-
Article type: Photogravure
1987 Volume 32 Issue 4 Pages
287-288
Published: December 28, 1987
Released on J-STAGE: January 15, 2018
JOURNAL
FREE ACCESS
-
Hitoshi YAMASATO
Article type: Article
1987 Volume 32 Issue 4 Pages
289-300
Published: December 28, 1987
Released on J-STAGE: January 15, 2018
JOURNAL
FREE ACCESS
The geographical distribution of the initial motions of explosion earthquakes was investigated in detail by analyzing the seismograms obtained by the Kagoshima Local Meteorological Observatory of the Japan Meteorological Agency (JMA) and the Sakurajima Volcanological Observatory ofKyoto University (SV0), of which the seismic stations are distributed around the active crater of Sakurajima volcano. To identify the initial motions accurately, the hypocenters of explosion earthquakes were determined and the travel times of the P-waves were examined. The hypocenters are located beneath the active crater at the depth of 1-2km below sea level. The differences between the epicenters determined by JMA network and those by SVO network were less than 200m. Travel time residuals by the hypocentral determination using both the networks were limited in a band between ±0.2sec. The apparent velocity of the P-waves was 4.7km/sec in the range of the epicentral distance from 15 to 30km, and the value coincides with the P-wave velocity in the upper crust in South Kyushu. These results reveal that the initial motions of explosion earthquakes were accurately identified. The identified initial motions are “compression” without exception at all the stations, of which the epicentral distances range from 1.5 to 50km. Hence, the focal mechanism of explosion earthquakes is inferred to be of a type such that compressional waves are radiated to all direction from the source.
View full abstract
-
Yuichi NISHIMURA, Hiromu OKADA
Article type: Article
1987 Volume 32 Issue 4 Pages
301-315
Published: December 28, 1987
Released on J-STAGE: January 15, 2018
JOURNAL
FREE ACCESS
During the summer of 1978, numerous small eruptions had occurred intermittently from the Gin-numa Crater at Mt.Usu, Hokkaido, Japan. From July 14 to August 14, 1978, seismic signals from SRM, the seismic station at the south rim of the summit crater, were continuously recorded by a drum-recorder at the temporary base of Usu Volcano Observatory, Hoaakido University. 374 volcanic tremors were identified on the seismograms. Since all the known eruptions which produced ash fall in the flanks are registered by a seismometer at SRM as a tremor, and no tremor which is not related to an eruption was identifed in this period, we can assume reasonably that all tremors are originating from the eruption. Hence, those tremor data give us a homogeneous data set of the eruptive activity. The amplitude and the duration of a tremor are closely related to the eruption intensity. Duration was mostly less than five minutes. Nearly equally spaced termor activity (“banded tremor”) were observed on the drum recorder seismogram during this period. Similar phemmena to banded tremor are widely observed at active volcanoes: directly corresponding to magmatic eruptions (Klyuchevskoy, Galunggung, etc.) -phreatic eruptions (Usu), or even during the pre-eruption stage (Karkar, Izu-Oshima, etc.) or during other active stages (Kilauea, Suwanosejima, etc.). About thirty percents of the continuous tremor (116 events) were accompanied with long-period isolated tremors (LT). Characteristics of LT were studied in detail using digital seismograms: LT indicates the dispersive long-period (ca,2Hz) and the very low velocity transmission (near to the sound velocity). LT always appears at the end of the eruption and never overlapped one another. The amplitude-frequency relation of LT shows a remarkable band at the large amplitude, which suggests aphysical limitation of LT generation. The waveform similarity among LT at a given station indicates that they are originating from nearly identical and repeatable source process. The time difference of the differential travel times of a pair of LT between two stations can be precisely calculated from the cross-correlation functions of the entire LT waves. The calculated time differences are consistent with the theoretical ones assuming that the LT source is exactly corresponding to each known vent (craterlet) in the Gin-numa crater. Our preferred model of LT excitation is the air-coupled Rayleigh Wave due to the successive puffiing at the shallowmost vent. When the eruptive power declines gradually towards the end of the eruption, materials temporarily close the vent. However, Puffing may occur and reopen the vent. Such process may continue until the eruptive power could not overcome the critical pressure.
