Journal of Geodynamics最新文献

In early March 2021, three shallow earthquakes, two mainshocks with M6.3 and M6.0 and one major aftershock with M5.6 impacted both the mountainous Damasi-Tyrnavos region (northern Thessaly, Greece) and the adjacent Plio-Quaternary basin. Each major event was followed by rich aftershock activity recorded by local and regional seismographs and accelerographs. Herein, we present a comprehensive analysis of the seismic sequence, from its foreshock activity starting on 28 February, 2021 and for a period of two months using new high-resolution catalogues of relocated earthquakes and hundreds of focal mechanisms. The results indicate that the aftershocks form a zone that spans ~50 km NW-SE, while focal depths range between 5 and 15 km. More than 400 focal mechanisms, computed for events with M≥ 2.5, mainly exhibit normal faulting in a NW-SE direction, while WNW-ESE to E-W normal faulting is also evidenced, in particular after the occurrence of the last major event on 12 March. The stress-field was reconstructed on a local and broader scale by inverting focal mechanism data, revealing a rotation of the σ₃ axis trend from NNE-SSW, in the Damasi-broader region, to NW-SE northwards, to the region of Kozani-Grevena that hosted an M_w = 6.6 shallow mainshock in 1995. Subcrustal seismicity, present beneath those areas, implies that large-scale tectonics and plate dynamics are likely involved in the deformation of the upper crust. Coulomb stress transfer after the 3 major events of the 2021 Damasi-Tyrnavos sequence reveals that stress-loaded areas include those where most aftershocks were triggered. The analysis provides implications to the seismic hazard of the activated area, as a major NW-SE active normal fault close to Larissa city became stress-loaded, constituting a possible candidate source for significant future earthquakes.

Water levels in anthropogenic reservoirs are often studied in terms of the influence of their fluctuation to pressure perturbations in the bedrock and possible triggering of nearby seismic activity. In this paper, we examine the possibility of a similar relationship in the West Bohemia/Vogtland region on the border of the Czech Republic and Germany. This area is well known for the occurrence of earthquake swarms that are located mainly around Nový Kostel village with the Horka dam nearby, just 5 km to the E-SE of the seismogenic zone. We are looking for any evidence of a mutual relationship between rainfall and the water level at the Horka dam and the seismic catalog that contains more than 25,000 nearby events for the period 1995 − 2019. For this purpose, we applied the methods of cross-correlation and Singular Spectrum Analysis (SSA). The analysis was performed on both full and declustered seismic catalogs and on the full time series and the series averaged over a single-year period. No significant correlation was found between the hydrologic and seismic data; the seismic activity occurs randomly in time. The SSA method found strong seasonal variations of the water level in the dam with annual periodicity; however, no similar periodicity was found in the rainfall and seismicity data. Our results show that not only the earthquake swarms, but also the background seismic activity have no relationship to the rainfall or water level in the Horka dam. The hypothesis of hydrologic triggering of the seismic activity in the area appears rather unlikely and other mechanisms should be studied in more detail to account for the earthquake swarms’ occurrence.

The Black Sea is a deep marine basin formed by lithosphere extension and active rifting in a back-arc tectonic setting, by general consensus, in the Cretaceous. Its present structural architecture, however, is mainly defined by compressional tectonics during the Cenozoic when large scale “basin inversion” reactivated extensional fault systems formed in the Cretaceous. Rifting during the Cretaceous is usually taken to represent the main process forming the present-day basin (that is, producing crustal thinning and concomitant subsidence prior to its modification during Cenozoic inversion). Rifting at this time took place within continental lithosphere that had been accreted to and, by the Cretaceous, formed part of the Eurasian lithospheric plate. The precise history of how and when pre-Cretaceous aged tectonic domains were accreted to Eurasia forming the continental lithosphere underlying the Black Sea is poorly known. A critical issue to the tectono-thermal evolution of the Black Sea basin with important implications for paleogeography and sedimentary depositional environments is the degree of crust (and lithosphere) thinning during Cretaceous rifting and whether oceanic or “sub-oceanic” crust was formed at that time. The main focus of this paper, in order to illuminate this issue, is on kinematic observations related to the Cretaceous (Albian-Cenomanian) rifting phase, including subsidence analysis, as well as the immediate post-rift sedimentation and stratigraphy. The results suggest that rifting during the Cretaceous was insufficient in its own right to reveal exhumed mantle or to promote ocean crust formation beneath the deep basins of the Black Sea. It is concluded that an important contribution to observed present-day crustal and lithosphere architecture of the Black Sea area are legacy extensional tectonic events affecting the area in pre-Cretaceous times, with implications for the Late Palaeozoic-Mesozoic paleogeography and paleotectonic evolution of this area.

