Numerous high-resolution seismological and magnetotelluric observations depict a sharp and distinct Lithosphere-Asthenosphere Boundary (LAB) at the base of oceanic lithosphere, in some cases beneath the subducting slab. Many lines of evidence indicate ponding of partial melts at the LAB. A melt-rich oceanic LAB is expected to have a low viscosity to affect plate motion, subduction, and earthquake deformation. Therefore, it is important to seek direct geodetic evidence for the rheological weakness of the LAB and its effects on deformation. Here we summarize our recent progress in finding the evidence. (1) Immediately after several recent large subduction earthquakes (e.g., the 2011 Mw=9 Tohoku-oki and the 2010 Mw=8.8 Maule) in the Japan-Kuril and Chile subduction zones, GNSS observations show enhanced landward motion (ELM) of coastal areas 100s of km outside the rupture area. Using 3-D viscoelastic finite element models, we explained the postseismic ELM in terms of mechanical decoupling of the subducting slab from the underlying asthenosphere due to a low-viscosity LAB (Sun et al., 2024). The ELM observation is thus considered the first geodetic evidence for a weak LAB beneath subducting oceanic lithosphere. Assuming a thickness of no more than 10 km for the LAB, key characteristics of the observed ELM can be explained to first order by an LAB viscosity of no more than 5e16 Pa s, lower than typical mantle viscosities by 2-3 orders of magnitude. (2) In a more detailed investigation of the postseismic deformation following the 2011 Tohoku-oki earthquake, constrained by extraordinarily dense onshore and offshore (seafloor GNSS/Acoustic) geodetic measurements, we find that both near-field deformation and the more distant ELM can be optimally explained by having a thin (~5 km) and low-viscosity (~5e16 Pa s) LAB down to a depth of ~120-150 km. Our geodesy-based research adds a new dimension to the geophysical studies of the LAB and contributes to understanding the origin, spatial distribution, and consequence of the ponded partial melts.
Sun, T., Wang, K., & He, J. (2024). Geodetic signature of a weak lithosphere-asthenosphere boundary in postseismic deformation of large subduction earthquakes. Earth and Planetary Science Letters, 630, 118619, https://doi.org/10.1016/j.epsl.2024.118619
How to cite: Sun, T., Wang, K., He, J., Tomita, F., Iinuma, T., Hino, R., Kido, M., and Ohta, Y.: A Thin and Weak Lithosphere-Asthenosphere Boundary (LAB) Beneath the Oceanic Lithosphere and its Effects on Subduction Earthquake Cycle Deformation , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13084, https://doi.org/10.5194/egusphere-egu25-13084, 2025.
A viscoelastic deformation cycle at subduction zones has been revealed following the surge of great megathrust earthquakes in the early 21st century. This cycle is broadly divided into inter-, co-, and post-seismic phases, constrained by deformation data collected before, during, and after these earthquakes. However, the framework for understanding the longer term earthquake-cycle process remains unclear, particularly from the early postseismic to the late interseismic phases, primarily due to the lack of observations covering these century-long periods.
Building on previous work, we have demonstrated that landward viscoelastic relaxation driven by megathrust locking is necessary to produce the long-wavelength late interseismic deformation patterns commonly observed at global subduction zones. Using the unique century-long leveling data combined with contemporary GNSS observations in southwest Japan, we further propose that a short-wavelength deformation emerges during the early interseismic phase, eventually evolving into a long-wavelength pattern.
Incorporating early postseismic offshore observations, we synthesize an updated earthquake-cycle framework featuring four detailed phases following a megathrust earthquake. This refined framework supports a general model capable of reproducing deformation patterns across all phases. The model underscores two fundamental processes common to different subduction zones and phases of the earthquake cycle: cyclical stick-slip behavior along the megathrust and associated landward-seaward viscous mantle flow.
As a further advancement, this model simulates continuous horizontal and vertical deformation in space and time, revealing three critical spatiotemporal data gaps at global subduction zones. By predicting deformation patterns at various subduction zones, including those vulnerable to global sea-level rise, the model provides valuable guidance for future instrumentation planning to fill the data gaps and offers insights into potential breakthroughs in addressing key challenges in earthquake-cycle research.
How to cite: Li, S.: Toward an Updated Earthquake-Cycle Framework at Subduction Zones: Evidence, Processes, and Implications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5498, https://doi.org/10.5194/egusphere-egu25-5498, 2025.
Upper-plate deformation during the subduction zone seismic cycle is classically modeled as elastic, assuming the only non-reversible strain occurs on the megathrust. However, recent geomorphological studies indicate a slow build-up of distributed deformation across the upper plate over hundreds of thousands of years, with a spatial distribution that bears similarities with the interseismic strain field (e.g., Meade, 2010; Saillard et al., 2017; Malatesta et al., 2021). This suggests that non-reversible strain somehow related to seismic cycle deformation accumulates over hundreds of cycles. Oryan et al. 2024 recently suggested that portions of the upper plate could be brought to brittle failure during the interseismic period, manifesting as diffuse seismicity. Extrapolating the cumulative displacements due to this seismicity over many cycles further yielded patterns of surface uplift consistent with geomorphological observations, and correlating with the megathrust locking state. It did not, however, explicitly tie the occurrence of brittle failure to the rheological properties of the upper plate.
In this work, we investigate the hypothesis that the accumulation and release of elastic deformation between and during earthquakes can produce unrecoverable deformation, leaving a distinct signature in subduction relief. We use the commercial finite element code Zset (http://zset-software.com/) to simulate multiple cycles of loading and unloading of a wedge-shaped upper plate domain imparted by interseismic megathrust locking and coseismic slip. We model the upper plate as a Bingham elasto-visco-plastic material where irreversible viscous deformation can be activated wherever a certain yield stress threshold is exceeded. This typically occurs over the area where the megathrust transitions from fully locked to fully creeping during the interseismic phase. As a result, small increments of irreversible strain accumulate at each cycle, which manifests as persistent surface uplift above the downdip end of the locked portion of the megathrust. We perform a parametric study to examine the relationships between relief development, the plastic strength of the upper plate, and the coupling state of the megathrust. This provides a blueprint for assessing how locking patterns may become encoded in subduction landscapes, and how persistent these patterns may be.
How to cite: Boulze, H., Olive, J.-A., Jolivet, R., Oryan, B., Malatesta, L., and Garaud, J.-D.: Non-recoverable strain during the megathrust seismic cycle, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5995, https://doi.org/10.5194/egusphere-egu25-5995, 2025.
Geodetic imaging of interseismic coupling in subduction zones enhances our understanding of seismic potential and hazard assessments, particularly in low-seismicity regions where tectonic risks may be underestimated or remain unrecognized. This study focuses on the Western Makran Subduction Zone (WMSZ), where the Arabian plate converges with the Eurasian plate. The WMSZ shows no significant thrust events at shallow depths, with most seismicity occurring at intermediate depths within the downgoing plate. Our approach begins with isolating the interseismic deformation signal, through an InSAR time series analysis method that targets the estimation and filtering of atmospheric effects. Then we utilize the corrected deformation rates to estimate the spatial distribution of interseismic coupling in the (WMSZ). This approach employs Bayesian inference for modeling interseismic coupling without imposing rigid smoothing constraints, allowing for improved model flexibility to capture localized variations in coupling distribution. The results reveal a partially locked zone in the WMSZ, notably at intermediate depths (35-40 km) beneath the southern Jazmourian plain. This area coincides with a cluster of moderate-magnitude earthquakes observed at approximately 40 km depth. Furthermore, pre-event coupling was detected in the region affected by the Mw 5.1 earthquake of March 5, 2024 (Fanuj). The presence of dip-elongated partially locked zones suggests the potential existence of local asperities along the subducting slab at intermediate depths, which may have significant implications for seismic hazard assessment in the WMSZ. These findings provide a basis not only for understanding the seismic potential in WMSZ but also offer insights applicable to other subduction zones, advancing methodologies that enhance geodetic monitoring and risk assessment in tectonically similar environments.
How to cite: Sobouti, A., Samiei-Esfahany, S., Sharifi, M. A., Abolghasem, A., Bahroudi, A., and Friedrich, A.: Partial coupling in low-seismicity subduction areas: an example of the western Makran subducrion zone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18246, https://doi.org/10.5194/egusphere-egu25-18246, 2025.
Continental rift systems are characterised by spatial and temporal changes in the style (distributed vs. focused), location and mechanisms (magmatic vs. tectonic) of plate spreading. Understanding the long-term evolution of continental rift systems thus requires investigation of magmatic and tectonic processes across the spatial and temporal scales. However, this understanding is limited by relatively short temporal coverages of geophysical techniques and by spatially discontinuous geological datasets. Detailed maps of rift structures (i.e., tectonic faults), combined with independent geophysical and geological observations are key for a thorough view on the long-term evolution of strain during rifting.
In this study, we developed a novel method for the automatic extraction of faults and the calculation of time-averaged strains using Digital Elevation Models. We extended the Python-based Fault Analysis Toolbox (Fatbox) developed by Wrona et al. (2022) by implementing new filters, and building up a novel workflow for analysing fault-related deformation, such as the horizontal extension and the second invariant of strain. In Fatbox, the extraction of linear elements, such as faults, is performed through edge detection algorithms that can be applied on several type of data (e.g., seismic profiles, analogue and numerical models, and DEMs). Faults are then distinguished from noise using a normalized scale-dependent linearity filter that considers the area covered by linear elements. Dense displacement measurements are finally obtained at the scale of individual fault-scarp portions and converted to maps of strain or horizontal extension. A comparison with manually mapped datasets indicate that our method successfully resolves 93.4% of the total strain.
We applied this method to investigate a ~330 x 275 km-wide area in the Afar rift (East Africa), the locus of the spreading of Nubian, Arabian and Somalian plates. Rifting in Afar began approximately 31 Myrs ago after the impingement of a mantle plume, the eruption of flood basalts (Stratoid Series), and is currently accommodated along three main rift branches. The Stratoid series has covered fault scarps, which resets fault scarps and thereby provides an essential time marker for our strain analysis.
We combined our data with literature rock dating and geodetic measurements to reconstruct the evolution of the rift during the last 4.5 Ma and its relationship with tectonic and magmatic activity. We showed that the margins of the central Afar rift have been abandoned, and rifting processes have migrated toward todays axis where increased strain rates are likely due to magmatic emplacement. A northwest-directed increase of strain suggests a progressive migration of the rifting process in the same direction, responding to the Danakil block rotation. Conversely, the southern portion of Afar shows two systems of cross-cutting faults that respond to different co-acting tensional forces induced by the separations of the Arabian and Somalian plates from Nubia (Maestrelli et al., 2024).
References
Wrona, et al. (2022) Fatbox - Fault Analysis Toolbox, https://doi.org/10.5880/GFZ.2.5.2022.002
Maestrelli, et al. (2024). Reconciling plate motion and faulting at a rift-rift-rift triple junction, Geology, 1–5, https://doi.org//10.1130/G51909.1
How to cite: La Rosa, A., Gayrin, P., Brune, S., Pagli, C., Muluneh, A. A., Tortelli, G., and Keir, D.: Combined automatic fault mapping and geodesy to investigate the spatial and temporal evolution of tectonic strain across time scales: an application to the Afar rift (East Africa), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4458, https://doi.org/10.5194/egusphere-egu25-4458, 2025.
We observe active seismicity and crustal deformation in subduction zones. Since earthquake occurrences are closely related to strain accumulation, it is important to accurately estimate a strain-rate field. Many studies have estimated spatially continuous strain-rate fields from spatially sporadic geodetic data such as GNSS (Global Navigation Satellite System). However, localized strain rates near fault zones have tended to be underestimated, because most studies have applied a smoothness constraint (e.g., Okazaki et al., 2021, EPS). To overcome this difficulty, we introduce sparse modeling into the estimation of a strain-rate field. In this study, for simplicity, we consider the anti-plane strain problem.
