Importance of Broadband Seismic

and Barometric Observations at Magnetic Observatories

Toshihiko Iyemori1, Kent Taira1, Mitsuru Matsumura1,

and Desheng Han2

1Graduate School of Science, Kyoto University, Kyoto, Japan2Polar Research Institute of China, Shanghai, China

NAK - H 2009.07.17 16:00 – 17:00UT

1-sec averaged data fromDMI Fluxgate magnetometer (FGE-91)(Spec.: 0.1nT resolution)

(NAK)

Nakanoshima

100km

Noise or Signal ??

KNY - H 2009.07.17 16:00 – 17:00UT NAK - H 2009.07.17 16:00 – 17:00UT

Shimazu Fluxgate magnetometerat Kanoya observatory KNY

NAK

Kanoya Nakanoshima

100kmSome similarity!

KNY - H 2009.07.17 16:00 – 17:00UT

KNY & NAK - H 2009.07.17 16:00 – 17:00UT

NAK - H 2009.07.17 16:00 – 17:00UT

These variations ( ～ 160sec) are not a noise but a signal !

Acoustic wave

Phimai

-1

-0.5

0

0.5

1

1.5

0 5 10 15 20 25 30 35 40 45 50 55 60

Minutes

nT

H

D+0.5

Z+1.0

(UT)01:09

(UT)01:11

(UT)01:00

★Phimai (PHI), Thailand: 　　　　 Period = 3.6min. Vertical acoustic resonance + Ionospheric dynamo

★Tong Hai (THJ ), China:

　　 Period=25sec.

Crustal dynamo effect

Two different types of magnetic pulsations at the Great Sumatra Earthquake

Z

HD

1nT

12min

(Kanamori, 2004)

Internal gravity wave

Acoustic wave

Acoustic cutoff frequencyBrunt-Vaisala frequency

Short period waves in the atmosphere

270sec=4.5min (3.7mHz)

229sec=3.8min (4.4mHz)

196sec=3.3min (5.1mHz)

(K. Nishida, 2000)

200km

100km

0km

Principal modes of vertical acoustic resonance

-1

-0.5

0

0.5

1

1.5

0 5 10 15 20 25 30 35 40 45 50 55 60

Minutes

nT

H

D+0.5

Z+1.0

(UT)01:09

(UT)01:11

(UT)01:00

Magnetic pulsation observed at Phimai, Thailand just after the earthquake (Iyemori et al., GRL, 2005)

Acoustic ResonanceVertical WindIonospheric J=σVxB Magnetic Pulsation

Ionosphere

Sudden vertical motion3.6 min (4.6mHz)

515

15

2004 Sumatra earthquake

Acoustic Resonance

mHzNo micro-barometric observation was available near Phimai to confirm acoustic resonance

Electric Current

Wind

地磁気

Origin time

1010

Acoustic resonance effects at 1991 Mt. Pinatubo eruption

3.7 min

(Kanamori&Mori, 1992)

Power spectrum of magnetic variation observed at Lunping(Taiwan)

.

3.7 min. Power spectrum of the seismic wave observed in Japan

Sensor of barometer(VAISALA PTB210)

0.01hPa(0.0025hPa A/D)

DC ～ 1Hz 1 sec recording

Aso

Kyoto

Sakurajima

Shigaraki

～ 500km

Mineyama

Importance of micro-barometric observation

Typhoon No.14 Pressure at SGA and Mag-D at ASO (14-15LT)

Pressure at SGA

Mag-D at ASO

Period (min)

Magnetic effect caused by a Typhoon

Mie Earthquake SGA-P 2007.04.15 03:00 - 05:00UT

-0.1

-0.05

0

0.05

0.1

10800 11400 12000 12600 13200 13800 14400 15000 15600 16200 16800 17400 18000

UT (SEC)

Pres

sure

(hPa

)

M5.4 ?

