HR: 1330h
AN: S22A-0435    [PDF]
TI: On the recovery of effective elastic thickness using spectral methods: examples from synthetic data and from the Fennoscandian Shield
AU: * Perez-Gussinye, M
EM: martap@earth.ox.ac.uk
AF: Dept. Earth Sciences, Univ., Parks Road, Oxford, OX1 3PR United Kingdom
AU: Lowry, A R
EM: arlowry@brennan.colorado.edu
AF: Dept. Physics, Univ. Colorado, CAMPUS BOX 390, Boulder, 80309-0390 United States
AU: Watts, A B
EM: Tony.Watts@earth.ox.ac.uk
AF: Dept. Earth Sciences, Univ., Parks Road, Oxford, OX1 3PR United Kingdom
AU: Velicogna, I
EM: isabella@giove.colorado.edu
AF: Dept. Physics, Univ. Colorado, CAMPUS BOX 390, Boulder, 80309-0390 United States
AB: The effective elastic thickness, $T_e$, represents the response to long-term loading of the lithosphere; it is thus a useful measure of its strength. However, the use of different methods and assumptions to calculate $T_e$ yield different results, leading to controversial interpretations of the relationship of $T_e$ to rheology. We investigate the ability of the Bouguer coherence and free air admittance to recover $T_e$ assuming that surface and subsurface loads exist. We use synthetic data to show that the estimated Te using both functions is similar; the recovery with admittance is somewhat poorer due to leakage problems. When the underlying $T_e$ is constant, the bias and variance of the resulting $T_e$ increases with decreasing analysis window size and increasing underlying $T_e$ value. When $T_e$ varies spatially, $T_e$ estimation using sliding, overlapping windows retrieves a structure that approximates the true spatial variability, but window sizes must be chosen carefully. In light of these results, we analyse $T_e$ in Fennoscandia using both techniques and obtain similar estimates. $T_e$ is 20-40 km in the Caledonides, 40- 60 km in the Swedish Svecofennides, 40-60 km in the Kola peninsula and 70-100 km in southern Karelia and Svecofennian central Finland. These estimates are not biased by unrecovered post-glacial rebound and also potential noise introduced by long-term erosion and sedimentation does not appear to affect $T_e$. An independent estimate of $T_e$ using rheological modelling, confirms that $T_e$ in central Finland should be high. Because $T_e$ exceeds crustal thickness ($\sim 60$ km), the mantle must contribute significant strength to the total. $T_e$ is also larger than the seismogenic thickness, thus indicating that they represent different physical behaviours. In general, $T_e$ in Fennoscandia increases with tectonic age, seismic lid thickness and decreasing heat flow. $T_e$ is low where seismicity is frequent and high where it is reduced. In Proterozoic and Archean lithosphere, the relationship of $T_e$ to age breaks down, indicating that compositional effects might be more important for the strength of stable continental lithosphere than tectonothermal age.
DE: 1234 Regional and global gravity anomalies and Earth structure
DE: 8110 Continental tectonics--general (0905)
DE: 8122 Dynamics, gravity and tectonics
DE: 8159 Rheology--crust and lithosphere
DE: 8164 Stresses--crust and lithosphere
SC: Seismology [S]
MN: 2003 Fall Meeting