Tectonophysics最新文献

Seismic azimuthal anisotropy within the crust and upper mantle offers important information of past and present tectonic deformation. We used ambient seismic noise to map azimuthal anisotropy in the lithosphere beneath W and SE Brazil, providing new insights into the amalgamation history of the various cratonic blocks in SW Gondwana, which are now partly buried by Phanerozoic basins. We used 72 stations from January 2016 to September 2018. To correct the non-uniform distribution of the energy flow around each inter-station path, the weighted rms (WRMS) stacking method was applied. The inter-station empirical Green's functions provided Rayleigh-wave group and phase velocity dispersion curves, which were used in a tomographic inversion to obtain the fast anisotropy directions, and the isotropic (mean) group and phase velocities in the period range of 4–70 s. At the shortest period, both group and phase low-velocity anomalies are observed in the sedimentary basins, while the fast direction is parallel to the deformation in the surrounding fold belts (e.g., beneath the shallow Pantanal basin). At 40 s period, group and phase velocities are affected by crustal thickness variations. During the longest period of the 70s, the fast anisotropy directions are mostly N-S, in general agreement with the azimuthal anisotropy of the global model of Debayle et al.(2016, updated to 2022), which is interpreted as due to compressional deformation in the lithospheric lid. This deformation-induced anisotropy suggests that the final Neoproterozoic collision occurred between the two groups of cratonic blocks: (I) the Amazon craton, the Rio Apa, and the Rio Tebicuary cratonic blocks in the Amazon domain, and (II) the Paranapanema block on the Atlantic domain. The isotropic V_S model generally agrees with the proposed West Paraná Suture zone (inferred from gravity and magnetotelluric data). In the lower crust (20 to 35 km), predominantly low velocities are seen in the central and southern part of the Paraná basin, and higher velocities are observed around the Pantanal basin, in general agreement with Cedraz et al. (2020) proposal of underplating in that region.

Monchique is a prominent 902 m topographic high in SW Iberia, which stands out in the general flat landscape of southern Portugal. It lies to the north of the Africa-Eurasia plate boundary, which locally accommodates a slow oblique convergence (∼5 mm/yr). Monchique comprises alkaline magmatic rocks of Late Cretaceous age, intruded in a post-rift context. It hosts the most active seismic cluster in mainland Portugal and important hydrothermal activity.

This work investigates the relationship between the alkaline intrusion, local seismicity and hydrothermalism.

We present magnetic and gravity modeling based on new drone-borne magnetic data and ground gravity data. New magnetic mapping of Monchique shows a ∼ 15 km long dipolar anomaly with 7–8 km wavelength and 2000 nT amplitude. 3D magnetic inversion models the main Monchique intrusion as a high-susceptibility body, 15 km long and 6 km wide, located below the Monchique mountain and extending 5–7 km depth. 2D forward modeling and geological interpretation further support the existence of ENE-WSW oriented dike-like gabbroic bodies that may extend deeper, around which syenite units have later emplaced.

We relocate the seismicity using NonLinLoc and a 3D regional tomographic model, and find that earthquakes align along four main lineations that radiate outwards from the intrusion. We also find that most earthquakes cluster between 8 and 18 km depth, below the magmatic intrusion. The b-value at the core of the seismic cluster is higher than at the surrounding region, possibly related to the local hydrothermalism. We present five new focal mechanisms that are compatible with the regional stress field, supporting a regional tectonic control.

The emplacement of the Monchique alkaline intrusion left fractures in the lithosphere that currently act as preferred pathways for fluids. In the context of the present-day stress field, the enhanced fracturing and fluid circulation facilitate the localization of small-magnitude earthquakes.

