京都大学防災研究所年報第 号 B 平成 年 月 Annuals of Disas. Prev. es. Inst., Kyoto Univ., No. B, 9 8 9 Yokoo and Ishihara, 7;, 8, 8a Tameguri et al. () Iguchi et al. (8), 8a 7 8 3 o 3 3 o 39 3 o. km 3 o 3 3. kmku 9.3 kmam Pa HA Showa crater KU 3 Figs. and 9 33 AM km m km Fig. 3 93 km, 9 Fig. Map of Sakurajima volcano with infrasound and seismic stations of AM and HA (solid symbols), respectively. A white symbol labeled by KU denote a station equiped with visible and infrared video monitoring systems. 8 39
cloud temp( o C) 3 / / 7/ / / / 7/ / / 7/ / / / 7/ (8) (9) date (MM/DD) no data Fig. Temporal changes in the recent. years of cloud temperatures measured by an infrared thermal camera from KU (upper) and peak amplitudes of infrasound waves recorded at AM (lower). Gray colored periods indicate the occurrences of eruptions at Showa crater (data was obtained until the end of May 9). No thermal data was obtained since May, 9, due to maintenance of the observatory itself at KU. Ishiahra (98) Yokoo et al. (8) Ishihara (98) 3 km. Tameguri et al., Yokoo et al. (8) Fig. 3 Snapshots of the explosive eruption occurred at Showa crater at :3 on May 3, 9, which were captured from the internet streaming video of Kyushu egional Development Bureau, MLIT. A picture of upper left (a view from Nojiri, southwest of Sakurajima) was unfortunately captured at the different time of the eruption due to a failure of our system. KDB holds the copyright of these pictures.. m 3 3, 8b; 9, 8 8, 8 9 8 3
(a) (b) (c) - - - 3 time (7::ss) - - - 3 3 time (:8:ss) - - - 3 3 time (::ss) - 9.... time (7::ss) - 7. 8. 9.. time (:8:ss) -. 7. 8. 9. time (::ss) velocity ( - m/s) velocity ( - m/s) velocity ( - m/s) - - - 3 time (7::ss) - - - 3 3 time (:8:ss) - - - 3 3 time (::ss) - - -... 7. time (7::ss) - - -. 3... time (:8:ss) - - -.. 3.. time (::ss) (d) - - - 3 3 time (::ss) -. 3... time (::ss) velocity ( - m/s) - - - 3 3 time (::ss) - - - 7. 8. 9.. time (::ss) Fig. Infrasound and seismic waveforms observed at AM (two columns at left-handed side) and HA (those at right one), respectively; Events at (a) 7: on February 3, (b) :8 on April, (c) : on March, and (d) : on March. Close-up waveforms of each initial part with a fixed time window of 3 s are also displayed. AM HA Fig. AM.Hz, 338/7HA bita/d Hz AM 3AM.3 kmha 3. km 9 S/N Fig., 999, ; Yokoo et al., 8 Pa Fig. 3 Fig. [] no preceding 3
infrasound seismic (vertical) seismic (radial) (a) 3 - - -3 -. - -. - -..... -. - -. st nd pseudo-lp - -3 -. - -. - -..... -. - st nd pseudo-lp -. -3 -. - -. - -... (b) 3 - - -3 -. - -. - -..... -. - -. st nd pseudo-lp - -3 -. - -. - -..... -. - st nd pseudo-lp -. -3 -. - -. - -... (c) 3 -.. -. - -. st nd pseudo-lp.. -. - st nd pseudo-lp - -3 -. - -. - -... - -3 -. - -. - -... -. -3 -. - -. - -... (d) 3 -.. -. - -. P+D LP.. -. - P+D LP - -3 -. - -. - -... - -3 -. - -. - -... -. -3 -. - -. - -... Fig. Stacked waveforms of infrasound and seismic signals (vertical and radial components) drawn by gray lines and their average responses by black lines. Infrasound waveforms were categorized into three types with (a) no preceding ( events), (b) normal preceding (37 events), and (c) stagnated or pulse-like preceding phases (33 events). Nine events of the recent summit eruptions are also displayed by the same manner in (d). Figs. a and a7 Pa [] normal preceding37 Figs. b and b3 Pa [3] stagnated or pulse-like preceding33 Fig. c Fig. d Fig. c 98 Pa Fig. AM [][][3] Fig. [] [3] SONY SSC-E.AGCKU 3
(a) st nd pseudo-lp no preceding normal preceding stagnated or pulse-like preceding (b) st nd pseudo-lp... time difference (s) Fig. elation between time difference of arrival times between a preceding and a main phase of infrasound waves at AM, and peak amplitudes of a (c) st nd pseudo-lp main phase of them. 3 Fig. 3 HA m LP Tameguri et al., LP AM.8 LPHA.3 LP 3 Fig. Fig. 7 3 3 Fig. - (d) P+D LP Fig. 7 Particle motions of each phase of the averaging seismic responses in Fig.. PFig. 7[3] Fig. 7c..8[][][3] Fig. [][][3] Fig. 7 [] [][3] 3LP Fig. [][] [3] Fig. 7 [] Fig. alp 33
