Crustal magma plumbing of the Santorini volcanic system

Overview:

Models of how magma evolution at arc volcanoes generates the dominantly silicic magmas that form the continental crust, and of the dynamics that control magma migration, storage and eruption, require better physical constraints on the geometry, crystal content, and the nature of interconnections of magmas at all depths throughout the crust. To address these outstanding issues, we propose a high-resolution seismic experiment at the active and semi-submerged Santorini volcano that takes advantage of high-density spatial sampling of the seismic wavefield and state-of-the-art travel time and waveform inversion methods to provide new insights into the structure of the whole crustal magmatic system and its surroundings. To assess the dynamics of the volcanic system, the seismic imaging will be complemented with a seismicity study that assesses the evolving state of stress.

Santorini – a typical arc volcano that is well studied – recently experienced significant unrest. Importantly, the volcanic system is semi-submerged making it an ideal site for collecting dense 3D marine-land seismic data using the large, well-tuned R/V Langseth airgun source, 93 short period ocean bottom seismometers, and 26 land seismometers. This will allow us to image the lower crustal magmatic structure with unprecedented resolution. Our proposed analysis includes three complementary seismic approaches: (1) Dense 3D isotropic and anisotropic travel time tomography to resolve the first order structure of the magma plumbing system and surrounding crust, including an initial estimate of the volume and geometry of melt bodies throughout the crust and uppermost mantle as well as the thermal and compositional structure of the edifice and its surroundings; and (2) Full waveform inversion tomography and waveform modeling to refine travel time tomography images and to obtain higher resolution and more accurate recovery of the elastic properties throughout the crust, including an estimate of the sharpness of magma chamber boundaries, and the spatial connections, melt content and distribution of magma bodies.

Intellectual Merit:

The results from our proposed study will test the following three hypotheses: (1) Crystallization of mafic melts occurs in shallow crustal magma chambers, (2) Magma evolves continuously as it resides in, and moves through, multiple levels of magma reservoirs, and (3) Differentiation and/or mixing with melts of surrounding rock occurs almost entirely in the lower crust.

To test these scenarios, we propose to densely sample the seismic wavefield that propagates throughout the entire crust beneath the volcano by conducting a high-density, marine-land seismic experiment. 3D anisotropic travel time tomography together with the novel application of full waveform inversion to this dataset will provide unprecedented resolution, allowing us to determine the depth, geometry and melt content of magma reservoirs throughout the crust and at the Moho, whether these magma bodies are connected by dike systems or by vertical, crystal-rich complexes, and the structure and properties of the surrounding crust.

Broader Impacts:

Santorini provides millions of dollars to the Greek economy annually, and any renewed volcanism and/or seismicity could have a substantial economic impact. Our two Greek collaborators, Dr. Paraskevi Nomikou and Prof. Costas Papazachos, will work with us to: (1) Interface with the Greek public and civil authorities and help inform disaster management planning, (2) Repair a permanent seismic station thus bolstering Greek monitoring abilities, and (3) Facilitate a Greek workshop on natural hazards for geoscientists and community stakeholders. We will also jointly produce podcasts, video diaries, a YouTube animation and other educational resources in both Greek and English. The collaboration with Prof. Joanna Morgan, UK, will train UO graduate students in advanced seismic methods that require high-level, parallel cluster computational skills and will be the basis for several thesis projects.