Electromagnetic ELF radiation from earthquake ... - Wiley Online Library

GEOPHYSICAL RESEARCHLE/q•RS, VOL. 19,NO. 2, PAGES91-94,JANUARY24, 1992

ELECTROMAGNETICELF RADIATIONFROM EARTHQUAKEREGIONSAS OBSERVED BY LOW-ALTITUDE

SATELLITES

O.N.Serebryakova •, S.V.Bilichenko x,V.M. Chmyrev •, M. Parrot :, J.L. Rauch 2,F. Lefeuvre 2,andO.A. Pokhotelov •

Abstract. Seismo-Electromagnetic (SEM) wavesobserved

January20 to February17, 1989, and analysedthe data over

bylow-altitude satellites passing overseismic regions were the epicentralregion in Armenia. The region and the time studied. The data of the COSMOS-1809 satellite were

intervalwas chosento studythe possibleionosphericeffects of strongaftershocks of crucialearthquakein Spitak(40.7øN, 44.0øE;December7, 1988,M=6.7). Thesedataarecompared

analysed overtheearthquake regionin Armeniaduringthe period fromJanuary 20 to February 17, 1989.Intense EM radiationat frequenciesbelow 450 Hz was observedat the L-shellsof the earthquake,during12 orbitsout of the 13 that

with the data obtained from the AUREOL-3

passed within6ø in longitude fromtheepicenter, andduring 1 out of 6 in the range of 6o-8ø longitudeaway from this

region.The otherorbits,whichpassed10ø-12 ø from the epicentre, showed noeffect.To complete thisstudy,we used the emissions observed by another low-altitude satellite

(AUREOL-3). It is shownthat duringthe eventthe seismic regionispermanently radiating;theintensityandtheenvelope shape of thewavedependonits timerelativelyto thetimeof theearthquake. Their frequencyspectraare comparedto the averagespectrum recordedin the samegeomagnetic regions. Similar wave intensities and spectral distributionswere observedon the two satellitesduringthe seismicperiods. Introduction

satellite.

Experimentalresults

The COSMOS-1809satellitewasoperatingin near-circular orbits(970 km, i=82.5ø). ELF/VLF measurements were made with a 5-channel parallel-spectrumanalyzer, both in the

electric (Ex)andthemagnetic (By)fields,forwhichtheX and Y axes were in a horizontalplane, being, repectively, North-Southand East-West.The central frequenciesof the analyzerwere Fo = 140, 450, 800, 4500 and 15000 Hz, the filter bandwidthdF = Fo/ 6 and the samplingrate 0.39 Hz. Accordingto Arefyevet al. (1989), duringtheperiodfrom January 20 to February 17, 1989, 729 aftershockswith energeticclass5.5 < K < 12.0 were registeredwithin the zone 40.5ø < Lat. < 41.5ø and 43.5ø < Long. < 44.5ø. The distributionof theseaftershocks with energeticclassis shown in Figure 1A. To characterizethe energy of the seismic processes, we represented in Figure lB the logarithmof

Severalreportshavebeenpublishedon the observations on groundof SEM emissions[Gokhbergeta!., 1982; Warwick et al., 1982; Fraser-Smith et al., 1990; Fujinawa and E= •10 • Takahashi,1990]. Descriptionsof mechanismsthat might i•l produceSEM emissionsare availablein the literature.Two main mechanismsare generallyinvoked:the first concerns where n is a number of aftershocks within considered 3 hour direct-wave production by compression of rocksnearthefocal intervalsand Ki is an energeticclass of aftershocks.The point [Ogawa et al., 1985; Cresset al., 1987], whereasthe asterisksmark the periods of observationonboard the secondis relatedto a redistributionof the electricchargesin COSMOS-1809 satelliteover the Spitak zone. the Earth'satmospheric system,which produceselectrical For analysiswe selected thedatafrom 24 orbits:8 of them

discharges [Gokhberg et al., 1988;EnomotoandHashimoto, passingwithin 3ø in longitudeto the westof the epicentral 1990]. Perturbationsof the ionosphereare also known to region,5 beingbetween4ø and6ø to the eastof this region,

occur,and SEM emissionshavealreadybeenobservedfrom satellites [Gokhberget al., 1983;Larkinaet al., 1983;Parrot and Lefeuvre, 1985; Chmyrev et al., 1989; Parrot and Mogilevsky,1989;Parrot, 1990a;Bilichenkoet al., 1990].