The origin, tectonic development, and lithosphere structure of the East Black Sea Basin (EBSB) are governed by the evolution of the northern branch of the Tethys ocean. The most spectacular features of its evolution could retain their imprints in geophysical fields and models, which we used to constrain a geophysical transect for the crust and upper mantle crossing the EBSB and the Shatsky Ridge (SR) from the Eastern Pontides to the Northern Caucasus. 2D gravity and magnetic modeling, constrained by wide-angle seismic data, revealed thin high-density and high-velocity sub-oceanic crust of the EBSB with the Moho shallowing up ~20 km depth. A spectacular feature of the Black Sea magnetic field is the Alushta-Batumi anomaly (ABA) above the SR that could be an imprint of subduction-related Middle Jurassic magmatic arc, whereas the Cretaceous (in Eastern Pontides) magmatic arc manifests itself by a chain of magnetic anomalies on the southern shoreline of the Black Sea. The high-velocity heterogeneity, revealed by seismic tomography, could be an image of a slab due to Mesozoic (Middle Jurassic and Cretaceous) subduction of the northern branch of Neotethys ocean. It shows rather a flat subduction slab that plunges northwards from subcrustal depths south of Eastern Pontide to the depth of > 70–80 km below the SR. Middle Jurassic and Cretaceous subduction fronts are located closely in the region of Eastern Pontides, whereas the related magmatic arcs are spaced differently – over the SR for the Middle Jurassic arc and along the southern coastline for Cretaceous Eastern Pontide magmatic arc correspondingly. The latter could be caused by the opening of the EBSB in the Cretaceous that separated the eastern segment of the BS onto the Eastern Pontides – Arkhangelsky Ridge and the SR – Northern Caucasus domains.

In a recent paper published in the Journal of Geodynamics (vol. 137, June 2020, 101733), Fonseca et al. (2020) proposed a thought-provoking model aiming to elucidate the exhumation history of the Neoproterozoic Brasília Fold Belt (BFB) between the Devonian and Cretaceous periods. Exclusively based on information from the literature and new thermochronological data, Fonseca et al. (2020) presented an alternative model that tries to bind tectonic uplift, erosion, and the influx of clastic material coming from the BFB into the intracratonic Paraná Basin. Although the welcome proposal and reliable quality of the analytical data, the hypothesis presented diverges from several previously published works. In the light of the presented apatite fission-track ages, we disagree with their paleogeographical model, which puts the Brasília Fold Belt as a major source for clastic detritus to the Paraná Basin between the Devonian to Permian. The primary goal of our comments is to clarify the state-of-art of the intricate source-to-sink system of the Paraná Basin. Secondarily, we try to demonstrate why the model proposed by Fonseca et al. (2020) presents some geodynamic and interpretative problems and do not characterize an adequate paleogeographic scenario for southwest Gondwana between the Devonian to Permian periods.

The 2017 Chiapas earthquake with moment magnitude M_w = 8.2, caused seismic induced surface motion which has been well recorded and analyzed globally using broadband seismometers. In contrast, Global Navigation Satellite System (GNSS) measurements of absolute receiver positions at cm accuracy have been marginally used for seismic wave analysis. We show that GNSS station displacement measurements, located in North America, can detect traveling seismic surface waves through a GNSS network for the 2017 Chiapas earthquake with a single station precise point positioning (PPP) measurement accuracy of 1–2 cm, evaluating 1 Hz data. We found that the network data show a total amplitude in temporal filtered horizontal displacement data of up to 5 cm, which is in good agreement with absolute measurements of a broadband seismometer. The multi constellation (primarily GPS and GLONASS) GNSS measurements are most sensitive to seismic surface waves such as e.g. given by Love and Rayleigh wave components in the frequency range of 20–35 s determined by FTAN (Frequency Time Analysis) where the Rayleigh component dominates the measured GNSS signals. We provide estimates of phase velocities and epicenter location determined by a cross-correlation procedure and evaluate its accuracy within the framework of a comparison to state-of-the-art seismic models. Hereby GNSS station data suffer from double measurement noise in the vertical displacement component, which results in a low signal to noise ratio that deny proper pressure wave analysis. While the derived phase velocities have typical uncertainties of 200 m/s in standard deviation, which may seem inappropriate for geophysical interpretation of a single station they might be appropriate in a large and dense GNSS network (spatial distance < 25 km). Determination of the seismic source location is possible and even offers the ability to provide tsunami early warning. Consequently, we see GNSS network station data may be a complementary and independent observation type – prior to well established geophone or accelerometer measurements – which is suited for seismic wave detection and analysis, although limited in accuracy.

