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Infrasound Technology Workshop 2007 (ITW2007) 14 November 2007, at Tokyo. Infrasonic Observation near Active Volcanoes and its Results in Japan. Usu, Hokkaido-Komagadake, Asama, Miyake, Unzen, Sakurajima. Hitoshi YAMASATO*, Takayuki SAKAI* and Yoshiaki FUJIWARA**

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infrasonic observation near active volcanoes and its results in japan

Infrasound Technology Workshop 2007 (ITW2007)14 November 2007, at Tokyo

Infrasonic Observation near Active Volcanoes and its Results in Japan

Usu, Hokkaido-Komagadake, Asama, Miyake, Unzen, Sakurajima

Hitoshi YAMASATO*, Takayuki SAKAI* and Yoshiaki FUJIWARA**

*Meteorological Research Institute, Japan Meteorological Agency** Japan Meteorological Agency (present : Geographical Survey Institute)

volcano observation of jma
Volcano Observation of JMA

Real-time telemeter

Tiltmeter

傾斜計

Volcano Observation andInformation Centers

(Sapporo, Sendai, Tokyo, Fukuoka)

Mobile Observation(Thermal, Geodetic,Geomagnetic etc.)

GPS

InfrasonicMicrophone

High-sensitive Visual Camera

Seismometer

infrasonic observation of jma

Detected infrasounds by JMA

Tokachi②

Infrasonic Observation of JMA

Infrasonic microphone:ACO type7144/3348 Response : 0.1-1000Hz, 70-150dB

Telemeter : 100Hz, 12-16bit

Usu②

Meakan

Tarumae

Hokkaido-Komagadake③

Iwatesan

Nasu

Kusatsu-Shirane

Adatara

Asama③

Aduma

1983- Sakurajima

1989- Tokachidake

1991- Unzen

1996- Aso etc.

2000- Usu, Miyake etc.

2001- Suwanosejima etc.

2006- Fuji

Ontake

Aso③

Bandai③

Izu-Tobu

Unzen②

Izu-Oshima③

Kirishima②

Fuji

Miyakejima⑧

Satsuma-Iojima

Kuju

Sakurajima⑤

Kuchinoerabujima

Suwanosejima

Active volcanoes in Japan and infrasonic stations of JMA (as of 2007). Encircled figures represent the number of microphones.

infrasonic observation at sakurajima
Infrasonic Observation at Sakurajima

Typical seismic and infrasonic signal from an explosive eruption at Sakurajima volcano.

Monthly number of explosions at Sakurajima.

Narita Aviation Weather Center

VOIC

An example of C type (harmonic) tremor, infrasonic signals and their spectra. (Sakai et al., 1996)

Tokyo VAAC

VAA

results at unzen 1991 95 eruption
Results at Unzen 1991-95 eruption

Nov. 1990 Phreatic eruption

May 1991 Lava dome and PFs

-1995

Infrasonic observation by JMA

1 station (1991-)

4 station (1992-)

Dome collapse

Pyroclastic flow

Low frequency earthquake

Seismic and infrasonic observation atUnzen volcano by JMA (1992-)

●:seismographs

△:infrasonic microphone

◆:visual camera

dome collapse
Dome collapse

An example of seismic (left) and infrasonic (right) signals from a dome collapse. SPs are seismograms obtained by short period seismographs. LP is by a long period seismograph. Seismic records are for the vertical component. Infrasonic records were obtained by low frequency microphones. The records are arranged according to the horizontal distance from the source. The phases, A and B, are considered to correspond respectively to the start of dome collapse and to the fall of lava blocks onto the slope. (Yamasato et al., 1993)

infrasonic signal from pyroclastic flow
Infrasonic signal from pyroclastic flow

Dome

(Left) An example illustrating the migration of a medium sized pyroclastic flow front and the corresponding seismic and infrasonic signals. (Flow distance=3km) Seismic and infrasonic waves were excited while the pyroclastic flow front ran down the slope.

(Right) Source locations of infrasonic sources from pyroclastic flows.

after Yamasato (1997; JPE)

waveform correlation of pf signals
Waveform correlation of PF signals

C

K8(+8s)

●A-course

(05:34 May 21, 1993)

C

K8(+8s)

●B-course

(00:38 April 4, 1993)

C

K8(+8s)

●C-course

(10:31 June 22, 1992)

Examples of infrasonic signals from pyroclastic flows that ran to different three directions.

Good correlations are observed among the waveforms of different stations.

The source location of the infrasonic signal can be estimated from the travel time differences of phases in the signal, assuming the sound velocity is 340 m/s and the source is on the ground surface.

infrasound energy from pf
Infrasound Energy from PF

Energy of the infrasonic waves

Energy of the seismic waves Es=CP, P=square sum of the waveform C is calculated using the relation of Es(J)=1.5M+4.8for low frequency earthquakes.

