CONVERGENCE DIRECTION AT SUBDUCTION ZONES

 

THE RATE AT WHICH THE PLATE SUBDUCTS - THE CONVERGENCE RATE OR RELATIVE PLATE MOTION RATE - CANNOT BE FOUND DIRECTLY AS AT SPREADING RIDGES

INSTEAD, IT IS FOUND BY ADDING UP DATA FOR MOTIONS OF OTHER PLATES

THE CONVERGENCE DIRECTION IS FOUND FROM THE DIRECTION OF MOTION IN THE SHALLOW EARTHQUAKES - AT DEPTHS LESS THAN 70 KM - THAT REFLECT MOTION AT THE BOUNDARY INTERFACE BETWEEN THE SUBDUCTING AND OVERRIDING PLATES

(Press & Siever)