III. Geophysical Study

The works on volcano physics done in the last 4 years in Japan are summarized according to the following five categories. (1) volcano earthquake and tremor events, (2) structure of volcanoes, (3) monitoring of volcanic activity, (4) physical process of volcanoes, (5) new technology and instrumentation.

Volcano Earthquake and Tremor Events

Various types of vibration observed in volcanoes stimulated many works on volcanic earthquake and tremor events. Long period earthquakes (LP earthquakes), among them, are intensively studied in the last 4 years. Observations using broadband seismographs are made to search for unknown phenomena which cannot be detected with short-period sensors (Kaneshima et al., 1996; Ohminato and Ereditato, 19 97; Tsuruga et al., 1995; Tsuruga et al., 1997). Source process of LP earthquakes are studied using records of broadband seismograph (Uhira et al., 1995; Ohminato et al., 1998; Nishimura, 1998). Observation record of strainmeter, which can record much lower frequency signal than any broadband seismograph, are also used to know the volcanic process of Izu-Oshima volcano (Fukao et al., 1998). Studies using existing short period seismometers are also made. Moment tensor and/or single force inversion with short period records are frequently made to study source mechanism (Nishitomi and Takeo, 1996; Uhira et al., 1995; Nishimura, 1995a; Nishimura et al., 1995; Odaka et al., 1997). Source mechanisms of LP earthquakes are studied based on spectral characteristics using Fourier transform (Fujita et al., 1995) and newly developed spectral analysis (Nakano et al., 1998). Relationship betwee n the physical process of volcanoes and LP events and/or volcanic tremors are discussed based on more realistic physical model (Iguchi, 1995; Uhira et al., 1995; Nishimura 1995a). Nishimura (1995b) studied the statistical characteristics of volcanic tremor. Infrasonic wave generated associated with LP events also drew attention (Sakai et al. 1996; Yamasato 1997a, b).

In summary, broadband observations and analysis of LP earthquakes have shown the potential to reveal some basic process of volcano, such as mass movement, pressure buildup or release in relatively low frequency range. Source process of LP events in high frequency range that can be recorded with usual short period sensors still needs intensive study.

Structure of Volcanoes

Structure of volcanoes is most intensively studied in the field of volcano geophysics in Japan for the last four years. The results from the joint project for the exploration of volcano structure by explosion experiments are reported. Initial reports for the 1994 experiment at Kirishima volcano, Kyushu, Japan are made in the following two years (Kagiyama, 1997; Kagiyama et al, 1995; Kagiyama et al., 1997; Mikada et al., 1995; Maeda et al, 1997; Matsushima et al., 1995; Tsutsui et al., 1996). Details of the experiment are reported in another section in this national report on volcano science. The data sets obtained in these experiments stimulate new approach for volcano structure study (Mikada, 1996; Tomatsu et al., 1997; Nishi, 1997). Tomography studies are also made for velocity structure at Kuju volcano (Sudo and Matsumoto, 1998), Nikko-Shirane volcano (Hasegawa and Matsumoto, 1997) and Unzen volcano (Ohmi and Lees, 1995). Attemuation structures are extimanted with tomograpy at Kuju volcano (Sudo et al., 1996). Velocity and/or Q anomaly are interpreted with several kind of analysis (Yamamoto and Ida, 1997; Horiuchi et al., 1997; Yamazaki, 1996). Reflection or scattering of seismic wave are also used to reveal the heterogeneity of volcanic structure (Nishimura et al., 1997; Matsumoto and Hasegawa, 1997; Mikada et al., 1997; Hashimoto et al., 1995). Experiments using vibrator source as well as exploration one are made in Aso volcano (Tsutsui et al., 1997). Electromagnetic methods are also intensively used to survey magnetic or resistivity structure of volcanoes. Magnetotelluric survey for resistivity structure of volcanoes are made in various volcanoes in Japan; Usu volcano in Hokkaido (Ogawa et al., 1998; Nishida et al., 1996), Hokkaido-Komagatake volcano (Michiwaki et al., 1995), volcanoes in Nikko area (Ogawa et al., 1997), Aso volcano (Handa et al., 1998) and Kirishima volcano (Kagiyama et al., 1996; Munekane et al., 1997). After the cessation of the activity of Unzen volcano air-bone electromagnetic surveys are made to know the magnetic structure (Mogi et al., 1997; Honkura et al., 1995). Density distribution is also surveyed in Fuji volcano (Tanaka and Satomura, 1995), Sanbe caldera (Komuro et al., 1996) and Kirishima volcano (Kobayashi et al., 1995). Petrological inte rpretation are made for velocity and attenuation structure beneath volcanic area including mantle wedge by Sato (1995) and Sato and Hasegawa (1996).

