The Central Weather Bureau and local scholars are at odds over the cause of the earthquake that rattled southern Taiwan March 4.

Because the epicenter was 8 kilometers east of the Chaozhou fault near Jiaxian Township in Kaohsiung County, the CWB's preliminary analysis indicates the temblor was not directly related to that fault, and may have been caused by a blind fault, one that does not reach the surface, previously undetected by the Ministry of Economic Affairs' Central Geological Survey.

Chen Wen-shan, head of the Department of Geosciences at National Taiwan University, said the Qishan and Pingxi faults 20 kilometers north of the Chaozhou fault could have triggered the quake.

Chen said 7,000 years ago the Qishan fault broke through the earth's surface, and is believed to be similar to the Chelungpu fault, cause of the major earthquake of Sept. 21, 1999, in that both store up energy for long periods, which is then released in major temblors. In these terms, the 6.4-magnitude quake of March 4 can only be considered "a small release of energy," so that a major earthquake cannot be ruled out at any time.

Ma Kuo-fong of National Central University's Department of Earth Science said gauging from the quake, its aftershocks and wave patterns, the earthquake mechanism in this instance was not the Chaozhou fault, but a previously undetected conformation north of that fault at an angle of 30 degrees with respect to the surface, running northwest to southeast for 30 to 50 kilometers.

Yen Horng-yuan of the same department pointed out that according to historical records, earthquakes above magnitude 3 in the Chaozhou fault have been extremely rare. This fault is quite inactive, and has been little studied due to its isolated location.

Immediately following the March 4 temblor, NCU, the Academia Sinica and National Chung Cheng University sent six teams of experts with 20 seismological instruments into the Liugui mountains of Kaohsiung County to determine the location of the fault and supply disaster response authorities with more accurate data on aftershocks.

Regarding public concern about an even larger quake, Ma said judging by preliminary investigation of the conformation north of the Chaozhou fault, later earthquakes would not be of greater intensity than the first one. As long as people are prepared, they need not worry, she said.

However, Chen Chau-huei of NCCU's Institute of Seismology said southern Taiwan could still be jolted by temblors exceeding a magnitude of 6, and reminded the public to be well prepared. County and city governments should also have their disaster response plans ready, he added.