View full abstract
-
Nobuo MATSUSHIMA, Yuichi NISHIMURA, Atsuo SUZUKI, Hiromu OKADA
Article type: Article
1987 Volume 32 Issue 4 Pages
317-328
Published: December 28, 1987
Released on J-STAGE: January 15, 2018
JOURNAL
FREE ACCESS
Mt. Tokachi is an active volcano situated at the central part of Hokkaido, Japan. Its recent major eruptions occurred in 1926 and 1962. There are several craters in summit area. Among them the 62-IICrater is the most active one and shows continuous plume activities since the 1962 eruption. In the neighbouring 62-ICrater, geothermal activity renewed at the end of 1983, and then gradually intensified and enlarged its area. Various phenomena such as ejection of hot mud, small eruptions with column height of less than 100m, and natural ignition of sulfer were observed at the 62-ICrater in 1985. A vault, 30m long, was newly established in 1985 for volcano observation by Usu Volcano Observatory(UVO), Hokkaido University as a part of the National Project for Prediction of Volcanic Eruptions. The facility named Tokachidake-Kansoku-Koudou (TKC) is located at about 2.0 km northeast from the active craters and operated by the solar battery and radio telemetry successfully in the mountaneous environment under heavy snow and severe cold temperature in long winter. Seismic and geodetic data from TKC are telemetered to UVO together with the data from other staions at Mt.Tokachi. Those new data provide us a good homogeneous seismic data with especially improved signal-to-noise ratio. In this study, classfication of volcanic earthquakes is discussed based on the data observed at TKC by examining their frequency characteristics for the period from December, 1985 to March, 1987 (1178 events). Spcctral analysis of the classified earthquake groups and seismicity of each group will give us better knowledge about source mechanism of those volcanic earthquakes and hence the processes taking place under Tokachi volcano. Seismicity in this period is characterized by relatively steady one, though minor earthquake swarms sometimes occurred. In the last part of the period from December 20. 1986 to the present (as of March 1987), volcanic tremors appeared on the seismograms 8 times. For classifying earthquake groups, firrst, we selected two groups according to their frequency characteristics on the monitor seismograms (4 cm/sec), and labelled HF (high-frequency earthquakes, 418 events) or LF (low-frequency earthquakes, 268 events), respectively. Most of other earthquakes were labelled MF (medium-frequency earthquakes, 415 events) unless their frequency characteristics are unique and not regarded those between HF and LF. Spectra of HF, MF, and LF are generally characterized by broad spectral peak located at about 10 Hz or more, several Hz and 3 Hz, respectively.
View full abstract
-
Ichiro KANEOKA, Hiromitsu YAMAGISHI, Masahiro YAHATA
Article type: Letter
1987 Volume 32 Issue 4 Pages
329-333
Published: December 28, 1987
Released on J-STAGE: January 15, 2018
JOURNAL
FREE ACCESS
The Mt.Karibayama area is located at the northwestern part of the Oshima Peninsula, Hokkaido. This area is regarded as the northern extension of the inner belt of the North Japan Arc, and is almost occupied by the Neogene submarine volcanic rocks and associated sedimentary rocks, both of which are mostly covered by Quaternary subaerial lavas (Fig. 1) (YAMAGISHI and KUROSAWA, 1987). For this area, there have been few radiometric age data and their relative ages are presumed in view point of lithologic stratigraphy. In addition, it is difficult to evaluate the length of the time interval if some unconformities are observed. For example, an unconformity has been found between the upper Tertiary formation, such as the Okotsunai Formation, and the Quaternary Anatokomae Lava. The former is identified to be products of submarine effusion, whereas the latter to be those of subaerial one. Thus, it is important to obtain information on the time interval between the submarine and subaerial volcanism. Because the information suggests ane evolution process of a northern part of the North Japan Arc. Hence, we tried to determine K-Ar ages of the volcanic rocks from the representative formations in this area. Five samples from typical formations in this area were selected for the present purpose (Fig.1). The samples of Chihasegawa 16 and Karibayama 65A were taken from Quaternary subaeria lavas, while the samples of Karibayama 63, Karibayama 134A and Oy-103 from Tertiary submarine lavas and hyaloclastites. Their stratigraphical successions are shown in Fig. 2. The sample Chihasegawa 16 is a hornblende dacite lava (the Karibayama Lava), containing phenocrysts of plagioclase, hornblende, biotite, quartz, orthopyroxene and clinopyroxene in the order of abundance. The hornblende and margins of the biotite crystals hav ebeen oxidized. Some of hornblende phenocrysts have been altered into sericite flakes, but no alteration minerals are observed on the biotite phenocrysts. The Karibayama 65A is an olivine basaltic lava (the Anatokomae Lava).
