Some reliable fault plane solutions

Summary The reliability of earthquake fault plane solutions usingP andPKP first motion data is discussed. Effects of the usefulness of the individual data, of the number and distribution of data around the focus, of great velocity contrasts in the focal region, and of the kind of projection technique are considered. The increase of the number of inconsistent data by a change in position of the three principal axes can be used as a more or less objective measure for the reliability of a solution.A selection of 52 mantle shock solutions is presented. More than 75% of these shocks is of the thrust (or block) and the normal or reverse fault motion type. Transcurrent type shocks decrease from 40 to 50% in the upper 200 km of the mantle to less than 15% below this level. Thrust (or block) type fault motions clearly represent the normal reaction of the deeper mantle material to earthquake generating stresses.