The 1957 Andreanof, Aleutian Is., earthquake (1957 March 9, 51.53 degrees N, 175.63 degrees W, d = 25 km) is among the most enigmatic great earthquakes instrumentally recorded. The length of the aftershock area is very long (about 1200 km), and tsunami excitation has been recently confirmed to be very extensive, yet its instrumental seismic magnitude Ms is only about 8.1 to 8.3. Detailed analyses of long-period surface waves in the past gave an Mw = 8.4, and the seismic-tsunami disparity remains unresolved. The main difficulty in seismic studies is the absence of high-quality seismic data. Here we investigate the cause of this disparity by carefully analysing some historical seismograms with modern digitization methods. We also take advantage of the 1996 Aleutian Is. earthquake (Mw = 7.87) that occurred very close to the 1957 event. For the 1996 event, high-quality modern broad-band seismograms are available which can be effectively used as empirical Green's functions for the analysis of the 1957 event. Using the Wiechert (Strasbourg, Uppsala), Milne-Shaw (Wellington) and Benioff (Uppsala, Pasadena) seismograms of the 1957 event, we could determine that the 1957 event had significant secondary excitation of long-period (150 s) waves during about 1000 s following the first event. The Mw of the combined source is approximately 8.4. Because of the limited bandwidth of the old instruments, we cannot detect long-period energy beyond 150 s. However, the unusually long-lasting excitation over nearly 1000 s suggests that the event had significant excitation at periods longer than 150 s with a much larger Mw for the total event. Although we cannot address this question quantitatively because of our band-limited data, our numerical experiment using a source with a slow component shows that if the time scale of the slow source is longer than 500 s, our data can be made compatible with an Mw = 8.8 to 8.9 event, thereby reconciling the results from seismic and tsunami data.

We report an extraordinary observation of ground motion in Japan after the moment magnitude (MW) 9.0 2011 Tohoku-Oki earthquake attributed to a multiplate-interface slip event triggered by shear wave that traveled to the Earth's core and back. The megathrust earthquake generated a strong ScS phase with a peak-to-peak amplitude exceeding 1 centimeter in Japan. Superposed on this waveform, an eastward steplike displacement of up to 5 to 6 millimeters was recorded in Global Navigation Satellite System (GNSS) data throughout Japan. This likely originated from slip on the megathrust interfaces triggered by the nearly simultaneous arrival of the ScS wave across Japan. Such an ScS triggering is a previously unrecognized source of seismic hazard, which can potentially (re)activate the mainshock area and the broader surrounding megathrust interfaces.

The growing volume of InSAR time series offers new opportunities to systematically detect transient aseismic deformation, but identifying low-amplitude slow slip events (SSEs) remains challenging due to noise and limited temporal resolution. Here, we adapt the geodetic matched filter, originally developed for GNSS data, to InSAR displacement time series in the context of shallow strike-slip faults. The method relies on correlations between physics-based templates and relative displacement time series constructed between pixels located on either side of the fault, enhancing the signal-to-noise ratio and mitigating atmospheric artifacts. Using synthetic experiments with realistic noise, we quantify detection thresholds and show that SSEs with magnitudes as small as Mw 4–4.5 can be reliably detected at shallow depths. A validation strategy based on spatial coherence and weighted stacking of displacement time series significantly reduces false detections. We apply this approach to the Izmit and Ismetpasa segments of the North Anatolian Fault using multi-level processed InSAR datasets. The method successfully retrieves previously documented SSEs and shows that advanced post-processing improves detection capability. Detected events have magnitudes Mw 4.0–4.3, shallow depths (< 2–4 km), and durations of days to weeks, consistent with independent geodetic observations. These results demonstrate that physics-based template matching provides a robust and scalable framework for automatic SSE detection in InSAR time series.

