Originally published as: Holohan, E., Schöpfer, M. P. J., Walsh, J. J. (2015): Stress evolution during caldera collapse. - Earth and Planetary Science Letters, 421, p. 139-151. DOI: http://doi.org/10.1016/j.epsl.2015.03.003 1 Stress evolution during caldera collapse 2 E.P. Holohan(1,2), M.P.J. Schöpfer(1,3), & J.J. Walsh(1) 3 (1) GFZ Potsdam, Section 2.1 – Physics of Earthquakes and Volcanoes, Telegrafenberg, Potsdam 14473, Germany. 4 (2) Fault Analysis Group, UCD School of Geological Sciences, Dublin 4, Ireland. 5 (3) Department for Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14, Vienna, Austria. 6 Email:
[email protected] 7 8 Abstract 9 The dynamics of caldera collapse are subject of long-running debate. Particular uncertainties 10 concern how stresses around a magma reservoir relate to fracturing as the reservoir roof collapses, 11 and how roof collapse in turn impacts upon the reservoir. We used two-dimensional Distinct 12 Element Method models to characterise the evolution of stress around a depleting sub-surface 13 magma body during gravity-driven collapse of its roof. These models illustrate how principal stress 14 directions rotate during progressive deformation so that roof fracturing transitions from initial 15 reverse faulting to later normal faulting. They also reveal four end-member stress paths to fracture, 16 each corresponding to a particular location within the roof. Analysis of these paths indicates that 17 fractures associated with ultimate roof failure initiate in compression (i.e. as shear fractures). We 18 also report on how mechanical and geometric conditions in the roof affect pre-failure unloading and 19 post-failure reloading of the reservoir.