Microseismicity of the upper Clutha valley, South Island, New Zealand

Abstract

The spatial distribution of microseismicity observed during a 16-day survey of the upper Clutha valley is broadly similar to that of the longterm seismicity, All but one of the microearthquakes were located within the crust, with the proportion of lower crustal events being greater than in the Lake Pukaki region to the northeast. The single subcrustal event, located at 73 km depth, exhibited a definite phase between the P- and S-phases, similar to the S to P conversion at the base of the crust recently identified in records of 2 subcrustal earthquakes west of Lake Pukaki. A composite focal mechanism for all the crustal microearthquakes indicates strike-slip faulting with a P-axis acting southeast-northwest. This mechanism is very similar to that found previously for crustal microearthquakes to the west and northeast of the study area.