The interseismic crustal strain-rate distribution in Japan has traditionally been estimated from coordinate time series derived from GEONET, the nationwide GNSS network operated by the Geospatial Information Authority of Japan (GSI). Beginning with Sagiya et al. (2000) and subsequent studies, these analyses have revealed the existence and broad extent of inland strain-concentration zones. However, because the average spacing of GEONET stations is ~20 km, its ability to resolve highly localized deformation, such as strain accumulation associated with individual active faults, has remained limited.

In contrast, SoftBank Corp. (hereafter SoftBank), a Japanese telecommunications company, has operated an independent nationwide GNSS network of more than 3,300 stations since late 2019, nearly three times the number of GEONET stations. The suitability of SoftBank stations for crustal deformation monitoring was demonstrated by Ohta and Ohzono (2022).

By integrating GNSS data from GEONET and SoftBank, we constructed an unprecedentedly dense observation network and estimated interseismic crustal strain-rate fields at substantially higher spatial resolution. The integrated network achieves an effective station spacing of <10 km, enabling us to resolve localized strain features that are not captured by GEONET-only solutions. For example, our results suggest that the Niigata–Kobe Tectonic Zone, previously interpreted as a continuous belt, may instead comprise a series of smaller, spatially localized strain-concentration zones.

Moreover, the improved resolution enables a more direct comparison between the strain-rate field and the spatial distribution of earthquake epicenters. We find that seismicity tends to be more active along the margins of strain-concentration zones rather than directly above their cores. This pattern is consistent with the interpretation of Hasegawa et al. (2004), which proposes that stress preferentially accumulates at boundaries between regions undergoing rapid inelastic deformation and surrounding regions deforming more slowly, thereby promoting earthquake occurrence along the edges of strain-concentration zones. 

Acknowledgments: The SoftBank's GNSS observation data used in this study was provided by SoftBank Corp. and ALES Corp. through the framework of the "Consortium to utilize the SoftBank original reference sites for Earth and Space Science".

How to cite: Ohtate, M., Ohta, Y., Ohzono, M., and Takahashi, H.: High-Definition Strain-Rate Mapping of Japan from a Public–Private GNSS Network , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3318, https://doi.org/10.5194/egusphere-egu26-3318, 2026.

Dense GNSS station networks and derived highly accurate 3D velocities offer the potential to image small-scale surface deformation fields. The robustness and sensitivity of the applied algorithm are crucial for the reliable detection of local and potentially small horizontal or vertical deformation zones. Based on a multivariate median estimation of strain rate and plate rotation, the imaging approach R3DI (Robust 3D Imaging) enables robust estimation, with the achieved spatial resolution dependent solely on the density of the station network and the local strain rate.

In this contribution we will discuss the impact of significance tests applied to the second invariant of the strain rate tensor and to the dilatational rate. The achievable spatial resolutions will be tested using synthetic deformation patterns (checkerboard tests) and real GNSS velocity fields in Europe. In a second step, the optimal grid spacing as trade-off between surface deformation recovery, density of the GNSS station network, and computational costs will be investigated.

How to cite: Männel, B. and Kreemer, C.: Assessing small-scale Surface Deformation zones in Europe, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8897, https://doi.org/10.5194/egusphere-egu26-8897, 2026.

It is well established that we can estimate the spatially continuous 3D velocity field of the Earth’s surface by combining InSAR and GNSS. One notable example is the VELMAP¹ approach which solves for the surface 3D motions in addition to reference frame alignment parameters and topography-correlated atmospheric noise. With this 3D surface velocity model, it is then a trivial step to convert to a strain map containing the spatial details of tectonic processes. One key challenge for our community is to extend such strain analysis as a function of time. This is because we know that tectonic velocities change significantly over human observable timescales, especially after moderate to large earthquakes and sometimes during interseismic periods.

