New InSAR and seismology analysis of the 1995 Aigion M_w 6.2 earthquake (Greece)

Abstract

As early rifts initiate and evolve, different fault geometries and kinematics may form. In particular, it is debated at what stage low–angle normal faulting can develop in continental rifts. Addressing this debate requires a thorough exploration of the variability and uncertainties of fault models derived from geophysical observations in order to constrain how faults slip during earthquakes. In addition, assigning earthquakes to particular faults is important for future hazard assessment. We study the M _w 6.2 Aigion earthquake that occurred in the Corinth Rift, Greece on 15 June 1995, using InSAR and seismic waveforms. Corinth is a rift in its early stages, currently extending at a rate of up to 15–20 mm yr ^-1 in the N-S direction and characterized by normal faults defining a graben. The Corinth Rift has experienced major destructive earthquakes and is densely populated. Still, the subsurface geometry, orientation, dip angle and location of the fault source of major earthquakes in the area, particularly the 1995 earthquake, is debated. We compute both ascending and descending co-seismic interferograms of the Aigion earthquake, which show up to 25.2 cm of ground motion away from the satellite (i.e., subsidence) on the north coast of the Gulf, with more deformation likely to have occurred offshore. We invert the interferograms for the best-fit fault model exploring the full range of fault parameters that explain the data. The modelling of only the InSAR data shows that either a north-dipping (39°) or south-dipping (45°) normal fault, striking roughly E-W, fit the data equally well. However, joint inversion of InSAR and teleseismic data favours a south-dipping fault (43°), in contradiction to the fault geometry interpreted so far in the literature. The use of multidisciplinary methodology to obtain robust fault models could better constrain subsurface definition of faults, both for past and future deformation events.

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