The 29 July 2025 Mw 8.8 Kamchatka megathrust earthquake was the largest global earthquake since the 2011 Mw 9.0 Tohoku earthquake and provides an important opportunity to investigate the rupture process of giant subduction events. Here, we combine low-frequency W-phase inversions with high-frequency image deconvolution back-projection (IDBP) to resolve jointly the spatial distributions of coseismic slip and radiated seismic energy. Point-source and finite-fault W-phase inversions show that low-frequency slip is concentrated in the shallow, trenchward portion of the megathrust. In contrast, multi-array IDBP imaging indicates that high-frequency radiation is primarily emitted from the deeper, downdip part of the seismogenic zone.This pronounced high-frequency–low-frequency partitioning closely resembles that observed in other giant megathrust earthquakes, particularly the 2011 Mw 9.0 Tohoku earthquake. The depth-dependent frequency segregation likely reflects mechanical heterogeneity along the plate interface, controlled by along-dip variations in interplate coupling, effective normal stress, and frictional properties. To quantitatively characterize this separation, we combine W-phase waveform modeling with IDBP constraints and calculate the Frequency Dependence Index (FD Index). For the Kamchatka earthquake, the FD Index is 55%, and the centroids of the high- and low-frequency source regions are separated by approximately 70 km. These results provide quantitative constraints on the along-dip mechanical structure of the megathrust and offer new insight into the generation of strong ground motion and tsunami hazards during giant subduction earthquakes.

Based on measurements of near-trench deformations of the oceanic and overriding plates, in this investigation, we elucidate the tectonic and mechanical processes leading to the Mw7.0 (moment magnitude of 7.0) Acapulco, Mexico, earthquake in 2021. We exploit unprecedented ocean-bottom observations using ultralong-period "tilt mechanical amplifiers," along with hydrostatic pressure, global navigation satellite system, and satellite interferometric synthetic aperture radar data. The joint inversion of these geodetic data, template-matching seismicity, and repeating earthquakes, revealed the first two shallow slow slip events (SSEs) observed in Mexico. The first one migrated from the trench to the earthquake hypocenter before rupture, and the second one occurred following an Mw7.3 long-term SSE induced by the earthquake. Episodic near-trench oceanic-crust deformations (i.e., tilt transients) associated with shallow and deep synchronous decoupling of the plate interface reveal the occurrence of "slab-pull surges" before three regional earthquakes of magnitude 7 or greater, including the Acapulco event, suggesting that they may serve as rupture precursors observable in subduction zones.

Seismic waves from large earthquakes are known to trigger slip on distant faults, but the underlying mechanisms remain unclear. Using interferometric synthetic aperture radar and local geodetic and seismic data, we show that the 1000-kilometer-distant, February 2023 Kahramanmaraş earthquakes in southeastern Türkiye triggered deformation and/or eruption at 56 mud volcanoes and centimeter-scale aseismic slip on seven faults over tens of kilometers within the fluid-rich Kura Basin in the West Caspian region. This transient deformation event, with an equivalent moment magnitude of 6.1, was coupled with local inflation below major hydrocarbon fields. We postulate that seismic waves led to a change in pore pressure at depth, which in turn triggered aseismic slip along several crustal faults crossing the basin and its surroundings.

We present a novel finite fault inversion algorithm that combines W-phase finite fault inversion with Image Deconvolution Back-Projection (IDBP) for the determination of coseismic slip models following large earthquakes. This integrated algorithm leverages the strengths of both methods, enabling rapid determination of moment tensor, slip distribution, and centroid location. The application of this integrated algorithm to the analysis of the 2015/04/25 Mw 7.8 Nepal and the 2013/01/05 Mw 7.5 Craig Alaska earthquakes yielded results closely aligned with detailed post-earthquake studies, highlighting the algorithm's accuracy and reliability. By overcoming inherent limitations of individual methods, it provides a comprehensive understanding of the earthquake source process. The algorithm's potential for automated implementation, requiring few parameters, enhances its suitability for near real-time earthquake analysis.

