Impact of bending-related faulting on the seismic properties of the incoming oceanic lithosphere offshore of Nicaragua

The subduction of H2O is inherently related to the hydrogeology of the oceanic lithosphere entering the trench. Water transported within the subducting oceanic plate affects a number of processes, such as intraslab earthquakes and arc magmatism. Bending related faulting in the subducting lithospheres may intensify hydrothermal flow through aged crust and provide pathways for seawater to reach lower crustal and upper mantle depths. A number of seismic wide-angle reflection and refraction experiments were conducted offshore of Nicaragua to investigate the impact of bending related normal faulting on the seismic properties of the oceanic lithosphere prior to subduction. Based on the reflectivity pattern of multi-channel seismic reflection (MCS) data collected offshore of Nicaragua it has been suggested that bending-related faulting facilitates hydration and serpentinization of the incoming oceanic plate. First seismic wide-angle and refraction data were collected along the profile p50 which extends from the region well seaward of the outer rise, not yet affected by subduction, into the trench northwest of the Nicoya Peninsula, where multibeam bathymetric data show prominent normal faults on the seaward trench slope. A tomographic joint inversion of the seismic refraction and wide-angle reflection data yields a decrease in P-wave velocities in the crust and uppermost mantle as the plate approaches the trench. Seaward of the outer rise velocities are typical for »24 Myr old oceanic lithosphere. In the near-trench region, however, crustal velocities are reduced by 0.2-0.5 km/s compared to normal mature oceanic crust. Seismic velocities of the uppermost mantle are 7.6-7.8 km/s and hence 5-7% lower than the typical velocity of mantle peridotite. These systematic changes in P-wave velocity indicate an evolutionary process in the subducting slab consistent with percolation of seawater through the faulted and fractured lithosphere and serpentinization of mantle peridotites. Two other profiles, located northwest of the profile p50, are parallel to the trench axis. This geometry was chosen to reveal if serpentinization is a common process in the subducting Cocos plate offshore of Nicaragua and not just a local feature. Tomographic inversion of both data sets indeed has shown that seismic velocities are profoundly reduced along the entire lenght of the profiles, both in the crust and uppermost mantle. Upper crustal velocities are not higher than 3.8-4.0 km/s, and the upper mantle is characterized by strong alteration that has i ii caused a reduction of the seismic velocities by 8-10%. The anomalous behaviour is more profound here than in the profile p50, but this observation is most likely due to the geometry of the lines, i.e. fault density is higher along a line parallel to the trench than along one which lies perpendicular. The modeling of the impact of water-filled microcracks on the elastic properties of rocks shows that they could significantly influence the seismic behavior of fractured media. The modeling of the S-wave velocities of the profile p50 has revealed that velocities in the crust are more profoundly reduced than in the P-wave structure. This is an indication that fracture porosity is extensively developed and, thus, has a significant impact on the seismic properties of the crust. One can assume a similar scenario for the upper mantle within a few kilometers just below the Moho. As both processes, hydration and fracturing, are related to each other, it is difficult to separate their effects on seismic properties. Thus, an estimate of 12-17% serpentinization in the uppermost 3-4 km of the mantle is just an upper limit of hydration, i.e. if the reduced velocities we observe in our velocity models were due solely to hydration

Serpentinization in the trench-outer rise region offshore of Nicaragua: constraints from seismic refraction and wide-angle data

Recent seismic evidence suggested that most oceanic plate hydration is associated with trench-outer rise faulting prior to subduction. Hydration at trenches may have a significant impact on the subduction zone water cycle. Previous seismic experiments conducted to the northwest of Nicoya Peninsula, Northern Costa Rica, have shown that the subducting Cocos lithosphere is pervasively altered, which was interpreted to be due to both hydration (serpentinization) and fracturing of the crustal and upper-mantle rocks. New seismic wide-angle reflection and refraction data were collected along two profiles, running parallel to the Middle American trench axis offshore of central Nicaragua, revealing lateral changes of the seismic properties of the subducting lithosphere. Seismic structure along both profiles is characterized by low velocities both in the crust and upper mantle. Velocities in the uppermost mantle are found to be in the range 7.3–7.5 km s−1; thus are 8–10 per cent lower than velocities typical for unaltered peridotites and hence confirm the assumption that serpentinization is a common process at the trench-outer rise area offshore of Nicaragua. In addition, a prominent velocity anomaly occurred within the crust beneath two seamounts. Here, velocity reduction may indicate increased porosity and perhaps permeability, supporting the idea that seamounts serve as sites for water percolation and circulation

Mineralogical and geochemical analysis of Fe-phases in drill-cores from the Triassic Stuttgart Formation at Ketzin CO₂ storage site before CO₂ arrival

