Continental Plate Research Articles

Lithospheric delamination as the driving mechanism of intermediate-depth seismicity in the Bucaramanga Nest, Colombia

The Bucaramanga nest (BN) is an area of exceptionally strong intermediate-depth seismicity localized in a narrow zone at 150–170 km depth beneath the continental plate in Colombia. To explain the very unusual mantle seismicity cluster in this area, we built a seismic velocity model in the vicinity of BN with the use of local earthquake tomography and developed a numerical hydromechanical model. Our seismic model shows a strong high-velocity anomaly at 130–167 km coinciding with the BN seismicity. The relocated seismicity can be separated in two clusters. We propose that the upper BN cluster at ~ 130 km depth is attributed to dehydration embrittlement, whereas the lower BN cluster at ~ 150 km depth coinciding with the high-velocity body is caused by lithospheric delamination, creating a “drip” that falls down over the subducting oceanic plate, enhancing fluid release from the slab, potentially increasing seismicity.

Scaling of earthquake waiting time distributions in northern Chile

SUMMARY In this study, we examine the scaling of earthquake waiting time distributions in Northern Chile. For this purpose, we analysed 7-yr high spatial resolution and low completeness magnitude IPOC seismic catalogue and 43-yr USGS catalogue. A unified earthquake moment–space–time scaling relation is empirically evaluated by calculating waiting times for different ranges of magnitude and epicentral area linear dimension and estimating the associated scaling coefficients, β analogue to b-value and γ, the correlation fractal dimension. We find a scaling function that can be characterized with three distinct regions, regions whose behaviour depends on whether seismicity is in the coastal area or at intermediate depth. Moreover, high resolution localizations from the IPOC catalogue allows us to further observe differences: the lower plane seismicity of the double seismic zone behaves just like that at intermediate depth, while the crustal upper plate and the upper plane from the double seismic zone seismicity behaves more like interface seismicity. Thus, the earthquake waiting time distribution primarily depends on whether seismicity is located in a crust-on-crust or in a crust–mantle system: having, respectively, high/low correlated behaviour in the short scale region, non-exponential/exponential decay in the transition middle region and, in all cases, long-term clustering with a slower than exponential decay in the long scale.

Crustal and Lithospheric Variations along the Western Passive Continental Margin of the Indian Peninsula

The western passive continental margin (WPCM) of the Indian Peninsula is one of the world's largest and most remarkable escarpments, signifying a boundary between oceanic and continental lithospheres. It traverses distinct lithological units, majorly the SGT, WDC, and DVP, each characterized by distinct geological structures, geochronological histories, and petro-physical properties. Despite numerous research efforts, the exact mechanisms governing the WPCM evolution and its developmental connections remain unclear due to limited data and significant uncertainties. In our study, we meticulously analyzed global and local models, focusing on the Western Ghats (WG), to examine crust and lithosphere thickness. Our analysis revealed significant uncertainties in crustal and lithospheric variations, with a maximum difference of 10.68% in crust thickness and 20.04% in lithospheric thickness across different major lithological formations in the WG. These differences can have a substantial impact on the geodynamic analysis of lithospheric structures and tectonic evolution. Additionally, we developed a 2-D lithospheric density model over the WG, crossing the major geological units, which delineates the crust and lithospheric structure between the eastern and western sides of the escarpment. Our results, in conjunction with geomorphological data, suggest that the WPCM’s thick lithosphere with elevated topography illustrates a continuous upwarp, supported by flexural compensation of uplifted terrain. The movement of the Indian plate, primarily in the N-S and NW-SE directions, subsequently modified the entire escarpment. This model offers insights into the evolution of the WPCM and potentially contributes to the formation of the NE-SW fault in the southern part of the South Indian Shield, with potential implications for the Palghat gap.

