Shear wave effects in hydroacoustic recordings of the Comprehensive Nuclear-Test-Ban Treaty International Monitoring System

Abstract

The hydroacoustic (HA) component of the Comprehensive Nuclear-Test-Ban Treaty Organization’s International Monitoring System (IMS) comprises six stations with triplets of moored hydrophones suspended in the SOFAR channel and five near-shore seismometer stations for T-phase detection. Understanding the conversion between compressional and elastic waves at the crust-ocean boundary or at large bodies of ice can contribute to better identification and association of arrivals. In this talk, examples recorded by the IMS HA network are presented with a view to stimulating discussion and further analysis: (i) T-phases from the September 2017 announced DPRK underground nuclear test recorded by the hydrophones of HA11 (Wake Island); (ii) a “precursor” southerly arrival at HA04 (Crozet Islands), associated with the hydroacoustic anomaly related to the loss of the Argentine submarine ARA San Juan, which is inter alia compatible with a Lamb wave propagating through the Antarctic ice-sheet; (iii) T-phases from earthquakes along the Nazca subduction zone scattered horizontally by the Juan Fernandez sea-mounts and recorded by HA03 (Chile); and (iv) conversion of signals from distant underwater explosions at the crust-ocean boundary near IMS T-stations. Benchmark studies to assess the accuracy of spectral element model setups previously used for scenarios (iv) would be particularly desirable.