282010-284137,284800-284802,285010-285830

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Sakurajima Volcano Research Center (SVO)
Disaster Prevention Research Institute (DPRI)
Kyoto University
Sakurajima-cho
Kagoshima-ken 891-14
Japan

Sakurajima Volcano Observatory (SVO) - CPRI, Kyoto University:

National Research Institut for Earth Science and Disaster Prevention (NIED):

Scientific Staff :

Dr. Masato Iguchi - Volcano Geophysics
Haruhisa Nakamichi - Volcano Geophysics
Takeshi Tameguri - Volcano Geophysics
Daisuke Miki - Paleomagnetism
Dr. Keigo Yamamoto - Volcano Geophysics

Collaborative staff :

Dr. Yoshiyuki Tatsumi - Petrology
Dr. Yasuaki Sudo - Volcano seismology
Dr. Masayuki Torii - Paleomagnetism
Shigetomo Kikuchi - Volcano geodesy
Hiroyasu Ono - Volcano seismology
Dr. Yoshikazu Tanaka - Volcano geomagnetism
Dr. Tomoki Tutui - Volcano structure
Dr. Jun-ichi Hirabayashi - Geochemistry

Technical staff :

Tadayoshi Sonoda
Tetsuro Takayama
3 temporary staff

OBSERVATORY

Sakurajima Volcanological Observatory (SVO) was founded in 1960, after the beginning of eruptive activity in 1955 at Minami-dake (South peak) crater, for the purpose of fundamental research for prediction of volcanic eruptions. SVO is made up of the main observatory, 3 branch observatories and more than 30 satellite stations. The main observatory is located 5.6 km west to the active crater. There, data are gathered from satellite stations by telemetering systems and analyzed with the help of computers. The branch observatories and satellite stations are arranged not only at Sakurajima land-tied island but also in Caldera areas, those are Kakuto (40 km north to Sakurajima), Aira in which Sakurajima Volcano lies, and Ata Caldera (50 km south to Sakurajima). In May 1996, SVO was reformed to Sakurajima Volcano Research Center associated with reformation of DPRI.

Harutayama Branch is 2.8 km apart from the active crater. Kurokami Branch is the eastern base of seismic and geoelectric observation. Yoshimatsu Branch is established for monitoring seismic activity in Kakuto Caldera.

SEISMIC OBSERVATION

Network in Sakurajima consists of 10 seismic stations which surround the active crater and are equipped with short period (1s) and 1- or 3-components seismometers. Type of seismometer and method of telemetering is listed as follows :

• 3 borehole seismometers, PCM telephone line,
• 2 borehole seismometers, PCM radio,
• 3 borehole seismometers, FM telephone lines,
• 1 seismometer on the ground surface, FM telephone lines,
• 1 seismometer on the ground surface, FM radio.

Borehole seismometers are installed at the depth of 85-350 m. A tripartite network consisting of 3 borehole accelerometers is connected to the main observatory via optical fiber in order to determine propagation direction of seismic wave generated by felt earthquakes associated with large flank eruptions. Long-period seismometer is installed in the underground tunnel of Harutayama.

Network outside Sakurajima Island covers Kirishima volcanic zone, ranging from the northeastern part of Kyushu Island to Ryukyu Islands. The length of network is more than 500 km. Short Period (1s) and 3-components seismometers are installed at each site. 7 of them are installed in the underground tunnels and the others are on the bed rocks. From 8 stations, seismic signals are constantly telemetered to the main observatory, digitizing in 12 bit and 300 Hz sampling frequency, and transmitting at the speed of 9600 bps through telephone lines. At the other stations, seismic waveforms are stored temporarily in the personal computer, digitizing in 12 bit and 100 Hz sampling frequency and the waveform data are transmitted when it is connected to the master computer in the main observatory via public telephone networks twice a day. Seismic signals are recorded on VHS cassette tape by a PCM data recorder (128 channels) and magneto-optical disk (650 Mbyte) by personal computers. Seismic signals are automatically processed by personal computers (IBM-PC compatible), to show hypocentral determination in Sakurajima and in south Kyushu area, classification of type of volcanic earthquakes (A, BH, BL, explosion, harmonic tremor and non-harmonic tremor) and determination of apparent velocity and azimuth from the data of tripartite network. The information processed by PCs are transferred to a workstation for data storage and evaluation of volcanic activity combining seismic, geodetic and geochemical data. Seismic data analysis is made by using PC and workstations, picking up the onset time of P and S-phase, digital filter, spectrum, particle motion, correlation.

GEODETIC MEASUREMENT

Precise levelling has been carried out along 5 routes by Zeiss Ni 1 and 2, every one or two years. Distance measurement has been repeated on 21 lines every 6 months by Wild DI-3000. Levelling routes and EDM networks cover the areas of Sakurajima and Aira Caldera.