The Gulf of Corinth, Central Greece, is a highly active half-graben, characterized by seismicity which is more intense in its western part, while destructive earthquakes have also occurred towards its eastern end. We herein present an analysis of the seismicity in the Central Gulf of Corinth, for the period from June 2018 to December 2022. We applied the EQTransformer machine-learning model to enhance the initially available data, adding missing P- and S-wave arrival-times or improving existing ones. The events were initially located using a new local velocity model and then relocated using the double-difference method, including waveform cross-correlation data from local stations. The hypocenters, generally distributed at depths between 5 and 15 km, along with the focal mechanisms of significant earthquakes (1965 through 2022) and the geometry of mapped faults on the surface were co-examined to better understand their possible connection. It is shown that major outcropping north-dipping structures, such as the East Helike fault and its eastward offshore extension, match only with the southern bounds of seismicity. The M_w = 5.9, 1970 Antikira and M_w = 5.7, 1992 Galaxidi earthquakes cannot be associated with known mapped faults on the surface and likely occurred on low-angle, north-dipping planes. The variability in slip behavior of the low-angle detachment in the Gulf of Corinth, ranging from seismic slip to aseismic creep, probably accounts for the most part of the N-S extensional deformation. The spatial pattern of the 2018–2022 microseismicity delineates the edges of the rupture planes of major events that occurred during the instrumental era, including the M_w = 6.3, 1995 Aigion earthquake. The lack of aftershocks for significant earthquakes, including the M_w = 5.0, 8 October 2022 event, south of Desfina, is interpreted in terms of different pore pressure conditions, variations in fault-rock strength, and the preferred accumulation of high stress inside the upper crust.

The Burma Plate is a microplate that extends along the boundary between the Indian and Eurasian plates. It is characterized by an extraordinarily complex lithospheric tectonic setting, resulting from the continental collision in the north, the oceanic crustal subduction in the south, and the large amount of sediment from the Tibetan Plateau. The lithospheric strength is a key to understanding the tectonic evolution of the Burma Plate. In this study, we use topography and gravity disturbance data to estimate the spatial distribution of effective elastic thickness $\mathrm{Te},$ which is a measure of lithospheric strength. The $\mathrm{Te}$values range from $\sim$10 km to 80 km, with higher values in the Indian Plate than those in the other regions. The non-isostatic flexural effects of sediment loading and subducting slab pull can bias the $\mathrm{Te}$ estimation, with maximum reductions of $\sim$50 km and $\sim$10 km, respectively. The consistent distributions of the $\mathrm{Te}$ and the shear wave velocity anomaly $\Delta \mathrm{Vs}$at 100 km depth suggest that the lithospheric strength is generally controlled by the thermal structure of the upper mantle. Meanwhile, the $\mathrm{Te}$ variations are highly related to the geometry of the subducting Indian Plate along the collision and subduction zones, indicating that the plate tectonics play a dominant role in determining the lithospheric strength of the Burma Plate.

The Bayan Har block (BHB) is one of the areas with the strongest seismicity in China. Since 1997, six earthquakes with magnitudes of 7 or greater have occurred in this block. The activity of earthquakes has shown a trend of increasing from the edge of the BHB to its interior. In this article, three-dimensional inversion was used to generate the electrical resistivity structure in the Maerkang earthquake area based on magnetotelluric data in the Maerkang earthquake area in the southeast of the BHB. Combined with the electrical resistivity structure characteristics of the Maduo earthquake area in 2021 and the Jiuzhaigou earthquake area in 2017, the seismogenic environment and tectonic deformation in the BHB were revealed and analyzed. The electrical resistivity structure revealed that the Songgang fault was an electrical resistivity contrast zone that extends into the middle and lower crust, and connects to the Dari fault zone to the northwest, which is the seismogenic fault of the 2022 Maerkang earthquakes. The resistivity structure of the BHB exhibits a layered structure with a widespread high-conductivity layer in the middle and lower crust. The burial depth of the high-conductivity layer is undulating in waves along the profile, which may be a deep manifestation of the strong shortening deformation in the middle and lower crust of the region. The lower crust of the BHB is a medium with a high melt fraction, which may provide a material source for the flow of the middle and lower crust in the northeastern part of the Tibetan Plateau and may be an important controlling factor in the occurrence of moderate and strong earthquakes in the region.

