Alexandra Elise Hatem

On 28 March 2025, the Mw 7.7 Mandalay earthquake ruptured ∼475 km of the Sagaing fault. The surface rupture was mapped using high-resolution satellite optical images guided by displacements from subpixel optical image correlation. The surface rupture was generally continuous where remotely observable (i.e., not tree-covered) and very simple without large steps or bends along strike. We analyze remote surface rupture mapping from pixel tracking and optical images and determine that ∼10% of the surface rupture passed through potentially saturated ground. The ground saturation observed on high-resolution satellite images was compared with Sentinel-2 normalized differential water index and generally agrees spatially. We test for correlations between ground saturation observations and the presence or absence of surface rupture and of strike-slip geomorphology. We infer that transient near-surface conditions, such as ground saturation, may influence the geomorphic and paleoseismic preservation of surface rupture, as well as infrastructure (dam) performance, both in this earthquake and globally.

On 24 June 2026, moment magnitude (Mw) 7.2 and 7.5 earthquakes struck northern Venezuela along the right-lateral Boconó and San Sebastián faults, initiating on land west of Morón. Intense shaking and damage, with preliminary subsurface slip estimates, indicate >215 km long, ∼70% offshore eastward rupture propagation, complicating understanding of the shallow rupture process. We investigate surface deformation near five coastal towns intersecting the fault through mapping and subpixel correlation of high-resolution (0.4–10 m) optical imagery. Near Morón, ∼0.78 m of fault-parallel displacement is distributed over >3 km without surface rupture. To the east, displacements increase within narrower zones along towns built on alluvium, from an average of 2.7 m within 69 m at Caraballeda tapering to an average of 0.3 m within 340 m at Camurí Grande. Despite >3 m displacement at Caraballeda, <300 m long discontinuous surface rupture was identified. Airport runway cracking between June 25 and 26 coincides with 0.1–0.2 m of secondary fault afterslip. Shear strains support primarily elastic surface deformation in the west above a fault slip deficit and permanent inelastic deformation consistent with plastic yielding above shallow fault slip in the east. These observations highlight the importance of characterizing distributed near-surface strain and material properties for understanding fault displacement hazard.

How much tectonic geodetic strain is accommodated as earthquakes? Can estimates of tectonic geodetic strain be used in probabilistic seismic hazard analyses? Understanding the balance of moment accumulation (i.e., geodetic moment) and accommodation (i.e., geologic and seismologic moment) is a necessary step toward leveraging corrected geodetic strain rates to quantify earthquake budgets. We investigate these questions using updated geodetic, geologic, and seismologic datasets compiled for the western United States (WUS) portion of the 2023 U.S. National Seismic Hazard Model (NSHM23-WUS) to provide new views of moment rates across the WUS. We compare moment rates using a floating footprint approach across the extent of the NSHM23-WUS fault sections database. We make these comparisons using “moment rate deviation (MRD),” which is defined as a surplus or deficit of geodetic moment rate relative to the sum of geologic and seismologic moment rates. We find that, in general, higher strain rate areas of the WUS (i.e., plate boundary) have smaller values of MRD, meaning that geodetic moment rates approximate the earthquake record preserved by geologic and seismologic moment rates well. In contrast, the lower strain rate, eastern portions of our analysis domain (i.e., intraplate) have very high values of MRD, with geodetic moment rates exceeding measured geologic and seismologic moment rates. We find that geodetic moment rates appear to be representative of the earthquake budget in relatively well-characterized, interplate regions, and geodetic estimates of off-fault deformation could be considered in seismic hazard analyses where MRD is minimized.

The Cascadia subduction zone (CSZ) is capable of producing large megathrust earthquakes and tsunamis, posing substantial risks to the Pacific Northwest. This article examines the seismic characteristics of the CSZ, including its offshore coupling, sparse seismicity, and a complex paleoseismic record. Recent advances in geophysical methods and data collection have improved our understanding of subduction zone processes, but important uncertainties remain regarding rupture dynamics, ground shaking, and tsunami impacts. The Cascadia Region Earthquake Science Center (CRESCENT) has been established to address these challenges through coordinated research, education, and community engagement. By integrating scientific studies, fostering collaboration, and leveraging new technologies, CRESCENT seeks to improve hazard assessment and resilience in the region. This article outlines the primary challenges and opportunities for advancing subduction-zone science and supporting societal preparedness for future CSZ events.

