Another small earthquake hit Cleburne late Friday night, and a city spokesman said it could be helpful to geologists trying to determine whether natural gas drilling is causing the seismic activity.

The quake was the sixth minor tremor to hit the city this month. A group of researchers from Southern Methodist University recently put four seismographs in the ground to measure the depth of the activity, said city spokesman Charles Hodges.

Hodges said city officials had worried that they wouldn’t be able to gather evidence from a live quake, making it impossible to find a cause. He likened the situation to a mechanic who can’t hear the clanging sound that a driver hears in his car.