Fault-weakening process governs the earthquake rupture dynamics and energy partitioning and is of great importance for understanding earthquake physics and seismic hazards. The 2023 Mw 7.8 Türkiye-Syria earthquake was well recorded by dense strong motion stations near ruptured faults, providing a rare opportunity to explore parameters controlling the fault-weakening behavior. This work investigates the Dc″ value as a proxy of the slip-weakening distance, defined as double the fault-parallel displacement at the time of peak ground velocity. The Dc″ values are directly estimated from observations of near-fault stations whose final displacements are carefully corrected from original acceleration recordings and validated by coseismic horizontal displacements from geodetic techniques. Our results show that estimated Dc″ values ranging from 0.9 m to 2.4 m are spatially variable and generally follow the scaling relationship of Dc″ versus the final slip, consistent with previous observations. We also analyze the earthquake energy budget based on a well-constrained finite-fault model. The results reveal that the radiation efficiency of the event is relatively low and may not favor the sustained generation of supershear rupture. These results provide important insights into heterogeneous frictional properties on natural faults and implications for seismic hazard assessment.

We investigated the active tectonics and earthquake potential of the eastern Siena Basin, a slowly deforming portion of southern Tuscany in the inner Northern Apennines. This region hosts several historical settlements and valuable cultural heritage, but also frequent background seismicity and rare damaging earthquakes in the M_w range 5.0–6.2. We describe in detail an active, capable, and seismogenic fault system that we identified in the eastern Siena Basin, a few kilometers south-east of the city of Siena, thanks to the presence of an active quarry (Cava Capanni) that exploits travertines of Middle Pleistocene-Holocene age. Travertines are unique rock masses that may preserve living evidence of active and seismogenic faulting, thus providing remarkable seismotectonic insight. The active fault system consists of at least two segments rupturing travertines younger than 45 ka, with a cumulative vertical displacement of 111 cm, and an estimated minimum slip rate of 0.02–0.03 mm/y. We maintain that this displacement is the result of at least three coseismic movements accompanied by clastic dykes injected within the fault damage zone due to liquefaction phenomena. The fault system is seen to extend east of the quarry, affecting Pliocene and Mesozoic deposits.

The Cava Capanni fault system is evidence of a poorly understood but potentially seismogenic tectonic mechanism of regional extent. Its orientation and kinematics are compatible with the activity of faults that are oriented obliquely or orthogonally to the main chain axis, in contrast with the setting of the axial and outer zone of the Northern Apennines, where extension and compression are accommodated by Apennines-parallel faults.

Structural fractures in carbonate reservoirs contribute prominently to hydrocarbon migration and accumulation. In this paper, the accuracy of structural fracture prediction is improved by two aspects of numerical simulation of traditional tectonic stress field and fracture distribution prediction methods in carbonate reservoirs. (1) The grid generation of finite element models for geological models is prioritized. Next, uniaxial and triaxial compression tests, well logging data, and 3D seismic data volume inversion are used to create a 3D volume of heterogeneous rock mechanics data that accurately reflects the geological body. Then, using the data, attribute assignments are made in the finite element model to create the three-dimensional heterogeneous rock mechanics model. This enhancement significantly diminishes the error induced by attributing rock mechanics parameters to individuals. (2) The size and orientation of in-situ stress are measured using acoustic emission, paleomagnetic, and wave velocity anisotropy tests in combination with imaging logging data. By introducing an adaptive boundary condition method to precisely calculate the in-situ stress magnitude at the applied boundary, we simulate the paleo- and current tectonic stress fields within the study area. The fracture rates for tension and shearing are calculated using the Griffith and Coulomb-Mohr fracture criteria. Based on the statistical results of characteristic fracture parameters at the core and imaging logging scales in the study area, the proportion of tensile and shear fractures is determined, and then the comprehensive fracture coefficient of carbonate reservoirs is calculated. A model for quantitatively predicting the multiperiod linear density of fractures suitable for carbonate reservoirs is developed following a thorough analysis of the various effects of multiperiod tectonic stress on the formation and alteration of reservoir fractures. The utilization of this technique in quantitatively forecasting the linear density of multiperiod fractures in carbonate reservoirs in the Tahe Oilfield, Tarim Basin, exhibits favorable feasibility.

