Two-stage model of propagation and arrest explains ubiquitous patterns of dyke seismicity

Lateral dyke intrusions are magma-filled fractures that propagate horizontally through the Earth's crust, posing significant hazards to local populations. Since 2020, four major lateral dyking events have forced the evacuation of at least 10,000 people (Bato et al., 2021, Lewi et al., 2025). Although the underlying physical processes are well established, current models are complex, and it is unclear which factors control lateral propagation speed and the movement of magma within the dyke.  

By comparing data from intrusions from around the world, we show that the spatio-temporal patterns of seismicity and ground deformation are ubiquitous, and can be split into two phases:  

Lateral propagation: The seismic events migrate, delineating the location of the lateral dyke tip. The migration speed decays with time and the ground deforms along the entire length of the dyke.  

Widening post-arrest: After the dyke reaches its final lateral extent, it continues to open.  Seismicity propagates back into the previously quiet regions, and the ground deforms at the distal end only. 

We use these observations to motivate a two-stage model of dyke intrusion: lateral propagation followed by widening after arrest. The three-dimensional hydro-mechanical process associated with dyking can be reduced through scale separation to a single Partial Differential Equation (PDE) resembling the classical heat equation (Zia and Lecampion, 2020, Nordgren, 1972). Scaling this shows that a dyke fed by a constant pressure source grows as t^1/2 while those fed by a constant flux grow as t^1/5 (Bunger et al., 2013). By solving the PDE we determine the time-dependent dyke opening distribution and the resulting stress field. We compare predictions of seismicity rates and changing surface deformation to observations from seismology and geodesy. We show that dykes are driven by a near-constant source pressure throughout lateral propagation and that patterns of seismicity and surface deformation are a result of the changing widths of the dyke both during propagation and after arrest. 

Once arrested, changes in the dyke's opening become confined to a zone near the lateral tip, shifting the observed ground deformation towards the distal end. We find static stress changes on faults surrounding the dyke cannot satisfactorily explain the observed spatio-temporal pattern of seismicity.  During rapid stressing, seismicity rates depend on both the magnitude and rate of stress change (Heimisson et al., 2022). The observed spatio-temporal seismicity pattern corresponds well with locations of positive of stress change rates, reflecting the combined influence of deviatoric stressing and early-time poroelastic effects. 

References: 

Bato, M.G. et al. 2021, Geophysical Research Letters, doi:10.1029/2021GL092803. 

Lewi, E. et al. 2025, Bulletin of Volcanology, doi:10.1007/s00445-025-01852-x. 

Zia, H. & Lecampion, B., 2020, Computer Physics Communications, doi:10.1016/j.cpc.2020.107368. 

Nordgren, R.P., 1972, Society of Petroleum Engineers Journal, doi:10.2118/3009-PA. 

Bunger, A.P. et al., 2013, Earth and Planetary Science Letters, doi:10.1016/j.epsl.2013.05.044. 

Heimisson, E.R. et al., 2022, Geophysical Journal International, doi:10.1093/gji/ggab467.