Elastic Fault Interactions and Earthquake Rupture Along the Southern Hellenic Subduction Plate Interface Zone in Greece

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.

Displacement Accumulation and Sampling of Paleoearthquakes on Active Normal Faults of Crete in the Eastern Mediterranean

“…By contrast, more northerly striking faults predominately have Quaternary plus postglacial scarps (41 vs. 23), from which we conclude that onshore northerly striking faults have been more active and accommodated a greater number of surface-rupturing earthquakes during the postglacial interval. This interpretation is consistent with GPS data which indicate that upper plate extension in Crete is predominately east-west, with relatively minor northsouth extension along the south coast (e.g., Floyd et al, 2010;Saltogianni et al, 2020).…”

“…Crete forms part of the subaerial forearc of the Eastern Mediterranean Hellenic subduction margin, which accommodates 35–40 mm/year of oblique convergence between the African and Eurasian plates (Figure 2, inset) (Floyd et al., 2010; McClusky et al., 2000; Reilinger et al., 2006). Although the subduction process along the Hellenic margin has been characterized as largely aseismic (Floyd et al., 2010; Reilinger et al., 2006; Vernant et al., 2014), recent global positioning system (GPS) studies show that locally locked patches beneath southwest Peloponnese and southern Crete may accommodate up to 85% of the plate‐motion (either on the main subduction thrust or on splay‐thrust faults) (Howell et al., 2017; Saltogianni et al., 2020). These locked patches are also reflected in the instrumental seismicity catalog where moderate‐to‐large thrust and strike‐slip events are commonly produced in the deeper (>15 km) sections of the crust beneath Crete, and normal‐fault focal mechanisms in the overlying upper crust (<15 km) (Kiratzi & Louvari, 2003; Konstantinou et al., 2017).…”

“…Peloponnese and southern Crete may accommodate up to 85% of the plate-motion (either on the main subduction thrust or on splay-thrust faults) (Howell et al, 2017;Saltogianni et al, 2020). These locked patches are also reflected in the instrumental seismicity catalog where moderate-to-large thrust and strikeslip events are commonly produced in the deeper (>15 km) sections of the crust beneath Crete, and normal-fault focal mechanisms in the overlying upper crust (<15 km) (Kiratzi & Louvari, 2003;Konstantinou et al, 2017).…”

Earthquake Swarms, Slow Slip and Fault Interactions at the Western‐End of the Hellenic Subduction System Precede the Mw 6.9 Zakynthos Earthquake, Greece

“…Slow‐slip events that trigger swarm activity and/or moderate‐to‐large‐sized earthquakes have been recorded before in major subduction zones globally, including New Zealand, Japan, Ecuador, Chile, and Mexico (Beavan et al., 2007; Colella et al., 2017; Kato et al., 2012; Obara & Kato, 2016; Ruiz et al., 2014; Vallée et al., 2013). Although the detailed distribution of interseismic coupling beneath western Peloponnese in Greece has not been constrained, a first‐order difference between the global examples and the Greek case is that the SSEs here occur on a weak plate‐interface that largely creeps (Saltogianni et al., 2020; Vernant et al., 2014). The only other references for SSEs along creeping sections of the plate‐interface (or sections with heterogeneous interseismic coupling) is at the central/northern Hikurangi margin in New Zealand (Wallace et al., 2016), in Ecuador (Vallee et al., 2013), Costa Rica (Davis et al., 2015), and the Boso Peninsula in Japan (Ozawa et al., 2007).…”

Does Deep Tectonic Tremor Occur in the Central‐Eastern Mediterranean Basin?

“…Very recently SSEs have been found at the down‐dip limit of the seismogenic zone, at depths of 20–40 km beneath western Peloponnese (Mouslopoulou et al., 2020) leaving open the possibility that they occur along other segments of the Hellenic Subduction Zone (Saltogianni et al., 2020). Limitations on publicly available geodetic data may have prevented their detection elsewhere.…”