A sign placed along the sidewalk reads ‘Common Sense Against Earthquakes’ as a small group with Frack Free Denton protest outside city hall, Tuesday, July 15, 2014, in Denton, Texas. CREDIT: AP Photo/Tony Gutierrez The agency that regulates oil and gas activity in Texas is considering new, tougher regulations governing the practice of injecting leftover water used to frack natural gas wells deep into the ground — a process which is believed to be responsible for an increase in human-caused earthquakes across the state.