Abundant Quasi-Repeating Earthquakes Occurring Within Repeater Sequences on the Erkenek-Pütürge Fault (SE Turkey)

Abstract

Repeaters are known as earthquakes that rupture the same asperity in similar manners. However, the complexity of repeater asperities is poorly investigated. In this study, we developed a new strategy to systematically detect quasi-repeaters that rupture the same asperities in different ways. It begins by identifying repeaters using waveform cross-correlation (CC) ≥0.9 and CC-measured Δ(S-P) times ≤0.01 s. We then adopt a much lower CC threshold to detect quasi-repeaters, classifying repeater sequences as simple (lacking quasi-repeaters) or complex (including quasi-repeaters). Applying this workflow to the Erkenek-Pütürge fault in Turkey, we detected 43 repeater sequences during 2020–2023/04. Notably, 30 sequences (∼70%) are complex. The repeater magnitudes show weak correlation with their recurrence interval, with only complex sequences following the 2023 M_w 7.8 mainshock an exception. Moreover, ∼74% sequences have the first two events following the mainshocks exhibiting decreasing magnitude. These results suggest that slip rate and asperity complexity may be key factors in such modulation.