Journal of Geodynamics最新文献

This paper presents an overview of research conducted for more than five decades around Vladislav Babuška and collaborators on large-scale seismic anisotropy in tectonically different regions of continental lithosphere in Europe. A wide range of independent data sets and methods are covered. It also briefly touches laboratory measurements of velocity anisotropy on rock samples from the crust and the upper mantle, and emphasizes the importance of considering anisotropy in studies of the Earth structure. The anisotropy is responsible for even larger velocity variations than those due to composition of the most abundant upper mantle rocks (peridotites). The large-scale in-situ measurements of the upper mantle anisotropy capture fabrics of the mantle lithosphere, and enables mapping lateral changes in its structure. The joint inversion/interpretation of the teleseismic body-wave anisotropic parameters, such as variations of directional terms of relative travel time residuals of P waves, shear-wave splitting or the coupled anisotropic-isotropic teleseismic P-wave tomography, image the continental lithosphere as a mosaic of anisotropic domains. Each of the domains has its own thickness and fossil fabric characterized by tilted symmetry axes. We map boundaries of the domains in dependence on the fabric changes. The boundaries can be either narrow and steep or broader and inclined, with an offset relative to boundaries of the related crustal bocks, which can reach several tens of kilometres. This overview presents the European lithosphere-asthenosphere boundary (LAB) and shows examples of anisotropic fabrics of the mantle lithosphere domains and their boundaries in different parts of the European plate.

We collected data from the continuous Global Positioning System (cGPS) sites across the Kashmir Valley, situated at latitude 34^◦N, spanning from 2008 to 2021. Inter-site velocities define a region of approximately 15,000 km² with broadly distributed strain accumulation at −7.22×10⁻⁸ nano strain/year (compression component) and the maximum shear strain γ_max of 1.9051×10⁻⁷ nano strain/year. The estimated site velocity in the ITRF14 ranges between 30.5±1–42.85±3 mm/yr. It was observed that the average deformation rate of the GPS sites in the Kashmir region ranges between 2.86±1–15.47±3 mm/yr relative to the India fixed reference frame, suggesting a predominant N-S directed compressional tectonic regime. The focal mechanism solutions of the earthquakes in and around the Kashmir Valley suggest dominant thrust faulting followed by normal faulting. Analysis of the vertical component of the GPS time series shows that the northwest segment of the valley subsides at the rate of −1.71± 0.70 mm/yr, while the southeast segment uplifts at the rate of 5.4 ± 0.5 mm/yr. In addition to vertical component, we observed differential movement of the sites relative to IISC site on the northwest and southeast segments. The rate of baseline change of the GPS sites indicates 7.30 ± 0.75 mm/yr extension in SE-NW direction and −5.32 ± 0.75 mm/yr NE-SW compression across and along the Kashmir Valley. Geodetic observations reveal a transition that aligns with the Magam lineament/fault previously identified by Ganju and Khar (1984) using gravity and magnetic data. The observation was supported by the field investigations and remote sensing techniques, confirming the existence of Magam Fault. During the field investigations, various geomorphic expressions of fault were observed, including fault ruptures, fault scarps, offset ridges, deflected drainages/rivers, linear alignment of springs, linear drainage lines, triangular facets and offset Recent sedimentary deposits (Karewas) were observed. The field evidence suggests exposure of normal faults at Kondabal, Nasrullapora, Biru and Radbugh. These exposed extensional structures, trends in NE-SW direction and dip in NW direction with varying offset and dip amount. GPS observations supplemented by geomorphic evidences infer the presence of normal fault ̴ 80 Km extending from northeast to southwest.