In this EGU 2026 contribution, I will be showing the progress made in characterizing continental surface strain as a function of time by applying trajectory models² and a variation of the VELMAP approach to time series of InSAR displacements and GNSS coordinates. InSAR displacements come from the multi-interferogram time series processing of the European Ground Motion Service³, while the GNSS coordinates come from the European Plate Observing System GNSS community (EPOS-GNSS⁴).

References:

[1] Wang, H. and Wright, T.J., 2012. Satellite geodetic imaging reveals internal deformation of western Tibet. Geophysical Research Letters, 39(7).

[2] Bedford, J. and Bevis, M., 2018. Greedy automatic signal decomposition and its application to daily GPS time series. Journal of Geophysical Research: Solid Earth, 123(8), pp.6992-7003.  [https://github.com/TectonicGeodesy-RUB/Gratsid]

[3] European Ground Motion Service: Basic 2019-2023 (vector), Europe, yearly. European Union's Copernicus Land Monitoring Service information, https://land.copernicus.eu/en/products/european-ground-motion-service/egms-basic (Accessed on 15.01.2026). DOI: doi 10.2909/7eb207d6-0a62-4280-b1ca-f4ad1d9f91c3

[4] Fernandes, R., Bruyninx, C., Crocker, P., Menut, J.L., Socquet, A., Vergnolle, M., Avallone, A., Bos, M., Bruni, S., Cardoso, R. and Carvalho, L., 2022. A new European service to share GNSS Data and Products. Annals of Geophysics, 65(3), p.DM317.

How to cite: Bedford, J.: Tracking tectonic strain changes over time using InSAR, GNSS, and trajectory models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15224, https://doi.org/10.5194/egusphere-egu26-15224, 2026.

The response of seismic activity to external stress perturbations provides important insights into the physical processes governing earthquake triggering, nucleation, and rupture. Among various perturbations, annual hydrological loading is ubiquitous and offers an opportunity for investigating earthquake triggering processes. However, the physical mechanisms governing seismic responses to such periodic stress variations are not yet fully understood. Here, we explore the hydrologically induced crustal stress changes and their impact on seismicity in Greece by integrating a ~14-year earthquake catalog, GNSS time series, and GRACE-derived hydrological loading. We find that a significant variation in the rate of seismicity in Mainland Greece at annual time scale coincide with hydrological loading. The surface displacements predicted from GRACE-based loading models show good agreement with observed GNSS displacements, confirming that hydrological mass redistribution produces geodetically detectable crustal deformation. Our results demonstrate that hydrological loading produces geodetically observable surface deformation and induces stress perturbations that, although small in amplitude, modulate seismicity rates in Mainland Greece. We further find that historical earthquakes from 424 BC to 1903 (Mw > 5) exhibit a seasonal pattern, with peak seismicity occurring during the May–June period, consistent with the present-day seismicity modulation. The observed correlation among surface deformation, hydrological loading, and seismicity rates indicates that elastic stresses induced by hydrological loading play a key role in modulating seismic activity in Mainland Greece.

How to cite: Senapati, B. and Konstantinou, K.: Hydrologically induced crustal stress changes and their impact on seismicity in Greece, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3716, https://doi.org/10.5194/egusphere-egu26-3716, 2026.

