The earthquake-prone Virgin Islands-Puerto Rico region reported 622 small tremors in 1998, the Associated Press has reported.
The strongest, on Dec. 7, registered 5.6 and was centered six miles south of Anegada. Most were so small that only seismographs could detect them. Thirteen were strong enough to be felt by residents of Puerto Rico, the U.S. Virgin Islands or the British Virgin Islands.
Most of the 1998 quakes were centered north of the Virgin Islands, in the Mona Passage between the Dominican Republic and Puerto Rico, and in southern Puerto Rico, the AP reported.
The most active month was April with 73 tremors.
The most active year this decade was 1993 with 820 tremors, followed by 1994 with 819.
Puerto Rico and the Virgin Islands are close to the boundary of two pieces of the Earth's crust, the North American plate and the Caribbean plate, the AP story noted. Pressure between the plates causes tremors.