Another earthquake shook Cleburne Tuesday evening -- the third tremor in three days and the fourth in a week.
The U.S. Geological Survey said a 2.4-magnitude earthquake rattled Cleburne at 5:10 p.m. at a depth of 3.1 miles. An aftershock occurred about an hour later.
The Cleburne City Council voted unanimously to hire a "geological professional" to investigate the cause of the recent earthquakes.
"In a city that's never had one before, it's a coincidence," Mayor Ted Reynolds said. "Two, three, four is truly phenomenal."
Specifically, the mayor said he and many residents want to know if recent natural gas drilling could cause quakes in a city that had never experienced them before.
Cleburne has more than 200 natural gas wells within the city limits.
The city leases 3,000 acres to Chesapeake Energy Corp., said city manager Chester Bolen. Drilling started in 2002.
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Most geologists downplay any connection between earthquakes and natural gas drilling because earthquakes occur much further underground.
"I think it would be in all our interests to get a second or third opinion on that just to make sure," Reynolds said.
Minor quakes measuring 2.3 and 2.6, respectively, shook the Cleburne area on Monday morning and Sunday night, and a 2.8 magnitude quake was reported June 2.
"We feel four (earthquakes) in a seven-day period is enough to warrant further investigation," Bolen said.
Experts say it's not unusual for earthquakes to occur in groups.