Seismic strain rates in regions of distributed continental deformation

Abstract

We compare the rates and configurations of seismic deformation determined from moment tensor mechanisms of earthquakes in five continental regions with the rates and configurations expected if the seismicity reflected the relative plate motions in the regions. The five regions (the Aegean, Iran, California, Western New Guinea and Central Asia) are characterized by high levels of seismicity distributed over hundreds to thousands of kilometers from the accepted plate boundaries. The earthquake mechanisms are compiled primarily from the catalog of centroid moment tensor solutions, which is nearly complete over the interval 1977–1987 for earthquakes greater than MS ≈ 5. The thickness of the seismogenic layer in each region is constrained by the results of modeling broadband body wave phases and of previous earthquake studies. In the Aegean, California, and Western New Guinea, the observed configurations of deformation agree with a simple model of distributed accommodation of relative plate motion. In Iran and Central Asia, the moment tensors indicate that there is appreciable strain parallel to the strikes of the belts. We augment our 10‐year estimates of seismic deformation with the available historical moment and magnitude estimates for the five regions and find that moderate and large earthquakes account for between 25 and 70% of the deformation of the seismogenic layer.