资源环境科技发展态势分析平台

A major eruption sequence of Ruapehu volcano began on 17 September 1995, with only hours of local precursory seismicity. However, from about 10 to 5 months prior to the eruption, an unusually high number of tectonic earthquakes occurred between 15 and 20 km west of Ruapehu. Diffusion chronometry of zoned crystals within erupted scoria from the 1995 eruptions of Ruapehu provide a petrological timescale of magmatic processes before the eruption. This timescale coincides with the seismicity to the west of Ruapehu. Stress modeling shows that stress changes due to movement of newly mixed magma from a sill under Ruapehu would have significantly added to the stress on preexisting faults, thereby providing a mechanism to explain the observed pre-eruption seismicity. This shows that tectonic earthquakes in the vicinity of an active volcano may be an indication of magma movement and should be viewed as a possible eruption precursor.

Plain Language Summary The only significant seismicity under Ruapehu volcano preceding its 1995-1996 eruption sequence occurred during the last few hours before the first explosion through its crater lake. There had been earthquakes 10 or more kilometers west of the volcano some months earlier, at a time of elevated temperatures of the crater lake, but there was no obvious reason to link these earthquakes to the later eruption. Studies of the margins of crystals in rocks ejected from the 1995 eruptions have recently shown that fresh magma injections under Ruapehu began about the end of 1994, about the same time as the seismicity to the west. A model of the stresses under the volcano shows that deflation of a horizontal magma body, as magma started to move toward the surface, could have added to the stresses on preexisting faults and produced the earthquakes. This suggests that these earthquakes were an unrecognized precursor of the eruption.