On 15 January 2022, the Hunga Tonga-Hunga Ha'apai volcano erupted, producing tsunamis worldwide including first waves which arrived more than 2 hours earlier what is expected for conventional tsunamis. We investigated generation and propagation mechanisms of tsunami "forerunner," our simulation found that fast-moving atmospheric Lamb drove leading sea height rise whereas scattering related to bathymetric variations in Pacific Ocean produced subsequent long-lasting Tsunamis arriving later...

Abstract On 8 October 2023, mysterious tsunamis with a maximum wave height of 60 cm were observed in Izu Islands and southwestern Japan, although only seismic events body‐wave magnitudes m b 4–5 have been documented to the west Sofugan volcano. To investigate source process, we analyze tsunami waveforms recorded by an array network ocean bottom pressure gauges. Stacked gauge records suggest recurrent arrivals multiple trains. Deconvolution stacked from earlier event revealed over 10 that...

Abstract Ocean-bottom pressure gauges of wide and dense ocean-bottom observation networks around Japan, S-net DONET, observed ocean waves caused by the Tonga eruption that started at approximately 13:00 JST (UTC + 0900) on January 15, 2022. We scrutinized waveform records arriving to evaluate their nature found two significant disturbances between 20:00 21:00 after 22:00. The first disturbance with a positive-polarity pulse dominated long-period components (1000–3000 s) arrived DONET...

Abstract On 8 October 2023 UTC, significant tsunamis were observed around Japan without any major tsunamigenic earthquake, associated with a series of 14 successive minor earthquakes ( m b = 4.5–5.4) near Sofugan in the Izu‐Bonin Islands. To examine cause this tsunami, we estimated horizontal locations tsunami source and temporal history seafloor displacement, using data recorded by ocean‐bottom pressure gauges >∼600 km away. Our results showed main was an uplift located at caldera‐like...

Ocean-bottom observations are essential for studying earthquake and tsunami processes in the ocean. Traditionally ocean-bottom pressure gauges (PGs) were used to observe tsunamis, while recent studies have revealed that they capture geophysical phenomena across a wide period range from seconds years. Utilizing this capability, I analysed in-situ PG data, recorded inside source region, reveal physics of massive generation. In presentation, introduce my works related analyses which provides...

Abstract The spatiotemporal characteristics of shallow slow earthquake activity are linked to the tectonic environments plate boundaries. In this work, variations very low frequency (SVLFE) along Nankai Trough were investigated using a cross‐correlation analysis. SVLFEs migrated or spread eastward strike direction trench during large SVLFE episodes. Migrations and clusters suggest occurrence slip events. observed lateral in patterns reflect heterogeneous distributions effective strengths at...

SUMMARY Due to complex 3-D heterogeneous structures, conventional 1-D analysis techniques using onshore seismograms can yield incorrect estimation of earthquake source parameters, especially dip angles and centroid depths offshore earthquakes. Combining long-term seismic observations numerical simulations wave propagation in a model, we conducted moment tensor (CMT) inversions earthquakes along the Nankai Trough between April 2004 August 2019 evaluate decade-scale seismicity. Green's...

Abstract A new dense and widely distributed tsunami observation network installed off northeast Japan detected millimeter‐scale tsunamis from an Mw 6.0 shallow interplate earthquake on 20 August 2016. Based the fault model deduced this data set, we obtained a stress drop of 1.5 MPa for event, similar to those associated with typical earthquakes. The rupture area was unlikely overlap regions where slow earthquakes occur, such as low‐frequency‐tremors very‐low‐frequency‐earthquakes. results...

Abstract Although most tsunamis are generated by the sea‐bottom deformation caused earthquakes, some excited sea‐surface pressure changes. This study theoretically investigated changes and derived solutions in three‐dimensional (3‐D) space, whereas past studies employed two‐dimensional equations. Using solutions, we simulated visualized tsunami generation a growing change. Negative change made sea surface uplifted inside source region negative leading waves were radiated from region. We also...

Abstract This study reports an ocean‐bottom pressure gauge (OBP) network, S‐net, which captured meteotsunamis with amplitudes as small a few cm, and investigates its validity limitation for meteotsunami research studies through data analyses numerical simulations. On July 1, 2020, S‐net recorded tsunami‐like signals, although no earthquake was reported. These waves, propagating northward velocity of ∼110 m/s, were explained by atmospheric low maximum amplitude −0.5 ± 0.1 hPa moving...

This article reviews tsunami modeling and its relation to recent developments of deep-ocean observations. Unlike near-coast observations, observations have enabled the capture short-wavelength dispersive tsunamis reflected waves from coast. By analyzing these waves, researchers can estimate sources earthquake slip distributions more reliably with higher spatial resolution. In addition, fractional speed reduction due elasticity Earth medium is now clearly detected. Densely widely distributed...

Offshore ocean bottom pressure gauges (OBPs) are often used to estimate the spatial distribution of initial sea-surface height associated with offshore earthquakes (the tsunami source model). However, sensors sometimes record changes that neither related tsunamis nor seafloor coseismic displacements non-tsunami components) due sensor rotation or tilt ground shaking long-term mechanical drift. These components can be a error when accurately estimating model and thus need removed provide...

