Published: June 16, 2009 03:12 pm      

Earthquake detector installed by SMU reps

Southern Methodist University representatives installed a seismograph in Cleburne on Monday morning and plan to install three more around town later this week.

The instruments measure ground motion by collecting 200 samples per second, said Dr. Brian Stump, SMU chairman of geological sciences.

The occurrence of five low-magnitude quakes recorded in or near Cleburne over the last two weeks prompted SMU officials to install the devices.

“These instruments are sensitive enough that they may catch some activity too small to be felt by people,” Stump said.

Stump and Dr. Chris Hayward, SMU Geophysics Research Projects director, set up the device along with Ashley Howe, a junior majoring in earth science.

The instruments will stay in place for two weeks, at which time they will decide whether to move them, or leave them in place, Stump said.

Project members will retrieve data collected by the instruments periodically in an attempt to glean a better understanding of the cause and frequency of area seismic activity.

Some have attributed the quakes to natural causes, others to the presence of drilling activity.

“I’m thinking there’s probably some kind of fault,” Stump said. “What relation that has to do with fluids in the ground or drilling is the question. These have all been really small events, though that doesn’t mean there won’t be anything bigger as you can never rule out what Mother Nature will do.”

Area quakes registered between 2.3 and 2.8 in magnitude. All lasted a few seconds and generated no reports of injury or damage.

The U.S. Geological Survey records such activity but generally doesn’t pursue investigation of events measuring less than a magnitude of three, Stump said.

Placing seismographs in town should provide a fuller picture of any seismic activity occurring in the area, he said.

Officials plan to measure activity for up to six months, Hayward said.

Independent Research Institute in Seismology officials loaned 10 seismographs to SMU for that amount of time, he said.

Others have been placed south of DFW International Airport in response to area quake activity recorded in October. News of last week’s events in Cleburne prompted SMU officials to place the instruments in town as well, Stump said.

SMU is conducting its research independently although city officials are cooperating by providing storage locations and information to help the team, said City Manager Chester Nolen.

City officials await results from the study to determine what else needs to be done, Nolen said.

The city council, in a June 9 emergency meeting, voted to hire a geophysicist to study the recent earthquakes.

Officials subsequently decided to work with SMU instead, Nolen said, and “... at at this point, there’s no cost to the city,” Nolen said. “We get the research we need without spending money.”



Mysterious booms

Several residents reported a noise at the time of the earthquakes, variously described as an explosion or sonic boom.

Some said it sounded like something hit their house.

But small quakes like those recorded in Cleburne shouldn’t generate sound, said Ken Morgan, Texas Christian University geology professor.

Stump agreed with Morgan but said he has heard reports of booms, or noise, from low-level quakes.

The USGS Web site addresses the phenomenon, citing earthquakes recorded near Spokane, Wash., in 2001.

Those quakes, which registered between 2.0 and 3.0 magnitude, originated one to two miles underground. Cleburne’s quakes were about 3.1 miles below ground, according to the USGS.

“Many of the Spokane quakes were definitely accompanied by booming sounds,” according to the Web site. “The quakes in Spokane were shallow, sometimes only a mile or two deep. This probably contributed to all the noise they made.

“Higher-frequency vibrations make the booming sounds, and when quakes are deeper, those vibrations are gone by the time they reach the surface. Sometimes the quakes boom even when no vibration is felt.”