Potential Slichter Triplet Detection Using Global Superconducting Gravimeter Data

Abstract

The eigenperiods of the translational oscillation modes of the Earth’s solid inner core, also referred to as the Slichter modes or Slichter triplet, are the key parameters that constrain the density jump across the inner core boundary (ICB). Definite observations of the Slichter triplet are still open. Here, we discuss and investigate this problem using the current most extensive superconducting gravimeter (SG) data, which include 49 records from 35 global stations, altogether spanning about 22 years. Two multi-station stacking methods are employed to process the available SG data, including full-time data and data collected before and after seven major earthquakes, corresponding to persistent and intermittent excitations, respectively. Based on the relationship between the theoretical Slichter periods and the density jump at the ICB, several sets of candidates that could serve as the Slichter triplet are suggested. We identified a complete triplet set that almost coincides with different predictions made based on the PREM Earth model. The synthetic experiments show that Slichter signals excited by continuous sources of excitation may achieve an amplitude of at least 0.04 nGal, which can be detected using our full-time SG data, and the large earthquakes ( $$M_{\mathrm w}\ge 8.4$$ ) that occurred during our detection period might not excite the Slichter modes to a detectable level.