Tectonophysics最新文献

We characterize and quantify the microstructure, hydrogen concentrations, and seismic properties of a tectonically exhumed sliver of oceanic lithospheric mantle outcropping in the Moa Island (Leti archipelago, Timor-Tanimbar outer-arc). The 18 spinel peridotites (lherzolites and harzburgites) have coarse-porphyroclastic microstructures and olivine crystal-preferred orientations (CPO) with axial-[010] (also known as AG-type) or [100](010) (A-type) patterns, similar to those observed in peridotitic xenoliths from oceanic mantle lithosphere. These coarse-porphyroclastic microstructures are variably overprinted by growth of strain-free olivine neoblasts and crystallization of secondary pyroxenes. Recrystallized fractions vary from 6.9 up to 31.3%. The interstitial (cuspate) shapes and CPOs of clinopyroxene, uncorrelated with the olivine CPOs, indicate that refertilization by a reactive melt percolation post-dated deformation. Seismic properties are calculated based on the modal compositions and CPOs of all samples. Increase in the recrystallized olivine fraction decreased the seismic anisotropy, since static recrystallization produced some dispersion of the CPO, but did not change drastically the texture acquired during deformation. Mean seismic velocities (mean Vp = 7.9 km.s⁻¹; mean Vs = 4.5 km.s⁻¹) and anisotropy (mean maximum S wave polarization anisotropy = 4.5%), estimated by considering coherent orientation of the foliation and lineation of all samples, are within the range of typical values for the uppermost mantle. The nominally anhydrous minerals contain small amounts of hydrogen (olivine: 13–18 ppm H₂O by weight; orthopyroxene: 58–175 wt ppm H₂O and clinopyroxenes: 244–288 wt ppm H₂O). A bulk water content of 50 wt ppm H₂O is estimated based on nomminally anhydrous minerals for the Moa peridotites, in agreement with previous estimates for the oceanic mantle lithosphere based on peridotitic xenoliths. This is the first direct measurement of hydrogen concentrations in peridotites from an oceanic mantle lithosphere which experienced melt extraction.

We studied fault core geometry and mechanical properties of exhumed basement rocks at two localities (Storskora and Lislaskora) in Sotra Island, western Norway. We combine outcrop studies with in-situ measurements of the rock stiffness (Young's modulus) to characterize the faults. Faults were investigated both along and across strike using multiple 1D scanlines on the outcrop. Our results show that both fault core thickness and stiffness values vary along the faults. Thicker fault cores (up to 0.8 m and 1.9 m in Storskora and Lislaskora loaclities, respectively) show higher values of stiffness (Young's modulus) up to 70 GPa. The stiffness values of the fault core are generally higher than those measured on the damage zone of the faults in this area. The presence of epidote and compacted fault gouge in the fault core can cause the increase in estimated fault core stiffness. In contrast, fractures are dominant in the damage zones causing local reductions in the stiffness. A map of recent seismic events in this area shows potential seismic activities along some of the major exposed faults in the Sotra Island (e.g. Rustefjorden Fault). Based on the evidence from outcrop, inferred displacements, and interpretation of an available reflection seismic section, we found that the exposed faults could be secondary and part of the damage zone of the Øygarden Fault Complex in the east margin of the rift system in the North Sea. The results of this study could be utilized to predict the architecture and changes in rock stiffness of basement-involved faults in the subsurface.

The Kosi River flows from the eastern Nepal Himalaya into the state of Bihar (India) and has experienced frequent avulsions, causing extensive flood-related damage. Because of this avulsive behavior, the Kosi is called the “Sorrow of Bihar.” The avulsion of 2008 was the most catastrophic avulsion event recorded for the Kosi and has been attributed primarily to hydrological and sedimentological processes that formed a super-elevated river channel and caused avulsion. Detailed topographic analysis of the region near the Kosi exit from the Himalaya, using mean-corrected and resampled 1-arc, Shuttle Radar Topography Mission (SRTM) and Real Time Kinematic Global Positioning System (RTK-GPS) datasets, reveals that the Kosi channel is super-elevated only relative to its eastern floodplain. The western floodplain elevation is similar to or higher than the Kosi channel in the region between the Kosi River exit from the main eastern Nepal Himalaya and the Kosi barrage at the Indo-Nepal border. Structurally, the Kosi exits the Himalaya in the transition zone between the closed Trijuga dun to the west and the Dharan salient to the east. The Trijuga dun is closed by the Main Frontal thrust (MFT)-related frontal topography or the Outer Churia Hills. The eastern slopes of these hills induce west-to-east topographic slope in the channel, such that topographic avulsion indices are highest only in the Outer Churia Hills affected parts of the Kosi Channel and the 2008 avulsion region. Therefore, our preferred model for the primary control on the channel's asymmetric, metastable, super-elevation is the influence of the tectonically controlled MFT-related Outer Churia Hills on the Kosi River channel. Geomorphological processes have operated in the Kosi channel in this backdrop. This study emphasizes that detailed structural and topographic analysis of river exits from mountain belts like the Himalaya can provide better insights into river channel metastability and avulsion worldwide.

Simple mechanical arguments suggest that slip along interlocked, rough faults, damages surrounding rocks. The same arguments require that the scale of secondary damage is proportional to the size of geometric irregularities along the main fault. This relationship could apply at all scales, but has, so far, been difficult to observe at the 10s to 100 s of km scales of large, natural faults, often because large-scale deformation is distributed across wide, complex plate-boundary fault systems, like the San Andreas Fault. The geometry and geology of another large-scale plate-boundary strike slip fault—the Queen Charlotte Fault (QCF)—is, in contrast, especially simple. Here, we show that observations of secondary deformation are well-aligned with predictions of stress variations caused by geometric irregularities along the QCF, suggesting a geometric relationship between primary fault geometry and secondary deformation. The analytic stress solution reveals that the highest stresses and highest likelihood of failure are confined to a zone of influence (ZOI) with a width quantified by $\mathrm{ZOI}=\lambda /2\pi$, where λ is the wavelength of geometric variations along the main fault. This simple model is consistent with ∼100-km-scale observations along the QCF and can theoretically be used to predict the width of secondary deformation at all scales.

The most abundant serpentine mineral in subduction settings, antigorite has one of the highest water storage capacities and is involved in seismicity. Seismic wave velocities of antigorite are important for detecting and quantifying serpentinization within the mantle wedge and the subducting oceanic plate. At present, the elastic properties of antigorite at high pressures and temperatures are unclear. In this study, we have investigated pressure-volume-temperature (P-V-T) data and thermodynamic properties of antigorite using first-principles molecular dynamics (FPMD) simulations. Using these simulations results, we computed the relevant thermoelastic parameters and estimated compressional and shear wave velocities ($v_P$ and $v_S$) of antigorite in subduction conditions. A simplified velocity model of antigorite with its coexisting mantle anhydrous phases was introduced to help us understand the potential effect of serpentinization on the seismic velocity of mantle rocks. Combined with seismic observations, we re-evaluated some velocity anomalies within forearc mantle wedges and established reliable serpentinization budgets. These results can provide preliminary evaluations and reliable constraints on serpentinization and water content in mantle rocks, which has important implications for understanding global plate dynamics and the deep water cycle.

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.