Toward Unraveling Sub‐Seismic Frequency Signals Using Stacked Global Broadband Seismological Data

Abstract Seismological data from broadband seismometers have been used for decades to study various signals in the seismologically interesting frequency band between 0.0003 and 30.0 Hz. However, broadband seismometers are seldom used to explore gravity variations in sub‐seismic periods larger than 1 hr because seismometers are exceeded in performance by superconducting gravimeters when considering a single sensor. In this study, we demonstrate how to leverage the existing network of global broadband seismometers to resolve tidal harmonics as small as 1 nanogal, equivalent to modern superconducting gravimeters. The presented seismic array analysis, based on the stacking of coherent signals in the frequency domain, is robust and can be used to track the spatial and temporal evolution of solid earth and oceanic tides. Our findings indicate that high‐quality long‐term seismological data provide a new and complementary data set for tracking gravitational changes over time, offering novel insights into geodynamics and atmospheric processes.