HR: 09:15h
AN: H51B-06 INVITED     [PDF]
TI: Active Faulting and Regional Flow in the Corinth Rift
AU: * Cornet, F H
EM: cornet@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussieu, Paris, 75252 France
AB: The Corinth Rift, in western Greece, opens at the yearly rate of 1.5 cm/year with an uplift of its southern shore reaching locally 1 mm/year and elevations reaching 2500 m. The fault system on this southern shore involves a set of parallel fault segments with lengths reaching up to 40 to 50 km and offsets of the order of 1000 m. In the context of the European Corinth Rift Laboratory development, a 1000 m deep borehole has been drilled on the seashore, through the smaller Aegion fault, re-activated during a magnitude 6.2 earthquake, in 1995. The upper 490 m of the well intersects a series of quaternary conglomerates interbedded locally with horizons of calcilutite (calcite mud) which become predominant in the lower 250 m of this section. From 490 m to 690 m a strongly tectonized radiolarite series is encountered till the well penetrates a cretaceous series of fractured limestone, locally karstified. The 15 m thick fault zone, encountered between 750 m and 790 m, within the limestone, has been cored through its whole length and shows crystalline calcite grown in multidecimetric open cavities, within the fault breccia. A one-meter thick siliceous fault gouge made up from the radiolarite is intersected at 760 m. Laboratory permeability measurements yield 9 to 15 10$^{-18}$ m$^{2}$ for the calcilutite and 0.9 to 2.0 10$^{-18}$ m$^{2}$, for the fault gouge. Production tests conducted during the drilling operation yield a hydraulic conductivity of 10$^{-5}$ to 10$^{-4}$ m/s for the upper conglomerates (200m depth) with no artesian flow. The limestone encountered just above the fault, below the radiolarite, is artesian with a 0.5 MPa overpressure and a flow rate equal to 0.7 m$^{3}$/h. Its hydraulic conductivity has been measured to be about 10$^{-7}$ m/s. Below the fault, an artesian flow is produced through local karsts observed down to 960 m, with a total flow rate of about 50 m$^{3}$/h and a 1MPa overpressure, in no flow conditions. The down-hole temperature is only $32\deg$ C, for an upper-hole temperature of $17\deg$C. The fault is intersected some 250 m below the local sea-floor in the rift. Hence this active normal faults system acts as a strong hydraulic barrier, east-west oriented, while the mountainous terrain of the southern shore produces a natural hydrostatic load that induces downward flow down to depths, which remains to be ascertained. Geological observations, in the nearby Cyclades islands, some 300 km to the east, suggest meteoritic flow may reach the brittle-ductile transition.
UR: http://www.corinth-rift-lab.org
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 8010 Fractures and faults
DE: 8045 Role of fluids
DE: 8164 Stresses--crust and lithosphere
SC: Hydrology [H]
MN: 2003 Fall Meeting