Comparison of numerical approaches for modeling gravitationally-induced horizontal deviatoric stresses within a Hawaiian basaltic shield volcano

Abstract:

Basaltic shield volcanoes are subjected to important gravitational loads that lead to their spreading. Such deformation influences the stress state within the volcano, thus the formation of faults and the location of earthquakes and the propagation of magmas and the potential eruption location.

Using distinct numerical approaches constrained by geophysical data from the Hawai`i Island Shield Volcano (HISV), we studied the extent to which horizontal deviatoric stresses (HDS) induced from gravitational loading drives the process of volcanic spreading. Two distinct numerical approaches based on similar models were used: 1- the thin-sheet method, and 2- finite element models using COMSOL Multiphysics.

We quantified depth integrals of vertical stress (i.e., the gravitational potential energy per unit area or GPE) and then we derived the HDS that balance the horizontal gradients in GPE. We performed the integration over series of single layers that encompasses the surface of variable topography down to a uniform depth of 10 km b.s.l. consistent with the base of the HISV. To compare the results of our numerical approaches we built a fine-scale, Island-wide, set of kinematically constrained deformation indicators (KCDI) using the slip-rate and fault style information from a comprehensive fault database for the HISV. We measure the success of each numerical approach by how well model HDS match the horizontal styles of the strain rates associated with KCDI.

Thus far we find that the HDS obtained using the thin-sheet method match well with the KCDI. This may indicate that to first order that patterns of observed surface deformation on the HISV are governed by gradients in GPE. This provides a balance to the gravitationally-induced stresses associated with the volcano load. These HDS do not account for other competing sources of stress (e.g., flexure, magmatic, or hoop) that taken all together may combine to better explain the volcano spreading process for basaltic shield type volcanoes.