Mechanism of phreatic eruptions at Aso volcano inferred from near- field broadband seismic observations

Science

Volumn 273, Issue 5275, 1996, Pages 642-645

  Kaneshima, Satoshi ^a,f   Kawakatsu, Hitoshi ^a   Matsubayashi, Hirotoshi ^a   Sudo, Yasuaki ^b   Tsutsui, Tomoki ^b   Ohminato, Takao ^c   Ito, Hisao ^c   Uhira, Koichi ^d   Yamasato, Hitoshi ^e   Oikawa, Jun ^a   Takeo, Minoru ^a   Iidaka, Takashi ^a  

^a UNIVERSITY OF TOKYO   (Japan)

^b KYOTO UNIVERSITY   (Japan)

^c GEOLOGICAL SURVEY OF JAPAN   (Japan)

^d JAPAN METEOROLOGICAL AGENCY   (Japan)

^e METEOROLOGICAL RESEARCH INSTITUTE   (Japan)

^f UNIVERSITY OF BRISTOL   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

DYNAMICS; EARTHQUAKE; JAPAN; MEASUREMENT; PRIORITY JOURNAL; REVIEW; VOLCANO;

ERUPTION MECHANISM; PHREATIC ERUPTION; SEISMIC SURVEY; VOLCANIC ERUPTION;

JAPAN, KYUSHU, ASO VOLCANO;

EID: 0029659887     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.273.5275.642     Document Type: Review

References (37)