The Mediterranean is a broad continental deformation zone at the junction between the African and Eurasian plates, where plate convergence is accommodated by distributed faulting, subduction, and transform systems associated with significant seismic and tsunami hazard. Despite the rapid densification of GNSS networks, how plate motion is partitioned into elastic strain accumulation versus aseismic deformation across this region remains unresolved or largely debated, particularly along offshore subduction interfaces, such as the Hellenic and Calabrian subduction zones, and the Dinarides-Albanides thrust front. We present a new regional kinematic block model constrained by an integrated horizontal GNSS velocity field obtained by merging multiple solutions to achieve dense, homogeneous spatial coverage. We implement three-dimensional geometries of the subduction interfaces and thrust systems within a unified block-model framework, allowing surface velocities to be jointly inverted for rigid block rotations, fault slip rates, volcanic deformation, and interseismic coupling (IC), enabling a regional-scale assessment of where elastic strain accumulates along major plate-boundary structures. The model is more detailed in the southern Adriatic and Ionian domains and across the Calabrian and Aegean arcs, including the Albanides–Dinarides margin. We present a first attempt toward a synoptic mapping of interseismic coupling for the Central Mediterranean, providing new insights into strain buildup and associated seismogenic potential of the involved structures. Low but non-zero coupling is inferred along the Hellenic subduction zone beneath Crete, while higher coupling patches are identified along the Cephalonia Transform Fault, and locally along the Albanian and Montenegrin coasts. These regions represent zones of enhanced elastic strain accumulation with implications for future earthquake and tsunami potential. IC along the Calabrian subduction zone is also investigated; however, its spatial distribution remains weakly constrained due to the lack of offshore geodetic observations. Our results highlight the critical role of the poorly defined Nubia–Apulia plate boundary in controlling block kinematics, strain partitioning, and coupling patterns in the Calabrian subduction zone.

How to cite: Nucci, R., Serpelloni, E., and Armigliato, A.: Block Kinematics and Interseismic Coupling of Major Subduction Systems in the Central Mediterranean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13054, https://doi.org/10.5194/egusphere-egu26-13054, 2026.

Natural stress magnitudes are a basis for informed decisions on the safety of underground activities, but they are incompletely constrained. As natural stresses are the consequence of tectonic processes, a physically consistent force model of the entire Eurasian lithosphere is used to constrain the intraplate stress field based on observed GNSS velocities.

We consider forces due to lateral gradients in gravitational potential energy, tractions by bounding plates, and mantle convective tractions. Our thin sheet model includes variable lithosphere thickness, major fault zones and viscoelastic geological provinces. We use a Metropolis-Hastings algorithm to sample fault resistive shear tractions, slip rates, viscosities and magnitudes of driving and resistive tractions.

Our median model fits observed velocities well in many regions. Trench suction along the Ryukyu and Hellenic forearcs in conjunction with resistive shear tractions on the Makran, Himalayan, Sumatra, Philippine and Nankai megathrust reproduce the complex observed velocities in these regions. However, significant misfit remains in other regions. Fault slip rakes and rates agree with observations along most fault zones. The satisfactory fit in Western Europe can be attributed to plate boundary tractions from Nubia convergence.

Some model parameters are well constrained. Low resistive shear traction rates (<3 MPa/m) are obtained for faults involved in the clockwise velocity rotation of the East Himalayan Syntaxis (Xianshuihe, Kunlun and Sagain). Higher resistive shear traction rates (>8 MPa/m) are estimated for faults that accommodate the India-Eurasia convergence (Karakorum, Main Pamir, and Altyn Tagh).

The median model matches maximum horizontal compressive directions from the World Stress Map fairly well. It shows high maximum shear stresses (50 MPa) in the Pannonian-Aegean-Anatolian region and Fennoscandian shield. Contrasting lithospheric thicknesses between the East European Craton and western Europe result in a stress contrast. Low maximum shear stresses (10 MPa) are estimated in the Pyrenees region, Ligurian-Provençal basin, Northern Apennines, Armoriscan massif, and the Massif central.

How to cite: Gutierrez Escobar, R. and Govers, R.: Tectonic stress estimates for Europe through Bayesian inversion of GNSS velocities, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11881, https://doi.org/10.5194/egusphere-egu26-11881, 2026.

