Tectonophysics最新文献

The Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) and the Long Term Borehole Monitoring System (LTBMS), installed above the source region of the 1944 Tonankai earthquake, revealed that crustal deformation is driven by slow slip events (SSEs) in the shallower extension of megathrust earthquakes. However, there are unresolved questions about (A) the duration of the SSE in February 2012, which was longer than expected for SSEs with similar magnitudes, and (B) the relationship of the spatial distribution of fault slip between the SSEs in February and December 2012 under the condition of drilling disturbance. To clarify these questions, we re-analyzed the pore/seafloor pressure data associated with the SSEs. Our refined fault models show that the SSE in February had a significantly slower propagation speed and a longer duration than others, while the SSE in December was comparable to others. We interpret that the difference in duration and propagation speed is related to external and internal stress perturbations, respectively. Using the ocean modeling JCOPE (Japan Coastal Ocean Predictability Experiment), we identified that the decrease and subsequent increase in seafloor pressure due to the passage of the Kuroshio meander coincided with the latter part of the longer duration of the SSE in February and its termination, respectively. This suggests that the Kuroshio meander might affect the duration of SSEs. Our refined fault model also indicates that the amount of shear stress accumulation was small before the occurrence of the SSE in February, which triggered the slow propagation of aseismic slip based on a rate- and state-dependent friction law. These results imply that we need to consider the variety of SSEs from the viewpoint of stress perturbation due to not only interaction between fault segments but also external forces from oceanographic phenomena.

The northwestern Sichuan-Yunnan block (NW SYB), located in the southeastern Tibetan Plateau, is characterized by complex fault systems. Its detailed crustal deformation is crucial to comprehending the kinematics of the Tibetan expansion. In this study, we integrate the Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) data to obtain the high-resolution present-day deformation of the NW SYB, which provides insights into the strain partitioning, fault kinematics, and block motion characteristics in this region. Our results show that the elastic strain is not only built up around faults but also widely distributed in the off-fault areas. The Ganzi segment of the Ganzi-Yushu fault and the Luhuo segment of the Xianshuihe fault in the study area accommodate 5.31 mm/yr and 8.41 mm/yr left-lateral strike-slip motion, respectively. The small-scale faults show certain deformation, among which the left-lateral and right-lateral slip rates of the Litang and Zhongdian faults are 2.53 mm/yr and 1.97 mm/yr, respectively. The spatial patterns of the strain partitioning and block motion show that the active strike-slip faults accommodate displacements from Cenozoic block extrusion and rotation, which partially coordinate the kinematic discrepancy of the Tibetan expansion. Our geodetic measurements and existing structural observations indicate that the southeastward expansion of the Tibetan Plateau is absorbed mainly by E-W shortening and N-S extension in the NW SYB, may accommodated by continental strike-slip faults in the upper crust and distributed shear in the lower crust.

This study presents a local magnitude scale (M_L) based on the original Richter definition and designed for use within the Algerian Digital Seismic Network (ADSN). The magnitude scale is derived from the analysis of 17,377 zero-peak maximum amplitude traces extracted from the vertical component, simulated as Wood-Anderson seismograms. These traces are taken from a dataset of 1901 earthquakes recorded between January 1, 2010, and June 1, 2022, at a minimum of five stations in the ADSN network. To better account for the attenuation of direct and refracted waves in northern Algeria, amplitude decay analysis reveals the presence of two transition distances at 90 and 190 km, resulting in three segments. A distance correction term, −log₁₀(A0), is introduced and described by the following trilinear function:$-log\left(A0\right)=\left(\begin{array}{c}0.6747\ast \mathrm{lo}{g}_{10}\left(R\right)+0.0002\ast R+1.6306R\le 90\\ 1.7736\ast \mathrm{lo}{g}_{10}\left(R\right)+0.0002\ast R-0.516990<R\le 190\\ 2.4580\ast \mathrm{lo}{g}_{10}\left(R\right)+0.0002\ast R-2.0765R>190\end{array}\right)$

R represents the hypocentral distance in kilometers. The derived distance correction formula provides a well-constrained M_L relationship for northern Algeria that is valid over a distance range of 5 to 600 km. Compared to other local magnitude relationships, the methodology proposed in this study consistently gives M_L values slightly higher than those calculated by the Southern California relationship over all distances, with an average difference of 0.2 units. We computed corrections for 72 stations by minimizing the M_L residuals. These corrections range from −0.50 to 0.54, highlighting the influence of local site effects on the amplitude of the seismic signal. The magnitude residuals using our magnitude relationship and incorporating the station corrections, show that the standard deviation has improved significantly, from 0.34 to 0.24. An M_L relationship specific to the northern Algerian region provides a valuable tool for seismic monitoring, hazard assessment, and earthquake research in the region.

Seismic activity induced during the development of Enhanced Geothermal Systems (EGS) is frequent and poses significant hazards. This study aims to accurately forecast the maximum magnitude (M_max) of induced earthquakes to effectively manage seismic risks. Focusing on the EGS project in Gonghe County, Qinghai Province, we evaluated and optimized various widely-applied M_max forecasting models, while also endeavoring to directly forecast maximum magnitudes in the post-closure phase. Initially, advanced deep learning models (such as PhaseNet and GaMMA) were employed to process seismic data, coupled with VELEST and HypoDD methods for earthquake relocation. Subsequently, four currently widely recognized maximum magnitude (M_max) forecasting models (H14, NRBE, V16, and G17) were utilized to forecast and assess M_max during nine hydraulic fracturing stages, six post-closure stages exhibiting tailing effects, and the entirety of the 2019–2021 period in the Gonghe EGS project. The findings indicate significant disparities in the efficacy of different forecasting models during hydraulic fracturing stages, with no model fully aligning with the complex physical mechanisms of induced seismicity. NRBE and G17 models tend to overestimate M_max forecasting, potentially escalating production costs, whereas H14 and V16 models yield results closer to actual values but are susceptible to the influence of real seismic breakthroughs. Furthermore, distinct discrepancies were observed in the M_max forecasting performance of the same model between hydraulic fracturing and post-closure stages. Attempts to directly forecast M_max post-closure achieved certain efficacy, likely due to the cumulative injection volume exerting a degree of control over induced seismic activity in both stages. Lastly, to overcome limitations in current M_max forecasting models, a hybrid model Y24, integrating the advantages of four forecasting models, was proposed, demonstrating higher accuracy and reliability in forecasting during both hydraulic fracturing and post-closure stages. The study's findings provide crucial technical support and decision-making basis for the seismic risk management of EGS projects or shale gas development projects employing hydraulic fracturing, underscoring their significance in ensuring the safety and sustainability of new energy and resource development endeavors.

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.