1. R. Y. Koyanagi et al., Volcanism in Hawaii (Government Printing Office, Washington, DC, 1987), pp. 1221-1257.
2. K. Kamo and K. Ishihara, Bull. Disaster Prev. Res. Inst. 29B, 1 (1986); A. T. Linde et al., Nature 365, 737 (1993).
3. K. Kamo and K. Ishihara, Bull. Disaster Prev. Res. Inst. 29B, 1 (1986); A. T. Linde et al., Nature 365, 737 (1993).
4. So-called single-force models have been applied to explain long-period seismic wave forms attributable to such mass advection at different volcanoes of the world [H. Kanamori and J. W. Given, J. Geophys. Res. 87, 5422 (1982); K. Uhira and M. Takeo, ibid. 99, 17775 (1994)]. Recent advances in seismometry have now made such observations rather straightforward; portable equipment covering a wide frequency band (50 to 0.01 Hz) can be easily installed at volcanoes, and the broadband nature of volcanic activity is becoming increasingly clear [H. Kawakatsu et al., Geophys. Res. Lett. 19, 1959 (1992); T. Ohminato et al., Eos 74, 648 (1993); R. Dreier et al., Acta Vulcanol. 5, 165 (1994); S. Falsaperta et al., ibid., p. 173; J. Neuberg et al., Geophys Res. Lett. 21, 749 (1994); P. Hellweg et al., Eos 75, 313 (1994)].
5. So-called single-force models have been applied to explain long-period seismic wave forms attributable to such mass advection at different volcanoes of the world [H. Kanamori and J. W. Given, J. Geophys. Res. 87, 5422 (1982); K. Uhira and M. Takeo, ibid. 99, 17775 (1994)]. Recent advances in seismometry have now made such observations rather straightforward; portable equipment covering a wide frequency band (50 to 0.01 Hz) can be easily installed at volcanoes, and the broadband nature of volcanic activity is becoming increasingly clear [H. Kawakatsu et al., Geophys. Res. Lett. 19, 1959 (1992); T. Ohminato et al., Eos 74, 648 (1993); R. Dreier et al., Acta Vulcanol. 5, 165 (1994); S. Falsaperta et al., ibid., p. 173; J. Neuberg et al., Geophys Res. Lett. 21, 749 (1994); P. Hellweg et al., Eos 75, 313 (1994)].
6. So-called single-force models have been applied to explain long-period seismic wave forms attributable to such mass advection at different volcanoes of the world [H. Kanamori and J. W. Given, J. Geophys. Res. 87, 5422 (1982); K. Uhira and M. Takeo, ibid. 99, 17775 (1994)]. Recent advances in seismometry have now made such observations rather straightforward; portable equipment covering a wide frequency band (50 to 0.01 Hz) can be easily installed at volcanoes, and the broadband nature of volcanic activity is becoming increasingly clear [H. Kawakatsu et al., Geophys. Res. Lett. 19, 1959 (1992); T. Ohminato et al., Eos 74, 648 (1993); R. Dreier et al., Acta Vulcanol. 5, 165 (1994); S. Falsaperta et al., ibid., p. 173; J. Neuberg et al., Geophys Res. Lett. 21, 749 (1994); P. Hellweg et al., Eos 75, 313 (1994)].
7. So-called single-force models have been applied to explain long-period seismic wave forms attributable to such mass advection at different volcanoes of the world [H. Kanamori and J. W. Given, J. Geophys. Res. 87, 5422 (1982); K. Uhira and M. Takeo, ibid. 99, 17775 (1994)]. Recent advances in seismometry have now made such observations rather straightforward; portable equipment covering a wide frequency band (50 to 0.01 Hz) can be easily installed at volcanoes, and the broadband nature of volcanic activity is becoming increasingly clear [H. Kawakatsu et al., Geophys. Res. Lett. 19, 1959 (1992); T. Ohminato et al., Eos 74, 648 (1993); R. Dreier et al., Acta Vulcanol. 5, 165 (1994); S. Falsaperta et al., ibid., p. 173; J. Neuberg et al., Geophys Res. Lett. 21, 749 (1994); P. Hellweg et al., Eos 75, 313 (1994)].
8. So-called single-force models have been applied to explain long-period seismic wave forms attributable to such mass advection at different volcanoes of the world [H. Kanamori and J. W. Given, J. Geophys. Res. 87, 5422 (1982); K. Uhira and M. Takeo, ibid. 99, 17775 (1994)]. Recent advances in seismometry have now made such observations rather straightforward; portable equipment covering a wide frequency band (50 to 0.01 Hz) can be easily installed at volcanoes, and the broadband nature of volcanic activity is becoming increasingly clear [H. Kawakatsu et al., Geophys. Res. Lett. 19, 1959 (1992); T. Ohminato et al., Eos 74, 648 (1993); R. Dreier et al., Acta Vulcanol. 5, 165 (1994); S. Falsaperta et al., ibid., p. 173; J. Neuberg et al., Geophys Res. Lett. 21, 749 (1994); P. Hellweg et al., Eos 75, 313 (1994)].
