On recent physical models of lithosphere-atmosphere-ionosphere coupling before earthquakes

13 Pages·2012·0.15 MB·English

On recent physical models of
lithosphere-atmosphere-ionosphere coupling before
earthquakes
1 1 2 1
V.A.Liperovsky ,O.A.Pokhotelov ,C.-V. Meister ,andE.V.Liperovskaya
1
InstituteforPhysicsoftheEarth,123995Moscow,Russia,[email protected]
2
Project(cid:147)PhysicsofStellarandPlanetaryAtmospheres(cid:148),14482Potsdam,Germany,
[email protected]
Manuscriptsubmittedto
NATURALHAZARDANDEARTHSYSTEM SCIENCES
Manuscript-No. nhess-2007-June
NATURALHAZARDANDEARTHSYSTEM SCIENCES(2007)0000:0001(cid:150)12
On recent physical models of lithosphere-atmosphere-ionosphere
coupling before earthquakes
1 1 2 1
V.A.Liperovsky ,O.A.Pokhotelov ,C.-V.Meister ,andE.V.Liperovskaya
1InstituteforPhysicsoftheEarth,123995Moscow,Russia,[email protected]
2 Project(cid:147)PhysicsofStellarandPlanetaryAtmospheres(cid:148),14482Potsdam,Germany,[email protected]
Abstract.Inthepresentwork,anattemptismadetoexplain (cid:2)ndingstimulatedthesearchforearthquakeprecursorsinthe
and to evaluate the most interesting and physically impor- ionosphere. Ionosphericphenomenawhichwere causedby
tant models of lithosphere-atmosphere-ionospherecoupling the seismic eruption and by the propagationof the seismic
beforeearthquakes.Insomeofthemodelsitisassumedthat wavesaftertheeruptionwerefrequentlyregistered.Besides,
inthenear-Earthatmosphereabovetheregionofearthquake various rarely and incidentally found effects were consid-
preparationatmosphericacousticandacoustic-gravitywaves ered.
are excited and propagate through the atmosphere up into Theobservationof(cid:147)anomalous(cid:148)pulsesofelectromagnetic
ionosphericaltitudes, wheretheycauseelectric (cid:2)elddistur- emissions in the frequency interval between a few Hz and
bances and changes of the density of the chargedparticles. some tens of kHz as well as the changes of the density of
Other models suggest that ionospheric disturbances are the thechargedparticlesregisteredbysatelliteswereastimulus
consequenceofmodi(cid:2)cationsofelectric(cid:2)elds andcurrents forthefurtherexperimentalinvestigationofthelithosphere-
whicharecausedbyelectricprocessesofthelithosphereor ionospherecoupling[Gokhbergetal.1982,1983;Migulinet
near-Earthatmosphere. Itisunpossibletoconsideronlyone al 1982, Larkina et al. 1983]. For the physical understand-
oftheexplainedmodelsandtoneglectalltheothermodelsas ing of the processes in the system lithosphere-atmosphere-
the characteristic spatial scales of the observedionospheric ionosphere, such works were of special importance, which
phenomenabeforeearthquakesliebetween200-300kmand were dedicatedto the noti(cid:2)cationof disturbancesof the at-
afewthousandsofkilometres,andthecharacteristictempo- mosphericelectric(cid:2)eld[Gokhbergetal.1988a],to(cid:147)anoma-
ralscalesareintheintervalbetweensomeminutesandafew lous(cid:148) geomagnetic pulsations [Gogatishvili 1984, Fraser-
days.Onemayconcludethatthereallithosphere-ionosphere Smithetal.1990],and(cid:147)anomalous(cid:148)disturbancesintheiono-
couplingistheresultoftheactionofsomedifferentphysical sphere[Kolokolovetal.1992]andthemagnetosphere[Sere-
mechanisms. bryakova et al. 1992, Parrot 1994]. Thereat also the con-
nection between ionospheric disturbances and the discrete
structureoftheEarth’score(radioemissionsabovefracture
regions of the Earth) [Shaftan et al. 1986] at seismic quiet
1 Introduction
timeswasmentioned.
Recently,itisveryactualandimportanttoinvestigatephysi- One has to underline that since about 1980, and up to
cal processes accompanyingdifferent phases of earthquake now,thenumberofpublicationsconcerningthecouplingin
preparation and to develop methods of earthquake predic- thesystemlithosphere-atmosphere-ionosphereconnectedto
tion. Thus many experimental and theoretical works were earthquakeshasbeenincreasingeveryyear. Recently,some
performed,anditseemsthatsciencemadeanessentialstep hundred articles come out the year. The most full lists of
into the direction of a possible solution of the problem of referencesisgiveninthebooksbyGokhbergetal.(1988b),
earthquakeprediction. Tothemostessentialandinteresting Liperovskyetal.(1992)andPulinetsandBoyarchuk(2004).
results, obtainedduringthelast twodecadesbyradiophysi- According to an article by Pulinets [2006], ionospheric ef-
calobservations,therebelongaboveallelectromagneticand fectsofearthquakesarestudiedin20countries,andalonein
ionospheric disturbances occurring before and during seis- Russiathereworkonthetopic10groupsofscientists.
micactivities. Nearlythewholeresearchwork, performeduptonowin
Forthe(cid:2)rsttime,modi(cid:2)cationsofionosphericparameters the (cid:2)eld of lithosphere-atmosphere-ionospherecouplingre-
were mentionedby Davies and Baker (1964)in connection latedtoearthquakes,hadtheaimtoidentifyionosphericpre-
withtheextremelystrongearthquakeinAlaskain1964.This cursorsofearthquakesandtosolvetheproblemofshort-time
1
2 V.A.Liperovskyetal.:Lithosphere-atmosphere-ionospherecouplingbeforeearthquakes
earthquake prediction. To (cid:2)nd solutions was more compli- theearthquakeanddirectlyabovetheepicenterabout12min
catedthansupposed.Itturnedoutthattheearthquakeprecur- beforetheevent. Theregionswheretheeffectwasobserved
sorspossessdif(cid:2)culttemporalandspatialstructures,thatthe hadalatitudinaldimensionofabout1.0grad-1.5grad,and
maximum effects are not always obtainable directly above theamplitudeoftheobservedmagneticpulsationsamounted
the epicenter, and the amplitude of the precursor does not to3nTatafrequencyofabout1Hz[Sorokinetal.1998].