Reactive iron (Fe) oxides and sheet silicate-bound Fe in reservoir rocks may affect the subsurface storage of CO2 through several processes by changing the capacity to buffer the acidification by CO2 and the permeability of the reservoir rock: (1) the reduction of three-valent Fe in anoxic environments can lead to an increase in pH, (2) under sulphidic conditions, Fe may drive sulphur cycling and lead to the formation of pyrite, and (3) the leaching of Fe from sheet silicates may affect silicate diagenesis. In order to evaluate the importance of Fe-reduction on the CO2 reservoir, we analysed the Fe geochemistry in drill-cores from the Triassic Stuttgart Formation (Schilfsandstein) recovered from the monitoring well at the CO2 test injection site near Ketzin, Germany. The reservoir rock is a porous, poorly to moderately cohesive fluvial sandstone containing up to 2–4 wt% reactive Fe. Based on a sequential extraction, most Fe falls into the dithionite-extractable Fe-fraction and Fe bound to sheet silicates, whereby some Fe in the dithionite-extractable Fe-fraction may have been leached from illite and smectite. Illite and smectite were detected in core samples by X-ray diffraction and confirmed as the main Fe-containing mineral phases by X-ray absorption spectroscopy. Chlorite is also present, but likely does not contribute much to the high amount of Fe in the silicate-bound fraction. The organic carbon content of the reservoir rock is extremely low (<0.3 wt%), thus likely limiting microbial Fe-reduction or sulphate reduction despite relatively high concentrations of reactive Fe-mineral phases in the reservoir rock and sulphate in the reservoir fluid. Both processes could, however, be fuelled by organic matter that is mobilized by the flow of supercritical CO2 or introduced with the drilling fluid. Over long time periods, a potential way of liberating additional reactive Fe could occur through weathering of silicates due to acidification by CO2

Editorial for the Special Issue "Studies of Seismic Reservoir Characterization"

Seismic reservoir characterization plays an essential role in the study of integrated reservoirs, with applications from prospect identification to detailed reservoir delineation [...

Routing Deployment of CC(U)S in the Baltic Sea Region

Much potential exists in the Baltic Sea region (BSR) regarding CC(U)S and at least on the research side, there has been a steady stream of activities over the years. Potential storage sites are localized in the Baltic Basin within several countries such as Sweden, Latvia, Lithuania, Poland and Russia. However, the BSR is still lagging behind in deploying a large-scale CC(U)S due to the national policy and regulatory frameworks which create unfavorable conditions for the technology, as well as the low public awareness and acceptability in most of the countries in the region. Consequently, CO2 injection is forbidden in Lithuania, CO2 storage on an industrial scale is banned in Estonia, Latvia and Finland and some federal states of Germany, while in Denmark, Poland and Sweden is permitted with limitations. However, it should also be noted that some positive developments and attitudes towards CC(U)S have also taken place recently in some of the BSR countries. This paper provides an overview of the current CC(U)S status and development in the BSRpublishedVersio

Towards an Open Access Data Policy for Deep Seismic Sounding data

Resumen del trabajo presentado en el 19th International Symposium on Deep Seismic Profiling of the Continents and their Margins (SEISMIX 2020), celebrado del 15 al 19 de marzo de 2020 en AustraliaControlled source seismic data acquisition experiments have produced a vast amount of Deep Seismic Sounding (DSS) data since its origins in the late 70¿s. These data provide high valuable information on the structure and nature of the crust and lithosphere, which constitutes a fundamental and solid basis for research within Solid Earth Sciences. These datasets are unique and constitute the output of an enormous and very expensive scientific effort. Their uniqueness and recognized value evidence the need for their preservation, not only recently acquired DSS data but also the old and legacy data. Furthermore, the new developments in processing and achievements in imaging technologies generates new possibilities for these vintage datasets. The availability and accessibility of these data, therefore, is of foremost importance for the society (scientists, decision-makers and general public). The research community, aware of the value of these data, has pushed forward Open Data policies based on the FAIR principles (findable, accessible, interoperable and reusable). A long-term plan has been launched by the European Plate Observation System (EPOS, https://www.epos-ip.org/) e-infrastructure. The focus is to streamline the integrated use of scientific data, data products and services. Closely linked with EPOS, the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA, http://www.sera-eu.org/home, also a Horizon 2020 project) includes a working package to set up a data access service for DSS transects. This initiative should ensure the traceability of the data and data products ensuring that third parties can freely access, exploit and disseminate the data by means of a permanent, international identifier, such as Digital Object Identifier (DOI); and provide related information to use the raw data following the FAIR principles. Furthermore, the current aim is to go beyond FAIR by linking the data with its related peer-reviewed publications, other scientific contributions and technical reports, enhancing the visibility and facilitating its use. A prototype DSS data exchange system has been developed jointly between the DIGITAL.CSIC services and the department of Structure and Dynamics of the Earth of the CSIC-Institute of Earth Sciences Jaume Almera (e.g., https://digital.csic.es/handle/10261/101879). Any data exchange system requires well established data formats, which in the case of seismic data is well established (SEGY format, www.seg.org). Also, metadata must be included to inform on the context, nature of the data itself, specific details in file format and the relevant legal aspects. In addition, technical aspects include the acquisition parameters, data processing and format of data storage. In the current protocol, once the data meets the previous requirements, a permanent identifier such as a DOI or handle is assigned. Thus, any data, visit, download, or access is accounted for. This information enters into the statistics referencing database and reveals a measure of the impact of the data and/or data product

