A 4.2-magnitude earthquake struck Italy's Campi Flegrei region, the biggest tremor in 40 years. Although the quake startled residents, it caused no injuries or damage. The Campi Flegrei is a flat volcano that has recently shown increased activity. Experts believe that there may be more intense tremors in the future. The area is home to half a million people, and the last eruption occurred in 1538. The recent spike in activity is likely caused by gas bubbling up, making an eruption less likely.