always increase when the time approaches the moment of Duringtheregistrationofthevariationsoftheplasmaden-
theearthquake.Correspondingly,itbecamenecessarytode- sityandtheELF/VLFnoisesby(cid:148)KOSMOS-1809(cid:148)nearSpi-
velopadequatephysicalmodelstointerpretethelithosphere- tak,somedays-hoursbeforetheeruption,intensivemagnetic
atmosphere-ionospherecoupling. disturbanceswerefoundinaregionof(cid:6)6oinlongitudeand
In the present work, a series of - according to the view- (cid:6)4oinlatitudewithrespecttotheepicentreofthepreparing
point of the authors - basic experimental results and most earthquake (that means at distances of up to 500 km from
interesting physical models of lithosphere-ionosphere cou- the epicentre). There the amplitude of the magnetic distur-
plingsomedaysbeforeearthquakesarereviewed. Phenom- bances rose up to about 10 nT at a frequency of 140 Hz,
enaconnectedtoearthquakes,whichoccuraftertheseismic andup to about 3 nT at 450Hz. In the same regionwhere
eruptions, areof less interest. First, in the article some im- theanomalousELFmagneticdisturbanceswereexcited,also
portant experimental results demonstrating the lithosphere- small-scale (4-10 km along the orbit) inhomogeneities of
atmosphere-ionospherelinksareanalysed. Thenanattempt the plasma density of (cid:1)N=N (cid:25) 3(cid:0)8 % were observed.
o
ismadetoexplainandtodiscussthemostinterestingphysi- Besides sudden temperature changes and density decreases
calmodelsproposeduptonowtodescribetheselinks.Ithas werefound(seee.g.[Sorokinetal.1998]).
tobementionedthatuptonownogenerallyacceptedmodels Duringtheneweststudiesofearthquakepreparationphe-
exist. nomena using data registered by the satellite DEMETER,
one found a damping of VLF radiosignals by external
sources at F-region altitudes at distances of 1000-5000km
2 Somemostimportantexperimentalresults from the earthquake epicentres about 0-3 weeks before the
event[Molchanovetal.2006].
Theobservationofdisturbancesofaseriesofcharacteristic Thusbysatellite experiments,episodesofspikes oflow-
parameters of the ionospherebeforeearthquakesis of prin- frequencyplasmaturbulence,andregionsofincreasedtem-
cipal importance for the understandingof the possible per- perature and decreased density in the upper part of the F-
spectiveofearthquakepredictionsbysatellites. Suchsatel- layeraboveseismo-activezonesatdistancesupto1000km
lite experiments essentially accelerated the investigation of fromtheepicentreareobtained. Becauseofsuchdistances,
seismo-ionosphericearthquakeprecursors. Inthefollowing, theobservationswereofless interestforthesolutionofthe
someexamplesaregiven. prognoseproblem, but they remainedimportantfor the un-
Searching for possible seismo-ionospheric effects, dur- derstanding of the physical mechanisms. Besides there do
ing the analysis of data obtained beforeearthquakesby the notexist statistical provesofthe effectsfoundbysatellites.
satellite (cid:148)Interkosmos-19(cid:148)at F-region altitudes an increase These phenomena were rarely obtained - and only during
of both the intensity of VLF noise with frequencies be- tenths of seconds during the satellite (cid:3)ights above seismo-
tween140Hzand15kHzandthedisturbancesoftheelec- activeregions.
tron density at distances from the epicentres up to a few
1000kmwerefoundforthe(cid:2)rsttimein[Migulinetal.1982, 2.1 Lithosphere-ionospherephenomenaintheF-layer
Gokhberget al. 1982, 1983, Larkinaet al. 1983]. In 1981,
duringtheanalysisofthedistributionoftheelectrondensity Aratherlargepartofstatisticallyreliable-oralmoststatisti-
intheupperpartoftheF2-layerregisteredby(cid:148)Interkosmos- callyreliable-seismo-ionosphericeffectsisfoundbyiono-
19(cid:148) [Pulinets and Boyarchuk 2004] it was concluded that sphericsoundingexperiments. Aspecialanalysisofthein-
aboutonedaybeforeanearthquakethealtitudeofthemax- vestigations of the ionosphere before earthquakes showed,
imumoftheelectrondensityoftheF2-layerincreasedfrom that speci(cid:2)c kinds of anomalous ionograms before earth-
about280kmtoabout360km,butthemaximumoftheelec- quakes practically do not occur. For a long time, scientists
trondensitydecreasedfrom3(cid:1)105cm(cid:0)3 to105cm(cid:0)3. This have been looking especially for such ionograms, but they
phenomenonwasveryestonishing,anditstimulatedthefur- did not (cid:2)nd them. Thus, investigating ionospheric effects
thersearchforionosphericandmagnetosphericprecursorsof duringtimesofearthquakepreparation,itbecamenecessary
earthquakes. to show the main laws of the temporal behaviour of some
Registeringvariationsofboththecomponentsofthemag- ionospheric parameters statistically. It had been suggested
netic (cid:2)eld in the frequencyregionof 0.1-8 Hz and the ver- thatthemodi(cid:2)cationsintheionospherecausedbyprocesses
tical component of the quasi-constant electric (cid:2)eld by the ofearthquakepreparationareratherweak. And,nottotake
satelliteIK-B1300,beforetheearthquakewiththemagnitude into account direct solar in(cid:3)uences, usually, (cid:2)rst only the
M = 4:8 on January 2, 1982, pulses of the vertical quasi- night-timeionospherewasstudied.
static electric (cid:2)eld of 3-7 mV/m were observed twice, at a Of course, during the investigation of the seismo-
distanceof2000kmfromtheepicentreabout15minbefore ionospheric effects, there arose questions about their char-
V.A.Liperovskyetal.:Lithosphere-atmosphere-ionospherecouplingbeforeearthquakes 3
acteristictimescalesandlengthscales. Thetimescaleswere of the sporadic layers changes between some hundreds of
foundtobeintheintervalfromafewminutestosomehours, meters andsome kilometres. Often sporadiclayerspossess
andthelengthscaleswereshowntobebetweenafewhun- an inhomogeneous horizontal structure - spots and isles of
dreds and a few thousands of kilometres [Liperovskyet al. ionization.Andtheyhavealsoverticalinhomogeneities-the
2002,Meisteretal.2002]. Thelargeintervalofcharacteris- Es-spread.
tic time scales of lithospheric-ionosphericeffects expresses Studyingthe dynamicsof sporadiclayersusing ionoson-
thecomplexityofaseriesofphysicalmechanisms-andnot des,onecanmeasurethemodi(cid:2)cationsofthemaximumion-
ofasinglemechanism-happeningduringthetimeofearth- izationdensityofthelayerandthecharacteristicsofthein-
quakepreparation.Uptonowitisnotyet(cid:2)nallyclear,which homogeneityortheturbulizationofthelayer.Thelarge-scale
mechanismsbelongtothiscomplexofprocesses. turbulization(hundredsofmeters)maybeobservedbytheE-
Investigating seismo-ionospheric effects of the F-layer, spreadeffect-thediffusivityofthetracesofthelayersinthe
it was found that the maximum ionization density growths ionograms. Thesmall-scale(tenths ofmeters)turbulization
about 3-7 days before earthquakes, and then it decreases. is characterized by the coef(cid:2)cient of the semi-transparency
The minimumwas obtained0-2 days before the event [Pu- ofthelayer.
