Abstract
Tomographic imaging based on ambient seismic noise measurements has shown to be a powerful tool, especially in areas like Iceland, where the microseism illumination is excellent. In this paper, we produce a 3D S-wave tomographic image over the western Reykjanes Peninsula high-enthalpy geothermal fields and evaluate the reliability of the tomographic results for different resolutions through simulated and real data. We use 30 broadband stations operating for approximately one-and-a-half year and apply ambient noise seismic interferometry for each station-pair. This results in empirical Green's functions in which especially the ballistic surface waves (BSW) are well resolved. The retrieved BSW exhibit a high signal-to-noise ratio between 0.1 and 0.5 Hz, and the beamforming analysis indicates an apparent surface-wave velocity of 3 km/s over a broad azimuthal range. For the tomographic inversion, we invert the estimated phase velocities between all station pairs to frequency-dependent phase velocity maps in four different resolutions (1, 2, 3, and 4 km) using a Tikhonov regularisation. With the estimated regularisation parameter per frequency per resolution, we invert simulated data for checkerboard sensitivity tests per frequency for different combinations of velocity anomaly sizes and resolutions.Finally, after the inversion to depth, we detect S-wave velocity anomalies with variations between −15% and 15% with reference to an estimated average velocity using 1 km and 3 km of lateral resolutions and 1 km of vertical resolution. This study shows the potential of ambient noise tomography as complementary seismological tool for reservoir characterization.
Highlights
IntroductionThe Western Reykjanes Peninsula (WRP), located at the southwestern tip of Iceland (Fig. 1) is a transitional zone between a tectonic spreading centre (the extension over Iceland of the MidAtlantic Ridge) and a transform zone (Pálmason and Sæmundsson, 1974; Sigmundsson et al, 2018)
The Western Reykjanes Peninsula (WRP), located at the southwestern tip of Iceland (Fig. 1) is a transitional zone between a tectonic spreading centre and a transform zone (Pálmason and Sæmundsson, 1974; Sigmundsson et al, 2018)
We use the fundamental mode Rayleigh-wave arrival time produced by ambient noise seismic interferometry (ANSI) in a tomographic inversion scheme, to obtain frequency-dependent velocities
Summary
The Western Reykjanes Peninsula (WRP), located at the southwestern tip of Iceland (Fig. 1) is a transitional zone between a tectonic spreading centre (the extension over Iceland of the MidAtlantic Ridge) and a transform zone (Pálmason and Sæmundsson, 1974; Sigmundsson et al, 2018). At this transitional zone, an extensional component with northeast-southwest trending normal faulting, and a transform component with strike-slip faulting oriented north-south can explain observed displacement components (Klein et al, 1973; Einarsson, 2008). The authors interpret the low-ratio anomaly of compressional- over shear-velocity as being due to the absence of a sizeable magmatic body at the tip of Reykjanes Peninsula, which was confirmed by Friðleifsson et al (2018)
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