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CORSEIS Informe resumido

Project ID: EVG1-CT-1999-00002
Financiado con arreglo a: FP5-EESD

Detection of buried fault scarp on the west Helike fault with Ground Penetrating Radar (GPR)

In order to assess whether the western Eliki Fault has experienced recent tectonic reactivation, ground-penetrating radar surveys were made across a stepped sequence of morphological scarps along the main escarpment base. GPR investigations were focussed on the Nikolaiika Fan (NF), part of the Kartoula Fan (KF) complex, above the Eliki Plain. In the field, morphological scarps often coincide with agricultural terrace edges and so, in some cases may be of anthropogenic rather than tectonic origin. It is to ascertain whether these surficial scarps relate to concealed near-surface faults that recourse was made to ground penetrating radar studies.

GPR surveys using PulseEKKO 50, 100 and 200MHz antennae were collected on three roads cutting across the fan surface, which run perpendicular to 0.5-1.0m high surface scarps identified in the field. On one road (L1) profiles were collected at 50, 100 and 200MHz. These profiles were collected across two scarps, which were visible in the field to the side of the road. On the other roads profiles were only collected at 50MHz. Data was post processed using Gradix 1.10 software. Around 250m of profiles were taken to image the faults beneath the Nikolaiika Fan.

The results reveal near-surface tectonic disturbances on all profiles. In most cases, the subsurface disturbances can be correlated with breaks in slope in the surrounding fields. The faults are manifest in three ways:

- Visible offsets in near-surface strata.
- Concave features in the stratigraphy, representing zones of fracture and warping.
- At depths of 2-5m, where some fault planes are steeply dipping, faults are imaged on GPR profiles as incoherent scattering from rupture planes.

The GPR profiles confirm recent (Late Holocene) tectonic activity under the Nikolaiika Fan. Such recent activity in front of the footwall of the Western Eliki Fault may suggest that recent earthquake activity has been concentrated on fault splays from the main footwall fault, rather than along the footwall fault plane itself.

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Reported by

BRUNEL UNIVERSITY
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