linetsandBoyarchuk2004,KorsunovaandHegai2005,Liu Duringtheinvestigationoftheionosphericphenomenait
et al.2006]. Thementionedphenomenawereregisteredby was shown statistically, that one day before an earthquake
verticalsoundingstationsatdistancesof500-1000kmfrom the maximum electron density decreases, but two days be-
theepicentres. fore the event, the number of modi(cid:2)cations of the density
About0-2daysbeforetheearthquakesalsotheturbuliza- with characteristic time scales of 15 minutes very often in-
tionoftheF-layerweakens[Liperovskayaetal.2006],which creases. The large-scale turbulence (E-spread) is strength-
istobeseenasdecreaseoftheF-spreadandofthevariability ened,butthesmall-scaleturbulenceoccursmorerarely.This
of the maximumionization density with characteristic time phenomenon is observed for earthquakes with magnitudes
scales of2-3hours[Popovet al.2004]. Ontheotherhand, M > 5. Thespatialdimensionsofthementionedphenom-
the variability of the ionization density below the electron ena amount up to 300-500 km [Alimov et al. 1989, Liper-
densitymaximumoftheF-layer,ataltitudesof200-250km, ovskayaetal.1994a,Liperovskaya2006].
increases.Thespatialscalesoftheseeffectsareupto500km ButintheE-layeralsoeffectswithscalesof500-1000km
[Liperovskyetal.1992]. werefound.Especially,itwasshownthatthecorrelationco-
Recently ionospheric phenomena related to earthquakes ef(cid:2)cientofsporadiclayersaboveverticalsoundingstations,
are obtained by satellites using GPS. There one studies the whicharesituatedatadistanceofsomehundredsofkilome-
totalelectroncontentinaverticalaircolumnebetweenEarth tres,decreases1-2daysbeforeearthquakes,iftheepicentre
surface and altitude of satellite observation. The electrons oftheearthquakeislocatedatdistances(cid:20)1000kmfromthe
of the F-layer mainly contribute to the total electron con- soundingstations[Liperovskyetal.2002].
tent. In the works by Pulinets et al. [2004] and Liu et al. Thementionedexperimentalresultsmaybeinterpretedas-
[2004],itwasshownusingGPS,thatabout1-7daysbefore sumingthatintheionospheresomeprocessescompete. The
strong earthquakes the variability of the total electron con- observationsshowthatbeforeearthquakesintheionosphere
tentgrows,providedthatthepointoftheobservationliesin acoustic and acoustic-gravity waves (AGWs) with periods
theearthquakepreparationregion. betweenparts of minutesand hours propagate,that electric
(cid:2)eldsandcurrentsareexcited,andthatheatingprocessesoc-
2.2 Lithosphere-ionospherephenomenaintheE-layer cur.ThemainexperimentalresultsarelistedinTable1.
At altitudes of the ionosphericE-layer at night, the regular
electrondensityamountsto102(cid:0)103cm(cid:0)3,whichisbelow
3 Lithosphere-atmosphere-ionospherecouplingmodels
theworkingleveloftheionosonde.Thus,oneusuallystudies
sporadicE-layersthedensityofwhichis2-3ordersofmag- Now, the physical coupling mechanisms in the system
nitude larger. The formation of sporadic layers is believed lithosphere-atmosphere-ionosphere at seismic activity will
to be connectedwith the wind-sheareffect. If thedirection bereviewed.
ofthehorizontalwindintheE-layerchangesitsdirectionby
180deg.andtheverticalgradientofthewindreachesvalues 3.1 Acoustic-gravitymodels
of 0.05-0.06s(cid:0)1, then the chargedparticles are accelerated
intothe directiontothe pointwith vanishingvelocityvalue Theacoustic-gravityhypothesis(AGH) is nowadaysoneof
(moreexactly,intothedirectionofthezerovalueofthediver- the most popular hypotheses. According to it, some days
gencyofthewindvelocity). Asaresult,asporadicE-layer before the eruption, in the region of earthquake prepara-
forms.ThedestructionofsporadicE-layersismainlycaused tion near the Earth’s surface atmospheric acoustic-gravity
byambipolarandturbulentdiffusion. waves (AGWs) are excited, which propagate through the
The maximum electron density in sporadic E-layers atmosphereandreachionosphericaltitudes.Further,thedis-
amountsto105(cid:0)106cm(cid:0)3,andtheirhorizontaldimensions turbancesoftheneutralcomponentoftheionosphere,dueto
varybetween10and100kilometres. Theverticalthickness
4 V.A.Liperovskyetal.:Lithosphere-atmosphere-ionospherecouplingbeforeearthquakes
Table1.Ionosphericprecursorsofearthquakes(experiment)
altitude method parameter anomaly distance timebefore
(km) earthquakes
above satellite 0.11-8Hz "(cid:2)10(cid:0)103 1000 hours
F-layer satellite (VLF-noise)
140Hz-15kHz "(cid:2)10(cid:0)103 longitude:1000, hours-days
latitude:6000
F-layer ion-sound F-spread "10% 500 days
ion-sound densitydisturbances "(cid:2)2,(cid:28) =2h 500 days
photometer 630nm "15(cid:0)40% 1000 days
Es-layer ion-sound density #10% 500 hours-days
ion-sound strongdensity "10% 500 days
disturbances
atthelayer
boundaries
ion-sound E-spread "20% 300 days
photometer 557.7nm "7% 200 hours
D-layer SDW disturbancesof " 1000 hours-days
thesignalphase
thecollisionsoftheneutralparticleswiththeions,causedis-
nismwhereAGWsplaythemainrole. Weunderlineatthis
turbancesofthedensityofthechargedparticlesoftheiono-
place, that the generation process of the AGWs is not yet
sphere[Mareevetal.2002,GokhbergandShalimov2004].
suf(cid:2)cientlystudiedexperimentallyuptonow.
3.1.1 Rayghleigh-TaylorinstabilitybyAGWsatlargerdis-
tancesfromtheepicentres 3.1.2 AGWactionatsmallerdistancesfromtheepicentres
becauseofseismicmosaic-likestructure
In the work by Shalimov and Gokhberg [1998], using
numerical models, it was shown that atmospheric AGWs
which are excited in the near-Earth atmosphere a few days Anothergroupofscientists[Mareevetal.2002,Molchanov
beforeearthquakesmaypropagateupwarduntilaltitudesof 2004]consideredAGWsofsmallerperiodsofsomeminutes
120-150 km. Thereat the transfer of disturbances into the anduptotenthsofminutes. WiththeseAGWsonemayex-
ionosphere proceeds in many steps. It is assumed, that the plaintheexistenceofionosphericphenomenaatsmallerdis-
atmospheric AGWs are generated by non-stationary (cid:3)uxes tancesfromtheepicentres. Theauthorsconsideredamosaic
of gases from the lithosphere into the atmosphere. The structure of the sources of AGWs of seismic origin. Such
waves then propagatesup to ionosphericaltitudes and may sources, formed by chaotic inhomogeneities, may be much
causeionosphericplasmabubbles. ThereattheAGWscause moreeffectiveAGW generatorsthansourceswhichareho-
only the initial plasma disturbances which then give the mogeneouslydistributedinspace.Intheworks,theregionof
reason for the plasma Rayghleight-Taylorinstability which earthquakepreparationwas modeled as a mosaic source of
isconnectedwithoforderslargerenergies.Theinvestigation heatandmasshavingacharacteristictimescaleoftheorder
of the effectivity of the possible generation mechanisms of oforlargerthantheBru¤nt-Va¤issa¤la¤periodoftheatmosphere.