We firstly express a velocity field by the superposition of cubic B-spline functions. Then, considering that a strain-rate field is smooth in most areas but can change abruptly in a narrow zone such as a fault zone, we impose both the sparsity constraint and the smoothness constraint of strain rates, which are expressed by the L1-norm and the L2-norm of the second derivatives of the velocity field, respectively. The relative weights of these terms are specified by two hyperparameters; the optimal values of which are determined by using the leave-one-out cross-validation method. We obtain the optimal values of the expansion coefficients of the cubic B-spline functions by minimizing the objective function, which consists of the terms of data fitting, the sparsity constraint, and the smoothness constraint.
To investigate the validity and limitation of the proposed method, we conduct synthetic tests, in which we consider an anti-plane strain problem due to a steady slip on a buried strike-slip fault. As a result, we find: (1) regardless of the locking depth of the fault, the proposed method reproduces localized strain rates near the fault with almost equal or better accuracy than the L2 regularization method, which imposes only the smoothness constraint, (2) the advantage of the proposed method over the L2 regularization method is clearer when fewer observation points are available, and (3) the proposed method can be applied when observation errors are small.
Next, we apply the proposed method to the GNSS data across the Arima-Takatsuki fault zone, which is one of the most active strike-slip faults in Japan. The proposed method estimates about 1.0×10-8/yr faster strain rates near the fault zone than the L2 regularization method, which corresponds to a 20-30% greater strain-rate concentration. The faster and more concentrated strain rates result in the estimation of a shallower locking depth. Fitting the analytical solution to the estimated strain-rate profile, we obtain the optimal values of locking depth and steady slip rate as 11 km and 4 mm/yr for the proposed method, while 17 km and 5 mm/yr for the L2 regularization method. Since the former is closer to the depth of D90, 12-14 km (Omuralieva et al., 2012, Tectonophysics), above which 90% of earthquakes occur, this result suggests that the proposed method estimates a more realistic locking depth than the L2 regularization method.
How to cite: Nozue, Y. and Fukahata, Y.: Geodetic data inversion to estimate a strain-rate field by introducing sparse modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4167, https://doi.org/10.5194/egusphere-egu25-4167, 2025.
The development of geodetic tools, such as Interferometric Synthetic Aperture Radar (InSAR), has revolutionized our exploration of earthquake physics and the assessment of seismic hazard. Over the past 20 years, InSAR has been increasingly used to determine the interseismic strain rate across major seismogenic faults. Strain derived from geodetically mapped crustal deformation rates serves as an indicator of a fault’s earthquake potential, in alignment with classical elastic rebound theory. However, InSAR observation periods are often relatively short compared to much longer large earthquake recurrence intervals. This raises questions about how well geodetic strain rates represent the long-term strain accumulation on faults. It is therefore critical to understand how strain rate evolves during the interseismic period.
We observe the interseismic period prior to the 2021 Mw 7.4 Maduo Earthquake: a left-lateral strike-slip earthquake that ruptured a slow-moving fault approximately 70 km south of the major block-bounding East Kunlun fault in the Eastern Tibetan Plateau. Using six years of Sentinel-1 data, we explore the temporal evolution of strain rate over time. We derive eastward velocity and maximum shear strain rate for the six-year period prior to the Maduo earthquake, before segmenting the time-series and analysing strain rate with a two-year moving time window. Our results indicate that the geodetically derived strain rate may not be constant over the interseismic period, implying that strain may not accumulate at a fixed rate in the seismogenic crust. Additionally, strain rate on the seismogenic fault does not appear to accelerate prior to the Maduo earthquake, at least on the timescales resolvable by InSAR used in this study.
How to cite: Rutland, C., Bie, L., Johnson, J., Ou, Q., and Mildon, Z.: Temporal evolution of strain rate before the 2021 Mw 7.4 Maduo Earthquake. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-865, https://doi.org/10.5194/egusphere-egu25-865, 2025.
Tectonic deformation in northern Central America, driven by the interactions between the Cocos, Caribbean, and North America plates, is accommodated by the Motagua and Polochic left-lateral faults, grabens located south of the Motagua Fault, the Middle America subduction zone, and right-lateral faults along the Middle America volcanic arc. Major earthquakes associated with these faults include the 1976 MW 7.5 Motagua and the 2012 MW 7.5 Champerico events.
To investigate current deformation in this setting, we employed a permanent and distributed scatterers (PSDS) InSAR technique (Adam et al. 2013; Ansari et al. 2018; Parizzi et al. 2020), using Sentinel-1 radar images (2017-2022) along two ascending and two descending tracks covering most of Guatemala, El Salvador and western Honduras. The resulting time series, corrected for tropospheric and ionospheric phase delays, and solid earth tides, are referenced to GNSS data and decomposed into one linear term, dominated by tectonics, and two seasonal terms.
We present the line-of-sight (LOS) velocity fields for the linear term, highlighting spatial variations across key faults. To emphasize the added value of InSAR compared to GNSS, we decompose the LOS velocity fields into horizontal and vertical components. We use the Bstrain code (Pagani et al. 2021), based on a Bayesian inversion method using a transdimensional approach, to interpolate the GNSS velocity field to align with the InSAR data resolution, providing a probability density function of GNSS north and east velocities, their median values and azimuths. The horizontal component of the InSAR velocity field is computed using these azimuthal directions or as an eastern component, assuming that the northern component is constrained solely by GNSS.
Our results show good agreement with GNSS data and associated elastic block models for the region (Ellis et al., 2019; Garnier et al., 2021), highlighting (1) the North America and Caribbean plates' relative motion, accommodated primarily by the Motagua fault and secondarily by the Polochic fault, (2) east-west extension of the Caribbean plate (3) right-lateral slip along the Mid-America volcanic arc. Additionally, the unprecedented high resolution InSAR data uncovers a ~40 km-long creeping section along the Motagua fault. We discuss the along-strike creep variations relative to local geology and the slip distribution of the 1976 earthquake. InSAR data also helps investigate how extension is partitioned across multiple active structures in the Caribbean plate’s wedge. Finally, the InSAR velocity fields reveal velocity variations along the coast, previously unresolved by GNSS, suggesting coupling variations along the subduction interface.
Adam, et al. (2013). Proc. IEEE Geosci. Remote Sens. Symp., doi:1857-1860.10.1109/IGARSS.2013.6723164
Ansari, et al. (2018). IEEE Transactions on Geoscience and Remote Sensing, doi:10.1109/TGRS.2018.2826045
Ellis, A., et al. (2019). Geophys. J. Int. https://doi.org/10.1093/gji/ggz173
Garnier, B., et al. (2021). Geosphere. https://doi.org/10.1130/GES02243.1
Pagani, C., et al. (2021). Journal of Geophysical Research: Solid Earth. https://doi.org/10.1029/2021JB021905
Parizzi, A., et al. (2020). IEEE Transactions on Geoscience and Remote Sensing. doi:10.1109/TGRS.2020.3039006
How to cite: Cosenza-Muralles, B., Lasserre, C., Gomba, G., De Zan, F., DeMets, C., Métois, M., and Lyon-Caen, H.: Investigating continental-scale deformation and fault coupling in northern central America (Guatemala, El Salvador, Honduras) using Sentinel-1 InSAR , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13626, https://doi.org/10.5194/egusphere-egu25-13626, 2025.
Posters on site: Fri, 2 May, 10:45–12:30 | Hall X1
The Longmenshan Fault Zone forms the eastern boundary of the Bayan Har Block in China and results from the block’s eastward movement being strongly resisted by the South China Block. In 2008, the Wenchuan earthquake ruptured the central-northern segment of the fault zone. Five years later, the Lushan earthquake struck the southern segment. The epicenters of these two events were approximately 90 km apart, with an unruptured section, known as the Dayi Gap, located between the two fault zones.
Previous research has explored the pre-earthquake deformation characteristics of the Longmenshan Fault Zone. However, due to sparse observational data prior to the Wenchuan earthquake, the resolution of fault locking state models was limited. This study addresses the issue of data sparsity by using the Least Squares Collocation (LSC) method to enhance the existing dataset, enabling a more detailed inversion of the fault’s pre-earthquake locking state. The results provide partial explanations for the co-seismic rupture patterns of the Wenchuan earthquake and show good agreement with the distribution of pre-Wenchuan earthquakes of magnitude 3 and above in the region.
Based on the findings, future earthquakes are more likely to occur south of the Dayi Gap, with the fault potentially rupturing into the gap itself. Additionally, the results demonstrate that the LSC method can effectively densify sparse surface deformation data. While the resolution may not match that of inversions based on dense, high-quality observations, the method successfully identifies the main locked zones of the fault.
How to cite: Wang, Q., Xu, X., Zhao, J., and Jiang, Z.: Crustal Deformation And Seismic Hazard of Longmenshan Fault Zone With Limited Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2659, https://doi.org/10.5194/egusphere-egu25-2659, 2025.
The Sürgü-Cardak fault ruptured ~9 hours after the Mw 7.8 mainshock on the East Anatolian Fault zone (EAFZ) during the 2023 Kahramanmaraș earthquake sequence. With a moment magnitude Mw 7.5, involving up to 11 m slip, this event featured comparable slip magnitudes as the mainshock. Published strain rate fields based on geodetic observations do show strain accumulation around the EAFZ, but strain accumulation around the Sürgü-Cardak fault appears to be absent. We therefore reexamine the GNSS-based interseismic strain rate field to see whether, or not, the Sürgü-Cardak fault accumulated significant slip deficit prior to the earthquake.
We use GNSS data from eastern Anatolia. To estimate strain rates and their uncertainties in regions that experience both fast and slow deformation rates, we employ a tailored stochastic interpolation technique. With this method we show that the strain rate peaks around the Sürgü-Cardak fault. To better interpret 2D strain rate fields around faults, we develop a novel decomposition of the strain rate tensor and its covariance, that allows us to estimate the strain rate in a fault-oriented frame. The decomposition method is analogous to descriptions of deformation in structural geology, and allows for direct comparison with slip types from focal mechanisms. Not only does the strain rate peak around the Sürgü-Cardak fault exceed the uncertainty, the direction of interseismic slip deficit accumulation is also compatible with the coseismic slip direction.
We conclude that interseismic slip deficit accumulation on the Sürgü-Cardak fault was previously missed. Coseismic slip is consistent with the loading history. The Sürgü-Cardak earthquake thus has most likely been triggered by the mainshock.
How to cite: Broerse, T., Ozbakir, A. D., and Govers, R.: Did the Mw 7.5 Sürgü-Cardak Event Occur During the 2023 Kahramanmaraș Sequence Without Prior Slip Deficit?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4589, https://doi.org/10.5194/egusphere-egu25-4589, 2025.
The Hengduan Mountains in the southeastern Tibetan Plateau develop one of the most complex active fault systems on Earth. GPS measurements and seismic data reveal that these fault systems drive present-day eastward crustal transport and clockwise rotation around the Eastern Himalayan Syntaxis. In this study, we investigate regional block rotation kinematics based on fault slip displacement, spacing, and the orientations of block-bounding strike-slip faults in the Hengduan Mountains. The results of block rotation rates, angles, and rotation radius are then comprehensively analyzed, combined with existing paleomagnetic, geodetic, and multi-timescale slip rate data. Our findings highlight the influence of the development of block-bounding faults and associated sub-blocks on regional block rotation deformation during the southeastward growth of the Tibetan Plateau. The Late Cenozoic block rotation of the Chuandian Block in the Hengduan Mountains exemplifies the transition from a single to a multi-block system, which has critically influenced the spatiotemporal distribution and rates of strike-slip faulting processes along block boundaries. Our study reveals the possible evolution processes of block rotation in regions dominated by large-scale strike-slip fault systems, such as the Hengduan Mountains in southeastern Tibet.
How to cite: Li, F., Willett, S. D., and Shi, X.: Multiscale Analysis of Fault Systems in the Hengduan Mountains: Implications for Block Rotation Processes in Southeastern Tibet, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5019, https://doi.org/10.5194/egusphere-egu25-5019, 2025.
Eastern Taiwan is located in the transition zone where the Philippine Sea plate subducts beneath the Yangtze plate along the Ryukyu Trench and collides with the continental margin along the Longitudinal Valley suture zone. These complex tectonic interactions have led to frequent and devastating earthquakes. The GNSS-acoustic measurements in the southernmost Ryukyu margin characterize an eastward growing convergence rate from 92 mm/yr offshore Hualien to 123 mm/yr near the Gagua Ridge, suggesting a capability of hosting Mw 7.5-8.4 earthquakes. Along the Longitudinal Valley, the east-dipping Longitudinal Valley fault and the west-dipping Central Range fault form a dual-verging conjugate suture zone. The GNSS velocities relative to the Yangtze plate generally decrease northwestward from the Coastal Range, through the Longitudinal Valley, to the Central Range. Along the Coastal Range, GNSS velocities range from 67 to 72 mm/yr between Taitung and Fengbin. This rate then drops significantly to approximately 38 mm/yr at Shoufeng and further decreases to 24 mm/yr near Hualien. The shortening rate between the east coast and the Longitudinal Valley decreases northward, from 30 mm/yr between Taitung and Guangfu to approximately 10 mm/yr near Hualien. Additionally, shallow crustal earthquakes along the east coast indicate a significant clockwise rotation of P and SH axes from convergence-parallel (N120˚) south of Fengbin to about (N140˚) near Hualien. The orientations of GNSS velocity exhibit a similar clockwise rotation of 10˚ from Taitung to Hualien as well. These observations suggest a spatial change in seismotectonic stress as approaching the junction between the subduction of the Ryukyu Trench and the collision of the Longitudinal Valley suture zone. A significant portion of the accumulated strain is likely accommodated by offshore faults near Hualien, as evidenced by frequent large offshore earthquakes and interseismic subsidence along the Hualien coast. Continuous investigation of GNSS interseismic velocity, seismic activity, the long-term uplift rates of marine terraces, and coseismic uplift during historic earthquakes are crucial for revealing the long-term seismic hazard of eastern Taiwan.
How to cite: Hsu, Y.-J., Tung, H., Chen, H.-Y., Wang, Y., Lin, Y., and Tang, C.-H.: Unraveling crustal deformation and seismogenic signatures in eastern Taiwan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5285, https://doi.org/10.5194/egusphere-egu25-5285, 2025.
Steady-state secular motions of the Earth’s surface (i.e., motions not influenced by transient processes such as earthquakes or volcanic eruptions) reflect plate boundary interseismic strain accumulation, plate motions, post-glacial rebound, sea-level rise, or dynamic topography. Over the past three decades, the expansion of Global Navigation Satellite System (GNSS) networks has densified the number and spatial coverage of station position and velocity observations with improved measurement accuracy. In this study, we focus on horizontal motions and aim to create the most up-to-date, spatially dense velocity field. We gather secular velocities at ~35000 unique GNSS stations distributed globally, covering both tectonically active and stable regions. Roughly 18000 velocities are determined at the Nevada Geodetic Laboratory (NGL) from time-series of mostly continuous GNSS observations. However, the spatial coverage of the NGL velocity solution suffers from the absence of available RINEX (Receiver Independent Exchange Format) data in places such as most of the India-Eurasia collision zone. We therefore compile about 17000 additional continuous and campaign GNSS velocities from ~400 published studies and transform these auxiliary velocities onto the NGL velocity solution through a least-squares inversion. For several large earthquakes with sufficient GNSS observations (e.g., 2004 M9.1 Sumatra, 2011 M9.1 Tohoku, 2010 M8.8 Maule, and others), we correct GNSS time-series and auxiliary velocities for postseismic viscoelastic deformation using forward modeling based on a gravitational spherical Earth with a 1D rheological structure. For other earthquakes, we correct the GNSS time-series by removing the postseismic time-series fitted by an empirical logarithmic function. Additionally, we develop and apply a velocity outlier detection and removal algorithm to generate our final global velocity database. Our velocity field is an update to the compilation from the 2014 Global Strain Rate Model (GSRM) and greatly extends the scope of existing global velocity solutions. Our new database will be used to produce the next GSRM and to provide a starting velocity field for future integration with InSAR analysis.
How to cite: Cheng, G., Kreemer, C., Klein, E., Young, Z., Argus, D., and Blewitt, G.: A New Global Database of Secular Horizontal GNSS Velocities, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7187, https://doi.org/10.5194/egusphere-egu25-7187, 2025.
The strike-slip faults of the Tibetan Plateau plays a crucial role in understanding the response of the continental lithosphere to the ongoing India-Eurasia collision and associated deformation. However, the slip rate along the East Kunlun Fault, particularly its eastern segment, remains contentious. In this study, we combine ascending and descending Sentinel-1A InSAR data with GNSS measurements to derive a high-resolution velocity field spanning from the Tuosuo Lake segment to the Maqin-Maqu segment of the East Kunlun Fault. We then apply a 2D elastic dislocation model (Savage and Burford, 1973) in conjunction with the Markov Chain Monte Carlo (MCMC) method to invert the fault slip rate. Our results reveal that the slip rate in the Tuosuo Lake segment of the East Kunlun Fault is 6.6–8.1 mm/yr, while in the section extending from Tuosuo Lake to the Anyemaqen Mountain, it ranges from 4.4 to 4.9 mm/yr. In the compressional step-over region at Anyemaqen Mountain, the slip rate decreases to 2.7 mm/yr. Further to the east, the slip rate gradually decreases from 4.7–5.9 mm/yr to 2.7 mm/yr in the Maqin-Maqu segment. The slip rate along the East Kunlun Fault exhibits a non-monotonic decrease from west to east, likely influenced by the uplift of Anyemaqen Mountain and the contribution of secondary faults on the southern flank of the fault system.
How to cite: Yu, P., Qiao, X., and Chen, W.: Slip Rate Variation Along the East Kunlun Fault (Tibet) From InSAR & GNSS Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8451, https://doi.org/10.5194/egusphere-egu25-8451, 2025.
