Using hydroacoustic stations as water column seismometers

Abstract

Getting seismic data from the deep oceans usually involves ocean‐bottom seismometers, but hydrophone arrays may provide a practical alternative means of obtaining vector data. We here explore this possibility using hydrophone stations of the International Monitoring System, which have been used to study icebergs and T‐wave propagation among others. These stations consist of three hydrophones at about the depth of the deep sound channel in a horizontal triangle array with 2 km sides. We use data from these stations in the very low‐frequency regime (0.01–0.05 Hz band) to demonstrate that these stations can also be used as water column seismometers. By differencing the acoustic pressure, we obtain vector quantities analogous to what a seismometer would record. Comparing processed hydrophone station records of the 2004 Great Sumatra‐Andaman Earthquake with broadband seismograms from a nearby island station, we find that the differenced hydrophones are indeed a practical surrogate for seismometers.

Hydroacoustic Travel Time Variations as a Proxy for Passive Deep‐Ocean Thermometry—A Cookbook

“…Love surface waves (LQ) are horizontally polarized and so would yield energy in the horizontal plane only. Love surface waves, being horizontally polarized, are not expected to couple into water column and therefore are not expected to be found in the hydrophone recordings and therefore the CCFs (Yildiz et al, 2013). The ZR phase lag of the signal-windowed CCFs of H03S1 and RAR in the vertical plane, that are, IM.H03S1..EDH-IU.RAR.10.BHZ and IM.H03S1..EDH-IU.RAR.10.BHR, is used to further distinguish with the 95% confidence interval as a function of time.…”

T‐phase and tsunami pressure waveforms recorded by near‐source IMS water‐column hydrophone triplets during the 2015 Chile earthquake

“…Recent work by Yildiz et al . [] shows that differentiation of pressure records in a IMS hydrophone triplet can be used to further distinguish the wave type (e.g., P and Rayleigh waves versus Love waves). Further information about the IMS is provided at http://www.ctbto.org/.…”

“…T phases obtained by IMS HA stations contributed to the description of the earthquake source process [e.g., Graeber and Piserchia, 2004;Guilbert et al, 2005]. Recent work by Yildiz et al [2013] shows that differentiation of pressure records in a IMS hydrophone triplet can be used to further distinguish the wave type (e.g., P and Rayleigh waves versus Love waves). Further information about the IMS is provided at http://www.ctbto.org/.…”