Abstract Despite decades of study, the detailed geometry of the Connector fault at the Alaska–Canada border remains poorly constrained. We investigate the rupture complexity and directivity of the 6 December 2025, Mw 7.0 Hubbard Glacier earthquake using hypocenter relocations, moment tensor inversions of the mainshock and aftershocks, and finite‐fault modeling. We model seismological data using bootstrap and Bayesian‐based probabilistic inversion. Observations indicate that the mainshock rupture was complex, nucleated with a right‐lateral strike‐slip mechanism and propagating northwestward, ultimately terminating in a restraining bend. Source inversion of the mainshock reveals shallow right‐lateral oblique‐slip on a fault striking 303° and dipping 63° NE. Relocated aftershocks delineate an ∼60 km‐long seismic zone characterized by strike‐slip mechanisms along the ruptured area and reverse/thrust at the left stepover of the fault. Our results provide a detailed mechanism for a buried Connector structure and highlight the role of fault bends in controlling rupture evolution.

Rupture directivity significantly increases horizontal peak ground acceleration, elongates aftershock clouds and enlarges meizoseismal areas beyond the fault end in front of the direction of rupture propagation. In this study, we examine the directivity of 25 moderate to large earthquakes (Mw >= 6) from 1968 to 2017 in the Iranian plateau by employing relocated earthquake clusters, mapped surface ruptures, focal mechanisms of earthquakes, slip distribution models, spatial distribution of peak ground acceleration amplitudes and macroseismic effects. The methodology overcomes the lack of dense seismic networks required to study directivity using methods based on the azimuthal variation of the spectrum of seismic waves. We show that 16 out of the 25 (i.e. 64 per cent) of the earthquakes investigated have mostly unidirectional rupture. This implies that unidirectional ruptures in a slow deforming continental collision zone such as the Iranian plateau is only slightly less common than those observed globally. With the understanding that unidirectional rupture increases the probability of ground shaking off the termination of the causative faults, our findings highlight the importance of considering the directivity effect in earthquake hazard assessment in Iran and also in other slow deforming continental regions.

In the past decade, six $M_w\, \ge$5.5 earthquakes struck the mountainous Golden Triangle region (Laos, Thailand, Myanmar) of the southeast India-Eurasia collision zone. The largest of them, the 2019 $M_w$ 6.2 Sainyabuli earthquake in western Laos, shook river communities, dams and a UNESCO World Heritage Site, prompting a need to understand regional earthquake potential. We used Interferometric Synthetic Aperture Radar (InSAR) data and modelling to solve for the 2019 main shock source parameters, revealing right-lateral strike-slip along a 24 km-long NNW-trending fault which has limited topographic expression and was previously unmapped. InSAR modelling of its largest ($M_w$ 5.5) aftershock in 2021 revealed a 7 km-long splay fault, also previously unrecognized. The 2022 $M_w$ 5.9 Keng Tung earthquake in the northern Golden Triangle also ruptured an unknown, NW-trending right-lateral fault conjugate to longer, NE-trending faults nearby. Collectively, this shows that the region contains faults which are little evident in global digital topography and/or obscured by vegetation but long enough to generate sizeable earthquakes that should be accounted for in seismic hazard assessments. We relocated well-recorded aftershocks and other background seismicity (1978-2023) from across the Golden Triangle using the mloc software. Calibrated hypocentres span focal depths of 5-24 km and are distributed away from the main InSAR-modelled fault traces, another indication of fault structural immaturity. For the three 2019-2022 InSAR-constrained events, we also obtained moment tensor solutions from regional seismic waveform inversion. InSAR-derived peak slip depths and seismological centroid depths are mostly shallow (3-5 km), while focal depths are generally located in areas of low coseismic slip near the bottom of InSAR model faults. More broadly, we estimate a regional seismogenic thickness of $\sim$17 km (the 90 $\rm \,per\,cent$ seismicity cut-off depth), a crucial parameter for seismic hazard calculations and building codes. Our integration of remote-sensing and seismologic analyses could be a blueprint for assessing earthquake potential of other regions with sparse instrumentation and limited topographic fault expression.

