SUMMARY The Global Navigation Satellite System (GNSS) now makes it possible to monitor crustal deformation with unprecedented accuracy and spatial coverage. However, transient tectonic signals are obscured in raw GNSS time-series due to complex triggering mechanisms and a low signal-to-noise ratio. We here propose a multiscale spatiotemporal inversion filter method based on dense GNSS network. First, multiscale spatial decomposition of the regional GNSS deformation field is performed to identify anomalous strain accumulation zones. Then, continuous GNSS observations from targeted regional stations are incorporated to extract transient fault slip signals and constrain their spatiotemporal evolution by the variational Bayesian Independent Component Analysis-based inversion approach. Numerical simulations are conducted to verify the minimum GNSS network density required for detecting Mw 5.5-level slip events and evaluate the fault slip detection capability of the current GNSS observation network. We further apply this method to continuous GNSS time-series associated with the 2021 Ms 6.4 Yangbi earthquake. Distinct pre-seismic deformation anomalies are identified during the preparatory stage of the earthquake, with strain accumulation concentrated at a small spatial scale of approximately 11 km. The inversion results reveal that the rupture zones of foreshocks and the mainshock are dominated by extensional motion and right-lateral strike-slip. The corresponding released moment magnitude reaches Mw 5.5, and the induced Coulomb stress changes amount to 0.021 and 0.036 MPa in the hypocentral regions of the foreshock and mainshock, respectively. These results demonstrate that the detected pre-seismic slip anomaly may have facilitated the occurrence of subsequent foreshocks and mainshock, further verifying that aseismic creep and stress perturbation-induced foreshocks can coexist and interact during earthquake nucleation.

The mechanisms driving the uplift and outward expansion of the Tibetan Plateau remain debated. The Qinghai Lake region at the plateau front, characterized by pronounced basin–range differential uplift, provides a key natural laboratory. Here, we first predict vertical deformation induced by the horizontal GPS velocity field and then construct a three-dimensional (3D) viscoelastic finite-element model to evaluate how lithospheric rheology shapes present-day 3D deformation. Horizontal GPS velocities predict higher uplift in the Songpan–Ganzi Terrane and the Qilian Orogen and lower values in the intervening basins, capturing the first-order basin–range pattern; the predicted uplift in the Qilian Orogen is ~1.0 mm/yr and agrees with observations, indicating that its dominant mechanism is crustal shortening and thickening. However, horizontal constraints alone leave vertical-velocity residuals of ~0.8–1.5 mm/yr in several localized areas, including the West Qinling Orogen, the southern Elashan region, the Qinghai–Nanshan region, and areas south of the Lenglongling Fault. Lateral rheological heterogeneity in the mid–lower crust, acting under mantle-flow drag, can better account for these residuals and more accurately reproduce the present 3D velocity field in the basin–range system. We further propose northeastward mid–lower crustal flow along a weak channel; when the flow is impeded by rigid domains (e.g., the Gonghe Basin and the Qinghai Lake Basin), it promotes material accumulation and localized deformation. These results support a hybrid mechanism that combines crustal shortening and mid–lower crustal flow for the Qinghai Lake basin–range system.

Early aftershock sequences and afterslip provide key insights into crust rheology and the triggering mechanisms of seismicity sequences. Three recent moderate-large strike-slip earthquakes in eastern Tibet, including the 2021 Yangbi Mw 6.1, the 2021 Maduo Mw 7.4, and the 2022 Menyuan Mw 6.4 events, provide an ideal opportunity to investigate the driving processes of aftershocks and the regional crustal rheology. In this study, we inverted for the early afterslip and statistically analyzed the spatiotemporal evolution of these three aftershock sequences. Our results reveal a significant spatial complementarity between the relocated aftershocks, coseismic slip and early afterslip, suggesting aftershocks were triggered by afterslip driven by the coseismic stress changes. The depth of the aftershock sequences consistently shallows over time, which we interpret as a transient response of the brittle-ductile transition zone to early postseismic relaxation. For the first time, we quantify the depth-dependent variations of aftershock-derived rheological and frictional parameters along these three strike-slip faults in eastern Tibet. The recurrence times derived from early aftershocks are generally shorter than those estimated from geodetic or geological data, demonstrating that fault loading rates are not constant throughout the seismic cycle. This spatiotemporal comparison between aftershocks, coseismic slip and afterslip allows for the discrimination of different aftershock driving mechanisms. The framework presented here is generalized to other similar tectonic settings, providing a method to identify the dominant aftershock driving mechanism and to constrain the rheological properties, frictional parameters and recurrence times of regular earthquakes.

