Laoag city: A magnitude 4.9 earthquake shook Cagayan and nearby provinces in northern Luzon at 5:39 a.m. Thursday, state seismologists said. With the epicenter located 20 kilometers northwest of Dalupiri Island (Calayan) in Cagayan, the earthquake was tectonic in origin with a depth of 16 kilometers. According to Philippines News Agency, residents in these areas are advised to take precautionary measures as aftershocks are expected. No damage has been recorded so far, authorities stated. Reported intensity is the traditional way of knowing the intensity based on reports of those who felt the earthquake, while instrumental intensity is measured using an intensity meter that calculates ground acceleration. Magnitude measures the size of an earthquake at its source or the amount of energy released.