Displacement Accumulation and Sampling of Paleoearthquakes on Active Normal Faults of Crete in the Eastern Mediterranean. (28th October 2020)

• Record Type: Journal Article
• Authors: Nicol, Andrew; Mouslopoulou, Vasiliki; Begg, John; Oncken, Onno
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 21:Number 11(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-10-28
• Subjects: normal fault -- paleoearthquakes -- displacement rates -- Crete -- seismic hazard; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2020GC009265
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: Active normal faults on the 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 northerly trending faults being a factor of 3 more abundant. Lengths, displacements, and displacement rates have been analyzed for 84 active faults sampled over 2 ± 0.5 Ma (long‐term) and 16.5 ± 2 ka (short‐term) time‐intervals, with half showing no resolvable short‐term activity. Active faults record earthquake processes on timescales of thousands to million years and constrain sampling biases, which can lead to under and over estimates of fault parameters. The available data provide no evidence for fault propagation and support a model in which fault lengths were established early in the development of the fault system. Short‐term displacement rates (0.09–1.2 mm/year) are generally higher than long‐term rates (0.002–0.7 mm/year), with a factor of 4 disparity in the average recurrence intervals for the two time periods (∼2.5 Kyr vs. ∼11 Kyr). We attribute these differences to "clustering" of surface‐rupturing (e.g., > M w 6) earthquakes on individual faults over millennial timescales, and to preferential sampling of the most seismically active faults during the short‐term. Displacement rates are comparable when averaged for each time interval on the longest faults (>10 km), indicating that for these faults earthquake "clustering" spans time‐intervals of <∼16.5 Kyr. Paleoerthquakes > M w 6 on Crete are at least three times more frequent than historical earthquakes since ∼1920, possibly because multi‐fault surface‐rupturing earthquakes are double counted in the paleo‐record. Key Points: Displacement and fault length constrain earthquake and fault growth processes on orthogonal fault sets Millenial displacement rates are a factor of 4 higher than million‐year rates, with the greatest disparity for short (<10 km) faults Paleoearthquakes on Crete three times more frequent than historical earthquakes for the last 100 years, possibly due to multi‐fault ruptures.