The Lajishan-Jishishan Tectonic Belt (LJTB) experienced several strong earthquakes in recent decades despite its low slip rate and low strain rate. The latest 2023 Jishishan M-S 6.2 earthquake received special attention for its unusual secondary disasters, which raises the question about the mechanism of frequent strong earthquakes in the tectonic belt. In this study, we construct a three-dimensional (3D) viscoelastic finite element model to analyze the crustal deformation and stress-strain state around the LJTB, considering the effects of fault geometry and lateral rheological heterogeneity. The results show that with the uniform rheology in the mid-lower crust, there is a significant strike-slip component at both end segments and a thrust component in the middle segments of the tectonic belt, and strike-slip and weak thrust deformation in the north segments of the belt, indicating the important role of fault geometry in controlling the regional crustal deformation. The strengthening of rheology in the mid-lower crust benefits the fault slip but subtly influences crustal deformation. For the middle and south segments of the LJTB, the crust experiences intense horizontal compression, and the heterogeneous rheology in the mid-lower crust facilitates fault thrust motion, as indicated by the 2023 Jishishan M-S 6.2 earthquake. The crustal deformation around the tectonic belt is attributed to the hybrid crustal shortening and localized mid-lower crustal flow. Under the compressive tectonic stress field, the strain energy gradually increases on the Jishishan fault zone located above the mid-lower crust with high rheology, eventually generating the Jishishan M-S 6.2 earthquake.

Abstract The anisotropy of magnetic susceptibility (AMS) has great potential in deciphering weakly deformed fabrics that may be related to tectonic stress. Previous studies have suggested that magnetic lineation is a good indicator of paleostrain direction. It is unclear whether the magnetic fabric can also be used to indicate the present‐day strain field. To verify this idea, we measured the AMS of freshly consolidated lacustrine fine‐grained sediments at 11 locations in the Qaidam and Chaka‐Gonghe basins of the northeastern Tibetan Plateau and compared it with the present‐day strain field deduced from the global position system (GPS) velocity field. The magnetic lineations of both room‐temperature and low‐temperature AMS are roughly perpendicular to the GPS‐derived tectonic shortening direction within the error range, suggesting that the AMS of freshly consolidated muds is an effective indicator of the present‐day strain field, even if the sediments appear undeformed at the outcrop scale.

The Ordos block is a rigid portion of the North China Craton lying within the India-Eurasia collision zone that experiences little internal deformation, but is surrounded by active faulting, extensional grabens, and seismicity. In the surrounding region, geodetic studies have imaged complex crustal deformation, while seismic studies have suggested that the lithosphere is encountering regional modification by mantle convection. The Ordos block thus presents a valuable opportunity to compare seismic and geodetic constraints and investigate geodynamic processes affecting the region’s lithosphere. We here robustly image vertical land motion and horizontal strain rates using observations from the geographically extensive Global Navigation Satellite System and leveling networks in and around the Ordos block. Our results indicate that the Ordos block uplifts with some lateral variability at 0.5−2.0 mm/yr. In the northeastern Ordos block and Datong volcanic area, the crustal uplift rates are 2.0−4.0 mm/yr on average, much faster than those elsewhere on the block. We correct for non-tectonic vertical motion from surface hydrological loading and glacial isostatic adjustment, finding that these do not explain the vertical rate anomalies. Horizontal crustal extension and uplift are accompanied by a pattern of crustal contraction at the Datong volcanic field. Additionally, we find uplift west of and subsidence east of the Qinling Orogenic Belt, which are inconsistent with eastward crustal extrusion along it, suggesting instead a negligible migration of crustal materials especially to the east of 106°E. Comparing the geodetic measurements to evidence from seismic velocity anomalies and numerical simulation, we argue that the motions are consistent with lithospheric re-equilibration resulting from the heterogeneous thinning of the lithosphere by convective mantle upwelling and radial flow as well as shortening from the India-Eurasia collision.