Normal-faulting earthquakes in mountain ranges are key for studying the dynamics of mountain building. Two styles of high mountain extension have been observed: range-perpendicular and range-parallel. To date, range-parallel extension has only been reported in southern Tibet, limiting our ability to test different models for its dynamic cause. Here, we investigate a new example of range-parallel extension: the 2020 Mw 5.7 Humahuaca earthquake in the Andes of Argentina. We combine InSAR time-series and body-waveform seismology to constrain a source model for the earthquake and show it ruptured a new fault that cross-cuts Neogene fold-thrust belt structures and accommodates pure range-parallel extension. The hypocentre lies ∼70 km west of the Andes range front at 5 km depth. Thrust-faulting earthquakes on the Andes range front adjacent to Humahuaca have slip vectors parallel to topographic gradients and are oblique to Nazca-South America relative motion, consistent with the pattern expected for crustal flow in response to gravitational potential energy contrasts. Interseismic GPS velocities, however, are oblique to the range front and topographic gradients. These velocities may be accommodated by range-parallel shear, with normal faulting at Humahuaca potentially occurring in the step-over of a strike-slip fault or due to clockwise rigid block rotation, although geomorphic evidence is lacking. Notably, we do not see evidence for widespread ‘lateral escape’ in the Andes, as proposed for southern Tibet. In conclusion, range-parallel extension in the Andes may be the result of crustal flow under gravity or back-arc strike-slip faulting. Both models indicate the potential for moderate-magnitude earthquakes within the Eastern Cordillera, which are an overlooked source of seismic hazard .
How to cite: Orrego, S., Biggs, J., and Wimpenny, S.: Range-Parallel Extension in the Argentinian Andes: The 2020 Mw 5.7 Humahuaca Earthquake , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9208, https://doi.org/10.5194/egusphere-egu25-9208, 2025.
Megathrust earthquakes at subduction plate interfaces have been extensively investigated, with their quasi-repetitive nature well recognized, yet their long return periods and sparse historical records complicate global assessments of this regularity. Slow earthquakes occurring in the brittle-to-ductile transition zone demonstrate a complex interplay with large subduction earthquakes, though their roles in triggering or delaying significant events remain poorly understood. The periodicity of slow earthquakes, characterized by recurrence intervals ranging from months to years, has facilitated the creation of comprehensive seismic and geodetic event catalogues. Here, we investigate the behaviour of slow earthquakes and megathrust ruptures using integrated constraints from natural observations, numerical simulations under the rate and state friction model and laboratory-based experimental results. Focusing on the best instrumentally monitored and mature subduction zones, namely, Cascadia and Nankai, we identified a depth-dependent pattern in slip periodicity and a corresponding increase in cumulative tremor counts downdip from the trench. Our numerical simulations suggest a logarithmic dependency between recurrence time and loading velocity, consistent with the depth dependency of the tremor activities and associated slip-periodicity observed in these subduction zones. Moreover, the long-term aseismic slip distribution patterns of these subduction zones match with the model-predicted displacements for the corresponding loading velocities, which never exceed the down-dip plate motion at these subduction zones. Laboratory experimental results validate the link between recurrence time and loading velocity, establishing a connection between recurrence time and force drop as well. Further, analysis of seismic data of slow and megathrust earthquakes across major subduction zones worldwide underscores a consistent logarithmic inverse relationship between the recurrence times of these events and plate convergence rates. Our numerical simulation results and stick-slip laboratory experiment observations complement the naturally observed logarithmic behaviour of both megathrust and slow earthquakes. Integrating these insights from natural observations, numerical modelling, and experimental data, we finally argue a possible stress transfer mechanism from the slow earthquakes source zone to the adjacent megathrust earthquake segments and suggest that the slow earthquakes can be used as a possible proxy or “stress-meters” for large megathrust earthquakes and probably modulate the megathrust earthquakes in the seismogenic zone. Understanding the interplay between slow and megathrust earthquakes is crucial for seismic hazard assessment and enhances our ability to identify regions at risk of large seismic events and improve mitigation strategies.
How to cite: Ray, S., Kundu, B., Senapati, B., and Singh, A. K.: Decoding Earthquake Cycles: Plate convergence rates shape recurrence intervals in Subduction Zones , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10106, https://doi.org/10.5194/egusphere-egu25-10106, 2025.
The central-northern part of Greece (Northern Thessaly and Macedonia) is part of the active geodynamic regime of the Aegean (Eastern Mediterranean), occupied by numerous on land and offshore active tectonic structures. These are represented mostly by E–W to NE–SW striking normal dip-slip fault zones, documenting a dominant N-S to NW-SE oriented extensional stress field. Many of these structures are related to instrumentally recorded seismic events: the July 20, 1978 (Mw6.5) Thessaloniki, the December 21, 1990 (Mw6.0) Goumenissa, the May 13, 1995 (Mw6.5) Kozani – Grevena, and the March 3, 2021 (Mw6.3) Elassona – Tyrnavos earthquakes are typical cases of normal faulting. Our objective is to calculate crustal strain and link it to specific tectonic structures.
The strain estimation is based on satellite geodetic monitoring (GPS/GNSS) and the analysis of recorded raw data. With a rate of 30 s in a 24/7 operation, a dataset of 24 stations during a 7-year period of continuous monitoring (2008 – 2014) is compiled.
Regarding the geodetic data processing, it involves i) the triangulation method which combines geodetic data of three stations each time for calculating certain strain parameters (maximum horizontal extension, minimum horizontal extension, maximum shear strain and area strain) on each triangle barycenter (approximately, 150 different triangles were constructed for the study area), ii) the “VISR” method which is a Fortran-based code producing an interpolation scheme, and iii) a micro-blocking model for which the second invariant of strain rates is calculated.