AGWsshowed,thattheobviouslymosteffectivegeneration Withotherwords,waveswithstructureswereassumed,and
is caused by the non-stationary gas (cid:3)ux [Perzev and Shal- fortheexplanationoftheionosphericphenomenathemosaic
imov1996](energy(cid:3)uxoftheorderof0.1erg/(cm2s)).The structureofthedisturbanceswasofimportance.
in(cid:3)uence of the processes of earthquakepreparationon the
Inaccordanceto[Molchanov2004],theKolmogorovtur-
F-layer may be obtainedat distances up to a few 1000km.
bulenceintheionosphereistheresultoftheevolutionofthe
Suchanin(cid:3)uencemaybeonlyexplainedbytheAGWmech-
AGWs,andthetimeoftransferofthedisturbancesfromthe
anism,andthewavesshouldhaveratherlargecharacteristic
Earth’ssurfacetotheionosphereamountstosomehoursand
timescales. Itshouldbementionedthatearthquakeprepara-
dependsonthewaveperiod.
tionprocessesdonotonlyin(cid:3)uencetheF-layer,butalsothe
ionosphericE-layerat distancesof upto1000kmfromthe Consequently, the both mentioned acoustic-gravity hy-
epicentre[Liperovskayaetal.1994]. Apossiblemechanism potheses may explain observations of ionospheric distur-
which might cause the formation or destruction of spo- bances before earthquakes, which may be obtained by
radicE-layersatsuchdistances-thisisonlysuchamecha- ionosondesandbysatellites,especiallyatdistancesfromthe
epicentrewhichareoftheorderoforlargerthan1000km.
V.A.Liperovskyetal.:Lithosphere-atmosphere-ionospherecouplingbeforeearthquakes 5
3.1.3 AGWsources NO+, thetemperatureoftheE-layer,andconsequently,the
intensityoftheair-glowincrease.
NowthereasonsfortheAGWoccurrenceinthenear-Earth Onemayassume that simultaneousobservationsof pres-
atmospherewillbediscussedindetail. Itisknownthatdur- sure and other meteorological parameters in seismo-active
ing seismic measurements the spectrum of seismo-gravity regions within a network of stations on the Earth’s sur-
oscillationsoftheEarthwithperiodsbetween30minand4h face, together with the ionospheric observations, would al-
are usually registered[Lin’kovet al.1989, 1990]. Besides, low to con(cid:2)rm experimentally the here presented hypothe-
observationsalsoshowedthatlong-periodicoscillationswith ses of lithosphere-atmosphere-ionosphereconnections. But
periodsintheintervalof1-5hmaybeexcitedafewdaysbe- suchexperimentsareratherdif(cid:2)cult,anduptonownobody
forestrongearthquakeswithmagnitudesM (cid:21)6:0[Garmash has them carried out. The main observationswhich are in-
et al. 1989]. The intensi(cid:2)cation of such oscillations obvi- terpretedbasingontheproposedhypothesisarelistedinTa-
ouslyoccurs,forinstance,inthemodulationoftheintensity ble2.
of the natural electromagnetic emissions (NEE) and of the
F-layerdisturbancesintheintervalofperiodsoft=2(cid:0)3h
Table 2: Acoustic-gravity wave (AGW) hypothesis of
beforeearthquakes[Liperovskyetal1992,Bellaetal.1992,
lithosphere-atmosphere-ionosphereconnectionsatlargehor-
Popovetal.2004].
izontal scales. The distance from the epicentre amounts to
The generationof AGWs (with periods of some minutes
500-2000km.
and up to some hours, whereat waves with periods larger
than one hour considered in the reviewed works are often
ObservationofVLFpulsesbysat- upperionosphere
calledinnergravitywaves)intheseismo-activeregionmay
elliteswhicharecausedbyplasma H >700km
becausedbydifferentreasons. Suchreasonsarethemotion
instabilitiesatAGWdissipation
oftheEarth’scorewhichpossessesablock-likestructure,un-
1.Changeofthewindsysteminthe D-andE-
stablethermalanomaliescausedbytheout(cid:3)uxofgreenhouse
E-layer,destructionofthe regionsofthe
gases into the atmospherein fractureregionsof the Earth’s
correlationsofthedensityof ionosphere
core,butalsotheunstableout(cid:3)owofmassesoflithospheric
sporadiclayersregisteredby
gases into the atmosphere [Gokhberg et al. 1996]. During
differentverticalsoundingstations
seismo-gravity oscillations, the Earth’s surface may act on
2.Increaseofthetemperature
the atmosphere like a stopper. Thereat variations of tem-
intheD-andE-layers,
perature,conductivityandpressurearegeneratedandcause
growthoftheturbulentmixing,
themselvesthe excitationofAGWs in theatmosphere. Be-
increaseofthenumberofNO+
sides, on the compressional phase, these oscillations may
intheD-layer,change
lead to an out(cid:3)ow of radon and other gases into the atmo-
ofthephaseoftheSDW-signal
sphere.
Pressuremodi(cid:2)cationsand atmosphere
On the basis of meteorological observations in Middle
excitationofAGWswitha
Asia short-time meteorological earthquake precursors were
periodofT >(10(cid:0)15)min.
detected-anomalousvariationsofatmosphericpressure,rel-
out(cid:3)owofgasesoutof
ative humidity, air temperature and wind velocity [Mil’kis
theEarth’ssurface,
1986]. Such anomalous variations were observed some
changeofthesurfacetemperature
hours-daysbeforesomeearthquakes. Itwassuggested,that
thereasonsofthepressurevariationsweretemperaturevari- compressionalprocessesandshifts Earth
ationsoftheEarth’ssurfaceonlargeareas.Onemaysuppose intheEarth’score,
thatthegenerationofAGWsmaybealsocausedbymeteo- excitationofseismo-gravitywaves
rologicalreasons.
It shouldbe mentioned, that in winter and autumn about 3.2 Models considering the modi(cid:2)cation of the atmo-
twodaysbeforeearthquakesonionogramssuf(cid:2)cientlyoften sphericelectric(cid:2)eld
theappearanceanddisappearanceoftracesofweaksporadic
layers with characteristic time scales of 30-60 min are ob- Now models will be considered which explain small-scale
served. Insuchcases,alargervariabilityisusuallyfoundat andshort-timeelectrical processes at rather small distances
distances up to 500 km from the epicentre, which is in ac- fromtheepicentresoftheearthquakes.
cordancewiththeeffectivepropagationdistancesofAGWs
withperiodsof30-60min. 3.2.1 Lithospheric-ionospheric coupling by radioactivity
The obtained growing intensity of the air-glow at night andelectricalconductivityincrease
(at a wave length of (cid:21) = 5577A(cid:9)) may also be interpreted
withinanacoustic-gravitymodel.Atwavedissipationonthe Accordingtothehypothesisoflithospheric-ionosphericcon-
non-linear stage of their propagation, due to turbulent ver- nections which bases on the increase of radioactivity and
tical mixingoftheneutralatmosphere,theconcentrationof electrical conductivity, in the near-Earth atmosphere the
6 V.A.Liperovskyetal.:Lithosphere-atmosphere-ionospherecouplingbeforeearthquakes
(cid:147)quasi-constant electrical (cid:2)eld is modi(cid:2)ed(cid:148) [Pulinets et al. 1998]duringthemodi(cid:2)cationofthe quasi-constantelectric
1997,Sorokin1998,SorokinandChmyrev1998]. (cid:2)eldbytheincreaseofthelocalradioactivity.
