Scripps Institution of Oceanography

Martian chronology is currently constrained using crater counting methodologies, in situ measurements onboard the Mars Science Laboratory (MSL) Curiosity rover, and significantly more precise radiometric isotope age measurements of meteorite samples. Each methodology has advantages and drawbacks. These include uncertainties surrounding crater counting accuracy and in situ ages from MSL, and the lack of field context and two age paradoxes associated with meteorite samples. Martian crater counting is calibrated to the less-than-certain lunar crater counting chronology, and in situ ages on Mars are difficult to calibrate to provide precise or accurate dates. The martian meteorite ‘surface age’ paradox details the observation that despite significant surface area on Mars with Hesperian ages (3.7–3.0 Ga), there are no meteorites with crystallization ages from this period. The other martian meteorite paradox, the ‘ancient Pb age’ paradox, is the discrepancy in relatively young shergottite crystallization ages (<600 Ma) determined by 87 Rb– 87 Sr, 147 Sm– 143 Nd, 176 Lu– 176 Hf, 187 Re– 187 Os, 40 Ar/ 39 Ar and 40 K– 40 Ar isotope systematics compared with some relatively ancient apparent crystallization ages (>4 Ga) from U–Th–Pb isotope systematics. The Mars Sample Return mission from Jezero crater holds great importance for the chronology of Mars, with its potential to elucidate the caveats within each of these chronology methods.

Tsunamis from large subduction earthquakes pose severe coastal hazards, yet their genesis near the trench remains poorly constrained by land-based seismic geodetic data and distant deep-water sensors. Following the 29 July 2025 magnitude 8.8 Kamchatka earthquake, the NASA/CNES Surface Water and Ocean Topography (SWOT) satellite captured a distinct train of short-wavelength tsunami waves, which we link to near-trench tsunamigenesis. Sensitivity analyses of earthquake slip indicated tsunamigenesis within 10 kilometers of the trench, an inference not attainable from land seismology and geodesy or sparse deep-water seafloor pressure records alone. These results provide the first high-resolution, two-dimensional spaceborne observation directly linking the measured dispersive tsunami wavefield to near-trench tsunamigenesis, extending earlier model- and gauge-based inferences. They establish SWOT as a constraint on source processes, with implications for tsunami hazard science and subduction-zone geodynamics.

Probably the most impressive geological feature of active fault zones hosted in carbonate rocks is the presence of several hundreds of meters thick damage zones, often composed of in-situ shattered rocks (ISRs, i.e. rocks fragmented into clasts < 1 cm in size). Despite their abundance, it remains unknown how ISRs form (during the propagation of seismic ruptures?), and how their presence affects (1) the propagation of individual mainshock seismic ruptures, (2) the near field wave radiation and associated strong ground motions, and (3) the evolution in space and time of aftershock seismic sequences. In this contribution, we will present preliminary results of a three-year Ph.D. project aimed at addressing these issues through an integrated field geology and numerical modelling approach.We exploit existing and newly acquired field geology data on fault damage zone distributions in the Central Apennines (Italy), and perform dynamic rupture earthquake sequence simulations with SeisSol (https://seissol.org). The fully-dynamic individual earthquake simulations with SeisSol rely on the discontinuous Galerkin method, which allows treating complex 3D geological structures, nonlinear rheologies (including off-fault plastic yielding) and high-order accurate propagation of seismic waves (Käser et al., 2010). The earthquake modelling simulations integrate laboratory-derived frictional constitutive laws with simplified and realistic representations of fault zone geometry and surface topography. Currently, our study is focused on the 25 km long Campo Imperatore fault system in the Gran Sasso Massif area (Italian Central Apennines) where the damage zones are pronounced and well mapped (Demurtas et al., 2016; Fondriest et al., 2020).We aim at using the dynamic rupture earthquake modelling simulations to discuss the formation and distribution of ISRs with respect to (1) the maximum magnitude (Mw 7.0) of the earthquake associated with the studied fault, (2) fault geometry (length, presence of step overs, fault bends, etc.), (3) topographic effects (valleys, etc.), and (4) lithology (limestones, dolostones, etc.) of the wall rocks. This approach is expected to identify the physical, geological, and loading conditions controlling seismic rupture propagation and the development of fault damage zones. The physically based, fully dynamic 3D simulations will also provide estimates of earthquake source parameters (e.g., fracture energy and seismic moment release rate) and synthetic seismograms (strong ground motions), which will be compared with seismological and strong-motion data from earthquakes in the Central Apennines. References Demurtas, M., Fondriest, M., Balsamo, F., Clemenzi, L., Storti, F., Bistacchi, A., & Di Toro, G. (2016). Structure of a normal seismogenic fault zone in carbonates: The Vado di Corno Fault, Campo Imperatore, Central Apennines (Italy). Journal of Structural Geology, 90, 185–206. https://doi.org/10.1016/j.jsg.2016.08.004Fondriest, M., Balsamo, F., Bistacchi, A., Clemenzi, L., Demurtas, M., Storti, F., & Di Toro, G. (2020). Structural Complexity and Mechanics of a Shallow Crustal Seismogenic Source (Vado di Corno Fault Zone, Italy). Journal of Geophysical Research: Solid Earth, 125(9), e2019JB018926. https://doi.org/10.1029/2019JB018926Käser, M., Castro, C., Hermann, V., & Pelties, C. (2010). SeisSol – A Software for Seismic Wave Propagation Simulations. In High Performance Computing in Science and Engineering, Garching/Munich 2009 (pp. 281–292). Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-13872-0_24