In the last 4 years scattering of seismic wave are more frequently used than ever, though it shows slow development. More efforts are needed for the development of observation technology as well as analysis method.

Monitoring of Volcanic Activity

Geophysical study of volcanoes has been developed through monitoring of volcanic activity. In the last 4 years many efforts are made on the development of volcano monitoring although no major eruption took place in Japan. Results of the monitoring of seismic activity, which is most traditional technique, are reported for some active volcanic area; Nikko-Ashio and Eastern Izu (Rocco et al., 1997), Kuju volcano (Sudo et al., 1998), Eastern Izu (Uk awa and Tsukahara, 1996), Unzen volcano (Hashimoto et al., 1997) Guntur volcano in Java(Suantika et al., 1997) and a submarine seamount in Mariana trough (Sato et al., 1995). Volcanic tremors usually indicate eruption impending in near future. Ueki et al. (1996) and Ueki et al. (1997) reported the activity of volcanic tremor of Iwate volcano, which was in crisis in 1998. Monitoring the scattering nature of seismic wave is thought to be useful for detecting temporal variation of volcanic activity, but did not made with only one exception (Hashimoto, 1995). Crustal deformation are also used for monitoring the temporal variation of pressure sources at Unzen volcano (Nishi et al., 1998), Eastern Izu (Ukawa, 1997) and Sakurajima volcano (Tanaka et al., 1996). Theoretical study of crustal deformation due to a source with directivity was studied by Tsukakoshi and Odaka (1998). GPS measurements are also used not direc tly for crustal deformation but used for estimate the change of geoid height which reflect the mass movement beneath the Sakurajima volcano (Tanaka, 1997a, b; Tanaka et al., 1995). Precise measurement of gravity also revealed the movement of magma after the 1986 eruption of Izu-Oshima volcano (Watanabe et al., 1998; Watanabe et al., 1998). Trial for monitoring volcanic activity using electromagnetic technique continued from the previous 4-year period. Geomagnetic change is monitored in the Eastern Izu, where large crustal deformation associated with earthquake swarms repeated for about 20 years (Oshiman et al., 1997), and Miyakejima volcano (Sasai et al., 1997). Electric self-potential, which reflects the hydrothermal circulation, is monitored in many volcanic are (Ishido et al., 1997; Hashimoto, 1997; Hashimoto and Tanaka, 1995; Oyamada et al., 1996; Nishida et al., 1996; Nishi et al., 1998; Nishi et al., 1998) . Direct observation of temperature is also reported for monitoring of volcanic activity (Fukui, 1995; Kagiyama, 1997; Sudo and Hurst, 1998). Monitoring and detection of eruption using satellite image (Sawada, 1996a,b; Sawada, 1998; Tokumo, 1997), radar data (Arao et al., 1996) and infrasonic acoustic wave (Tahira et al., 1997) are reported.

In summary, continuous efforts have been made during the last 4 years despite of general dormancy of Japanese volcanoes. Application of new technology such as SAR interferometry or monitoring of propagation characteristics of seismic wave is needed.

