Approbation of the Method for Examining the Performance of Seafloor Observatory Sensors Using Distant Earthquakes Records

Mikhail Nosov,Sergey Kolesov,Hiroyuki Matsumoto,Yoshiyuki Kaneda,Viacheslav Karpov,Kirill Sementsov

doi:10.3389/feart.2021.661337

Abstract

An algorithm is presented for testing the calibration accuracy of both z-accelerometers and pressure gauges (PG) installed in seafloor observatories. The test is based on the linear relationship between the vertical acceleration component of the seafloor movement and variations of the seafloor pressure, which is a direct consequence of Newton's 2-nd law and holds valid in the frequency range of “forced oscillations.” The operability of the algorithm is demonstrated using signals registered by 28 observatories of the DONET-2 system during 4 earthquakes of magnitude Mw ~ 8 that took place in 2018-2019 at epicentral distances from 55° up to 140°.

Highlights

During the first decades of the twenty-first century at least several hundred seafloor observatories equipped with ocean bottom seismometers (OBS) and pressure guages (PG) were installed in the oceans all over the World
We considered mutual verification of the calibration of a pressure gauges (PG) and a z-accelerometer (OBS that measures the vertical component of the ocean bottom acceleration)
In Nosov et al (2018) and Karpov et al (2020) we have shown it to be advisable to base accurate calculations on the value measured by PG, i.e., P – the total pressure averaged over time, and on the relationship of hydrostatics, m = P/g

Summary

Introduction

During the first decades of the twenty-first century at least several hundred seafloor observatories equipped with ocean bottom seismometers (OBS) and pressure guages (PG) were installed in the oceans all over the World. One should expect some human errors in calibration of ocean-bottom sensors. We revealed such an error in calibration of z-accelerometer of E18/DONET observatory (Nosov et al, 2018; Karpov et al, 2020). Strong ground motion during nearby earthquake can affect the orientation of ocean-bottom sensors (Nakamura and Hayashimoto, 2019). It results in changing output both OBS (Graizer, 2010; Javelaud et al, 2011) and PG (Chadwick et al, 2006). PG can be covered with a layer of sediments gradually year by year or suddenly due to a landslide or mud flow which can distort the frequency-response function of the sensor

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Conclusion