2021 | Probing magmatic systems at the Galápagos Archipelago (Ecuador) by joint seismic imaging and geodynamic modelling

Aims: The Galapagos Archipelago originates from a plume-like structure that rises into the mantle about 250 km south of the islands. This project targets the archipelago to offer new research links between Mainz and Frankfurt and develop existing cooperation and lines of research in Mainz. Dr Augusto Casas, an expert of ambient noise tomography, will perform a joint velocity and attenuation imaging of the upper crust under the archipelago using stations installed by IGEPN (Fig. 1a). The primary aim is to provide new crustal maps of the feeding systems of the volcanoes scattered across Southern Isabela Island through the expertise in both Mainnz and Frankfurt. The second aim is to link with research in Petrology and Geodynamics currently undergoing at partner institutions, in order for Dr. Casas to apply for fellowship funding. The project strengthens the link between TeMaS and relevant international partners for the SFB applications.

Cooperation: The present project originates from the international collaboration of JGU Mainz with inter-national institutions; the group comprises researchers from Mainz, Frankfurt and Kiel (Germany), Delft University of Technology (The Netherlands), the Observatorio Argentino de Vigi-lancia Volcánica (OAVV, Argentina), and the Geophysical Institute (IGEPN, Ecuador). It links to the recently signed Memorandum of Understanding between the University of Mainz and the OAVV for the installation of a temporal seismic network in the Andes. Dr. Casas already ap-plied (DAAD, unsuccessfully) for funding to carry on research in Mainz. TeMaS offers oppor-tunity for him to start developing necessary background research and learning Geodynamic codes for future applications.

Work plan: The seismic data to be used in this project are freely available within the IRIS (Incorporated Research Institutions in Seismology) database (Fig. 1). The data were downloaded and are ready for processing with the codes developed by the seismology groups in Mainz and Frank-furt to obtain subsurface maps of velocity and attenuation using ambient noise. The experi-ence of the Frankfurt group will be used to understand if earthquake data can be extracted from the continuous recording, in order to apply earthquake source and array imaging tech-niques. We plan to start the activities in September 2021. Based on the distribution of the array of stations, we will target the regional scale feeding systems of Sierra Negra and Cerro Azul, the most active volcanoes in the Galápagos Archipelago. However, the activity of the Petrology groups in Mainz and Kiel is centred on Alcedo volcano (north of the green array, Fig. 1). By combining all station data, we will provide the first image of the volumes connecting Southern and Northern Isabella, in order to link with the inferences from petrology obtained around Alcedo volcano. Casas will be hosted in Mainz (De Siena, Kaus) and Frankfurt (Reiss, Rümpker) and will use their expertise and codes to perform ambient noise tomography for velocity and attenuation. The ambient noise codes are readily available in the group of De Siena and Dragonov (Delft). The submission of the article is planned for September 2022. The group in Frankfurt will as-sess the feasibility of the earthquake-dependent characterization of the area. Casas will come to Mainz in order to work with the available codes and attend the Geodynamic Modelling class taught by Kaus. He will be trained in using LaMEM, to develop first a simplified 2D for-ward model to lay ground for more complex 3D modelling. The input will be built based on petrological and geochemical data (Botcharnikov, Mainz) and Rojas-Agramonte (Kiel), testing the hypothesis that the mantle plume was initially interacting with spreading but not anymore. The group will also analyse the internal deviatoric stress and surface deformation, comparing them with available seismic and GPS data. This is central for the revised applica-tion of Casas to DAAD.

Expected outcome: This project has been designed from start for improving the existing cooperation between TeMaS and Argentina (SEGEMAR - Argentine Geological Survey). Before COVID19, JGU Mainz was planning a field campaign to gather data across southern Argentina. However, the current research also focuses on the Galapagos Island, making it an alternative target for the deploy-ment of stations. The expected deliverables are: • Images of the Sierra Negra and Cerro Azul subsurface structure through ambient-noise seismic velocity and attenuation tomography. • Preliminary models of the dynamics of the volcanic system at different scales using own results and available tomographic models. • Preliminary model of the surface response to deformation in the subsurface based on inputs from geochemistry and geology. • In-sequence scripts for application of the methodologies to different volcanic zones, particularly for the linking geodynamics and seismology.