HR: 1330h
AN: T22A-0488    [PDF]
TI: Control of Fault Segmentation and Seismicity by Inherited Cross-strike Fabric in the Corinth Rift (Greece)
AU: * Ghisetti, F C
EM: francesca.ghisetti@stonebow.otago.ac.nz
AF: Department of Geology University of Otago, Leith Street, Dunedin, 9001 New Zealand
AB: Fault growth occurs in crust that is often strongly heterogeneous. Lateral variations of geometrical and mechanical properties are more difficult to recognize and model than simple horizontal layering, but they play an important role, especially in domains of superposed deformation. The Corinth Rift (Greece) is an ideal setting for analysing dimensions and displacement of seismically active normal faults that since the early Pleistocene propagated at right angles to the Neogene Hellenic thrust belt. The largest historical earthquakes of the last two centuries and 6 shocks within the last 30 years with 6$<${\bf M}$<$6.7 are evenly distributed along N-dipping faults that bound the southern margin of the Corinth Rift. However, the western regions of the rift (from Patras to Egion) differ from the eastern regions (from Dervenion to Corinth) in terms of extensional strain (15 mm/year versus 10 mm/year of N-S extension from GPS), dip of seismic fault planes (30\deg N versus 50\deg N) and maximum depth of seismic activity (8-11 km versus 12-15 km). New mapping along the southern shore of the rift documents different thickness and facies of the Pliocene-Pleistocene clastic sequence in two distinct sub-basins (Egion to the west and Dervenion to the east), separated by a N-S elongated ridge. This ridge is an inherited culmination of the Neogene thrust belt that exposes a stack of folded carbonate units basally detached above a low-grade metamorphic basement. The contour map of the basal detachment depicts the structural high as a large scale, N-plunging antiform truncated by E-W and N-S normal faults. Segmentation of the Quaternary syntectonic basins on the southern margin of the rift is a consequence of the lateral decay in offset of the largest E-W faults that have controlled the northward progradation of the sedimentary sequence in the basins. Both the Egion, Eliki and Pirgaki fault in the west and the Xilokastron fault in the east display a progressive tapering of their total throw, dying out laterally against the N-S structural high. A longitudinal crustal cross section along the southern margin of the rift shows lateral segmentation of the E-W normal faults with a wavelength comparable to the folding of the basal detachment surface and suggests that fault segmentation at the surface reflects structural heterogeneity at depth. Geometrical discontinuities inherited from the compressional thrust belt interfere with present-day kinematics and ultimately control individual seismic ruptures and the long-term growth of the normal faults.
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting