Atmospheric pressure gradient as a possible trigger of great earthquakes

Bondur V.G., Garagash I.A., Gokhberg M.B., Grekhova E.A., Kolosnitsyn N.I., Shalimov S.L., Veys V.A.

Possible Trigger Mechanisms• Seismic wave actionM. West, J.J. Sanchez, S.R. McNutt. Science, vol. 308, 1144 (2005)

• Electromagnetic action – MGD pulses and Geomagnetic storms 1) E.P. Velikhov, Theory and method of deep electromagnetic

sounding of crystalline shields. Apatity, 20062) N.T. Tarasov et al. USSR Doklady, vol. 353, 545 (1997);

Volcanology and Seismology, 4-5, 153(1999); 3) G.A. Sobolev et.al. Volcanology and Seismology, 3, 63 (2004)

• Atmosphere pressure gradient (APG)A.D. Sytinsky, USSR Doklady, vol. 245, 1337 (1979);V.G. Bondur, I.A. Garagash, M.B. Gokhberg et al. Doklady Ac.Si., vol.

430, 400-404 (2007)

0 90 180 270 3604

2

0

2

4

phase

kP

a,

cm

2 .315

2.315

xz ( )

zz ( )

xx ( )

10

uz ( )

3600

0 360

When σxz achieves maximum the values σxz, σxz, uz = 0

and local earthquakes are occured

Seismic records of the Sumatra earthquake and local events at Mount Wrangell

Rayleigh wave reconstruction:shear stress on depth 2 km – σxz = 1.95 kPa;amplitude uz = 0.75 cm;velocity U = 3.7 km·s-1;period T = 30 s;wave length λ = UT = 111km;decay depth for longitudinal (Ll) and transverse (Lt) components: Ll = 21 km, Lt =45 kmG = 3.5·1010 Pa

Energy density F = (1/4)( σxz)2/G Full energy E = F·VSadovsky formula: lg EL =lgV + 2

EL = 4.47·1014 erg (M = 1.9)

V = 4.5·105 m3 E = 1.3·108 ergEnergy relation E/EL ~ 10-6

Electromagnetic Trigger Mechanisms

• Central Asian (70-80): N. Tarasov et al. Earth crust investigation by means of electric dipole with energy impulse Eem ≈ 1014 erg. As a result seismic activity was recorded with seismic energy Esm ≈ 1019 erg so that the energy ratio is Eem/ Esm ~ 10-5

• G.A. Sobolev et al. showed that due to trigger mechanism of geomagnetic storms with sudden commencement the appearance of earthquakes with M > 2 in some events may be explained (G.A. Sobolev et al. Volcanology and Seismology 2001, № 11, 62-72; 2004, № 3, 63-75; Fizika Zemli 2002, № 4,3-15).

• Following E.R. Mustel et al. (Astron. J., vol. 42, 1232 (1965)) geomagnetic storm time variations can globally excite multiple regions with atmospheric pressure gradients. This results in increase of a chance to get by atmospheric gradient of a region with preparing EQs

Trigger Mechanism by APG

• The estimation of the trigger effect from APG is making on example of the biggest earthquake Sumatra M = 9.1

• Due to “inverse barometer” effect the deformations are confined only by Sumatra area S= 1000×200 km2.

• At pressure difference p = 1.33·103 Pa (10 mm Hg), the shear

• modulus – μ, Lame’s parameter – λ: μ = λ = 35·109 Pa and Poisson ratio σ = 0,25, using Boussinesq solution for deformation energy it has obtained the estimate

– E ~ 3·1019 erg

• Magnitude M = 9 correspond to energy EL of 2·1025 erg• As a result

– E/EL ~ 10-6

The pressure p created by atmospheric anomalies get in deeply and unlike seismic perturbations operate long enough within several days1. Distribution of

main shear stress arising in elastic earth crust under the influence of atmospheric anomaly is shown.