The Northeast India plate boundary is a globally significant convergence zone where the Indian, Eurasian, and Burmese plates interact. This area comprises two tectonic regions: the Himalayan collision zone in the north and the Indo-Burma Ranges to the east. Numerous major earthquakes have struck this region, such as the 1897 Shillong event (Mw ≥ 8.1) and 1950 Assam-Tibet earthquake (Mw ≥ 8.6). Despite its high seismicity, a comprehensive depth resolved stress analysis, across the area remains poorly defined. This research fills the gap by performing seismotectonic stress analysis using 377 focal mechanism solutions (Mw ≥ 4.0) between 1950 and 2025 gathered from global earthquake catalogues and major published sources. To identify lateral and vertical variations in the stress field, the study region (85°E-98°E, 13°N-31°N) was spatially subdivided into 21 seismotectonic zones based on seismicity clustering, focal depth distribution, slab geometry, and structural boundaries. The Hardebeck-Michael method is applied for linear stress tensor inversion, resolving fault plane uncertainty by rotational optimization and Mohr-Coulomb instability criteria. Iterative inversion was performed with Shape ratio (R)=0-1 and Friction coefficient (μ)=0.2-0.8, retaining only solutions where misfit angles are less than 45°, ensuring accurate determination of principal stress axes and Maximum horizontal compressive stress (SHmax) directions. The results indicate a N-S compressional stress regime extending from the Eastern Himalayas to the Bengal Basin aligning with the India-Eurasia convergence. This stress state is associated with major tectonic structures including the Main Central Thrust (MCT), the Main Boundary Thrust (MBT), the Dauki Fault, and Brahmaputra Fault. However, the Indo-Burma Ranges show strong depth-dependent stress heterogeneity. Shallow to intermediate depth earthquakes exhibit arc-perpendicular extension (ENE-WSW to ESE-WNW), interpreted as a response to slab pull and upward convex bending of the subducting Indian lithosphere. Deep focus events (>70 km) indicate slab parallel N-S compression, which shows lithospheric shortening within the descending plate rather than solely due to India-Eurasia collision. A separate NE-SW compressional regime appears in the northern Indo-Burma arc and Sagaing Fault region, indicating stress-strain partitioning between Indian, Burmese, and Sunda plates. The clockwise rotation of SHmax along the arc from NNE-SSW in the inner segment to ENE-WSW in the outer foreland supports a transition from dextral strike slip motion to arc-perpendicular shortening. In the Shillong Plateau and Assam Valley, the coexistence of N-S and E-W compression indicates eastward extrusion of a crustal block, consistent with geodetic measurements and borehole breakout results. The results indicate that the stress regime is influenced not only by India-Eurasia convergence, but also by slab geometry, crust-mantle interaction, and block extrusion processes. These insights will be helpful for seismic hazard assessment and tectonic modelling in one of the most seismically active complex convergent plate boundary zones.

How to cite: Ranjan, R., Shahabuddin, M., and Kumar Mohanty, W.: Stress regimes analysis in Northeast India, Indo-Burma Ranges: Stress field implications based on Moment Tensor solution data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6624, https://doi.org/10.5194/egusphere-egu26-6624, 2026.

The Pamir Range in Central Asia accommodates a significant portion of deformation resulting from the ongoing collision of India with Eurasia. The region hosts active faults that are fast-slipping and geomorphically well-expressed, and that have witnessed large- and moderate-magnitude earthquakes during the instrumental period. For example, the Vakhsh and Darvaz faults that bound the Pamir to the north and west, respectively, are characterized by some of the fastest slip rates in continental Asia (> 10 mm/year during Holocene time). Several large-magnitude earthquakes have been recorded within the Pamir, including the 1911 M 7.7 Sarez Lake and 2015 M 7.2 Sarez/Murghab earthquakes. These features and events present a natural laboratory in which to test fundamental questions regarding the nature of strain accumulation and release at collisional plate boundaries. Yet the region remains under-explored from both ground-based and remote sensing perspectives due to its relative inaccessibility, steep terrain, and seasonal changes in snow cover. In this study, we use 7 years of Copernicus Sentinel-1 satellite radar interferometry (InSAR) data processed using a combined permanent scatterer (PS) and distributed scatterer (DS) approach. This approach is more robust in the Pamir ranges where areas of low coherence (e.g., due to snow) can lead to errors in the timeseries displacement measurements.

