1986 Mt. Tihia/ Tokaanu quakes

1986 has only one event shown in the NZ Earthquake Catalogue, a 3.9ML on 7th August down in the Lake Rotoaira Valley.
The following map and data on other events in 1986 is taken from a paper presented to the 17th NZ Geothermal Workshop 1995 called “ Earthquake Swarm Activity Beneath Tokaanu-Waihi Geothermal System, Lake Taupo, New Zealand” researched by M..P. Hochstein, S. Sherburn and J. Tikku. Geothermal Institute and Geology Department, University of Auckland, NZ, IGNS Wairakei, NZ
There are no co-ordinates for the epicenters of the quakes available, so the map and co-ordinates have been created by hand from a sketch map within the above report and match to the original map as close as possible. The epicenters were computed using the iterative Geiger method and the original digital data recorded by the Taupo Seismic Network., a network of six telemetred seismographs that operated around Lake Taupo between 1985 September and 1991 July.

All epicentres are located inside the low resistivity structure which outlines hot and thermally altered rocks in the upper 0.5 km of the Tokaanu-Waihi geothermal reservoir.
There is no data available on the magnitudes save for the maximum size in each swarm.
The April 20th-21st swarm had a sequence of 20 events. The maximum magnitude of 16 events on the 20th was 3.1 and the sequence lasted 1 hour. The later part of the swarm on the 21st had 4 events over a period of 6.5 hours.
The 3 events of the small July 23rd swarm occurred close to the thermally active Hipaua area, the 3 events occurred over a period of 1.5 hrs and the largest event was 2.6ML.
The 18th December swarm of 5 events was over a period of 10 hours and the largest quake was a 2.1ML.

The locations are marked on the map below, the dates shown by colour.
 Mt. Tihia/Tokaanu quakes 1986

data by geonet. map by google maps. plots by highace using GPS Visualizer

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