A powerful 7.5 magnitude earthquake struck off northern Japan late Monday, injuring 23 people and triggering a tsunami in Pacific coast communities, officials said. Authorities warned of possible aftershocks and an increased risk of a megaquake.

The 417-day-long experiment, known as LUX-ZEPLIN (LZ), looked at the light signatures released as particles collide with xenon atoms in a giant vat, which is placed deep underground so that most particles from space cannot muddy the results.