First observation of 2S1 and study of the splitting of the football mode 0S2 after the June 2001 Peru earthquake of magnitude 8.4

The recent Peru earthquake with a moment magnitude Mw = 8.4 on June 23, 2001 presents a good opportunity for the observation of the seismic gravest normal modes. For the longest periods, below 1 mHz Superconducting Gravimeters (SGs) have been shown to be less noisy than long‐period seismometers. A stack based on the spatial and temporal properties of the modes of degree one in a spherical harmonic development applied to 164 h of common records at the Cantley, Canberra, Strasbourg, Sutherland and Vienna SG stations has led to the first clear observation of the 2S1 long‐period seismic modes with a central frequency close to 0.4 mHz. Moreover the spectrum of the SG record at the Strasbourg station confirms the benefit SGs can provide to normal mode seismology with the clear observation of the splitting of the fundamental mode 0S2 into 5 fairly well resolved singlets with only one record.