A seismic refraction experiment southeast of Ruapehu volcano

Abstract

A seismic refraction survey parallel to the strike of the Taupo Volcanic Zone, North Island, New Zealand, and about 9 km southeast of Ruapehu volcano, shows 3 principal refractors with velocities of 2.0 km s-1, 4.9 km S-1, and 5.4 km s-1. The first refractor underlies shallow surface layers, while the last 2 occur at average depths of approximately 600 m and 1700 m respectively. Delay time analysis shows that the 4.9 km s-1 refractor is approximately horizontal, but is upthrown 150 m on the Ruapehu side of a previously mapped fault which curves around the volcano. Surface layers are tephras and the 2.0 km s-1 layer is composed of lahar deposits. Seismograms from the southern portion of the survey show second arrivals with velocities of about 3.0 km s-1. These are attributed to Tertiary sediments which underlie and predate the volcanics. The velocities of 4.9 km s-1 and 5.4 km s-1 are within the range measured for Mesozoic greywackes which constitute the sedimentary basement of the surrounding region. © 1981 Taylor & Francis Group, LLC.