Active Source Seismic Experiment in Asama Volcano, Japan: The Outline of the Experiment and First Arrival

Bull. Earthq. Res. Inst. Univ. Tokyo Vol. 2-,**2 pp. +,0 : + +, -. / 0 * 1 2 3 + + / +* ++ +, +- +. + + + + +/ + + + + + + 1 +, / +0 1. P.K.B. Alanis T. Anggono +1 +2 +3 +2 2,*,+ +- /,,,- +3,+ +, +. 2 +- +*.,. +2 0 +1 ++ 3 +, -. / 0 1 2 3 +* ++ +, +- +. +/ +0 +1 +2 +3,*,+,,,-,. Active Source Seismic Experiment in Asama Volcano, Japan: The Outline of the Experiment and First Arrival Times + +, -. / 0 Y. Aoki *, M. Takeo, H. Tsuji, E. Koyama, H. Aoyama, J. Fujimatsu, S. Matsumoto, 1 2 3 + + / H. Miyamachi, H. Nakamichi, T. Ohkura, T. Ohminato, J. Oikawa, R. Tanada, T. +* ++ +, +- +. + Tsutsui, K. Yamamoto, M. Yamamoto, H. Yamasato, T. Yamawaki, M. Ichihara, + + + +/ + + + Y. Imoto, T. Kazama, T. Koyama, Y. Maeda, F. Maeno, Y. Morita, S. Nakada, S. + + + 1 +, / Nakamula, N. Osada, H. Watanabe, P.K.B. Alanis, T. Anggono, Y. Fujiwara, Y. +0 1. +1 +2 +3 Fukuyama, S. Hagiwara, T. Hashimoto, S. Hirano, K. Horiguchi, S. Iijima, Y. +2 2,*,+ +- / Ishihara, K. Ishikawa, K. Ishizaka, Y. Kitawaki, H. Kuroki, F. Kusano, T.,,,- +3,+ +, +. Maekawa, Y. Masuda, T. Matsumura, M. Nakamoto, T. Nishimura, K. Nogami, 2 +- +*.,. +2 0 T. Okuda, T. Sakai, M. Sato, A. Suzuki, G. Tange, S. Ueki, A. Watanabe, H. Yakiwara, Y. Yamazaki, S. Yoshikawa +1 ++ 3 +, Earthquake Research Institute, University of Tokyo, Komoro Observatory of Volcano-Chemistry, Earthquake Research Institute, University of Tokyo, Asama Volcano Observatory of Earth- -. quake Research Institute, University of Tokyo, Institute of Seismology and Volcanology, Hokkaido University, Seismological and Volcanological Department, Japan Meteorological Agency, / 0 1 Institute of Seismology and Volcanology, Kyushu University, Department of Earth and Environmental Sciences, Kagoshima University, Research Center for Seismology, Volcanology, and 2 Disas- * e-mail: yaoki@eri.u-tokyo.ac.jp ++- **-, + + + 1