Physical Process of Volcano

Theoretical and experimental studies are made on the physical process of volcanic eruption. Ida (1996) simulates the cyclic nature, which is generally seen in many aspects of volcanic activity, with a simple visco-elastic conduit system. Toramaru (1995) intensively studied the bubble grow th in the upwelling magma. Koyaguchi and Woods (1996) also studied the role of bubbles in the explosive eruption. Goto et al. (1997) estimated the viscosity of peraluminous silicate melts at high temperature. Takada (1997) developed the experimental study of dike intrusion.

New Technology and Instruments

Application of new technology and instruments is very important for new findings. A small-sized data-logger developed for seismic prospecting made an innovation in volcanic seismology in Japan. The detail of the data-logger is reported in Morita and Hamaguchi (1996) with a software (Tsutsui et al., 1995). Satellite telemetry is also used for volcano monitoring where wired telemetry is difficult (Neki et al., 1998).


Shimozuru (1996) summarize the case history of two eruption which occurred during his term of office as a chair of coor dinating committee for prediction of volcanic eruption.

(Koshun Yamaoka)


*Arao, K., Iwasaki, H., Fukui, K., Hayakawa, Y. and Takeda, T. (1996) A case study of structure and evolution of ash cloud derived from Unzen pyroclastic flow using radar data. Bull. Volcanol. Soc. Japan, 41, 149-158.

Fujita, E., Ida, Y. and Oikawa, J. (1995) Eigen oscillation of a fluid sphere and source mechanism of harmonic volcanic tremor. Jour. Volcanol. Geotherm. Res., 69, 365-378.

Fukao, Y., Fujita, E., Hori, S. and Kanjo, K. (1998) Response of a volcanic conduit to step-like change in magma pressure. Geophys. Res. Lett., 25, 105-108.

*Fukui, K. (1995) H2O and heat discharged from Aso volcano in noneruptive stage. Bull. Volcanol. Soc. Japan, 40, 233-248.

Glasby, G. P., and Kasahara, J. (1998) Influence of tidal effects on earthquake activities and its periodicity in diverse geological settings with particular emphasis on submarine hydrothermal systems. Bridge Newsletter, 15, 16-17.

Goto, A., Oshima, H. and Nishida, Y. (1997) Empirical method of calculating the viscosity of peraluminous silicate melts at high temperatures. Jour. Volcanol. Geotherm. Res., 76, 319-327.

Handa, S., Suzuki, A. and Tanaka, Y. (1998) The electrical resistivity structure of the Aso caldera, Japan. Bull. Volcanol. Soc. Japan, 43, 15-23.

*Hasegawa, A. and Matsumoto, S. (1997) Deep structure of Nikko-Shirane volcano group in the Northeastern Japan arc estimated from seismic observations. Bull. Volcanol.Soc. Japan, 42, S147-S155.

Hashimoto, T. (1995) Coda-Q Values around the Unzen area in the period from 1984 to 1991. Pap. Meteorol. Geophys., 46, 27-33.

Hashimoto,T. (1997) Self-Potential Changes and Subsurface Hydrothermal Activity Accompanying the 1990-1995 Eruption of Unzen Volcano. Jour. Geomag. Geoelectr., 49, 977-993.

Hashimoto, T. and Tanaka Y. (1995) Self-potential observations on Unzen volcano, Shimabara peninsula, Kyushu island, Japan. Geophys. Res. Lett., 22, 191-194.

Hashimoto, T., Yamasato, H., Uhira, K. and Seino, M. (1997) A tentative study on determination of earthquake magnitude at Unzen volcano. Pap. Meteorol. Geophys., 48, 25-29.

Hashimoto, T., Yamasato, H., Uhira, K. an d K.Goto (1995) Coda-Q estimated from earthquakes around Unzendake volcno. Bull. Volcanol. Soc. Japan, 40, 83-89.

*Honda, S. 91996) Volcanic tremor excited by the fluid flow through the condui with barriers -a model-. Mem. Geol. Soc. Japan, 46, 59-66.

