Remote sensing of seamounts: A geophysical study of lithospheric flexure, seamount statistics and intraplate volcanism

Seamounts are underwater volcanic constructs that form in three tectonic settings: near-ridge, island-arc, and intraplate environments. While underwater volcanism at ridges and island-arcs is concentrated along these tectonic boundaries, intraplate volcanism is ubiquitous on the seafloor. Locations of seamounts and the lithospheric deformation they cause provide an important window for Earth scientists seeking to understand variations in intraplate volcanism through time and space. Here, I propose a new dense core flexure model that approximates the effect of observed heterogeneous internal seamount structures and develop an automated inversion method to detect and characterize potential seamounts globally from the revised altimetry-derived vertical gravity gradient (VGG) data. The dense core model is first evaluated with analytic solutions derived for plate flexure beneath axisymmetric dense core loads. I confirm that the conventional flexure model with uniform seamount load underestimates elastic thicknesses of the lithosphere by at least 25% for a given dense core load. The dense core model is applied to predict lithospheric flexure beneath Howland Island in the Tokelau seamount chain. After examining synthetic and real cases, I conclude the dense core model approximates the true mass distribution of a seamount better than the uniform density model. Next, I approximate VGG anomalies at seamounts as sums of individual, partially over-lapping, elliptical polynomial functions and form a nonlinear inverse problem to minimize the misfit between model and observed VGG data. The automated inversion is guided by two model selection criteria (i.e., Akaike Information Criteria and F-tests) that examine the statistical significance of potential seamounts. My global search produced morphology parameters (i.e., height, geographical location, axes of the basal ellipse, and azimuth of its major axis) for 24,643 potential seamounts with height ≥ 0.1 km. Considering the ambiguity of gravity due to small seamounts and the overlap in scale with abyssal hills, I have tentatively estimated a new global seamount census of 40,000–55,000 (h ≥ 0.1 km). Finally, I use my new seamount database to estimate the intraplate volcanic budget and explore how the seamount distribution varies with seafloor properties such as age, spreading rate, and spreading direction.