Abstract

An 18-km-long segment of bed rock of the Dasht-e Baȳaz earthquake fault was studied in detail to define the 1968 earthquake-related and earlier tectonic deformations. Ground displacements that accompanied the earthquake coincided precisely with the pre-existing east-trending fault trace. Maximum components of offset were 4 m left-lateral and 1 m south side relatively down. The bedrock displacement occurred along new tension fractures that strike on average at 50°, as well as along reactivated pre-existing structures. Earlier tectonic deformation also produced tension fractures (post-Pliocene), conjugate shears (Pliocene), and tension joints (pre-Pliocene), and all are consistent with 47° to 55° tectonic compression. The study covered three points: (1) the 40° to 45° angle measured between the major principal stress direction indicated by the earthquake fractures and the fault; (2) the apparent constancy of the stress field direction during the three early phases and the 1968 deformation; and (3) the “gap” and “anti-Riedel” structure shown by the overall fault trace, which, we suggest, are characteristic of situations of kinematic restraint and are associated with a nonuniformly propagating rupture.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.