NEUTRON SCATTERING AND NEUTRON SCATTERING AND PHYSICS OF THE PHYSICS OF THE

EARTHQUAKE SOURCEEARTHQUAKE SOURCE

Rodkin M.V.Rodkin M.V.11, Nikitin A.N., Nikitin A.N.22, Vasin R.N., Vasin R.N.22

11 International Institute of Earthquake Prediction Theory and International Institute of Earthquake Prediction Theory and Mathematical Geophysics, Russian Academy of Science, Mathematical Geophysics, Russian Academy of Science,

Profsoyuznaya 84/32, Moscow 117997, RussiaProfsoyuznaya 84/32, Moscow 117997, Russia, , rodkin@mitp.ru;

22 Joint Institute for Nuclear Research, Joliot-Curie 6, Dubna Joint Institute for Nuclear Research, Joliot-Curie 6, Dubna 141980, Moscow Region, Russia141980, Moscow Region, Russia

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The common notion is that to get an effective earthquake prediction we need to understand the physics of the earthquake origin, but … The common notion of an earthquake origin because of brittle failure under high tectonic stress meets serious difficulties. 1) All estimates of the stress values in the Earth’s interior are much less than the fracturing stresses measured in the labs. 2) …3) …4) Besides the model of earthquake origin should explain the internal structure of the deep shear zones and the origin of weak layers in the Earth’s interior.

Should be explained also:The crustal earthquakes have a tendency to occur in sub-horizontal layers. The ancient eroded deep shear (seismogenic) zones consist of the fine-grain mylonitic layers with inclusions of small planar areas with remnants of high frictional heating. The active deep fluid flow regime is typical of the deep shear zones. Deep shear zones coincide with layers of high conductivity and low Vp, Vs values.

There is a negative correlation everywhere! Thus, the stress value is hardly a main factor of seismic origin???And a process of a decrease in the rock strength predominates ?! ?!

Correlation of the spatial density of earthquakes lg(of the number in the cell) and the corresponding mean apparent stress value (σa=μE/Mo).

Depth The spatial cell radius, км Number of events, interval, км (validity > 99% ) 25 50 100 2500 – 15 -0.20 -0.24 -0.28 -0.31 500015 – 30 -0.25 -0.26 -0.27 -0.29 600030 –70 -0.17 -0.20 -0.21 -0.26 650070 – 150 -0.11 -0.11 -0.07 -0.05 2500 150-700 -0.18 -0.17 -0.16 -0.11 2547

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The fluid-metamorphic (FM) model of seismicity is presented. Seismoactive layers are suggested to develop along the fronts of metamorphic change in the Earth’s interior. Factually complex model that takes into the account both the fluid involvement and the transformation induced anomalies of the physical properties of rock is discussed.

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Point 1From solid state (metal, ceramic) physics we have:During the solid-state transformations the fine-grain media develops, and the rhelogy of solids becomes similar to the rheology of viscous fluid with an effective viscosity depending on the velocity of the transformation.

It can be suggested, that similar processes occur in the Earth’s interior, where the layers of transformation will be subhorizontal weakened layers of low effective viscosity that can manifest themselves as the LVZs.

Point 2FM model gives possibility to explain all the main features of the deep and crustal seismicity.

Point 3.What’s about new results?

Point 4The program

The change during the phase transition in limestone.The change during the phase transition in limestone.

1, 2 - Vp and Vs velocities; 3 - change in the relative Vp wave amplitude; 4 - Poisson coefficient.

Change in the failure character in gabbroChange in the failure character in gabbro. . Strength value decreases and the Strength value decreases and the transformation area scatters into a sand-like structuretransformation area scatters into a sand-like structure ..

Example of the change of the permeability of rock with the temperature. The experimental data testify for a low permeability of rock that increase essentially at P/T conditions of transformations in the rock crystal structure.

The deep shear deformations are known to concentrate in the fine-grain mylonithe The deep shear deformations are known to concentrate in the fine-grain mylonithe layers where the deep fluid flows are the mostly active. layers where the deep fluid flows are the mostly active.

But the experimental results performed at the moderate P/T conditions testify of the But the experimental results performed at the moderate P/T conditions testify of the lower permeability and high strength of the fine-grain mylonithe layers.lower permeability and high strength of the fine-grain mylonithe layers.

Thus, the effect of mechanical weakness the increased permeability of the mylonithe layers is the especially deep effect inherent to high P/T conditions

.Both geophysical and petrologic data testify for the essentially higher permeabilities and higher activity of the fluid regime occurring (at least temporary) in deep rock These values were not found in the labs experiments.

The transitional non-equilibrium regime that can temporary occur in the deep shear zones is suggested to occur during metamorphic transitions in rock.