It is well knownthat theradioactivityoftheatmospheric Accordingtothemodel,thealtitudinaldistributionofthe
layers is mainly caused by radioactive elements like radon, electricalconductivityandtheelectric(cid:2)eldintheregionbe-
radium,torium,actiniumandtheirdecompositionproducts. tween Earth and ionosphere is modi(cid:2)ed. If the radioactiv-
Radioactiveelements get intothe atmospheretogetherwith ity grows near the Earth’s surface then also the electrical
theairoftheground.Togetherwiththeair(cid:3)ow,theypropa- conductivityincreases in a near-Earth atmospheric layer of
gateuptoaltitudesofsomekilometres. Thereatthevelocity awidthofsomekilometres,andtheverticalelectric(cid:2)eldis
oftheion-formationamountstoafewtenthsofpairsofions changed.NeartheEarth’ssurface,thestrengthoftheelectric
percubiccentimetreandpersecond. Theresultsoftheob- (cid:2)elddecreasesbecauseofthegrowingelectricalconductiv-
servationsshowanincreaseoftheamountofradioactivema- ity,butatlargeraltitudesitincreasesincomparisonwiththe
terial in the atmosphere before earthquakes. Consequently undisturbed state. The electric (cid:2)eld near the lower bound-
alsothespeedofionformationandtheelectricalconductiv- ary of the ionosphere may raise up a few times. Thus, as
ityraisedup[Pulinetsetal. 1997]. the lower atmosphere is additionally ionized before earth-
Forinstance,themeasurementsoftheradonconcentration quakes, the local electric (cid:2)eld increases and changesin the
atadistanceof300kmfromtheepicentreoftheearthquake ionosphere.
on 20.10.91 on the north of India [Virk and Singh 1994] Undertheactionoftheatmosphericelectric(cid:2)eld,anelec-
showed,thatanintensivepulseofhighradonconcentration tric current directed to the Earth’s surface is created. In
occurred about one week before the earthquake. The con- theearthquakepreparationregion,duringthecompressional
centrationofradonintheairgrewabout2.5times,andinthe phaseoftheseismo-gravitywaves,whichareexcitedbefore
water it raised up by more than 1.5 times. In another case the eruptions [Lin’kov et al. 1989, 1990], a radon out(cid:3)ow
[Heinicke et al. 1995], the radon concentration grew about intotheatmospheremayoccur.Theradonconcentrationmay
fourtimesinthe(cid:2)vepre-earthquakedays.Astatisticalanaly- increaseseveral times. The characteristictime scale of this
sistakingintoaccount300earthquakesshowedthatinabout processmayamounttooneorafewhours.Withtheincrease
70% of the cases the radon concentration grew essentially ofthe radiactivityat the Earth’s surfacealso the degreeeof
beforetheevents. ionization and the electrical conductivity in the near-earth
layeroftheatmosphereofafewkilometresincrease.
3.2.2 Modi(cid:2)cationsofthe(cid:147)quasi-constantelectric(cid:2)eld(cid:148)
The intensity of the vertical electric (cid:2)eld decreases. At
large altitudes, the intensity of the electric (cid:2)eld is larger
Intheworks[SorokinandChmyrev1997,1998,Sorokinet
thanatseismicquiettimes. Theelectric(cid:2)eldnearthelower
al.1998],aone-dimensionalmodelofthemodi(cid:2)cationofthe
boundary of the ionosphere may increase by some 100 %,
(cid:148)quasi-constant electric (cid:2)eld(cid:148) in the ionosphere by a local
andasaconsequence,theJouleheatingandtheelectrontem-
increaseofradioactivityand,correspondingly,degreeofion-
perature in the E-layer grow. As a result, the ionospheric
izationoftheatmosphere,wasproposed. Usingthismodel,
plasma moves locally and there are formed ionosphericin-
it is possible to interprete qualitatively the enhancement of
homogeneities. This phenomenonis then relatedto the oc-
the density of charged particles in the D- and E-layers of
currenceofULF-ELFmagneticvariations.
theionospherebasingonthephenomenonoftheincreaseof
theelectricalconductivityintheloweratmosphereinasuf(cid:2)- Hereithastobementionedthatthetemperatureincrease
cientlylargehorizontalarea. intheE-layercausesadecreaseoftherecombinationcoef(cid:2)-
cient.Thusitispossibletointerpretethelocalincreaseofthe
It has to be underlined that basing on the hypothesis of
densityofthechargedparticlesinthisionosphericregion.
quasi-constant chargesand electric (cid:2)elds, it is necessary to
proposethatthecharacteristictimescaleofthemodi(cid:2)cations
of theelectric(cid:2)eld originatinginthe lithosphere(cid:28) is much 3.2.3 DissipativeinstabilityofAGWs
larger than the Maxwellian relaxation time (cid:28) = " =(cid:27) (cid:25)
o o o
15min.Suchasuggestionis,ofcourse,linkedwiththesup- Anotherconsequenceofthedisturbanceoftheelectric(cid:2)eld
positionofastationaryworkingelectricgeneratorwhich,at intheconductingregionoftheloweratmosphereisthedis-
thesurface,wouldproducethesameamountofchargedpar- sipative instability of AGWs with a period near the Bru¤nt-
ticles as propagatesup into the atmosphere. Here it has to Va¤issa¤la¤ frequency of about 5 min [Chmyrev et al. 1999].
bementionedthataccordingto[ImyanitovandShifrin1962, Thephysicalmechanismofthedissipativeinstabilityofthe
Chalmers 1967] the Earth-ionosphere system possesses an AGWs is related to an additional Joule heating by the dis-
analogyto a spherical capacitor, where the potential differ- turbed currents during the modi(cid:2)cation of the ionospheric
ence between its clouds is determined by the thunderstorm electrical conductivityin the wave. In the E-layer, the ver-
activity. tical electrical current changes accordingly, an inhomoge-
The analysis of the experimental data formed the basis neousJouleheatingoccurs,thedissipativeinstabilitydevel-
of thetheoreticalinvestigationsresultingin theformulation opsandhorizontalperiodicdensityinhomogeneitiesappear.