The 23 February 2020 Qotur earthquake doublet (5.7 and 5.9 Mw) occurred near the Iran-Turkey border. The doublet ruptured along the northern segment of the Bashkale fault system, which forms the northernmost end of the Zagros' Main Recent Fault. To investigate the tectonics of the region, we combined geological fault mapping, precise location of the seismic cluster, moment tensors of the mainshocks and 28 larger fore- and aftershocks, InSAR source modeling, and inversion of source parameters for the regional stress field. We show that both mainshocks happened on NE-SW trending left-lateral strike-slip faults belonging to the Bashkale fault system. However, both NE-SW trending left-lateral and NW-SE trending right-lateral strike-slip faults were activated by the earthquake cluster. The InSAR images imply no surface rupture for the doublet event in agreement with the field observations. The first mainshock was deeper (centroid: 9 km) than the second mainshock (5 km). We model the InSAR data of the second mainshock as rupture along a 7-km-wide and 5-km-long fault with maximum displacement of 1.2 m at -3 km depth. The spatial distribution of aftershocks and the damaged region implies southwest directivity for the second mainshock. Stress inversion of the moment tensors indicates a transtensional regime with an NNW-SSE direction of maximum horizontal stress. This agrees with the stress regime deduced from the inversion of geologically measured fault planes and GPS vectors, and the focal mechanism of the 1930 Salmas earthquake. Our results show that strain accommodation at the northern end of the right-lateral strikeslip Main Recent Fault of the Zagros is distributed across a complex network of immature conjugate right and left-lateral strike-slip and normal faults.

The Makran Subduction Zone is unusual, with an ENE-WSW trending volcanic arc that is nonparallel to its similar to E-W trending accretionary prism. The discrepancy has been attributed to an eastward reduction of the subduction angle. To assess this theory, we relocated 146 moderate to large earthquakes in the region during the period 1968 to 2022. We found that in eastern Makran, the region with intermediate-depth earthquakes has a constant width of similar to 180 km, with a trend sub-parallel with the trend of the volcanic arc. The fault planes of most of the normalfaulting intermediate-depth earthquakes are also parallel to the trend of the volcanic arc. These observations suggest an ENE-WSW trending subducting plate hinge and a constant subduction angle in eastern Makran. The similar to E-W trend of the intermediate-depth earthquakes in western Makran indicates an similar to E-W trending subducting plate hinge. We relate the different orientation of the plate hinges in eastern and western Makran to the different shape of the overriding plates. The cumulative Wadati-Benioff zone for eastern Makran shows a subduction angle of similar to 15 degrees in the depth range of similar to 45-80 km, increasing to similar to 45 degrees at depths greater than 80 km. The significant component of strike-slip faulting of the intermediate-depth events in western Makran implies that the subducting plate in western and eastern Makran experience different stress regimes. Alignment of a considerable number of intermediate-depth earthquakes along narrow ENE-WSW lineaments implies a pre-existing weakness in the subducting plate.

Earthquake multiplets are an important but poorly understood class of seismic sequence. On October 7th-15th 2023, a multiplet comprising five damaging, moment magnitude (M-w) 5.9-6.4 earthquakes struck northwestern Afghanistan, a region previously lacking in well-recorded seismicity. We mapped ground deformation with Interferometric Synthetic Aperture Radar (InSAR) and characterized the causative faulting using elastic dislocation modelling. Because of the tight clustering in time, only the fifth mainshock is ever imaged on its own, so we apply independent seismological constraints from epicentral relocations and moment tensor inversions to distinguish the contribution of each mainshock to the observed surface deformation. Our results support sequential rupture of five colinear, shallow (similar to 5 km), north-dipping, blind reverse faults, with successive mainshocks stepping initially westwards and subsequently eastwards. Our modelling implies that gentle (10-15 degrees) fault bends and/or step-overs may have halted rupture propagation in individual mainshock, acting to divide the sequence into its five distinct events. The epicentral region shows abundant geomorphic evidence for active shortening, including a similar to 70 km-long anticlinal ridge whose growth is likely driven by the underlying reverse faults. This sequence confirms that while to a first degree northwestern Afghanistan is part of stable Eurasia, slow internal deformation can nevertheless generate damaging earthquakes.