Analysis of Sumatran Earthquake Coulomb Stress Changes in Geothermal Potential in Rianite, Samosir Regency

Increasing energy demand and high world oil prices are making countries turn to geothermal energy use. Indonesia is a country that has geothermal energy due to Indonesia's geographical location and geological conditions, which is located between three active earth plates so that Indonesia has 240 volcanoes and often experiences earthquakes. The 2003-2013 earthquake data obtained are coordinates, magnitude, depth, focal mechanism and all these data are analyzed in the coulomb stress method. Rianiate geothermal measurement data in March 2013 included geothermal location, hotspring and air temperature, pH, and geochemical measurements. The analysis results showed that the highest coulomb stress value was at a depth of 90 km of 0.56 bar while the shear and normal values were 0.452 bar and 0.251 bar. The result of the spread of coulomb stress is to the northeast, east and southeast. Then the results of the analysis of the direction of distribution of coulomb stress are compared to the location of the hotspring based on a decrease in temperature, the change in the potential of hotspring 1 leads to hotspring 2, 3, and 4 in the opposite direction, namely northwest or leads to the largest source of colulomb stress, so that Coulomb Stress Changes affect indirectly changes in the geothermal potential of Rianiate

Timeframe of eastern Paleo-Tethys closure: Constraint on the Songpan-Ganzi Complex by big data-based multiproxy provenance analysis

The Songpan-Ganzi Complex (SGC) is one of the largest turbidite complexes on Earth. The source-to-sink processes of the SGC are closely linked to the closure of the Paleo-Jinsha Ocean in the eastern Paleo-Tethys realm, so the spatiotemporal transitions in SGC provenance provide the potential to constrain the closure time. A comprehensive multiproxy provenance investigation, integrating detrital zircon UPb geochronology, whole-rock SmNd isotope data, and paleocurrent analysis, shed light on the origin of the Triassic SGC turbidites. In this study, it was determined that a significant proportion (exceeding 70%) of the detrital material comprising the SGC turbidites was sourced from the northwestern margin of the Yangtze Craton and the Qinling Orogen. A comprehensive and quantitative provenance study revealed that the Songpan-Ganzi turbidites primarily originated from collisional orogenic belts at convergent continental plate margins and secondarily from magmatic arcs and other tectonic units surrounding the basin. In this study, it was demonstrated that the SGC contains important information on the convergence of Eurasia and the tectonic evolution of surrounding terranes. (1) The South Qinling Orogen experienced significant rapid exhumation during the Ladinian to early Carnian. (2) The closure of the Paleo-Jinsha Ocean most likely occurred during the transition period between the upper and lower members of the Zhuwo Formation (ca. 231 Ma, middle Carnian). (3) During the Late Triassic, the crust of the Yidun Terrane underwent significant vertical accretion, resulting in a topography exceeding that of the Jomda-Weixi arc by the late Norian.

Mapping Mantle Flows and Slab Anisotropy in the Cascadia Subduction Zone

AbstractThe Cascadia margin is an unusual subduction zone characterized by the downdip movement of young and thin oceanic plates, where mantle flow and intraslab deformation are still unclear. Here we present new anisotropic tomography of the Cascadia subduction zone, in which the hexagonal symmetry axis of anisotropy is tilting rather than horizontal or vertical as assumed in previous studies of seismic anisotropy. Subduction‐induced entrained and toroidal flows under the Cascadia margin are discriminated well by the spatial relationship between tilting‐axis anisotropy and slab geometry. The obliquely entrained flow is trapped in a narrow zone (<100 km wide) above and below the subducting slab and reaches ∼200 km depth, which is surrounded by large‐scale sub‐horizontal toroidal flow. The intraslab anisotropy is trench‐normal above 80 km depth but changes to trench‐parallel at 100–400 km depths, which may reflect fossil anisotropy overprinted by deep deformation beneath the arc, or joint effect of serpentinization and hydrous faulting.

Theory of continental drift – causes of the motion. Outline of the theory

The theory of mantle convection currents as the cause of lithospheric plate movements has several major problems, including the absence of an adequate energy source. As shown in our previous contribution, an unbiased interpretation of geochemical data does not support the assumptions of a significant amount of radionuclides in the lower mantle or even in the core. It is our assertion that solar radiation is the primary energy source in the lithosphere. This energy is converted into mechanical energy via thermoelastic waves, even in depths with minimal temperature fluctuations. This has been confirmed by various methods of continuous stress measurement. The periodic and quasiperiodic thermoelastic reversible deformations, such as the circadian and annual cycles (including tidal periods), can also cause irreversible deformations due to the ratcheting mechanism. The 2D model showed that the strength limit is exceeded in 0.3 % of all diurnal cycles during the year. As a consequence, continents tend to extend while the oceanic lithosphere is pushed and overthrusted between continents. The middle-ocean ridges, similar to continental rifts, are filled by ascending magma which is one example of the ratcheting mechanism. The final plate movements are determined by the distribution of major continents and the overall westward drift of the lithosphere, which is slower for deep-rooted plates like the Indian one. Large asteroid impacts are important triggers (and possibly significant energy sources) of discrete events, like the formation of hotspots and large igneous provinces.