2007.04.15 03:19UT Mie Chubu Earthquake

SGA Epicenter

The epicenter was very close to the barometric observation site at Shigaraki (SGA) MU radar facility (only about 30 km apart)

250sec

Kyoto

Acoustic resonance caused by an earthquake

Mie-ken Chubu Earthquake(2007.4.15)

Shigaraki was close to epicenter ( ～ 30km) and amplitude of pressure oscillation was large. (Origin time=12:19LT, M=5)

Pressure at Shigaraki

Mag.(D) at Aso

Pressure at Aso

MIZ P 2008.06.14 01:00 - 02:00UT

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 100 200 300 400 500 600

Period (Sec)

Pow

er D

ensi

ty

KAK Mag. H&D 2008.06.14 01:00 - 02:00UT

0

1

2

3

4

5

6

0 100 200 300 400 500 600

Period (Sec)

Power

Density

0.00E+00

5.00E- 03

1.00E- 02

1.50E- 02

2.00E- 02

2.50E- 02

MIZ P 2008.06.13 23:00 - 24:00UT

0

0.01

0.02

0.03

0.04

0.05

0.06

0 100 200 300 400 500 600

Period (Sec)

Pow

er D

ensi

ty

Iwate-Miyagi Nairiku Earthquake 　2008.06.14 00:20UT

Before the main shock

260s225s

185s

260s

Just after the main shock

Mizusawa(Esashi)

Kakioka

Magnetic field data (H & D)

(taken from JMA HP)

270sec=4.5min (3.7mHz)

229sec=3.8min (4.4mHz)

196sec=3.3min (5.1mHz)

(K. Nishida, 2000)

200km

100km

0km

Principal modes of vertical acoustic resonance

　

★Coincidence of the magnetic variations at Tonghai(THJ) and that of the seismic wave arrival at Kunming(KMI) 　 → magnetic variations caused by the seismic waves

THJ magnetic field

KMI displace-ment

IRIS broad-band seismometer (20Hz1sec averaged )

Fluxgate magnetometer

● PHI

Importance of colocated Broadband seismic and magnetic measurements

1nT

0.4m

epicenter

Characteristics of the magnetic and seismic variations

17

・ Ground displacement: N-S component precedes vertical by 90 degrees　→ Rayleigh wave (E-W comp. → Love wave)

・ Period (frequency) shift 30 sec →20 sec

Power spectral density （ MEM ）　　 Red ：　 Mag. H-comp.　　 Blue ：　 Vertical displacement

V

Displacement at Kunming

N precedes V by 90 degrees Reyleigh wave

Time

18

Inclination of the sensors cannot reproduce the observed magnetic oscillation because; 1. amplitude is twice of the effect of the sensor inclination 2. magnetic oscillation is polarized in the H-Z plane

Observed H and Z

Effect of sensor inclination

Observed displace-ment

Crustal dynamo

19

J=σ(V×B+E)

V

V

Crustal dynamo mechanism is simple compared with Piezo magnetic effect or fluid effect

GGGrownd motion Induced mag.

Simulation of magnetic variation by the crustal dynamo mechanism

Assumption・ Displacement decreases to zero at the depth of 1.5x(wave length)・ Effective resistivity is 50Ωm including the upper mantle ・ The phase velocity of the Reileigh wave with period of 25 second is 3.83km/s 　 (Aki and Richards, 2002)

Depth dependence of amplitude of the Rayleigh wave (Uzu,2001)

Observed displacement is used as the surface displavement and the underground displacement is estimated by the model below.

Magnetic effect from sensor inclination

21

Estimation of the sensor inclination

Removing the sensor inclination effect

・ Phase velocity of the Rayleigh wave: 3.83km/s　　 Correction of the distance between KMI and THJ Magnetic data are shifted 31 seconds behind ・ Coordinate transformation (rotation) to separate the Rayleigh wave from the Love wave 　 The epicenter is in the direction of wave propagation

Displacement in 2 sec

Nenative H

Negative Z

Correction based on the velocity of the seismic wave necessary

22

Observation

Effect of sensor inclination

Observed – Effect of inclination For H and Z component.

