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Volume 41 (1990)
- Issue 4 Pages 129-
- Issue 3 Pages 83-
- Issue 2 Pages 43-
- Issue 1 Pages 1-
Volume 41, Issue 3
Displaying 1-3 of 3 articles from this issue
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Analysis of data by JMA networkHitoshi Yamasato, Takashi Yokota, Shizuo Kashiwabara1990 Volume 41 Issue 3 Pages 83-95
Published: 1990
Released on J-STAGE: October 20, 2006
JOURNAL FREE ACCESSOn June 30, 1989, an earthquake swarm started off the east coast of the Izu Peninsula in Japan. During the activity, volcanic tremors were observed from July 11 and submarine volcanic eruptions were visually observed on July 13. In this paper, some characteristics of the volcanic tremors are investigated by analyzing the data obtained by the permanent seismic network of the Japan Meteorological Agency (JMA).
The volcanic tremors occurred when the earthquake swarm activity was on the decline. The spectra of these tremors are composed of low-frequency waves (about 1Hz) and high-frequency waves (more than 3Hz). The ratio of the amplitudes of the former to those of the latter increased from July 11 to July 12, and more low-frequency waves are observed in July 13. Four isolated events which were observed from 19h 03m to 19h 05m of July 13 simultaneously with a continuous low-frequency tremor (about 1Hz) show similar spectra with those of the continuous tremor during the submarine eruptions. Hence, the continuous tremor during the submarine eruptions seems to include a lot of such events. The high-frequency waves in the tremors were predominant while explosive sounds and water domes were frequently observed, and seem to be P-waves associated with explosions at the sea bottom. The low-frequency tremors are classified into continuous tremors (about 1Hz) and surface waves associated with the explosions. As the result of particle motion diagrams at the KMT station, the low-frequency tremors associated with the explosions seem to be composed of both Rayleigh waves and Love waves and the continuous tremors seem to be composed of only Love waves.
After the eruptions, intermittent volcanic tremors with small amplitude were observed until July 21. Very little high-frequency waves are found in these tremors. The predominant frequency of the tremors was about 1Hz until July 16, changing to about 1.5Hz from July 17.View full abstractDownload PDF (927K) -
Takeshi Koizumi, Takashi Yokota, Hitoshi Yamasato, Sumio Yoshikawa1990 Volume 41 Issue 3 Pages 97-104
Published: 1990
Released on J-STAGE: October 20, 2006
JOURNAL FREE ACCESSWe devised a low-cost continuous digital recording system, which consists of a personal computer as CPU, 2 sets of A/D converter and buffer memory, DAT (Digital Audio Tape) data storage system, clock and UPS (Unbroken Power Supply). This system, having 1000-megabyte recording capacity, can make continuous data acquisition for about 70 days in case of 4-channel input and 20 Hz sampling. Also, portability of this system enables us to start field observation quickly. The acquired data are edited for every 10 minutes and stored on the DAT data storage system in binary format. We made test observation at Ajiro Weather Station (which belongs to JMA) and have confirmed the reliability of this system.View full abstractDownload PDF (942K) -
Fumiaki Fujibe1990 Volume 41 Issue 3 Pages 105-128
Published: 1990
Released on J-STAGE: October 20, 2006
JOURNAL FREE ACCESSThe coastal front is defined as a local front between warm air associated with an onshore wind and colder air trapped inland. This paper presents some examples of the coastal front in the Kanto plain and describes its climatological features obtained from statistical analyses. Data for eleven years are stratified according to the wind at coastal stations, seasons, weather and time of the day.
According to a composite analysis of surface wind and temperature, coastal fronts are found to be more conspicuous for southerly onshore winds than for northeast winds, from late autumn to winter than in warmer seasons, and in the nighttime than in the daytime if precipitation is absent or limited. A case-by-case analysis reveals that fronts are usually located near the coastline, but tend to be located inland in the warm season, under a strong onshore wind, and in the daytime if precipitation is absent.
In case of widespread precipitation under southerly winds, the precipitation amount increases by several tens of percent at coastal fronts.View full abstractDownload PDF (1840K)
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