Xu Rui

SUMMARY: By leveraging a significantly expanded GNSS data set (997 vectors, 335 new), we construct a high-resolution crustal strain rate model for the Southeastern Tibetan Plateau (SETP) that approximately doubles the resolution of previous studies. Our model delineates a prominent J-shaped high-strain zone that follows the Xianshuihe–Xiaojiang fault system (XXFS) and extends ∼600 km southwestward. This feature, combined with unsupervised Euler pole clustering machine learning results, provides further evidence for a mid-to-lower crustal linkage between the XXFS and faults southwest of the Red River fault (RRF), suggesting the active XXFS is propagating across this ancient boundary (RRF) at depth. Within the SETP interior, our model reveals widespread extensional deformation characterized by a systematic clockwise rotation of its principal axes from north to south, alongside discrete rotational domains partitioned by major faults. Shear strain patterns within the SETP indicate that major strike-slip faults, predominantly sinistral, drive regional strain localization. Moreover, the close association between modelled high-strain zones and historical M ≥ 6.0 earthquakes suggests that our high-resolution model can serve as a refined, physically based perspective for regional seismic hazard assessment.

We use recently compiled GNSS velocities across the Zemuhe‐Daliangshan fault zone, part of the central Xianshuihe‐Xiaojiang fault system, to reconcile a long‐standing mismatch between geodetic and geologic slip‐rate estimates. We show that conventional elastic dislocation models yield slip rates and locking depths that conflict with seismic and geologic constraints. In contrast, models incorporating a viscoelastic rheology for the lower crust yield geologically consistent slip rates, with the Zemuhe fault slipping 7 mm/yr and the Daliangshan fault slipping 2 mm/yr, and locking depths more consistent with microseismicity (17–20 km). In contrast with major strike‐slip faults worldwide, deformation in this immature system appears distributed over a broad lower‐crustal region. These findings indicate that interpreting interseismic deformation with purely elastic models in fault zones that lack a mature, localized shear zone at depth can lead to misleading results.

We use recently compiled GNSS velocities across the Zemuhe-Daliangshan fault zone, part of the central Xianshuihe-Xiaojiang fault system, to reconcile a long-standing mismatch between geodetic and geologic slip-rate estimates. We show that conventional elastic dislocation models yield slip rates and locking depths that conflict with seismic and geologic constraints. In contrast, models incorporating a viscoelastic rheology for the lower crust yield geologically consistent slip rates, with the Zemuhe fault slipping 7 mm/yr and the Daliangshan fault slipping 2 mm/yr, and locking depths more consistent with microseismicity (17-20 km). In contrast with major strike-slip faults worldwide, deformation in this immature system appears distributed over a broad lower-crustal region. These findings indicate that interpreting interseismic deformation with purely elastic models in fault zones that lack a mature, localized shear zone at depth can lead to misleading results; surface strain rates may correlate poorly with seismic hazard in these regions.

Previous studies have constrained the fault slip rates and block geometries of the SoutheasternTibetan Plateau (SETP) with contradictory results due to complex deformation patterns, limited datasets, and subjective choices of block boundaries. In this work, we address the issue of uncertain block geometries by employing an unsupervised machine learning (Euler pole clustering) algorithm that automatically resolves regions that behave as rigid blocks (clusters) using ~1000 GNSS velocity vectors. The optimal clustering results, determined by F-test and Euler-vector overlap analyses, indicate 4 elongated blocks exist in the SETP that are approximately parallel and delineated by a set of arcuate sinistral-slip faults. Our clustering results redefine the kinematicsof the SETP region with new block definitions which elucidate the dominance of sinistral-slipfaults.

SUMMARY: Assumptions about lithospheric composition and fault discretization schemes are crucial for estimating seismic hazards. This study aims to examine the impact of these two variables in the Southeastern Margin of the Tibetan Plateau, with a specific focus on the Daliangshan mountain area. This area, located along the central segment of the Xianshuihe–Xiaojiang fault system, has been considered in the last few decades to host the highest seismic hazards in mainland China given its historical recurrence intervals of large magnitude earthquakes. Previous studies have constrained the kinematics of the region, including estimates of fault slip and accumulated moment magnitudes, assuming (1) the crust is compositionally homogeneous and isotropic and (2) the discretized fault patches (nodes) are coupling independent. In this work, we use constraint from an updated GNSS velocity solution comprised of 287 sites to test the influence of a compositionally heterogeneous crust and two fault patch (node) parametrizations to assess predicted fault slip rates and several seismic hazard quantities. The two fault node parametrizations are: (1) node depth-dependent (NDD; locking coefficients of nodes along a depth profile are dependent) and (2) node depth-independent (NDI; locking coefficients of all nodes are independent). Statistical tests (F-tests) indicate that the NDD model fits GNSS data significantly better than the NDI model even with less than ∼50 per cent of to-be-estimated parameters. We further examine the impact of lithospheric composition on regional kinematics by incorporating data from high-resolution seismic tomography. Comparisons between homogeneous and heterogeneous models for our preferred NDD fault locking parametrization scheme suggest that the material heterogeneity has minimal influence on the predicted recurrence interval estimates of large (e.g. Mw = 7) earthquakes but some influence on discerning the details of the fault coupling distribution. These results show that the crustal medium and parametrization scheme have an impact on the description of fault kinematics, which should be considered as one of the sources of uncertainty in hazard assessment.