3 +* ter Mitigation, Nagoya University, Aso Volcanological Laboratory, Kyoto University, Faculty of ++ Engineering and Resource Science, Akita University, Sakurajima Volcano Research Center, +, Disaster Prevention Research Institute, Kyoto University, Department of Geophysics, Tohoku +- University, Seismology and Volcanology Research Department, Meteorological Research Insti- +. +/ tute, Volcanic Fluid Research Center, Tokyo Institute of Technology, Department of Earth and +0 Planetary Sciences, Tokyo Institute of Technology, Sapporo District Meteorological Observatory, +1 Japan Meteorological Agency, Nansei-Toko Observatory for Earthquakes and Volcanoes, Kagoshima University, Research Center for Prediction of Earthquakes and Volcanic +2 Eruptions, +3,* Tohoku University Karuizawa Weather Station, Japan Meteorological Agency, Department of,+ Earth Sciences, Kumamoto University, Department of Earth and Planetary Sciences, Kyushu,, University, Usu Volcano Observatory, Institute of Seismology and Volcanology, Hokkaido Uni-,-,. versity, Fukuoka District Meteorological Observatory, Japan Meteorological Agency, Sendai District Meteorological Observatory, Japan Meteorological Agency Abstract In order to investigate the subsurface seismic structure beneath Asama Volcano, Japan, an active seismic experiment was conducted in October,,**0 with 0* participants from nine national universities and Japan Meteorological Agency as the +, th joint experiment under the National Project for Prediction of Volcanic Eruptions. The experiment was conducted by recording seismic waves exerted from five dynamite shots with charges of,/*.-** kg. The seismic waves were recorded by.0. seismometers with a natural frequency of, Hz and,+* seismometers with a natural frequency of./. Hz and data loggers temporally deployed around Asama Volcano. To reveal the P-wave velocity structure, +2-3 useful arrival times were picked from the seismograms. Observed data suggests that the subsurface structure is likely to be highly heterogeneous and seems to be consistent with previous geophysical and geological studies. Key words : Asama Volcano, Seismic exploration, Seismic velocity structure, National Project for Prediction of Volcanic Eruption + +31/,**- +31-, +32,, +32-,,**. Takeo Fig. + *. 2 et al.,**0,**. +*. Ma *-. *.. Ma GPS *.. Ma *2. Ma,**. *.. Ma + km Fig. + Aramaki +30- Ogawa et al.,**0 +,,,*** km, km,**/,**/ GPS +/,*** Fig. + Ogawa et +/,*** al.,**0 +* km ++*2 +12-,* +30* 2

: Fig. +. Locations of shots (stars) and temporal seismic sites (dots). The red triangle represents the location of Asama Volcano. Black trangles and the square denote Eboshi Volcano Group, Kurofu Volcano, and the Hotokeiwa lava, respectively. Sawada, +33., Fujita and Ida, +333, Aoyama and Takeo,,**+ P,**/,**. +** -** -, Fig. + + km Takeo et al.,,**0 Minakami et al. +31* +32- P Aoyama and Takeo,,**+,**/ 3

GPS +/* m T L Table, - Fig., -. S +, S -, S/ +** m Fig. / 0 1 S,S,S, -. Mark Products L-,, D, Hz, kw * *1. 0kms DataMark LS-2*** SH +330. ms,/* Hz +0 bit S,S,S -. /, S,S +, +, km GPS S-,/* kg / +* m Table + -** kg.0. -3. + 1* - Takeo et al.,**0 S- 2km Fig. -* m Geo Space GS-++ D../ Hz, +, km Fig. 0 2 km. kw LS-2,**,**0 ms,/* Hz,. bit P. GPS *+. */. m,+* +,**2 / Fig. + Table, +* ms A +* -* ms -* +** ms +**,** +.0 mm S- /* m ms B, C, D 0* m L ++..- mm../ mm +33/ +330 A, B, C, D,**0 +* +- +, +.3/ 0/,.0-,, /,/* kg S -,,3 +, 2-3 -** kg Table, Table - + ms + khz Fig. 2 +* +, km 4

: Table +. Site codes and coordinates. Latitude and longitude are based on the WGS2. reference frame. In the Component column, U, E, and N stand for the vertical, east-west, and north-south components, respectively. In the Line column, NS and EW show that the site is on the northsouth line and east-west line, respectively. 5

Table +. (Continue) 6

: Table +. (Continue) 7

: Table +. (Continue) Table,. Locations, times, and sizes of explosions. Latitude and Longitude are based on the WGS-2. reference frame. Shot times are based on Japanese Standard Time. 13