ofthehypothesisoftheconnectionbetweenlithosphereand Theneutralcomponentoftheairstarts tooscillate withthe
ionosphere[Sorokinetal.1998,SorokinandChmyrev1997, sameperiod,(cid:2)eld-alignedcurrentsaregenerated,andmov-
V.A.Liperovskyetal.:Lithosphere-atmosphere-ionospherecouplingbeforeearthquakes 7
inglayersof(cid:2)eld-alignedcurrentsandplasmadensitiesare ityforce,sothatthelargeparticles,whicharemainlynega-
formed. tivelychargedfalldown,andthesmaller,mainlynegatively
Horizontal variations of the conductivity with scales of charged particles, are situated at larger altitudes [Frenkel’
l=(cid:21)=2=(cid:25)V =! =(cid:25)a=! n(! )((cid:21)-wavelength)change 1949]. Consequently, strong gradients of the atmospheric
g g g g
the ionospheric electric (cid:2)eld. The high conductivity along electric (cid:2)eld within a near-Earth layer with a thickness of
themagnetic(cid:2)eldlinescausesthepropagationofthedistur- somemetresoccur.
bancesoftheelectric(cid:2)eldintotheupperlayersoftheiono- Theelectric(cid:2)eldabovethelayerincreasesthemeanquasi-
sphereandmagnetosphere.Thethusappearingelectricalcir- stationaryelectric(cid:2)eld,andthevectorofthis(cid:2)eldshowsto
cuitconsistsof(cid:2)eld-alignedcurrentswhichtransfertheelec- theEarth’ssurface. Theeffectivityoftheprocessofcharge
tric(cid:2)eldalongthemagnetic(cid:2)eldlines,andofperpendicular separationisdeterminedbytheintensityofthesourceofion-
currents which are brought about by the Pedersen conduc- ization. The model interprets preearthquake phenomena in
tivity. Thereat, the (cid:2)eld-alignedcurrents are transferred by theatmosphereandionosphereasconsequencesoftheoccur-
the electrons, but the transversalcurrentsare caused by the renceofaverticalelectostatic(cid:2)eldwithanintensityofsome
ionmotion.Theclosingcurrentsareaccompaniedwithlocal kV/mattheEarth’ssurface. Asresultofnumericalcalcula-
variationsoftheplasmaconcentration.Thus,theappearance
ofahorizontalstructureoftheelectricalconductivityofthe
Table 3. Hypothesis of lithosphere-ionosphere coupling
ionosphere gives reason to the formation of currents along
based on the consideration of the increase of radioactivity
the geomagnetic(cid:2)eld. Theperpendicularscales ofthe cur-
andelectricalconductivityaswellasonthemodi(cid:2)cationof
rentlayerscoincidewiththescalesofthehorizontalstructure
thequasi-constantelectrical(cid:2)eldinthenear-Earthlayer.
oftheconductivity.
Thisphysicalmechanismmaybeappliedfortheexplana-
propagationofacoustic-gravitywaves upper
tion of satellite observations. When a satellite moves with
transferofdisturbancesoftheelectro- ionosphere
avelocityV throughaplasmainhomogeneityofhorizontal
s
magnetic(cid:2)eldalongmagnetic(cid:2)eldlines andF-re-
scale l, then the registered disturbances of the plasma den-
excitationofVLFoscillations gion
sityandofthemagnetic(cid:2)eldpossesstimescales(cid:28) = l=V .
s
ofthemagnetic(cid:2)eld
By satellites (cid:3)ying through the ionosphere, magnetic (cid:2)eld
disturbanceswithscalesoftheorderof(cid:28) (cid:25) 10(cid:0)5 sareob- increaseoftheverticalcurrent,Joule E-layer
served. According to quantitative estimates one has to do heating,developmentofthedissipative
with relative density changes of the plasma of (cid:1)N=N (cid:25) instability,formationofhorizontal
o
1:6(cid:6)16%,amplitudesofthemagnetic(cid:2)eldof(cid:1)B (cid:25)5nT, periodicdensityinhomogeneities
and a time interval during which the satellite crosses the generationofacoustic-gravity ionosphere
(cid:2)eld-alignedcurrentandtheplasmainhomogeneityofabout oscillationswithperiodsneartheBru¤nt-
(cid:1)t(cid:25)0:3(cid:0)3s[Serebryakovaetal.1992,Sorokinetal1998, Va¤issa¤la¤one(5min.),occurrence
Chmyrevetal.1998]. of(cid:2)eld-alignedcurrents
radonout(cid:3)ow,increaseofatmospheric atmosphere
3.2.4 Quasi-elecrostaticmodel electricalconductivity,increaseofthe
verticalcurrent
One of the latest models of lithosphere-atmosphere-
shiftsandcompressions
ionosphere coupling is the (cid:147)quasi-electrostatic(cid:148) one. This
intheEarth’score
modelalsobasesontheout(cid:3)owofradonintothenear-Earth
tionsitwasfound,thatthe(cid:2)eld(cid:147)penetrates(cid:148)evenintoiono-
atmosphere above fracture regions before earthquakes [Pu-
spheric altitudes of 1000 km under quasi-stationary condi-
linetsetal.1998,2000,2006,PulinetsandBoyarchuk2004,
tions. Theobtainedtheoreticalresultsareinagreementwith
Pulinets and Lui 2004]. The authors tried to explain ob-
experimentalobservations.
servations of the vertical electric (cid:2)eld of the Earth of up to
103 V/mandofanincreaseoftheradonconcentrationnear
the Earth’s surface at earthquake preparation times. In the 3.3 Acoustico-electricmodel
model,itissuggestedthatradoncausesanadditionalioniza-
tion and the formationof negativelyand positivelycharged The (cid:148)acoustico-electric(cid:148) hypothesis of the formation of an
ions.Thus,neartheEarth’ssurfacepositivelyandnegatively Es-generatorandofsmall-scalecurrentsundertheactionof
chargedions,andbecauseofprocessesofhydratation,more acousticpulsespropagatingupfromtheEarth’ssurface-this
complicated complexes of ions (ion clusters) occur. The is one of the last hypotheses which is not yet suf(cid:2)ciently
ionsaretrappedbyaerosols,andthusone(cid:2)ndsasystemof provenexperimentally[Liperovskyet al. 1997, 2000]. Ac-
aerosolswithchargesofdifferentsignswithinalayerwitha cording to this hypothesis which explains ionospheric phe-
thicknessofaboutonemetre. Inthelowerpartofthelayer, nomenaatsuf(cid:2)cientlyneardistancesofafewhundredkilo-
therearemainlypositivelychargedparticles,andintheupper metres from the earthquake epicentres, it is suggested that
partonehasaboveallnegativelychargedones. Theprocess pulsesofneutralwindswithtimescalesofsomeminutesex-
of chargeseparationproceeds under the action of the grav- ist.
