Χωρο-χρονική μεταβολή της σεισμικότητας στις μεσο-ωκεάνιες ράχες

• Main Authors: Teza, Eleni, Τέζα, Ελένη
• Format: Doctoral or Postdoctoral Thesis
• Language: Greek
• Published: Aristotle University Of Thessaloniki (AUTH) 2020
• Subjects: Μεσο-ωκεάνιες ράχες; Χρονικά ανεξάρτητη σεισμικότητα; Χρονικά εξαρτημένη σεισμικότητα; Εύρωστη εκτίμηση παραμέτρων σεισμικότητας; Mid-ocean ridges; Time-independent seismicity; Time-dependent seismicity; Robust estimation of seismic parameters; Γεωεπιστήμες και Επιστήμες Περιβάλλοντος; Φυσικές Επιστήμες; Γεωλογία; Γεωφυσική; Earth and Related Environmental Sciences; Natural Sciences; Geology; Geophysics; Antarctic; Indian; Mid-Atlantic Ridge; Pacific; The Antarctic; Antarc*
• Online Access: http://hdl.handle.net/10442/hedi/48882; https://doi.org/10.12681/eadd/48882

The aim of the present thesis was the study of the spatial and temporal variation of seismicity in divergent oceanic boundaries. In order to achieve this objective, bulletins of several seismological agencies (ISC, NEIC, GCMT), as well as several published earthquake catalogs (Pacheco and Sykes 1992, Engdahl and Villaseñor 2002) were considered for the period 1900-2014. The main goal was to create individual seismic catalogs for the six mid-ocean ridges under study: the mid-Atlantic ridge, the Pacific-Nazca ridge, the Pacific-Antarctic ridge, the Central Indian ridge and the ridges along the boundaries of SE & SW Indian plates with the Antarctic plate. A qualitative analysis of the compiled catalogs was performed by checking their focal depths, declustering them and defining completeness magnitudes with several methods. Three different complete periods were identified (before 1964, 1964-1995, 1996-2014) with relatively high completeness magnitudes especially for the period before 1964. This observation is justified by the typical geographical location of most mid-ocean ridges. In the context of studying the time-independent seismicity the parameters at, b of the G-R relation, the most probable maximum magnitude over one year (Μt) and the probabilities of exceedance of certain magnitudes thresholds within several time windows were calculated. Using an appropriate quantitative model, deformation rates (seismic/total strain rate ratios) expressed in terms of velocity tensors were estimated for a large number of indicative areas along several mid-ocean ridges, while a correlation of them with ages of lithospheric plates and heat flow values was attempted. The results indicate that as the distance from the ridges increases, increasing age and decreasing heat flow are observed, associated with an increase in seismicity, a decrease in b values, an increase in the maximum earthquake magnitude and an increase in deformation rates. Based on synthetic catalogs, seismicity parameters were recalculated applying several ...