6 other orbits were between 6 ø and 8 ø west and 5 more from

10ø to 12ø east of the epicentre.Parts of these orbits in geographic coordinates are shownin Figure2A. The dashed lines indicate the location where anomalous radiation (see below) was observed. The asterisk marks the location of

The aim of this studywas to determinethe zonein the ionosphere overanearthquake regionwhereSEMwavescan

epicentralregion,andthe solidline corresponds to the L-shell of its projectionat an altitudeof 100 km (L = 1.42). An exampleof theELF intensityfor the channels140 and

be observed and to find their characteristic time scale. The

intensity and the frequency dependence of the signalsare discussed. Forthispurpose we carriedouta special program 450 Hz over the earthquakeregion is shownin Figure 2B. It of observations onboard the COSMOS-1809 satellite from

is seenthat an intenseSEM emissionof about 10 m•/around Fo = 140 Hz wasobservedfrom 33.7ø up to 30ø in latitude.

Institute ofTerrestrial Magnetism, Ionosphere andRadio

Enhancement of noise was also observed in the channel of

450 Hz, althoughits intensitydid not exceed3 m7. In both Laboratoire dePhysique etChimie de!'Environnement,channelsthe maximumoccurredat the geomagneticlatitude CNRS of the epicentre(L = 1.42). At higher frequenciesno Institute ofPhysics oftheEarth emissionswere observed.In this example of January20, 1989, the ELF emissionwas registered2.5 hoursbefore the Copyright 1992by theAmerican Geophysical Union. earthquake,with the energeticclassK = 10.5, at the distance ~ 1.5ø to the west of the epicentre.A similar example Papernumber91GL02775 0094-8534/92/9!GL-02775 $03.00 (January23, 1989) is presentedin Figure 2C. In this case,as

WavePropagation

91

92

Serebryakova et al.: ELF radiationfromearthquake regions

in the previousone,SEM emissionsat frequencies - 140 Hz were observedwithin a zoneof about4ø lengthin latitude, with a maximumof intensityin the magnetic-fieldtubeof the earthquake region(L ~ 1.42). This eventwasregisteredat a distanceof ~ 1.5ø in longitudeto the west of the epicentre approximately10 minutesbeforea shockwith K = 9.0 and about 2.9 hours before a shock with K = 10.7. Other similar characteristics that were observed within 3-hour intervals

beforethe main shocksare the quasi-regularmodulationof the wave intensity. The example shown in Figure 2D illustratesthe observationover the same region during the long seriesof weaker and numerousshocks. The examplespresentedabove were obtainedalong the orbits that crossedthe L-shell of the earthquakeregion not more than 3ø away in longitudefrom the epicenter.All 8 passages within this3ø-intervalrecordedemissions similarto thoseshownin Figures2B to 2D. Similar radiationpatterns wereobservedduring4 of 5 orbitsthat passedfrom 4ø to 6ø awayfrom longitudeof the epicentre,but only in onecaseof 6 where the satellite

was between

thoseobservedon COSMOS-1809.As a comparison, thetime variationof the signalson the magneticcomponentBx in the

140-240Hz bandandin the 400-500Hz bandwasplotted, respectively, in Figures3B andC. Regularblanksare dueto the on-board calibrations that were removed from the data. As in the COSMOS-1809 cases, an increase is observed at the

lowestfrequencies(Figure3B), when the satellitewas in the magnetic-field tubeof the earthquake region(L- 1.34).The increase is slightly seen in the band 400-500 Hz and

disappearsat higher frequencies(Figure 3C). However, looking at the filterbankdata it can be seenthat the noise level was high in the 15 kHz filter. It is thus likely that two differentwave phenomenaoccurredover the seismicregion, but, it is difficult to know if they were related or no.t. Let

A

epicenter

36

6 ø and 8 ø distant. No

effectswere seenduringthe 5 orbitsthat passedat a distance from 10ø to 12ø in longitude.it should be noted that in all caseswhen ELF emissionswere observedover the Spitak region, only normal backgroundnoise was observedat the sameL-shellsduringthe following and precedingorbits. The same phenomenon was observed on the VLF experimentARCAD-3 [Bertheliereta!., 1982]of the satellite AUREOL-3 (a= 2000km, p= 400km, i= 82.5ø).Waveform data in the band 5 - 1500 Hz were recordedat Suggadeira (Japan) when the satellite was over an earthquakein preparation(M=4.9, April 9, 1982, 23.41 UT, 41.38øN, 142.14øE).A partof the AUREOL-3 orbitis plottedin Figure 3A. The starindicatesthe epicentreof the earthquake,which occurredroughly5 hoursafter the passof the satellite.A spectralanalysisshowsthe sameturbulentpower spectraas

*

40

38

34

32

'

L=!.42

t

30

3'5

40

4'5

5'0

"C05•05 - 1809"

55

Long

JJ•t/AR¾ 20, 198.9

4--.,{,

B

o

00.0•*.25 59.6

•

•.1.?