8 V.A.Liperovskyetal.:Lithosphere-atmosphere-ionospherecouplingbeforeearthquakes
In the cited works, it was shown that during the action 3.4 Electromagneticmodels
of the neutral winds on a sporadic layer of (cid:2)nite horizon-
tal dimensions at altitudes between 95 km and 130 km at 3.4.1 (cid:147)Resonance(cid:148)model
night, thesporadiclayeracts as non-stationarycurrentgen-
erator. It was assumed that the winds at E-region altitudes One of the (cid:2)rst models of lithosphere-ionospherecoupling
maybecausedbyacousticdisturbanceswhicharegenerated before earthquakes was the (cid:147)resonator(cid:148) model [Gokhberg
byearthquakepreparationprocessesandpropagatefromthe et al. 1985]. There it was suggested, that before earth-
loweratmosphereintotheE-layerwithinpartsofminutesor quakes, near the epicentres, there occur processes of short-
withinsomeminutes.Further,athree-dimensionalsystemof time charge separation at the planetary surface with time
electric(cid:2)eldsandcurrentsforms.Theelectric(cid:2)eldsandcur- scalesof10(cid:0)3s. Theseprocessescausecurrentsandcharges
rents,ifcertainconditionsaresatis(cid:2)ed,maybethereasonof in the ionosphere, and further oscillatory processes in the
plasma instabilities and plasma turbulence. In [Liperovsky system lithosphere-ionosphere- in analogyto usualcurrent
etal.1997,2000]presentingthemodel,itwasassumedthat systemswithcapacity,inductioncoilandresistivity.
the sporadic layers are situated in an environmentof lower Thereat, electromagnetic energy is transferred from the
plasmadensity. Ithastobementionedthattheacousticdis- lithosphere into the ionosphere, and heating and its conse-
turbances propagating from the Earth’s surface up into the quencesoccurin the E-layer. Takingthe blockstructureof
atmospherecanreachionosphericaltitudesandin(cid:3)uencethe theEarth’scoreintoaccount,andsuggestingthatthecharac-
ionosphereonlyundertheconditionthattheirperiodsarein teristic dimensionsL ofthe earthquakepreparationzoneof
theintervalbetween1minand5min[Blanc1985]. Bythe not too strong earthquakesare of the orderof H, where H
dissipation of the infrasound emitted from the earthquake istheeffectivedistancebetweenthesurfaceoftheEarthand
epicentre some hours before the eruption, according to the the E-layerofthe ionosphere,it is possible to roughlyesti-
hypothesis, also variations of the air glowing are possible matethecapacityofthelithosphere-ionospheresysteminthe
[Fishkova1983]. earthquakepreparationzoneasC = " H andtheinduction
o
as L = (cid:22) H. Therefromfollowsan estimate forthe oscil-
o
lation period T = 2(cid:25)(LC)1=2 = 2(cid:25)H(" (cid:22) )1=2. Thus at
Further, basing on the experimentallyveri(cid:2)ed fact that a o o
H =100km,one(cid:2)ndsafrequencyoff (cid:25)0:5kHz. Butal-
systemoftwosporadiclayers,situatedoneabovetheother,
thoughforaseriesofearthquakestheelectromagneticeffects
is a usual phenomenonof the mid-latitudinalionosphere,it
wereanalysedintheVLFinterval[Gokhbergetal.1988],up
wasstraightforwardtoinvestigateathree-dimensionalmodel
tonow,thereexistnoexperimentalcon(cid:2)rmationsofthereso-
oftwolayerswith(cid:2)nitehorizontaldimensionstoo. Theone
nancehypothesis.Thusitfollowsthatresonanceionospheric
layerwasconsideredtobethecurrentgenerator.Thesecond
effects, if they even cannot be neglected principally during
layerwastakentobetheload. Itwasassumedthatthe(cid:2)rst
earthquakepreparation[TateandDaly1989,Tate1990],do
layer,the(cid:148)generator(cid:148),isin(cid:3)uencedbytheactionoftheneu-
notplayanimportantroleinthelithosphere-ionospherecou-
tralwindwhichiscausedbytheacousticwaves. Butonthe
pling.
second layer, the (cid:148)load(cid:148), situated below the (cid:2)rst layer, the
neutral wind does not act. In such a currentsystem of two
3.4.2 Model considering the transformation of broadband
horizontalsporadicEs-layersofdifferentplasmadensityand
electromagneticemissionstoAlfve·nwaves
with currents along the magnetic (cid:2)eld lines connecting the
bordersofthesporadiclayers,accordingtotheanalysis,the
IntheworkbyMolchanov[1991]amodelwasproposedac-
generation of Farley-Bunemanturbulence with a frequency
cording to which during the shift and distruction of blocks
of 103 s(cid:0)1 is possible. Besides, if the sporadic layers are
oftheEarth’scorealongactivefractures,nearthecentreof
suf(cid:2)cientlythickanddense,thecurrentsalongthemagnetic
a preparing earthquake, broad-band electromagnetic emis-
(cid:2)eldlinesintheexternalcurrentsystemmayexcitetheion-
sions are generated. There it was assumed that the region
soundinstability,andtheplasmaoftheionosphereisinten-
of the generationof the emissions has a dimension of 100-
sivelyheated.
150km. Electromagneticemissionsgeneratedbyelasticos-
cillations in the Earth’s core are considered in [Guglielmi
Thus,ifbeforeorduringtheearthquakeinthenear-Earth andPokhotelov1996,Sgrinyaetal.,2004]. Thereexisttwo
atmosphere near the epicentre appears a suf(cid:2)ciently strong mechnismsof the excitationofthe emissions, the inductive
low-frequency acoustic activity, so the mentioned mecha- one and the electrokinetic one. The (cid:2)rst mechanism bases
nism of seismo-ionospheric coupling may occur. It has to ontheappearanceofFukocurrentsduringthemotionofthe
beunderlined,thatthemodelsupposesspatiallocalization- Earth’s core in the geomagnetic (cid:2)eld. The second mecha-
thehorizontalscaleofthelocalcurrentsmaybeoftheorder nismisconnectedwiththemotionofthe(cid:3)uidsinthepores
ofsomekilometres.Therelatedatmosphericheatingmaybe and fractures of the rocky material. The emissions propa-
alsothereasonofalocalincreaseoftheatmosphericoptical gate through the Earth’s crust and surface, the atmosphere
emissions. The characteristic horizontal dimensions of the and ionosphere. Their spectrum changes by the interaction
opticalphenomenashouldbeoftheorderofsometenthsof of the charged particles of the near-Earth plasma, and they
kilometres. cause Alfve·n waves with frequencies of 0.3-10 Hz in the
V.A.Liperovskyetal.:Lithosphere-atmosphere-ionospherecouplingbeforeearthquakes 9
plasmaoftheupperatmosphereandmagnetosphere.Thehy- gatedin [Alimovet al. 1989, Kolokolovet al. 1992, Liper-
pothesiswasmadetoexplainanomalousverylow-frequency ovskyet al. 1993], may be interpreted, if one suggests that
(VLF) emissions in the ionosphereabove seismo-active re- heating occurs and that the temperature change is of the
gions,whichwereobtainedbysatellites. order of the electron temperature, (cid:1)T (cid:25) T . The re-
e e
lation for the Joule heating of the ionospheric plasma un-
3.4.3 Couplingbyseriesofelectromagnetic(cid:2)eldpulses dertheconditionofa(cid:2)eld-alignedcurrentreads@T =@t (cid:25)
e
mV2(cid:23) (cid:0)(cid:14)(T (cid:0)T )(cid:23) . Here(cid:14) describesthepartofthe
k en e n en
WithinthemodelbyKolokolovetal.[1992],itwasassumed energywhichistransferredfromtheelectronstotheneutral
thattheconnectionbetweenionosphericandlithosphericdis- particlesduetocollisions.Inthecaseofelasticcollisionsone
turbancesisrealizedbyaseriesofpulsesoftheelectromag- has(cid:14) =1:6(cid:1)10(cid:0)3.At(cid:28)1 (cid:25)1s,neglectingthenon-stationary
netic (cid:2)eld. It has to be mentioned (cid:2)rst, that in a series of term,itfollowsT (cid:0)T = (cid:1)T (cid:25) mV2=(cid:14). Thus,atave-
e en k
works it was found that a few days before an earthquake, locity V (cid:25) (T (cid:14)=m)1=2 (cid:25) 3(cid:1)103 m/s and a temperature
neartheepicentrepulsesoftheatmosphericelectric(cid:2)eldof k e
T =0:03eV,accordingtoOhm’slaw,m(cid:23) V =e(cid:14)E ,the
(cid:14)E (cid:20) 103 V/m were repeatedly obtained. And the ampli- (cid:2)eeld-alignedelectric(cid:2)eldamountsto(cid:14)E e(cid:25)n7k(cid:1)10(cid:0)4Vk/m.
