Imaging the anisotropic structure of the Reykjanes Peninsula across the 2021 Fagradalsfjall dyke intrusion through local shear-wave splitting analysis

Since late 2019, the Reykjanes Peninsula in Iceland has experienced elevated seismic activity, which culminated in a dyke intrusion beneath Fagradalsfjall on 24^th February 2021, and an eruption on 19^th March. Seismic anisotropy – the directional dependence of seismic wave speed – can be used to study structural properties of the crust, which may be controlled by the state of stress through preferential closure of micro-cracks. This provides an opportunity to investigate changes in crustal stress regime caused by a dyke intrusion, with potential applications in eruption monitoring and forecasting.

 

A dense seismic network spanning Fagradalsfjall recorded more than 130,000 earthquakes between June 2020 and August 2021; detected and located using QuakeMigrate¹. From this dataset, we calculate the seismic anisotropy of the upper crust through shear-wave splitting analysis. Exceptional ray-path coverage allows for imaging at high spatial and temporal resolution. We present these results in relation to the regional stress regime and tectonic structure, and search for changes in anisotropy before, during, and after the dyke intrusion and eruption.

 

1: Winder, T., Bacon, C., Smith, J., Hudson, T., Greenfield, T. and White, R., 2020. QuakeMigrate: a Modular, Open-Source Python Package for Automatic Earthquake Detection and Location. https://doi.org/10.1002/essoar.10505850.1