SUMMARY On 2020 January 9, an Mw 6.4 earthquake struck the central Koryak Highlands of eastern Siberia, northeast of the diffuse triple junction between the North American, Pacific and Eurasian plates. The largest earthquake recorded in the central Koryak Highlands to date, it provides an excellent opportunity to study the little-known active tectonics of this remote, sparsely instrumented region. We mapped coherent, coseismic surface deformation with Sentinel 1 Interferometric Synthetic Aperture Radar (InSAR), making this one of the highest latitude earthquakes to be captured successfully with satellite radar, in spite of the rugged, snow-covered terrain. Elastic dislocation modelling, teleseismic backprojections, calibrated hypocentral relocations and teleseismic moment tensor solutions are used to resolve a left-lateral fault trending northwestwards, proximal but perpendicular to a regional geological suture zone, the Khatyrka–Vyvenka Thrust. The earthquake probably ruptured unilaterally northwestwards along a 20 km long segment that appears indistinct in the local topography, and likely generated no surface rupture. We interpret that these observations are indicative of a structurally immature fault zone and estimate a seismogenic zone thickness of 10–15 km. The Koryak Highlands earthquake illustrates how terrane boundaries within cordilleran belts may continue to accommodate tectonic strain long after accretion, resulting in significant earthquakes even along hidden faults.

We produced a globally distributed catalog of earthquakes and nuclear explosions with calibrated hypocenters, referred to as the Global Catalog of Calibrated Earthquake Locations (GCCEL). This dataset currently contains 18,782 events in 289 clusters with > 3.2 million arrival times observed at 19,258 stations. The term "calibrated" refers to the property that the hypocenters are minimally biased by unknown Earth structure. In addition, we calculate uncertainties using empirically determined variability of the arrival-time data itself, specific to each calibrated cluster of hypocenters. Outliers in the arrival-time dataset are removed based on measured variability of the data. In each cluster, we estimate the empirically determined uncertainty for each set of station-phase arrival times. We use a version of the hypocentroidal decomposition multiple event relocation algorithm specifically adapted for calibrated relocations of clusters of seismic events. Most clusters are calibrated by fitting the subset of direct crustal first arrivals (Pg and Sg) with a locally appropriate travel-time model to estimate the cluster hypocentroid. A few clusters are calibrated by aligning the pattern of relative locations in space and time with one or more events for which a ground-truth hypocenter is available from an independent source with known uncertainty, such as a nuclear explosion. Epicentral uncertainties in GCCEL typically range from 1 to 5 km with a 90% confidence interval. Most events have depth constraint from one or more sources, usually with an uncertainty of <= 5 km. GCCEL is a significant resource for research at local, regional, and global scales because it provides minimally biased absolute hypocenters, meaningful associated error estimates, and curated arrival times as a reference dataset that can be used as prior constraints in the development of new regional, national, and global earthquake catalogs; validation of new location techniques; and the generation of advanced Earth models.