Estimated crustal dynamo effect

Ground displacement

Comparison of observed magnetic variation with the estimation by a crustal dynamo simulation

SUMMARY

23

1. Magnetic variations caused by the vertical acoustic resonance between the ground and ionosphere via the ionospheric dynamo have been detected at various occations.

2. To identify the cause of small amplitude magnetic oscillations, micro-barometric observation is important. It could also be useful for meteorological research.

3. Magnetic variation with amplitude of about 0.1-0.2 nT was observed during the passage of the Rayleigh wave just after the Great Sumatra earthquake.

4. The amplitude and phase relation of H and Z component agree well with an estimation by a crustal dynamo simulation with observed seismic wave (Rayleigh wave) data.

5. The effective resistivity necessary to explain the observed amplitude is about 50(Ωm).

6. For quantitative analysis, it is desirable to put a broad-band seismometer at the same location with high-

resolution magnetometer. 　

The 1st ICSU World Data System Conference – Global Data for Global Science

September 3 – 6, 2011 in Kyoto, Japan

Thank you for your attention !

26

Chishima Islands Oki Earthquake (2007.01.13) Mag. at MMB & Displacement at KNPMemambetsu (MMB) Geomagnetic fields

Kunnep (KNP) Broadband seismometer

D

Another example

27

Love wave dominates in this event Direction of VxB vector is parallel to the wave propagation　 Electric current does not flow(?) 　 V

B

VxB

Wave propagation

(J)

Crustal dynamo origin

Acoustic wave origin

Internal Gravity wave origin

Pi2, Pi1

SC

Substorm, Storm

Sq

( ～ upper limit)

Period (second)

Frequency (Hz)

nT

Amplitude Spectra of Rapid Magnetic Variations

Almost all of the short period magnetic variations have been assumed to be of ionospheric or magnetospheric origin. Events of Crustal and/or lower atmospheric origin

30

Acoustic wave

Dynamo

Field-line resonance

PhimaiTong-Hai

-1

-0.5

0

0.5

1

1.5

0 5 10 15 20 25 30 35 40 45 50 55 60

Minutes

nT

H

D+0.5

Z+1.0

(UT)01:09

(UT)01:11

(UT)01:00

★ スマトラ地震 12 分後 にタイ・ピマーイ (PHI) で観測された　　周期 3.6 分の地磁気脈動の他に　中国 TongHai (THJ ) で　　周期約 25 秒 の地磁気脈動が観測され、当初は磁力線共鳴　　現象の可能性が示唆された　 (Iyemori et al., 2005)

32

1995 2000 2005 2009

太陽風の長期変化　 ( 速度と粒子数密度 ) 　　　 (OMNI database)

01:12UT

-1

-0.5

0

0.5

1

1.5

0 5 10 15 20 25 30 35 40 45 50 55 60

Minutes

nT

H

D+0.5

Z+1.0

(UT)01:09

(UT)01:11

(UT)01:00

Magnetic data

ＧＰＳ TEC data

Earthquake

High coherence between magnetic and TEC oscillations Key role of dynamo ?

“TEC Pulsation”

Magnetic Pulsation

Resonance peak at a period of 3.6min.

5 15

10

20

4.953.852.751.65 6.05 7.15 mHzOrigin time

SGA Pressure 2007.04.15 06:00 - 07:00UT

0

0.050.1

0.15

0.2

0.250.3

0.35

0 100 200 300 400 500 600

Period (sec)

Power D

ensity (h

Pa**2/

Hz)SGA Pressure 2007.04.15 07:00 - 08:00UT

00.10.20.30.40.50.60.70.8

0 100 200 300 400 500 600Period (sec)

Powe

r Dens

ity (h

Pa**2

/Hz)

Before the Earthquake 03 – 04 UT 04 – 05 UT

05 – 06UT 06 – 07 UT 07 – 08UT

Spectral peaks and their temporal variation