Microearthquakes, geothermal activity, and structure, central North Island, New Zealand

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Abstract
Microearthquakes are very frequent in the Taupo Fault Belt and very infrequent in the neighbouring Taupo-Reporoa Basin and Kaingaroa Plateau; the distribution of microearthquakes does not correlate with areas of geothermal activity. Larger earthquakes follow much the same distribution pattern. They have similar characteristics to the microearthquakes in other respects, including the prominence of swarm activity in the Taupo Fault Belt. From the seismicity of the region it is inferred that under the Taupo-Reporoa Basin the shear strength is reduced to a very low level by the presence of molten and semi-molten magma extending to within a few kilometres of the ground surface, while under the Taupo Fault Belt there is strong material, interpreted as cooled magma, at about 2–6 km depth.