9. So-called single-force models have been applied to explain long-period seismic wave forms attributable to such mass advection at different volcanoes of the world [H. Kanamori and J. W. Given, J. Geophys. Res. 87, 5422 (1982); K. Uhira and M. Takeo, ibid. 99, 17775 (1994)]. Recent advances in seismometry have now made such observations rather straightforward; portable equipment covering a wide frequency band (50 to 0.01 Hz) can be easily installed at volcanoes, and the broadband nature of volcanic activity is becoming increasingly clear [H. Kawakatsu et al., Geophys. Res. Lett. 19, 1959 (1992); T. Ohminato et al., Eos 74, 648 (1993); R. Dreier et al., Acta Vulcanol. 5, 165 (1994); S. Falsaperta et al., ibid., p. 173; J. Neuberg et al., Geophys Res. Lett. 21, 749 (1994); P. Hellweg et al., Eos 75, 313 (1994)].
10. So-called single-force models have been applied to explain long-period seismic wave forms attributable to such mass advection at different volcanoes of the world [H. Kanamori and J. W. Given, J. Geophys. Res. 87, 5422 (1982); K. Uhira and M. Takeo, ibid. 99, 17775 (1994)]. Recent advances in seismometry have now made such observations rather straightforward; portable equipment covering a wide frequency band (50 to 0.01 Hz) can be easily installed at volcanoes, and the broadband nature of volcanic activity is becoming increasingly clear [H. Kawakatsu et al., Geophys. Res. Lett. 19, 1959 (1992); T. Ohminato et al., Eos 74, 648 (1993); R. Dreier et al., Acta Vulcanol. 5, 165 (1994); S. Falsaperta et al., ibid., p. 173; J. Neuberg et al., Geophys Res. Lett. 21, 749 (1994); P. Hellweg et al., Eos 75, 313 (1994)].
11. So-called single-force models have been applied to explain long-period seismic wave forms attributable to such mass advection at different volcanoes of the world [H. Kanamori and J. W. Given, J. Geophys. Res. 87, 5422 (1982); K. Uhira and M. Takeo, ibid. 99, 17775 (1994)]. Recent advances in seismometry have now made such observations rather straightforward; portable equipment covering a wide frequency band (50 to 0.01 Hz) can be easily installed at volcanoes, and the broadband nature of volcanic activity is becoming increasingly clear [H. Kawakatsu et al., Geophys. Res. Lett. 19, 1959 (1992); T. Ohminato et al., Eos 74, 648 (1993); R. Dreier et al., Acta Vulcanol. 5, 165 (1994); S. Falsaperta et al., ibid., p. 173; J. Neuberg et al., Geophys Res. Lett. 21, 749 (1994); P. Hellweg et al., Eos 75, 313 (1994)].
12. Seismic signals were recorded continuously with portable data loggers either on digital tapes, hard disks, or magneto-optical disks, with a sampling rate of 20 Hz and dynamic range of either 16 or 24 bits. Recorder clocks were either locked with GPS (Global Positioning System) or adjusted by radio time signals, providing accurate enough timing for later analyses of long-period signals.
13. Disturbances commonly called long-period events at volcanoes are in the period range 0.2 to 2 s [B. J. Chouet, Nature 380, 309 (1996)].
14. Long-period seismometers installed at the Aso volcano 60 years ago revealed the presence of long-period (3.5 to 7 s) volcanic tremors [K. Sassa, Mem. Coll Sci. Kyoto Univ. Ser. A 18, 255 (1935)]. The observation of long-period volcanic tremors has been repeatedly reported [M. Churei, Bull. Volcanol. Soc. Jpn. 30, 71 (1985); T. Hashida, ibid. 35, 323 (1990); H, Kawakatsu et al., Geophys. Res. Lett. 21, 1963 (1994)], but those observations have fallen short of unraveling their origin because of the limited number of instruments near the crater.
15. Long-period seismometers installed at the Aso volcano 60 years ago revealed the presence of long-period (3.5 to 7 s) volcanic tremors [K. Sassa, Mem. Coll Sci. Kyoto Univ. Ser. A 18, 255 (1935)]. The observation of long-period volcanic tremors has been repeatedly reported [M. Churei, Bull. Volcanol. Soc. Jpn. 30, 71 (1985); T. Hashida, ibid. 35, 323 (1990); H, Kawakatsu et al., Geophys. Res. Lett. 21, 1963 (1994)], but those observations have fallen short of unraveling their origin because of the limited number of instruments near the crater.
16. Long-period seismometers installed at the Aso volcano 60 years ago revealed the presence of long-period (3.5 to 7 s) volcanic tremors [K. Sassa, Mem. Coll Sci. Kyoto Univ. Ser. A 18, 255 (1935)]. The observation of long-period volcanic tremors has been repeatedly reported [M. Churei, Bull. Volcanol. Soc. Jpn. 30, 71 (1985); T. Hashida, ibid. 35, 323 (1990); H, Kawakatsu et al., Geophys. Res. Lett. 21, 1963 (1994)], but those observations have fallen short of unraveling their origin because of the limited number of instruments near the crater.
17. Long-period seismometers installed at the Aso volcano 60 years ago revealed the presence of long-period (3.5 to 7 s) volcanic tremors [K. Sassa, Mem. Coll Sci. Kyoto Univ. Ser. A 18, 255 (1935)]. The observation of long-period volcanic tremors has been repeatedly reported [M. Churei, Bull. Volcanol. Soc. Jpn. 30, 71 (1985); T. Hashida, ibid. 35, 323 (1990); H, Kawakatsu et al., Geophys. Res. Lett. 21, 1963 (1994)], but those observations have fallen short of unraveling their origin because of the limited number of instruments near the crater.