tudesofthevariationsofthemagnetic(cid:2)eld,registeredatthe k
Thegenerationofsuch(cid:2)eld-alignedelectric(cid:2)eldsispos-
sametime,amountedto(cid:14)B =1(cid:0)10nT[Gogatishvili1984,
sible,ifattheEarth’ssurfacelocalchargesoccurwithQ >
Kolokolovetal.1992]. Letusmakenowanroughestimate
200Coriftherearequickerprocessesofchargeseparation
whichshowsthattheexcitationofdisturbanceswithcharac-
(e.g.withtimescales(cid:28) =0:2(cid:0)03s)andthechargeintensity
teristictimescalesof(cid:28)1 =1(cid:0)0:1sispossible.
isless.UsingfortheblurringtimeofthesporadicE-layerthe
It is assumed that at the Earth’s surface, due to any rea-
relation
sons, during the preparationprocess of a strong earthquake
withM =5(cid:0)6,thechargesaredividedintogroupsofposi-
(cid:28) (cid:25)1:6=D(cid:25)1:6a2M(cid:23) =k(T +T );
tiveandnegativeoneswithacharacteristictimescale(cid:28)1 and D in e i
with a characteristic lengthscale equal to the dimensionof withathicknessofthesporadicE-layerofa=100(cid:0)1000m,
theearthquakepreparationregionL (cid:25) (10(cid:0)100)km. The
the ambipolar diffusion coef(cid:2)cient D, and T and T - the
e i
totalelectricalcurrentequalsI = Q=(cid:28), andtheestimateof
temperaturesin Joule, one (cid:2)nds for a thickness of the spo-
theintensityoftheelectrical(cid:2)eldneartheEarth’ssurface,in
radic layer of a = 150 m and a coef(cid:2)cient of ambipolar
thecaseofanhomogeneousdistributionofthechargesonan
diffusion D = 60 m/s a life time of the sporadic layer of
area oftheorderof L2, gives(cid:14)E (cid:25) Q=2"oL2. If, besides, (cid:28) (cid:25)15min,whichisinagreementwiththestrongdecrease
D
the electric currentis homogeneouslydistributedin a plane
ofthedensityofthesporadiclayerbeforeearthquakes.
sheathofwidthL,oneobtainsforthevariationsofthemag-
Thus, electric (cid:2)elds of seismic origin of the order of
netic (cid:2)eld (cid:14)B = (cid:22)oQ=2L(cid:28)1. From that it follows for the 103V/mnearthesurfaceoftheEarthwithhorizontaldimen-
characteristictimescaleoftheprocess(cid:28)1 (cid:25) (cid:22)o"oL(cid:14)E=(cid:14)B. sionsoftheorderof100kmmaystrengthenprocessesofam-
Substitutingtheabovementionedexperimentalvaluesof(cid:14)E,
bipolardiffusionintheionosphereanddecreasethecharac-
(cid:14)B and L, one has (cid:28)1 (cid:25) 1 s, and a maximum charge teristictimescaleoftheblurringofsuf(cid:2)cientlynarrowspo-
of Q = 200 C. Thus, the here made estimate shows that
radicE-layers(withathicknessbelow100m).Moreintense
electromagneticprocesseswith characteristictimescales of
heatingprocessesandtheblurringofthickerlayersmustbe
0.1-10s are possiblein the earthquakepreparationzoneon
causedbymuchstrongerelectric(cid:2)elds. Thusthehypothetic
condition that an ratherquickseparationof chargesoccurs.
mechanismofchargeseparationattheEarth’ssurfaceisnot
Some results of observations of activity pulses of electro-
suf(cid:2)cienttoexplainallobservations.
magnetic processes before earthquakes with the discussed
time scales are publishedin [Fraser-Smithet al. 1990, Tate
1990]. In the E-layer of the ionosphere, at altitudes of the
4 Conclusions
same scales of L (cid:25)100 km above the region of the charge
separation, there shouldoccur inducedchargesof the same Thusinthereview,acriticalanalysisofpresentexperimen-
orderofmagnitudeQ(cid:3) (cid:20) Q",distributedinaregionofthe tal data and theoretical models concerning the lithosphere-
same length scale. The corresponding (cid:2)eld-aligned poten- atmosphere-ionospherecouplingduringearthquakeprepara-
tial electric (cid:2)elds (cid:14)Ep may be found using the Ohm’s law tion times is presented. Up to now, no generally accepted
k
m(cid:23)enVk (cid:25) e(cid:14)Ek andtherelationQ(cid:3)=(cid:28)1 (cid:25) SeffneVk,with theoretical hypothesis exists, which would allow to inter-
Seff (cid:25)L2cos(cid:11)((cid:11)isthetiltingangleofthe(cid:2)eldlinesofthe pretethe observationsof ionosphericdisturbancesoccuring
magnetic(cid:2)eldtothevertical).Theestimateofthemaximum some days before even strong earthquakes. On the other
(cid:2)eld-alignedelectric(cid:2)eld in the ionosphereat L = 105 m, hand,nomistakesofthedifferent,recentlyexistinghypothe-
n = 103 cm(cid:0)3, (cid:23)eff = 4(cid:1)104 s(cid:0)1 andcos(cid:11) = 0:3gives ses could be found - not of the hypothesis of the genera-
(cid:14)Ek (cid:20)Q(cid:3)m(cid:23)en=(cid:28)1L2ne2 (cid:25)3(cid:1)10(cid:0)4V/m,whichisinagree- tion of acoustic-gravity waves, the hypothesis of the mod-
mentwiththeobservations. i(cid:2)cation of the electrical conductivity in the near-Earth at-
TheeffectsofanomalousblurringofthesporadicE-layer mospherebecause of radon injection, the hypothesis of the
in the ionosphere before earthquakes, which were investi- generation of an Es-generator and of mini-current systems