Pn wave tomography in Greece

• Κύριος συγγραφέας: Μπαντούνα, Αθανασία
• Άλλοι συγγραφείς: Σώκος, Ευθύμιος
• Μορφή: Thesis
• Γλώσσα: English
• Έκδοση: 2018
• Θέματα: Pn tomography; Inversion; Mohorovicic; Discontinuity; Τομογραφία pn; Αντιστροφή; Ασυνέχεια; 551.13

In this study, we use Pn seismic wave arrivals to obtain structural information for the upper mantle, lower crust i.e. the Moho discontinuity, in Greece. Previous studies indicate that crustal thickness varies significantly across Greece. In detail, crust has the largest thickness in the Hellenides mountain range that belong to the Alpine orogeny, with a mean thickness of ~ 40-50km. In the Aegean Sea the crust is thinner, due to extension that takes place in the area and ranges from ~25km in the north to ~ 30km in the south. Furthermore, geophysical data show that a Benioff zone submerges underneath Peloponnesus, Crete and the Aegean Sea. Data for this study were gathered from stations located in the wider Greek region with Latitude range (34.15 to 41.85) and Longitude range (18 to 30.2). Our database consists of 452220 arrivals that cover the time period from 1974 to 2013 and were retrieved from the International Seismological Centre bulletin. In order to increase the data quality, we only used events with magnitude above 3, also from our dataset we left out events without pre-defined residuals and events with missing origin, depth and we only kept data having residuals within a ± 4 sec limit. An additional filter was also used based on epicentral distance, data having epicentral distance less than this critical distance (1.799°) was removed along with data with epicentral distance above 15°. We have used the Pn arrival times to invert mainly for a) Moho velocity, b) velocity gradient below Moho while c) crustal modifier term was also calculated. Methodology is described in detail in Mayers et al, 2010. We have used an initial seismic velocity model of the crust, following the global regional seismic travel time model, proposed by Mayers et al, 2010, in detail the latest version of the model was used. Results, indicate that Moho depth varies across Greece, as expected. More specifically it is lower in the Ionian compared to central Greece and Peloponnese, where the highest depth is observed while in the Aegean Sea Moho depth is the lowest. In the area around Crete is deeper than the Ionian but not as deep as in the rest of the Aegean. Moho deepens as we travel North above central Greece. Our results are in good agreement with previous studies.