The 2025 Mw 7.8 Myanmar earthquake produced one of the longest continental strike-slip ruptures ever recorded. Expanding beyond a known seismic gap, it struck a densely populated region with vulnerable infrastructure. Study of this earthquake is hampered by limited seismic data coverage, yet uniquely informed by exceptional CCTV footage, a near-fault station, and comprehensive satellite geodetic imagery.To understand the earthquake’s dynamics, we explore hundreds of 3‑D dynamic rupture simulations, all informed by a static slip model on a helix‑shaped fault geometry, which we geodetically inferred from Sentinel-1A/2 and ALOS-2 satellite data. Exploring various fault friction‑initial stress combinations, we identify a family of models characterized by near-critical prestress, low strength drop, and short slip‑weakening distances proportional to slip. These unexpected dynamic parameters are required to reconcile the inferred fast rupture speed with the low crustal wave velocities and the low inferred stress drop of the event. These preferred dynamic rupture models can explain space‑geodetic fault offsets, CCTV‑derived on‑fault slip‑rates, teleseismic waveforms and back-projection, and a near‑fault strong‑motion record. They spontaneously initiate unilateral supershear rupture shortly after nucleation, predominantly propagating at supershear speeds southward within a deep band. In contrast, shallow rupture, although driven by the underlying faster supershear rupture, remains sub‑shear, causing strong curvature of the rupture front. This depth‑dependent rupture speed reconciles the fast average rupture speed imaged by teleseismic back‑projection and confirmed by the early S‑wave onset at station NPW, and the subshear pulse-like phase captured by CCTV. Our dynamic rupture models imply low fracture energy, characteristic of a structurally mature, clay‑rich fault zone, potentially facilitated by hydrothermal alteration and elevated pore-fluid pressure. Additional rupture models incorporating bimaterial effects show that while a bimaterial contrast may explain the subshear–supershear dichotomy between northward- and southward-propagating rupture, such a contrast is inconsistent with the NPW record, suggesting that bimaterial conditions were likely localized. Our results demonstrate that dynamic rupture ensembles informed from a static slip model and validated by interdisciplinary observations can offer a physically grounded route for earthquake characterization, complementary to kinematic modeling. Our results indicate that the Myanmar earthquake was critically influenced by spatial variations in frictional properties and fault stress across low-fracture-energy faults with important implications for assessing seismic hazard of major strike-slip faults.

The High-Resolution Earth System Modeling, Analysis and Prediction for a Society Resilient to Hydrometeorological Hazards (EarthRes) is a program of the International Decade of Sciences for Sustainable Development (IDSSD), endorsed by UNESCO in 2025. EarthRes aims to build global societal resilience to hydrometeorological hazards through five pillars: (1) establishing cooperative observation networks; (2) advancing process-based understanding of Earth system dynamics; (3) enhancing prediction and early warning capabilities; (4) fostering indigenous and local knowledge and data sharing; and (5) strengthening capacity building among international partners.This presentation will introduce the program's recent progress, including collaborative observations for understanding Earth system dynamics, the integration of a regional climate model with a coupled land surface-hydrology-ecology model that accounts for human activities (e.g., reservoir regulation, irrigation, urbanization), and the development of a forecasting framework. This framework connects the regional model with an AI model to predict droughts, floods, and compound events at synoptic to sub-seasonal scales.Other activities under EarthRes will also be introduced, and future plans will be discussed. Through international collaboration and targeted capacity-building, EarthRes seeks to enhance sub-seasonal prediction and early warning capabilities, with particular benefits for vulnerable regions.

