The 2015 Mw 7.8 Gorkha earthquake was followed by numerous aftershocks that provided important information on active faulting in central Nepal. Accurate moment tensor estimations are essential for determining the source parameters of these seismic events. In this study, we determine double-couple and full moment tensor solutions for selected aftershocks of the 2015 Nepal earthquake sequence using a regional 1D velocity model.

The waveform data recorded by the temporary broadband network (NAMASTE) are used to analyse 51 aftershocks with M > 3.5. A library of Green’s functions is computed using the frequency–wavenumber method based on a 1D velocity model of the Nepal region. Synthetic waveforms derived from the Green’s functions are used to invert the waveform data for moment tensor estimation. Both body waves and surface waves are used in the inversion, and they contribute separately to the moment tensor solutions. The analysis focuses on regional waveforms in relatively higher frequency ranges.

Both double-couple–constrained and full moment tensor inversions are performed, and the resulting source parameters are examined in terms of waveform fit, centroid depth, and fault-plane orientation. This work presents a set of moment tensor solutions for the 2015 Nepal aftershocks using a 1D regional velocity model and provides a reference for future studies using more complex velocity structures.

How to cite: Lahon, P., Silwal, V., and Mahanta, R.: Double-Couple and Full Moment Tensor Solutions of the 2015 Nepal Aftershocks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21099, https://doi.org/10.5194/egusphere-egu26-21099, 2026.

The Rif’s belt is characterized by low to moderate seismic activity resulting from the continental collision between the African and Eurasian plates. This seismic activity, which involves devastation and human losses, requires an in-depth study of its origins and mechanisms. This study aims to identify the geological structures responsible for seismic activity in the eastern Rif by adopting an integrated methodological approach. The methodology relies on the use of a Geographic Information System (GIS) to process and analyze multiple geological, seismological, and geophysical datasets. Various filters were applied to magnetic and gravimetric data (vertical derivatives) to characterize the subsurface. The analysis of earthquake focal mechanisms helped identify active faults. The results show that the seismicity, with a NW-SE orientation, is localized within a fragile depression south of the city of Selouane. The final geological model highlights a system of faults and strike-slips oriented NE-SW and NW-SE. A significant spatial correlation is observed between epicenters and Messinian-aged NW-SE strike-slips, suggesting their reactivation. The analysis indicates that a system of dextral strike-slips is likely the source of this seismic activity. The proposed geodynamic model represents a major advancement in understanding local seismic activities and serves as an essential reference for future studies. These results significantly contribute to the assessment and management of seismic risks, thereby enhancing the safety and resilience of populations in this high-risk area.

KEYWORDS: Geodynamic model; Seismotectonic; Focal mechanism; Magnetic; Gravimetric; ·
Eastern Rif. 

How to cite: Iken, H., Nouayti, A., Nouayti, N., and Khattach, D.: An integrated geodynamic analysis of seismic sources in the Eastern Rif: Insights from geological, seismological, gravimetric, and aeromagnetic data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22669, https://doi.org/10.5194/egusphere-egu26-22669, 2026.

Regular monitoring of small to moderate sources of continuous earthquake events in the complex tectonics of Himalayan region helps in clearly defining the ongoing seismotectonic process. The study of moment tensor inversion to decipher the fault planes responsible for current seismic activity in the Kishtwar region of Northwest part of Himalaya has been undertaken by establishing a six-station network in 2022 and among them 15 events of shallow origin with magnitude ranging from M_L ~ 3.0 to 4.0 occurred in the local region of seismic network are used for the moment tensor inversion. A few number of studies didn’t able to clearly demarcate the actual scenario of seismotectonics in the northwest part of Himalaya due to its difficult terrain and complex geology. This area has been studied for fault plane solution by a software package ISOLA based on MATLAB programming environment. The source inversion is performed via iterative deconvolution method and synthetic seismogram is generated through green’s function computation via discrete wavenumber method using the regional crustal velocity model. However, the inversion is performed at several trial source position and at various frequency bands based on the epicenter distance and the magnitude of earthquake to find the best solution resulting from the maximum correlation between the recorded and synthetically generated waveforms. A 2D space-time grid search is performed for determining the optimal time and positon of earthquake generation. Perhaps calculating source parameters such as moment magnitude, centroid depth and fault parameters equally with describing uncertainty quantities such as variance reduction factor and condition number will deliver the reliability and stability to the solution. A strong follow-up uncertainty quantification can justify the best estimated fault plane solution. Quality of earthquake event can be calculated through their DC and CLVD percentage and maximum & minimum compression stress direction. Focal mechanism solution of these events following thrust with strike-slip focal mechanism and represents the compressional regime in north-northeastern direction. The centroid depth obtained by moment tensor inversion of all events falls within the depth zone of Main Himalayan Thrust (MHT) suggesting seismicity is concentrated along the major detachment in the region.

How to cite: Tiwari, S. and Gupta, S. C.: Moment tensor analysis and uncertainty quantification of local earthquake events: tectonic implication in the northwestern Himalayan region, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13656, https://doi.org/10.5194/egusphere-egu26-13656, 2026.

