Origins of oblique-slip faulting during caldera subsidence

Holohan, E.P.^1,2, Walter, T.R.², Schöpfer, M.P.J.^1,3, Walsh, J.J.¹, van Wyk de Vries, B.⁴ & Troll, V.R.⁵
1 - Fault Analysis Group, School of Geological Sciences, University College Dublin, Dublin 4, Ireland.
2 - GFZ Potsdam, Telegrafenberg, Potsdam, D-14473, Germany.
3 - Present Address: Department for Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.
4 - Laboratoire Magmas et Volcans, 5 rue Kessler, 63038 Clermont-Ferrand, France.
5 - Department of Earth Sciences, Uppsala University, SE-75236, Uppsala, Sweden.

Abstract - Although conventionally described as purely dip-slip, faults at caldera volcanoes may have a strike-slip displacement component. Examples occur in the calderas of Olympus Mons (Mars), Miyakejima (Japan) and Dolomieu (La Reunion). To investigate this phenomenon, we ran numerical and analog simulations of caldera subsidence caused by magma reservoir deflation. The numerical models constrain mechanical causes of oblique-slip faulting from the three-dimensional stress field in the initial elastic phase of subsidence. The analog experiments directly characterize the development of oblique-slip faulting, especially in the later, non-elastic phases of subsidence. The combined results of both approaches can account for the orientation, mode and location of oblique-slip faulting at natural calderas. Kinematically, oblique-slip faulting originates to resolve: (1) horizontal components of displacement that are directed radially toward the caldera centre; and (2) horizontal translation arising from ff-centered or ‘asymmetric’ subsidence. We informally call these two origins the "camera iris" and "sliding trapdoor" effects, respectively. Our findings emphasize the fundamentally three-dimensional nature of deformation during caldera subsidence. They hence provide an improved basis for analyzing structural, geodetic and geophysical data from calderas, as well as analogous systems, such as mines and producing hydrocarbon reservoirs.

Journal of Geophysical Research, 118, 1-17, doi:10.1002/jgrb.50057, 2013.