Detection of shallowest submarine seismicity by acoustic coupled shear waves

Sugioka, Hiroko; Fukao, Yoshio; Okamoto, Taro; Kanjo, Kenji

doi:10.1029/2000jb900476

Cited by 6 publications

(5 citation statements)

References 28 publications

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“…Acoustic-coupled Rayleigh (ACR) waves 12 generated by earthquakes have been observed on the seafloor 13 14 15 . Generation of ACR waves requires the presence of low-velocity marine sediments within which several wavelengths of short-period Rayleigh modes can be contained (<5 Hz 15 ).…”

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Ambient seafloor noise excited by earthquakes in the Nankai subduction zone

et al. 2015

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Excitations of seismic background noises are mostly related to fluid disturbances in the atmosphere, ocean and the solid Earth. Earthquakes have not been considered as a stationary excitation source because they occur intermittently. Here we report that acoustic-coupled Rayleigh waves (at 0.7–2.0 Hz) travelling in the ocean and marine sediments, retrieved by correlating ambient noise on a hydrophone array deployed through a shallow to deep seafloor (100–4,800 m) across the Nankai Trough, Japan, are incessantly excited by nearby small earthquakes. The observed cross-correlation functions and 2D numerical simulations for wave propagation through a laterally heterogeneous ocean–crust system show that, in a subduction zone, energetic wave sources are located primarily under the seafloor in directions consistent with nearby seismicity, and secondarily in the ocean. Short-period background noise in the ocean–crust system in the Nankai subduction zone is mainly attributed to ocean-acoustic Rayleigh waves of earthquake origin.

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Ambient seafloor noise excited by earthquakes in the Nankai subduction zone

et al. 2015

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“…Yet, it is often challenging to investigate submarine volcanoes due to the lack of on-site monitoring systems. Many previous studies remotely detected geophysical signals from submarine volcanoes, such as, seawater acoustic waves (Metz et al, 2016;Tepp & Dziak, 2021), seismic waves (Cesca et al, 2020;Saurel et al, 2021;Sugioka et al, 2001), or tsunami waves (Fukao et al, 2018;Sandanbata et al, 2018;Y. Wang et al, 2019), shedding light on volcanic processes in submarine volcanoes.…”

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Quantifying magma overpressure beneath a submarine caldera: A mechanical modeling approach to tsunamigenic trapdoor faulting near Kita-Ioto Island, Japan

Sandanbata,

Saito

2023

Preprint

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Submarine volcano monitoring is vital for assessing volcanic hazards but challenging in remote and inaccessible environments. In the vicinity of Kita-Ioto Island, south of Japan, unusual M~5 non-double-couple volcanic earthquakes exhibited quasi-regular repetition near a submarine caldera. Following the 2008 earthquake, a distant ocean bottom pressure sensor recorded a distinct tsunami signal. In this study, we aim to find a source model of the tsunami-generating earthquake and quantify the pre-seismic magma overpressure within the caldera’s magma reservoir. Based on the earthquake’s atypical focal mechanism and efficient tsunami generation, we hypothesize that submarine trapdoor faulting occurred due to highly pressurized magma. To investigate this hypothesis, we establish a mechanical earthquake model that links pre-seismic magma overpressure to the size of the resulting trapdoor faulting, by considering stress interaction between a ring-fault system and a reservoir of the caldera. The model reproduces the observed tsunami waveform data. Our estimates indicate trapdoor faulting with large fault slip occurred in the critically stressed submarine caldera accommodating pre-seismic magma overpressure of ~10 MPa. The model infers that the earthquake partially reduced magma overpressure by 10–20%, indicating that the magmatic system maintained high stress levels even after the earthquake. Due to limited data, uncertainties persist, and alternative source geometries of trapdoor faulting could lead to estimate variations. These results suggest that magmatic systems beneath calderas are influenced much by intra-caldera fault systems. Monitoring and investigation of volcanic tsunamis and earthquakes help to obtain quantitative insights into submarine volcanism hidden under the ocean.

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“…Yet, it is often challenging to investigate submarine volcanoes due to the lack of on‐site monitoring systems. Many previous studies remotely detected geophysical signals from submarine volcanoes, such as seawater acoustic waves (Metz et al., 2016; Tepp & Dziak, 2021), seismic waves (Cesca et al., 2020; Saurel et al., 2021; Sugioka et al., 2001), or tsunami waves (Fukao et al., 2018; Sandanbata et al., 2018; Y. Wang et al., 2019), shedding light on volcanic processes in submarine volcanoes. However, only a limited number of studies have utilized these remote signals to examine the magma pressure or the stress state of submarine volcanoes.…”

Section: Introductionmentioning

confidence: 99%

Quantifying Magma Overpressure Beneath a Submarine Caldera: A Mechanical Modeling Approach to Tsunamigenic Trapdoor Faulting Near Kita‐Ioto Island, Japan

Sandanbata,

Saito

2023

JGR Solid Earth

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Submarine volcano monitoring is vital for assessing volcanic hazards but challenging in remote and inaccessible environments. In the vicinity of Kita‐Ioto Island, south of Japan, unusual M ∼ 5 non‐double‐couple volcanic earthquakes exhibited quasi‐regular recurrence near a submarine caldera. Following the earthquakes in 2008 and 2015, a distant ocean bottom pressure sensor recorded distinct tsunami signals. In this study, we aim to find a source model of the tsunami‐generating earthquake and quantify the pre‐seismic magma overpressure within the caldera's magma reservoir. Based on the earthquake's characteristic focal mechanism and efficient tsunami generation, we hypothesize that submarine trapdoor faulting occurred due to highly pressurized magma. To investigate this hypothesis, we establish mechanical earthquake models that link pre‐seismic magma overpressure to the size of the resulting trapdoor faulting, by considering stress interaction between a ring‐fault system and a reservoir of the caldera. The trapdoor faulting with large fault slip due to magma‐induced shear stress in the submarine caldera reproduces well the observed tsunami waveform. Due to limited data, uncertainties in the fault geometry persist, leading to variations of magma overpressure estimation: the pre‐seismic magma overpressure ranging approximately from 5 to 20 MPa, and the co‐seismic pressure drop ratio from 10% to 40%. Although better constraints on the fault geometry are required for robust magma pressure quantification, this study shows that magmatic systems beneath calderas are influenced significantly by intra‐caldera fault systems and that tsunamigenic trapdoor faulting provides rare opportunities to obtain quantitative insights into remote submarine volcanism hidden under the ocean.

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Detection of shallowest submarine seismicity by acoustic coupled shear waves

Abstract: Abstract. An outstanding slow wave train similar to T wave in appearance has

Cited by 6 publications

References 28 publications

Ambient seafloor noise excited by earthquakes in the Nankai subduction zone

Ambient seafloor noise excited by earthquakes in the Nankai subduction zone

Quantifying magma overpressure beneath a submarine caldera: A mechanical modeling approach to tsunamigenic trapdoor faulting near Kita-Ioto Island, Japan

Quantifying Magma Overpressure Beneath a Submarine Caldera: A Mechanical Modeling Approach to Tsunamigenic Trapdoor Faulting Near Kita‐Ioto Island, Japan

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