Fault slip rates are critical for understanding the evolution of active faults, earthquake recurrence, and crustal deformation. Yet variations in slip rate along the Haiyuan Fault Zone (HYFZ), a large-scale sinistral strike-slip fault in the northeastern margin of the Tibetan Plateau, remain disputed. Here, we investigate in detail late Quaternary and present-day fault slip rates for several segments across the HYFZ based on previously published geologic and geodetic (i.e. GNSS and InSAR) estimates. Our results reveal that the strike-slip rates increase from ~1.6±0.4–1.8±0.3 mm/a on the Halahu (HLH) fault to ~5.2±1.3–6.2±0.9 mm/a on the Lenglongling (LLL) and Jinqianghe (JQH) faults, then decrease to ~3.9±0.8–4.6±0.3 mm/a on the Maomaoshan (MMS) and Laohushan (LHS) faults, subsequently remain relatively constant (i.e. ~4.6±0.8–4.8±0.7 mm/a) on the Haiyuan (HY) fault (in narrow sense), and finally decrease to ~1.3±0.1–1.5±0.3 mm/a on the Liupanshan (LPS) fault, from west to east. These results indicate that the strike-slip rates on the LLL and JQH faults are highest and decrease toward fault tips along the HYFZ, approximating an asymmetrical bell-shaped distribution. Furthermore, geodetic (short-term) and geologic (long-term) slip rates are in general agreement, indicating that the slip rates were relatively constant in the recent geologic history. Despite the shallow creep on the LHS fault, the Tianzhu Seismic Gap, Tuolaishan (TLS), LLL, and LPS faults have a large locking depth, strain accumulation, and/or long seismic quiescence period, underscoring the substantial seismic hazard in these areas. Our study contributes to characterizing the total slip rate budget across the HYFZ and provides insight into further understanding of seismic hazard and regional crustal deformation.

SUMMARY This study acquires the coseismic deformation field and the high-frequency dynamic displacement of the MW 7.4 earthquake that occurred in Maduo, China, on 2021 May 22, based on the BeiDou Navigation Satellite System (BDS), and the comparison with the results obtained by the Global Positioning System (GPS) reveals that the two systems are certain differences in their ability to acquire the coseismic deformation field. The maximum difference in the horizontal coseismic deformation is <5 mm, and the maximum difference in the vertical coseismic deformation is 8.7 mm. The dynamic displacement waveforms of the 2021 MW 7.4 Maduo earthquake acquired by BDS and GPS are very similar, which confirms that BDS can acquire ground-shaking images with an accuracy comparable to that of GPS. Based on the empirical relationship equation of the peak ground displacement (PGD) and moment magnitude (MW), this study verifies and calculates both the MW of the 2021 MW 7.4 Maduo earthquake and the error and finds that the MW can be quickly and accurately obtained by using the empirical PGD and MW equations, and this MW value can be used as a supplementary means of calibrating the MW of the large earthquake early warning systems, which can be quickly determined by seismic wave data. Finally, by comparing the slip distributions inverted from the BDS and GPS coseismic deformation fields, this study finds that BDS is equally effective as GPS.

This study acquires the coseismic deformation field and the high-frequency dynamic displacement of the M-W 7.4 earthquake that occurred in Maduo, China, on 2021 May 22, based on the BeiDou Navigation Satellite System (BDS), and the comparison with the results obtained by the Global Positioning System (GPS) reveals that the two systems are certain differences in their ability to acquire the coseismic deformation field. The maximum difference in the horizontal coseismic deformation is <5 mm, and the maximum difference in the vertical coseismic deformation is 8.7 mm. The dynamic displacement waveforms of the 2021 M-W 7.4 Maduo earthquake acquired by BDS and GPS are very similar, which confirms that BDS can acquire ground-shaking images with an accuracy comparable to that of GPS. Based on the empirical relationship equation of the peak ground displacement (PGD) and moment magnitude (M-W), this study verifies and calculates both the M-W of the 2021 M-W 7.4 Maduo earthquake and the error and finds that the MW can be quickly and accurately obtained by using the empirical PGD and M-W equations, and this M-W value can be used as a supplementary means of calibrating the M-W of the large earthquake early warning systems, which can be quickly determined by seismic wave data. Finally, by comparing the slip distributions inverted from the BDS and GPS coseismic deformation fields, this study finds that BDS is equally effective as GPS.