Application of Regional Gravity and Magnetic Data in Yambajan and Gudui Geothermal Fields, Tibet

Yambajan geothermal field is the first wet steam field developed in the Chinese mainland. It is also the geothermal power station with the highest elevation in the world. It is rich in geothermal resources and its exploration and development level is relatively high. The Gudui geothermal field is the second largest geothermal display area in Tibet. It is rich in geothermal resources, second only to Yambajan Geothermal field, but its energy construction is relatively backward. In this paper, satellite gravity and aeromagnetic data are used to make a comprehensive comparative analysis of the two regions. The results show that they are both low gravity value areas and weak magnetic, and both of which are located on the fault zone. There is a very obvious relationship between the regional tectonic characteristics and the distribution law of hydrothermal activities, and the tectonic activities provide favorable conditions for the formation of hydrothermal activities. The fault depth in the south of the study area is deeper than that in the north, which is inferred to be caused by plate movement.

On the distribution of tangential mass forces in the Earth's lithosphere

The study aims to determine and interpret the distribution of the global tangential mass force (TMF) vector field by azimuthal orientation and intensity. Using cluster and correlation analysis, we compared the direction of the TMF vector field with the direction of movement of permanent GNSS stations and the direction of movement of the GSRM model continental velocities from the Global Strain Rate Map Project. Methodology. The author continues their study of additional planetary stresses in the lithosphere caused by distributed mass forces. The forces in question may be linked to the repositioning of the Earth's lithosphere, which can create stresses aimed at aligning the distribution of lithospheric masses with the geoid's figure. This repositioning happens through the mechanism of gravitational forces and the principle of minimum potential energy. The presence of a deviation of the plum line from the normal to the surface of the solid Earth determines the appearance of TMF acting in the upper shell of the Earth. It is proposed to calculate the amplitudes and directions of the vectors of such TMF based on data regarding the difference in the parameters of two global ellipsoids that approximate the physical surface of the lithosphere and the geoid. Originality. For the modern era, the value of the angle of rotation between the smallest axis of the ellipsoid approximating the surface of the lithosphere and the axis of rotation of the Earth is 2.6°. The distribution of the TMF vector field is consistent with the contours of the continents, i.e., the arrows of the vectors indicate the directions of lateral movement of tectonic plates and the movement of continents during the Earth's evolution. As a result of the change in the orientation of the ellipsoid describing the lithosphere, an updated field of potential horizontal forces is formed, which, by the conservation of the momentum of motion, move lithospheric masses and generate stresses and deformations in the lithospheric shell. Since the TMF has different directions and intensities, a cluster analysis of the TMF distribution was performed. It revealed certain regularities in the distribution of these parameters. We also compared the directions of the TMF vector field with the directions of movement of permanent GNSS stations and the directions of movement of model velocities of the continents of the GSRM (digital model of the tensor field of the global velocity gradient). Scientific novelty. The study detailed the peculiarities of the connection between the directions of the TMF vector field, the directions of movement of permanent GNSS stations, and the ones of the model velocities of the GSRM continents. Studies of the TMF, which arise as a result of the reorientation of the thin solid shell of our planet, have shown that a deformation field of shear is formed on its surface. In our opinion, this is one of the likely factors of the process that triggers global movements of lithospheric blocks. As a result, the shape of the lithosphere is transformed, which is characterized by a change in the size of the axes of the ellipsoids describing the surface of the lithosphere and their orientation. Practical significance. The research results make it possible to more reliably interpret the peculiarities of the TMF distribution. These forces can trigger mechanisms for discharging accumulated stresses, which is important for studying seismicity.