ABSTRACT The 15 May 2020 Mw 6.5 Monte Cristo Range earthquake (MCRE) in Nevada, United States, is the largest instrumental event in the Mina deflection—a zone of east-trending left-lateral faults accommodating a right step between northwest-trending right-lateral faults of the Walker Lane. The MCRE ruptured a highly distributed faulting area with muted geomorphic expressions, motivating us to characterize the behavior of an earthquake on a structurally immature fault system. Inverse modeling of Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) displacements reveals left-lateral slip on an east-striking, eastern fault and left-lateral–normal slip on an east-northeast-striking, western fault. Unusually, the two faults cross one another and ruptured together in the mainshock. The maximum slip of 1 m occurs at 8–10 km depth, but less than 0.1 m of slip reaches the surficial model fault patches, yielding a pronounced shallow slip deficit (SSD) of 91%. Relocated hypocenters indicate that the mainshock initiated at 9 km depth and that aftershocks span depths of 1–11 km, constraining the local seismogenic thickness. Our new field observations of fracturing and pebble-clearing in the western MCRE characterize a third, shorter, northern fault that is at the resolution limit of the InSAR–GNSS modeling. The segmented and intersecting fault geometry, off-fault aftershocks with variable mechanisms, distributed surface fractures, limited long-term geomorphic offsets, and a 600–700 m (cumulative) bedrock offset are all characteristic of a structurally immature fault system. However, the large SSD is not unusual for an earthquake of this magnitude, and a larger compilation of InSAR models (28 Mw≥6.4 strike-slip events) shows that SSDs correlate with magnitude rather than structural maturity. This study demonstrates the importance of integrating geodesy, seismology, and field observations to capture the full complexity of large earthquakes, and further suggests that seismic hazard assessments in shattered crustal regions consider the potential for multi- and cross-fault rupture.

On 2021 April 18, an Mw 5.9 earthquake struck the Genaveh region in the south Dezful embayment of the Zagros, Iran. Here, we investigate the active tectonics of the region, the geometry and slip distribution of the causative fault plane, and its aftershock behavior. We applied a combination of different geodetic and seismological methods (slip distribution inversion of the mainshock using Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR), relocation, and moment tensor inversion of aftershocks and background seismicity of the region). Co-seismic InSAR modeling shows that the slip is confined to the sedimentary cover at depths of 4-7 km with a maximum slip of 1 m and highlights the influence of lithology in the rupture propagation. Moment tensors and centroid depths of aftershocks down to Mw 4 show that the distributed aftershocks sequence is dominated by reverse faulting at centroid depths of 4-10 km. The causative fault is compatible and parallel to the trend of the Gulkhari anticline and the coseismic uplift of the Genaveh earthquake implies that the growth of this particular fold is linked to the fault(s). However, still, due to the absence of surface rupture, the clear relationship between buried faulting and surface folding remains unclear.

We present a new catalog of calibrated earthquake relocations from the 2019-2020 Puerto Rico earthquake sequence related to the 7 January 2020 Mw 6.4 earthquake that occurred offshore of southwest Puerto Rico at a depth of 15.9 km. Utilizing these relocated earthquakes and associated moment tensor solutions, we can delineate several distinct fault systems that were activated during the sequence and show that the Mw 6.4 mainshock may have resulted from positive changes in Coulomb stress from earlier events. Seismicity and mechanisms define (1) a west-southwest (- 260 degrees) zone of seismicity comprised of largely sinistral strike-slip and oblique-slip earthquakes that mostly occurs later in the sequence and to the west of the mainshock, (2) an area of extensional faulting that includes the mainshock and occurs largely within the mainshock's rupture area, and (3) an north-northeast (- 30 degrees)-striking zone of seismicity, consisting primarily of dextral strike-slip events that occurs before and following the mainshock and generally above (shallower than) the normal-faulting events. These linear features intersect within the Mw 6.4 mainshock's fault plane in southwest Puerto Rico. In addition, we show that earthquake relocations for M 4+ normal-faulting events, when traced along their fault planes, daylight along east-west-trending bathymetric features offshore of southwest Puerto Rico. Correlation of these normal-faulting events with bathymetric features suggests an active fault system that may be a contributor to previously uncharacterized seismic hazards in southwest Puerto Rico.

