Resistivity Lows Near Paeroa Fault (TVZ, NZ) Caused by Topographic Effects

Abstract

Modelling of two-dimensional resistivity structures has been undertaken using a finite elements scheme that allows for accurate matching of the elevation of the ground surface. With this modelling program, interpretations were made of apparent resistivities measured with the multiple-source bipoledipole array along several lines crossing the northern part of the Fault. On a line crossing the Paeroa Scarp near its highest point, where the throw is 425 m, the topographic effect is inferred to cause the apparent resistivities to be lowered by about 40 %, which accounts for the measured resistivity anomaly at the fault scarp. At the north-west of the Waikite-Puakohurea thermal region on another line, the topographic effect of a m high ridge on Mt Waikorapa causes the apparent resistivities to be reduced by about 15 This is to explain the measured low-resistivity anomaly. Thus, low-resistivity rock is inferred to underlie the site, suggesting that the thermal region extends about 1 further to the north-westward than previously thought.