A search for the Slichter modes in superconducting gravimeter records using a new method

Abstract

A detection of the Slichter modes is attempted using a new method that focuses on the use of the spectra of individual superconducting gravimeter (SG) records to test if the latitudinal and longitudinal dependence of amplitudes and phases of the Slichter modes are satisfied in a statistical point of view. The new method allows considerations of lower peaks in the spectra as possible candidates of the Slichter modes. As the new method searches for the three Slichter modes individually, it does not rely on the theory of splitting which remains controversial, and is still valid even if not all of the three Slichter modes are excited to the observable level. A loose splitting rule is used to check if a set of candidates of the prograde, axial and retrograde modes may constitute the whole Slichter modes. The attempted detection is made using three sets of SG records selected from the Global Geodynamics Project (GGP) network based on criteria including data spans, geological locations, and the quality of the gravity time-series. The selected three data sets are the simultaneous records of five SGs located in Canberra, Matsushiro, Strasbourg, Sutherland and Vienna. The data spans are 30, 17 and 12 months, with the later two data sets after the 2001 Peruvian Earthquake of magnitude 8.4 that might have excited the Slichter modes to larger amplitudes. Our results suggest two possible scenarios that are still inconclusive. The first is a candidate of the prograde mode with a frequency around 4.485 cycle per day (cpd) that is present in all three data sets. The second is a combination of a prograde and an axial modes with frequencies around 7.098 and 7.546 cpd that are present in the two data sets after the Peruvian Earthquake. © 2006 The Authors Journal compilation © 2006 RAS.