Tidal gauges are distributed at the east, west, north and south coast of Sakurajima and 1 at Kagoshima harbor as reference point. Data of sea level are telemetered to the main observatory by telephone lines. Tilt and strain are measured by water tube tiltmeters and super-invar-bar extensometers, respectively, in an underground tunnel of which length is 250 m and its depth is 70 m. Tilt and strain data at the tunnel site are telemetered to the main observatory and state of volcanic activity is judged automatically by a personal computer. The results of judgement about the volcanic activity are transferred to WS, and transmitted to Japan Meteorological Agency, Ministry of Construction and Japan Air Lines via telephone lines. 6 borehole tiltmeters are installed with seismometers above mentioned and transmitted to the main observatory. 6 GPS (Leica SR299E) stations are located in Sakurajima and one station in Kagoshima as reference point. GPS observation is repeated from 22h to 2h every day with a sampling interval 15 s. The GPS data are collected by PC in the main observatory by dial-up data link and 21 baselines are automatically analyzed by mono SKI 1.09 software. Furthermore 9 GPS are installed along Kirishima volcanic zone as mentioned later.

OTHER GEOPHYSICAL MEASUREMENT

Air-shocks by explosive eruptions are observed by 2 mechanical microbarographs and an infrasonic microphone. Geothermal measurement has been repeated by infrared scanners (8-12 microns and 3-5 microns) from 8 land based points temporarily. Precise gravimetry has been carried out using more than 2 LaCoste Romberg gravimeters every 2 or 3 years. About 50 gravimetric points are distributed in Sakurajima and around Aira Caldera.

GAS GEOCHEMISTRY

Volcanic gases are continuously emitted from the active crater. Gas monitoring has been conducted, cooperating with Kusatsu-Shirane Volcano Observatory, Tokyo Institute of Technology. Concentration of HCI and SO₂ gases in the air are measured automatically at Harutayama Branch. Observation of soil gas and hot spring has been carried out in 3 boreholes (Harutayama 405 m deep, Hamamoto 10 m, Kurokami 100 m). Gases are analyzed automatically by gas chromatographs every 6 hours and concentration of CO₂ and H₂ are recorded. Temperature of the groundwater and electric conductivity are also measured continuously. These data are stored in the PCs at observation site and are collected by a PC in the main observatory by dial-up data link.

VOLCANO ROCK MAGNETISM

A magnetically shielded room is installed in the main observatory to make geomagnetic analysis of rock samples under the lower perturbation of outside magnetic field (< 50 nT). The shield room is equipped with a rock magnetometer (SSM-2A), initial susceptibility meter (MS-2), thermal demagnetizers (TDS-1, TDE-91), a AF demagnetizer(DEM-8600) and a fluxgate magnetometer (APS-520A).

JOINT OBSERVATION AND MOBILE OBSERVATORY

Joint study was repeated on seismic observation, geodetic measurement, geothermal, geoelectric, geomagnetic survey, gravimetry, geochemical measurement, and petrological analysis, in collaboration with volcano observatories of Japan in 1974, 1976, 1978, 1980, 1983, 1986, 1990, 1993 and 1996. The results have been published on Report of Joint Observation on Sakurajima Volcano, 1st-8th, in Japanese.

The mobile observatory is equipped with seismic (5 radio telemeters, amplifiers, and 16-channels-recorder, pen-recorder) and deformation (tiltmeters, EDM, GPS, Levelling) and other geophysical instruments for volcanic and seismic emergency at volcanic area in Kyushu and Ryukyu Islands.

MONITORING OF VOLCANOES IN RYUKYU ISLANDS

There are several active volcanoes in Ryukyu Islands. The activities of the volcanoes are continuously monitored by the interactive system of personal computer above mentioned. When phenomena of volcanic unrest are detected at the volcanoes in Ryukyu Islands, observation at these volcanoes will be reinforced by the mobile observatory.

Satsuma-Iojima Volcano

A 3-component seismometers is installed on the foot of the lava dome (Iodake). Permanent GPS station is installed on the rim of Kikai Caldera. 5 GPS benchmarks are installed in Satsuma-Iojima and one in Takeshima Island, to detect deformation of Satsuma-Iojima volcano and Kikai Caldera.

Kuchinerabujima Volcano

A 3-component seismometer is installed at 0.5 km west of the active crater and seismic signal is transmitted to the relay station near the coast by radio. An infrasonic microphone is installed at the relay station. GPS system is installed at the relay station. Benchmarks are distributed around the volcano, 13 for GPS, 3 for EDM and 17 for levelling survey.

Nakanoshima Volcano

A 3-component seismometer and a GPS is located at 3.0 km south-east of the summit crater.

Suwanosejima Volcano

Eruptive activity has continued at the summit crater since 1957. A 3-component seismometer, an infrasonic microphone and GPS are installed at the station 3.3 km south of the crater. Joint observations were carried out in 1984 and 1989, collaborating with other volcano observatories in Japan.

INTERNATIONAL COLLABORATION

In 1993, Disaster Prevention Research Institute of Kyoto University and Directorate General of Geology and Mineral Resources, Ministry of mines and energy of the Republic of Indonesia made arrangement concerning research on physical volcanology and tectonics of Indonesia. SVO has installed 3 seismic stations and a tiltmeters at Guntur volcano, West Java, and 2 tiltmeters in Merapi, central Java in collaboration with Volcanological Survey of Indonesia.