Comparing the results of these methodologies, two distinct areas are highlighted: the western-central part, where low to medium values are documented, and the eastern part, which is characterized by higher values. The higher values can be related to active structures, documented in both areas; however, it is worth focusing on the eastern part, where the higher values are observed. Two major active faults/fault zones are noted: the E – W, dip-slip normal antithetic faults of Mygdonia basin, related to the 1978 Thessaloniki earthquake, the NW – SE dip-slip normal antithetic faults of Strymon basin and the E – W, oblique-slip Kavala-Xanthi fault zone. No recent seismic events are linked to these structures, while additionally the high strain rates indicate the potential strain charge. Moreover, it is worth noting that all structures above are adjacent to the North Aegean Trough, which is one of the most active strictures globally, as it is the prolongation of the North Anatolian fault in the Aegean Sea, and therefore they are directly affected.
How to cite: Lazos, I., Wang, J., Jiang, G., Sboras, S., Bedford, J., Pikridas, C., and Bellas, S.: Geodetic strain pattern analysis of northern-central Greece – Correlation to tectonically active structures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11377, https://doi.org/10.5194/egusphere-egu25-11377, 2025.
In recent years, numerous studies have focused on quantifying the variation of surface deformation to obtain estimates of interseismic locking and thus identify areas of high seismic risk. However, most of these works have used plate models with homogeneous physical properties.
In this study, heterogeneous plate models have been developed considering the geometry of the profile at 21°S in northern Chile, where a shortening of the deformation in the Andean backarc is observed. Variations in elastic and viscous properties have been incorporated into the different models to evaluate their effect on the propagation of the interseismic deformation observed at the surface.
The results indicate that heterogeneities in the areas near the plate interaction zone play a crucial role in surface deformation. Using real data showing an increase in bulk and shear modulus with depth, higher near-field deformation and lower far-field deformation are observed compared to a homogeneous viscoelastic model.
This study highlights the importance of incorporating heterogeneities in interseismic deformation models, as these can provide a better fit to surface measured deformation patterns and thus improve interseismic locking estimates.
How to cite: Leal, D., Tassara, A., Moreno, M., and Barra, S.: Role of elastic variations in the interseismic deformation of the Andean subduction margin: case of study at 21°S, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14112, https://doi.org/10.5194/egusphere-egu25-14112, 2025.
Studies have shown that the postseismic transient following the 2004 Parkfield earthquake is dominated by aftersllip. However, the studies are mainly focus on the horizontal deformation and ignore the vertical deformation. The focus of this study is the postseismic deformion in vertical caused by 2004 event. We examine the time series of 20 near San Andreas fault CGPS stations in the vicinity of the Parkfield segment to infer the time-dependent postseismic slip. We firstly use the time series to derive an afterslip distribution model for the Parkfield earthquake using only horizontal components, and compare the model’s agreement with the measured vertical deformation. The results show the migration of groundwater is the main reason for the vertical postseismic deformation.
How to cite: Tan, W., dong, D., and Chen, J.: The vertical postseismic deformation following the 2004 Parkfield earthquake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15361, https://doi.org/10.5194/egusphere-egu25-15361, 2025.
In this study, we seek to quantify bulk viscoelastic flow, afterslip and locking, within a rheological framework that ensures a consistent formulation of strain accumulation and release throughout the entire earthquake cycle. To achieve this, we use Bayesian inference in the form of an ensemble smoother with multiple data assimilation (ESMDA) to estimate geodynamic model parameters. In our earlier study, we successfully reproduced both interseismic and postseismic observations for the Tohoku margin including the 2011 earthquake using a 2D model (Marsman et al. 2025). Building on these insights, we extend our analysis to a 3D configuration.
We construct a 3D finite element seismic cycle model. We incorporate a priori information into the model, including a realistic geometry of slab and overriding plate, the temperature field, multiple asperities, and the observed coseismic slip distribution of the 2011 Tohoku-Oki earthquake. The model has a steady-state power-law rheology. Away from asperities, different parts of the megathrust respond by power-law viscoelastic relaxation, simulated by a thin low-viscosity shear zone, or instantaneous slip. By assimilating observations of 3D surface deformation, we constrain power-law flow parameters for both the asthenosphere and the megathrust. Specifically, we estimate the pre-exponent factor and the activation energy of the mantle wedge and oceanic mantle, as well as the pre-exponent factor and stress power of the shear zone using ESMDA.
We assimilate 3D GNSS displacement time series spanning from 1997 onwards. Preliminary results with actual GNSS data indicate that power-law flow parameters can be retrieved remarkably well and are consistent with estimates from laboratory experiments. The trade-off between the pre-exponent factor and activation energy hinders their individual estimation but does result in a well-constrained viscosity structure. Consistent with our 2D models, our 3D results demonstrate that enhanced landward motion near the rupture zone occurs postseismically without the need for a separate low-viscosity sub-slab layer. Instead, the release of elastic stresses accumulated interseismically beneath the oceanic plate significantly contributes to the observed offshore postseismic landward motion near the trench on the overriding plate.
How to cite: Marsman, C. P., Vossepoel, F. C., and Govers, R.: Towards a 3D Earthquake Cycle Model Powered by Data Assimilation for Northeastern Honshu, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16704, https://doi.org/10.5194/egusphere-egu25-16704, 2025.
We use a 2D mechanical model in the context of Bayesian inference to constrain the relative contribution of driving and resistive forces to observed stress directions and GNSS velocities in the Eurasia plate. Plate boundary tractions will be dependent on the relative velocity of the bounding plates. The finite element model includes major fault zones and viscoelastic geological provinces following Hasterok et al. (2022). Horizontal gravitational forces from lateral variations of gravitational potential energy are derived from the density model of Fullea et al. (2021). We use the Metropolis-Hastings algorithm to sample fault resistive shear tractions, viscosities, and magnitudes of horizontal gravitational forces, mantle convective tractions, and plate interaction tractions with adjacent plates. We discuss first results of marginal distributions of fault slip rates and rakes, vertical axis rotation rates, and horizontal stress magnitudes.
How to cite: Gutierrez Escobar, R. and Govers, R.: Numerical modelling of stresses and deformation in the Eurasian tectonic plate through Bayesian inversion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16972, https://doi.org/10.5194/egusphere-egu25-16972, 2025.
Hayes, G.P., Moore, G.L., Portner, D.E., Hearne, M., Flamme, H., Furtney, M., Smoczyk, G.M., 2018. Slab2, a comprehensive subduction zone geometry model. Science 362 (6410), 58–61. https://doi.org/10.1126/science.aat4723.