Honkura. Y., M. Matsushima, N. Oshiman, Y. Sasai, M. Ohno, Y. Tanaka, T. Yamamoto, K. Ikeda, and Y. Wakino (1995) Magnetization structure of the Unzen Volcano determined from blimp-borne magnetic survey data. Jour. Geomag. Geoel ectr., 47, 231-236.

Horiuchi, S., Tsumura, N. and Hasegawa, A. (1997) Mapping of a magma reservoir beneath Nikko-Shirane volcano in northern Kanto, Japan, from travel time and seismogram shape anomalies. Jour. Geophys. Res., 102, 18071-18090.

Ida, Y. (1995) Magma chamber and eruptive processes at Izu-Oshima volcano, Japan: Buoyancy control of magma migration. Jour. Volcanol. Geotherm. Res., 66, 53-67.

Ida, Y. (1996) Cyclic fluid effusion accompanied by pressure change: Implication for volcanic eruptions and tremor. Geophys. Res. Lett., 23, 1457-1460.

*Iguchi, M. (1995) Source mechanisms of volcanic earthquakes and tremors and their field of origin. Bull. Volcanol. Soc. Japan, 42, S47-S57.

Ishido T., Kikuchi, T., Matsushima, N., Yano, Y., Nakao, S., Sugihara, M., Tosha, T., Takakura, S. and Ogawa, Y. (1997) Repeated self-potential profiling of Izu-Oshima volcano, Japan. Jour. Geomag. Geoelectr., 49, 1267-1278.

*Ishihara, K. (1997) Research on the mechanism of volcanic eruption with geophysical observation. Bull. Volcanol. Soc. Japan, 42, 445-458.

*Kobayashi, S. (1996) Fluid motion induced by flotation/sedimentation of immiscible particles -applications to magmatic convection. Mem. Geol. Soc. Japan, 46, 43-57.

*Kagiyama, T. (1997) Experiment on volcanic struc ture and magma supply system for prediction of volcanic eruption. Bull. Volcanol. Soc. Japan., 42, 115-118.

*Kagiyama, T. and Koyama, E. (1997) On a relation between fumarolic temperature an d atmospheric pressure. Bull. Volcanol. Soc. Japan., 42, 423-428.

*Kagiyama, T., Tsutsui, T., Mikada, H. (1995) 1994 explosion experiment in Kirishima volcanoes. Bull. Earthq. Res. Inst., 70, 33-60.

*Kagiyama, T., Utada, H., Mikada, H., Tsutsui, T., Masutani, F. (1997) Structure of the Kirishima volcanic region and its magma supply system. Bull. Volcanol. Soc. Japan, 42, S157-S165.

*Kagiyama, T., Utada, H., Ueshima, M., Masutani, F., Kanda, W., Tanaka, Y., Masuda, H., Murakami, H., Shiozaki, I., Ichiki, M., Yukutake, T., Mogi, T., Amita, K., Oshiman, N. and Mishina, M. (1996) Resistivity structure of the central and southeastern part of Kirishima Volcanic region, Bull. Volcanol. Soc. Japan, 41, 215-225.

Kaneshima, S., Kawakatsu, H., Matsubayashi, H., Sudo, Y., Tsutsui, T., Ohminato, T., Ito, H., Uhira, K., Yamasato, T., Oikawa, J., Takeo, M. and Iidaka, T. (1996) Mechanism of phreatic eruptions at Aso Volcano inferred from near-field broadband seismic observations. Science, 273, 642-645.

*Kobayashi, S. and Fukao, Y. (1997) Fluid mechanical effects of gravitational differentiation of immiscible two phases -structure, self-sustainment and non-linearity-. Bull. Volcano. Soc. Japan, 42, S281-292.

*Kobayashi, S., Shichi, R., Nishinaka, H., Watanabe, H. and Onizawa, S. (1995) Densegravity survey in the Kirishima volcanoes and its surrounding calderas, southern Kyushu, Japan, Bull. Earthq. Res. Inst., 70, 103-136.

