An Mw 8.8 earthquake on 29 July 2025 generated a tsunami near the Kamchatka Peninsula. The interferometric Synthetic Aperture Radar (InSAR) satellite Surface Water and Ocean Topography (SWOT) produced images of sea surface height anomalies (SSHAs) approximately 600 km from the epicenter about 70 min after the earthquake. The image shows concentric dispersive tsunamis as SSHA and we inverted the observed SSHA for the earthquake fault slip distribution using dispersive tsunami modeling. We adopted the Normalized Cross-Correlation (NCC) to determine the tsunami start time and to assess the agreement between the observed and synthetic images. The obtained slip distribution revealed a large slip of approximately 16 m in the southern region concentrated near the trench axis. This suggests a localized rupture extending to the trench axis at the shallowest part of the plate interface along the Kamchatka trench, where the Pacific Plate subducts beneath the North American Plate. The estimated magnitude of Mw 8.8 is consistent with the United States Geological Survey (USGS) estimate. Synthetic tsunami waveforms at the three nearest tsunami stations in the deep sea showed good agreement with the observed sea level time series. For the first time, we demonstrated that the earthquake slip can be estimated solely from SWOT satellite tsunami imagery. Our slip model revealed local spatial variability in the slip distribution that far exceeds the slip expected from plate motion and recurrence intervals. Such unexpectedly large fault motion that directly impacts the tsunami hazard forecast can be estimated quickly if SWOT-like imagery becomes available in near real time.

The July 2025 Mw 8.8 Kamchatka earthquake triggered a transoceanic tsunami across the Pacific Ocean, with noticeable wave heights and coastal oscillations observed as far away as Chile. We compiled a comprehensive observational dataset consisting of 40 high-quality deep-ocean buoys and 10 coastal tide gauges distributed along the Pacific margins. We applied three fault slip models developed by the USGS and employed a dedicated framework to calculate the tsunami generation process in a multi-layered elastic Earth. A reliable source model was identified by comparing its output with tsunami observations. Detailed waveform, spectral, and energy-distribution analyses for deep-ocean and coastal tsunami data were conducted. Spectral analyses indicate that tsunami energy is concentrated within a broad source period band of 8-128 min, with stations normal to the fault strike dominated by 8-42 min periods and those aligned with the fault strike dominated by 42-128 min periods. This broad spectral content enabled resonance with coastal basins of varying spatial scales, producing prolonged oscillations at Pacific tide gauges, while local bathymetric shielding strongly attenuated tsunami energy even in the near field. Overall, transoceanic tsunami behavior reflects the combined influence of source geometry, directional energy radiation, and region-dependent coastal morphology, explaining the spatially heterogeneous and long-lasting impacts observed across the Pacific Ocean.

Abstract Landslides often generate long‐period seismic waves that propagate over large distances. During volcanic island collapses and their intrusion into seawater, seismic signals of >1 min periods are widely observed. The physical sources of these signals remain poorly understood due to complex landslide‐water interactions. In this paper, we perform coupled landslide‐tsunami‐seismic simulations for the 2018 Anak Krakatau flank collapse, and compare the results with seismic records at regional and teleseismic distances. We find that the landslide alone cannot explain the observed signals. The reaction force from the disturbed seawater also generates long‐period seismic waves, with a contribution comparable to that of the landslide. A combined landslide‐seawater source model better reproduces the recorded waveforms overall. These findings advance our understanding of seismic excitation by tsunamigenic landslides and underscore the importance of water‐induced forces in seismic source studies.

