The effect of dynamic topography and gravity on lithospheric effective elastic thickness estimation: a case study

Abstract

Lithospheric effective elastic thickness (T-e), a proxy for plIate strength, is helpful for the understanding of subduction characteristics. Affected by curvature, faulting and magma activity, lithospheric strength near trenches should be weakened but some regional inversion studies have shown much higher T-e values along some trenches than in their surroundings. In order to improve T-e-estimation accuracy, here we discuss the long-wavelength effect of dynamic topography and gravity on T-e estimation by taking the Izu-Bonin-Mariana (IBM) Trench as a case study area. We estimate the long-wavelength influence of the density and negative buoyancy of the subducting slab on observed gravity anomalies and seafloor topography. The residual topography and gravity are used to map T-e using the fan-wavelet coherence method. Maps of T-e, both with and without the effects of dynamic topography and slab gravity anomaly, contain a band of high-T-e values along the IBM Trench, though these values and their errors are lower when slab effects are accounted for. Nevertheless, tests show that the T-e map is relatively insensitive to the choice of slab-density modelling method, even though the dynamic topography and slab-induced gravity anomaly vary considerably when the slab density is modelled by different methods. The continued presence of a high-T-e band along the trench after application of dynamic corrections shows that, before using 2-D inversion methods to estimate T-e variations in subduction zones, there are other factors that should be considered besides the slab dynamic effects on the overriding plate.