Segmented Up‐Bending of the Arabian Continental Plate Revealed by Pn Attenuation Tomography

AbstractThe Zagros orogen in the Iranian Plateau serves as a natural laboratory for studying the tectonic evolution of the transition from oceanic subduction to continental collision. Various observations from both geology and geophysics show that deep oceanic slabs may have detached one after another from the Arabian continental margin, forming a complex plate front beneath the Zagros orogen. However, where slab detachment occurred and how slab detachment affects shallower continental underthrusting remain poorly understood. The mechanism behind the complex post‐collision magmatism remains elusive. While the uppermost mantle is often considered the heart of the mantle lid, its rheological variations can provide insights into the underlying thermal structure. Here, we construct a high‐resolution Pn‐wave attenuation model for the uppermost mantle beneath the Iranian Plateau and surrounding areas using a newly compiled data set and constrain the lithospheric structure by combining the Lg‐wave attenuation within the crust. Weak Pn‐wave attenuation outlines the boundary of the Arabian Plate near the Moho discontinuity, extending further in the direction of underthrusting in the northwestern and southeastern regions. This is likely due to the up‐bending and underplating of the Arabian lithosphere following the cessation of slab pull. The overlying crusts in northwestern and southeastern Zagros thickened under the compressive force from plate underplating. The correlations among the surface Miocene‐Quaternary volcanism, strong Lg attenuation in the crust and strong Pn attenuation in the uppermost mantle suggest that asthenospheric materials escaped from slab windows and further intruded into the upper mantle and crust to feed the post‐collision volcanoes.

The Correlation between Ionospheric Electron Density Variations Derived from Swarm Satellite Observations and Seismic Activity at the Australian–Pacific Tectonic Plate Boundary

Swarm electron density (Ne) observations from the Langmuir probe (LP) can detect ionospheric disturbances at the altitude of a satellite. Along-track satellite observations provide a large number of very short observations of different places in the ionosphere, where Ne is disturbed. Moreover, different perturbations occupy various Ne signal frequencies. Therefore, such short signals are more recognizable in two dimensions, where aside from their change in time, we can observe their diversity in the frequency domain. Spectral analysis is an essential tool applied here, as it enables signal decomposition and the recognition of composite patterns of Ne disturbances that occupy different frequencies. This study shows a high-resolution application of short-term Fourier transform (STFT) to Swarm Ne observations in the Papua New Guinea region in the vicinity of earthquakes, tsunamis, and related general seismic activity. The system of tectonic plate junctions, including the Pacific–Australian boundary, is located orthogonally to Swarm track footprints. The selected wavelengths of seismically induced ionospheric disturbances detected via Swarm are compared with the three sets of three-month records of seismic activity: in the winter solstice of 2016/2017, when seismic activity was highest, and in the summer solstice and vernal equinox of 2016, which were calmer. Moreover, more Swarm data records are analyzed at the same latitudes for validation purposes, in a place where there are no tectonic plate boundaries that are orthogonal to the Swarm orbital footprint. Additional validation is supplied through Swarm Ne observations from completely different latitudes, where the Swarm orbital footprint orthogonally crosses a different subducting plate boundary. Aside from the seismic energy, the solar radio flux (F10.7), equatorial plasma bubbles (EPBs), and geomagnetic ap and Dst indices are also reviewed here. Their influence on the ionospheric Ne is also found in Swarm observations. Finally, the Pearson correlation coefficient (PCC), applied to the pairs of 3-month time series created from Swarm Ne variations, seismic energy, ap, Dst, and F10.7, summarizes the graphical inspection of mutual correlations. It points to the predominant correlation of Swarm Ne disturbances with seismicity, especially during nighttime. We show that most of the Ne disturbances at a selected wavelength of 300 km correlate more with seismicity than with geomagnetic and solar indices. Therefore, Swarm LP can be assessed as being capable of observing the lithosphere–atmosphere–ionosphere coupling (LAIC) from the orbit.

Long-term circatidal rhythms of heart rate, gill ventilation, and locomotion in the American horseshoe crab, Limulus polyphemus (Arthropoda: Chelicerata: Merostomata: Limulidae).

While several marine species exhibit biological rhythms of heart rate, gill ventilation, or locomotion, the relationship between these three measures in any species remains unexplored. The American horseshoe crab, Limulus polyphemus, Linnaeus, 1758, expresses circalunidian locomotor rhythms and circadian eye sensitivity rhythms but it is not clear if either heart and ventilation rates are controlled on a circadian or circatidal basis or the nature of the relationship between these three measures. The goal of this study was to determine the extent to which the heart and ventilation rates of Limulus polyphemus are coordinated with its endogenous rhythms of locomotion. To address this goal, rhythmic beating of the heart and movements of the gill plates were recorded in freely moving horseshoe crabs. Most animals exhibited robust circatidal rhythms of locomotion, heart rate, and ventilation that were highly correlated with each other over three weeks of continuous recording. These results are the first showing long term rhythms of all three measures in any marine species and suggest that heart rate and ventilation rhythms are coordinated in Limulus polyphemus both with each other, and with locomotion, and thus are all modulated on a tidal basis.