•

"COb"•O$- '1809"

JAtiUARY2),

1989.

A 140 Hz

L-Lc

&8

œ

2

3

4

:5

6

7

8

9

19

11

12

-.,

? o

25.•,6.19

5.57.a0

25.58.22

2•.59.25

40.2

56.8

N

55.2

N

29.8

N

11.1.6

½2.0 E

•2.5

I•

•2.9

s

u lONG

1{

i1

[

i

i

i

i ! 25

[

i

i

i r 30

[

[

i

i

r [ 5

!

i

i

[ i 10

i

i

!

i i 15

i

Fig. 2. Observations madeby COSMOS-1809.A.- Location of theepicentreandorbitsof the satellitewhereemissions are

observed. B.- Observations in twofrequency bands(140and 450 Hz) 2.5 hoursbeforean earthquake. The time UT, the [Fig.1. A.- Numberof aAershocks as a functionof energetic latitude andlongitude areindicated. C.-Observations recorded 10 minutes and 2.9 hours before two shocks. D.- Observations class.B.- Characterization of seismicactivity(seetext). The asterisksshowwhen the satellitewas operatingover Spitak. duringthelongseriesof weakerandnumerous earthquakes. 20

JA

H U I%•¾

FEBRU

•

31¾

Serebryakova et al.'ELFradiation fromearthquake regions Discussion

The observationsof ELF/VLF waves onboardCOSMOS-

1809 over the Spitak region show that SEM emissionsat

frequencies below450Hz wereregularly observed around the

93

the PLHR, its intensityat an altitudeabout100 km is much lower than the intensitywe observed.No othersourcesof ELF radiation(eithernaturalor man-made)in this narrow (-6ø) low-latituderegionareknownto the authors.

An important featureof thewavephenomenon observed on L-shellof theearthquake, whenthesatellitepassed within6ø COSMOS-1809 is the modulation of the wave intensity. This in longitude fromtheepicentre. Thefactthatsuchemissions at 140Hz wasmodulated with a periodabout5 sec. wereneverobservedduring the orbitslocatedmore than 10ø intensity during 4 passages from the 8 within the 3ø-interval(January awayfromtheearthquake, andtherightmagnetic conjugacy between theregistration zoneandthe epicenter, supportthe 20 and23, February11 and16). Threeof these4 eventswere lessthan3 hoursbeforethe earthquakes with K = conclusion that these emissionsare of seismicorigin. registered 10.5, 10.7 and 10.4. It must be noted that during the Principally,low-altitudeemissionsat 100-500 Hz can be observations lessthanonepercentof the earthquakes had an stimulated in the ionosphere by powerfulground-based VLF transmitter (Chmyrevet al., 1990;Parrot, 1990b)or radiated energeticclassK > 10 (FigureIA). So we suggestthat this modulationcan characterizethe preparationprocessesof from power lines harmonicradiations(PLHR) of 50 Hz. strongearthquakes. Two explanations can be considered:an interactionof ELF and VLF wave processes in the source regionin the Earth, or, a formationof strongfield-aligned in the ionosphereover the at thefragments of orbitsshownin Figure2A. Concerning plasmadensityinhomogeneities

However there are no VLF transmitters where we collected

the data for this study. The nearest VLF transmitter (Krasnodar: 45øN,38øE)wasnot seenin thechannel15 kHz

earthquakeregion. Such a modulationis less clear from the ARCAD-3

•

data. If such a modulation was to be a constant

feature, it could be interestingfor the forecastingof earthquakes. SinceELF emissions wereregistered practically duringeach of the passesat lessthan 6ø of the earthquake region, we can considerthat this region was permanently radiatingduringthe activeperiod.The characteristics of the

