Comparison of surface slip and focal mechanism slip data along normal faults: an example from the eastern Gulf of Corinth, Greece

Focal mechanism and surface slip data are used to investigate: whether kine matics are similar at depth and at the surface along an active normal fault in the Gulf of Corinth. Greece. We present a new database of slip data fro m the lateral termination of the South Alkyonides fault segment (SAFS) and the en echelon stepover between it and on adjacent fault, and use published data on surface slip and focal mechanism data pertaining to slip at depth during the 1981 Alkyonides earthquake sequence. The focal mechanisms exhibi t similar fault plant orientations and kinematics to those measured at the surface. Within the stepover, both data sets show that contemporaneous c. N -S and c. E-W extension is being accommodated by c. E-W- and c. N-S-oriente d normal faults, and the overall deformation is distributed oblate vertical flattening. The deviation of the surface slip direction from 350 degrees i ncreases with distance from the centre of the SAFS. The deviation of the fo cal mechanism T-axes from 350 degrees fit well with the surface data, imply ing that the coseismic slip on the SAFS tit depths of 7-10 km exhibits a si milar kinematic pattern as that observed at the surface. Our results imply that it is critical to know the along-strike position of data on a fault if tither focal mechanisms or surface slip are to be used to infer regional s train and stress trajectories. (C) 2001 Elsevier Science Ltd. All rights re served.