Near‐field surface displacement measurements allow us to quantify the on‐ and off‐fault proportion of earthquake‐related deformation. The Hebgen Lake earthquake was a large normal event with a complex surface rupture, which broke across mountainous terrain. This study takes advantage of high‐resolution historical aerial stereo‐imagery to measure three‐dimensional displacement from correlation of the orthorectified pre‐ and post‐earthquake image mosaics. The results reveal new strike‐slip ruptures which are possibly associated with the aftershocks from 18th August 1959. These structures likely reflect internal block deformation induced by the complex geometry of the mainshock. Additionally, comparison of our results with the existing displacement data shows that the optical image correlation‐derived offsets often exceed the field measurements by >50%. We attribute this difference to inelastic off‐fault deformation.

The Kepingtag (Kalpin) fold-and-thrust belt of the southern Chinese Tian Shan is characterized by active shortening and intense seismic activity. Geological cross-sections and seismic reflection profiles suggest thin-skinned, northward-dipping thrust sheets detached in an Upper Cambrian décollement. The January 19 2020 Mw 6.0 Jiashi earthquake provides an opportunity to investigate how coseismic deformation is accommodated in this structural setting. Coseismic surface deformation resolved with Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) is centered on the back limb of the frontal Kepingtag anticline. Elastic dislocation modelling suggests that the causative fault is located at ~7 km depth and dips ~7° northward, consistent with the inferred position of the décollement. The narrow slip pattern (length ~37 km but width only ~9 km) implies that there is a strong structural or lithological control on the rupture extent, with up-dip slip propagation possibly halted by an abrupt change in dip angle where the Kepingtag thrust is inferred to branch off the décollement. A depth discrepancy between mainshock slip constrained by InSAR and teleseismic waveform modelling (~7 km) and well-relocated aftershocks (~10-20 km) may imply that sediments above the décollement are velocity strengthening. We also relocate 148 regional events from 1977 to 2020 to characterize the broader distribution of seismicity across the Kepingtag belt. The calibrated hypocenters combined with previous teleseismic waveform models show that thrust and reverse faulting earthquakes cluster at relatively shallow depths of ~7-15 km but include abundant out-of-sequence events both north and south of the frontal Kepingtag fault.

&lt;p&gt;The 1949 M&lt;sub&gt;w&lt;/sub&gt;7.4 Khait and 1907 M&lt;sub&gt;w&lt;/sub&gt;7.6 Karatag earthquakes are the two largest earthquakes of the last ~100 years within Tajikistan, in a zone of convergence between the Pamir and Tian Shan ranges at a rate of ~1cm/yr. The historical nature of these events means seismological and geodetic data are lacking. As such, their locations and source parameters have been very uncertain &amp;#8211; preventing our understanding of how they fit into the tectonic model of the north-western Pamir. &amp;#160;&lt;/p&gt;&lt;p&gt;Here we present calibrated earthquake relocations for the 1949 earthquake and focal mechanisms determined from digitised seismograms for the 1949 and 1907 earthquakes. We also present a catalog of precise relocations for moderate magnitude earthquakes from 1949 to the present in vicinity of the Vakhsh Thrust. Finally, we present earthquake surface rupture mapping from the Vakhsh Valley, determined from ultra-high resolution elevation models derived from satellite stereo-imagery. &amp;#160;&lt;/p&gt;&lt;p&gt;We find that the 1949 Khait earthquake did not occur on the Vakhsh Fault, a major right-lateral fault that bounds the northern margin of the Pamir, as previously thought. Instead it occurred on an unmapped fault in the Tian Shan basement. However, 10-20m scarps observed on the south Vakhsh valley show this fault is capable of producing large earthquakes. This tells us the Pamir&amp;#8211;Tian Shan convergence is distributed across several basement faults capable of producing large earthquakes. It also tells us that the largest earthquakes may occur on faults which may appear minor in the landscape, which has implications for seismic hazard in the region. &amp;#160;&lt;/p&gt;