AbstractWhile shallow creep along the Haiyuan fault is a key element in estimating earthquake potential, both the creep rate and spatial distribution inferred from InSAR and repeating earthquakes are still controversial. In this study, we resolve two potentially separated creeping patches along the Laohushan fault (LHSF) based on dense near‐field GPS measurements of 39 stations. The largest creeping patch, which extends ∼20 km along‐strike and ∼9 km down‐dip with a slip rate of 4.2 mm/yr, spatially correlates with seismicity, especially repeating earthquakes. The locked segment is capable of producing an earthquake of Mw 7.3 ± 0.1, with moment rate of (1.08 ± 0.39) × 1017 N⋅m/yr, possibly following the cycle since the 1092 M8 event. The lack of GPS measurements in the near‐field makes it unclear whether the 8 km section between these two patches is slowly creeping below detection threshold or has relocked due to change in environmental condition.

The Indian-Eurasian convergence has formed the Himalayas, one of the most youthful and dynamic orogeny on Earth, which is characterized by a unique "perfect arc" observed by seismicity, crustal deformation, and topographic relief. However, the presence of a significant topographic descent at the eastern end of the Himalayas, near the Eastern Himalayan Syntaxis (EHS) challenges the existing paradigm. The reason behind such significant topographic difference compared to other regions along the Himalayan mountains is still unclear. Based on the GPS velocity field, we determined the clockwise rotation of the North Indian Block (NIB) relative to the stable India plate with a Euler pole estimation of (89.566 f 0.06 degrees E, 26.131 f 0.05 degrees N, 1.34 f 0.11 degrees/Myr), implying that the NIB has broken away from the stable India plate. By reconstructing the position of the Northeast Indian Block (NIB) based on the Euler pole, we found that the collisional boundary between India and Eurasia is moving southward. Subsequently, a coupled fault model that accounted for continuous motion of fault can effectively match the topographic descent. Our result underscored the significant impact of the NIB rotation on regional geological evolution, an aspect that has received less attention in previous studies.

Abstract Understanding lithospheric rheology is crucial in investigating tectonic evolution of intra‐continental tectonic boundary. Here, we use geodetic observations to infer lithospheric rheology across the northeastern Tibet based on a 2D viscoelastic model. Our findings reveal a lower‐crust viscosity of <1022 Pa·s underneath its margins, lower than those estimated underneath its vicinities. By comparing deformation patterns and lithospheric rheology here with those observed in the eastern Tibet, we propose that lateral variations in lower‐crust viscosity control deformation patterns and topographic gradients along the Tibet margins. The presence of low viscosity lower‐crust can lead to the development of contrasting topographic gradients and shape the plateau's geomorphology and deformation characteristics during outward growth of the Tibet. We here emphasize the subtle variations in the lower‐crust rheology between deforming blocks and the corresponding mountain ranges, which play an important role in orogeny along the intracontinental convergence boundary.

On 21 May 2021, an Mw 6.1 earthquake occurred in Yangbi County, Dali Bai Autonomous Prefecture, Yunnan Province, with the epicenter located in an unmapped blind fault approximately 7 km west of the Weixi-Qiaohou fault (WQF) on the southeastern margin of the Qinghai–Tibetan Plateau. While numerous studies have been conducted to map the coseismic slip distribution by using the Global Navigation Satellite System (GNSS), Interferometric Synthetic Aperture Radar (InSAR) and seismic data as well as their combinations, the understanding of deformation characteristics during the postseismic stage remains limited, mostly due to the long revisiting time interval and large uncertainty of most SAR satellites. In this study, we refined coseismic slip and afterslip distributions with nonlinear inversions for both fault geometry and relaxation time. First, we determined the fault geometry and coseismic slip distribution of this earthquake by joint inversion for coseismic offsets in the line-of-sight (LOS) direction of both Sentinel-1A/B ascending and descending track images and GNSS data. Then, the descending track time series of Sentinel-1 were further fitted using nonlinear least squares to extract the coseismic and postseismic deformations. Finally, we obtained the refined coseismic slip and afterslip distributions and investigated the spatiotemporal evolution of fault slip by comparing the afterslip with aftershocks. The refined coseismic moment magnitude, which was of Mw 6.05, was smaller than Mw 6.1 or larger, which was inferred from our joint inversion and previous studies, indicating a significant reduction in early postseismic deformation. In contrast, the afterslip following the mainshock lasted for about six months and was equivalent to a moment release of an Mw 5.8 earthquake. These findings not only offer a novel approach to extracting postseismic deformation from noisy InSAR time series but also provide valuable insights into fault slip mechanisms associated with the Yangbi earthquake, enhancing our understanding of seismic processes.

