Geodetic and seismic moment calculations for caldera collapse events
Savannah C. Devine1, Eoghan P. Holohan1, Claire E. Harnett1, Chris J. Bean2
Affiliations: 1UCD School of Earth Sciences, University College Dublin, Dublin 4, Ireland; 2Geophysics Section, Dublin Institute for Advanced Studies, Dublin 2, Ireland.
Presentation type: Poster
Presentation time: Thursday 16:30 - 18:30, Room Poster Hall
Poster Board Number: 52
Programme No: 3.11.12
Abstract
Calderas form when a magma chamber is emptied (either fully or partially), causing the roof to collapse into itself. In a piston style collapse, a mass in the middle of the structure subsides as a single block. This has been inferred by using seismic and geodetic methods during caldera-forming events. In the case that the piston is entirely frictional, the observed geodetic and seismic moments should be equal. If the geodetic moment is larger, this indicates some amount of aseismic (ductile) deformation, and the collapse is not entirely frictional; if the seismic moment is larger, this indicates incorrect or missing information in the final moment calculations. Using literature review and recalculations based on values cited in past studies, we compared geodetic and seismic moments for 8 caldera collapse events. The moment values generally fall above a 1:1 line when the logarithms of geodetic and seismic moments are plotted against each other, meaning that for these events, the geodetic moment is larger than the seismic moment. This implies some ductile (aseismic) deformation along with the existing brittle deformation during the collapses. These results may be used to determine how the discrepancy in depth to chamber and bulk shear modulus relate to gaps in seismic and geodetic moment calculations.