Finite-fault inversion of tsunami waveforms requires prior knowledge of fault geometry, which is often subject to considerable uncertainty. Quantifying effects of such uncertainty is essential for evaluating the reliability of inversion results derived from inadequately constrained fault models. Although previous studies have examined tsunami sensitivity to fault geometry, they typically relied on forward modeling and assumed planar faults. Using the 2011 Tohoku earthquake as a case study, this paper investigates the impact of fault geometry uncertainty on the inverted slip distribution and tsunami predictions. We consider 2D non-planar fault geometry, defined by depth as a function of distance from the trench. 9592 fault depth profiles are generated by densely sampling the region of historical seismicity, representing the maximum uncertainty in the absence of other geophysical constraints. For each sampled geometry, we invert near-field tsunami observations for slip distribution and evaluate the waveform fitting quality. The results show that these fault samples introduce moderate (20–30

To understand the characteristics of seismic waves and tsunamis recorded simultaneously by the ocean-bottom observation networks, the coupling between the solid Earth and the ocean has to be modeled in the presence of gravity. However, previous coupled simulations adopted approximate equations that did not fully incorporate the effects of gravity. In this study, we derived correctly linearized governing equations under gravity and compared them with those of previous studies. Numerical experiments were performed for a two-dimensional P-SV wavefield, using the finite difference method (FDM). To validate the accuracy of the calculated tsunamis, we computed the theoretical tsunami dispersion relation using a propagator matrix and compared it with our results and those of previous studies. We found that our proposed method provided more accurate results than those of previous studies, particularly in the short-period band. We also investigated the applicability of the proposed method to distant tsunamis by examining the difference between calculated and theoretical tsunami phase velocities in the long-period band. The proposed formulation provides accurate results that properly incorporate gravity into the simultaneous simulation of seismic waves and tsunamis.

The Torsion-Bar Antenna (TOBA) is a torsion pendulum-based gravitational detector developed to observe gravitational waves in frequencies between 1 mHz and 10 Hz. The low resonant frequency of the torsion pendulum enables observation in this frequency band on the ground. The final target of TOBA is to observe gravitational waves with a 10 m detector and expand the observation band of gravitational waves. In this paper, an overview of TOBA, including the previous prototype experiments and the current ongoing development, is presented.

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 with body‐wave magnitudes mb 4–5 have been documented to the west of Sofugan volcano. To investigate the source process, we analyze tsunami waveforms recorded by an array network of ocean bottom pressure gauges. Stacked waveforms of pressure gauge records suggest recurrent arrivals of multiple wave trains. Deconvolution of the stacked waveforms by tsunami waveforms from an earlier event revealed over 10 source events that intermittently generated tsunamis for ∼1.5 hr. The temporal history of this sequence corresponds to the origin times of T‐phases estimated by an ocean bottom seismometer and of the seismic swarm, implying a common origin. Larger events later in the sequence occurred at intervals comparable to the tsunami wave period, causing amplification of later phases of the tsunami waves.

Two unusual submarine earthquakes (Mw 5.8) occurred near volcanic islands, called Curtis and Cheeseman, in the Kermadec Arc in 2009 and 2017. Following both earthquakes, similar tsunamis with wave heights of about a meter, that are disproportionate to their moderate seismic magnitudes, were observed by coastal tide gauges. We investigate the source mechanism for both earthquakes by analyzing tsunami and seismic data of the 2017 event. Preliminary analysis of tsunami data indicates that the earthquake uplifted a submerged caldera around the islands. Source modeling using tsunami and seismic data reveals that a trapdoor faulting, involving ring-faulting and deformation of an underlying magma reservoir, occurred due to magma overpressure in the reservoir, possibly in association with caldera resurgence. The relationship between the maximum fault slip and the seismic magnitude for trapdoor faulting events found at global calderas is different from that for regular earthquakes, reflecting the peculiarity of the volcanic earthquakes.

Abstract The explosive 2022 Tonga submarine volcanic eruption produced a globally propagated atmospheric disturbance. A leading Lamb wave pulse was recorded as a pressure pulse worldwide. A weather‐station network in Japan recorded the pressure pulse together with temperature and wind conditions during the passage of the pulse. Individual temperature and wind records indicate little simultaneous change. However, after alignment of records at the time of pressure pulse arrivals and stacking, clear temperature and wind changes synchronized with the pressure change are evident. Assuming Lamb wave propagation, the synthesized temperature and wind changes from the pressure record show a good match with the observed waveforms. The observed wind speed and pressure change of the Lamb pulse yielded a total energy transported by the pulse of 4.2 × 1016 J.