A global zircon U–Th–Pb geochronological database

Abstract. Since the start of the 21st century, the widespread application of ion probes has promoted the mass output of high-precision and high-accuracy U–Th–Pb geochronological data. Zircon, as a commonly used mineral for U–Th–Pb dating, widely exists in the continental crust and records a variety of geological activities. Due to the universality and stability of zircon and the long half-lives of U and Th isotopes, zircon U–Th–Pb geochronology can provide nearly continuous records for almost the entirety of Earth's history and is thus essential to studying the growth and evolution of the continental crust and Earth system evolution. Here, we present a database of zircon U–Th–Pb geochronology that samples the global continental crust and spans nearly all of Earth's history. This database collects ∼2 000 000 geochronology records from ∼12 000 papers and dissertations. This paper describes the compiled raw data, presents the relationship between dating error and zircon age, compares the error levels of different dating instruments, and discusses the impact of sampling bias on data analysis as well as how to evaluate and minimize this impact. In addition, we provide an overview of the temporal and spatial distribution of global zircon ages and provide key insights into the potential research value of zircon ages for Earth system science, such as crustal evolution, plate tectonics, and paleoclimate changes, as well as commercial use in mining and energy exploration. Overall, this data collection provides us with a comprehensive platform with which to study zircon chronological data in deep time and space. The described zircon database is freely available via Zenodo at https://doi.org/10.5281/zenodo.7387566 (Wu et al., 2023).

Heterogeneous Crustal Structure of the Hikurangi Plateau Revealed by SHIRE Seismic Data: Origin and Implications for Plate Boundary Tectonics

AbstractMarine multichannel and wide‐angle seismic data constrain the distribution of seamounts, sediment cover sequence and crustal structure along a 460 km margin‐parallel transect of the Hikurangi Plateau. Seismic reflection data reveals five seamount up‐to 4.5 km high and 35–75 km wide, with heterogeneous internal velocity structure. Sediment cover decreases south‐to‐north from ∼4.5 km to ∼1–2 km. The Hikurangi Plateau crust (VP 5.5–7.5 km/s) is 11 ± 1 km thick in the south, but thins by 3–4 km further north (∼7–8 km). Gravity models constructed along two seismic lines show the reduction in crustal thickness persists further east, coinciding with a bathymetric scarp. Gravity data suggest the transition in crustal thickness may reflect spatial variability in deformation and lithospheric extension associated with plateau breakup. Variability in the thickness of subducting crust may contribute to differences in megathrust geometry, upper‐plate stress state and high‐rates of contraction and uplift along the southern Hikurangi margin.

Decoding subcontinental lithosphere processes: The key role of fractional crystallization in Central Andes monogenetic volcanism - Insight from El Negrillar volcanic field, Chile

