The possibility of aftershocks cannot be ruled out for a month after a 6.4-magnitude earthquake - the biggest in the south of Taiwan in a century - that rocked Kaohsiung County yesterday, according to seismologists.

The quake struck at a depth of 5km, making it a shallow one.

The immediate cause of most shallow earthquakes is the sudden release of stress along a fault, or a fracture in the earth's crust, said Lu Pei-ling, deputy head of the Central Weather Bureau's (CWB's) Seismological Center.

Shallow earthquakes are more damaging than deeper earthquakes due to there being less rock to absorb the shaking, and they tend to have a lot more aftershocks. Therefore, there is a possibility that Kaohsiung could be hit by aftershocks of at least magnitude 5, Lu added.

Since the earthquake yesterday morning, several aftershocks have shaken the area, with the biggest one - magnitude 5.7 - occurring at 4:16 pm, 17.1km southeast of the 6.4 quake's epicenter.

The earthquake was the most powerful to hit Kaohsiung since 1900, Lu said.

CWB Director General Shin Tzay-chyn said yesterday's quake was related to the Chaochou Fault in Pingtung County and was caused by the movement of the Eurasian Plate against the Philippine Sea Plate.

China Daily/CNA

(HK Edition 03/05/2010 page8)