TY - JOUR
T1 - Pressure sources beneath Unzen Volcano inferred from leveling and GPS data
AU - Kohno, Yuhki
AU - Matsushima, Takeshi
AU - Shimizu, Hiroshi
N1 - Funding Information:
We are grateful to the Joint Research Team of National Universities and to the Geographical Survey Institution for the use of their leveling data and GPS data. Comments by Dr. P. Lundgren and an anonymous reviewer helped improve the manuscript. Some figures were drawn using GMT ( Wessel and Smith, 1998 ). This work was partially supported by a grant from Kyushu University, Interdisciplinary Programs in Education and Project in Research Development (P&P No. 17052).
PY - 2008/7/30
Y1 - 2008/7/30
N2 - 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.
AB - 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.
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U2 - 10.1016/j.jvolgeores.2008.03.022
DO - 10.1016/j.jvolgeores.2008.03.022
M3 - Article
AN - SCOPUS:50049130437
VL - 175
SP - 100
EP - 109
JO - Journal of Volcanology and Geothermal Research
JF - Journal of Volcanology and Geothermal Research
SN - 0377-0273
IS - 1-2
ER -