Infrasonic Observation near Active Volcanoes and its Results in Japan

Hitoshi YAMASATO*, Takayuki SAKAI* and Yoshiaki FUJIWARA** *Meteorological Research Institute, Japan Meteorological Agency** Japan Meteorological Agency (present : Geographical Survey Institute)

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

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

Volcano Observation of JMA

傾斜計

High-sensitive Visual Camera

SeismometerInfrasonicMicrophone

GPS

Tiltmeter

Volcano Observation andInformation Centers(Sapporo, Sendai, Tokyo, Fukuoka)

Real-time telemeter

Mobile Observation(Thermal, Geodetic,Geomagnetic etc.)

Infrasonic Observation of JMAInfrasonic microphone:

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

Telemeter : 100Hz, 12-16bit Meakan

Tokachi②

Tarumae

Usu②

Hokkaido-Komagadake③Iwatesan

Adatara

Aduma

Bandai③

Nasu

Kusatsu-ShiraneAsama③

Ontake

Fuji

Izu-Tobu

Izu-Oshima③

Miyakejima⑧Kuju

Aso③

Unzen②

Kirishima②

Sakurajima⑤

Satsuma-Iojima

Kuchinoerabujima

Suwanosejima

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

Detected infrasounds by JMA

1983- Sakurajima1989- Tokachidake1991- Unzen1996- Aso etc.2000- Usu, Miyake etc.2001- Suwanosejima etc.2006- Fuji

Infrasonic Observation at Sakurajima

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

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

Monthly number of explosions at Sakurajima.

Tokyo VAACTokyo VAAC

VOICVOIC Narita Aviation Weather Center

VAAVAA

Results at Unzen 1991-95 eruption

Nov. 1990 Phreatic eruptionMay 1991 Lava dome and PFs -1995

Infrasonic observation by JMA 1 station (1991-) 4 station (1992-)

Dome collapsePyroclastic flowLow frequency earthquake

Seismic and infrasonic observation atUnzen volcano by JMA (1992-)●： seismographs△： infrasonic microphone◆： visual camera

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

(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)

Dome

Waveform correlation of PF signals

●A-course (05:34 May 21, 1993)

●B-course (00:38 April 4, 1993)

●C-course (10:31 June 22, 1992)

C

K8(+8s)

C

K8(+8s)

C

K8(+8s)

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

0 2 4 6

Flow distance (km)

1

2

3

En

erg

y ra

tio

(E

a/E

s)

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)

E rp r

cdta

e2 22

( )

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.

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.

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)

Dome

Volcanic eruption at Usu, 2000

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)

Photo taken from north of the craters.

An example of the infrasonic record.

N-BK-B

K-A

Sequence of eruptive activity

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

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)

Eruption at Miyake volcano, 2000

Date Plume Infrasonic signal July 8 2000 800 m No observationJuly 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

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

22:13, 4 September 2000

02:42, 28 October 2000

2x10-6m

5 Pa

2x10-6m

60sec

60sec

5 Pa

Relation between Infrasonic and Seismic Amplitude

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)

Usu (impulsive infrasound)

Hokkaido-Komagadake 2000 (continuous infrasound)

Miyakejima (impulsive infrasound and tremor)

Miyakejima (continuous infrasound and tremor) Height of dense ash plume(m above the caldera)

Eruption at Asama, 2004

20:02, 1 Sep. 2004

19:44, 23 Sep. 2004

12:17, 29 Sep. 2004

23:10, 10 Oct. 2004

20:59, 14 Nov. 2004

>30Hz

200Pa

10s

↓Onset of explosion-quake +10s

8Pa

80Pa

40Pa

40Pa

80Pa

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

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

Infrasonic records from Successive eruptions.

1min

Infrasonic wave propagating far away

Distribution of infrasonic microphones of JMARed 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).

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

Asama

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

(a)

(b)

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

END