In the Southern Hemisphere, the prevalence of oceans and the difficulty of access to land result in reduced coverage of seismological stations, limiting our detailed knowledge of Earth 's structures and of large earthquakes sources. This situation is exacerbated inside the antarctic continent, where only two permanent seismic stations are currently available (IU.QSPA at South Pole and G.CCD). The CCD station, built in early 2000s with state -of -theart surface instrumentation and located at the French -Italian Concordia base (75 degrees S, 123 degrees E), has been providing seismological data since 2008. However, it suffers from several problems: the vault is deformed by the hydrostatic pressure of the snow, the firn waveguide traps anthropogenic noise from the base causing strong noise below 1 s, and a coupling defect limits the performance above 30 s on the horizontal channels. To ensure the continuity of CCD and to improve its overall performance, we started in 2014 to plan the installation of a borehole seismometer at the site. In this article, we describe in detail this renovation of CCD and some examples of data analysis. The new borehole sensor shows that short -period disturbances are largely attenuated ( -20 dB at 0.1 s) compared to the surface installation and that the horizontal channels have a lower noise level at long periods ( -8 dB at 100 s). Data for all components are below the standard noise model between 0.1 and 0.2 s, which makes this sensor one of the quietest installations in the world for this bandwidth. For periods > 600 s we observe atmospheric pressure-related perturbations on the vertical component. Despite this problem, the new CCD borehole station is a success with better-than-expected performances at all periods < 600 s. The data produced are now distributed in the world 's data centers as G.CCD.20 and we encourage the scientific community to use the data for all studies requiring seismograms from Antarctica.

On 18 November 2022, a large earthquake struck offshore southern Sumatra, generating a tsunami with 25 cm peak amplitude recorded at tide gauge station SBLT. Our W-phase solution indicates a shallow dip of 6.2 degrees, compatible with long-period surface wave radiation patterns. Inversion of teleseismic body waves indicates a shallow slip distribution extending from about 10 km deep to near the trench with maximum slip of similar to 4.1 m and seismic moment of 1.05x1020 $1.05\times {10}<^>{20}$ Nm (MW 7.3). Joint modeling of seismic and tsunami data indicates a shallow rigidity of similar to 23 GPa. We find a low moment-scaled radiated energy of 4.15x10-6 $4.15\times {10}<^>{-6}$, similar to that of the 2010 MW 7.8 Mentawai event (3.1x10-6 $3.1\times {10}<^>{-6}$) and other tsunami earthquakes. These characteristics indicate that the 2022 event should be designated as a smaller moment magnitude tsunami earthquake compared to the other 12 well-documented global occurrences since 1896. The 2022 event ruptured up-dip of the 2007 MW 8.4 Bengkulu earthquake, demonstrating shallow seismogenic capability of a megathrust that had experienced both a deeper seismic event and adjacent shallow aseismic afterslip. We consider seismogenic behavior of shallow megathrusts and concern for future tsunami earthquakes in subduction zones globally, noting a correlation between tsunami earthquake occurrence and subducting seafloor covered with siliceous pelagic sediments. We suggest that the combination of pelagic clay and siliceous sediments and rough seafloor topography near the trench play important roles in controlling the genesis of tsunami earthquakes along Sumatra and other regions, rather than the subduction tectonic framework of accretionary or erosive margin.

The GEOSCOPE observatory (Institut de physique du globe de Paris [IPGP] and École et Observatoire des Sciences de la Terre de Strasbourg, 1982) provides more than four decades of high-quality continuous broadband data to the scientific community. Started in 1982 with only two stations, the network has grown over the years thanks to numerous international partnerships. At present, 34 stations operate in 18 countries across all continents and on islands throughout the oceans, filling important gaps in global Earth coverage. Most of the first installed stations are still running today, allowing for long-term observations, and new sites are being prospected to further improve global coverage. Over the years, GEOSCOPE has contributed to defining today’s global seismology standards (data format, data quality level, instrumentation requirements), being the French contribution to the international effort for global seismic observations. The stations are instrumented with the best quality seismometers (from the very first STS-1 in the early 80s to the last STS-6A and Trillium T360 today) and digitizers (Q330HR and Centaur) to record with high fidelity the ground motions generated by all types of seismic sources. Real-time data are sent to the tsunami warning centers and both validated and real-time data are available at the IPGP, Epos-France and Earthscope data centers. The quality of GEOSCOPE data and metadata is ensured by daily and yearly validation that enables issue detection and mitigation. GEOSCOPE, in collaboration with the other global networks, has played and continues to play a crucial role in the study of Earth’s structure and global dynamics and the characterization of all types of seismic sources.

