Andrew Nicol, Vasiliki Mouslopoulou, John Begg, onno oncken

Active normal faults on the eastern Mediterranean island of Crete form prominent limestone scarps together with basin and range topography. These faults mainly strike E-ESE and N-NNE in southern and northern Crete, respectively, with fault sets commonly intersecting and northern-trending faults a factor of three more abundant. Displacements, lengths and displacement rates have been analysed for 84 active faults sampled over 2±0.5 Ma (long term) and 16.5±2 ka (short term) time-intervals, with about half showing no resolvable short-term activity. Active faults record earthquake processes on timescales of thousands to millions of years and constrain sampling biases, which can lead to under and over estimates of the numbers, rupture lengths, recurrence intervals and single event displacements of paleoearthquakes. The available data indicate no fault propagation and, for the Quaternary, higher displacement rates on longer faults, supporting a model in which fault lengths and maximum earthquake magnitudes were established early in the development of the fault system. Short-term displacement rates (0.09-1.2 mm/yr) are generally higher than long-term rates (0.002-0.7 mm/yr), with a factor of four disparity in the average recurrence intervals for the two time periods (~2.5 kyr vs ~11 kyr). We attribute these differences to ‘clustering’ of >Mw 6 earthquakes on individual faults over millennial timescales, and to preferential sampling of the most seismically active faults in the post-~16.5 kyr time interval (i.e. faults with highest displacement rates or mid ‘cluster’). Displacement rates are comparable when averaged for each time interval on the longest faults (>10 km), interpreted to indicate that for these faults earthquake ‘clustering’ spans time-intervals of 16.5±2 kyr or less. Paleoarthquakes >Mw 6 on Crete are a factor of three more frequent than historical events for the last 100 yrs, which could be partly due to paleoevents rupturing multiple faults, either in the same event or in triggered slip events.