The Gravity Recovery and Climate Experiment (GRACE) mission provides uniquely high-precision observations for monitoring ocean mass changes (OMC), allowing for the establishment and evaluation of the ocean mass budget in conjunction with satellite altimetry and temperature and salinity observations. However, it is challenging to perform OMC closed-loop validation in the East China Sea (ECS) due to potential biases in the individual model and the lack of certain data processing. In this study, we comprehensively analyze the ocean mass budget in the ECS during the GRACE era (2005–2015) by utilizing multiple datasets, mainly consisting of three official GRACE RL06 solutions, three altimetry products, and four ocean reanalysis products. The effect of ocean bottom deformation, neglected in previous studies, is −0.38 ± 0.06 mm/yr, and we estimate a more accurate ensemble sea level change to be 4.05 ± 1.50 mm/yr in the ECS from the altimetry products. There are discrepancies between leakage-corrected GRACE OMC observations and steric-corrected altimeter OMC estimations in both the seasonal signals and the long-term trends (e.g., 6.25 mm/yr vs. 4.22 mm/yr). These discrepancies are strongly correlated with sediment runoff from the Yangtze River and in-situ sediment observations, suggesting that ocean sediment accumulation should be considered in the ocean mass budget in the ECS. Since in-situ sediment data are estimated over ∼100 years, we employ an empirical estimation method to determine the corresponding data during the period 2005–2015, to avoid potential biases caused by inconsistencies in observational timespans. The results show that sediment mass changes can explain about 96 % of residual trends. Our results emphasize the significant impact of sediment on improving the ocean mass budget in the ECS, offering a novel perspective for estimating ocean mass changes in other coastal regions.

Some faults in the Qilian tectonic belt are seismogenic areas for strong earthquakes, including the western section of the Lenglongling fault, which frequently occures moderate-strong Menyuan earthquakes. In this study, using GPS velocity data of 1991–2015 as the boundary constraints, a three-dimensional viscoelastic finite element dynamic model is constructed by comprehensively considering the regional dynamic environment, crust-mantle transverse-longitudinal inhomogeneity, and spatial spreading of a complex fault system. The objective is to investigate the long-period characteristics of fault movement and stress change in the Qilian tectonic belt caused by tectonic loading, and to discuss the seismogenic conditions of the Menyuan earthquakes. The results show that the annual change of long-period movement and stress of the major faults in the Qilian Mountain tectonic zone are characterized by significant segmentation. Due to its unique geometric bend morphology, the western section of Lenglongling fault has a low movement rate, significant slip deficit and high shear stress accumulation, which are conducive to the gestation and occurrence of earthquakes. Furthermore, the seismogenic area of the Menyuan earthquake series is jointly subjected to NE-SW compressive and NW-SE tensile stress fields, and the maximum shear stress and elastic strain energy accumulate faster than in the surrounding areas. Overall, the western section of the Lenglongling fault has a strong dynamic background and favorable conditions for the frequent occurrence of the Menyuan earthquake series.

Recent progress on the study of olivine LPO after (Karato et al., 2008) is reviewed with the emphasis on three issues: (i) LPO formed by the rotation of olivine crystals with anisotropic shape (euhedral crystals) in diffusion creep (Miyazaki et al., 2013), (ii) B-type LPO in the olivine + basaltic melt (Holtzman et al., 2003), and (iii) pressure change in the influence of LPO (Ohuchi and Irifune, 2013). Regarding the role of euhedral crystals, we show that euhedral olivine crystals occur in a mixture of forsterite and diopside (used by (Miyazaki et al., 2013)) but not in a mixture of olivine and enstatite. Consequently, the results by reported by (Miyazaki et al., 2013) are not applicable to the Earth’s upper mantle where olivine co-exists mostly with enstatite. Also we show that the LPO reported by (Miyazaki et al., 2013) is not consistent with the shape of olivine, and the observed LPO is likely due to dislocation glide (A-type fabric) under the conditions near the diffusion-dislocation creep regime boundary.

Regarding the LPO of olivine with the presence of melt, (Qi et al., 2018)’s experimental study with the torsion geometry did not reproduce the B-type fabric reported by (Holtzman et al., 2003) indicating that the B-type fabric reported by (Holtzman et al., 2003) was indeed an artifact of the direct shear experiments. The weak LPO found by (Qi et al., 2018) (compared to that by (Zimmerman et al., 1999)) can be explained by the smaller grain size in their experiments. I conclude that a majority of the experimental results on olivine LPO at relatively low pressures (<2 GPa) can be understood based on the basics of deformation mechanism map and LPO caused by various slip systems in olivine. Regarding a claim by (Ohuchi and Irifune, 2013) that the A-type LPO (a-slip) dominates at high water content and c-slip dominates at low water content at pressures higher than ∼7 GPa, a compilation of experimental studies by (Masuti et al., 2019) and the observed LPO of the ultra-deep xenolith do not support their claim. However, experimental studies under these high-pressure conditions are limited and there remain large uncertainties regarding the LPO at high pressures (P>3 GPa).