View full abstract
-
M. Takeo
Article type: Abstract
1987 Volume 32 Issue 4 Pages
335-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
S. Uehara, T. Kumagai, H. Takahashi, S. Kishi, S. Yazaki, K. Takemura
Article type: Abstract
1987 Volume 32 Issue 4 Pages
335-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
Y. Tamura
Article type: Abstract
1987 Volume 32 Issue 4 Pages
336-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
H. Taniguchi
Article type: Abstract
1987 Volume 32 Issue 4 Pages
336-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
M. Yui, T. Fujii
Article type: Abstract
1987 Volume 32 Issue 4 Pages
336-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
K. Okumura
Article type: Abstract
1987 Volume 32 Issue 4 Pages
337-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
O. Oshima
Article type: Abstract
1987 Volume 32 Issue 4 Pages
337-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
H. Yamagishi
Article type: Abstract
1987 Volume 32 Issue 4 Pages
338-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
T. Chiba
Article type: Abstract
1987 Volume 32 Issue 4 Pages
338-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
H. Watanabe
Article type: Abstract
1987 Volume 32 Issue 4 Pages
339-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
T. Soya, K. Sakaguchi, K. Uto, K. Ono, A. Takada, M. Aoki
Article type: Abstract
1987 Volume 32 Issue 4 Pages
339-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
S. Itaba, J. Sato, H. Takahashi, K. Sato
Article type: Abstract
1987 Volume 32 Issue 4 Pages
339-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
M. Shirao
Article type: Abstract
1987 Volume 32 Issue 4 Pages
340-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
T. Noda, H. Funabiki, K. Tanida, M. Uchiumi
Article type: Abstract
1987 Volume 32 Issue 4 Pages
340-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
K. Endo, T. Chiba, H. Taniguchi, S. Tachikawa, M. Sumita, R. Uno, T. M ...
Article type: Abstract
1987 Volume 32 Issue 4 Pages
341-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
K. Nagao, J. Matsuda, K. Notsu
Article type: Abstract
1987 Volume 32 Issue 4 Pages
341-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
Y. Hayakawa, M. Shirao, M. Yui
Article type: Abstract
1987 Volume 32 Issue 4 Pages
342-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
I Kaneoka, H. Shimazaki, Y.J. Lee
Article type: Abstract
1987 Volume 32 Issue 4 Pages
342-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
H. Watanabe, K. Yamaoka, S. Sakashita, T. Shimomura
Article type: Abstract
1987 Volume 32 Issue 4 Pages
343-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
H. Sawatari, H. Shimizu, Y. Kawata, A. Masuda
Article type: Abstract
1987 Volume 32 Issue 4 Pages
343-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
Y. Ida
Article type: Abstract
1987 Volume 32 Issue 4 Pages
344-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
H. Sato, H. Sakai
Article type: Abstract
1987 Volume 32 Issue 4 Pages
344-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
T. Hashimoto, M. Seino, H. Tatehata
Article type: Abstract
1987 Volume 32 Issue 4 Pages
344-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
J. Ossaka, T. Matsuda, M. Kurosaki
Article type: Abstract
1987 Volume 32 Issue 4 Pages
345-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
J. Oikawa, Y. Ida
Article type: Abstract
1987 Volume 32 Issue 4 Pages
345-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
T. Kizawa
Article type: Abstract
1987 Volume 32 Issue 4 Pages
346-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
K. Yamaoka, S. Sakashita, H. Watanabe
Article type: Abstract
1987 Volume 32 Issue 4 Pages
346-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
M. Kusakabe, S. Aramaki, S. Kanari, T. Osumi
Article type: Abstract
1987 Volume 32 Issue 4 Pages
347-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
M. Hashimoto, T. Tada
Article type: Abstract
1987 Volume 32 Issue 4 Pages
347-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
S. Hayashi, M. Kasahara, N. Zana
Article type: Abstract
1987 Volume 32 Issue 4 Pages
347-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
E. Yamamoto, S. Shimada
Article type: Abstract
1987 Volume 32 Issue 4 Pages
348-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
M. Kasahara, S. Ueki, E. Murakami, H. Hamaguchi, M. Akumbi, N. Zana
Article type: Abstract
1987 Volume 32 Issue 4 Pages
349-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
T. Miyazaki, S. Sakashita, N. Gyoda, N. sada, T. Eto, H. Shimizu
Article type: Abstract
1987 Volume 32 Issue 4 Pages
349-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
K. Tanaka, M. Kasahara, M. Seto, S. Hayashi, H. Hamaguchi, M.S. Kamba, ...
Article type: Abstract
1987 Volume 32 Issue 4 Pages
349-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
H. Watanabe, S. Okubo, M. Sawada, K. Tajima, S. Sakashita, I. Yokoyama ...
Article type: Abstract
1987 Volume 32 Issue 4 Pages
350-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
M. Seto, K. Tanaka, M.S. Kamba, N. Zana
Article type: Abstract
1987 Volume 32 Issue 4 Pages
350-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
I. Yokoyama
Article type: Abstract
1987 Volume 32 Issue 4 Pages
351-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
K. Murakami, K. Kaminuma
Article type: Abstract
1987 Volume 32 Issue 4 Pages
351-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
M. Ohno, Y. Hamano
Article type: Abstract
1987 Volume 32 Issue 4 Pages
352-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
K. Kaminuma, K. Shibuya, K. Murakami
Article type: Abstract
1987 Volume 32 Issue 4 Pages
352-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
K. Kazahaya, M. Takahashi, N. Ando, T. Soya, T. Osumi, J. Hirabayashi, ...
Article type: Abstract
1987 Volume 32 Issue 4 Pages
352-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
S. Miura, K. Kaminuma, E. Koyama
Article type: Abstract
1987 Volume 32 Issue 4 Pages
353-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
K. Notsu, Y. Nakamura, Y. Sano, H. Wakita
Article type: Abstract
1987 Volume 32 Issue 4 Pages
353-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
M. Takeuchi, T. Ui
Article type: Abstract
1987 Volume 32 Issue 4 Pages
354-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS
-
K. Sato, H. Takahashi, J. Sato
Article type: Abstract
1987 Volume 32 Issue 4 Pages
354-
Published: December 28, 1987
Released on J-STAGE: February 13, 2018
JOURNAL
FREE ACCESS