Subduction zones are complex geodynamic settings in which volcanic arcs form due to the interaction between subducting slabs, water, and continental materials. Investigating this extensive Earth recycling system offers valuable insights into the exchange of materials between the crust and mantle. While previous research has primarily focused on analyzing polygenetic volcanoes to explore this interaction, monogenetic volcanic fields (MVF) present an opportunity to delve into the mechanisms operating within the upper and lower mantle. Monogenetic volcanoes are a class of volcanoes that are typically smaller in size but showcase a range of eruptive styles and compositions. These volcanoes can be found in various locations along the arc, including the main Central Volcanic Zone (CVZ) (arc-front volcanoes), and even far from the tectonic plate boundaries in the back-arc region (intraplate volcanism).We carried out a detailed geochemical study of El Negrillar (EN) MVF, located in the Central Andes main-arc, on the Altiplano-Puna Plateau's southwestern border. The volcanic field has 35 eruptive centers and a total of 86 eruptive phases originating from its three clusters: Northern, Central, and Southern. EN magmas range in composition from basaltic andesite to dacite and have produced over 6.8 km3 (DRE) of lava and pyroclastic material, which makes it the most voluminous volcanic field in the Central Andes, and therefore, an excellent example to study MVF in arc-systems. We have conducted an extensive study encompassing major and trace elements, as well as isotopic analysis using whole rock Sr-Nd-Pb. We also present an analysis of our results with available geochemical data from the back-arc and main-arc volcanoes, including other monogenetic volcanoes near EN (<80 km, EN's neighbors). The results revealed that EN magmas and their neighbors are strongly related and exhibit a clear similarity in major and trace element compositions and isotopic ratios, indicating a common source and origin of their melts. Our comparison across the arc surprisingly reveals similarities between EN and back-arc monogenetic volcanism. Both regions indicate geochemical signatures that do not support melting via slab metasomatism, typical of subduction zones. Instead, they show low Th/Ce (<0.1 ppm) and Ba/La (<30 ppm) and high Ce/Pb (>6 ppm), Ba/Th (>100 ppm), high 143Nd/144Nd > 0.51240, and La/Yb ratios at a given La/Sm compared to the main-arc polygenetic volcanoes. Interestingly, EN also exhibits adakite-like signatures with increasing SiO2 content (high Sr > 600 ppm, Sr/Y > 40, and high La/Yb > 20), a term used for igneous rock suites with chemical characteristics that are identical to those of adakites but produced through petrogenetic processes that do not include a slab component. We explore how fractional crystallization and crustal assimilation participate in the development of monogenetic volcanoes, and our findings underscore the significant influence of fractional crystallization on the monogenetic volcanic processes in the Salar de Atacama region. The geochemical changes observed in this area can be attributed to a combination of varying degrees of fractional crystallization within magmas generated through the partial melting of a garnet-enriched environment, which could be primary lower crust or partial melting of a peridotite mantle that has later equilibrated with garnet-bearing crustal melts.

The Coupling Effects Between Floating Insulation Plates and the Thermal Convection in their Bottoms---- An Understanding of Continental Drift

The phenomenon of dumpling drift was discovered during a cooking process, which triggered our thinking of the continental drift. After refining the existing common problems, an experiment on the thermal convection interaction between the floating heat insulation plates and the bottoms is designed. Through controlling variables, this paper investigates the floating patterns of floating insulation plates of different sizes on a thermally convective surface and the principles behind them. The findings show that the appropriate sizing of a floating plate can result in the manifestation of cyclic reciprocating movement on the water’s surface. The periodic movement observed in this phenomenon can be attributed to the obstruction of heat exchange between the water surface and the surrounding air by the floating plate. Consequently, alterations in the direction of water flow induce corresponding shifts in water temperature, which subsequently affect the movement direction of the floating plate. The final outcome is characterized by a periodic reciprocal movement of the floating plate as it interacts with the heat convection occurring at the bottom. Floating plates that are either undersized or oversized would remain stationary without exhibiting any cyclic drift. The decrease in water depth leads to a diminished thermal drive, thereby amplifying the cyclical nature of the motion shown by the floating plate. The above findings indicate that the dimensions of the continental plates present on the Earth's surface have an impact on both the velocity and duration of their movement. The observation that a plate that is too small stagnates on top of a subduction current, while a plate that is too large stagnates on top of an upwelling current, suggests that the smaller continent of New Zealand is likely to experience a decrease in elevation due to its location above a subduction current. Conversely, the larger continent of Africa is expected to undergo uplift and attain a higher elevation as a result of its position above an upwelling current.

Monitoring of Icelandic plate movement with GNSS method and GPS signal jamming effects in Iceland

Abstract Jamming is electromagnetic radiation or reflection that impairs the function of electronic instruments and equipment or communication tools. Intentionally disrupting or interfering with GPS signals, which are used for positioning, navigation, and timing, known as “GPS jamming”, is accomplished using a radio frequency emitting device. On January 8, 2022 (the day of a NATO exercise), it was investigated how GPS signal jamming affected the position accuracy at three IGS points in Iceland. The obtained coordinate differences between kinematic processing and static processing reached values of about 0.5–10 meters for the MAYV, and HOFN stations in this study. In addition to GPS signal jamming effect in Iceland, horizontal and vertical velocity fields of the three IGS stations in Iceland covering a twenty-two year period (2000–2022) in this study. According to the obtained results, a motion of about 2cm–2.5cm per year (horizontal) and 0.1cm–2.1cm per year (vertical) was computed at the three IGS stations (HOFN, REYK, and MAYV) located in Iceland.