We use the ground surface velocity maps (averaged over the 7-year observation period) computed from the InSAR data to explore tectonic strain accumulation and release patterns. Spatial patterns of deformation will better constrain the kinematics and relative activity of different faults in the region. Comparison of the geodetic data to paleoseismic earthquake records and offset geomorphic features will provide insights into the temporal behavior the fault network. These combined datasets will address questions including: What portion of the India-Eurasia strain budget is accommodated on mapped, throughgoing tectonic structures such as the Vakhsh and Darvaz faults? What effects have recent, large-magnitude earthquakes (e.g., along the Sarez-Karakul fault system) had on the interseismic strain accumulation rates of surrounding faults? Have the faults experienced significant changes in strain accumulation and release rates over time, as indicated by discrepancies between geodetic and geologic slip rates?

How to cite: Zinke, R., Metzger, S., Faccenna, C., Gomba, G., and Mollinnier, L.: Exploring tectonic strain accumulation and release patterns in the Pamir region using Sentinel-1 InSAR data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21446, https://doi.org/10.5194/egusphere-egu26-21446, 2026.

The Korean Peninsula provides a unique natural setting to investigate intraplate deformation driven by far-field Pacific and Philippine Sea plate forces. Despite its location along the nominally stable interior of the Eurasian Plate, the region hosts frequent seismicity and historical Mw ≥ 5.5 earthquakes, yet the spatial distribution and mechanisms of strain accumulation remain insufficiently constrained. Here we fuse multi-frame Sentinel-1 InSAR time series with dense GNSS observations (2017–2024) to produce a peninsula-scale, three-component surface deformation field. After rigorous frame corrections, GPS filtering, and removal of the Eurasia-fixed plate motion, the resulting velocity field reveals a sharp rheological and kinematic segmentation across the peninsula.

The fused horizontal field identifies a rigid western domain—the Gyeonggi Massif and western Okcheon Belt—with negligible residual motion, contrasted by a kinematically mobile southeastern domain (Yeongnam Massif and Gyeongsang Basin) showing coherent SW–WSW residual flow up to 3.5 mm/yr. Independent InSAR-derived vertical and E–W velocity components exhibit strong lateral gradients that correspond with mapped active faults and clusters of seismicity. Strain-tensor inversion indicates peninsula-wide ENE–WSW shortening, locally partitioned into dextral transpression along the Yangsan Fault System and distributed shear throughout the southeastern crust.

Integrating these geodetic observations with published crustal seismic-velocity models, we propose a rheology-driven strain-partitioning mechanism. The western peninsula is underlain by strong, felsic, low-Vp/Vs crust and acts as a continental backstop, whereas the southeastern block comprises weaker, mafic and magmatically modified crust that responds more readily to far-field compression. This lithospheric contrast explains the concentration of deformation, shear localization, and seismic strain accumulation within the southeastern block.

Our findings demonstrate that inherited crustal rheology—not block rotation alone—controls present-day intraplate deformation in Korea, offering a unified framework for understanding its seismicity distribution and improving seismic hazard assessment in slowly deforming continental interiors.

How to cite: Kandregula, R. S., Bae, S.-Y., Kim, J.-Y., and Kim, Y.-S.: Rheological Segmentation and Distributed Strain Partitioning in the Korean Peninsula Revealed by Fusion of InSAR–GNSS Velocity Fields, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-759, https://doi.org/10.5194/egusphere-egu26-759, 2026.

