Transdimensional ambient-noise surface wave tomography of the Reykjanes Peninsula, SW Iceland

Six en-echelon arranged volcanic systems are aligned NE-SW along the Reykjanes Peninsula, each comprising a fissure swarm with the central area marked by a maximum volcanic production. Five out of six systems host a high-temperature geothermal field. In this study, we image the shear wave velocity structure of the entire Reykjanes Peninsula using a recently developed one-step 3D transdimensional surface wave tomography. The transdimensional tomography algorithm uses a variable model parametrization by employing Voronoi cells in conjunction with the reversible jump Markov chain Monte Carlo method. We use the frequency dependent-travel times (with a frequency range of 0.1-0.5 Hz) derived from the recorded ambient noise data to image the area. The data are recorded between April 2015 until August 2015 using seismic stations from four different seismic networks (i.e., IMAGE, ÍSOR/HS Orka, REYKJANET, and SIL). The area covered by all stations is 120 km by 70 km. Approximately 45 km by 25 km of the station areal coverage is onshore; the rest is offshore. Additionally, based on the previous studies, using a frequency range of 0.1-0.5 Hz, it is expected to resolve the shear wave velocity structure up to a maximum depth of 10 km. The results show that the algorithm successfully recovered the velocity structure below the areas sampled with sufficient ray paths coverage. The areas with fewer ray paths result in a smoother velocity structure. We observe a few low-velocity anomalies at depths around 4-6 km, which are likely to be associated with the high-temperature fields around those depths. In other words, the low-velocity anomalies appeared below the location of the known high-temperature fields, which are Reykjanes, Eldvörp, Svartsengi, and Krýsuvík.