The interference of pumping is common and significant on borehole strain observations, to detect true seismic precursor information from borehole strain strainmeter, the mechanisms of the disturbances generated by pumping must be studied. With the development of urbanization, foundation pit engineering and its associated engineering dewatering gradually increases. It is easy to understand that the interference magnitude of engineering dewatering to borehole strainmeter is more severely than ordinary single-well pumping since more wells are pumping. Studying how the engineering dewatering interferes with the borehole strain observation, what the interference mechanism is, and whether the interference data can be corrected, are of great significance for the detecting of seismic precursor anomalies. In this paper, based on an observation case of TJ-2 volume strainmeter at Laiyang seismic station (short for Laiyang volume strainmeter), which is interfered by engineering dewatering of nearby Yulongwan housing project, the interference characteristics are studied, the disturbed solid tide distortion is corrected, and the interference mechanism is determined by numerical simulation. The results show that: (1) Based on the trend change of Laiyang volume strainmeter caused by the engineering dewatering, solid tide distortion with definite direction and stable magnitude has been superimposed, and we find that the solid tide distortion can be corrected by inverse operation of first-order difference. After correcting the solid tide distortion and deducting the long-term background rate, the interference magnitude caused by engineering dewatering reaches -15.65×10-9/d; (2) We used a concentrated load model and meshed the research area to simulate the volume strain field of the surrounding area caused by the engineering dewatering. The simulation results show that the concentrated force loads of 6.61×109 N and 1.73×1010 N are generated respectively in the early and late period of the volume strain anomaly caused by the engineering dewatering, which is significantly greater than that of single pumping well. The compressive interference concentrates on the vertical direction of the line between the volume strainmeter and the pumping well; (3) Through the analysis of solid tide distortion characteristics and mechanical mechanisms, we found the periodic behavior characteristics of the volume strain observation generated by engineering dewatering. The period can be divided into three stages, the first stage is the decreasing trend of compression caused by pumping of dewatering, the second stage is the increasing tension step caused by suspension of pumping, and the last stage is the decreasing trend of compression caused by resumption of pumping. It shows obviously synchronization between the solid tide distortion time interval (frequency) and borehole water level, where the linear coefficient is 0.737.

As a crucial segment of the oblique Indian-Eurasian convergence zone, the southeast (SE) Tibetan Plateau exhibits intricate crustal deformation and frequent seismic activity. The complex lithospheric deformation characteristics and associated dynamic mechanisms have been subjects of intense debate. By integrating geophysical data, active tectonics, and geodetic observations, we analyze the lithospheric deformation features and geodynamic processes in SE Tibetan Plateau. Our analysis reveals that the upper crust in SE Tibetan Plateau undergoes clockwise rotation around the Eastern Himalayan syntaxis, indicating distributed deformation between the Sagaing and Xianshuihe-Xiaojiang faults. In the lower crust, deformation direction significantly differs from striking of surface structures. Approximately bounded by 26°N, the seismic anisotropy observations in the northern part of the study area mainly originates from the crust, while that in the southern part stems from the asthenospheric mantle. Additionally, significant variations in crustal and lithospheric thickness and topography are observed along this boundary. The northern region features a crustal thickness of 60–70 km, lithospheric thickness of 140–180 km, and average elevations exceeding 4000 m, whereas the southern region shows a crustal thickness of about 30 km, lithospheric thickness of 80–100 km, and average elevations decreasing to 2000 m. The lithosphere in SE Tibetan Plateau is mechanically weak, characterized by a thin equivalent elastic thickness. Seismogenic layers are present in both the crust and upper mantle. The existence of two middle-to-lower crustal weak zones suggests potential material flow over geological timescales driven by gravitational (topography) variations. We argue that complex lithospheric deformation in SE Tibetan Plateau results from multiple geodynamic processes. North of approximately 26°N, lithospheric deformation can be attributed to gravitational collapse and induced middle-to-lower crustal flow, and extrusion of upper crustal blocks. South of this boundary, in addition to block extrusion and gravitational collapse, tractions from mantle flow may dominate, possibly influenced by the retreat/rollback of the Burma and Sunda plates or mantle upwelling from the Hainan mantle plume.

