About 3,00,000 people could die in the event of a potential 'mega' earthquake in Japan.The potential earthquake, known as a 'megaquake', could cause $1.81 trillion damage to Japan's economy.The megaquake is expected to occur along the Nankai Trough, a seismically active area for the country.The government estimates an 80% chance of a magnitude 8 to 9 earthquake along the Nankai Trough.