The study focused on the eastern Sulaiman fold-and-thrust belt, an active part of the western Indo-Eurasian collision zone where crustal shortening and strain accumulation have produced major earthquakes. The western part of the range is better known because it experienced the magnitude 7.1 Quetta earthquake in 1997 and events of magnitude 6 or greater at Ziarat in 2008 and Harnai in 2021. The eastern segment has received less attention, even though historical records describe several magnitude 6 or larger earthquakes there. No instrumental event larger than magnitude 6.0 had been recorded in the eastern Sulaiman Range since 1976, according to the study, but that absence does not imply inactivity.

The authors analyzed standardized focal mechanism solutions from the Harvard Global Centroid Moment Tensor catalog covering 1981–2024. These solutions describe the style and orientation of fault movement during earthquakes and provide the principal inputs for stress-tensor inversion. The study divided the region qualitatively into eastern, central and western seismotectonic zones, a working framework based on the distribution of events, mapped structures and geological setting rather than a formal statistical classification. Six events fell in the eastern zone, nine in the central zone and eight in the western zone, with one normal-faulting event later excluded from stress inversion.

Thrust mechanisms were concentrated in the eastern and western zones. In the east, six earthquakes were predominantly reverse-faulting events associated with structures including the frontal Sulaiman fold-and-thrust belt and the north–south, eastward-verging Zindapir anticline. The selected fault planes generally had relatively low to moderate dips and a dominant north-northeast to south-southwest strike. Stress inversion gave an SHmax orientation of approximately 118 degrees with an uncertainty of 25 degrees for this zone. By comparison, eight thrust events in the west, spatially associated with the mapped Pir Koh and Karmari thrust fault systems, yielded an SHmax of about 132 degrees with an uncertainty of 24 degrees, broadly northwest–southeast to north-northwest–south-southeast.

The nine central events all recorded strike-slip movement, and their fault planes generally struck close to north–south. Their spatial distribution and orientation correspond broadly with the mapped Kingri fault system, previously identified as a left-lateral structure with evidence of Holocene activity. Inversion of these mechanisms produced an SHmax of approximately 142 degrees with an uncertainty of 12 degrees. Although the eastern, central and western estimates differ somewhat, the combined pattern shows a coherent first-order northwest–southeast compression. The study’s authors cautioned that focal mechanisms alone cannot establish the subsurface geometry, continuity or direct connection of an earthquake fault with a named mapped fault.

Stress inversion was performed with Win-Tensor software through an initial Right Dihedron screening step and a subsequent Rotational Optimization stage. The procedure tested the two nodal planes of each focal mechanism, progressively selected the plane with the lower misfit and iterated until the stress tensor stabilized. Events with angular misfit greater than 60 degrees were rejected. Solutions with uncertainty of 15 degrees were assigned the highest quality class, while progressively larger uncertainties up to 40 degrees remained eligible for interpretation. The method assumes a homogeneous stress field within each zone, an assumption that may be imperfect in a structurally complex fold-and-thrust belt. Nodal-plane ambiguity and the limited number of focal mechanisms further constrain the resolution of the stress estimates.

The study also examined earthquake frequency and magnitude in a homogenized catalog assembled from Pakistan’s Centre for Earthquake Studies and Pakistan Meteorological Department records for 2020–2025. Magnitude of completeness was calculated separately for each zone using the maximum-curvature technique and was estimated as 2.3 throughout. After applying that threshold, the catalog contained 300 earthquakes in the central and western zones and 105 in the eastern zone. Their Gutenberg–Richter b-values were 0.73 plus or minus 0.03 in the west, 1.05 plus or minus 0.08 in the central strike-slip zone and 0.81 plus or minus 0.05 in the east. The higher central value means that its catalog contains a greater proportion of smaller earthquakes relative to larger events than the thrust-dominated catalogs do.

That contrast does not by itself establish the cause or future earthquake behavior of the region. A higher b-value is generally associated with a larger proportion of low-magnitude events and can be compatible with greater structural heterogeneity, denser fracturing or lower differential stress, while lower values can be associated with relatively greater stress accumulation. The measured pattern is consistent with reports that strike-slip settings tend to have higher b-values than compressional thrust settings. The authors noted that b-value variations may also reflect compositional and structural properties, loading rate, tectonic regime, depth, acoustic emissions from rocks, stress conditions, thermal gradients, crack density and material heterogeneity. Their interpretation therefore links greater heterogeneity and distributed fracturing to the strike-slip domain without claiming that the b-values alone predict a major earthquake.

