The push-pull distribution of the first pulse of P and PKP waves of 33 deep earthquakes which occurred in north Argentina in the last 30 years is studied using a graphical statistical method. Also the direction of polarization of S waves is studied, and is determined for both linear and non-linear motion at the surface.

Results show that the earthquakes have approximately the same focal mechanism. The pattern of stresses causing the earthquakes should be the same along this deep seismic region.

The average focal mechanism can be represented by a double couple without moment. The pressure axis direction is perpendicular to the trend of spatial location and it dips 54° toward the continent. A table to derive the direction of polarization of S from non-linear particle motion is given, assuming a simplified earth model.

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