A magnitude 6.4 earthquake struck southern Taiwan early Saturday, collapsing a 17-story residential block in Tainan City and killing at least 37 people.

According to catastrophe modeling firm AIR Worldwide, the earthquake caused nine buildings to collapse, and five were left leaning in Tainan. The extent of the damage was aggravated by site conditions and building configuration, AIR said.

It is too early to assess the full toll of the earthquake, as damage reports and insurance loss estimates are still being tallied.

Building codes in Taiwan were overhauled in 1999 after the Chi-Chi earthquake collapsed more than two dozen apartment buildings and killed more than 2,400 people, AIR said, and performance-based engineering was included in the codes in 2005.

According to AIR, multistory concrete, steel and masonry are the dominant construction types in Taiwan, particularly in urban areas. A common practice in Taiwan is to widen openings at the ground level for commercial use such as accommodating shopping areas. AIR said the practice can cause a “soft-story” effect that results when designs of load-bearing walls differ between the first and upper stories of a building, which can compromise a building’s seismic performance.

AIR noted that there is speculation that the collapsed residential block may not have conformed to codes or that the construction was defective.

The earthquake occurred along the Chishan fault line in southern Taiwan. This is the third significant earthquake (magnitude 6 or larger) in the last five years in southern Taiwan, according to the catastrophe modeler.

Source: AIR Worldwide