Coastal uplift, earthquakes and active faulting of Rhodes Island (Aegean Arc): modeling based on geodetic inversion

The geodetic inversion technique was used to model the fault pattern responsible for the uplifted Holocene notches along the NE Rhodes Island coast (SE edge of the Hellenic (Aegean) Arc). Input in the modeling was the elevation of uplifted notches, up to 6000 yr old, which are interpreted to reflect remains of fossil shorelines, to testify to a series of earthquakes producing both uplift and subsidence (i.e. to elastic dislocations) and to correspond to geodetic data senso lato. These shorelines, up to 3.8 m high, were probably originally continuous along the whole of the 75-km-long SE Rhodes coast, possibly locally disturbed by minor normal faults, and reflect the last phases of the uplift and tilting of the island as a rather rigid block since Late Pliocene. Their radiocarbon dating was further refined from archeological data testifying to an about 1-m subsidence associated with the 227 BC earthquake, followed by >3-m seismic uplift. Inversion, constrained by the hypothesis of a compressional fault offshore Rhodes, was based on standard, uniform-slip, elastic dislocation analysis; it proved to depend only weakly even on extreme glacio-isostatic corrections and indicated that coastal uplift is dominated by a main compressional fault zone offshore, sub-parallel to the island coast, with normal faults inland reflecting thin-skin tectonics. This fault pattern, similar to that of western Crete, is confirmed by seismic reflection profiles indicating a major reverse close to the modeled fault and can explain (1) the occurrence of strong (M>7.5) historical earthquakes producing tsunamis and destruction on an East Mediterranean scale, (2) the alternation of uplift and subsidence as a result of fault shift inside the same fault zone, and (3) the long-term uplift of the island as a rather conjugate effect of the formation of an about 4.5-km-deep, 5-Myr-old marine basin SE of Rhodes, bounded to the NW by the modeled fault zone. The seismic risk of Rhodes, higher in its NE part of the island and than what was previously believed, is associated with strong (M>7.5) earthquakes producing widespread destruction, tsunamis, coastal uplift and coastal subsidence.