Elastic Fault Interactions and Earthquake Rupture Along the Southern Hellenic Subduction Plate Interface Zone in Greece. Issue 13 (6th July 2020)

• Record Type: Journal Article
• Authors: Saltogianni, Vasso; Mouslopoulou, Vasiliki; Oncken, Onno; Nicol, Andrew; Gianniou, Michail; Mertikas, Stelios
• Is Part Of: Geophysical research letters. Volume 47:Issue 13(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-07-06
• Subjects: subduction seismogenesis -- GPS -- locking degree -- fault interactions -- earthquake rupture segmentation; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2019GL086604
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The importance of splay‐thrust faults in subduction seismogenesis is increasingly acknowledged; however, their elastic interaction with the plate interface remains unclear. Here, we use GPS velocities, constrained by millennial fault slip rates, to study elastic fault‐interactions between the plate interface and its upper‐plate splay‐thrust faults from the southern Hellenic Subduction System (HSS). We find that, despite its largely aseismic character, the HSS plate interface zone is kinematically segmented, with slip rate deficits locally reaching ~85% and ~45% of the plate convergence rate on the western and eastern segments, respectively, and on structures different from those that ruptured historically. Although western Crete has been more active seismically during late Holocene, we find that the eastern HSS has higher seismic potential for large‐magnitude ( M > 6) earthquakes and its interface zone is closer to failure. Elastic fault interactions are responsible for both significant intersegment variability in strain accumulation and uniformity in earthquake rupture segmentation along the HSS over millennial timescales. Plain Language Summary: The southern Hellenic Subduction System (HSS) hosted at 365 CE the greatest earthquake (~ M 8.3) ever recorded in the Mediterranean. This earthquake, unlike other large subduction earthquakes, did not rupture the main contact between the two sliding tectonic‐plates (i.e., the plate interface) but, instead, it was generated on a steep large fault that branches upward from the plate interface to extend within the upper plate. As the main plate interface fault and its branch(es) are linked at depth and accumulate strain interdependently, rupture on one controls the locus and timing of rupture on neighboring faults. Thus, to better assess the seismic hazard along the HSS it is crucial to chart and quantify the amount of strain stored on each of these structures. Here, we use dense GPS data and normal fault displacements to derive, for the first time, a detailed "locking" map of each fault in the southern HSS. We find that the western and eastern sections of the HSS rupture during different earthquakes (HSS is segmented), with these earthquakes breaking interchangeably the plate interface and its branches. Further, we find that although western HSS has been more active seismically in the last 5, 000 years, the eastern HSS has higher potential for M > 6 earthquakes in the near future. Key Points: Spatially variable elastic strain accumulation in the Hellenic plate interface zone produces persistent earthquake rupture segments Slip rate deficit up to 85% and 45% of the plate convergence rate on the western and eastern segments of the interface zone, respectively Potential for large‐magnitude ( M > 6) earthquakes in the eastern Hellenic margin elevated compared to that in the western