In the minutes following a large earthquake, robust characterization of the seismic rupture can be obtained from full wavefield records at local distances or from early signals recorded by regional broadband seismometers. We focus here on the latter configuration, and evaluate the individual and joint performances of the early low-frequency elastic phases (W phase) and the recently discovered prompt elastogravity signals (PEGS). The 2011 Mw 9.1 Tohoku-Oki earthquake is a natural target for this evaluation, because the high quality of global and regional networks enabled to gather the best PEGS data set so far. We first confirm that the well-established W-phase method, using records from global seismological networks, is able to provide a reliable centroid moment tensor solution 22 min after the earthquake origin time. Using regional stations, an accurate W-phase solution can be obtained more rapidly, down to 10 min after origin time. On the other hand, a PEGS-based source inversion can provide even earlier, starting 3 min after origin time, a lower bound of the seismic moment (Mw 8.6) and constraints on the focal mechanism type. However, relying solely on PEGS introduces uncertainties caused by the hindering seismic noise and trade-offs between source parameters that limit the accuracy of source determination. We show that incorporating even a few early W phase signals to the PEGS data set reduces these uncertainties. Using more complete W phase and PEGS data sets available 5 min after origin time enables to converge towards a result close to the Global Centroid Moment Tensor solution.

The occurrence of aseismic creep along seismogenic faults significantly impacts seismic hazard assessment by releasing accumulated stress and reducing the slip deficit. Since the 1999 M(w)7.6 Izmit earthquake on the North Anatolian Fault in Turkiye, while aseismic creep has been observed as a postseismic response to the Izmit rupture, additional slow slip events were detected in 2015 and 2016, accommodating several millimeters of relative displacement over periods of approximately one month. By automating Interferometry Synthetic Aperture Radar time series processing from 2016 to 2021 (FLATSIM project) and applying specific post-processing, we extract the tectonic signal to estimate the slip dynamics of the Izmit segment, including the detection and characterization of slow slip events. Modeling the slip distribution at depth on a 2D fault interface within a layered elastic half-space, we estimate a locking depth of 11 km and steady creep between 2 and 5 km. Above the steady creep zone, we identify two new shallow slow slip events in March 2018 and November 2019, with moment magnitudes of 4.3 and 4.4, respectively. Based on creepmeter measurements, we estimate a lateral propagation velocity of 6.4 km/day for the 2019 event. The location of these shallow slow slip events above the sedimentary-bedrock interface suggests a critical role of variations in frictional properties in the occurrence of transient slip events.

Climate change is increasingly predisposing polar regions to large landslides. Tsunamigenic landslides have occurred recently in Greenland ( Kalaallit Nunaat ), but none have been reported from the eastern fjords. In September 2023, we detected the start of a 9-day-long, global 10.88-millihertz (92-second) monochromatic very-long-period (VLP) seismic signal, originating from East Greenland. In this study, we demonstrate how this event started with a glacial thinning–induced rock-ice avalanche of 25 × 10 6 cubic meters plunging into Dickson Fjord, triggering a 200-meter-high tsunami. Simulations show that the tsunami stabilized into a 7-meter-high long-duration seiche with a frequency (11.45 millihertz) and slow amplitude decay that were nearly identical to the seismic signal. An oscillating, fjord-transverse single force with a maximum amplitude of 5 × 10 11 newtons reproduced the seismic amplitudes and their radiation pattern relative to the fjord, demonstrating how a seiche directly caused the 9-day-long seismic signal. Our findings highlight how climate change is causing cascading, hazardous feedbacks between the cryosphere, hydrosphere, and lithosphere.

