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A total of 24 scenes ALOS PALSAR satellite data between 2006-10 and 2011-03 were used to monitor the deformation for the Changbaishan volcano area; based on the PSInSAR approach for data processing, the time series and mean rate were obtained for deformation in the Changbaishan volcano region. These results show that the magma activity for the Changbaishan volcano was weak, since ionly near the crater there was there a 10 mm/a deformation rate. Based on the deformation results, a Mogi model was used to inverse the source parameters in volcanic area; the magma volume increased nearly 1 × 106 m3/a. [ABSTRACT FROM AUTHOR]

Considering the spherical visco-elastic structure, the post-seismic deformation inversion mode had been constructed based on the visco-elastic earth model. We developed the inversion mode and inversion software package based on the post-seismic fault dislocation model considering the crust-stratified structure. Using the genetic algorithm to invert the different fault dislocation parameters due to strike slip fault, dip slip fault respectively and comparing to the result inverted from the homogenous dislocation model, the result shows that the inversion algorithm used here could invert the dislocation parameters from the large region using the genetic algorithm and the inversion result is better to use. The inversion mode proposed here could better invert the seismic source parameters to different types fault. There is also a important find to suggest us that we could not use the minimum of VTPV as the only rule to judge the inversion result whether good or not when the model mode is not obvious. We should find other ways to make a supplement judge. [ABSTRACT FROM AUTHOR]

This paper reviews the progress and the theoretical achievements in stress-strain calculation using geodetic measurements over the past ten years and profiles domestic and international research with a discussion about the relationship between the gravity and stress-strain fields. Studies and applications of stress-strain inversion using geodetic data are summarized, and the outstanding problems are analyzed. The development of geodesy technology will continue pushing for the perfection of the inversion theory of the crustal stress-strain field using geodetic data. We suggest that the analytically elastic, visco elastic, and elastoplastic crust models relating ground gravity to the stress-strain field can be completely articulated and applied. We also conclude that studies concerning the relationship between spatio-temporal tectonic stress-strain fields and seismic stress triggering in the crust, as well as joint inversion for spatio-temporal tectonic stress-strain fields with multi-source data, should be developed. [ABSTRACT FROM AUTHOR]

Abstract: We invert the stressing rates of major strike-slip faults in the Tibetan Plateau using GPS measurements by the method of Least-Squares Collocation. From the comparison results of the influence of different distance intervals and covariance functions on the fit to GPS velocity field and the statistics of variance and covariance, we choose 40km as the distance interval and exponential function as the covariance function to calculate the stressing rates. The results show that the root-mean-square error of GPS observations is only 0.061cm. The stressing rates of the faults in the eastern Tibetan Plateau are generally higher than those in the west. The faults, whose maximum stressing rates are larger than 2.0kPa/yr, account for about 41.4% of selected faults. Specifically, the stressing rate of the northwest segment of the XSHF is the highest with a value of 7.05kPa/yr. Our stressing rates of the KLF and XSHF are consistent with published values or deduced results from published stress drops and earthquake recurrence intervals. The comparison results of stressing rates with fault slip rates show that the ratios of the stressing rates to the slip rates range broadly from 0.4 to 7.5bar/m, which may be due to different kinds of data and methods used to calculate the slip rates besides varying petrophysical properties in the Tibetan Plateau. However this variation of the same fault is less distinct than that in different faults. The GYFF, HYF, JLF, LCRF and RRF with low slip rates and high stressing rates may be located in brittle shear zones. Inversely, the ATF, KLF, KRKRF and KRKXF may be located in ductile zones. Additionally, the statistical results between the stressing rates and the seismicity rates show that the seismicity roughly grows with the tectonic stressing rates. And we deduce that the KRKXF and MCRCF with high seismicity rates and low stressing rates are the strike-slip faults mostly prone to rupture in the Tibetan Plateau. [Copyright &y& Elsevier]

