Abstract - Although conventionally described as dip-slip, some faults at collapse calderas also display evidence for a strong strike-slip component. To investigate the origin and significance of this oblique-slip faulting, we firstly analysed Boundary Element Method (BEM) models of caldera collapse caused by subsidence of a magma reservoir roof.
This constrained the initial elastic 3D stress field, from which the location, orientation and nature of faulting were
predicted by assuming a simple Mohr-Coulomb failure envelope. We then compared the numerical model results
to analogue models of caldera subsidence that we analysed by means of Particle Imaging Velocimetry (PIV) and
by cross-sectioning. This constrained the geometry and kinematics of faulting as deformation progressed beyond
the initial elastic phase. The results of both modelling approaches show that oblique-slip faults should occur during
caldera subsidence and can account for their orientation, mode and location. The joint analysis of the models also
identifies two main processes for producing oblique-slip faulting during caldera collapse: (1) pre-failure horizontal
inward motion and (2) post-failure off-centred subsidence. This work hence indicates that the often presumed
dip-slip nature of caldera-related faults may be less common in nature than previously recognised.
Abstract of talk given to:
EGU General Assembly, Vienna, April 2011.