Nijholt, N. Simons, W.,Riva, R., Efendi, J. Sarsito, D., Broerse, T., 2024. Triggered and recurrent slow slip in North Sulawesi, Indonesia, Tectonophysics, 10.1016/j.tecto.2024.230416, 885, (230416)
Walpersdorf, A., Vigny, C., Subarya, C., Manurung, P., 1998. Monitoring of the Palu- Koro Fault (Sulawesi) by GPS. Geophys. Res. Lett. 25 (13), 2313–2316.
How to cite: Nijholt, N., Govers, R., and Simons, W.: How do plate boundaries talk to each other in North Sulawesi, Indonesia?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17060, https://doi.org/10.5194/egusphere-egu25-17060, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot 1
EGU25-9503 | Posters virtual | VPS23
Seismotectonics of the Intracontinental High Atlas Mountains, Morocco, Derived from Regional Seismic Moment Tensor Analysis: Insights into tectonics and stress regimes.Thu, 01 May, 14:00–15:45 (CEST) | vP1.22
This study investigates the present-day seismotectonic framework of the High Atlas Mountains, Morocco, with a specific focus on the area affected by the devastating Mw 6.8 Al Haouz earthquake of September 8, 2023. Leveraging a high-resolution seismic dataset encompassing over twenty moderate earthquakes (M 3.5-6.8) recorded by regional networks between 2008 and 2024, the research aims to refine earthquake locations and characterize the regional stress field. Initially located using P-wave arrival times, earthquake hypocenters were subsequently relocated using the double-difference method, which yielded more precise locations by minimizing travel-time residuals between pairs of events recorded at common stations. The high degree of agreement between the initial and relocated solutions validates the robustness of the location estimates. Notably, the observed seismicity is confined to shallow crustal depths, consistently shallower than 30 km, corroborating the shallow rupture observed for the Al Haouz earthquake, which occurred at a depth of approximately 31 km. This shallow seismicity suggests a shallow deformation style within the High Atlas.
To determine the state of the present-day tectonic and stress regimes across the western and central segments of the High Atlas, the study uses two complementary approaches: regional seismic moment tensor inversion and P-wave first motion focal mechanism analysis. Fault plane solutions were calculated using P-wave first motion polarities and further constrained through regional moment tensor inversion. The majority of analyzed earthquakes exhibit reverse faulting mechanisms, often with a significant strike-slip component, indicating a complex deformation pattern. Analysis of the principal stress axes (P, B, and T) derived from the focal mechanisms reveals average orientations of 16/189, 39/036, and 08/104 (plunge/azimuth), respectively. Subsequently, tectonic stress tensor properties were derived through inversion of the focal mechanism parameters. The results of this stress inversion indicate a predominantly N-S oriented maximum horizontal stress (σ1) in the Western High Atlas, closely aligned with the faulting style of the Al Haouz earthquake. In contrast, the stress field in the Central High Atlas exhibits a transition to a NW-SE to NNW-NNE orientation of σ1. These spatially varying stress orientations are consistent with independently derived GPS velocities and available neotectonics data, which document ongoing shortening across the High Atlas. This integrated analysis provides a comprehensive understanding of the active tectonic deformation within the High Atlas, shedding light on the complex interplay of faulting styles and stress orientations, and providing crucial insights into the source mechanism and broader tectonic context of the Al Haouz earthquake within the Western High Atlas region.
How to cite: Oujane, B., El Moudnib, L., Zeckra, M., Badrane, S., and Nouayti, A.: Seismotectonics of the Intracontinental High Atlas Mountains, Morocco, Derived from Regional Seismic Moment Tensor Analysis: Insights into tectonics and stress regimes., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9503, https://doi.org/10.5194/egusphere-egu25-9503, 2025.
EGU25-9618 | ECS | Posters virtual | VPS23
Horizontal tectonic stresses and its implications in the Shillong Plateau and its adjoining using gravity dataThu, 01 May, 14:00–15:45 (CEST) | vP1.27
North East India (NEI) is situated between the Himalayan collision arc to the north and the Indo-Burmese Ranges (IBR) to the east. The tectonic unit of the NEI, Shillong Plateau (SP), is one of the most active seismotectonic zones of the Indian subcontinent, as demonstrated by its seismicity. It is crucial to identify active faults in populated areas for human safety and the sustainable development of society. The gravity method is one of the convenient methods to delineate the shallow to deeper subsurface discontinuities, i.e., it is useful to detect active faults in the subsurface compared to other geophysical methods (e.g., Electrical, and Electromagnetic methods). In this study, detailed multilayer horizontal tectonics stress (HTS) was calculated using the approach of multi-scale decomposition of gravity anomalies data. HTS can be helpful in demarcating shallow to deep-seated tectonic structures. The tectonic features exhibit a strong correlation with the distribution of HTS at different depths. Major faults and earthquake epicentre align with areas of high stress, while stable zones correspond to regions of low stress. It means that HTS is employed to deduce the distribution and stability of faults. The high value of HTS is increased from shallow to deep depths for SP, Mikir Hills, IBR and Eastern Himalaya in the NEI region, and it varies as ~ 0.2-0.53 MPa, ~ 0.24-0.61 MPa, ~ 0.3-0.84 MPa, ~ 0.4-1.2 MPa, ~ 0.57 1.86 MPa, ~ 0.8-2.4 MPa, ~ 0.84-3.0 MPa at 4, 8, 12, 20, 40, 50, and 60 km depths, respectively. While the Brahmaputra Valley and the Surma Basin show relatively less stress, where HTS varies between ~ 0.1-0.33 MPa for 4, 8, 12, 20, 40, 50, and 60 km depths. It can be interpreted that the populated SP and Mikir Hills are highly unstable or earthquake-prone regions due to high stress.
How to cite: Pathak, P. and Kumar Mohanty, W.: Horizontal tectonic stresses and its implications in the Shillong Plateau and its adjoining using gravity data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9618, https://doi.org/10.5194/egusphere-egu25-9618, 2025.