Based on the GNSS observations before and after the earthquake of the LenglonglingTuolaishan Fault and its vicinity, the coseismic displacement field of Menyuan Ms6. 9 earthquake in 2022 is obtained, and the coseismic fault slip distribution is also derived by our inversion model. Based on the above results, we discussed the characteristics of coseismic ruptures and its regional interseismic deformation background. The results show that, first, the earthquake produced coseismic permanent deformation of >= 10 mm within the range of similar to 90 km from the epicenter. However, the coseismic displacement recorded by far-field GNSS continuous station (160 similar to 200 km away from the epicenter) is very slight, generally below the scale of millimeter. Second, the coseismic displacement image takes on the typical left-lateral strike-slip coseismic deformation pattern. The coseismic displacement is 445.9 perpendicular to 3.3 mm in the south of the seismic ruptures, 3 km away from the epicenter. While in the far field of the seismic ruptures, there is remarkable "four-quadrant" pattern that symmetrically distributed shortening or extensional tail deformation zone, matching with the requirements of an almost pure left-lateral strike-slip earthquake. Third, the coseismic displacement is bounded by the Lenglongling Fault and the Tuolaishan Fault. The coseismic displacement on its north and south walls is asymmetrical, and the deformation of the south wall is larger than that of the north wall. Lastly, significant accumulation of interseismic sinistral shear strain energy exists on the western segment of the Tolaishan Fault. Although the pattern of coseismic deformation shows the characteristics of "elastic rebound" that decays with the increase of epicentral distance, the near-field GNSS stations across the fault show the features of uncoordinated coseismic deformation mode, inferring it did not participate in the rupture of the earthquake, so its seismic risk of strong earthquakes in the future is worthy of attention.

The 2021 Yangbi Ms 6.4 earthquake in Yunnan, China, occurred in an area where the Global Positioning System (GPS) geodetic observations are particularly intensive. Based on a detailed retrospective analysis of the GPS observations of about 133 stations distributed in the proximately 400 km × 400 km region that contains the area affected by the earthquake., we obtain a high-resolution GPS velocity field and strain rate field and then derive the present-day slip rates of major faults in the region with the commonly used half-space elastic dislocation model and constraints from the GPS velocity field. Furthermore, by calculating the seismic moment accumulation and release and deficit rates in the main fault segments and combining with the distribution characteristics of small earthquakes, we evaluate the regional seismic risk. The results show that (1) there was a localized prominent strain accumulation rate around the seismogenic area of the impending Yangbi Ms 6.4 earthquake, although this was not the only area with a prominent strain rate in the whole region. (2) The seismogenic area of the earthquake was just located where the strain direction was deflected, which, together with the localized outstanding maximum shear strain and dilatation rates, provides us with important hints to determine the potential areas of future strong earthquakes. (3) Of all the seismogenic fault segments with relatively high potentials, judged using the elapsed time of historical earthquakes and effective strain accumulation rate, the middle section of the Weixi–Qiaohou fault has a higher earthquake risk than the southern section, the Midu–Binchuan section of the Chenghai fault has a higher risk than the Yongsheng section and the Jianchuan section of the Jianchuan–Qiaohou–Lijiang–Xiaojinhe fault has a higher risk than the Lijiang section.