23H 41'

radiation depend on the time difference between the observationsand the actualonsetof the earthquakes. Different observations on COSMOS-1809

i

130

i

,

135

140

145

LONG

ARCAD3

9 18

1.0x10

37

4 1982 0

0

0

invariant latitudes less than 30 ø. The ARCAD-3

-5

A

•• 3.2xl0-7

t.OxlO

data of this

paper(Figure3) areplottedasdash-dotlines at 19.39.49UT. The long-dashline in Figure 4B representsthe average amplitude observed during the Armenian earthquakes, completed(at low frequency)by Bilichenko et al. (1990). Otherexamplesfrom AUREOL-3 measurements are shownas a dashedline (Parrotand Mogilevsky, 1989) and as a dotted line (Parrot,1990a).Figure4 illustratestwo differentpoints: first, the power of the wavesassociatedwith earthquakesis higherthan the power of the naturalnoisesat thoselatitudes;

B

1.OxlO

and AUREOL-3

of SEM waves have been combinedto identify a powerspectrumsignature(Figure4). The upperpanel (E) is related to the electric amplitudeand the lower (B) to the magnetic one. As a reference,the solid lines representthe average amplituderecordedby AUREOL-3 all aroundthe Earth at

-8

F lO -3

-5

.• lO-•,

c

...........................................

>•, 10-5

.• 10 -6 •'• 3.2x10 -7 _

•. 10-7

--

10

1 O0

1000

Frequency(Hz)

10-1

. 10-2 18.37

18.39

18'.4!

1.48

1.38

1.31

18.43UT 1.27

L

Fig.3. Observations madeby AUREOL-3.A.- Orbitof the satellitewith time as a functionof thelatitudeandlongitude.

13.-Average amplitude recorded in thefrequency band140240 Hz as a function of the time UT and the L value. C.-

Same asB butin thefrequency band400-500 Hz.

.•10-3

ß -• 10-4

• lO-5, lO

1 O0

1000

Frequency(Hz)

Fig. 4. Amplitudes,as a functionof the frequency,of the electric(upperpanel) and magnetic(lower panel) signals recordedby COSMOS-1809 and AUREOL-3 (seetext).

94

Serebryakova et al.: ELF radiation fromearthquake regions

second,the amplitudesobservedduring differenteventsby two differentlow-altitudesatellitesare very similar. As a comparison, the amplitude(B) of the signalreceived on the COSMOS-1809magneticcomponents overSpitakhas beenexpressed in termsof the amplitude(E) of the electric components. We assumethatE and B are relatedthroughthe equation:E = c B / n with c being the velocityof the light in vacuum and n the refractive index. The observedplasma frequencybeing of the order of 1.2 MHz and the electron gyrofrequencybeing about780 kHz, we have estimatedthe n values for a medium with 50 to 80% of H + ions. We obtain

valuesof about2. 104 V/m at 10 Hz, 5. 10'6 V/m at 150 Hz

and10'6V/m at450Hz, whicharein perfectagreement with the electricmeasurements performedon AUREOL-3. Conclusion

Measurements

of

ELFFv'LF

ChmyrevV.M., A.B. Draganov,Yu. N. TaranenkoandD. Teodosiev,Accelerationof particlesin the upper

ionosphereand the magnetosphere due to decay interactionsof whistlers,i, PhysicaScripta, 43, 495, 1991.

Cress G.O., B.T. Brady and G.A. Rowell, Sourcesof electromagnetic radiationfrom fractureof rock samples in the laboratory,Geophys.Res. Lett., 14, 331, 1987. EnomotoY. andH. Hashimoto,Emissionof chargedparticles from indentationfracture of rocks, Nature, 346, 64!, 1990.

Fraser-SmithA.C., A. Bemardi, P.R. McGill, M.E. Ladd,

R.A. Helliwell and O.G. Viilard Jr., Low-frequency magneticfield measurements neartheepicenterof theIV[ 7.1 Loma Prieta earthquake,Geophys.Res. Lett., 17, 1465, 1990.

waves

onboard

the

COSMOS-1809 satellite in the ionosphere,during the seismically-activeperiod from January20 to February 17, 1989 over the Spitak region, have shownthat intenseELF radiationwas generatedin the zone of 6ø in longitudeand 2ø - 4ø in latitudearoundtheearthquake. The intensityof this

FujinawaY. andK. Takahashi, Emissionof electromagnetic radiationprecedingthe Ito seismic swarm of 1989, Nature, 347, 376, 1990.

