Joint Inversion of Geodetic and Seismic Data Using Physics Based Models of Dike Intrusions Applied to the 2014 Bardarbunga Intrusion, Iceland.

Kinematic dislocation models are commonly used to invert geodetic data to image magmatic intrusions. These models are subject to limitations due to non-uniqueness and non-physical regularization on crack surface displacement. Implementing physics based crack models reduces the number of free parameters and removes the need for ad hoc regularization. Moreover, such models can be formulated to predict realistic temporal evolution of an intrusion and its near field stresses, thus allowing for inclusion of seismicity in estimating the spatiotemporal evolution of the dike. Lately, high quality data from continuous GPS stations and dense arrays of seismometers calls for physical models that satisfy both seismic and geodetic data. In this study, we develop a physics based model of a laterally propagating dike. The model is applied to the well-instrumented 2014 Bardarbunga dike intrusion in Iceland. We relate changes in stress to rates of seismicity by implementing the Dieterich 1994 seismicity rate theory. In order to predict realistic stresses at the dike tip we model it as a crack with a cohesive zone, and solve for the length of the cohesive zone given the closing pressure (remote stress in excess of tip pressure) for an arbitrary crack geometry. This allows us to investigate the importance of the cohesive zone in nucleating earthquakes and from the seismic data put constraints on near tip properties of the dike. The two data types are complementary in constraining pressure, assuming bilateral excess pressure in depth, and length of the dike. The model is in excellent agreement with the GPS time series in spite of only having these two time-dependent free parameters (pressure and length). The model has potential for near real time imaging of dike intrusions as well for understanding properties that are generally difficult to constrain from field data, including near tip properties of dikes, constitutive friction parameters and crustal stresses.