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Kumamoto Earthquake Underscores Seismic Resistance of 2×4 Homes in Japan

Shawn Lawlor

By Shawn Lawlor

Director, Canada Wood Japan

August 5, 2016

This year Japan experienced the strongest earthquake since the 2011 Great East Japan Earthquake and Tsunami. Centered in Japan’s Kyushu region, the Kumamoto earthquakes in April registered a strong magnitude 7.3. The strong jolts in Kumamoto and Oita Prefectures caused extensive loss of life and damage to structures. The town of Mashiki near the epicenter lost approximately 30% of its buildings to the quake.

The Japan 2×4 Home Builders Association recently conducted a survey among its members to ascertain the extent of the damage to 2×4 housing as a result of the Kumamoto quake. A total of 2,940 platform frame homes were surveyed in the affected area. The rankings to assess the extent of the damage in ascending order are: (A) No Damage; (B) Light Damage – non-structural such as cracks in the wallpaper, dents in the floor caused by fallen furniture, etc…homeowner can continue to live in the structure as is;  (C) Partial Damage – some structural damage requiring repairs, but nothing extensive; (D) Half Destroyed – extensive structural damage to between 20% to 70% of total floor area; (E) Completely Destroyed. The survey results are as follows. Of the 2,940 2×4 homes reported none experienced category D half destruction or E complete destruction or collapse. A total of 79 homes or 2.7% sustained partial damage: of these 46 homes suffered some structural deformation by the force of the earthquake; 30 suffered either degraded soil conditions or liquefaction of the soil; and 3 homes classified the cause as other. The balance of 2,861 homes (97.3%) were categorized as either A, no damage, or B, light non-structural damage.