*Komuro H., Shichi, R., Wada, H. and Itoi, Y. (1996) Basement relief under Sanbe caldera inferred from gravity anomaly. Bull. Volcanol. Soc. Japan, 41, 1-10.

Koyaguchi, T. and Woods, A.W. (1996) On the formation of eruption columns following explosive mixing of magma and surface -water. Jour. Geophys. Res., 101, 5561-5574.

Kumagai, I. and Kurita, K. (1998) Interaction of periodic wave trains in magma conduits. Phys. Earth Planet. Int., 107, 131-141.

Maeda, M., Yomogida, K., Umakoshi, K., Okamatsu, N., Fujii, Y. and Matsushima, T. (1997) Broadband seismic observation of 1995 explosion experiment in the Unzen volcano. Bull. Volcanol. Soc. Japan, 42, 331-343.

Matsumoto, S. and Hasegawa, A. (1996) Distinct S wave reflector in the midcrust beneath Nikko-Shirane volcano in the northeastern Japan arc. Jour. Geophys. Res., 101, 3067-3083.

*Matsumoto, S. and Hasegawa, A (1997) Distribution of Midcrustal S wave reflectors beneath Nikko-Shirane volcano in the northeastern Japan arc. Bull. Volcanol. Soc. Japan, 42, 127-139.

*Matsushima, T., Iguchi, M., Nishimura, Y., Kagiyama, T., Watanabe, H., Mikada, H., Oikawa, J., Yamamoto, K., Yamaguchi, M., Masutani, F., Okuda, T., Tsutsui, T., Miyamachi, H. (1995) GPS survey of shot and receiver locations in the explosion experiment of Kirishima volcanoes. Bull. Earthq. Res. Inst., 70, 60-67.

*Michiwaki, M., Matsushima, N., Ichikawa, R., Yamaguchi, K., Nishida, Y., Oshima, H. and Mori, H. (1995) Volcano-electromagnetic survey on Hokkaido Komaga-take. Bull. Volcanol. Soc. Japan, 40, 367-374.

*Mikada, H. (1994) A seismic reflection analysis on refraction data from the 1994 Kirishima explosion experiment. Bull. Volcanol. Soc. Japan, 41, 159-170.

*Mikada, H., Tsutsui, T., Morita, Y. (1995) Standard digital format of seismic waveform data in structural analyses of volcanoes. Bull. Earthq. Res. Inst., 70, 68-78.

Mikada, H., Watanabe, H. and Sakashita, S. (1997) Evidence for Subsurface Magma Bodies beneath Izu-Oshima Volcano Inferred from a Seismic Scattering Analysis and Possible Interpretation of the Magma Plumbing System of the 1986 Eruptive Activity. Phys. Earth Planet. Inter., 104, 257-269.

*Mogi. T., Tanaka, Y., Morikawa, T., Kusakabe, K., Tanahashi, M., Nakatsuka, T., Tanaka, K. and Utada, H. (1995) Subsurface structure of Unzen-Fugen and Mayu-yama volcano inferred from aribone electromagnetic method and magnetic survey. Bull. Volcanol. Soc. Japan, 40, 263-276.

*Morita,Y. and Hamaguchi, H. (1996) Development of a small-size data logger for seismic prospecting at volcanoes. Bull. Volcanol. Soc. Japan, 41, 127-139.

*Munekane, H., Kagiyama, T., Utada, H., Kanda, W., Masutani, F., Koyama, S., Amita, K., Oba, S., Mishina, M., Yamamoto, T., Yamasaki, A., Kato, W. and Umeda, K. (1997) Resistivity survey across the southern part of the Kyushu Island. Bull. Earthq. Res. Inst., 72, 19-65.

