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.
| Original language | English |
|---|---|
| Article number | 106685 |
| Number of pages | 16 |
| Journal | Journal of Volcanology and Geothermal Research |
| Volume | 391 |
| DOIs | |
| Publication status | Published - 1 Feb 2020 |
Funding
The research leading to the results in this manuscript has received funding from the EC Seventh Framework Programme under grant agreement No. 608553 (Project IMAGE). The authors would like to thank ISOR, H.S. Orka, the Iceland Meteorological Office (IMO), the Geophysical instrumental Pool of Potsdam and the DEPAS (Deutsche Geräte Pool für Amphibische Seismologie) for their work in gathering and providing us the seismic data for this study. We would like to thank the anonymous review, Dr. Kasper van Wijk and Prof. Gudmundsson for their insightful comments and constructive criticism during the review process. Finally, the authors would like to thank Pall Einarson and Kristján Sæmundsson for their imense geological contributions in Iceland, for which some are nicely described in Voight et al. (2018) . Appendix A In we show the tomographic results for each frequency (steps of 0.02 Hz) used for the inversion from frequency to depth. As it can be observed, the anomalies identified for each frequency are smooth when compared with the adjacent frequencies. Considering that each frequency is inverted independently, the observed smoothness reinforces the reliability of the tomographic results. Fig. 13
Keywords
- Empirical green functions
- Model resolution
- Reservoir characterization
- Seismic interferometry
- Surface-waves
- Velocity anomalies