Forecasting the fate of vertically propagating dikes from geodetic data

Abstract

Magmas, especially mafic ones, usually intrude into the upper crust as dikes. The intruded dike is often arrested before reaching the surface to make an eruption. Many geophysical observations, including geodetic measurements, have documented dike intrusions and arrests. Also, many theoretical considerations and analog experiments explored the mechanics of dike propagation and arrest. However, insights gained from theoretical considerations, analog experiments, and geophysical observations have yet to be well reconciled. This study attempts to reconcile geodetic measurements with insights gained from theoretical considerations and analog experiments to investigate how to forecast whether an intruded dike results in an eruption or not. This study considers four causes of dike arrests: (1) solidification of the intruded magma, (2) insufficient volume of dike intrusion, (3) negative buoyancy acting on the intruded magma, and (4) stress perturbation near the dike tip by a large earthquake. Then, this study investigates the cause of dike arrests associated with the 1997 and 1998 seismic swarm off the Izu Peninsula, Japan, and the 2015 failed eruption of Sakurajima volcano, Japan, as an example. This study suggests that the dike intrusions associated with the 1997 and 1998 seismic swarm off the Izu Peninsula are caused by insufficient volume of the dike, the loss of buoyancy, or both. The failed eruption of the 2015 Sakurajima eruption is most likely by insufficient volume. To investigate the contribution of geodetic data in understanding the cause of dike arrests, it is essential to consider the characteristics of geodetic data. They are: (1) geodetic data constrain the intruded volume and the location relatively well, (2) geodetic data cannot constrain the geometry of the intruded dike very well, (3) an assumption of the host rock as homogeneous halfspace underestimates the volume of the intruded dike and estimates the depth of the dike shallower than the true value. These limitations indicate that we cannot fully understand the cause of dike arrests solely from geodetic data. Independent information gained from, for example, the location of dike-induced earthquakes, seismic structures, or density structure from gravity anomalies or muon radiography helps better understand the cause of dike arrests.Graphical