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Temporal Seismic Velocity Changes Associated With the Mw 6.1, May 2008 Ölfus Doublet, South Iceland: A Joint Interpretation From dv/v and GPS

par Çubuk-Sabuncu, Yeşim;Jónsdóttir, Kristín;Árnadóttir, Thóra;Mordret, Aurélien;Caudron, Corentin ;Lecocq, Thomas;De Plaen, Raphael
Référence Journal of Geophysical Research B: Solid Earth, 129, 4, e2023JB027064
Publication Publié, 2024-04-01

Article révisé par les pairs

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Résumé :

In South Iceland, populated and agricultural areas are at risk of earthquakes due to their location within the South Iceland Seismic Zone (SISZ). In 2008, two moderate-sized earthquakes (M5.8 and M5.9) occurred in Ölfus, the western end of this highly active transform zone. We analyze temporal seismic velocity variations (dv/v) related to the Ölfus earthquake doublet, using cross-correlations of ambient noise in the frequency range of 0.1–3.0 Hz. The two mainshocks decrease the average velocity by 0.8% at the nearest stations. The co-seismic changes are most noticeable from 0.7 to 1.7 Hz and affect a 40 km wide region. We present a first-time comparison of dv/v to crustal deformation, seismicity, co-seismic volumetric stress changes and reported PGA distribution for the Ölfus doublet. Ground accelerations caused by mainshocks at intermediate distances suggest that strong shaking-related damage may contribute to the co-seismic dv/v decrease. A rapid velocity increase (0.3%) in a month after the co-seismic drop indicates crustal rock healing. We find 3-months of post-seismic decorrelation, followed by a nearly permanent velocity decrease (0.2%) confined to a shallow layer (1 km) until the end of the observation period. Afterslip and pore fluid effects in the near-source region are likely to influence post-seismic dv/v. We demonstrate that seismic interferometry can contribute to future fault-zone monitoring operations in the SISZ by detecting small changes in velocity.