Numerical simulations of earthquake cycles provide essential insights into fault mechanics and the physical interpretation of frictional parameters. Here, we utilize a spring-block system governed by rate-and-state friction to systematically compare earthquake cycle behaviors under quasi-dynamic and fully dynamic conditions. Our simulations demonstrate that for both approaches, the static stress drop, dynamic stress drop, and peak stress scale linearly with the logarithm of the loading rate [ln(Vpl/V0)]; however, the scaling coefficients are distinct and are modulated by both frictional parameters and the system stiffness. Specifically, we observe stress overshoot during the coseismic phase in dynamic models, contrasting with the undershoot observed in quasi-dynamic simulations. Additionally, parameter sweeps reveal that stress drops decrease as the stiffness ratio kc/k increases. This study highlights the importance of the inertial term effect in interpreting earthquake cycle behaviors.

How to cite: Chai, L. and Hu, F.: Scaling of Stress Drop with Rate-and-State Frictional Parameters in Spring-Block Models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6568, https://doi.org/10.5194/egusphere-egu26-6568, 2026.

Seismic hazard assessment is crucial for the design of critical facilities, whose damage could lead to severe consequences. The design of such facilities typically requires the definition of seismic actions associated with recurrence periods on the order of 5,000-10,000 years. Earthquakes with such low frequencies are well documented in highly deforming regions, where paleoseismic records commonly encompass several seismic cycles of active faults. In contrast, in slow-deforming regions or areas of low seismicity, the scarcity of seismic data hinders the definition of seismogenic zones. In this context, geological studies of active seismogenic faults are essential, as they allow the characterisation of seismic behaviour over time spans far exceeding those covered by instrumental or historical records. These data can contribute to constraining fault’s seismic cycles and estimating earthquake magnitude–frequency distributions at the fault scale.

Despite their importance, the incorporation of faults into seismic hazard models remains challenging, particularly in low strain regions such as the western margin of the Valencia Trough. This region of the NE of Iberia (from the Vallès-Penedès Graben to the Valencia Depression) corresponds to a passive margin characterised by a basin-and-range structure, bounded by multiple NNE–SSW-oriented normal faults formed during the Neogene rifting episode. Those faults are usually associated with mountain fronts, although our recent studies have found some new faults crosscutting Pleistocene alluvial fans. These newly discovered faults are being studied by means of geomorphology, geophysics, paleoseismology and geochronology in order to estimate their seismic parameters. Several challenges arise when analysing these faults, including fault identification, incomplete geological records, and the need for complex dating techniques.

Moreover, in regions characterised by fault systems, fault interactions may play a significant role. In regions such as the studied area, these interactions may result in long quiescent periods followed by phases of increased activity or even cascading events. Under such conditions, distinguishing between quiescent and active phases is especially difficult, as recurrence intervals are expected to span several thousands of years in both cases.

In this work, we explore existing methodologies for the computation of seismic hazard incorporating geological data from faults and fault systems in slow-deforming regions, using the western margin of the Valencia Trough as a case study. To this end, a detailed geometric characterization of the fault system is carried out to establish the geometric relationships among faults. Recent morphotectonic analyses and newly acquired geological data are then used to constrain the seismic parameters of the studied faults and to estimate their earthquake frequency distributions. Finally, several alternative seismic source models are proposed, forming the basis for the construction of a logic tree for subsequent seismic hazard calculations. These
models, although in progress, provide a framework for improving seismic hazard assessments in slow-deforming regions, contributing to safer design of critical infrastructure.

How to cite: Ollé-López, M., García-Mayordomo, J., Scotti, O., and Masana, E.: A seismogenic modelling approach for rift-basin fault systems in slow-deforming regions: application to the western margin of the Valencia Trough, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20741, https://doi.org/10.5194/egusphere-egu26-20741, 2026.

The east-west-trending, north-dipping Dauki Fault System (DFS) is among the well-identified active fault systems in the North-Eastern part of India, and it marks the southern geological boundary of the Shillong Plateau, separating it from the Bengal alluvium basin and Sylhet trough. With a length of about 350 km stretching from about 89.9° E to 93° E, DFS is reverse in nature and can be divided into 4 segments, namely, Western, Central, Eastern and Easternmost with variable dip and strike values. Mitra et al. (2018) has indicated that this fault can produce an Mw ∼8 earthquake.
Fault segmentation, fault connectivity, and multi-segment rupture scenarios have been explicitly incorporated into a fault-system-based probabilistic seismic hazard framework for the Dauki Fault System. The SHERIFS (Seismic Hazard and Earthquake Rates In Fault Systems) methodology has been employed to enforce a global magnitude–frequency distribution while converting geological and geodetic slip rates into earthquake rates at the system scale. To account for geometric complexities such as bends and step-overs, a range of rupture hypotheses has been explored, including single-segment ruptures, partial multi-segment ruptures, and through-going system-wide ruptures. Epistemic uncertainties associated with maximum magnitude, rupture connectivity, slip-rate variability, and off-fault seismicity have been quantified using a logic-tree approach.
The resulting earthquake rupture forecasts are tested against available seismicity data of the region. The findings underscore the critical role of fault interactions in determining the seismic hazard along the DFS and indicate the need for system-level modelling to provide a reliable assessment of seismic hazard.
This study is the first to offer a seismic hazard framework based on the multi-rupture scenario for the Dauki Fault System and it also contributes to the improvement of seismic risk assessment for northeastern India and the Indo–Burman–Shillong tectonic domain.

How to cite: Pandey, A. K., Venkitanarayanan, R., and Sharma, M. L.: Multi-rupture Fault-based Seismic Hazard Assessment for the Dauki Fault System, Northeastern India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16763, https://doi.org/10.5194/egusphere-egu26-16763, 2026.