*Muro, K., Sato, H., Hasegawa, A. and Hashizume, K. (1997) 3-D distribution of partial melt and seismic activity in the northeastern Japan arc. Bull. Volcanol. Soc. Japan, 42, S139-S146.

Nakano, M., Kumagai, H., Kumazawa, M., Yamaoka, K. and C houet, B. A. (1998)The excitation and characteristic frequency of the long-period volcanic event: An approach based on an inhomogeneous autoregressive model of a linear dynamic system. Jour. Geophys. Res., 103, 10,031-10,046.

*Neki, M., Kagiyama, T., Masutani, F., Osada, N. and Munekane, H. (1998) Observation of volcanic activity by Argos System. Bull. Volcanol. Soc. Japan., 43, 167-172.

*Nishi, K. (1997) Three dimentional subsurface P-wave velocity structure of Kirishima volcano derived from shot data inversion. Bull. Volcanol. Soc. Japan, 42, 165-170.

*Nishi, K., Ishihara, K., Kamo, K., Ono, H. and Mori, H. (1995) Positioning of magma reservoir at Unzen volcano by GPS survey. Bull. Volcanol. Soc. Japan, 40, 43-51.

*Nishi, Y., Ishido, T. and Matsushima, N. (1998) Num erical simulation of hydrothermal system in Aogashima volcano based upon self-potential data. Jour. Geotherm. Soc. Japan, 20, 139-153.

Nishi, Y., Ishido, T., and Matsushima, N. (1998) The geothermal system in Aogashima volcano based upon self-potential data and numerical simulation. Geotherm. Resour. Council Trans., 22, 20-23.

Nishi, Y., Sherburn, S., Scott, B. and Sugihara, M. (1996) High-frequency earthquakes at White Island volcano, New Zealand: insights into the shallow structure of a volcano-hydrothermal system. Jour. Volcanol. Geotherm. Res., 72, 183-197.

Nishida, Y., Matsuhima, N., Goto, A., Nakayama, Y., Oyamada, A., Utsugi, M. and Oshima, H. (1996) Self-potential studies in volcanic areas (3) -Miyake-jima, Esan and Usu-. Jour. Fac. Sci., Hokkaido Univ., Ser. VII, 10, 63-77.

*Nishida, Y., Utsugi, M., Oshma H., Kagiyama, T., Inoue, T., Morita, Y., Shigehara, S. and Maekawa, T. (1996) Resistivity structure of Usu volcano as revealed by the magnetotelluric measurements. Geophys. Bull. Hokkaido Univ., 59, 151-162.

Nishimura, T. (1995a) Source parameters of the volcanic eruption earthquakes at Mount Tokachi, Hokkaido, Japan, and a magma ascending model. Jour. Geophys. Res., 100, 12465-12473.

Nishimura, T. (1995b) Estimation of Ishimoto-Iida's m-value for seismic sources included in volcanic tremor. Bull. Volcanol. Soc. Japan, 40, 53-57.

Nisihmura, T. (1998) Source mecanisms of volcanic explosion earthquakes: Single force and implosive sources. Jour.Volcanol. Geotherm. Res., 86, 97-106.

Nishimura, T., Hamaguchi, H. and S. Ueki, S. (1995) Source mechanisms of volcanic tremor and low-frequency earthquakes associated with the 1988-89 eruptive activity of Mt Tokachi, Hokkaido, Japan. Geophys. Jour. Int., 121, 444-458.

Nishimura, T., Fehler, M., Baldridge, W. S., Rob erts, P. and Steck L. (1997) Heterogeneous structure around the Jemez Volcanic FieldCNew Mexico, USA, as inferred from the envelope inversion of active-experiment seismic data. Geophys. Jour. Int., 131, 667-681.

*Nishitomi, I. and Takeo, M. (1996) Seismicity and a focal mechanism of low-frequency earthquakes occurring in the western part of Tochigi prefecture, Japan. Bull. Volcanol. Soc. Japan, 41, 43-59.