Cumulative event counts showed broadly similar growth in all three zones during 2020 and 2021, followed by faster accumulation in the central zone through 2022 and a clustered sequence in the western zone. The central zone then remained comparatively steady for about six months before accelerating again toward 2023, while the west experienced a year-long lull from 2023 to 2024. Magnitude 5.0 events occurred in the eastern zone in 2024 and the central zone in 2025 but did not produce a comparably large increase in total event counts. The authors suggested that coseismic stress release in the strike-slip zone may have unclamped thrust faults optimally oriented to the regional stress, although they did not establish a causal triggering relationship.

The spatial pattern is broadly compatible with a preliminary Riedel shear model associated with the regional left-lateral motion of the Chaman Fault zone. In this conceptual framework, the Kingri Fault could be compatible with a synthetic R-shear, while the right-lateral Harnai Fault could act as an antithetic R-prime shear. Such an arrangement could allow strike-slip and thrust deformation to operate together in a transpressional system. The authors emphasized that this remains a working hypothesis: similar fault orientations can arise from other strain-partitioning mechanisms, and the focal mechanism dataset cannot uniquely determine whether the named faults form a single Riedel system or resolve their subsurface connections. The occurrence of a single normal-faulting event in the east may also fit localized extension in a releasing or transtensional segment, but one event cannot confirm that mechanism, and alternative explanations cannot be ruled out.

The study proposes that the relatively rigid Katawaz block acts as a tectonic buttress that obstructs northward motion of the Indian Plate and deflects strain around the eastern Sulaiman belt. Frontal and lateral ramps in this model could accommodate shortening, uplift and displacement transfer along the block’s margins, while the Kingri and Harnai faults accommodate part of the lateral shear. This arrangement may help explain the belt’s curved geometry, en-echelon structural patterns and abrupt changes between thrusting and strike-slip faulting. The study used 24 focal mechanisms to estimate stress orientation, faulting style and spatial patterns, while the 2020–2025 catalog was used to compare seismicity and magnitude-frequency behavior. Detailed fault mapping, paleoseismic evidence and geodetic strain measurements would be required to test the proposed geometry and determine how robustly the limited focal mechanisms represent the region’s full present-day stress field.

Subject of Research: Seismotectonic stress, faulting styles and earthquake magnitude-frequency patterns in Pakistan’s eastern Sulaiman fold-and-thrust belt

Article Title: Seismotectonics and structural dynamics of the eastern Sulaiman fold-and-thrust belt, Pakistan

Article References: Tahir, M., Shaukat, A. Z., Tahir, S., Saif, B., & Iqbal, T. (2026). Seismotectonics and structural dynamics of the eastern Sulaiman fold-and-thrust belt, Pakistan. Discover Geoscience, 4(1), Article 410. https://doi.org/10.1007/s44288-026-00780-3

Image Credits: AI Generated

DOI: 10.1007/s44288-026-00780-3

Keywords: eastern Sulaiman Range, Pakistan tectonics, focal mechanisms, stress inversion, thrust faulting, strike-slip faulting, strain partitioning, Katawaz block, Riedel shear, Gutenberg–Richter b-value, seismicity, Seismotectonics

The earthquake struck within the Kunar-Spin Ghar fault system, a zone of active crustal deformation in the Hindu Kush region where the ongoing convergence between the Indian and Eurasian plates is absorbed through a complex interplay of strike-slip, reverse and transpressional faults. The event caused widespread infrastructure damage, triggered landslides and rock avalanches, and left visible surface deformation across terrain so steep and inaccessible that ground-based investigation was severely limited. For a region with a long and destructive seismic history but sparse instrumental coverage, the quake offered a rare and urgent opportunity to observe how deformation is actually distributed in this part of the collision zone.

Led by Hamedullah Torabi of Kabul Polytechnic University, with colleagues from institutions in Afghanistan, India, South Korea and the United Kingdom, the research team carried out field reconnaissance at accessible sites along the affected valleys. Their observations documented structural damage to buildings, ground cracks, slope failures, rock avalanches and newly emerged springs along the Kunar River valley. These ground effects, recorded in difficult and sometimes dangerous conditions, provided the essential field anchor for interpreting what the satellite data would later reveal. Emergent springs in particular can indicate changes in subsurface permeability caused by shaking and fault movement, offering clues about where the crust was disturbed.

The technological heart of the study lies in Persistent Scatterer Interferometric Synthetic Aperture Radar, or PSInSAR, a technique that tracks millimeter-scale ground movements over time by comparing radar reflections from stable features such as rock outcrops, buildings and boulders. The team analyzed time series of Sentinel-1A radar data acquired by the European Space Agency’s Copernicus mission between April and October 2025, processing both ascending and descending orbital passes. Because each viewing geometry is sensitive to a different combination of horizontal and vertical motion, combining the two allows researchers to decompose the observed radar signal into east-west and vertical components of surface displacement, effectively reconstructing a two-dimensional picture of how the ground moved during the earthquake period.