In this case two different regimes of permeability can take place: the equilibrium of low permeability and the transitional one of high permeability.

Typical character of transformation-induced deformation Т (transformational superplasticity) occurring at low stresses; deformation essentially increases during transformation even at low

stress level: (at a circle of transformation) ~= k(/) σ/ + k1* ( /) σn

(rheology has a linear type similar with viscous liquid)

Examples of strong increase in AE in quartz in connection with Examples of strong increase in AE in quartz in connection with -- phase transformationphase transformation....

14:00 17:00 20:00 23:00 2:00 5:00 8:00 11:00 14:00 17:00

В р е м я эк сп ер и м ен та , ч

0

50

100

150

200

250

300

350

Акт

ивно

сть

АЭ

, 1/5

с

20°

560°

580°

600°

620°

АЭ

Температура, С

А Э 1

А Э 2

А Э 3

Change of the inner friction and the resonant frequency with T in quartz

An increase in prolongation of earthquake process with

strong earthquake approaching

Point 2Point 2

If the phase transformation occurs at close to equilibrium PT conditions the weak If the phase transformation occurs at close to equilibrium PT conditions the weak zone will develop.zone will develop.

If process takes place in highly non-equilibrium conditions it can proceed in an If process takes place in highly non-equilibrium conditions it can proceed in an avalanche-like manner. Such process can cause the earthquake origin. avalanche-like manner. Such process can cause the earthquake origin.

Such non-equilibrium process appears to be especially typical of the subduction Such non-equilibrium process appears to be especially typical of the subduction zones. zones.

1. 1. Because of low temperatures in the subduction zones that stimulates the persistence Because of low temperatures in the subduction zones that stimulates the persistence of non-equilibrium phases. of non-equilibrium phases.

2. 2. The heat release is typical of majority of metamorphic reactions with density The heat release is typical of majority of metamorphic reactions with density increase that will accelerate the transformation when it will begin in the downgoing increase that will accelerate the transformation when it will begin in the downgoing

slabs.slabs.

The problems were discussed and the FM model was presented in the monographers (1989, 1993,

and 2003) and in a number of papers.

Model of the deep subhorizontal shear zone in the lithosphere and the real rather typical example.

. The depth intervals with increased The depth intervals with increased values are shown by red color. values are shown by red color. These depths correlate with the depth values of the mainThese depths correlate with the depth values of the mainsolid-state transformations in the subducting slabs: 1 – deserpentinization solid-state transformations in the subducting slabs: 1 – deserpentinization area (double seismic zones); 2 – eclogitization?; 3 – A-phase formation (Liu,1993);area (double seismic zones); 2 – eclogitization?; 3 – A-phase formation (Liu,1993);4 - 4 - transition zone; 5 - transition zone; 5 - transition; 6 – y-phase transition; 6 – y-phase Pv+Mw phase. Pv+Mw phase.

The dependence of density of number of quakes with the depth

200 400 600

H , km

0.01

0.1

1

10

de

nsity

of

qu

ake

s

1

2

3

4

56

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Scheme of slab bending (Rodkin, 1985, left) and the real data (Carato, Riedel, Yuen, 2001, right panel).

. The complex of change in the parameters values is the similar with that

occurring in the vicinity of strong earthquakes - evidence of similarity of properties of mater at transformations and in

strong quakes’ areas.

The change of the mean values of the residual parameters in the norm depth intervals (depth intervals of the solid-state transformations)

-1.2 -0.8 -0.4 0 0.4 0.8 1.2

norm depth

- 1

- 0 . 5

0

0 . 5

1

1 . 5

mea

n n

orm

chan

ge

m b /m w

H , k m

-, sec

Vp velocities in different quartz containing rocks (I – кварцит, II – гранулит, III – гранит) P= 200 MPа

Change in modulus K, G and in Vs and Vp velocities at phase

transiton T Pmm ↔ I4/mcm in perovkite (above) and during P42/mnm ↔ Pnnm in stishovite[Carpenter,

2006]

Dependence of crystal cell size in quartz from T Dependence of width of reflection

peak in quartz - the role of possible inner stresses

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CONCLUSION AND THE PROGRAM

Despite the rather convincing evidences in support of FM model a few very important problems are unresolved yet.

Firstly, the character of inner stresses connected with the solid state transformations should be investigated.Neutron scattering appears to be the best possible experimental approach for such investigation because it gives possibility to examine the stress state of the inner parts of the specimen that model the rock properties in the strictly constrained (free volume limited) conditions of the Earth’ interior. The problem of permeability of rock under solid state transformations is not resolved yet also. This problem is argent also in connection with the waste deposits construction and with the problem of ore deposits origin and accumulation.

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