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Grabens, or valleys formed during extensional tectonic events, are common but rarely observed during formation. In November 2023, inelastic surface deformation formed abruptly along Iceland's plate boundary in Grindavík. We documented graben formation in real‐time through satellite mapping (InSAR), seismicity, GNSS data, repeated lidar surveys, and field mapping. Five normal faults and ∼12 fissures ruptured the surface delineating two grabens separated by a horst, a context not present in other contemporary case studies. The graben normal faults slipped rapidly (over hours) and maximum surface motions coincided with the occurrence of turbulent seismic swarms in both space and time. Although 3 eruptions took place ∼15 km northeast of Grindavík from 2021 to 2023, attributed to magma intrusions (i.e., dikes), none of these also formed grabens. Thus, the Grindavík grabens shows evidence for tectonic origins. Real‐time monitoring of these phenomena provide insight into graben formation on Earth and potentially on other planets. Valleys known as grabens, typically caused by extensional tectonic events, are a common geological feature, yet their formation is rarely observed. In November 2023, such two grabens suddenly emerged along the boundary between tectonic plates in the town of Grindavík, Iceland. The grabens were shaped by tectonic activity expressed by a swarm of earthquakes and associated ground deformation and resulted in normal faults rupturing the surface and cutting through houses, linear infrastructure including water pipelines and roads within Grindavík. We document the grabens and horst in real time using satellite mapping (InSAR), geodetic GPS data, repeated drone surveys, field mapping, and seismic recordings from a local seismic network. The combination of these data provide unprecedented level of precision in characterizing surface and sub‐surface deformations, especially when maximum surface motions correlate with a turbulent seismic activity in both space and time. Critically, following the formation of the grabens, a series of intensive through short‐lived eruptions happened in December 2023, January 2024, February 2024, March, and May 2024 within the northernmost portion of the grabens. Our observations provide valuable insights into the natural laboratory of Iceland and contribute to the understanding of plate tectonics both on Earth and other planets. The 2023 seismic swarm and extension lead to a graben forming that coincides in time and space along Iceland's plate boundaryDuring 2021 to December 2023 only one tectonic graben formed, although 4 eruptions have taken placeThe graben in Grindavík, Iceland is wider at the surface than most recently documented grabens (∼4,500 m vs. <1,000 m) The 2023 seismic swarm and extension lead to a graben forming that coincides in time and space along Iceland's plate boundary During 2021 to December 2023 only one tectonic graben formed, although 4 eruptions have taken place The graben in Grindavík, Iceland is wider at the surface than most recently documented grabens (∼4,500 m vs. <1,000 m)

Tonga is a convergent plate boundary between the Pacific and Australian plates and is the fastest and the most seismically active deep subduction system in the world. We focused on southern Tonga (south of latitude 22°S) and the mantle transition zone (depths of 410–670 km), where seismic activity forms two subparallel bands of events in the east and west. We performed stress analysis by inverting focal mechanisms of earthquakes available in the Global Centroid Moment Tensor catalog and revealed two distinct stress regimes in the slab. While the stress orientation in the eastern slab segment conforms to the down‐dip compressional stress along the entire slab, the stress orientation in the western slab segment is different, having the maximum compression in the vertical direction. This suggests that the western segment can represent a stagnant slab with flattening and bending, as proposed by modeling studies. Its connection with the younger actively subducting slab is supported by the horizontal westward shift at 520 km depth. The stress analysis also indicates substantially different fault orientations in both segments. In the actively dipping slab, the majority of activated faults are predominantly sub‐horizontal. However, they are significantly inclined from vertical in the stagnant slab segment. A higher scatter in fault orientations in the stagnant slab suggests deformation, fragmentation and rheological complexity resulting from bending and flattening. Tonga is a part of Tonga‐Kermadec, the 2,550‐km long subduction system in SW Pacific. It represents a convergent plate boundary between the Pacific and Australian plates. It is the fastest converging and the most seismically active deep subduction in the world. In the mantle transition zone, especially at depths greater than 500 km, the geometry of the slab becomes complex, forming separated slab segments. We performed stress analysis in the mantle transition zone (depths 410–670 km) with a focus on southern Tonga (south of latitude 22°S) where seismicity forms two subparallel bands of events in the east and west. We inverted publicly available data, focal mechanisms of earthquakes from the Global Centroid Moment Tensor catalog, and revealed two distinct stress regimes. While the stress orientation in the eastern segment matches the down‐dip compression of the subducting slab, the stress orientation of the western segment is different with the maximum compression in the vertical direction. This suggests that the western segment represents a stagnant slab with flattening and bending. Such findings are supported by the horizontal westward shift at 520 km depth and by substantially different fault orientations in both segments. We performed stress analysis in southern Tonga mantle transition zone from focal mechanisms of earthquakes listed in Global Centroid Moment Tensor catalogWe revealed two distinct stress regimes: down‐dip compression matching subducting slab in the east and vertical compression in the westWestern segment suggests a stagnant slab with flattening and bending supported by horizontal shift and different fault orientations We performed stress analysis in southern Tonga mantle transition zone from focal mechanisms of earthquakes listed in Global Centroid Moment Tensor catalog We revealed two distinct stress regimes: down‐dip compression matching subducting slab in the east and vertical compression in the west Western segment suggests a stagnant slab with flattening and bending supported by horizontal shift and different fault orientations