Ogawa, M. and Nakamura, H. (1998) Thermochemical regime of the early mantle inferred from numerical models of the coupled magmatism-mantle convection system with the solid-solid phase transitions at depths around 660 km. Jour. Geophys. Res., 103, 12161-12180.

Ogawa, Y., Honkura, Y., Ohtani, F., Kuroki, H. and Mitsuhata, Y. (1997) Preliminary magnetotelluric modeling in the Nikko volcanic area -potential break of fluid trap by volcanic intrusion-. Jour. Geomag. Geoelectr., 49, 1065-1071.

Ogawa, Y., Matsushima, H., Oshima, S., Takakura, M., Utsugi, K., Hirano, K., Igarashi, M. and Doi, T. (1998) A resistivity cross-section of Usu volcano, Hokkaido, Japan, by autdiomagnetotelluric soundings. Earth Planets Space, 50, 339-346.

Ohmi, S. and Lees, J. M. (1995) Three-dimensional P- and S-wave velocity structure below Unzen volcano. Jour. Volcanol. Geotherm. Res., 65, 1-26.

Ohminato, T. and Ereditato, D. (1997) Broadband seismic observation at Satsuma-Iwojima volcano, Japan. Geophys. Res. Lett, 24, 2845-2848.

Ohminato, T., Chouet, B.A., Dawson, P. and Kedar, S. (1998) Waveform inversion of very long period impulsive signals associated with magmatic injection beneath Kilauea Volcano, Hawaii. Jour. Geophys. Res., 103, 23839-23862.

*Okada,T., Matsuzawa, T., Matsumoto, S., Kono, T., Nida, K., Hasegawa, A., Ito, A., Fujita, E., Obara, K., Kasahara, K.and Kosuga, M. (1997) Moment tensor inversion for microearthquakes and isolated volcanic tremors near Nikko-Shirane volcano, Northeastern Japan. Jour. Seismol. Soc. Japan, 50, 37-48.

Oshiman, N., Sasai, Y., Honkura, Y., Ishikawa, Y. and Tanaka, Y. (1997) Geomagnetic changes correlated with crustal movement in the north-eastern part of the Izu Peninsula, Japan. Ann. Geofisica, 60, 479-494.

Oyamada, A., Oshima, H., Nishida, Y., Goto, A. and Furukawa, H. (1996) Self-potential studies in volcanic areas (4) -An attempt to estimate the in-situ value of the electrokinetic coupling coefficient-. Jour. Fac. Sci., Hokkaido Univ., Ser. VII, 10, 79-87.

Rocco, G.F.E., Horiuchi, S., and Hasegawa, A. (1997) Study on the state of stress around earthquake swarm areas using P-wave polarity data: Nikko-Ashio and Teishi Kno ll areas. Jour. Phys. Earth, 45, 29-40.

*Sakai, T., Yamasato, H. and Uhira, K. (1996) Infrasound accompanying C-type tremor at Sakurajima volcno. Bull. Volcanol. Soc. Japan, 41, 181-185.

Sasai, Y., Zlotnicski, J, Nishida, Y., Yvetot, P., Morat, P., Murakami, H., Tanaka, Y., Ishikawa, Y., Koyama, S. and Sekiguchi, W. (1997) Electromagnetic monitoring of Miyake-jima Volcano, Izu-Bonin Arc, Japan: A preliminary report. Jour. Geomag. Geoelectr., 49, 1293-1316.

*Sato, H. (1995) Thermal structure of the upper mantle beneath the Japan arc determined from seismic velocity data - Implications for island arc magmatism-. Jour. Seismol. Soc. Japan, 48, 139-149.

*Sato, H. and Hasegawa, A. (1996) Mapping of partial melt zones in the upper mantle beneath northeastern Japan -Ascent of magma in island arc-. Bull. Volcanol. Soc. Japan, 41, 115-125*Sato, H. and Aida, S. (1997) Veolcity anisotropy in crustal and upper mantle rocks at high pressure. Bull. Volcanol. Soc. Japan, 42, S123-130.