Abundant high-quality distant tsunami records from the 2010 Maule (Chile) and 2011 Tohoku-Oki earthquakes have revealed two distinctive features compared to long-wave tsunami simulations. The records show that the traveltime delay of the tsunami increases with distance from the earthquakes, and the initial phase reversal of tsunamis appears and grows systematically. The conventional tsunami theory cannot explain the observed waveforms and traveltimes of distant tsunamis, leading to the need for a new theory to explain and synthesize distant tsunamis. The propagating elevated sea surface of a tsunami compresses seawater and deforms the seafloor and the solid Earth. A propagating tsunami changes the mass distribution of the Earth and results in a spatiotemporal change in gravity, thereby altering the propagating tsunami itself. Incorporating these physics, we developed a new tsunami propagation theory in which a tsunami is naturally treated as a wave in a gravitationally and elastically coupled Earth system composed of solid Earth layers and an ocean layer. Two distinct tsunami simulation techniques based on the new tsunami propagation theory were introduced and confirmed to produce nearly identical tsunami waveforms. One technique treats tsunamis as free waves within a deformable Earth system, while the other treats tsunamis as external pressure and gravitational forces acting on the surface of a deformable Earth system. With the new techniques, the waveform and traveltime differences between the observed and simulated distant tsunamis disappear. Past distant tsunamis recorded by coastal tide gauges, which were not previously studied due to the traveltime and waveform mismatch problems, have become the focus of quantitative tsunami studies analyzing waveforms. New tsunami propagation techniques have been applied to the analysis of distant tsunami waveforms from the past 19 events and have helped to unveil the slip distributions of the past large earthquakes and to determine the earthquake origin time of the trans-Pacific tsunami events recorded by tide gauges since 1854.

On 9 October 2023 (JST), mysterious tsunamis with a maximum wave height of 60 cm were observed in Izu Islands and southwestern Japan, although only seismic events of body-wave magnitudes mb 4–5 have been documented in the southwest of Torishima Island. To investigate the source process, we analyze tsunami waveforms recorded by an array network of ocean-bottom pressure gauges. A stacked waveform of 16 records suggests recurrent arrivals of multiple wave trains. Deconvolution of the stacked waveform by a tsunami waveform from the first event revealed over 10 source events that intermittently generated tsunamis for ~1.5 hours. The temporal history of this sequence corresponds to the origin times of T-phases estimated by an ocean-bottom seismometer, and the mb 4–5 seismic swarm, implying a common origin. Larger events later in the sequence occurred at intervals comparable to the tsunami wave period, causing amplification of later phases of the tsunami waves.

The main cause of tsunamis is large subduction zone earthquakes with seismic magnitudes M-w > 7, but submarine volcanic processes can also generate tsunamis. At the submarine Sumisu caldera in the Izu-Bonin arc, moderate-sized earthquakes with M-w < 6 occur almost once a decade and cause meter-scale tsunamis. The source mechanism of the volcanic earthquakes is poorly understood. Here we use tsunami and seismic data from the recent 2015 event to show that abrupt uplift of the submarine caldera, with a large brittle rupture of the ring fault system due to overpressure in its magma reservoir, caused the earthquake and tsunami. This submarine trapdoor faulting mechanism can efficiently generate tsunamis due to large vertical seafloor displacements, but it inefficiently radiates long-period seismic waves. Similar seismic radiation patterns and tsunami waveforms due to repeated earthquakes indicate that continuous magma supply into the caldera induces quasi-regular trapdoor faulting. This mechanism of tsunami generation by submarine trapdoor faulting underscores the need to monitor submarine calderas for robust assessment of tsunami hazards.

The 15 January 2022 climactic eruption of Hunga volcano, Tonga, produced an explosion in the atmosphere of a size that has not been documented in the modern geophysical record. The event generated a broad range of atmospheric waves observed globally by various ground-based and spaceborne instrumentation networks. Most prominent was the surface-guided Lamb wave (≲0.01 hertz), which we observed propagating for four (plus three antipodal) passages around Earth over 6 days. As measured by the Lamb wave amplitudes, the climactic Hunga explosion was comparable in size to that of the 1883 Krakatau eruption. The Hunga eruption produced remarkable globally detected infrasound (0.01 to 20 hertz), long-range (~10,000 kilometers) audible sound, and ionospheric perturbations. Seismometers worldwide recorded pure seismic and air-to-ground coupled waves. Air-to-sea coupling likely contributed to fast-arriving tsunamis. Here, we highlight exceptional observations of the atmospheric waves.

Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Solid Earth. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing an older version [v2]Go to new versionSub-decadal Volcanic Tsunamis Due to Submarine Trapdoor Faulting at Sumisu Caldera in the Izu-Bonin ArcAuthorsOsamuSandanbataiDShingoWatadaiDKenjiSatakeiDHirooKanamoriLuisRiveraZhongwenZhanSee all authors Osamu SandanbataiDCorresponding Author• Submitting AuthorNational Research Institute for Earth Science and Disaster ResilienceUniversity of TokyoiDhttps://orcid.org/0000-0002-2361-8482view email addressThe email was not providedcopy email addressShingo WatadaiDUniversity of TokyoiDhttps://orcid.org/0000-0001-9924-968Xview email addressThe email was not providedcopy email addressKenji SatakeiDUniversity of TokyoiDhttps://orcid.org/0000-0002-3368-3085view email addressThe email was not providedcopy email addressHiroo KanamoriCaltechview email addressThe email was not providedcopy email addressLuis RiveraUniversité de Strasbourgview email addressThe email was not providedcopy email addressZhongwen ZhanCalifornia Institute of Technologyview email addressThe email was not providedcopy email address

Abstract An unusual devastating tsunami occurred on September 28, 2018 after a strike‐slip faulting earthquake in Sulawesi, Indonesia. The induced tsunami struck Palu city with ∼4‐m flow depth. We performed two analyses to investigate the source of the tsunami. We first conducted the teleseismic source inversion and obtained the overall slip distribution of the strike‐slip fault. Our tsunami simulation from the coseismic deformation of the seismically estimated strike‐slip faulting produced a tsunami comparable to the leading part of the observation at Pantoloan. In order to reconstruct the detailed slip distribution on the fault plane, we then jointly utilized the tsunami waveform and Synthetic Aperture Radar (SAR) data. Because of the lack of SAR data in the bay, the tsunami data is necessary to constrain the offshore slip distribution, which directly induces the tsunami. The inverted source model shows a strike‐slip fault which consists of three segments extending from the epicenter to the south of 1.4°S with two bends and two asperities around Palu city. The joint inversion model accurately reconstructs the observed surface displacements and the leading part of the tsunami waveform. Our result exhibits the significant contribution of the strike‐slip faulting to the tsunami, but it also suggests additional tsunami sources, such as landslides, for the high inundations near Palu bay. The result also indicates that regional devastating tsunamis can be generated by an onshore strike‐slip fault with localized large dip slip.

Descriptions This datasets are parts of the supplementary materials for the following research article: Sandanbata, O., Kanamori, H., Rivera, L., Zhan, Z., Watada, S., & Satake, K. (2021). Moment Tensors of Ring‐Faulting at Active Volcanoes: Insights into Vertical‐CLVD Earthquakes at the Sierra Negra Caldera, Galápagos Islands. Journal of Geophysical Research: Solid Earth, 126, e2021JB021693. https://doi.org/10.1029/2021JB021693 We conduct moment tensor (MT) inversion for the 2005 earthquake at the Sierra Negra caldera, the Galapagos Islands. For the inversion, we assumed different centroid locations in 3D space, i.e., on the x–y (longitude-latitude) plane at a depth of 2.5 km below the solid surface, and the x–z (longitude–depth) plane along a latitude of 0.83°S across the Sierra Negra caldera. Data Sets S1 and S2 contain MT solutions obtained by the MT inversion with a constraint of zero trace; those solutions are used for Figure 7 in "Main Text". Data Sets S3 and S4 contain MT solutions obtained by the MT inversion with constrains of zero trace and zero DS component (\(M_{r\theta}=M_{r\phi}=0\)); those are are used for Figure S1 in "Supporting Information". For the detailed methodology and data, see Section 3 in "Main Text" and Text S1 in "Supporting Information" of our manuscript.

