Post-glacial slip history of the Sparta fault (Greece) determined by 36Cl cosmogenic dating:: Evidence for non-periodic earthquakes -: art. no. 1246

[1] Using Cl-36 cosmic ray exposure dating we obtained continuous exposure histories for 7-12 m-high limestone surfaces at two sites (10 km apart) on the Sparta normal fault scarp. As each major earthquake adds new surface to the cumulative scarp exposing new material to cosmic-ray bombardment these exposure histories allow the slip history to be constrained. The results show that an earthquake occurred on this fault 2800 +/- 300 yr ago. We infer that this is the seismic event that destroyed ancient Sparta in 464 B. C. Four earlier earthquakes ruptured the Sparta fault in the last 13 ka with similar slip amplitudes of about 2 m and with time intervals ranging from 500 yr to 4500 yr. The observations also confirm that the Sparta scarp is post-glacial, supporting the hypothesis that similar scarps elsewhere in the Mediterranean region have a comparable age. The absence of any event since 464 B. C. could suggest a future event is imminent. However, the irregularity of earthquake time intervals could also be due to changes of loading with important consequences for the mechanics of continental deformation.