18. One of the possible mechanisms generating the LPT may be resonance of a vertical crack filled with fluid [B. J. Chouet, J. Geophys. Res. 91, 13967 (1986); V. Ferrazzini and K. Aki, ibid. 92, 9215 (1987)]. The presence of waves trapped in the crack that propagate with a phase velocity much slower than the sound velocity of the fluid - the so called "crack wave" - has been proposed. Consideration of the crack wave would greatly reduce the estimate of the size of the resonator.
19. One of the possible mechanisms generating the LPT may be resonance of a vertical crack filled with fluid [B. J. Chouet, J. Geophys. Res. 91, 13967 (1986); V. Ferrazzini and K. Aki, ibid. 92, 9215 (1987)]. The presence of waves trapped in the crack that propagate with a phase velocity much slower than the sound velocity of the fluid - the so called "crack wave" - has been proposed. Consideration of the crack wave would greatly reduce the estimate of the size of the resonator.
20. N. Neidel and M. T. Tarner, Geophysics 36, 483 (1971). To improve the resolution of source depth, we extended conventional single-component semblance analyses to three-component wave forms [H. Matsubayashi, thesis, Tokyo University (1995)].
21. N. Neidel and M. T. Tarner, Geophysics 36, 483 (1971). To improve the resolution of source depth, we extended conventional single-component semblance analyses to three-component wave forms [H. Matsubayashi, thesis, Tokyo University (1995)].
22. Moment tensor inversion of LPT wave forms gives a best point source solution corresponding to a combination of isotropic expansion (contraction) and inflation (deflation) of a vertical crack aligned from north-northwest to south-southeast, parallel or sub-parallel to the chain of older craters (Fig. 1). A LPT source with a finite extent can be approximated by a summation of point sources. As long as we retain the above moment tensor solution throughout the source, LPT amplitudes at the stations located northeast or southwest of the crater (KHE and AWS) are greatly increased by putting point sources near these stations, and particle motions at these stations become too steep to match the observations, which may indicate that the effective extent of the LPT source does not exceed several hundred meters from the center of the crater.
23. S. Kikuchi, Bull. Disaster Prev. Res. Inst. 17B, 1 (1974).
24. The meteorological station at Aso reported that the ash and smoke went up as high as 1 km when one of the eruptions took place at 06:31 (GMT) on 15 September. Shock waves were not reported for any of the eruptions. At the largest eruptions, ejecta of fragmented rocks ascended to a height of nearly 150 m above the crater lake, with corresponding initial velocities of the order of 50 m/s. The velocities of the steam that entrained those solid ejecta is bounded by the sound velocity in the atmosphere (330 m/s) and that of solid ejecta.
25. The presence of many different kinds of short-period tremors are known at Aso volcano (6), and here we specifically call the kind associated with phreatic eruptions SPT. Note also that the short-period tremors that we call SPTs here may be referred to as long-period events or tremors at other volcanoes (5).
26. G. S. Steinberg and A. S. Seinberg, J. Geophys. Res. 80, 1600 (1975).
27. Larger eruptions tend to excite larger pressure waves at the time of mass ejection, which is recorded at a microbarograph near the crater (Fig.1), although the correlation is rather weak.
28. K. Mogi, Bull. Earthquake Res. Inst. 36, 99 (1958).
29. If we assume a radius of 200 (± 92) m for the spherical source, the pressure change is on the order of 0.1 (± 1.0) MPa for typical large eruptions, which amounts to about 0.5 (± 5.0)% of the lithostatic pressure (20 MPa).
30. Y. Tanaka, J. Volcanol. Geotherm. Res. 2, 319 (1993).
31. K. Wohletz and G. Heiken, Volcanology and Geothermal Energy (Univ. of California Press, Berkeley, 1992).
32. S. W. Kiefer and B. Sturtevant, J. Geophys. Res. 89, 8523 (1984).
33. S. W. Kiefer, ibid. 82, 2895 (1977).
34. o ≈ 100 m/s in the conduit and V/A may be approximated with the length of the conduit, 1000 m, the duration of the flow would be 40 to 50 s, which is close to the observed values. The temperature below the crater at Aso is poorly known, but the above scenario would be rather insensitive to the details of temperature profiles.
35. o (19), corresponding to a larger SPT amplitude.
36. T. Gold and S. Soter, Pure Appl. Geophys. 122, 492 (1985).
37. We thank Aso meteorological station for allowing us to deploy our instruments at its observation sites and for providing various data on the surface activity of Aso volcano. B. Chouet provided helpful comments on an earlier version of the manuscript. R. J. Geller critically reviewed the manuscript.