[][3] LP Yokoo et al. (8) 97 7 AM HA.7Figs. d and 7d.3 Yokoo et al., 8 Tameguri et al. () PDLP P D PD.8Fig. dpd- PFig. 7dLP Fig. d LP P- Fig. 7 8, 8 3 Figs. and LP Fig. LP P+DLP P Fig. 7 3 Fig. LP LP 3
9 HA AM Fig. 3 9 (9): 3, 3, pp. -. (8):, 9, pp. 3-3. (999):,, ol. 33B, pp. -. (8a):,, pp.-8. (8b):, 8, pp. 78-78. (9):, 9 CD-OM, 9-3. ():,, pp. -. (8):,, pp. 9-. (8): 7,, ol. B, pp. 7-73. Iguchi, M., Yakiwara, H., Tameguri, T., Hendrasto, M. and Hirabayashi, J. (8): Mechanism of explosive eruption revealed by geophysical observations at the Sakurajima, Suwanosejima and Semeru olcanoes, J. olcanol. Geotherm. es., ol. 78, pp. -9, doi:./j.jvolgeores.7.. Ishihara, K. (98): Dynamic analysis of volcanic explosion, J. Geodyn., ol. 3, pp. 37-39. Tameguri, T., Iguchi, M. and Ishihara, K. (): Mechanism of explosive eruption from moment tensor analysis of explosion earthquakes at Sakurajima olcano, Japan, Bull. olcanol. Soc. Japan, ol. 9, pp. 97-. Yokoo, A. and Ishihara, K. (7): olcanic activity around Showa crater of Sakurajima olcano monitored with infrared and video cameras, Annuals of Disas. Prev. es. Inst., Kyoto Univ., ol. C, pp. 9-. Yokoo, A., Tameguri, T. and Iguchi, M. (8): Swelling of a lava plug associated with a ulcanian eruption at Sakurajima olcano, Japan, as revealed by infrasound record: case study of the eruption on January, 7, Bull. olcanol., doi:.7/s-8-7- Table A AM 3
Table A List of eruptions at Showa crater in 9 analyzed in the present study type of infrasound date (mm/dd) time (hh:mm) peak amplitude at AM (Pa) no preceding / 9: 3. (shock) / 9:7 78. / : 3. / :9. /3 7: 9.9 3/8 : 3. 3/8 :.9 / : 73.8 /3 : 3. /3 9:.9 / 9:. normal / :.3 preceding / 8:3 8. / : 3. / :7 39.8 / : 7. /3 :3. / :.7 3/ 7:3 79. 3/3 : 78. 3/8 9:. 3/8 9: 3. 3/8 :3.3 / :8.3 / 7:39. / 9: 3. / :3.9 /3 8:. /3 9: 7.8 /3 9:7 8. /3 9:3 3. /3 :9 33. /3 : 7.7 /3 :8 89.7 /3 8:37 3.7 /3 9:. /3 9:9. / :7 3. / 3:7 3. / :7 3. / 8:37. / :9. / : 7. Table A (continued) type of infrasound date (mm/dd) time (hh:mm) peak amplitude at AM (Pa) normal / : 89. preceding / 7:3.8 / : 8. / 7:. /9 :3 8.8 stagnated or / 7:7 8.7 pulse-like /3 :9 9.3 preceding / :.7 / 7: 3. 3/7 : 3. 3/8 : 39. 3/9 :3.9 3/9 3:3 7.9 3/9 3: 3.9 3/ : 8. 3/ :3. 3/ :.9 3/ : 99. 3/ 8: 8. 3/ : 9.9 / 3:7 3. / :9. / 7: 9.8 / 7:3 7.3 / 8:3 7.9 /3 3: 9.7 /3 :8.8 /3 3:3 7. /3 : 3. /3 : 7. /3 :. /3 : 3.8 / 3:8 77.9 / :7.9 / :3 33.9 / :.7 / 8:7 8.3 / 9:. 3
Characteristics of Infrasound and Seismic Signals Associated with Eruptions at Showa Crater of Sakurajima olcano Akihiko YOKOO* and Takeshi TAMEGUI * JSPS esearch Fellow Synopsis We investigated the characteristics of observed infrasound and seismic records associated with 8 eruptions at Showa crater of Sakurajima volcano that occurred during the period from February to April 9, 9. From a staking procedure of infrasound records, three types of the preceding phase were clearly recognized as no preceding type, normal preceding type and stagnated or pulse-like preceding type, prior to the onset of the main impulsive phase. On the other hands, applying same method to seismic records, three characteristic phases could be identified in the initial part; the first one was the P wave which would produced at a deeper portion of the volcano and the third one was the ayleigh wave as same as the LP phase of explosion earthquake of the summit explosion. However, the second phase of the ayleigh wave have not been observed at the summit eruptions, which would become a key feature for understanding eruption processes of Showa crater. Keywords: Sakurajima volcano, Showa crater, infrasound wave, seismogram, stacking, eruption mechanisms 37