TAIPEI, Taiwan (AP) — A magnitude 5.6 earthquake shook buildings in Taiwan on Thursday morning, as a series of temblors hit the island, causing little damage but possibly portending more seismic activity in the near future.

The biggest of the quakes hit at 10:11 a.m. (0211 GMT) in Chiayi county’s Dapu township at a depth of 10 kilometers (6 miles), according to the Central Weather Agency and the U.S. Geological Survey. The epicenter was about 250 kilometers (155 miles) south of the capital, Taipei, where buildings swayed slightly.

That was followed shortly afterward by at least a dozen smaller quakes in Dapu. No damage or casualties were immediately reported.

All were aftershocks from a magnitude 6.4 earthquake that struck Dapu on Jan. 21 and sent 15 people to the hospital with minor injuries and damaged buildings and a highway bridge.

Last April, a magnitude 7.4 quake hit the island’s mountainous eastern coastal county of Hualien, killing at least 13 people, injuring more than 1,000 others, collapsing a hotel and forcing the closure of Toroko National Park. That was the strongest earthquake in 25 years and was followed by hundreds of aftershocks.

Taiwan is going through a period of increased seismic activity that could lead to further aftershocks or new quakes, according to the CWA and earthquake experts.

Taiwan lies along the Pacific “Ring of Fire,” the line of seismic faults encircling the Pacific Ocean from Chile to New Zealand where most of the world’s earthquakes occur.

The 1999 magnitude 7.7 quake killed 2,415 people, damaged buildings around the island of 23 million people and led to tightened building codes, better response times and coordination and widespread public education campaigns on earthquake safety.

Schools and workplaces hold earthquake drills, while cellphones buzz whenever a strong earthquake is detected.