barton Springs Fault created in Surfer

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Seismic refraction data displaying the newly discovered normal fault with a throw of approximately 45 feet.

Geophysical Survey Findings

Previously mentioned, the Barton Springs Pool water source was initially thought to have been fed by waters flowing along the Barton Springs fault. The findings of the new fault challenge this and suggest the groundwater flow-path may instead follow the new fault.

Here is a link to the full, published survey: Integrated geophysical investigations of Main Barton Springs, Austin, Texas, USA.

Dr. Mustafa Saribudak at Barton Springs Pool
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