Relation between the flow distance and the energy ratio of the infrasonic waves to the seismic waves from pyroclastic flows. Only the pyroclastic flows that flowed eastward (B-course) and have clear infrasonic signals were taken. The flow distances are horizontal ones as observed by Unzendake Weather Station. Purple circles indicate the pyroclastic flows for which the flow fronts were out of the range of the video camera, therefore, those distances might be larger than those shown here. (Yamasato, 1997)

low frequency earthquakes in the lave dome
Low frequency earthquakes in the lave dome

An example of seismic (left) and infrasonic records from a low frequency earthquake beneath the dome. An infrasonic signal was excited at the time of the earthquake occurrence.

Dome

Source locations of the infrasonic pulses from low frequency earthquakes (red circles) and dome collapses (crosses). Arrows indicate the direction of pyroclastic flows.

The 9-th lobe appeared in Dec. 4.

after Yamasato (1998)

volcanic eruption at usu 2000
Volcanic eruption at Usu, 2000

An example of the infrasonic record.

Distribution of infrasonic microphones and source location of infrasonic signals from eruptions at Usu volcano. N-B, K-A, K-B are active craters.

(Yamasato et al., 2002)

N-B

K-A

K-B

Photo taken from north of the craters.

sequence of eruptive activity
Sequence of eruptive activity

An example of the time-sequence of activity at each crater.

(Upper) Sequence since mid-April to May 2000 (Yellow in the left figure)

(Lower) Since May to July, 2000 (Blue in the left figure)

Numbers and amplitudes of infrasonic signals since mid-April 2000. (Yamasato et al., 2002)

eruption at miyake volcano 2000
Eruption at Miyake volcano, 2000

Date Plume Infrasonic signal

July 8 2000 800 m No observation

July 14-15 1,500 m Continuous (8 Pa)

Aug. 10 8,000 m Continuous (16 Pa)

Aug. 18 14,000 m Continuous (>20 Pa)

Aug. 21-29 - Impulsive (8 Pa)

Aug. 29 8,000 m Continuous (14 Pa)

2001- <1,000 m Impulsive or continuous (<8 Pa)

Infrasonic record in 03h-06h, 29 August 2000 at Miyake volcano

eruption at hokkaido komagadake 2000
Eruption at Hokkaido-Komagadake, 2000

22:13, 4 September 2000

2x10-6m

5 Pa

60sec

02:42, 28 October 2000

2x10-6m

5 Pa

60sec

Volcanic tremors and infrasound associated with phreatic eruptions at Hokkaido-Komagadake volcano in 2000.

relation between infrasonic and seismic amplitude
Relation between Infrasonic and Seismic Amplitude

Miyakejima

(continuous infrasound and tremor)

Height of dense ash plume

(m above the caldera)

Miyakejima

(impulsive infrasound and tremor)

Usu (impulsive infrasound)

Hokkaido-Komagadake 2000 (continuous infrasound)

Relation between seismic and infrasonic amplitudes of signals associated with eruptions during July – September 2000 at Miyakejima. Ash plume height indicated. (Δ=2km for seismic , Δ=4km for infrasonic signals)

eruption at asama 2004
Eruption at Asama, 2004

Activity in 2004

1 Sep. 2004 First explosion

15 Sep. Lave cake appeared

16-17 Sep. Successive eruptions

23 Sep., 29 Sep., 10 Oct.,14 Nov. Explosions

↓Onset of explosion-quake +10s

200Pa

20:02, 1 Sep. 2004

8Pa

>30Hz

80Pa

19:44, 23 Sep. 2004

40Pa

12:17, 29 Sep. 2004

23:10, 10 Oct. 2004

40Pa

80Pa

20:59, 14 Nov. 2004

10s

1min

Infrasonic records from explosions at Asama in 2004.The station is 8 km distant of the summit crater.

Infrasonic records from Successive eruptions.

infrasonic wave propagating far away
Infrasonic wave propagating far away

Asama

(a)

Amplitude of infrasonic signal from an explosion of Asama, 20:02, 1 September 2004.

Infrasonic records from an explosion of Asama, 20:02, 1 September 2004.

Distribution of infrasonic microphones of JMA

Red triangles indicate ones that detected the infrasonic signal excited by explosions of Asama, 20:02, 1 September 2004 (a) and 19:44, 23 September 2004 (b).

(b)

summary
Summary

Detection of volcanic eruptions and the sequence of eruptive activities

Explosive infrasonic pulses (Sakurajima, Usu etc.) Continuous infrasonic waves (Miyake etc.)

Determination of source locations using infrasonic network

Locations of dome collapses and pyroclastic flows (Unzen) Identification of activities in plural craters (Usu)

Scaling / classification of magnitudes / styles of volcanic eruptions