Flooding is a major natural hazard across the global tropics. Although flood occurrence is shaped by rainfall characteristics—including duration, frequency, and intensity—accurate prediction remains challenging. A key limitation is the lack of reliable, long-term flood databases that capture events across all spatial scales and durations, hindering a clear understanding of how rainfall variability translates into flood onset. This limitation is particularly critical in the Maritime Continent, where extreme rainfall is common and many small, short-lived, yet severe, floods remain undocumented. To address this limitation, we investigate whether a relatively new approach, global navigation satellite system reflectometry (GNSS-R), can help close this observational gap.In this work, we assess whether data from the CYGNSS small-satellite constellation can be used to identify small- to regional-scale floods, including short-lived events. Our study focuses on Sumatra, an island within the Maritime Continent that is frequently affected by such hazards. A joint analysis of CYGNSS inundation estimates and two independent flood databases allowed us to evaluate how CYGNSS measurements can be used for flood detection. Three detailed case studies demonstrate that CYGNSS provides an unprecedented ability to monitor day-to-day changes in surface water extent, including floods at the urban scale. Specifically, we show that CYGNSS-derived inundation anomalies can clearly capture evolution of a flooding event, with the largest signature one day after known flood initiation. A systematic analysis of 555 flood events over a 21-month period enabled us to identify characteristic patterns in inundation anomalies that reliably distinguish flood events from non-flooding conditions, through the definition of an inundation-anomaly threshold and a maximum distance between CYGNSS detections and reported flood locations. We established that CYGNSS observations within 15 km not-only significantly differ from base-line conditions, but they allow tracking day-to-day flood dynamics as well.The proposed methodology is transferable and can be applied to establish flood-inundation thresholds for any region within the global tropics, enabling automated detection of previously unreported flood events or the study of relationships between extreme precipitation and flood evolution. An example of its application is the automatic detection of flooding from CYGNSS data associated with subseasonal variability in tropical circulation: the passage of multiple convectively coupled Kelvin waves embedded within an active Madden–Julian Oscillation in July 2021. These waves propagated eastward across the Maritime Continent, triggering extreme rainfall and widespread flooding in equatorial Indonesia and East Malaysia. The day-to-day evolution of floods could be observed alongside the propagating waves, with the termination of the MJO coinciding with the cessation of the flood events.Relying on low-cost small satellites, this approach shows strong potential for future scalability with larger constellations, ultimately improving flood monitoring and advancing our understanding of how rainfall patterns shape flood dynamics across global tropics.

NASA and ESA launched the PACE and Earthcare satellites in 2024 to provide unique aerosol and cloud measurements. We use these measurements to constrain model uncertainty on aerosol Effective Radiative Forcing (ERF). Perturbed Parameter Ensembles (PPEs) are extremely powerful tools that offer an effective approach to evaluate and constrain the model uncertainty of aerosol using observations.We create a PPE for July 2024-August 2025 based on 250 simulations by the aerosol -climate model ECHAM-HAM and co-locate the 3-hourly output with aerosol and cloud products from PACE and Earthcare. We define regional monthly mean observations for 19 regions of fine- and coarse Aerosol Optical Depth (AOD), Aerosol Index (AI), Single Scattering Albedo (SSA), cloud droplet number concentration (Nd), Cloud Effective Radius (CER), and fraction of extinction below 2km altitude, resulting in almost 1600 observations. An emulator is used to extend the PPE to simulate these observations to 2 million PPE members and constrain the PPE by applying least-squares minimization. resulting in 0.2% of accepted ensemble members.Both PACE and EarthCARE independently and consistently constrain several model parameters that affect ERFaci and RFari. These observations fundamentally and consistently change where and how ERF uncertainty is controlled and alter the global spatial ERF distribution. The constrained ensemble indicates a stronger negative global aerosol ERF than previous mean estimates, alongside a more positive forcing over Central Africa. The observations suggest a reduction of emission of DMS, Organic, and Black Carbon (anthropogenic and biomass burning), and accumulation mode sea salt. Also, the absorption capability (imaginary refractive index) of different aerosol species is reduced. Cloud observations constrain ‘activation’ and ‘vertical velocity’ parameters, resulting in smaller aerosol-Nd susceptibility. However, some parameter uncertainties, such as biomass burning emission particle size, remain mostly unchanged. These results demonstrate that new satellite observations can robustly and consistently constrain aerosol ERF uncertainty, while also identifying key processes where additional or complementary observations are required.

