Geologists capitalise on opportunity

Press, 5 March 1988, Page 34

Geologists capitalise on opportunity

I PA Wellington Geologists had a rare opportunity to study the effects of the Edgecumbe earthquake within hours of its hitting the Bay of Plenty town last March, according to the D.S.I.R. A display in Wellington by the Department of ■Scientific and Industrial Research’s Geological Purvey shows the earthi quake was a devastating : experience. ! It was the first earth--quake to inflict major ( damage in New Zealand since 1968 and geologists were able to study what could be done to reduce the damage in future ones. Geologists found the damage was worst on ridge crests and steep slopes round the margins of the Rangitikei Plain. On the plain it was worst where underlying peat layers were thick and in old abandoned channels of the Tarawera and Rangitikei rivers. Mapping of soils could identify problem areas likely in future earthquakes. The Edgecumbe fault had the most serious shaking but 10 secondary faults on the plain also moved. The hills west of the plain moved, resulting in twisting of the previous survey network pattern. Problems arose over the definition of property

boundaries and other legal markers. During the earthquake a large area of land subsided between 0.5 m and 2m. The hole extends south of Edgecumbe in a V-shape from Matata to Thornton and research has helped the catchment board and other groups to plan drainage and flood control measures during the earthquake recovery period. Geologists measured survey marks straddling the Edgecumbe fault throughout the year. These indicated the land on the downward side of the fault had continued to move’ down about ; scm compared with the |.scm movement during ) the earthquake. The movement I was caused by a continued slip on the fault plane and might be related to the continued occurrence of small earthquakes, the researchers said. I Geologists found that in the Rangitikei Plain'there was a greater chance of another similar -quake than in the countryside to the west and east. I Large earthquakes occurred about every 200 years in the Matata-Kawerau-Thornton ' triangle but less often in Whakatane. The research was done by the Geological Survey, other divisions of the D.S.I.R. and universities.