Çubuk-Sabuncu, Y. ; Jónsdóttir, K. ; Árnadóttir, T. ; Mordret, A. ; Caudron, C. ; Lecocq, T. ; De Plaen, R.

published in Journal of Geophysical Research: Solid Earth, 129 issue e2023JB027064 (2024)

Abstract: 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.

Keyword(s): earthquake ; triggering ; velocity variation ; interferometry ; deformation
DOI: 10.1029/2023JB027064
Links: link
Funding: Icelandic Centre for Research 217738-051, 185209-051/Icelandic Centre for Research 217738-051, 185209-051/Icelandic Centre for Research 217738-051, 185209-051