The Vardar Zone is a product of the Triassic-Jurassic opening of the Neotethys, Jurassic obduction, Late Cretaceous/Paleogene consumption of the oceanic crust and continental collision. During the last process, the Eastern Vardar Zone was thrust over the Central and eventually both onto the Western Vardar Zone. The present paleomagnetic and structural study provided new results from the first two zones in the Belgrade area. The younger set of data, together with published ones from the third zone, provide firm evidence for about 30° clockwise vertical axial rotation of the Vardar Zone between 23 and 18 Ma, connected to extension driven by the roll-back of the Carpathians lithosphere.

Earlier, the Vardar Zone was affected by intensive compression generating a nappe pile, comprising the Eastern, Central and Western Vardar Zones. This assembly was eventually thrusted over CCW rotating Adriatic elements in the Paleogene. The rotation triggered a system of right lateral strike slip faults between different tectonic slices in the Vardar Zone. This tectonic model offers a plausible explanation for the paleomagnetic directions of post-folding age of the Upper Cretaceous flysch of the Central Vardar Zone. Nevertheless, the possibility of remagnetization of the magnetite bearing flysch during Late Neogene uplift can not be excluded.

The position of the middle-upper Miocene volcanic arc, encompassing the Maghrebides, the Sardinia Channel and the Sardinia-Corsica block, implies that the Algerian and Tyrrhenian basins developed, respectively, as backarc and forearc extensional zones in the Western-Central Mediterranean. The opening of the Western-Central Mediterranean Neogene extensional basin has been commonly interpreted as a two-step process: the opening of the Provençal-Algerian basin during the early-middle Miocene, followed, in the late Miocene, by the formation of the Tyrrhenian Basin. This article is an attempt to synthesize knowledge about the hinge zone between Algerian and Tyrrhenian basins by combining the analysis of seismic reflection profiles with dredge and borehole data in order to investigate how the transition between the eastern Algerian backarc and Tyrrhenian forearc geodynamic settings took place. We identified three sectors: the western Tyrrhenian characterized by a Tortonian forearc extension; the Sardinia Channel, which preserves the architecture of the lower Miocene Maghrebian thrust belt formed during the collision between Europe and Africa plates; and the easternmost Algerian basin-Sicily Channel where a backarc–thrust belt system developed during the Tortonian stage. During the extensional events, we hypothesize the re-activation of inherited structures during Tortonian rifting, (that is a negative tectonic inversion of pre-existing Eocene and early Miocene thrust faults). The contemporaneity of two different geodynamic environments, the forearc extension in the northern area and backarc–thrust belt system in the southern area, can be directly related with a lateral variation of the lower plate paleogeography of the Africa continental margin. This evidence contributes to the understanding of how the paleogeography of the lower plate can control, to a certain extent, the tectonic evolution of the upper plate in a subduction setting.

The ability to mitigate and predict volcanic risk is a long-standing question in the Geosciences’ community, while the extent of volcanic activity may be regulated by a predictable and periodic external excitation induced by seasonal rainfall, hydrological loading, or Moon-Sun gravitational force. Moreover, the complex stress-triggering, hydro-mechanical coupling in response to seasonal rainfall, and associated feedback mechanism with deep magmatic process remains enigmatic and indeed deserves more attention in view of recent climate change scenario. In this letter, a compelling scenario of seasonal rainfall-triggered eruption cycles of Mount Etna (Italy) is found and presented on the eastern coast of Sicily which continuously erupting since last 200 kyr. Results show that the seasonal rainfall significantly weakened the Mount Etna edifice and initiated mechanical tensile failure in the complex magmatic plumbing system and adjacent flank surface by changing the pore pressure build-up, probably promoting dyke intrusion and eventual triggering of eruptive cycle. Further, the possibility of seasonal hydrological loading on the Mount Etna volcano and adjacent flank region, hydrological load-induced sliding along the impermeable outer ‘shell’ of the flank are discussed, and the effect of tidal stress perturbations on the eruptions cycle cannot be ruled out completely.

The Raohe accretionary complex (RHC) is located at the eastern of northeast China and adjacent to Russian Far East. As a part of the Circum-Pacific Orogenic Belt, it is the unique region of the accretionary orogenic belt, which is associated with the subduction process of the Panthalassic-Pacific Plate (PPP). We synthesize the detrital zircon ages of terrigenous clastic rocks of the RHC and tectonic units along the East Asian Continental Margin (EACM) to clarify its provenance. Then we place the docking position of the RHC adjacent to the South China Block, and determine that the final accretion of the RHC occur during the later Late Jurassic (~150 Ma) according to combination for ages of stitching plutons and terrigenous clastic rock. Integrating with the published global-scale plate kinematic frame, we restored the pre-docking motion path of the RHC using the Gplates software. The reconstructed scenario shows that it is a long distance of at least 1000 km between the proto-RHC and continent margin when the basaltic volcanism occurred subaqueously within the abyssal basin of the PPP. This model also provides a probability that the proto-RHC and the proto-Yuejingshan accretionary complexes have the same drift history, before their simultaneous emplacement into the continental margin.