We analyze waveforms of local earthquakes occurring before, between, and after the two consecutive 1999 Mw> 7 İzmit and Düzce earthquakes in NW Turkey. The waveforms were recorded at three seismic stations DOK, EKI, and GOK located around the Mudurnu segment of the North Anatolian Fault Zone. We focus on the interpretation of a distinct secondary phase contained in the Pwave coda that is well separated from the direct Pwave. The phase is visible in many waveforms of most seismicity clusters and has a specific constant time delay after the direct Pwave arrivals at each station, irrespective of epicentral distance, hypocentral depth, or back azimuth. Based on a polarization analysis of records at station GOK, this secondary phase is interpreted as a PSwave converted at an interface near the stations. Its particle motion is consistent with the direct Swave and displays Swave splitting produced by the anisotropic upper crust. Synthetic modeling indicates that this PSphase can be converted either at a horizontal interface or at a steeply inclined interface. The steep Mudurnu fault zone with the near‐surface setting indicating a juvenile pull‐apart structure fits well into these interpretations, which are in agreement with the eastward progressing transtensional tectonics known for the region. Detailed study of waveforms from seismic activity at the İzmit‐Düzce rupture zone in NW Turkey is presentedNew advanced waveform processing results in the detection of prominent secondary phases in Pwave coda well separated from direct PwavePolarization analysis reveals PSphase converted at the upper crustal structure in agreement with near‐fault setting of the Mudurnu segment

The Eger Rift is an active element of the European Cenozoic Rift System associated with intense Cenozoic intraplate alkaline volcanism and system of sedimentary basins. The intracontinental Cheb Basin at its western part displays geodynamic activity with fluid emanations, persistent seismicity, Cenozoic volcanism, and neotectonic crustal movements at the intersections of major intraplate faults. In this paper, we study detailed geometry of the crust/mantle boundary and its possible origin in the western Eger Rift. We review existing seismic and seismological studies, provide new interpretation of the reflection profile 9HR, and supplement it by new results from local seismicity. We identify significant lateral variations of the high‐velocity lower crust and relate them to the distribution and chemical status of mantle‐derived fluids and to xenolith studies from corresponding depths. New interpretation based on combined seismic and isotope study points to a local‐scale magmatic emplacement at the base of the continental crust within a new rift environment. This concept of magmatic underplating is supported by detecting two types of the lower crust: a high‐velocity lower crust with pronounced reflectivity and a high‐velocity reflection‐free lower crust. The character of the underplated material enables to differentiate timing and tectonic setting of two episodes with different times of origin of underplating events. The lower crust with high reflectivity evidences magmatic underplating west of the Eger Rift of the Late Variscan age. The reflection‐free lower crust together with a strong reflector at its top at depths of ~28–30 km forms a magma body indicating magmatic underplating of the late Cenozoic (middle and upper Miocene) to recent. Spatial and temporal relations to recent geodynamic processes suggest active magmatic underplating in the intracontinental setting. Multidisciplinary study of magmatic underplating and deep covered magmatic/fluid activity within new continental rift areaTwo types of magmatic emplacement with high‐velocity reflective lower crust and high‐velocity reflection‐free magma bodyDifferent character of the underplated material responds to two episodes with different times of origin of underplating events The Eger Rift, active element of the European Cenozoic Rift System, is associated with intense Cenozoic intraplate alkaline volcanism and system of sedimentary basins. The intracontinental Cheb Basin at its western part displays geodynamic activity with fluid emanations, persistent seismicity, Cenozoic volcanism, and neotectonic crustal movements at the intersections of major intraplate faults. In this paper, we study detailed geometry of the crust/mantle boundary and its possible origins. Based on seismic data from reflection and refraction profiles and from local seismicity, we identify significant lateral variations of the high‐velocity lower crust and relate them to mantle‐derived fluids and petrology. The observations point to a local‐scale magmatic emplacement at the base of the continental crust within a new rift environment. The concept of magmatic underplating is evidenced by detecting two types of lower crust: a high‐velocity lower crust with pronounced reflectivity and a high‐velocity reflection‐free lower crust. The character of the underplated material enables to differentiate timing and tectonic setting of two episodes with different times of origin of underplating events. Spatial and temporal relations to recent geodynamic processes suggest active magmatic underplating in the intracontinental setting.