Fig... Unfiltered record sections on the NS line for S /. Each trace is normalized by its maximum amplitude and reduced by 0kms. The horizontal and vertical axis represents the reduced time from the shot time and the horizontal distance from each shot point, respectively. Fig.,. Record sections on the NS line for S +. Each trace is normalized by its maximum amplitude and reduced by 0 kms. The horizontal and vertical axis represents the reduced time from the shot time and the horizontal distance from each shot point, respectively. Fig. -. Unfiltered record sections on the NS line for S -. Each trace is normalized by its maximum amplitude and reduced by 0kms. The horizontal and vertical axis represents the reduced time from the shot time and the horizontal distance from each Fig. /. Unfiltered record sections on the EW line for shot point, respectively. S,. Each trace is normalized by its maximum amplitude and reduced by 0kms. The horizontal and vertical axis represents the reduced time from the shot time and the horizontal distance from each shot point, respectively. +* +, km P //. 0kms 14

: Fig. 3 / km / km S +, S., S/, kms S,, S-, km, kms - kms S +, S., S/ S,, S- Fig. 0. Unfiltered record sections on the EW line for S -. Each trace is normalized by its maximum amplitude and reduced by 0kms. The horizontal and vertical axis represents the reduced time from the shot time and the horizontal distance from each shot point, respectively..,**0 +* P Fig. 1. Unfiltered record sections on the EW line for S.. Each trace is normalized by its maximum amplitude and reduced by 0kms. The horizontal and vertical axis represents the reduced time from the shot time and the horizontal distance from each shot point, respectively. Asama,*** +/ 15

Table -. Travel times and polarities of first arrivals for each shot. Code represents the station code. T represents the arrival time. P represents the polarization of each first arrival; indicates the upward motion of the first arrival. R represents the precision of the first arrival picks ; A, B, C, and D correspond to an arrival time uncertainty of less than +* ms, between +* and -* ms, between -* and +** ms, and between +** and,** ms, respectively, and L corresponds to an arrival with uncertain polarity. 16

: Table -. (Continue) 17

Table -. (Continue) 18

: Fig. 2. Travel times for all shots. Fig. 3. Travel time plots for (a) S +, (b) S,, (c) S -, (d) S., and (e) S /. Travel times are reduced by 0kms. 25

,**/,**.,**/ /* /1/ /2.. Aoyama, H. and M. Takeo,,**+, Wave properties and focal mechanisms of N-type earthquakes at Asama volcano, J. Volcanol. Geotherm. Res., +*/, +0- +2,. Aramaki, S., +30-, Geology of Asama Volcano, J. Fac. Sci. Univ. Tokyo, sec. II, +.,,,3..-. Fujita, E. and Y. Ida, +333, Low attenuation resonance of a spherical magma chamber : source mechanism of monotonic volcanic tremor at Asama Volcano, Japan, Geophys. Res. Lett.,,0, -,,+ -,,.. +33/ 1* -, /3.,**0 /3 +*1 ++0.,**- 12,2-.0-. +330.+ +,1 +-3. Minakami, T., S. Utibori, S. Hiraga, T. Miyazaki, N. Gyoda and T. Utsunomiya, +31*, Seismometrical studies of volcano Asama Part,. Anomalous distribution of the P arrival times and some information of the velocity of the P wave propagating through the volcano, Bull. Earthq. Res. Inst.,.2,.-+.23.,**/ GPS /* -.1-0+. Ogawa, Y., K. Aizawa, T. Hashimoto, T. Koyama and Asama Volcano EM field experiment group,,**0, Resistivity structure across the dyke intrusion of Asama volcano, +2th Electromagnetic Induction Workshop, El Vendrell, Spain. Sawada, M., +33., B-type and explosion earthquakes observed at Asama volcano, central Japan, J. Volcanol. Geotherm. Res., 0-, +++ +,2. +32- P,2 -*+ -*.. +31/ +31- /* ++/ +/+.,**..3 2- +*,. Takeo, M., Y. Aoki, T. Ohminato and M. Yamamoto,,**0, Magma supply path beneath Mt. Asama volcano, Japan, Geophys. Res. Lett., --, L +/-+*, doi: +*. +*,3 /,**0GL *,0,.1. +330.+,,1,.+.,**2 : 2-,1.+.,**/,**. /* -3-.**. Received June +2,,**1 Accepted January 1,,**2 26