Pressure sources beneath Unzen Volcano inferred from leveling and GPS data

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Abstract

Unzen Volcano erupted from 1990 to 1995 and the resultant volcanic deformations were measured by GPS, leveling, tilt meter, and EDM. The largest vertical displacement observed was subsidence of 8 cm in the western part of Shimabara Peninsula. Numerous magma chamber models were proposed based on the geodesic data obtained. However, these models could not explain the volcanic deformations observed around Chijiwa Bay after the eruption had finished because previous studies only used data collected during the eruption. We therefore re-examined the magma chamber model using leveling and GPS data, and included measurements collected both during and after the eruption on leveling. We applied the Mogi Model with a height correction applied to the measuring points. There are four parameters for each source: longitude, latitude, depth, and volume change. Each source parameter was estimated using a grid-search scheme. We also used AIC (Akaike Information Criterion) to fix the number of pressure sources beneath Unzen to explain the vertical and horizontal deformations during 1986-2004. The results show that there are four pressure sources under Unzen Volcano and that magma ascended obliquely at an angle of about 45° from beneath Chijiwa Bay to the crater created by this eruption. After the eruption had stopped, magma inflows into deep sources were identified based on our leveling survey conducted after 1996. We compare our source model with several seismic data sets. Before the Unzen eruption, an earthquake swarm occurred from 1989 to 1990 in which pressure sources were detected just below the earthquake hypocenters. Other seismic refraction studies support our estimates of the location of these pressure sources. Using volume change values we inferred that magma supply had continued into this deep source at the rate of 2.0-~ 2.5 m3/yr from at least 1984 until after eruption stopped.

Original languageEnglish
Pages (from-to)100-109
Number of pages10
JournalJournal of Volcanology and Geothermal Research
Volume175
Issue number1-2
DOIs
Publication statusPublished - Jul 30 2008

Fingerprint

Volcanoes
leveling
volcanoes
Global positioning system
GPS
volcano
volcanic eruption
volcanic eruptions
magma
Earthquakes
volume change
magma chamber
Subsidence
Refraction
earthquake hypocenter
volcanology
earthquake swarm
earthquakes
chambers
Akaike information criterion

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

Cite this

Pressure sources beneath Unzen Volcano inferred from leveling and GPS data. / Kohno, Yuhki; Matsushima, Takeshi; Shimizu, Hiroshi.

In: Journal of Volcanology and Geothermal Research, Vol. 175, No. 1-2, 30.07.2008, p. 100-109.

Research output: Contribution to journalArticle

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