The occurrence and specific properties of earthquake swarms in geothermal areas are usually attributed to a highly fractured rock and/or heterogeneous stress within the rock mass being triggered by magmatic or hydrothermal fluid intrusion. The increase of fluid pressure destabilizes fractures and causes their opening and subsequent shear-tensile rupture. The spreading and evolution of the seismic activity are controlled by fluid flow due to diffusion in a permeable rock (fluid-diffusion model) and/or by redistribution of Coulomb stress (intrusion model). These models, however, are not valid universally. We provide evidence that none of these models is consistent with observations of swarm earthquakes in West Bohemia, Czech Republic. Full seismic moment tensors of microearthquakes in the 2008 swarm in West Bohemia indicate that fracturing at the starting phase of the swarm was not associated with fault openings caused by pressurized fluids but rather with fault compactions. This can physically be explained by a fault-weakening model, when the essential role in the swarm triggering is attributed to degradation of fault strength due to long-lasting chemical and hydrothermal fluid-rock interactions in the focal zone. Since the rock is exposed to circulating hydrothermal, CO2-saturated fluids, the walls of fractures are weakened by dissolving and altering various minerals. The porosity of the fault gauge increases, and the fault weakens. If fault strength lowers to a critical value, the seismicity is triggered. The fractures are compacted during failure, the fault strength recovers, and a new cycle begins. The occurrence of earthquake swarms in geothermal areas is usually attributed to a highly fractured rock and/or heterogeneous stress within the rock mass being triggered by magmatic or hydrothermal fluid intrusion. The increase of fluid pressure destabilizes fractures and causes shear-tensile rupture. The spreading and evolution of the seismic activity are controlled by fluid flow due to diffusion in a permeable rock and/or by redistribution of Coulomb stress. This model, however, is not valid universally. We provide evidence that the model is inconsistent with observations of earthquake swarms in West Bohemia, Czech Republic. Microearthquakes in swarms in West Bohemia indicate that fracturing was not associated with fault openings but rather with fault compactions. This can be explained by a fault-weakening model, when the essential role in the swarm triggering is attributed to chemical and hydrothermal fluid-rock interactions in the focal zone. Since the rock is exposed to circulating hydrothermal, CO2-saturated fluids, the walls of fractures are weakened by dissolving various minerals. The porosity of the fault gauge increases, and the fault weakens. If fault strength lowers to a critical value, the seismicity is triggered. The fractures are compacted during failure, the fault strength recovers, and a new cycle begins. Earthquake swarms in West Bohemia are not caused by accumulation of crustal stress or by fluid overpressure but by fault weakeningFault is repeatedly eroded by fluids due to chemical and hydrothermal fluid-rock interactions and compacted during the swarm activityThe model of swarm recurrence is supported by observations of accurately determined nondouble-couple components of seismic moment tensors

The waveforms of microearthquakes are of high frequency and complicated. They contain many phases secondarily generated at crustal interfaces and at small‐scale inhomogeneities. They are highly sensitive to focal mechanisms and thus very different for each station of local networks. However, with a large number of microearthquakes, the scattered waves present in the waveforms can serve for identifying the prominent crustal discontinuities and for determining their depth. In this paper, we develop a new approach for extracting information on crustal structure from such waveforms and apply it for determining depth and lateral variations of crustal discontinuities. We show that strong dependence of microseismic waveforms on radiation pattern requires good station coverage and knowledge of focal mechanisms of the microearthquakes. Analysis of real observations is supported by waveform modeling and by analysis of radiation patterns of scattered waves. The robustness of the inversion for depth of crustal interfaces is achieved by stacking of a large number of waveforms and by applying a grid search algorithm. The method is demonstrated on two microseismic data sets of different origin: microseismicity induced during the Continental Super‐Deep Drilling Project (KTB) 2000 fluid injection experiment and natural seismicity in the West Bohemia swarm region. High‐frequency conversions at the KTB site indicate a prominent interface at depths of 2.3–4.1 km consistent with previous interpretations. Geologically, it may represent the contact of granitoids with much faster metabasites underneath. Seismicity in West Bohemia indicates a strong‐contrast interface at depths of 3.5–6.0 km. This interface is in agreement with previous profiling and might be related to trapping of fluid emanations ascending from the mantle. New approach for extracting information on crustal structure from waveforms of microearthquakesJoint focal mechanism analysis, waveform stacking, and inversion result in topography of interfacesApplication to KTB 2000 fluid injection microseismicity and swarm seismicity in West Bohemia

The paper focuses on the adaption of the theoretical models of the regional tourism competitiveness to the conditions of the Czech Republic. The authors of this study analyze a newly emerged theoretical model of regional competitiveness monitoring with respect to the current data availability. The ultimate aim is to specify a proposal for the Czech national tourism organization (CzechTourism) in terms of practical usage and monitoring of the competitiveness model. The principal question is how and why to monitor the competitiveness of a tourist destination at the regional and national levels in the Czech Republic. The next step of the project is the conducting of the research, testing of the model and the implementation.