The Arctic Cretaceous Tectonic and Igneous Mega-Province (Arctic TIMP) was active in the period 125–80 Ma. We define a TIMP as a region that is large on a global scale and experiences widespread magmatism and tectonic extension. This province has three main domains: (1) the North Atlantic with its continental rifting, (2) the High Arctic Large Igneous Province (HALIP – the Arctic Ocean and some islands), and (3) part of the Verkhoyansk-Chukotka Orogen where collapse, extension and magmatism occurred. The classical HALIP regional domain has three main elements: (1) intraplate basalt plateau traps (flood basalts), (2) areas of intraplate intrusive magmatism (dykes and sills), and (3) the Alpha-Mendeleev LIP magnetic domain. Nine magmatic seismic facies for the Alpha-Mendeleev LIP magnetic domain are recognized, including SDRs, half-grabens with SDR-like units, layered horizontal volcanic flows and large volcanic constructions. New data support the hypothesis that below all the magmatic seismic facies lies continental crust stretched on different scales and intruded by basalts. Three possible stages of HALIP-age magmatism and tectonics are recognized: (1) formation of basalt trap-type plateaus (±125–120 Ma); (2) synrift and postrift magmatism with SDR units containing both tholeiitic and alkali basalts in the Alpha-Mendeleev region along with conjugate basins (±120–100 Ma); and (3) formation of a number of large, Fedotov-type volcanic constructions in the Alpha-Mendeleev region (±100–80 Ma). At about 120 Ma orogenic collapse started in Verkhoyansk-Chukotka Orogen. The collapse was accompanied by regional uplift and magmatism. Granitoid syn-extension magmatism occurred commonly throughout the area. A large part of the land was covered by volcanics with variable compositions. Rift valleys were common. Orogenic collapse ended at about 100 Ma. The general timing of the orogenic collapse, extension, and magmatism in the Verkhoyansk-Chukotka region coincides with magmatic and tectonic events in the HALIP. The Arctic TIMP formed as a single, connected geodynamic system.

A dataset of ultrasound P-wave velocity measured in 132 independent directions and at confining pressure up to 400 MPa on 152 spherical samples is presented. The samples include sedimentary, metamorphic and igneous rocks from various geological settings and single crystals of quartz and plagioclase. The measured P-wave velocity data are accompanied by measured rock densities, calculated P-wave velocity anisotropies and by petrographic properties observed under the optical microscope. An example of analysis and interpretation of the dataset content is shown on a set of 27 eclogite samples and a set of 23 peridotite and pyroxenite samples included in the dataset. The impact of retrogression in eclogites and in peridotites and pyroxenites on the rock elastic properties is investigated. The eclogite retrogression has at its early stages only limited influence on the P-wave velocity. The progress of retrogression in eclogite is associated with gradual decrease in density and P-wave velocity. A more significant influence on P-wave velocity has been observed for the kelyphitization of garnet than for the pyroxene symplectitization. The serpentinization process associated with rapid density decrease is reflected by distinct decrease of P-wave velocity regardless of the rock type. The P-wave velocity anisotropy of analyzed sample sets is mostly dependent on the primary rock microstructure or on the later developed pore space. The pore space geometry documented by differences of P-wave velocity measured at increasing confining pressure is attributed to open microcracks in both rock types.

