RMS, the Newark, Calif.-based catastrophe risk management firm, estimated that economic property damage for both the April 15 moment magnitude (Mw) 7.0 earthquake and April 14 Mw6.4 earthquake in Japan’s Kumamoto Prefecture to be between $2.5 billion and $3.5 billion.

This includes damage to property and contents for residential, commercial and industrial buildings. This estimate does not include business interruption, shake and landslide-induced damage to infrastructure (roads, highways, bridges, airports, train transport, utilities, dams), or damage to Kumamoto Castle, RMS said in a statement.
The damage estimate is based on the findings of an RMS reconnaissance visit to the affected area, combined with a modeling analyses of how severe the shaking was in different locations, RMS said, adding that the modeling was carried out using RMS RiskLink version 15.0.

“There are hundreds of shallow crustal faults across the Japanese Islands,” said Chesley Williams, RMS senior geophysicist, who noted that the events on April 14 and April 15 were likely associated with the Futagawa – Hinagu Fault System.

“The damage from these events is concentrated in Kumamoto Prefecture in close proximity to this fault system and was primarily due to strong ground shaking and slope failures,” Williams added.

Key observations by the RMS reconnaissance team were:

The principal areas of damage are to the towns of Nishihara-mura, Minamiaso-mura, and Mashiki-machi.
The area has a local river network and hilly terrain where landslides or slope failures were triggered in some locations which caused localized pockets of damage.
Buildings located up-slope from small landslides were relatively undamaged or suffered light damage, whereas buildings on or beneath affected slopes experienced moderate to complete damage.
Nearly all buildings that collapsed or had partially collapsed on the slope or the area beneath it were within close proximity of each other.
Evidence of soft story failures (for example in stories with less strength due to extensive glazing, wide doorways or other openings) was observed in some buildings with older construction, in addition to pounding (impacts) between neighboring properties, which caused damage across multiple adjacent buildings.
Older mixed-use buildings were seen to have sustained damage or in some cases suffered complete collapse because they were inadequately constructed to withstand lateral (sideways) forces.
Older, traditional residential dwellings were found to be particularly susceptible to ground shaking and slope conditions.
Source: RMS