The Reykjanes Geothermal System (RGS) is a high-temperature geothermal system located on the Reykjanes peninsula, a transtensional plate-boundary zone located on the southwestern tip of Iceland. The area is characterized by high seismicity, recent volcanism, and high-temperature geothermal fields. We use seismic noise records from April 2014 to August 2015 to study stress changes and potential deformation of the subsurface caused by injection and production operations at RGS through seismic interferometry. We retrieve continuous time series of waveform similarity values and seismic velocity changes during this period. The S-transform of the similarity values allows us to clearly identify three variations in the mechanical properties of the Reykjanes peninsula related to rapid changes of RGS production. In addition, we observe a slow seismic velocity decrease of 0.36%/year in the reservoir due to the water deficit and seasonal variations associated with the energy production demand. ... Read more

The Spanish Central System is an intraplate mountain range dividing the Iberian Inner Plateau in two sectors – the Duero Basin (N) and, the Tajo Basin (S). The latter has an average altitude of 450-500 m while the former presents a higher average altitude 750-800 m. This intraplate orogen features a thick-skin pop-up and pop-down configuration formed by the reactivation of Variscan structures. Its high topography is the response of a tectonically thickened crust evidenced by 1) the geometry of the Moho discontinuity 2) an imbricated crustal architecture and/or 3) the rheological properties of the lithosphere. Research has been carried out to build a lithospheric-scale model across the orogen. A 400 km long multi-seismic transect has been acquired using natural and controlled source seismic data. The earthquakes and seismic noise data was acquired over a period of one to two months of continuous recording along a linear array (69 short-period seismic stations). The controlled source data included over 1000 stations and a series of acoustic sources. This effort has delineated the geometry of the base of the crust by: Global-Phase Seismic and, conventional noise interferometry, and, wide-angle imaging. The Global Phase approach used PK, PKiKP and PKIKP phases of earthquakes (> 120° epicentral distance). Stacking of the autocorrelations of these phases contribute to a pseudo zero-offset X-section. The application of ambient noise seismic interferometry complements the zero-offset reflection image, defining the geometry of the Moho. Further details on the lithospheric structure is provided by seismic wide-angle reflection images, which reveal a clear thickening of the crust below the Central System resulting, most probably, from an imbrication of the lower crust. Accordingly, the crust-mantle boundary is mapped as a relative flat interface at approximately 10 s two-way travel time except under the Central System, where this feature deepens towards the NW reaching more than 12 s. An intra-crustal boundary is well defined at 5 s. Reflectivity within upper-mantle depths is scattered throughout the profile, located between 13-18 s, and probably related with the Hales discontinuity. Funding resources: EU EIT-RawMaterials Ref: 17024_20170331_92304; MINECO: CGL2016-81964-REDE CGL2014-56548-P: JCYL: SA065P17) ... Read more

The Spanish Central System is an intraplate mountain range that divides the Iberian Inner Plateau in two sectors – the northern Duero Basin and the Tajo Basin to the south. The topography of the area is highly variable with the Tajo Basin having an average altitude of 450–500 m and the Duero Basin having a higher average altitude of 750–800 m. The Spanish Central System is characterized by a thick-skin pop-up and pop-down configuration formed by the reactivation of Variscan structures during the Alpine orogeny. The high topography is, most probably, the response of a tectonically thickened crust that should be the response to (1) the geometry of the Moho discontinuity, (2) an imbricated crustal architecture, and/or (3) the rheological properties of the lithosphere. Shedding some light on these features is the main target of the current investigation. In this work, we present the lithospheric-scale model across this part of the Iberian Massif. We have used data from the Central Iberian Massif Deformation (CIMDEF) project, which consists of recordings of an almost-linear array of 69 short-period seismic stations, which define a 320 km long transect. We have applied the so-called global-phase seismic interferometry. The technique uses continuous recordings of global earthquakes (>120∘ epicentral distance) to extract global phases and their reverberations within the lithosphere. The processing provides an approximation of the zero-offset reflection response of a single station to a vertical source, sending (near)-vertical seismic energy. Results indeed reveal a clear thickening of the crust below the Central System, resulting, most probably, from an imbrication of the lower crust. Accordingly, the crust–mantle boundary is mapped as a relatively flat interface at approximately 10 s two-way travel time except in the Central System, where this feature deepens towards the NW reaching more than 12 s. The boundary between the upper and lower crust is well defined and is found at 5 s two-way travel time. The upper crust has a very distinctive signature depending on the region. Reflectivity at upper-mantle depths is scattered throughout the profile, located between 13 and 18 s, and probably related to the Hales discontinuity. ... Read more