IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS011 Poster presentation 2157
To the problem of mechanism definition of earthquakes focuses of Armenia
Dr. Mariam Mkrtchyan
IAGA ISS011 IASPEI
In contradiction to the generally accepted definition method of earthquake focus our approach provides
for the accuracy estimation solution for each of nodal plane each taken separately. It becomes possible
by definition of the limitedly admissible turning of the nodal plane around an axis N and direction SLIP.
It allows in a quantitative way to formalize the geometric limitation of the confident sectors of pressure
and tension. The introduction of such accuracy solution characteristics is accounted for the necessity of
quantitative information on pressure and tension spheres with the aim of study of tectonic fields of
tensions and deformations according to the data on the earthquake focus mechanism. The data on the
earthquake focus mechanism allow describing by definitely spatial and temporal groups of focuses the
field of tectonic tensions existing in seismoactive spheres of litosphere. The obtained characteristics by
describing this field of orientations of main axes tensions in every earthquake focus allow in their, turn
to solve the apportionment problem of breach of plane realized in a focus proceeding from analysis
relation between orientations of these axes with a direction of strike-slip motion on each of these 2
nodal planes each taken separately. For the definition of the fault plane realized in a focus the data on
tectonic tension orientations were used for the of Armenia obtained on the basis of the earthquake
focus mechanism analysis with M ≥ 4.5 over a period of 1960-2000 years. Thus the utilization of this
method gave an opportunity to come to the description of multivariant solutions of focus mechanism to
more complex and more informative record. The algorithm program is based on the method of maximal
probability. As a result of this the totality of solutions of the given confident level (85%) is revealed
compatible with the true sphere characterizing the uncertainty degree of the unknown solution. As a
result of a count the values of angular coordinates X and Y are established corresponding to the
maximal value of probability function and also the values of coordinates Ix, Iy, θx, θy in 85% of
confidence interval sphere. The choice of confidence interval sphere is simple in view of discreet
disposition of the stations on the surface of the Earth. At a quite uniformity and density of disposition of
the stations many solutions are obtained having the same probability. In the end the values of angular
coordinates of pressure and tension axes are established corresponding to maximal value probability
function and 85% of confidence interval sphere disposed at an angle of 45o to X and Y axes. As a result
of dimensional analysis of confidence interval spheres of X,Y,P,T axes all the solutions are conditionally
divided into 3 groups. Thus in case of compact I and II groups of confidence of the possible solution
spheres the obtained results may be considered as confident. In case of confidence of the III group
with the majority of solution types the joint analysis of aftershock sphere definition results is required
and directions of rupture formation in earthquake focus. The analysis and accuracy estimation of the
earthquake focus definition mechanism with the utilization of the modern program provides with the
increase of the confidence of the obtained solutions.
Keywords: mechanismdirectiondefinition