Damage to unreinforced masonry structures by seismic activity

• Published in: Structural engineer (London, England : 1988) Vol. 89; no. 3; pp. 14 - 15
• Main Authors: Ingham, Jason, Griffith, Mike
• Format: Journal Article
• Language: English
• Published: 01-02-2011
• Subjects: Acceleration; Damage; Earthquake construction; Earthquake damage; Ground motion; Grounds; Masonry; Seismic phenomena
• ISSN: 1466-5123

At 4.35am on the morning of 4 September 2010 a magnitude 7.1 earthquake occurred approximately 40km west of the city of Christchurch, New Zealand, at a depth of about 10km (GNS 2010a), with the epicentre located near the town of Darfield. The ground motion had a peak ground acceleration of about 0.25g and a spectral acceleration in the plateau region of about 0.75g, with most of the Canterbury region reporting damage consistent with MM8 on the Modified Mercalli intensity scale. There were no fatalities directly associated with the earthquake (although there was one heart attack fatality and one person hospitalised due to a falling chimney), and the overall impression was that damage in the central business district (CBD) was restricted primarily to unreinforced masonry (URM) buildings and damage to windows in taller steel and concrete structures. The earthquake ground motion characteristics reflected the underlying soft soil conditions, which effectively acted as a filter and removed high frequency ground motion but amplified long period motion. Strong ground shaking in the CBD had a duration of approximately 30s with similar amplitudes in the two orthogonal recording directions.