The mechanisms that underlie crustal thickening and deformation along the northeastern margin of the Tibetan Plateau, as well as the interplay among different tectonic blocks and deep extension of the boundary faults, have been the subject of considerable debate. To investigate these issues, NE-oriented controlled-source seismic wide-angle reflection/refraction profiling was performed approximately 820 km from the Songpan-Ganzi Orogen to the Ordos Block via twelve controlled-source explosions. The resulting 2D velocity model indicates that crustal thickening in the Songpan-Ganzi and Western Qinling Orogens predominantly occurs in the lower crust, while the upper and lower crusts in the eastern segment of the Qilian Orogen have experienced concurrent thickening, primarily characterized by deformation via compressional shortening. The Songpan-Ganzi and Western Qinling Orogens exhibit similar lower crustal structures and may originate from the same tectonic unit. And a low velocity body of approximately 5.7 km/s that is situated around 25 km may serve as the medium that facilitates upper crustal decollement and deformation. The Eastern Kunlun fault converges at a decollement zone around 25 km in depth, indicating the fault is not a lithospheric fault propagating through the crust. However, the markedly distinct velocity on both sides of the northern margin fault in the Western Qinling Orogen indicate that the fault traverses the entire crust. The Haiyuan-Liupanshan fault converges in a wedge-shaped manner towards a decollement zone located approximately 25 km deep, and this fault does not separate the crust-mantle structures of the Tibetan Plateau from the Ordos Block. The significant structural differences between the Tibetan Plateau and the Ordos Block are likely due to pre-existing faults. These findings provide a novel geophysical reference model for the NE Tibet and significantly contribute to understanding the crustal deformation mechanisms and interplay among the tectonic blocks in this region.

Characterizing seismic sources is crucial for assessing seismic hazards, particularly for active faults like the Kachchh Mainland Fault (KMF), a 150 km long fault in the Kachchh region. The KMF is laterally displaced by transverse faults with different orientations (NW-SE to NE-SW). To better understand the KMF, a joint interpretation of the five North-South trending Magnetotelluric (MT) profiles (two recently acquired profiles and three earlier published ones) is conducted across various segments of the fault. These profiles covered diverse stretches across the fault, ranging from 15 to 81 km in length. Analysis of the geoelectric sections derived from 2-D MT data inversion revealed that the KMF dips to the south in the vicinity of the transverse faults while it takes on a steep north-dipping orientation farther away from the transverse faults. The central and eastern parts of the KMF are seismically active. Therefore, seismic hazard assessments is carried out by considering a magnitude Mw 7.6 scenario earthquake with a northward dip for all four segments of the KMF. To account for uncertainty, parametric testing was conducted, exploring a range of stress drop values, Kappa values, and quality factors (Q) as proposed by various studies in the Kachchh region. The maximum peak ground acceleration (PGA), of 0.85 g (under soft rock conditions with Vs of 500 m/s), is estimated due to the considered scenario earthquake along all four segments. The study revealed that the PGA decreased by 14–38% at sites south of the KMF (such as Bhuj and Bhachau) and increased by 30–47% at sites located north of the KMF (like Rapar and Khavda) compared to estimates based on a southward dipping KMF. This underlines the significance of considering and estimating variations in fault dip along its length and how such variations can impact seismic hazard assessments within tectonic plate interiors.