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- Title
Temporal Seismic Velocity Changes Associated With the M<sub>w</sub> 6.1, May 2008 Ölfus Doublet, South Iceland: A Joint Interpretation From dv/v and GPS.
- Authors
Çubuk‐Sabuncu, Yeşim; Jónsdóttir, Kristín; Árnadóttir, Thóra; Mordret, Aurélien; Caudron, Corentin; Lecocq, Thomas; De Plaen, Raphael
- 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. Plain Language Summary: Strong earthquakes can occur in southwestern Iceland due to plate motions, posing a threat to human life and infrastructure. In 2008, two earthquakes struck the Ölfus region, causing widespread damage in the epicentral area. Sensitive instruments record naturally occurring ambient seismic signals which are originated from ocean waves, wind, and anthropogenic activity. A dramatic drop in seismic wave velocity is common during major quakes. The state‐of‐the‐art seismic methods based on these ambient waves allow us to detect minor changes in the velocity of seismic waves. We employ continuously recorded seismic data from three instruments to analyze for the first time such seismic velocity fluctuations related to moderate size earthquakes in Iceland. To interpret the complex mechanisms underlying these changes, we make use of multiple available data sets and compare them to our observations. Our findings suggest that seismic velocities decreased over a wide area, possibly due to earthquake‐induced ground shaking and rock damage. This study shows that velocity variations can be effectively measured with even sparsely placed seismometers and that they can be used in the future to monitor seismic zones in Iceland. Key Points: We apply ambient noise seismic interferometry to the 2008 Mw 6.1 south Iceland earthquake doubletTemporal seismic velocities decrease at the time of the earthquakes and recover post‐seismically up to 40 km in the upper crustThe co‐seismic and post‐seismic velocity changes correlate with GPS displacements
- Subjects
ICELAND; SEISMIC wave velocity; MICROSEISMS; SURFACE waves (Seismic waves); SEISMIC waves; EARTHQUAKE zones; OCEAN waves; SEISMIC event location; PORE fluids
- Publication
Journal of Geophysical Research. Solid Earth, 2024, Vol 129, Issue 4, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2023JB027064