Abstract: On October 6, 2008, an Mw 6.3 earthquake occurred in Dangxiong county, southern Tibetan Plateau. In this study, Synthetic Aperture Radar (SAR) images from Envisat ASAR C-band descending Track 176 and ALOS PALSAR L-band ascending Track 500 are processed to generate the coseismic deformation caused by the earthquake. To estimate the source model, a downhill simplex non-linear inversion method is used to determine the fault rupture geometry, and an automatic fault discretization technique is employed to divide the fault plane to construct the optimal slip model, in which the uncertainties of the fault parameters are assessed by a Monte Carlo method. The inversion results show that the earthquake strikes almost south–north and has a normal faulting focal mechanism with rake angle and slip of −111.7° and 1.33m, respectively. Peak slip of 2.15m is located at a depth of 7.5km. The estimated geodetic moment is 4.06×1018 N m (Mw 6.37), 71.2% of which is released in the depth range 4.5–11km. The slip model suggests that coseismic slip also takes place at some fault patches near the earth’s surface and postseismic afterslip occurs below the coseismic rupture area after the earthquake. [Copyright &y& Elsevier]

Abstract: InSAR time series techniques can provide high-spatial resolution deformation fields across an active fault belt, even for zones with heavy vegetation coverage. An interseismic deformation map across the Garze–Yushu fault belt in the Tibetan Plateau, ∼300km by ∼100km, is derived from C-band Envisat/ASAR imagery collected between 2003 and 2010. Unlike previous research, we obtain a lookup figure which relates the slip rate with the fault locking depth, the dip angle and the rake angle. The estimated slip rate changes significantly with the locking depth and the rake angle, but relatively little with the dip angle. When considering the focal mechanism solutions of historical earthquake along the Garze–Yushu fault, the interseismic slip rate of the Garze–Yushu fault is close to a value of 6.4mm/yr, which is between the highest (18.2mm/yr) and the lowest (3.1mm/yr) slip rate from GPS estimations, but slightly less than the minimum value (∼ 7mm/yr) from the geological estimations. The earthquake recurrence interval on the Yushu part of Garze–Yushu fault equals 272yr, and the April 14, 2010 Mw 6.9 earthquake has not completely released the accumulated strain energy between 1738 and 2010. [Copyright &y& Elsevier]

Abstract: The Coulomb failure function (CFF) quantitatively describes static stress changes in secondary faults near the source fault of an earthquake. CFF can be employed to monitor how static stress transfers and then shed some light on the probability of successive events occurring around a source fault. In this paper we focus on the CFF and particularly on optimally oriented planes. We present a unified model to determine an optimally oriented plane and its corresponding Coulomb stress, then apply the model to the 2003 Mw 6.6 Bam (Iran) earthquake and the 2008 Mw 7.9 Wenchuan (China) earthquake, thereby checking its effectiveness. Our results show that spatial correlation between positive Coulomb stress changes and aftershocks are, for the 2003 Bam earthquake, 47.06% when elastic Coulomb stress changes are resolved on uniform planes and 87.53% when these are resolved on optimally oriented planes at depth; for the 2008 Wenchuan earthquake the correlations are 45.68% and 58.20%, respectively. It is recommended that account be taken of optimally oriented planes when drawing a Coulomb stress map for analyzing earthquake triggering effects. [ABSTRACT FROM AUTHOR]