Gokhberg M.B., V.A. Morgounov, T. Yoshino and I. Tomizawa,Experimental measurement of electromagnetic emissionpossiblyrelatedto earthquakes in Japan,J. Geophys.Res., 87, 7824, 1982. radiationwas about 10 my at 140 Hz (dF = 25 Hz) and about 3 mqtat 450 Hz (dF = 75 Hz). The intensityof the emissions Gokhberg M.B., V.A. Pilipenko and O.A. Pokhotelov, Seismicprecursorsin the ionosphere,lzvestiyaEarth observed less than 3 hours before earthquakeshad a Physics,19, 762, 1983. quasi-periodicmodulation.The amplitudeand the frequency dependence of the emissionsrecordedby differentsatellites Gokhberg M.B., V.A. Morgounov and O.A. Pokhotelov, Seismicelectromagnetic phenomena,Nauka, 169, 1988. are similar. However, due to the limited frequencyband Larkina V.I., A.V. Nalivayko, N.I. Gershenzon, M.B. observedby the satellites,only partsof the spectrumradiated Gokhberg, V.A. Liperovskiy and S.L. Shalimov, by an earthquakezone are known at the moment. Observation of VLF emissions, related with seismic

Acknowledgements. The ELF/VLF experimentof the COSMOS-1809satellitewas preparedunderleadershipof O.A. Molchanov

and Ya.P. Sobolev. The authors thank M.D.

Fligel for planningof satelliteoperations.The AUREOL-3 programwasundertakenjointly by CNES in France,andby INTERCOSMOS

and

IKI

in

the USSR.

We

thank

J.J.

BerthelJer,who is the principal investigatorof the VLF experiment,for the use of the data, and Yu I. Galperin who drew our attentionto the Suggadeiradata.

activity,on the INTERCOSMOS-19 satellite,Geomagn. Aeron., 23, 684, 1983.

OgawaT., K. Oike andT. Miura, Electromagnetic radiations from rocks,J. Geophys.Res., 90, 6245, 1985. Parrot M. and F. Lefeuvre, Correlation between GEOS

VLF emissionsand earthquakes, Ann. Geophys.,3, 737, 1985.

ParrotM. andM.M. Mogilevsky,VLF emissions associated with earthquakes andobservedin the ionosphereandthe magnetosphere, Phys.Earth PlanetInter., 57, 86, 1989. References Parrot M., Electromagneticdisturbancesassociatedwith earthquakes: an analysisof ground-based and satellite ArefyevS. S. et al., Previousresultsof Soviet-French seismic data, Journal of Scientific Exploration, 4, 203, 1990a. observationsat the Spitak earthquake region on ParrotM., World mapof ELF/VLF emissions as observed by December7, 1988, Thefoundsof Instituteof Physicsof a low-orbiting satellite, Ann. Geophys., 8, 135, 1990b. theEarth,USSRAcademyof Science,Moscow,1989. Warwick J.W., C. Stoker and T.R. Meyer, Radio emission BerthelJer J.J., F. Lefeuvre, M.M. Mogilevsky, O.A. associated with rockfracture:possibleapplicationto the Molchanov,Yu.!.Galperin,J.F. Karczewski,R. Ney, G. greatChileanearthquakeof May 22, 1960, J. Geophys. Gogly,C. Guerin,M. Leveque,J.M. Moreauand F.X. Sene,Measurementsof the VLF electric and magnetic

Res., 87, 2851, 1982.

components of wavesandDC electricfield on boardthe AUREOL-3 satellite:the TBF-ONCH experiment,Ann. Geophys.,38, 643, !982. Bilichenko S.V., A.S. Inchin, E.F. Kim, O.A. Pokhotelov, P.P. Puschaev,G.A. Stanev, A.V. Streltsov and V.M. Chmyrev, ELF responseof the ionosphereon pre-

earthquake processes. DAN USSR, 311, !077, 1990. ChmyrevV.M., N.V. Isaev,S.V. Bilichenkoand G. Stanev, Observationby space-borne detectorsof electricfields and hydromagneticwaves in the ionosphereover an earthquakecentre,Phys. Earth Planet Inter., 57, 110, 1989.

S.V. Bilichenko,V.M. Chmyrev and O.N. Serebryakova, Instituteof TerrestrialMagnetism,Ionosphereand Radio Wave Propagation, 142092Troitsk,Moscowregion,USSR. F. Lefeuvre, M. Parrot and J.L. Rauch, LPCE/CNRS, 3A Avenue de la Recherche,45071 Orleans cedex 2, France.

O.A. Pokhotelov,Institute of Physicsof the Earth, B. Gruzinskaya10, Moscow 123810,USSR. (Received: Mars 5, 199!;

Revised:September10, 1991; Accepted:October28, 1991.)