Earth Planets Space, Vol. 56 (No. 10), pp. e29-e32, 2004E-LETTER
Yousuke Miyagi1, Jeffrey T. Freymueller2, Fumiaki Kimata3, Toshiya Sato4, and Dörte Mann5
1Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University, N10W8 Kita-ku, Sapporo 060-0810, Japan
2Geophysical Institute, University of Alaska, Fairbanks, Fairbanks, Alaska 99775-7320, USA
3Research Center for Seismology and Volcanology, Graduate School of Environmental Studies, Nagoya University, Furou-cho, Chikusa-ku, Nagoya 464-8602, Japan
4Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
5Department of Geophysics, Stanford University, Stanford, CA 94305-2215, USA
(Received April 28, 2004; Revised August 31, 2004; Accepted September 2, 2004)
Annual GPS campaigns were carried out at Okmok volcano in the Aleutian Islands, Alaska, between 2000 and 2002. Surface deformation detected by these measurements reveals that Okmok volcano has been inflating over these 3 years at a variable inflation rate. The horizontal displacements show a radial outward pattern, and there has been significant uplift of the caldera center. The uplift of the caldera center relative to the caldera rim was ∼2.1 cm during 2000-2001, and ∼6.7 cm during 2001-2002. The latter rate is quite consistent with that deduced from InSAR measurements spanning 1997-2000, but the deformation rate during 2000-2001 was much slower than during the preceding and succeeding periods. Shallow pressure source was inferred at a depth of ∼3.1 km beneath the approximate center of the caldera. The location of the source, ∼5 km laterally from the active vent, is consistent with that inferred from InSAR data during 1997-1998. The total increase in volume during 2000-2002 of the inferred source is ∼044 × 107m3, which is 3-8% of the amount of volume erupted in 1997. The GPS and InSAR data show that magma accumulation beneath Okmok was steady in rate and location during 1997-2002, except for a pause at some time between 2000 and 2001.
Key words: Okmok, GPS campaign, significant inflation, shallow magmatic activity.