A climate-related continental strain tide identified from PBO borehole strainmeter data

Abstract:

We perform an analysis of tidal signals recorded in the strainmeters of the Plate Boundary Observatory (PBO) in the United States of America. The original strain data are decomposed into various components of tide signal and other terms of a trend, air pressure response and random noise, using BAYTAP, a program that applies a Bayesian modeling procedure to analyze the strainmeter data. The extracted tidal amplitudes and phase delays of some of the Sun-related tides (P₁, S₁K₁, S₂ and K₂) exhibit obvious annual cycles of variation, with some of the amplitude variations reaching 30% and phase delays 30° respectively, while those of the Moon-related tides (Q₁, N₂ and M₂) do not show annul cycles. The inferred annual cycles of the Sun-related tides cannot be explained by the inaccuracies of relative Earth-Sun positions at different seasons. Neither can they be explained by the annual variations of sea water loading. They can be best explained by existence of an additional climate-related strain tide induced by a combination of annual and daily changes of climatological variables (e.g. temperature and hydrology) in the continental areas.