Sato, T., Kasahara, J. and Fujioka, K. (1995) Observation of pressure change associated with hydrothermal upwelling at a seamount in the south Mariana Trough using an ocean bottom seismometer. Geophys. Res. Lett, 22,1325-1328.

Sawada, M. (1998) The source mechanism of B-type and explosion earthquakes and the origin of N-type earthquakes observed at Asama Volcano, central Japan. Bull. Earthq. Res. Inst. Univ. Tokyo, 73, 155-265.

Sawada, Y. (1996) Detection of explosive eruptions and regional tracking of volcanic ash clouds with geostationary meteorological satellites (GMS). In Scarpa, R. and Tilling, RI. (eds.), Monitoring and Mitigation of Volcano Hazards, Springer-Verlag Berlin Heidelberg, pp. 299-314.

*Sawada, Y. (1996) Estimation of masses of ash particles in dispersing volcanic clouds -simple apply of cloud physics data to volcanic clouds from Sakura-jima volcano. Bull. Volcanol. Soc. Japan, 41, 141-143.

*Sawada, Y. (1998) Corrections of underestimation of top altitude and apparent location of the extent of eruption cloud from the 1986 November 21 Izu-Oshima eruption, obtained in the GMS imagery. Jour. Remote Sensing Soc. Japan, 18, 45-54.

Shimozuru, D. (1996) Volcanic Emergency Management in Japan: Case Histories of Izu-Oshima and Unzen, In Scarpa, R. and Tilling, R.I. (eds), Monitoring and Mitigation of Volcano Hazards, Springer-Verlag Berlin Heiderberg, pp. 787-806.

Suantika G., Suganda O.K., Iguchi, M., Ishihara K. (1997) Hypocenter distribution and focal mechanism of volcanic earthquakes around Guntur volcano, West Jawa, Indonesia. Ann. Disas. Prev. Res. Inst., Kyoto Univ., No.40, IDNDR Spec. Issue, 5-11.

*Sudo, Y. (1997) A prediction of the case of the eruption of Kuju Volcano. Bull. Volcanol. Soc. Japan, 42, 75-81.

Sudo, Y. and Hurst, A.W. (1998) Temperature changes at depths to 150 meters near the active crater of Aso Volcano: preliminary analysis of seasonal and volcanic effects. Jour. Volcanol. Geotherm. Res., 81, 159-172.

Sudo, Y. and Matsumoto, Y. (1998) Three-dimentional P-wave velocity structure in the upper crust ben eath Kuju Volcano, central Kyushu, Japan. Bull. Volcanol., 60, 147-159.

Sudo, Y., Okamoto, S. and Tsutsui, T. (1996) Attenuation of seismic waves beneath Kuju Volcano. Bull. Volcanol. Soc. Japan, 41, 11-22.

Sudo, Y., Ono, H., Hurst, A.W., Tsutsui, T., Mori, T., Nakaboh, M., Matsumoto, Y., Hashimoto, T., Hoka T., Yamda, T., Masuda, H. and Kikuchi, S., (1998) Seismic activity and ground deformation associated with 1995 phreatic eruption of Kuju Volcano, Kyushu, Japan. Jour. Volcanol. Geotherm. Res., 81, 245-267.

Tahira, M., Nomura, M., Sawada, Y. and Kamo, K. (1997) Infrasonic and acoustic-gravity waves generated by the mound Pinatubo eruption of June 15, 1991. In Newhall, C.G. and Punongbayan, R.S. (Eds.), Fire and Mud, Eruptions and Lahars of Mount Pinatubo, Phillippines, PHIVOLCS and Univ. Wash. Press, pp. 601-613.

Takada, A. (1997) Cyclic flank-ven t and central-vent eruption patterns. Bull. Volcanol., 58, 539-556.

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(* In Japanese with English abstract. ** In Japanese)

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