The dynamics of subduction zones are influenced by the sediment supply to the trench, which determines whether the margin is erosive (low supply) or accretive (high supply). At present, trench-fill thicknesses ≥1 km promote accretion, which can lead to the construction of a crustal-scale accretionary complex. Here we discuss the dynamics of very large subduction-accretion complexes that encompass the entire upper plate. The formation of such large complexes due to high sediment supply to the periphery of Gondwana during the Cambrian and Ordovician has been inferred from Cenerian basement units within and outside the Alps. The units record Ordovician metamorphism and anatexis of metagreywackes and metapelites that host elongated sheets of peraluminous orthogneisses and banded amphibolites, indicating a peraluminous magmatic arc situated in a large, cratonized subduction-accretion complex. However, the formation and cratonization of such hot complexes has not been evaluated in mechanical terms and the relevance of some field constraints, including a prevalence of strike slip faulting and lack of late- to post-Cenerian uplift, have remained uncertain. We therefore corroborate the existing model by mechanical considerations and insights from active systems. We discuss the requirements for the formation of hot subduction-accretion complexes and address how high sediment supply affect the upper-plate stress conditions, fault kinematics, rock uplift, and development of topography.

Detailed field-based structural examination of the Kynsikangas shear zone (KSZ), a prominent structural discontinuity of the Svecofennian Province, allows us to better understand the rheological and kinematic behaviour of localized shearing in the lower continental crust. The analysis of deformation kinematics and mineral shape fabrics on multiple scales revealed that the KSZ formed by pure shear-dominated, left-lateral transpression under NW-SE shortening. A pronounced scale-dependent heterogeneity in the geometry and intensity of mineral shape fabrics as well as in the deformation kinematics are structural hall marks of the KSZ. An important result of our analysis is that small-scale kinematic indicators may not portray the regional sense-of-shear and, thus, questions their use for identifying shear zone kinematics in general. Furthermore, the ubiquitous presence of mesoscopic shear bands and S-C fabrics, both interpreted as precursor structures of scaly fabrics, known from active crustal shear zones, may constitute slip transients in a frictional-viscous material. Thus, the KSZ features structural evidence for slow-slip seismic events. In terms of paleotectonic significance, the KSZ is likely structurally linked and kinematically compatible with a major shear zone, the Kolinummi reverse shear zone, to the South of the KSZ. The KSZ can, therefore, be considered part of a network of crustal shear zones pervading lithotectonic terranes that amalgamated during the Svecofennian orogeny. Due to its distinct kinematics and orientation, the KSZ most likely served as a tectonic transfer zone among mostly easterly striking oblique reverse shear zones during later stages of the Svecofennian orogeny.

The Eurekan Belt is an intraplate orogen that extends for nearly 2000 kilometres across the Arctic Realm and is closely linked to large-scale transform faults. After orogenic movements ceased, the Eurekan Belt became dissected, the affected margins of Greenland and the Barents Sea became passive and the Arctic-North Atlantic gateway, the Fram Strait, opened.

To obtain information on the thermal imprint of rifting and continental breakup processes along a sheared margin, we investigated highly mature sedimentary rocks exposed along both of the conjugate margins using apatite fission track and (U‐Th)/He thermochronology.

Our data suggest that a large transform fault system played a major role in the development of the Eurekan Belt and the subsequent formation of the Barents and Greenland margins: along segments of the transform fault system heating occurred prior to and during the Eurekan Orogeny. Heat transfer may have caused or contributed to lithospheric weak zones which focussed deformation during the intraplate orogeny. Movements along the transform fault system continued after the end of the Eurekan Orogeny and caused further structural weakening of pre‐existing fault zones. These were utilised during the final continental breakup leading to the opening of the Fram Strait.

The formation of tight oroclines, notably how crust accommodates curvature increase kinematically, remains an outstanding topic in tectonics. Here, we focus on elucidating the kinematics of upper-crustal deformation of the eastern Hellenic arc. Apparently, this portion of the Hellenic arc rotated some 40° counterclockwise over the past 5 Ma due to arc tightening. GIS-and field-based mapping of kilometer-scale, first-order faults, UAV-based photogrammetry and recording the orientation of higher-order brittle shear faults, collected from Plio-Pleistocene deposits along the east coast of the Island of Rhodes, were combined for a multiscale kinematic analysis. Field-based observation revealed that deformation on the Island of Rhodes has been accommodated mainly by normal faults with variable orientations. Notably, NE-striking first-order faults are displaced by NW-striking ones, indicating the relative age of the two. Kinematic analysis of higher-order shear faults recorded at stations close to first-order faults allowed us to infer the principal strain axis orientations associated with the latter. Accordingly, NE-striking first-order faults formed under NW–SE, i.e., arc-normal, extension, while the younger, NW-striking faults were generated under NE–SW horizontal, i.e., arc-parallel, extension. We attribute the observed change in fault kinematics to upper-crustal distortion of the eastern Hellenic arc resulting from overall arc tightening. Specifically, arc-normal extension associated with early-formed first-order faults resulted likely from subduction roll-back, whereas arc-parallel (longitudinal) extension gained in importance at later stages of arc tightening.

The sinistral strike-slip Motagua Fault in Guatemala is part of the North American-Caribbean plate boundary system. A magnitude 7.5 earthquake that occurred on the fault in 1976 caused 230 km of surface rupture, up to 3 m surface offset, and the demise of ca. 23,000 people. Knowledge of earlier large earthquakes on this fault is largely lacking, hampering our understanding of the tectonic regime and the associated hazards for a largely vulnerable population. We used historical archives, aerial and satellite imagery, shallow geophysics, drone lidar surveys, and field mapping to identify a site that holds a geological record of past movements of the fault. In a paleoseismological trench at La Laguna (Sanarate), we found evidence for four surface-rupturing earthquakes. A small bend in the fault trace causes localized oblique-slip motion on the fault, leading to vertically offset strata and colluvial wedge formation in the hanging wall. Radiocarbon dating, optically stimulated luminescence, and archaeological findings of Mayan ceramics and obsidian blades show that the earthquakes occurred in the last ca. 1700 years. This implies a recurrence interval of 400-500 years along this part of the plate boundary.

In 2021, a period of volcanic unrest began on the Reykjanes Peninsula (Iceland). To date, eight eruptions have taken place with durations ranging from one day to half a year. The cumulative eruption volume is about 400 x 10⁶ m³ and covers an area of about 46 km². The eruptions can be divided into the Fagradalsfjall eruptions, directly fed by a deep-seated reservoir, and the Sundhnúkur eruptions, where the uprising magma is temporarily stored in a sill.

Magma travels in dykes, and breaks its way through the rock as long as the fluid pressure exceeds the host-rock strength. The earthquakes reflect this fracturing. Together with the inflation of the sill, earthquake swarms serve as predictors for imminent eruptions in the study area.

All the eruptions have taken place in the very close vicinity of the fishing town of Grindavík. One eruption started in the area protected by dams. Under the premise that magma transport can be traced by the earthquakes, I am improving the accuracy with which the location of the eruption site can be predicted.

I apply a fully automated and thus unbiased algorithm. The algorithm detects the number of clusters and assigns earthquakes from the subsequent time windows, according their spatial distribution, to the clusters. It then analyses the geometric properties of the clusters, ranks them and finally determines a location that presents the most likely eruption site for each time window. Finally, I compare the results with real world data and determine the applicability of my approach.