Distribution of dimensionless main

shear stress /p

1Garagash I.A., Ingel L.Kh. and Yaroshevich M.I. (2004) A Possible Mechanism of Atmospheric Effects on Seismic Activity near Ocean Coasts, Izvestiya, Phys. Solid Earth 40, p.692–698

Distribution of the relation of vertical deformation y

to characteristic deformation =p/2G

Distribution of the relation of horizontal deformation

x to characteristic deformation =p/2G

)sin22

( 3131

R

11*1 33

*3

R is parameter of closeness of stress state to strength limit

321 are the main stresses is the friction angle

, are the shear stress intensity and shear strain intensity, respectively

s kis the maximum strength value is the residual strength

The parameter R entered by us allows to watch for dynamics of stress state

3D Calculation of the stress-strain state on the Californian testing area “China Lake” with evidence of short-term earthquake prediction

range z -4800m -6400mrange z -3200m -4800m

Fault zones close to Coulomb-Mohr shear zone yields proper condition due to decreasing of atmospheric pressure by 2.5% Pap 2500max

1. Gokhberg M.B.,Garagash I.A.,Nechaev Yu.V.,Rogozhin E.A., Yunga S.L. Geomechanical model of seismic claster China Lake, South California Researches in the geophysics. IPE RAS, 2004

Only negative APG before EQ can produce trigger effect

Examples of the APG before EQ with M > 7.5 in the epicenter vicinity

Days (relative to an earthquake moment)

Atmospheric pressure

Days (relative to an earthquake moment)

APG statistical distribution relatively time before earthquakes

2000 – 2010 years. The number of events N ~ 50

Distribution of parameter R in the layer 1

If parameter R < 0 the earth crust keeps away from a limiting state, at R> 0 – it comes nearer. In calculations the transfer of pressure upon the earth crust is carried out only on areas which have been not

covered with ocean. The maximum value of pressure excess is no more than 1% from the average atmospheric pressure. It is evident that in the anomalous zone the top layer 1 keeps away from the

strength limit whereas the deeper layers 2, 3 and 4 – comes nearer. Thus, abnormal pressure approaches these zones to strength limit and hence can cause trigger effect.

Distribution of parameter R in the layer 4

Bondur V.G., Garagash I.A., Gokhberg M.B., Lapshin V.M., Nechaev Yu.V., Steblov G.M., Shalimov S.L., (2007) Geomechanical models and ionospheric variations related to strongest earthquakes and weak influence of atmospheric pressure gradients. Doklady Earth Sciences, Vol. 414, No. 4, pp. 666–669

Modeling of APG trigger for Sumatra M9.1

While seismic and electromagnetic impulses last seconds, and the sources of large earthquakes has the inertial action, the APG continue during the days and its scale is comparable with the scale of large earthquakes

1.The four-layer model has been designed for Sumatra

2. 3D distribution of the elastic energy density was calculated

3. Dynamic of parameter R induced by APG is presented

Conclusion

• For all trigger mechanism the ratio between input and output energies is estimated to be 10-5 – 10-6

• Large scale atmospheric pressure gradient (APG) can create the additional deformation deep enough in the earth’s crust

• The ocean – land boundary can effectively transform homogeneous atmospheric pressure into its sharp gradient acting on the earth’s crust

• APG is large scale process that can be considered as the trigger mechanism for strongest earthquakes

For discussion

APG trigger conception

can kill

the representation of the existence different precursor’s effects

APG and magnetic storms exist permanently.These phenomena with very well known physics produce a lot of different anomaly in the Earth-Atmosphere-Ionosphere-Magnetosphere systems which can be mistakenly considered as the precursor effects.

Model of earth crust of Southern California: a) general view, b) normalized distribution of the damage in the upper crust

and c) map GPS velocities

Normalized distribution of parameter R of nearness of stress state to strength limit for 15.12.2009 in the layer 1 (upper crust)

and in the layer 4 (middle crust)

Monitoring of strain and strength of earth crust on the basis of close to real geomechanical models for the purpose of the seismicity forecast on the interval week – month.

Changes of summary magnitudes (the dark blue graph) and strength parameter R in the upper crust (the red graph)

M

Distribution of the relation of horizontal deformation x to characteristic

deformation =p/2G

Distribution of the relation of vertical deformation y to characteristic

deformation =p/2G