Observation of Coriolis coupled modes below 1 mHz

• Published in: Geophysical Journal International
• Main Authors: Zürn, W., Laske, G., Widmer-Schnidrig, R., Gilbert, F.
• Format: Text
• Language: English
• Published: Oxford University Press 2000
• Subjects: Articles; Balleny Islands
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/143/1/113; https://doi.org/10.1046/j.1365-246x.2000.00220.x

We present observations of spectral energy at toroidal mode frequencies in vertical seismic recordings of the 1998 Balleny Islands earthquake. Since toroidal modes on a spherically symmetric, non-rotating Earth have horizontally polarized particle motion these observations call for an explanation. We first rule out local and instrumental effects as being responsible for the vertical-component signal of the toroidal modes 0 T 3 (0.59mHz) and 0 T 4 (0.77mHz). The global effects that we consider are general heterogeneous mantle structure, ellipticity of figure and rotation. We find that rotation through Coriolis coupling of low-order spheroidal and toroidal oscillations is the dominant mechanism.