Towards an Open Access European Database for Deep Seismic Sounding data

EGU2020: Sharing Geoscience Online, 4-8 may 2020Controlled source seismic data acquisition experiments have produced a vast amount of Deep Seismic Sounding (DSS) data since its development in the late 50¿s. These datasets provide critical information on the structure and nature of the crust and the lithosphere, which constitutes a fundamental research tool within Solid Earth Sciences. The DSS datasets are unique and constitute the output of an expensive (in time, effort and cost) scientific process, which evidences the need for their preservation, both the recently acquired and the legacy data. Furthermore, the new developments in processing and imaging techniques generate new possibilities for re-use of the vintage datasets. The availability and accessibility of these datasets, therefore, is of foremost importance for scientists, decision-makers and the general public. The research community, aware of the value of these data, has pushed forward Open Data policies based on the FAIR principles of data management (Findable, Accessible, Interoperable and Reusable). In this respect, a long-term plan has been launched by the European Plate Observation System (EPOS, https://www.epos-ip.org/) e-infrastructure. The focus is to streamline the integrated use of scientific data, data products and services. In close link with EPOS, the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA, http://www.sera-eu.org/home, a Horizon 2020 project) includes a working package to set up a network on DSS data and products management. This initiative ensures the traceability of the data allowing that third parties can freely access, exploit and disseminate the data by means of permanent, international identifiers: a Digital Object Identifier (DOI) and a Uniform Resource Identifier (URI) or handle. Furthermore, the current aim is to go beyond the FAIR principles by linking the data with its related peer-reviewed publications, other scientific contributions and technical reports, facilitating its re-use. A prototype DSS data exchange system has been developed jointly between the DIGITAL.CSIC (the Spanish National Research Council) services and the Institute of Earth Sciences Jaume Almera-CSIC (https://digital.csic.es/handle/10261/101879, last access January 2020). Within the platform, each dataset includes the acquired raw data and a metadata file. The metadata provides information of the nature of the data itself, list of authors, the context of the data (time and location of the experiments), funding agencies and other relevant legal aspects. The technical information includes the acquisition parameters, data processing and format of the data (SEGY standard in this case - www.seg.org-, broadly used in the geophysics community). In the developed storage protocol, a permanent identifier is assigned once it has been checked that the data meets all the described requirements. This permanent identifier ensures that any visit or download is accounted for. This information is entered into a statistics referencing database and can also be used as a measure of the impact of the data and/or data product.This work is funded by the European Commission (Grant Agreement no: 676564-EPOS IP, Call H2020-INFRADEV-2014-2015/H2020-INFRADEV-1-2015-1, SERA 730900)

Subsurface seismic imaging with a hammer drilling source at an exploration drilling test center in Örebro, Sweden

Seismic imaging while drilling (SWD) technology offers possibilities of imaging ahead of the drill-bit, which could be useful for determining when to go from hammer drilling to core drilling. Also, seismic images of the surrounding rock can improve geological models which could be then used to guide drilling programs. An SWD field test was carried out in August 2020 at an exploration drilling test site in Örebro, Sweden, with the aim to determine if the signals from hammer drilling can be used for seismic imaging around the drill-bit in a hard-rock environment where the strong drill-rig noise interference is one of the main challenges. The test site had previously been investigated with various geophysical methods, geological mapping and diamond core drilling, and it therefore represented an ideal location to perform this feasibility study. After data pre-processing and cross-correlation with the trace from the geophone closest to the rig, the shot-gathers were vertically stacked over the length of a drill pipe to achieve further signal improvement. A comparison with the active seismic data shows reasonable agreement, in spite of the fact that the noise level is significant even after careful processing. However, the lack of clear reflections in the active seismic data, indicating no detectable changes in the bedrock lithology in the near surface, hinders the full assessment of the seismic signal generated with hammer drilling at this site

Subsurface seismic imaging with a hammer drilling source at an exploration drilling test center in Örebro, Sweden

Seismic imaging while drilling (SWD) technology offers possibilities of imaging ahead of the drill-bit, which could be useful for determining when to go from hammer drilling to core drilling. Also, seismic images of the surrounding rock can improve geological models which could be then used to guide drilling programs. An SWD field test was carried out in August 2020 at an exploration drilling test site in Örebro, Sweden, with the aim to determine if the signals from hammer drilling can be used for seismic imaging around the drill-bit in a hard-rock environment where the strong drill-rig noise interference is one of the main challenges. The test site had previously been investigated with various geophysical methods, geological mapping and diamond core drilling, and it therefore represented an ideal location to perform this feasibility study. After data pre-processing and cross-correlation with the trace from the geophone closest to the rig, the shot-gathers were vertically stacked over the length of a drill pipe to achieve further signal improvement. A comparison with the active seismic data shows reasonable agreement, in spite of the fact that the noise level is significant even after careful processing. However, the lack of clear reflections in the active seismic data, indicating no detectable changes in the bedrock lithology in the near surface, hinders the full assessment of the seismic signal generated with hammer drilling at this site