Structural and geomorphological constraints on the activity of the Sparta Fault (Greece)

The ancient city of Sparti (Greece) suffered extensive damage from an estimated M_w 7.2 earthquake in 464 BCE, resulting in c. 20 000 fatalities, but questions remain about the short-(c. 10⁴ years) and long-term (10⁵–10⁶ years) activity of this important structure. This paper presents new structural data and fluvial geomorphological analysis from the Sparta Fault and, in particular, considers the less well-known northern fault segment. A new topographic profile on the well-developed post-glacial fault scarp from the northern strand indicates a 7.53 m offset over the last c. 15 ka, suggesting a throw-rate of c. 0.5 mm a⁻¹. The longitudinal profiles of rivers flowing across the fault allow the elucidation of longer term fault activity. Along the strike of the fault, rivers exhibit up to two slope-break knickpoints, which decrease in height from south to north. These knickpoints are interpreted to have formed as a result of the initiation of faulting and a subsequent slip-rate acceleration. The post-glacial fault scarp and fluvial geomorphology both indicate that the entire fault is active and has an asymmetrical throw profile that results in the highest slip-rate in the south.