It is well documented that many mountain belts - such as the Pyrenees, European Alps, Greater Caucasus, or Atlas - form through inversion of pre-collisional extensional basins. Looking in plan-view at these mountain belts, we observe along-strike variations in topography, orientation, and deformation patterns. However, the relationship between these characteristics and the inherited extensional architecture remains poorly known. Here, we use the 3D thermo-mechanical geodynamic model pTatin3D coupled to the landscape evolution model FastScape to investigate how pre-collisional rift-linkage influences rift inversion and mountain belt evolution. Presenting numerical models and a work minimization analysis, we show that rift basin offset and pre-existing weaknesses determine mountain belt evolution, which can be divided into a juvenile and mature stage. In the juvenile stage, extensional structures are reactivated, creating an orogen that resembles the rift structure. During the mature stage, the evolution depends on the subduction polarity, which is controlled by basin offset and existing structural weaknesses. Same polarity subduction retains the inherited basin configuration and creates an orogen with continuous high topography. Opposite polarity subduction overprints the pre-existing rift configuration and creates a discontinuous mountain belt with a characteristic topographic low in the transition zone. Comparison with the Greater Caucasus, Atlas, and Pyrenees suggests that the Greater Caucasus is a mature same-polarity orogen, the Atlas is a juvenile inversion orogen where subduction polarity plays no significant role, and the Pyrenees are a mature same-polarity orogen in which lateral variabilty is overprinted by differences in the amount of crustal shortening. Based on our results, we propose a simple diagnostic framework that establishes a direct link between topography and deep lithospheric structures, showing how extensional inheritance influences mountain building on Earth.Associated article:Wolf, S.G., Huismans, R.S., Muñoz, J.A., May, D.A. (2026) Rift linkage and inheritance determine collisional mountain belt evolution. Nature Communications 17, 84. https://doi.org/10.1038/s41467-025-66695-8

Heavy precipitation in Colorado (CO) is key to water resources, and the presence or absence of a few strong storms can make or break the yearly snowpack that delivers water to four major river basins. However, predicting precipitation in CO is challenging because it has high spatial and temporal variability. Atmospheric rivers (ARs) are one type of storm that results in a large fraction of extreme precipitation in the western U.S. and lends itself to improved forecasts over the region. Extensive knowledge of AR frequency, intensity, impacts, and key meteorological processes has been developed for U.S. West Coast landfalling ARs; however, relatively limited research has examined AR characteristics further inland, particularly for Colorado (CO), where high and complex topography, as well as the distance from the coast, complicate attempts to track ARs, AR-derived moisture, and AR-related impacts. Previous research efforts attributing precipitation to ARs based on their spatial footprint have yielded less than 30% of cool-season precipitation in CO as related to ARs. However, a large volume of anecdotal evidence suggests that ARs play a larger role in CO precipitation. To quantify this, we used trajectory-based methods to quantify the contribution of landfalling ARs to top-decile precipitation in subbasins throughout CO. Moisture sourced from landfalling ARs penetrates inland along relatively low-elevation corridors through the Interior West, and exhibits substantial geographic and interannual variability. Using the backward trajectory approach, we found that landfalling ARs contribute 21–78% of western CO’s top-decile cool season precipitation. Most of the AR-related precipitation across western CO during the cool-season is sourced from landfalling ARs near Southern California, the Baja Peninsula, and the Pacific Northwest. These results indicate a larger role for ARs in CO weather and hydroclimate than previous research suggests and highlight the importance of AR representation in forecast models to improve predictability of precipitation in CO.