The collision between Indian and Eurasian tectonic plates results in a series of earthquakes, releasing stored elastic strain accumulated over a long period. This research utilizes 22 new and 26 previously published GPS velocities along with nine years of InSAR observations to estimate high-resolution velocity and strain rate fields across the Kumaun Himalaya. The resulting high-resolution velocity field ranges between 0.5 and 14 mm/yr relative to the India-fixed reference frame. The geodetic strain rate is not uniform across the study region and the higher strain rates are observed along the Main Central Thrust. The areal change rate along the Kumaun Himalaya indicates a significant amount of tectonic compression, with an average value of − 0.08 μstrain∕yr, while the maximum shear strain rate in the region has a mean value of 0.08 μstrain∕yr. The moment deficit rate, based on accumulated strain and energy release over 200 years, turns out to be 7.59 × 10¹⁸Nm∕yr along the Kumaun Himalaya. This suggests that the study region can generate a great earthquake (Mw 8.1) in the future.

The Bangui magnetic anomaly (BMA) in Central Africa is one of the largest continental magnetic anomalies on Earth in terms of amplitude and lateral size. Determining the sources of the BMA can lead to an increased understanding of the crustal dynamic in the Central African sub-region and the African continent as a whole. Magnetic and gravity analysis-based derivative, two-dimensional forward modelling and a Curie isothermal depth, showed that (a) the bottoms of the magnetic sources were between 15 and 35 km; (b) the BMA is a coalescence of several anomalies that trend E-W and roughly NE-SW. These directions coincide with regional Pan African-aged shear zones along the Central African orogenic belt and to thrust sheets at the northern edge of the Congo Craton. The depth of magnetization does not exceed 35 km with the amplitude of magnetization becoming smaller in the Central African Republic. The potential magnetic susceptibility sources have an average density of 2850 kg/m3 and magnetic susceptibilities between 0.06 and 0.25 SI. The BMA is interpreted to be a combination of middle and lower crustal bodies that are not continuous and consist of magnetic mineral rich granulites and banded iron formations. The gravity and magnetic modelling indicate that the entire crust was involved in the Pan African collisional event similar to what is seen in the Mozambique belt in East Africa. Combined with geological and geochemical studies, the models add evidence that one or two subduction zones were involved in accreting terranes on the northern edge of the Congo Craton. The tectonic accretions caused a crustal remobilization along major shear zones that has locally contributed to a probable circulation of fluids enriched in ferromagnesian minerals during late Neoproterozoic magmatism that created the BMA sources.

The tsunamigenic potential of an earthquake depends on its size, source depth and focal mechanism. The Hellenic Subduction Zone (HSZ) has been selected in the paper to study this important issue. The HSZ was ruptured by 11 strong (M_w6.0) earthquakes in the time period 2009–2023. One earthquake ruptured onshore but only three out of ten offshore earthquakes produced tsunamis: 1 July 2009 (M_w6.4), 25 October 2018 (M_w6.8), 5 May 2020 (M_w6.6). For each one of the two more recent earthquakes of 5 May 2020 (tsunamigenic, thrust faulting) and 12 October 2021 (non-tsunamigenic, strike-slip faulting) we developed heterogeneous fault models from the inversion of teleseismic P-waveforms, and homogeneous fault models from published moment-tensor solutions. For each fault model tsunami generation and propagation was numerically simulated based on an advanced phase-resolving wave model with the use of higher-order Boussinesq-type equations. The modelled tsunami mareograms are consistent with tide records of the small tsunami (height ∼30 cm) produced by the 2020 earthquake. For the 2021 earthquake the modelled mareograms showed tsunami-like disturbance with amplitude not exceeding the noise level. The tsunamigenic earthquakes of 2009, 2018 and 2020 shared magnitude M_w≥ 6.4, shallow depth (h<20 km), moderate-to-high dip-angle and thrust faulting or oblique slip with significant thrust component. In the remaining seven non-tsunamigenic earthquakes, including the 2021 one, at least one of these features is missing. The results obtained help to better understand the seismic mechanisms of tsunami generation in the HSZ. Further investigation is needed for the central HSZ segment to the south of Crete Island, which historically has not been ruptured by large (M_w>7.0) tsunamigenic earthquakes. In contrast, the western and eastern HSZ segments ruptured by the large 365 AD and 1303 AD tsunamigenic earthquakes.