In May 2021, a Ms 6.4 earthquake occurred in the Yangbi Country, Yunnan, China, located in the northern region of the Red River fault, resulting in three deaths. It is a typical foreshock-mainshock-aftershock sequence. However, the kinematic rupture process and the interplay between foreshocks, the mainshock, and aftershocks associated with the Yangbi event remain controversial. Here, we decipher the detailed rupture process associated with this moderate event by jointly inverting the teleseismic body waves, three-component regional waveform, near-field Global Positioning System offsets, and Interferometric Synthetic Aperture Radar data. Results show that the rupture expands as a narrow slip-pulse that propagates southeastward. This event is dominated by the dextral movements with minor normal components, cohere with the tectonic shear and dilation strain partitioning. The high slip is concentrated within the depth range of 5-13 km, spanning similar to 12 km along strike. A significant shallow slip deficit is identified, perhaps related to the fault being immature. The foreshocks, coseismic slips, and aftershocks reveal a complementary pattern, together releasing the accumulated stresses on the fault. Their distribution areas and Coulomb stress changes suggest that the Yangbi seismic sequence follows the rupture cascade. The absence of large earthquakes, dispersed seismicity, and diffuse strain rate patterns indicate that strain accumulates over a wide area around the northern region of the Red River fault, leading to small-scale ruptures distributed over the area and a low possibility of M >= 6.5 events in the near future.

On May 22, 2021, an M(s)7. 4 earthquake struck in Madoi County, Guoluo Prefecture, Qinghai Province of China. The surface rupture caused by this earthquake shows obvious segmentation characteristics in space. Based on the observations of continuously operating GNSS networkes from different sources, we obtained the fine three-dimensional coseismic deformation field of the earthquake. The results show that the maximum horizontal displacement is 280 mm and the maximum vertical deformation is only 25 mm, indicating that the thrust component of this earthquake is small. The coseismic deformation, with obvious sinistral strike slip characteristics, is basically symmetrical with a wider influence range in NW-SE direction. The epicentral distance range with horizontal coseismic deformation greater than 3 mm in this direction exceeds to 500 km. Futher, constrained by the relocated results of the aftershocks and the 3D coseismic deformation field observed by GNSS, we constructed a fault model with a broken surface fracture line, a dip angle of 85 degrees and along the strike of SW. The result of coseismic slip distribution shows that the sliding fractures are unevenly distributed on both sides of the epicenter, and they all ruptured to the surface, with the depth of similar to 15 km, the maximum sliding amount is 4.73 m, and the calculated moment magnitude M-w 7. 37. This result is consistent with the relocated results of aftershocks. The maximum rupture area is just located in the early aftershock gap, so we speculated that the future seismic risk in this gap is low. At last, we simulated the deformation and strain fields in the epicenter area based on the inversion results, and by combining the compression characteristics of the strain values on the southeast side of the fault surface trace and the existing research results, we concluded that this earthquake enhanced the accumulation characteristics of the compressive stress of the Bayan Har block in the eastern region. As a result, the seismic risk in the eastern region is enhanced, which is worthy of a follow-up study.

作为地球陆地上最高、最大、最平坦的地貌单元,青藏高原晚第四纪—现今构造变形的运动学状态是研究其深部地球动力作用的重要基础.全球卫星导航系统能够观测几十年时间尺度的地壳运动定量资料,历史记载和仪器观测获得的历史地震资料提供着数百年时间尺度的构造运动和深部变形数据,而上万年时间尺度的活动断裂定量研究数据则揭示着长期、平均构造变形状态.综合这三类不同时间尺度的地表构造变形定量数据,就能够定性推测或定量模拟驱动地表构造变形的深部地球动力作用.本文综合利用上述三类资料,发现青藏高原晚第四纪—现今的运动状态受控于统一的应变场,地表与深部一致,现今与长期一致.最大剪切应变主要分布在高原周边的主要逆冲断裂带和内部的巨型活动走滑断裂带,产生众多的强震;收缩应变和地壳缩短主要发生在周边山系及其伴随的前陆盆地,形成逆冲断裂和逆冲型强震;面膨胀应变和地壳拉张发生在高海拔的青藏高原内部,形成近南北向正断层和北东/北西向共轭剪切断裂系,并控制着正断层型地震的发生;青藏高原的所谓"向东挤出",不是刚性岩石圈地块在走滑断裂夹持下的向东滑移,而是高原内部岩石圈物质的向东流动和绕喜马拉雅东构造结的顺时针旋转.这种运动状态只能被青藏高原之下岩石圈地幔对流剥离动力学模型很好解释.被对流剥离的岩石圈沉入中下地幔时伴随着负浮力的产生,不仅使得青藏高原发生垂向隆升,还对周边施加水平挤压应力,从而造成高原周边准同期地向外逆冲扩展,导致了起始于晚新生代并延续至今的构造变形,形成所观测到的不同时段的构造变形运动场.