Earth's Background Free Oscillations

Suda, Nobuhide; Nawa, Kazunari; Fukao, Yoshio

doi:10.1126/science.279.5359.2089

Cited by 202 publications

(127 citation statements)

References 12 publications

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“…This minimum in the vertical PSD and the difference between vertical and horizontal noise at these frequencies is nicely explained by the contributions from the atmosphere as described in detail by Zürn and Wielandt (2007) and . This special feature in the vertical noise PSD allows the clear detection of the Earth's background free oscillations ("Hum") in the vertical component records of many stations (e. g. Nawa et al, 1998;Suda et al 1998;Tanimoto et al 1998;Nishida et al 2002;Ekström, 2001;Fukao et al, 2002;Rhie and Romanowicz, 2004;Kurrle and Widmer-Schnidrig, 2006), while in contrast the horizontal hum can only be detected at barely a handful of them (Kurrle and Widmer-Schnidrig, 2008). Zürn and Wielandt (2007) were not able to directly demonstrate the reversal in the sign of the pressure admittance for vertical acceleration in real records.…”

Section: Introductionmentioning

confidence: 99%

Clear evidence for the sign-reversal of the pressure admittance to gravity near 3mHz

Zürn¹,

Meurers

2009

Journal of Geodynamics

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SUMMARYThe influence of the atmosphere on gravity measurements by Newtonian attraction and vertical displacements due to surface loading is well known and studied especially at frequencies below 1 mHz. Less work has been done at the higher seismic frequencies where inertial effects come into play. The sensor mass of a vertical accelerometer responds to several forces caused by the atmosphere, on global, regional and local scales. For the seismic frequencies the atmosphere above the observation site has the largest influence. A simple "Gedankenexperiment" demonstrates that the gravitational effect on one hand and the free air and inertial effects due to deformation on the other have opposite sign. Since the inertial effect is strongly frequency-dependent there should be a crossover-frequency where the pressure admittance to gravity changes sign. Simple analytical models clearly show this property near frequencies of a few mHz and are used here to amplify the variance reduction of the gravity residuals. The crossover-frequency depends on the properties of the models of the atmospheric phenomena and the elasticity of the Earth's crust. Therefore in reality it must be expected to vary in time and space.We show one extremely clear example of this sign-reversal detected in the gravity data from the superconducting gravimeter GWR-C025 in Vienna among other examples which demonstrate the reality of this effect.

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Section: Introductionmentioning

confidence: 99%

Clear evidence for the sign-reversal of the pressure admittance to gravity near 3mHz

Zürn¹,

Meurers

2009

Journal of Geodynamics

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“…Microseisms can be ground motions caused by storm-induced ocean waves, which have been studied from distances away from the storm (Tabulevich 1971;Sutton 1996;Suda 1998;Wilson et al 2003;Kedar and Webb 2005;Webb 2007;Gerstoft et al 2008;Koper and de Foy 2008;Wilson and Makris 2008).…”

Section: Introductionmentioning

confidence: 99%

Seismic monitoring of western Pacific typhoons

et al. 2010

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Typhoons inflict large damage to societies, but are usually difficult to monitor in close proximity in realtime without expensive instruments. Here we study the possibility of using seismic waveforms on the seafloor and on land to monitor the turning of a far away or approaching typhoon. Up to 67% of the typhoons making landfall in Taiwan come from the eastern shore, so that we deployed broadband ocean-bottom seismometers (OBSs) offshore eastern Taiwan in 2006 to study ground motion in close proximity to a typhoon. Typhoons generate ocean waves, which generate pressure signals in the water column before being transmitted to the seafloor as seismic waves and recorded by the OBSs. The ground motions on the seafloor correlate with locally increased (ocean) wave heights and wave periods, suggesting that the ground motions are mostly induced by in situ or nearby pressure fields, as shown by coherence function analyses. When a typhoon turns and changes wave-wave interaction near the source region, a new set of en echelon patterns develops which can be observed by OBSs and land stations. Similar features occur when a typhoon crosses a landmass and re-enters the ocean. The energy level ratio between the single-frequency and double-frequency microseisms also changes abruptly when the typhoon turns. These features can potentially help near real-time early warning with little cost to complement other conventional typhoon early warning methods.

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“…However, subsequently they were also observed on seismically quiet days (e.g. Lin'kov et al, 1991), much like the Earth free oscillations 0 S n with n % 15±65 of the 2±8 min period range (Suda et al, 1998;Tanimoto et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Penetration of the Earth's free oscillations at 54 minute period into the atmosphere

Shved

Petrova

Polyakova

2000

Annales Geophysicae

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Abstract. It is known that the fundamental spheroidal mode 0 S 2 of the Earth free oscillation with a period of about 54 min forces atmospheric oscillations. We present a certain phase relationship for components of the 0 S 2 multiplet, which is based on synchronous collocated microbarograph and seismograph observations. This relationship is both the ®rst observational manifestation of the Pekeris mode of global atmospheric oscillations with the 54 min period and a further proof of the Earth's 0 S 2 mode penetrating into the atmosphere. We show that the linear non-dissipative model of steady forced oscillations in isothermal atmosphere at rest does not describe the penetration of the 0 S 2 mode into the atmosphere adequately.

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Earth's Background Free Oscillations

Cited by 202 publications

References 12 publications

Clear evidence for the sign-reversal of the pressure admittance to gravity near 3mHz

Clear evidence for the sign-reversal of the pressure admittance to gravity near 3mHz

Seismic monitoring of western Pacific typhoons

Penetration of the Earth's free oscillations at 54 minute period into the atmosphere

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