Splay, or branch, faults are a common geometric feature of earthquake surface ruptures and may provide constraints on the rupture behavior of an earthquake. The 2023 Mw 7.8 Pazarcık and Mw 7.5 Elbistan, Türkiye, earthquakes are examples of ruptures with multiple small splays, and the Pazarcık earthquake nucleated on a splay fault, the Narlı fault, before rupturing bilaterally on the East Anatolian fault (EAF). Here, we present 3-m-resolution surface displacement from subpixel correlation of Planet Dove optical images for the entirety of both ruptures with corresponding surface slip distributions. For a 30-km-long study region spanning the Narlı-EAF intersection, we compare surface slip derived from five data sets with different resolutions (on-the-ground, WorldView, Planet Dove, Sentinel-2, and Sentinel-1) to elucidate complementary information. In addition, we integrate information from the surface expression of faulting with published dynamic rupture simulations and rupture process studies to constrain a rupture evolution for the Pazarcık earthquake that is consistent across data sets. This work highlights the complementary nature of disparate surface slip data sets and the role that high-resolution surface displacement information, including from fault splays, can play in constraining nonunique rupture models and refining understanding of the earthquake rupture process.

The 2025 Mw 7.7 Mandalay, Burma (Myanmar), earthquake ruptured 475 km of the central Sagaing fault and is the longest continental strike-slip rupture on record. The observed rupture length is 1.6–4.7 times the value expected (100–300 km) from existing length–magnitude scaling relations for strike-slip earthquakes. The earthquake resulted from shallow dextral faulting and ruptured bilaterally with supershear speeds south of the epicenter, rupturing close to three major cities in Myanmar and exposing more than six million people to violent or extreme shaking. We report on the surface rupture character, length, and slip distribution based on subpixel correlation of Sentinel-2 (10 m) and Planet Dove (3 m) optical images and visual analysis of SkySat and WorldView (0.3–0.5 m) optical images. The earthquake had moderate surface slip (average = 3.3 m, maximum = 5.6 m, 25%–75%, range = 3.0–4.0 m), narrow deformation zone width (1–10 pixels in subpixel correlation and ≤190 m for the detailed surface rupture mapping), and simple fault geometry (no stepovers or large changes in strike, 87% of the rupture that was mapped in detail is single stranded). We attribute the extreme length of the Mandalay earthquake to supershear rupture speed, simple fault geometry, narrow down-dip width, and moderate surface slip. Based on a compilation of 25 supershear strike-slip earthquakes (Mw 6.5–8.6; 1979–2025), we find that the rupture length of supershear earthquakes does not fit empirical scaling relationships for strike-slip earthquakes that predict length from magnitude. A length–magnitude scaling relationship based on supershear earthquakes has a best fit of log10 (surface rupture length) = 0.89 Mw – 4.44, indicating that supershear earthquakes tend to be longer than their subshear counterparts for any given magnitude and thus may expose a greater population to shaking.

A key use-case of geologic slip rates is within deformation models used in probabilistic seismic hazard analyses. Field-derived geologic slip rates have formed the cornerstone of deformation models in such applications for decades. Recent advancements in seismic hazard analyses have expanded the use of faults for which geologic slip rates are not well constrained using categorical slip rate estimates. Because of these advancements, application of a geologic deformation model for use in 2025 U.S. Geological Survey National Seismic Hazard Model Puerto Rico-U.S. Virgin Islands (NSHM25-PRVI) proved challenging due to: (1) a lack of field-based geologic slip rates, and (2) a lack of epistemic uncertainty distributions within a broad range of estimated slip rates. Preliminary versions of the NSHM25-PRVI model sampled these slip rate bins in a coincident manner along preferred and extreme value branches, which yielded untenable correlations in mean hazard results. To minimize the influence of correlated uncertainties amid these challenges, we develop a synthetic epistemic uncertainty distribution for deformation rate on each crustal fault. Each fault has a weighting schema across four possible distribution shapes: uniform, normal, triangular favoring local minima, and triangular favoring local maxima. The synthetic distributions are then sampled several times for each logic tree branch. The results provide a more realistic distribution of rates across the study region as compared with using correlated extrema sampling. This exploration of our method in a small region like PRVI can pave the way for larger-scale, more complicated applications (e.g., western United States).

