Ambient seismic wave field

Nishida, Kiwamu

doi:10.2183/pjab.93.026

Cited by 82 publications

(58 citation statements)

References 148 publications

(293 reference statements)

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“…where we assume no vertical winds at the interface. (Note that this approach is here limited to a spherical surface and that additional excitation terms could occur due to topography, in way similar to what occurs for Earth's hum [see, e.g., Nishida (2017)]. The vector n i is the normal to the surface, leaving the volume i, denoted + and − the volume against +, for which the normal vector is oriented in the opposite directions.…”

Section: Author's Proofmentioning

confidence: 99%

Mars’ Background Free Oscillations

et al. 2019

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Observations and inversion of the eigenfrequencies of free oscillations constitute powerful tools to investigate the internal structure of a planet. On Mars, such free oscillations can be excited by atmospheric pressure and wind stresses from the Martian atmosphere, analogous to what occurs on Earth. Over long periods and on a global scale, this phenomenon may continuously excite Mars' background free oscillations (MBFs), which constitute the so-called Martian hum. However, the source exciting MBFs is related both to the global-scale atmospheric circulation on Mars and to the variations in pressure and wind at the planetary boundary layer, for which no data are available. To overcome this drawback, we focus herein on a global-scale source and use results of simulations based on General Circular Models (GCMs). GCMs can predict and reproduce long-term, global-scale Martian pressure and wind variations and suggest that, contrary to what happens on Earth, daily correlations in the Martian hum might be generated by the solar-driven GCM. After recalling the excitation terms, we calculate MBFs by using GCM computations and estimate the contribution to the hum made by the global atmospheric circulation. Although we work at the lower limit of MBF signals, the results indicate that the signal is likely to be periodic, which would allow us to use more efficient stacking theories than can be applied to Earth's hum. We conclude by discussing the perspectives for the InSight SEIS instrument to detect the Martian hum. The amplitude of the MBF signal is on the order of nanogals and is therefore hidden by instrumental and thermal noise, which implies that, provided the predicted daily coherence in hum excitation is present, the InSight SEIS seismometer should be capable of detecting the Martian hum after monthly to yearly stacks.

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Section: Author's Proofmentioning

confidence: 99%

Mars’ Background Free Oscillations

et al. 2019

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“…For example, they are excited persistently along shorelines by incident ocean swell through nonlinear processes and travel across the ocean with a typical height on the order of 1 cm in pelagic regions (Rawat et al, ; Tonegawa et al, ). The background ocean infragravity wave activities are also key for understanding background seismic wavefields know as seismic hum, because they are the primary excitation source (Ardhuin et al, ; Nishida, , ; Rhie & Romanowicz, ). Observed equipartition of energy between Love and Rayleigh waves (Fukao et al, ; Nishida et al, ) suggests a topographic coupling between ocean infragravity waves and seismic surface waves.…”

Section: Potential Applications For Ocean Infragravity Wavesmentioning

confidence: 99%

Seismic Observation of Tsunami at Island Broadband Stations

2019

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Previous studies have reported seismic observations of tsunami recorded at island broadband stations. Coastal loading by the tsunami can explain them. For further quantification, we model tsunami propagation assuming an axisymmetric structure: a conical island with a flat ocean floor. The total tsunami wavefield can be represented by superposition between an incident tsunami wave and the scattering. The ground deformation due to the total tsunami wavefield at the center is calculated using static Green's functions for elastic half‐space with a first‐order correction for bathymetry. By fitting the modeled displacement to observed seismic data, we can infer the incident tsunami wave, which can be interpreted as the virtual tsunami amplitude without the conical island. First, we apply this new method to three components of seismic data at a volcano island, Aogashima, for the 2015 Torishima‐Oki tsunami earthquake. The estimated tsunami amplitude from the vertical component is consistent with the offshore array observation of absolute pressure gauges close to the island (1.5–20 mHz). The estimated incident azimuth from the three components is also consistent with ray theory. Second, we apply this method to seismic data at four island broadband stations in the Indian ocean for the 2010 Mentawai tsunami earthquake in Indonesia. Despite the limited observed frequency range from 0.5–2.0 mHz, the amplitudes and incident azimuths are consistent with past studies. These observations can complement offshore tsunami observations. Moreover, this method is applicable not only for a tsunami but also for background ocean infragravity wave activity.

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“…For example, they are excited persistently along shorelines by incident ocean swell through nonlinear processes and travel across the ocean with a typical height on the order of 1 cm in pelagic regions (Rawat et al, 2014;Tonegawa et al, 2018). The background ocean infragravity-wave activities are also key for understanding background seismic wavefields know as seismic hum because they are the primary excitation source (Ardhuin, Gualtieri, & Stutzmann, 2015;Nishida, 2013Nishida, , 2017Rhie & Romanowicz, 2004). Observed equipartition of energy between Love and Rayleigh waves (Fukao, Nishida, & Kobayashi, 2010;Nishida, Kawakatsu, Fukao, & Obara, 2008) suggests a topographic coupling between ocean infragravity waves and seismic surface waves.…”

Section: Potential Applications For Ocean Infragravity Wavesmentioning

confidence: 99%

Seismic observation of tsunami at island broadband stations

Nishida

Maeda

Fukao

2018

Preprint

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Previous studies have reported seismic observations of tsunami recorded at island broadband stations. Coastal loading by the tsunami can explain them. For further quantification, we model tsunami propagation assuming an axisymmetric structure: a conical island with a flat ocean floor. The total tsunami wavefield can be represented by superposition between an incident tsunami wave and the scattering. The ground deformation due to the total tsunami wavefield at the center is calculated using static Green's functions for elastic half-space with a first-order correction for bathymetry. By fitting the modeled displacement to observed seismic data, we can infer the incident tsunami wave, which can be interpreted as the virtual tsunami amplitude without the conical island. First, we apply this new method to three components of seismic data at a volcano island, Aogashima, for the 2015 Torishima-Oki tsunami earthquake. The estimated tsunami amplitude from the vertical component is consistent with the offshore array observation of absolute pressure gauges close to the island (1.5-20 mHz). The estimated incident azimuth from the three components is also consistent with the offshore array observation. Second, we apply this method to seismic data at four island broadband stations in the Indian ocean for the 2010 Mentawai tsunami earthquake in Indonesia. Despite the limited observed frequency range from 0.5-2.0 mHz, the amplitudes and incident azimuths are consistent with past studies. These observations can complement offshore tsunami observations. Moreover, this method is applicable not only for a tsunami but also for background ocean infragravity wave activity.

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Ambient seismic wave field

Cited by 82 publications

References 148 publications

Mars’ Background Free Oscillations

Mars’ Background Free Oscillations

Seismic Observation of Tsunami at Island Broadband Stations

Seismic observation of tsunami at island broadband stations

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