Long-term convergence across the Himalayan megathrust continues to pose a significant seismic threat to the adjoining Indo-Gangetic plains, one of the world’s most densely populated regions. Parts of the megathrust have not ruptured in the last 200 years and have been identified as seismic gaps. The Uttarakhand Himalayas are considered part of the central Himalayan seismic gap, and differing opinions exist on the strength of interseismic plate coupling along the Main Himalayan Thrust (MHT). This has led to varying assessments of the associated seismic hazards. The present study focuses on the kinematic status of the MHT in the Uttarakhand Himalaya using Global Navigation Satellite System (GNSS) data, along with Interferometric Synthetic Aperture Radar (InSAR) satellite imagery, to estimate the elastic strain accumulation. GNSS-derived horizontal displacements indicate a slip deficit of ~18 mm/year, with an MHT that is locked up to a width of ~115 km. ALOS-2 InSAR imagery shows interseismic vertical deformation with a peak uplift of 4–6 mm/year. Consideration of an Elastic Subducting Plate Model (ESPM) predicts well both horizontal and vertical displacement without introducing any artifacts. Both the GNSS and InSAR measurements indicate that the megathrust across the Uttarakhand Himalaya is highly coupled, and the accumulated strain energy is equivalent to one Mw 8.1 megathrust earthquake every 100 years.

How to cite: Panda, D., Yadav, M., Lindsey, E. O., and Rao, G. S.: Evidence of strong plate coupling in the Uttarakhand Himalayas: Constraints from GNSS and ALOS-2 InSAR observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4678, https://doi.org/10.5194/egusphere-egu26-4678, 2026.

The 2025 M_W 7.0 Dingri earthquake in southern Tibet provides a unique opportunity to investigate normal-faulting mechanisms within an active rift zone. By integrating geodetic (GNSS and InSAR) and field observations, we investigate the event’s interseismic and coseismic deformation and quantify the impact of the 2015 M_W 7.8 Gorkha earthquake. Our principal findings are: (1) The epicentral extensional strain rate is (1.5 ± 0.2) × 10^-8/yr, notably lower than in the northern aftershock zone, indicating strain partitioning. (2) The coseismic slip model reveals a graben structure formed by two near N-S striking normal faults, with a maximum slip of 4.1 m and a seismic moment of 4.2×10¹⁹ N·m. (3) Field measurements confirm a segmented surface rupture, where the central segment’s vertical slip (2.1–2.2 m) aligns precisely with the InSAR-derived Line-of-Sight deformation maximum (2.04 m), validating the geodetic model. (4) Critically, deformation analysis demonstrates that the 2015 Gorkha earthquake significantly promoted the rupture of the Dingri earthquake, potentially accelerating its seismic cycle by ~20 years. This event exemplifies rift propagation along the Shenzha-Dingjie system and offers crucial insights into post-seismic stress transfer, rift evolution, and deep crustal processes in southern Tibet.

How to cite: Guo, N.: Deformation Process and Mechanism of the 2025 Ms 6.8 Dingri Earthquake in Southern Tibet constrained by GNSS and InSAR, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4673, https://doi.org/10.5194/egusphere-egu26-4673, 2026.

On February 6, 2023, two significant earthquakes (MW 7.8 and MW 7.6) impacted the Kahramanmaras region, rupturing 340 km of the East Anatolian Fault (EAF) and 150 km of the Cardak Fault (CF). To investigate the relationship between pre-event fault coupling and coseismic slip, a three-dimensional kinematic model comprising 38 blocks was developed, incorporating mesh-based representations of the EAF and CF. The model utilizes approximately 50,000 InSAR velocities and represents slip rates using distance-weighted eigenmodes. Coupling is estimated through bounded quadratic programming. Pearson and Procrustes analyses are employed to compare pre-event coupling with observed coseismic slip. Along the western, approximately 75% of the EAF rupture, correlation is higher than in the easternmost 25% (east of the Surgu fault at 38.2 degrees longitude). Alignment tests indicate that the offsets required to maximize correlation vary along the fault, suggesting imperfect alignment of kinematic model patterns. Consequently, the actual correlation between coseismic slip and interseismic coupling remains equivocal.

How to cite: Carrero Mustelier, E. and Meade, B.: Spatial relations between pre-event interseismic fault coupling and coseismic fault slip associated with the 2023 Turkey-Syria Earthquake sequence., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-220, https://doi.org/10.5194/egusphere-egu26-220, 2026.

