S. Sherburn et al., SEISMICITY AT WHITE ISLAND VOLCANO, NEW-ZEALAND - A REVISED CLASSIFICATION AND INFERENCES ABOUT SOURCE MECHANISM, Journal of volcanology and geothermal research, 83(3-4), 1998, pp. 287-312
The classification of earthquakes at White Island volcano, New Zealand
, has been revised to address problems in existing classification sche
mes, to better reflect new data and to try to focus more on source pro
cesses. Seismicity generated by the direct involvement of magmatic or
hydrothermal fluids are referred to as volcanic, and that generated by
fault movement in response to stresses caused by those fluids, region
al stresses, thermal effects and so on are referred to as volcano-tect
onic. Spasmodic bursts form a separate category, as we have insufficie
nt information to classify them as volcanic or volcano-tectonic. Volca
nic seismicity is divided into short-duration, long-period volcanic ea
rthquakes, long-duration volcanic earthquakes, and harmonic- and non-h
armonic volcanic tremor, while volcano-tectonic seismicity is divided
into shallow and deep volcano-tectonic earthquakes. Harmonic volcanic
tremor is related to sub-surface intrusive processes, while non-harmon
ic volcanic tremor originates close to active craters at shallow depth
, and usually occurs during eruptive activity. Short-duration, long-pe
riod volcanic earthquakes come from a single source close to the activ
e craters, but originate deeper than non-harmonic volcanic tremor, and
are not related to eruptive activity. Long-duration volcanic earthqua
kes often accompany larger discrete eruptions. The waveform of these e
vents consists of an initial low-frequency part from a deep source, an
d a later cigar-shaped part of mixed frequencies from a shallow crater
source. (C) 1998 Elsevier Science B.V. AU rights reserved.