A rash of seismic activity across an arc of southern Japan in recent weeks – including the most powerful earthquake to strike Tokyo in a decade – has triggered renewed concern that a major natural disaster may be imminent, potentially the much-feared rupture of the Nankai Trough. Experts and government agencies have called for calm and insist there are no signs of an impending disaster to rival the March 2011 magnitude-9 quake, a tremor that unleashed a towering tsunami and caused devastation across much of northeast Japan. The Great East Japan Earthquake caused nearly 20,000 deaths and the meltdown of...