Geostationary BeiDou satellites monitor the total electron content (TEC) in the ionosphere over certain locations 24 hr per day without interruption and act as ionosphere‐based seismometers. The system detected perturbations in TEC before both the M6.1 Dali and M7.3 Qinghai earthquakes that occurred during the night of 21–22 May 2021. The TEC perturbations reside mainly over an area within a distance of ∼700 km from the epicenters of the earthquakes. The standing waves revealed the persistence of a subsurface wave source before the occurrences of the earthquakes, which differs from the co‐seismic ionospheric distributions propagating away from the epicenters. The resident waves in TEC and ground vibrations share a frequency of ∼0.004 Hz, which can be attributed to the resonant coupling between the lithosphere and ionosphere.

Periodic signals replaced noise that was found in continuous seismic data, particularly in the nighttime, from the broadband seismometer at the MVP-LAI (monitoring vibrations and perturbations in the lithosphere, atmosphere and ionosphere) system before the occurrence of the Luxian earthquake on 16 September 2021. A short distance of ~150 km between the MVP-LAI system and the epicenter of the Luxian earthquake suggests the periodic singles as promising seismo-phenomena, due to that the radius of the earthquake preparation zone is ~380 km for an M6 event. Integration of geophysical parameters, including atmospheric pressure, vertical electric field, radon concentration, groundwater level and precipitation, at the MVP-LAI system provides an excellent opportunity for studying the seismo-LAI coupling associated with the Luxian earthquake. Analytical results show that ground vibrations, atmospheric pressure and total electron content varied from ~10⁻³ to ~10⁻² Hz before the Luxian earthquake. The seismo-LAI coupling in the relatively low frequency band (~10⁻³ Hz) can be referred to as the acoustic-gravity waves triggered by the amplified ground vibrations. In contrast, the seismo-LAI coupling in a relatively high frequency band (~10⁻² Hz) would be caused by micro-cracks and/or the high-mode natural frequency that further drives changes of TEC due to the atmospheric resonance.

This study analyzed the total electron content (TEC) observed by 337 ground‐based Global Navigation Satellite System (GNSS) receivers over China and South Asia, the critical frequency of the ionospheric F₂ layer (f_oF₂) and its height (h_mF₂) recorded by the ionosonde at Puer (22.7°N, 101.05°E, 72% obscuration), Yunnan province, during and after the annular solar eclipse on June 21, 2020. The observations show that the eclipse induced not only a daytime major depression but also nighttime perturbations in the ionosphere. The TEC perturbed intermittently from noon to midnight between 85° and 125°E on the eclipse day. The positive and negative changes of the prereversal enhancement respectively occur in the nearby longitudinal sectors of 100°and 115°E. The TEC perturbations behave as a terminator wave that propagates in a northwestward direction after sunset.

The Xianshuihe‐Xiaojiang fault system (XXFS) plays a crucial role in accommodating relative motions of the south China block and the expanding Tibetan Plateau. Compared to the narrow southern and northern segments of the XXFS, the central section (also referred to as the Daliangshan mountain area) is broader and dissected by a network of faults. Geologic studies suggest that three major NNW trending faults may dominate slip partitioning of more recent faults in this region. However, due to accessibility issues, sparse geodetic studies have constrained geodetic fault slip rates with contradictory results. In this study, we use 17 new Global Navigation Satellite System sites combined with existing solutions to investigate slip partitioning of the region. We derive a tectonic velocity solution, develop a block kinematic model constrained by Euler pole clustering technique, and calculate geodetic fault slip rates to compare with geologic fault slip rates. We confirm that the Anninghe‐Daliangshan sliver (ADS) is a distinct, rigid block, and we resolve a new, rigid Daliangshan‐Yingjing‐Mabian block (DYB). Kinematic modeling predicts long‐term slip rates that suggest both the ADS and the DYB partition (~10.0–12.0 mm/year) relative motion between the Tibetan Plateau and south China block in the central XXFS, reconciling geologic observations. We suggest that both the continuum and microplate deformation patterns are present in our study area, of which the local tectonics is better explained by the microplate model, but scale of the kinematics makes its motion more consistent with the continuum model.