The Papuan Fold and Thrust Belt (PFTB) in Papua New Guinea is actively forming within a complex tectonic setting at the boundary of the obliquely converging Australian and Pacific plates. The tectonic setting and inaccessibility of the PFTB make it one of the least well‐understood fold and thrust belts on Earth. On February 25, 2018, a M w 7.5 earthquake occurred within the PFTB, triggering an aftershock sequence which included five events ≥M w 6. In this study, we combine seismological, GPS and remote sensing observations to investigate the spatiotemporal distribution of crustal deformation during these events. All earthquakes ≥M w 6 were related to reverse offset on northeast‐dipping fault planes and five out of the six, including the mainshock, were associated with midcrustal focal depths (∼15–30 km). During the sequence, the PFTB underwent up to 1.2 m of uplift and ground deformation occurred over 7,500 km 2 . Combining these observations with our geological knowledge of this convergent margin highlights the primary control of the northern Australian passive margin on PFTB structural style. We propose that the earthquake sequence was related to tectonic inversion on a hidden extensional fault system beneath the PFTB and lateral variations along this fault zone had significant influence on the complex distribution of ground deformation. It follows that this fault system has had an important control on the evolution of variable structural styles within the PFTB. This study highlights the complexity that can characterize the evolution and structural style of fold and thrust belts.

Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Geophysical Research Letters. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v3]The 2020 Mw 6.8 Elaziğ (Turkey) earthquake reveals rupture behavior of the East Anatolian FaultAuthors Léa Pousse Beltran iD Edwin Nissen iD Eric Bergman iD Musavver Didem Cambaz iD Élyse Gaudreau iD Ezgi Karasozen iD Fengzhou Tan iDSee all authors Léa Pousse BeltraniDCorresponding Author• Submitting AuthorUniversity of VictoriaiDhttps://orcid.org/0000-0003-2833-411Xview email addressThe email was not providedcopy email addressEdwin NisseniDUniversity of VictoriaiDhttps://orcid.org/0000-0002-0406-2706view email addressThe email was not providedcopy email addressEric BergmaniDGlobal Seismological ServicesiDhttps://orcid.org/0000-0002-7069-8286view email addressThe email was not providedcopy email addressMusavver Didem CambaziDBoğaziçi ÜniversitesiiDhttps://orcid.org/0000-0001-5395-2388view email addressThe email was not providedcopy email addressÉlyse GaudreauiDUniversity of VictoriaiDhttps://orcid.org/0000-0001-5975-8295view email addressThe email was not providedcopy email addressEzgi KarasozeniDAlaska Earthquake Center, University of Alaska Fairbanks,iDhttps://orcid.org/0000-0003-1140-1427view email addressThe email was not providedcopy email addressFengzhou TaniDUniversity of VictoriaiDhttps://orcid.org/0000-0003-1989-7017view email addressThe email was not providedcopy email address

The heterogeneous seafloor topography of the Nazca Plate as it enters the Ecuador subduction zone provides an opportunity to document the influence of seafloor roughness on slip behavior and megathrust rupture. The 2016 M-w 7.8 Pedernales Ecuador earthquake was followed by a rich and active postseismic sequence. An internationally coordinated rapid response effort installed a temporary seismic network to densify coastal stations of the permanent Ecuadorian national seismic network. A combination of 82 onshore short and intermediate period and broadband seismic stations and six ocean bottom seismometers recorded the postseismic Pedernales sequence for over a year after the mainshock. A robust earthquake catalog combined with calibrated relocations for a subset of magnitude >= 4 earthquakes shows pronounced spatial and temporal clustering. A range of slip behavior accommodates postseismic deformation including earthquakes, slow slip events, and earthquake swarms. Models of plate coupling and the consistency of earthquake clustering and slip behavior through multiple seismic cycles reveal a segmented subduction zone primarily controlled by subducted seafloor topography, accreted terranes, and inherited structure. The 2016 Pedernales mainshock triggered moderate to strong earthquakes (5 <= M <= 7) and earthquake swarms north of the mainshock rupture close to the epicenter of the 1906 M-w 8.8 earthquake and in the segment of the subduction zone that ruptured in 1958 in a M-w 7.7 earthquake.