Balcones fault line dead, but UT monitoring others

Austin is on an ancient geological formation known as the Balcones fault line which runs from just south of Dallas through Austin and San Marcos to Del Rio. It's one of several fault lines monitored by researchers at the University of Texas.

The overlook at the 360 bridge was a popular place Monday. Among those who climbed the rocky path to reach the top was Juan Ruiz and his friend. They were impressed by the view but didn't really realize what they were looking at was a fault line. 

"That, I wasn't aware of at all,” said Ruiz.

The limestone hills that run along the west side of Austin are part of what's known as the Balcones fault line.  Landslides are common but from a seismic point of view, it’s rock solid.

"The fault is geologically is dead,” said Dr. Peter Hennings.

Hennings, with UT's Bureau of Economic Geology, says the earthquake that formed the Balcones fault line happened a very long time ago.
“When the fault was most recently active, 10 million years ago, Texas was a flat coastal plain, and the faulting was a very subtle thing, that just dropped the Gulf Coastal Plain down hundreds of feet and leaving what would become the Hill Country geologically higher,” said Hennings.

The Balcones may be inactive, but other parts of Texas are moving. That’s why researchers at the University of Texas have built a network of sensors. 

TexNet went online in 2016, and since then the network has grown into a collection of 80 seismic sensors with most located in West and South Texas. The largest earthquake TexNet has recorded happened a few months ago.

"Magnitude 4.4 event in October of 2018 close to Amarillo in the Panhandle of Texas,” said UT research scientist Dr. Alexandros Savvaidis. 

Most of the tremors detected by TexNet only have magnitudes ranging from three to two. These are small but they yield a lot of information. New fault zones have been located and activity has been detected in old faults.

"It's a tool to be proactive, to make sure everybody is safe,” Savvaidis said. 

Locating risk areas can help urban planners and energy explorations avoid those spots. A new map for the Dallas area is expected to be released later this month. 

Meanwhile, the old Balcones fault line remains quiet, and according to researchers will eventually erode away.