The map of the 3.2-magnitude earthquake. Photo: Institute of Geophysics.

The National Earthquake and Tsunami Warning Centre under the Institute of Geophysics said that at 7.14pm on July 19, a 4.3-magnitude earthquake occurred in Muong La district with a focal depth of about 8.5 km.

The quake lasted about 30 seconds. It was followed by two quakes measuring 3.2 and 3.5 on the Richter scale at 8.23pm and 9.42pm respectively.

The aftershocks of the quakes were felt in Hanoi. Many people living in high-rise buildings in the capital, including Ha Dong District, said they experienced some tremors.

While the quakes were of very short duration, they caused panic among local residents with many fleeing their houses.

Residents said some home furnishings shook strongly when the quakes hit. They caused 40cm, 0.2cm wide cracks in the walls of a local household in It Ong Commune.

According to Nguyen Hong Phong, Director of the National Earthquake and Tsunami Warning Centre, Son La is one of seven key areas in the northwestern region that are prone to earthquakes as they sit on the Ma River Fault. The other areas are Dien Bien City, Lai Chau town, Muong La commune, Muong Lay town, Tuan Giao town and Tam Duong town.

He also warned that the quakes could recur as they were part of the operation of the Muong La-Bac Yen fault segment. "But it is impossible to forecast the magnitude of the earthquakes as they depend on the operation of the fault segment with each time period," he added. 

So far this year, five earthquakes occurred in Son La province, including a 2.6-magnitude earthquake on January 11; a 2.5 magnitude earthquake on February 9; and a 2.6 magnitude quake on February 12 in the districts of Thuan Chau and Quynh Nhai.

Zing/VNA