Ground damage and seismic response resulting from the 1987 Edgecumbe earthquake, New Zealand

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Abstract
A sequence of small earthquakes in the Bay of Plenty culminated in a Richter magnitude (M L ) 6. 3 event on 1987 Mar 2 under the Rangitaiki Plains, which produced felt intensities of up to MM IX and MM X in the epicentral area. The extent of the ground damaged is aligned in a northeast-southwest direction and the mesoseismal area of maximum shaking (c. MM IX) included the townships of Thornton, Edgecumbe. Te Teko, and Kawerau. Permanent inelastic deformation of the soft. saturated sediments of the Rangitaiki Plains led to structural and ground damage consistent with felt intensities of up to MM XI in Edgecumbe. Ground damage included surface rupture. liquefaction phenomena such as sand boils. lateral spreading of embankments. low-angle slope failures, and minor slope and cutting failures across the plains and in the surrounding hills. Observed slope failures occurred at distances of up to c. 30 km from the main (Edgecumbe) fault rupture. whilst soil liquefaction phenomena occurred at distances within c. 17 km of the earthquake epicentre. Topographic enhancement effects are considered to have contributed to housing damage on the hills above Whakatane and Awakeri. This study determined the local intensity of peak ground acceleration from an analysis of partial slope failures with known geotechnical properties.