Finding the concealed section of the Whakatane Fault in the Whakatane Township with a shear wave land streamer system: A seismic surveying report

Abstract

The principal objective of the presented study was to evaluate the usefulness of high-resolution shear wave seismic reflection profiling using a land streamer to locate buried faults in urban areas of New Zealand. A secondary objective was to locate the Whakatane Fault. In a calibration survey the method was first tested over a surface trace of the Edgecumbe Fault 30 km south-west of Whakatane township, that ruptured during the 1987 Mw 6.3 Edgecumbe Earthquake. This survey helped gain an understanding of the shear wave propagation characteristics across an active fault in the sediments of the area. These comprise pumiceous material from the Taupo Volcanic Zone redeposited in a Holocene marine and fluvial environment. Having established the characteristics of shear wave seismic images in a green field location, the main survey was conducted within the Whakatane township.

In total, 11 high quality profiles of 5.7 km total length were acquired, showing concealed displacements in sediments to a depth of 100 m. Normal fault displacements of up to 15 m are visible in depths from 20 to 40 m and deeper structures show displacements of up to 20 m. The technique proved useful for accurately defining the location of the Whakatane Fault beneath the township of Whakatane on several East/West profiles. Corroborative evidence for the location of the fault requires a drilling programme.