Fault creep along Northern California strike-slip faults is widespread but strongly variable in space and time. This heterogeneity complicates seismic-hazard models that assume steady interseismic coupling derived from kinematically smoothed slip inversions. Commonly used steady-state, stress-controlled creep formulations (e.g., Johnson et al., 2022) assume stressing rate is either zero or positive and tend to favor gradual spatial creep rate variations and therefore do not easily represent abrupt locking-creep transitions. This is a problem for capturing abrupt changes in creep rate due to creep fronts intruding into the locked zone, generating locally negative stress-rate changes. Independent observations and physical arguments suggest that transitions from locked to creeping behavior can be sharp, for example, through progressive asperity erosion. Here, we apply the asperity-erosion, non-stationary asperity inversion framework of Johnson and Sherrill (2026) to jointly estimate interseismic creep rates and distributions of locked asperities on the central San Andreas, Hayward, and Maacama faults. We integrate GNSS velocities and surface creep rates from InSAR, creepmeter records, and alignment array measurements, following the observational dataset used by Johnson et al. (2022). Fault geometry is represented with triangulated dislocation surfaces in an elastic half-space and evaluated using a backslip formulation. Physics-regularized constraints on locking-stress evolution allow for creep fronts to erode locked regions through time. The models reproduce the observed along-strike variability in surface creep rates and fit the GNSS-derived velocities with residuals generally below 3 mm/yr. Compared with steady-state approaches, the non-stationary inversion resolves larger locked areas and quantifies their uncertainties, consistent with recent applications of similar physics-regularized frameworks in subduction and continental collision environments (Acharya et al., 2026, in prep.; Johnson & Sherrill, 2026, in prep.). Interseismic creep varies widely with depth along strike, reaching more than 30 mm/yr on actively creeping sections of the Central San Andreas faults. At the same time, we resolve discrete embedded eroding asperities that persist at depths of roughly 10-20 km on the Hayward and Central San Andreas faults. These asperities show high locking probabilities (>0.8) and host localized slip-deficit accumulation that is low across most creeping reaches but increases to about 20-30 mm/yr within locked patches and near segment transitions. On the Hayward Fault, our results indicate a persistent central low-slip patch accompanied by enhanced shallow creep to the north, consistent with mixed locked-creeping behavior. By explicitly mapping where and how slip deficit concentrates within dominantly creeping fault systems, this approach refines moment-deficit estimates relative to steady-state creep models. 

How to cite: Johnson, K. and Acharya, D.: Non-stationary Creep Modeling on the Northern California Fault Systems , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14372, https://doi.org/10.5194/egusphere-egu26-14372, 2026.

The lack of dense geodetic data near the trench of most subduction zones has made it challenging to accurately infer the pattern of interseismic deformation and, consequently, seismic and tsunami hazard estimates. Most kinematic coupling models ignore the effects of realistic boundary conditions and material properties. Here, we develop a 2D finite element model that incorporates realistic slab thickness and variable shear modulus values to quantify potential biases in these models.

We show that models that do not incorporate a finite slab thickness and variable material properties potentially under-estimate uncertainty about shallow creep rates compared to a more realistic model, while exhibiting a bias toward shallower locking, especially on megathrusts that lack offshore geodetic data. This observation potentially explains a reported gap between the inferred down-dip edge of kinematic locking and the location of episodic tremor and slip in Cascadia. These results highlight the importance of using realistic material properties when estimating the pattern of locking on megathrusts.

How to cite: Chong, J. H. and Lindsey, E.: Improving geodetic constraints on subduction zone coupling using accurate physics-based models with variable elastic properties , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5733, https://doi.org/10.5194/egusphere-egu26-5733, 2026.

The earthquake seismic cycle consists of the gradual accumulation of elastic energy at plate boundaries during the interseismic period, followed by its release mainly during the coseismic and postseismic stages. Therefore, for the evaluation of the seismic moment accumulate rate along the plate boundary, we need to quantify the processes and rheologies that control the interseismic surface deformation that is observed by GNSS stations. 