We present the 2025 U.S. Geological Survey Puerto Rico and U.S. Virgin Islands (PRVI) time-independent earthquake rupture forecast (ERF), developed for the 2025 update to the National Seismic Hazard Model (NSHM) for PRVI. The updated ERF improves upon a prior model from 2003, including an expanded fault inventory with slip-rate estimates, updated seismicity catalogs, and refined subduction zone geometries and deformation models. It applies the fault-system inversion methodology to solve for rates of ruptures on modeled faults, adapted from the 2023 NSHM (NSHM23) for the western United States, including the first application of the inversion to model rates on a U.S. subduction interface. Off-fault and intraslab seismicity are constrained by observed seismicity and use updated methods developed for NSHM23. Uncertainties in model components are substantial, and the ERF represents epistemic uncertainties through a comprehensive logic tree consisting of 1.7 billion logic-tree branches combined across all sources.

The 28 March 2025 moment magnitude ( M _w ) 7.7 earthquake in Mandalay, Burma (Myanmar), ruptured 475 kilometers of the Sagaing Fault, which was more than twice the length predicted by magnitude scaling relationships. Kinematic slip models and observation of a Rayleigh Mach wave that passed through parts of Thailand confirmed that rupture occurred at supershear velocities of greater than 5 kilometers per second. The anomalous length exposed a vast population to violent near-fault shaking. The Mandalay earthquake is a modern analog for the M _w 7.9 1906 San Francisco earthquake, another atypically long and fast rupture. Probabilistic seismic hazard analyses use scaling relations that do not account for such long ruptures at moderate magnitudes. This limitation, in conjunction with a likely increased population and infrastructure exposure for atypically long ruptures, contributes to a potential mischaracterization of seismic risk.

Accurately characterizing 3D fault geometry is vital for improving our understanding of earthquake behavior and informing the development of seismic hazard models. Despite their importance, subsurface fault structures tend to be poorly constrained because of limitations in observational data. Improvements to the seismic networks and earthquake detection algorithms have increased the precision and volume of earthquake catalogs, which help illuminate detailed subsurface fault structure and provide the most direct information available about fault geometries at depth. We present a Python package to automate generating 3D fault geometries directly from hypocentral seismicity patterns. This method begins with clustering events based on their spatial density, identifying coherent patterns. Nearby clusters are then merged based on the similarity of their orientations. We fit nonplanar surfaces using support vector regression to balance surface accuracy with minimal deviations from planarity. The fault models are output as quadrilateral meshes at user-defined resolution. In the process of generating the 3D fault surfaces, we compute the spatial density of seismicity around the surface and the planarity as quantitative metrics of the model outputs. As a proof of concept, we apply this approach to the San Andreas–Calaveras fault junction region and the 2019 Ridgecrest earthquake sequence, both in California, which contain complex subparallel faults well defined at the Earth’s surface and abundant microseismicity. These case studies demonstrate the method’s ability to model complex fault structures, including long continuous fault surfaces, crossing faults, variably dipping segments, and subparallel faults. We test the method on both standard network catalogs and double-difference relocated catalogs. We find that our seismicity-based fault model results align with published 3D models that incorporate additional constraints and interpretations (Plesch et al., 2020; Aagaard and Hirakawa, 2021). This workflow provides a low-user-input solution for estimating fault geometries at depth from earthquake catalogs.