Abstract No great earthquakes have been historically documented at the Izu‐Bonin Trench, where subduction is believed to occur largely by aseismic slip, although details are poorly understood. We deployed an array of ocean bottom pressure gauges here for a year from May 2015. The recorded coseismic seafloor uplift/subsidence and tsunamis generated nearby Mw6.0 thrust earthquake. In association with this event, we detected two much larger slip events rise times around 1 h. total moment these...

Abstract We examined the dynamic pressure change at seafloor to estimate centroid moment tensor solutions of largest and second foreshocks ( M w 7.2 6.5) 2011 Tohoku‐Oki earthquake. Combination onshore broadband seismograms high‐frequency (~20–200 s) records provided resolution horizontal locations centroids, consistent with results tsunami inversion using long‐period (≳10 min) although depth was not constrained well, whereas source were poorly by seismic data alone. Also, waveforms...

Abstract Tsunamis with amplitudes of up to 40 cm, related the M w 7.1 normal‐faulting earthquake off Fukushima, Japan, on November 21, 2016, were clearly recorded by a new offshore wide and dense ocean‐bottom pressure gauge network, S‐net, high azimuthal coverage located closer focal area. We processed S‐net data found some stations included tsunami‐irrelevant drift step signals. analyzed infer tsunami source distribution. A subsidence region narrow spatial extent (∼40 km) large peak (∼200...

Abstract The 2011 Tohoku-Oki earthquake generated a surprisingly large near-trench slip, and earth scientists have devoted significant attention to understanding why. Some studies proposed special rupture mechanisms, such as extensive dynamic frictional weakening; others simulated this slip behavior without supposing the weakening. However, we not reached decisive conclusion for question due limited spatial resolution. Hence, in study use new tsunami data recorded just above area addition...

Abstract The Te Araroa earthquake occurred on 2 September 2016 (local time) offshore of the northeastern coast New Zealand's North Island (Mw 7.1). When this event occurred, ocean bottom pressure gauges (OBPs), installed ~170 km south source area, clearly recorded direct tsunami from to OBPs (~ −1.5 cm), and coastal reflections (~2 cm). We estimate centroid location that best reproduces OBP waveforms. using wave alone, is poorly constrained, with a horizontal uncertainty ~100 km. By...

Abstract Recent developments of ocean‐bottom pressure gauges (PG) have enabled us to observe various waves including seismic and tsunami covering periods T ∼ 10 0 –10 3 s. To investigate the quality for broadband observation, this study examined PG records (sampling rate 1 Hz) around Japan associated with 2010 Chile earthquake. We identified three distinct wave trains, attributed body waves, Rayleigh tsunamis. Clear dispersive features in tsunamis were explained by theories elastic gravity...

the Hunga Tonga-Hunga Ha'apai volcano erupted, causing tsunamis all around world; enigmatic arrived much earlier by > ~2 hr than conventionally predicted tsunami travel time.Here, we investigated generation and propagation mechanisms of "forerunner."The simulation found that fast-moving atmospheric pressure waves drove leading sea height rise, while scattering small islands in Pacific Ocean triggered coda tsunamis.The arriving later theoretically time are composed various generated both from...

Abstract Recent studies have shown that ocean‐bottom pressure gauges (OBPs) can record seismic waves in addition to tsunamis and seafloor permanent displacements, even if they are installed inside the focal area where signals extremely large. We developed a method extract dynamic ground motion waveforms from near‐field OBP data consisting of complex mixture various signals, based on an inversion analysis along with theory tsunami generation. applied this 2011 Tohoku‐Oki earthquake....

Abstract An unexpected major tsunami from the region near Sofu Seamount was observed on 8 October 2023. is located approximately 600 km coast of Japan. Due to far epicentral distances and successive occurrence seismic events, conventional analysis reveal accompanying sequence cannot work well. We investigated high‐frequency teleseismic P regional T waves during tsunamigenic events Seamount. Envelope shapes were similar, indicating that ‐wave envelopes also reflected source properties...

Abstract Dynamic wedge failure produces short‐wavelength seafloor uplift efficiently with diminishing shallow slip on the plate interface, generating impulsive tsunami. For ria coasts prevalent small‐wavelength bathymetric and geomorphologic features, such as Sanriku coast of Japan, tsunami can be amplified to produce large runup. We model propagation runup 1896 by using deformation from dynamic rupture models Ma Nie (2019) for a M W 8 earthquake inelastic deformation. The nonlinear...

On 8 October 2023 UTC, significant tsunamis were observed around Japan without any major tsunamigenic earthquake, associated with a series of 14 successive minor earthquakes (mb = 4.5–5.4) near Sofugan in the Izu-Bonin islands. To examine cause this tsunami, we estimated horizontal locations tsunami source and temporal history seafloor displacement, using data recorded by ocean-bottom pressure gauges > ~600 km away. Our results showed main was an uplift located at caldera-like bathymetric...