El sismo de Michoacán-Colima el 19 de septiembre de 2022 (Ms 7.6, Mw 7.6) rompió el límite NW de la interface entre las placas de Cocos y norteamericana, causando daño severo a muchas poblados y ciudades en los estados de Michoacán y Colima. El daño fue además agravado por una réplica de magnitud importante (Mw 6.7) el 22 de septiembre. El sismo principal inició debajo de la costa a una distancia hipocentral de 22 km de la estación sísmica de Maruata (MMIG) donde las aceleraciones y velocidades máximas registradas, PGA y PGV, fueron de 1g y 28 cm/s, respectivamente. El epicentro de la réplica más grande se localizó a ~30 km al SE del sismo principal. El modelado de falla finita del sismo principal presentado por el Servicio Geológico de los Estados Unidos (USGS), revela una propagación de la ruptura a lo largo del rumbo de la falla hacia la dirección NW con una caída de esfuerzos estáticos Δσs, of 3.7 MPa. Nuestra estimación de energía radiada, ER, es 3.44x1015J, de tal manera que ER /M0 es de 1.27 × 10−5 valor similar al calculado para otros grandes sismos de subducción cuyas área de ruptura no se extienden hacia la trinchera. El área que contiene las réplicas del sismo principal de 2022 se traslapa con el área de réplicas del sismo del 30 de enero de 1973 (Mw7.6). Los sismográmas Galitzin de los dos sismos registrados en la estación DeBilt (DBN) localizada en los Países Bajos son razonablemente similares de tal manera que pueden ser clasificados como eventos quasi-repetidos. Por otro lado, el sismograma DBN del sismo del 15 de abril de 1941 (MS 7.7), cuya localización no se conoce bien del todo, aunque se sabe que ocurre en la misma región, difiere sustancialmente de los sismogramas de 1972 y 2022, sugiriendo que el primero rompió un área diferente de la del sismo de 1941. Un análisis extensivo de registros regionales exhibe el efecto de directividad observada en los datos de movimientos fuertes y en los cocientes de aceleraciones del sismo principal y de las aceleraciones de la réplica mayor. La directividad explica la dependencia azimutal observada en los cocientes de PGA y PGV, los cocientes espectrales, la distribución de PGA y la respuesta espectral a 2s Sa (T = 2 s). Debido a la directividad, los valores de PGA, PGV y Sa (T = 2 s) en el Valle de México durante el sismo principal y la réplica mayor fueron muy similares a pesar de la diferencia en magnitud de 0.9. En CU (el sitio de roca firme de referencia en la Ciudad de México), PGA y PGV durante ambos eventos fueron de ~ 6 cm/s2 and 2 cm/s, respectivamente, valores más bajos que los esperados para el sismo principal y más altos que los esperados para la réplica mayor.

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.

In the Southern Hemisphere, the prevalence of the oceans and the difficulty of access to land result in a lack of coverage of seismological station which is a strong limitation Our knowledge of the Earth’s structures and of large earthquakes sources. This is particularly critical inside the Antarctic continent where only two permanent seismological stations are currently available (QSPA and CCD). Among them, the seismological station CCD is a joint program between EOST (Strasbourg) and INGV (Roma) and is installed at the Concordia scientific base (75°S 123°E). This observatory, built in 2000 with state-of-the-art surface instrumentation installed in a vault made of snow-covered containers, meets the required quality criteria and has been part of the GEOSCOPE network since 2008. However, it has become necessary to replace this installation for safety reasons, recurring snow coverage issues and seismological performances. The existing seismic vault is deformed by the hydrostatic pressure of the snow. Its proximity to the base causes strong daytime noise (~30 dB) at high frequencies (>1 Hz); the unconsolidated layer of snow about 100m thick forms a waveguide that traps anthropogenic noise from the base. In addition, a coupling defect of the instruments in contact with the snow limits the performance at low frequencies (< 0.03 Hz) on the horizontal channels.Eight years ago, we proposed to install a borehole seismometer at a depth of 120m to limit the waveguide effects. A new shelter on stilt and the borehole drilling were carried out in 2018/2019. The installation of all the instrumentation has been completed by our team in January 2020. The analyses of the data show that the high-frequency disturbances are very largely attenuated (-30 dB at 10 Hz) compared to the surface installation and that the horizontal channels have a lower noise level at low frequencies (-20 dB at 0.01Hz). In addition, data for all components are below the standard noise model for frequencies between 5 and 9Hz, which already makes this new station one of the quietest installations in the world for those frequencies. A few problems remain to be solved, such as atmospheric pressure-related perturbations for periods longer than 600s on the vertical component. We are currently implementing several patches to try to better insulate the borehole. Updates will be presented during the meeting. Despite this problem at long period, the new CCD borehole stations is a success with better-than-expected performances at all periods shorter than 500s. The data produced are now distributed in the world data centers as G.CCD.20.