Recent studies have shown that during the late interseismic phase, the GNSS-observed surface velocities can be explained by a combination of aseismic fault slip and viscoelastic deformation in the upper mantle. These works also demonstrate that the vertical GNSS component is particularly crucial for distinguishing between different rheological processes acting at depth. However, most of these deformation studies neglect the thermal structure of the lithosphere-asthenosphere system and its impact on the viscoelastic deformation processes in the upper mantle, and especially within the lower continental crust.

To explore the impact of the temperature field, we investigate four subduction zones with contrasting incoming plate geometries, ages, dips, and convergence rates. We use 2D interseismic deformation models  based on the Finite Element Method (FEM) with temperature-controlled viscoelastic power-law rheology that represent the Nankai, Japan, Cascadia, and northern Chile subduction systems.  We systematically compare linear and nonlinear rheological formulations across distinct thermal and tectonic environments to assess their impact on the interseismic deformation process. Our preliminary results indicate that thermally-controlled nonlinear viscoelasticity can alter both the magnitude and spatial distribution of vertical interseismic deformation. In regions with higher temperatures in the continental mantle (e.g., Nankai, Japan, and northern Chile) the nonlinear rheology can produce uplift and subsidence patterns that diverge from those predicted by linear viscoelastic models. This highlights the sensitivity of vertical deformation to the chosen rheological formulation and suggests that models with linear viscoelastic rheology may not always be sufficient to represent the details of the processes controlling the interseismic deformation signal. However, when the interseismic deformation signal is small (e.g. Cascadia), the difference between linear and non-linear rheology is too little to be resolved within the GNSS data uncertainty. 

Furthermore, our models predict differences in vertical surface deformation of ~20% near the trench and exceeding 100% in the far-field back-arc region between linear and nonlinear viscoelastic models, regions where GNSS data are generally absent or where there is poor coverage. Here seafloor geodetic observations from acoustic-GNSS and pressure gauges are especially valuable, as they provide direct constraints on near-trench deformation that cannot be resolved from land-based networks alone.

In this context, our models can help in identifying regions where nonlinear rheological effects are most likely to be observable and therefore offer guidance for the strategic deployment of offshore geodetic instrumentation to better resolve interseismic deformation processes in subduction zones.

How to cite: Crisosto, L., Peña, C., Heidbach, O., Schmidt, D., Tassara, A., and Cotton, F.: Influence of temperature-controlled non-linear viscoelastic rheology on interseismic surface deformation signals in subduction zones., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5297, https://doi.org/10.5194/egusphere-egu26-5297, 2026.

Viscoelastic relaxation following large subduction earthquakes is known to last from years to decades, and affect the interseismic loading rate up to hundreds of kilometers in the trench perpendicular direction. Post seismic relaxation also generates a rotation pattern close to the edges of the ruptured asperity. Recently, several observations reported an accelerated loading rate coeval with megathrust ruptures, at along-trench distances from the epicenter of hundreds of kilometers.

Proposed models involved so far viscoelastic relaxation in the mantle wedge and the oceanic mantle, as well as a weak oceanic LAB layer. However those models often fail to explain simultaneously the amplitude and the spatio-temporal patterns of the observations.

Here, we perform 3D viscoelastic models of post seismic relaxation and explore a range of structural and rheological settings to investigate the mechanisms responsible for the complex loading variations observed. The tested scenarios include a Burgers rheology, viscosity contrasts between the continental and oceanic mantles, a weak LAB, and a low-viscosity layer overlying the subducting slab.

The relevance of these different models is evaluated by comparing their predictions with geodetic observations following several large earthquakes along the Chile–Peru subduction zone, allowing us to assess to assess the relative importance of the proposed mechanisms.

How to cite: Radiguet, M., Cresseaux, J., Lovery, B., Moreno, M., and Socquet, A.: Loading rate changes following megathrust earthquakes explored with viscoelastic models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18409, https://doi.org/10.5194/egusphere-egu26-18409, 2026.