QUANTITATIVE ANALYSIS OF THE ARKITSA FAULT ZONE (NORTH EVIA GULF, CENTRAL GREECE): IMPLICATIONS FOR KINEMATICS, PALEOSEISMIC ACTIVITY AND FLUID FLOW

In order to better understand a variety of geological processes, such as earthquake nucleation, fault reactivation, fault seal and fluid flow in areas undergoing active crustal extension, a comprehensive geometrical, kinematic and dynamic fault analysis is needed. For this purpose, we selected the Arkitsa fault zone, which forms part of a major fault system bounding the southern coastal area of the Gulf of Evia in Central Greece, as a case study because even though it is considered as an active fault, having a spectacular 65 m high polished corrugated scarp, there is complete absence of any historical earthquake activity related to this fault zone.

Quantitative analysis of LiDAR data along three well-exposed fault panels allowed the spatial variation in various geometrical properties across the fault surface to be clearly shown. Fault-slip analysis from each panel shows that the local stress field is consistent with the regional velocity field derived from recent GPS data. Furthermore, we studied the fault-gouge mineralogy in order to understand the faults’ enigmatic aseismic behavior and if the conditions that characterize the fluid flow can be identified. Clay-gouge samples were collected within the fault core zone, as well as in the broader fault damage area and analyzed by XRD, SEM and Electron microprobe analyses. The absence of corrensite, a clay mineral usually formed in hydrothermal conditions, in the samples from the broader fault damage zone indicates that the circulation of hydrothermal fluids is mostly confined within and around the fault core zone. The assemblages within the fault gouge zone and especially the presence of corrensite, combined with the absence of laumontite, indicate hydrothermal alteration at neutral to alkaline conditions and at a temperature range of about 100-150 ^o C. Additionally, paleoseismological analysis was performed for the first time on this fault zone and ¹⁴C dating of soil samples, taken from a natural trench across the fault zone, revealed at least 4 strong earthquakes in the last 20 ka, with a recurrence interval ranging between 3.5-5 ka. The last seismic activity of this fault is estimated around 1300-1110 BC, confirming previously archaeologically dated destruction horizons from an adjacent ancient settlement and dated tsunami deposits.