A Deeper Look Into the 2021 Tyrnavos Earthquake Sequence (TES) Reveals Coseismic Breaching of an Unrecognized Large‐Scale Fault Relay Zone in Continental Greece. Issue 12 (11th December 2022)

• Record Type: Journal Article
• Authors: Mouslopoulou, Vasiliki; Sudhaus, Henriette; Konstantinou, Kostas I.; Begg, John; Saltogianni, Vasso; Männel, Benjamin; Andinisari, Ratri; Oncken, Onno
• Is Part Of: Tectonics. Volume 41:Issue 12(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-12-11
• Subjects: multi‐fault earthquake sequence -- InSAR -- normal fault -- stress‐drop -- relay fault zone -- fault intersection -- coseismic slip -- Thessaly -- Greece; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1029/2022TC007453
• Languages: English
• ISSNs: 0278-7407

Abstract

Abstract: Large magnitude (Mw ∼ ≥6) earthquakes in extensional settings are often associated with simultaneous rupture of multiple normal faults as a result of static and/or dynamic stress transfer. Here, we report details of the coseismic breaching of a previously unrecognized large‐scale fault relay zone in central Greece, through three successive normal fault earthquakes of moderate magnitude (Mw 5.7–6.3) that occurred over a period of ∼10 days in March 2021. Specifically, joint analysis of InSAR, GNSS and seismological data, coupled with detailed field and digital fault mapping, reveals that the Tyrnavos Earthquake Sequence (TES) was accommodated at the northern end of a ∼100 km wide transfer structure, by faults largely unbroken during the Holocene. By contrast, the southern section of this relay zone appears to have accrued significant slip during Holocene. InSAR‐derived displacements agree with the loci of eight subtle, previously undetected, faults that accommodated coseismic and/or syn‐seismic normal fault slip during the TES. Kinematic modeling coupled with fault mapping suggests that all involved faults are interconnected at depth, with their conjugate fault‐intersections acting largely as barriers to coseismic rupture propagation. We also find that the TES mainshocks were characterized by unusually high (>6 MPa) stress‐drop values that scale inversely with rupture length and earthquake magnitude. These findings, collectively suggest that the TES propagated north‐westward to rupture increasingly stronger asperities at fault intersections, transferring slip between the tips of a well‐established, but previously unrecognized, relay structure. Fault relay zones may be prone to high stress‐drop earthquakes and associated elevated seismic hazard. Key Points: Revised fault mapping reveals that the Tyrnavos Earthquake Sequence ruptured the tip of a large‐scale relay zone that remained unbreached during the Holocene InSAR‐derived coseismic and syn‐seismic fault slip in good agreement with the location of subtle, previously unmapped, geological faults Unusually high stress‐drop values likely suggest that rupture was arrested by strong asperities at normal fault intersections