Complex sentence: Dr. Brown's UWO study of the infrasound signals generated by asteroid impacts releasing more than one kiloton of explosive force, suggested that "city-killer" impact events actually occur about once a century, a rate previously unrecognized.
Split into simpler sentences: Dr. Brown's UWO study used the infrasound signals generated by asteroid impacts releasing more than one kiloton of explosive force. It suggested that "city-killer" impact events actually occur about once a century, a rate previously unrecognized.