What emerged from the radar analysis was striking. Both the ascending and descending line-of-sight velocity fields revealed a laterally continuous deformation pattern extending for several tens of kilometres along the strike of the fault system. Decomposition of the signal showed dominant horizontal motion, consistent with the strike-slip and transpressional character of the region, accompanied by broader and spatially variable patterns of uplift and subsidence. In other words, the ground was not simply sliding along one clean break; it was warping, rising and sinking across a wide swath of terrain in a manner that reflects the distributed nature of the forces at work beneath the Hindu Kush.

Swath-profile analysis, which examines how velocities change across cross-sections of the deformed zone, pinpointed the strongest east-west velocity gradients south of the mapped Kunar Fault and within or adjacent to the Spin Ghar mountain-front structural corridor. This detail matters enormously. The most intense deformation did not coincide neatly with the fault trace that appears on existing maps. Instead, it spilled into neighboring structures, indicating that the earthquake-period deformation signal was shared among multiple interacting faults rather than released on a single rupture plane. The pattern is exactly what geologists would expect from distributed transpressional deformation, a regime in which crustal blocks are simultaneously squeezed and sheared, forcing strain to spread across networks of faults rather than concentrate on one master structure.

The concept of transpression, formally described in the structural geology literature in the 1980s, describes deformation that combines pure compression with a component of shear, producing complex fault geometries and strain partitioning. Eastern Afghanistan sits squarely within such a regime. The India-Eurasia collision, which has built the Himalaya and the Tibetan Plateau, transmits enormous compressive stresses deep into the Asian interior, and the Hindu Kush is one of the places where those stresses find release through intracontinental faulting. Previous studies, including GPS-based measurements of plate convergence partitioning in the Pamir-Hindu Kush region and historical catalogs of Afghan earthquakes, have long suggested the region is tectonically active, but the density of observations needed to map how strain is actually distributed has been lacking.

The new results carry a direct and uncomfortable message for seismic hazard assessment. Hazard models typically rely on mapped fault traces to define the locations and widths of potential rupture zones, and building codes and land-use planning follow from those definitions. If deformation in the Kunar-Spin Ghar system is distributed across a corridor tens of kilometres wide rather than focused on individual mapped faults, then hazard assessments based only on those traces may underestimate both the width of the active deformation zone and the spatial extent of ground deformation and secondary hazards such as landslides, rock avalanches and liquefaction. Communities located well away from any mapped fault trace could still sit within the zone of strongest shaking and ground failure in a future event.

The vulnerability of the region amplifies these concerns. Eastern Afghanistan combines steep, landslide-prone topography, dense rural populations living in unreinforced masonry construction, and limited institutional capacity for emergency response, a combination that recent earthquakes in the region have shown to be lethal. The study’s authors, along with earlier researchers who have called for greater earthquake resilience across Central Asia, argue that satellite-based deformation monitoring offers a practical path forward in terrain where traditional field mapping and dense seismic networks are difficult to establish. Because Sentinel-1 radar data are freely available through the Copernicus Open Access Hub, the approach demonstrated here could be extended systematically across Afghanistan and neighboring countries to build a more realistic picture of active deformation corridors.

The 2025 Asadabad-Kunar earthquake lasted only seconds, but its scientific legacy may prove durable. By pairing boots-on-the-ground observation with space-based radar, the research team has shown that the Hindu Kush does not obey the tidy assumption that earthquakes follow the fault lines drawn on maps. The active deformation zone is wider, more interconnected and more structurally complex than previously recognized, and the seismic hazard it poses is correspondingly broader. For the millions of people who live in the shadow of the Spin Ghar mountains, that widened hazard corridor is not an abstract geodynamic detail. It is a warning that the ground beneath their villages can move in places no map currently marks, and that planning for the next earthquake must account for a danger that is distributed, not localized.

Subject of Research: Distributed transpressional deformation and seismic hazard implications of the 2025 Mw 6.0 Asadabad-Kunar earthquake in eastern Afghanistan

Article Title: Evidence for distributed transpressional deformation and seismic hazard implications from the 2025 Mw 6.0 Asadabad- Kunar earthquake, Eastern Afghanistan

Article References: Torabi, H., Kandregula, R. S., Naik, S. P., Shnizai, Z., Ghildiyal, D., Chufal, V. S., & Kim, Y.-S. (2026). Evidence for distributed transpressional deformation and seismic hazard implications from the 2025 Mw 6.0 Asadabad- Kunar earthquake, Eastern Afghanistan. Natural Hazards, 122(18), Article 624. https://doi.org/10.1007/s11069-026-08397-y

Image Credits: AI Generated

DOI: 10.1007/s11069-026-08397-y

Keywords: Afghanistan, Hindu Kush, earthquake, transpressional deformation, PSInSAR, Sentinel-1A, Kunar fault, Spin Ghar, seismic hazard, India-Eurasia collision, strain partitioning, landslides