Deformation of the Juan de Fuca Plate Beneath the Central Cascadia Continental Margin (44°-45°N) in Response to an Upper Plate Load

A 3D crustal model for the central Cascadia continental shelf and Coast Range between 44°N and 45°N shows that the crystalline crust of the forearc wedge beneath the coastline is characterized by a NW-trending, vertical slab of high-velocity rock interpreted to represent the dike complex that fed the Yachats Basalt, which was intruded into the forearc approximately 37 million years ago. A spatial correlation is observed between downward deflection of the crust of the subducting Juan de Fuca plate, inferred from inversion of PmP arrivals to image the Moho surface, and the high velocity (and consequently high density) anomaly underlying the Yachats Basalt. Apparent subsequent rebound of the subducting plate at greater depth suggests a primarily elastic response of the subducting plate to this load. Calculations for a range of plausible values for the magnitude of the load and the width and depth of the depression indicate that the effective elastic thickness of the subducted Juan de Fuca plate is &amp;lt; 6 km. Although our simple analytical models do not include partial support of the load of the slab by the adjacent upper plate crust or time dependence to account for the motion of the slab beneath the load, incorporation of those effects should decrease rather than increase the apparent strength of the subducted plate. We conclude that the subducted Juan de Fuca plate beneath the central Oregon margin is elastically thin and has the potential to store elastic strain energy before rupturing. Our model of a well-defined, focused and static upper plate load that locally deforms the subducted plate within the nominally seismogenic or transitional part of the Cascadia plate boundary may be unique in providing a relatively straightforward scenario for estimating the mechanical properties of the subducted Juan de Fuca plate. We extrapolate from these results to speculate that elastic deformation of the subducting plate may contribute to the low level of seismicity throughout much of the Cascadia forearc in the inter-seismic period between great earthquakes but note that our local results do not preclude faulting or elasto-plastic deformation of a thin and weak plate as it subducts. These results also suggest that the subducting plate should deform in response to larger scale variations in upper plate thickness and density.

Preliminary Seismo-Tectonic Analysis of the Catastrophic Earthquake in South-Eastern Turkey on Feb 6, 2023

Abstract—In this paper, we carried out a kinematic analysis of the movements of plates and blocks of the region based on a homogeneous database of displacement velocities of GNSS permanent monitoring stations for the region of southeastern Turkey, where strong earthquakes occurred on February 6, 2023. Along the East Anatolian fault zone from 2008 to 2018, the Arabian Plate was established to shift relative to the Anatolian Plate, corresponding to a left shift (without a normal component) at a rate of 1 cm/yr in the eastern part to 0.8 cm/yr in the western part. Displacements occurred along the Chardak fault, corresponding to a left-hand strike-slip fault, at a rate of less than 0.7 cm/year. The revealed kinematics is confirmed by focal mechanisms and cosesismic displacements of the studied earthquakes. The M7.5 earthquake that occurred directly on the Chardak fault is not an aftershock of the M7.8 earthquake, but is a relatively independent event. An analysis of the seismic regime shows that the stresses on the East Anatolian fault after the main event M7.8 are relieved by the first large latitudinal fault zone (the Chardak fault). The results of our study suggest that the counterclockwise rotation of the Anatolian and Arabian plates associated with the opening of the Red Sea Rift is most likely decisive for the general kinematics of the plates in the region.

Study of the Finite Strain of Bekhme Structure in Shaqlawa Area, Northeastern Iraq

This research includes the finite deformation study from five oriented samples of the sandstone rocks for the Injana Formation. in the SW flank of Bekhme Anticline in NE Iraq. Analysis and measurement of the finite deformation were carried out on sandstone beds that are mostly of continental environments. This work is based on the Fry method for strain analysis. The calculated strain was illustrated, in the form of ellipsoids, within three prepared orthogonal single surfaces in a single type, as well as, the method was used to estimate the ratio of the strain for these types of samples. The finite deformation in the study area is not considered high, this was mainly because the sandstone rock samples undergo brittle strain during the faulting and the folding. The computed ratios of strain, (3-D trend for deformation axes) of deformation rocks were equivalence to the Flinn chart that is usually used for plotting deformation ellipsoids, and accordingly method of stereographical projection, the maximum axis for that ellipsoid was parallel to the measured Bekhme Anticline axis and minimum axis was orthogonal to the axis of Bekhme Anticline in the studied region. This trend of those axes was related to the Arabian Plate movement.