The 2015 moment magnitude Mw=8.3 Illapel earthquake is the largest mega-thrust earthquake that has been recorded along the Chilean subduction zone since the 2010 M_W=8.8 Maule earthquake. Previous studies indicate a rupture propagation from the hypocenter to shallower parts of the fault, with a maximum slip varying from 10 to 16 meters. The amount of shallow slip differs dramatically between rupture models with some results showing almost no slip at the trench and other models with significant slip at shallow depth. In this work, we revisit this event by combining a comprehensive data set including continuous and survey GNSS data corrected for post-seismic and aftershock signals, ascending and descending InSAR images of the Sentinel-1A satellite, tsunami data along with high-rate GPS, and doubly integrated strong-motion waveforms. We follow a Bayesian approach, in which the solution is an ensemble of models. The kinematic inversion is done using the cascading capability of the AlTar algorithm, allowing us to first get a static solution before integrating seismic data in a joint model. In addition, we explore a new approach to account for forward problem uncertainties using a second-order perturbation approach. Results show a rupture with two main slip patches, with significant slip at shallow depth. During the rupture propagation, we observe two regions that are encircled by the rupture, with no significant slip, westward of the hypocenter. These encircling effects have been previously suggested by back-projection results but have not been observed in finite-fault slip models. We propose that the encircled regions correspond to regions where the yield stress largely exceeds the initial stress or regions where fracture energy is too large to be ruptured during earthquakes such as the Illapel one. These asperities may potentially break in the future and probably already broke in the past.

Rapid venting of volcanic material during the 15 January 2022 Tonga eruption generated impulsive downward reaction forces on the Earth of ~2.0 × 10 13 N that radiated seismic waves observed throughout the planet, with ~25 s source bursts persisting for ~4.5 hours. The force time history is determined by analysis of teleseismic P waves and Rayleigh waves with periods approximately <50 s, providing insight into the overall volcanic eruption process. The atmospheric acoustic-gravity Lamb wave expanding from the eruption produced broadband ground motions when transiting land, along with driven and conventional tsunami waves. Atmospheric standing acoustic waves near the source produced oscillatory peak forces as large as 4 × 10 12 N, exciting resonant solid Earth Rayleigh wave motions at frequencies of 3.7 and 4.6 mHz.

Four years ago, using survey GPS measurements, the first deep slow slip event (SSE) was detected in Chile (near Copiapó, Atacama region), unrelated to any major earthquake. It was located between 40 and 60 km depth on the subduction interface, lasted approximately 18 months (2014-2016.5) and reached an equivalent magnitude of Mw~6.9. The single permanent station operating in the region between 2002 and 2015 revealed that similar events had occurred at least twice before around 2006 and 2010, suggesting a 5-year repeat time. In anticipation of the next event expected for 2020, we densified the existing continuous GNSS network in the region with 5 new stations in early 2019.Here we show that the SSE occurred in 2020 as expected with the 5 year recurrence time. The event started around March 2020 and developed during 6 months, before it was perturbed by the 2020 Atacama seismic sequence that occurred nearby. During those initial 6 months, the 2020 event had the same characteristics as the 2014 SSE. It occurred in the same area and at the same depth, repeating similar a pattern of surface deformation. Before the occurrence of the nearby seismic sequence of September 2020, it had reached a third of the total amplitude of the 2014 SSE which had lasted three times longer. Whether the 2020 SSE was aborted when the nearby seismic sequence occurred or continued in the background is unknown but this will be resolved with longer times series.