Volcanic earthquakes increase from midnight on the 23rd ... Raise the eruption alert level of "Mt. Yakedake" in the Northern Alps that straddles Gifu and Nagano to 2.
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According to the Japan Meteorological Agency, Mt. Yakedake in the Northern Alps has continued to expand slowly near the summit, and weak volcanic earthquakes have increased since 23:11 pm on the XNUMXrd.
Regarding Mt. Yakedake, which straddles Takayama City in Gifu Prefecture and Nagano Prefecture, the Japan Meteorological Agency said that "volcanic activity is increasing" on the morning of the 24th, eruption police ... → Continue reading
"Tokai TV Broadcasting" (Fuji TV affiliate) news account. We will send you the latest news from Aichi, Gifu and Mie prefectures.
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Volcanic earthquake(Kazan Seijishin,British: volcanic earthquake) Is undergroundmagmaSuch as movingVolcanic activityCaused byEarthquake..The mechanism of occurrence is different from ordinary earthquakes,aftershock,ForeshockWithoutMain shockOnly is considered to occur alone.There is no globally unified definition.
Mechanism of volcanic earthquakes
VolcanoIn the basement of the surrounding area, there is a place that serves as a path for magma.This path is relatively sturdy and usually rarely collapses.However, when the magma rises,pressureOn top oftemperatureAlso rises.Especially the closer to the ground, the more undergroundmoistureContains, and the water heated by magmaevaporationAs a result, the volume increases several thousand times and the pressure increases at once.Then, in the path of magma that could not withstand the pressurebedrockBreaks and an earthquake occurs.In addition, after the pressure is increased by the magma, the pressure decreases as the magma passes by, and the rock that was being held down collapses, causing an earthquake.
Types of volcanic earthquakes
The Japan Meteorological Agency divides it into "earthquakes" and "fine movements" based on the characteristics of the vibration waveform and the distribution of frequency components.In addition, there are cases where each volcano has its own waveform, and the definition and classification are further subdivided...Also, the definition of details differs depending on the research institution..
Frequency and period
The classification of seismic frequencies in volcanology is different from the classification by general seismology.The background to this is that historically, seismographs with a natural period of 1 second have been used in volcanic observations..
- T = 0.1 seconds, short period (SP)
- T = 1 second, long period (LP)
- T = 10 seconds, very-long period (VLP)
- T = 100 seconds, ultra-long period (ULP)
Volcanic pulsationAlso called.From short to long, which lasts for more than a few days.Hawaii·Kilauea volcanoIn the observation example of, it is analyzed as the vibration caused by the hydrothermal system heated by the volcanic gas of magma origin..
- Volcanic continuous tremor
- It lasts for a relatively long time and is always present in active volcanoes.
- amplitudeIs very small.
- When volcanic activity becomes active, the amplitude may increase or the tremor may stop.
- Isolated tremor
- Mount AsoA peculiar, sudden short tremor.
- The cycle is slightly different from the volcanic continuous tremor.The amplitude is rather small.
- Isolated tremor
- A slight movement that lasts for a long time.The amplitude is large.
- Type A earthquake, VT earthquake
- It occurs in a relatively deep place in shallower than 10km.
- An earthquake caused by shear failure that occurs around the crater (volcanic pipe).
- The waveform is almost the first wave is the largest and gradually becomes smaller.triangleBecomes
- P waveとS waveIs easy to distinguish.
- The vibration cycle tends to be short, and it is rich in high-frequency components of 10 Hz or higher..
- Less during the quiet period of volcanic activity.
- The distinction from a normal earthquake is that the PS time is within 3 seconds (Mt. Aso).May vary from mountain to mountain.
- Type B earthquake
- Most of the epicenters are shallower than 1km and occur in very shallow areas.
- An earthquake caused by a change in volume, which occurs directly under a crater that erupts frequently.
- The waveform seems to repeat large and small with a constant rhythmSpindle shapeBecomes
- It is difficult to distinguish between P wave and S wave.
- The vibration cycle tends to be long.
- Explosion earthquake
- The waveform of the earthquake suddenly increases from the first wave, then gradually decreases while repeating large and small, and becomes a triangle close to a spindle shape.
- D-type earthquake,Eruption earthquakeIt is also called, and is accompanied by strong air vibration of 10 Pa or more at the time of appearance.
- The amplitude is larger than that of type B, and the period of vibration is almost constant.
- T-type earthquake
- At first, the cycle is short, and as the cycle gradually becomes longer, the cycle is constant and continues for a long time..
- AndesiteMany in quality volcanoes,N-type earthquakeAlso called.
- Deep low frequency earthquake
- The epicenter is relatively deep.
- Seismic waveforms include low frequency wavesWaveform(Low-frequency).
The movement of magmaeruptionIt can happen regardless, but it is possible that a volcanic eruption is imminent.Therefore, we grasped the movement of magma by observing volcanic earthquakes and studied the patterns of volcanic earthquakes and eruptions of the volcano.Eruption predictionI am making good use of it.JapanSo to dozens of active volcanoesSeismographInstruments and observatories have been set up, including the Japan Meteorological Agency.Volcano informationAn alarm system has been established by such means.
Volcanic earthquakes are generally small in scale and are often insensitive (less than seismic intensity 1) earthquakes.In addition, the period of earthquakes is also diverse.Around the volcano, several types of precision seismographs are installed for each cycle for observation.
Volcanic earthquake that caused damage
Volcanic earthquakes are small in scale even if they are felt, but in rare cases they can cause damage alone.As an example in Japan
- 1792/5/21 - Shimabara very Higo trouble,UnzendakeVolcanic earthquake and subsequent Mt. BizanMountain collapseThe number of people killed or missing due to the tsunami caused by the disaster reached 15,000, making it the largest volcanic disaster in Japan since the dawn of history.
- 1914/1/12 - Sakurajima earthquake, M 7.1, 29 dead, 111 injured.SakurajimaAt this timeeruptiondid.
- 2000/7/1(M 6.5)7/15(M 6.3)7/30(M 6.5)- Niijima-Kozushima-MiyakejimaEarthquake in the sea, one dead.Miyakejima is the same year8/10Erupted.
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- ^ a b (PDF)
- ^ Tomoyuki Sugano:Example of vibration waveform in a volcano that is constantly observed by the Japan Meteorological Agency Kyoto University Volcanic Volcanic Activity Research Center
- ^ Satsuma Iojima Volcano Seismic activity National Institute of Advanced Industrial Science and Technology
- ^ Hiroyuki Kumagai, Yu Nakano:Volcanic Earthquake Generation Process — Recent Achievements on Quantification — Earthquake No. 2 Vol.61 (2008-2009) No.Supplement p.379-390
- ^ Hiroyuki Kumagai,(PDF)
- ^ a b Japan Meteorological Agency Uchida and Sakai, 2002
- ^ a b c Kyoto University Disaster Prevention Research Institute Iguchi et al., 1999
- ^ Yasuhiro Tanaka, Hiroshi Jingu:Mt. Asamayama volcanic earthquake notation type and characteristics of the time of occurrence of the earthquake Papers in Meteorology and Geophysics Vol.30 (1979) No.1 p.61-74
- Terms related to volcano observation Asoyama Volcano Disaster Prevention Liaison Office
- Masato Iguchi:(PDF)
- Direct earthquake - Trench earthquake - Deep earthquake --Volcanic earthquake
- Air quake(Explosion sound)
- Volcanic earthquake Earthquake Research Promotion Division
- Japanese Meteorological Agency
- Seismic observation Kyoto University Disaster Prevention Research Institute