Scientists say a section of Kilauea volcano’s south flank moved about 1.2 inches toward the sea in a phenomenon known as a “slow earthquake” last week.

The Hawaiian Volcano Observatory said the slow earthquake began Oct. 14 and triggered a small swarm of regular earthquakes, including a magnitude-3.9 shake at 8:41 p.m. Oct. 15 centered about 10 miles south of Fern Acres.

Three earthquakes of magnitude 2.6 were also recorded Oct. 15, the first at 12:09 a.m., about 4 miles north-northeast of Pahala. The other earthquakes hit about 12 miles southwest of Leilani Estates at 8:43 and at 9 p.m.

A magnitude-2.8 earthquake shook the area at 7:55 p.m.

In a Volcano Watch article released Thursday, observatory scientists concluded that the earthquakes were connected to the slippage detected by a tiltmeter near Kaena Point on Hawaii island.

The movement took about two to three days. If it had happened rapidly, the movement of the earth would have generated an earthquake of around magnitude 6, scientists said.

The volcano scientists said the slow earthquake also coincided with an increase in seismic activity within Kilauea’s rift zones.

It’s not clear why that happens or what the relationship is with a slow earthquake and volcanic activity, scientists said. Researchers are busy studying the phenomena.

Slow earthquakes happen about every 26 months on Kilauea, usually on the south flank, the observatory said.

The last slow earthquake happened May 28, 2012, so scientists were expecting another slow earthquake and placed instruments on the volcano to record the phenomena.