Moderate earthquakes ( M w > 5) with moment tensors (MTs) dominated by a vertical compensated‐linear‐vector‐dipole (vertical‐CLVD) component are often generated by dip slip along a curved ring‐fault system at active volcanoes. However, relating their MTs to ring‐fault parameters has been proved difficult. The objective of this study is to find a robust way of estimating some ring‐fault parameters based on their MT solutions obtained from long‐period seismic records. We first model the MTs of idealized ring‐faulting and show that MT components representing the vertical‐CLVD and vertical strike‐slip mechanisms are resolvable by the deviatoric MT inversion using long‐period seismic waves, whereas a component representing the vertical dip‐slip mechanism is indeterminate owing to a shallow source depth. We then propose a new method for estimating the arc angle and orientation of ring‐faulting using the two resolvable MT components. For validation, we study a vertical‐CLVD earthquake that occurred during the 2005 volcanic activity at the Sierra Negra caldera, Galápagos Islands. The resolvable MT components are stably determined with long‐period seismic waves, and our estimation of the ring‐fault parameters is consistent with the ring‐fault geometry identified by previous geodetic studies and field surveys. We also estimate ring‐fault parameters of two earthquakes that took place during the 2018 activity at the caldera, revealing significant differences between the two earthquakes in terms of slip direction and location. These results show the usefulness of our method for estimating ring‐fault parameters, enabling us to examine the kinematics and structures below active volcanoes with ring faults that are distributed globally.

Dynamic earthquake rupture causes mass redistribution around the fault, and the emitted propagating seismic waves are accompanied by bulk density perturbations. Both processes cause transient gravity changes prior to the arrival of P-waves. Such pre-P gravity signals have been detected in previous studies of several large earthquakes. However, the detections were limited to the vertical component of the signal owing to the high noise level in the horizontal records. In this study, we analyzed dense tiltmeter array data in Japan to search for the horizontal components of the signal from the 2011 Mw 9.1 Tohoku-Oki earthquake. Based on the synthetic waveforms computed for a realistic Earth model, we stacked the horizontal records and identified a signal that evidently exceeded the noise level. We further performed a waveform inversion analysis to estimate the source parameters. The horizontal tiltmeter data, combined with the vertical component of the broadband seismometer array data, yielded a constraint on the dip angle and magnitude of the earthquake in the ranges of 11.5°–15.3° and 8.75°–8.92°, respectively. Our results indicate that the analysis of the three components of the pre-P gravity signal avoids the intrinsic trade-off problem between the dip angle and seismic moment in determining the source mechanism of shallow earthquakes. Pre-P gravity signals open a new observation window for earthquake source studies. Graphical Abstract

We re-examined the slip distribution on faults of the 2004 Sumatra–Andaman (M 9.1 according to USGS) earthquake by the inversion of tsunami data with phase-corrected Green’s functions applied to linear long waves. The correction accounts for the effects of compressibility of seawater, elasticity of solid earth, and gravitational potential variation associated with the motion of mass to reproduce the delayed arrivals and the reversed phase of the first tsunami waves. We used sea surface height (SSH) data from satellite altimetry (SA) measurements along five tracks, and the tsunami waveforms recorded at tide gauges (TGs) and ocean bottom pressure gauges (OBPGs) in and around the Indian Ocean. The inversion results for both data sets for different rupture velocities (Vr) show that the reproducibility of the spatiotemporal SSHs and tsunami waveforms is improved by the phase corrections, although the effects are not so significant within the Indian Ocean. The best slip distribution model from joint inversion of SA, TG and OBPG data with Vr of 1.3 km/s shows the largest slips of 16–25 m off Sumatra Island, large slips of 2–11 m off the Nicobar Islands, and moderate slips of 2–6 m in the Andaman Islands. The inversion results reproduce the far-field tsunami waveforms well at distant stations even more than 13,000–25,000 km from the epicenter. The total source length is about 1400 km and the seismic moment is Mw 9.2, longer and larger than that of our previous estimates based on TG records.