This study uses the least squares collocation method to fuse the leveling vertical deformation velocity in the Sichuan–Yunnan region with the GNSS observations of this region from 320 stations in the China Crustal Movement Observation Network (CMONOC) and the China Continental Tectonic Environment Monitoring Network (CMTEMN) from 1999 to 2017. Such fusion is to improve the accuracy of the vertical deformation rates in large spatial scales. The fused vertical deformation results show that: (1) the fused deformation field has a uniform spatial distribution, and shows detailed change characteristics of key regions; (2) the current vertical crustal motion in this region is featured by the contemporaneous occurrence of crustal compression, shortening and uplift and basin extensional subsidence; (3) most areas in this region experience uplifts, as the lateral push of the Qinghai–Tibet Plateau was blocked by the Sichuan Basin. The areas on the northwest side of the Longmenshan fault and the Lijiang-Xiaojinhe fault are dominated by uplifts, with the velocity of 1.5 mm/a–5.5 mm/a, and the region on the southeast side has slight uplifts, with the velocity of 1.0 mm/a–1.5 mm/a; (4) many areas have high gradient vertical deformation, especially the region close to the Wenshan fault and on the two sides of the Yarlung Zangbo fault that has the value of 3.0–4.0 × 10−8/a, deserving further attention to be paid to the long-term earthquake hazards. [ABSTRACT FROM AUTHOR]

Abstract: Geodetic–geophysical joint inversion is a hybrid inversion of different types of geodetic data, together with geophysical or seismic, geological data. In the joint inversion, weight scaling factors of different datasets are of vital importance and should be fixed properly. This paper aims to analyze the general weight scaling factor fixing methods and to study their impacts on joint inversion. The result, validated and evaluated by the cross validation test method, showed that it is not prudent to fix the inversion parameter only by considering the objective function to be a minimum and that the parameter should be determined by the actual circumstances. At last, a more reliable inversion result was obtained by using the Helmert method of variance components estimation (VCE) for the fixing of weight scaling factor. [Copyright &y& Elsevier]

The numerical manifold method (NMM) can calculate the movements and deformations of structures or materials. Both the finite element method (FEM) for continua and the discontinuous deformation analysis (DDA) for block systems are special cases of NMM. NMM has separate mathematical covers and physical meshes: the mathematical covers define only fine or rough approximations; as the real material boundary, the physical mesh defines the integration fields. The mathematical covers are triangle units; the physical mesh includes the fault boundaries, joints, blocks and interfaces of different crust zones on the basis of a geological tectonic background. Aiming at the complex problem of continuous and discontinuous deformation across the Chinese continent, the numerical manifold method (NMM) is brought in to study crustal movement of the Sichuan-Yunnan area. Based on the GPS velocity field in the Sichuan-Yunnan area, a crustal strain and stress field is simulated and analyzed. Moreover, results show that the NMM is a more suitable method than DDA in simulating the movement of the Sichuan-Yunnan area. Finally, a kind of mechanism of crustal motion in the Sichuan-Yunnan area is discussed in the paper. [ABSTRACT FROM AUTHOR]

The Ganzi‐Yushu fault (GYF) is one of the most seismically active fault systems in eastern Tibet, having experienced five M > 7.0 earthquakes over the past 300 years. Here, we use Sentinel‐1 InSAR data spanning from 2014 to 2023 to derive the interseismic velocity fields along the GYF. We calculate the strain rate fields for the entire fault system, which reveal localized strain accumulation along the GYF as well as along two secondary faults within the Bayan Har block. The inversion results obtained from the elastic block model indicate left‐lateral strike slip rates of 4.0–6.5 mm/yr along the GYF and five locked segments distributed along strike. Furthermore, we identify two shallow creeping segments on the InSAR velocity maps. Based on the locations of the creeping sections and their temporal decay characteristics, we infer that the shallow creep along the GYF is afterslip of the 2010 Yushu earthquake. Plain Language Summary: The 500 km‐long Ganzi‐Yushu fault is a main fault system in eastern Tibet. Investigating its slip behavior is crucial for assessing earthquake potential and understanding the deformation patterns in the region. Using space geodetic observations, we investigate the slip rate distribution along the Ganzi‐Yushu fault. The energy accumulation along the fault can be divided into five segments, which correspond remarkably well with the historical events. Besides the Ganzi‐Yushu fault, we find that two secondary faults within the Bayan Har block, which had not received much attention before, also exhibit significant seismic hazard. We identify two shallow creeping sections along the fault. By analyzing the spatio‐temporal characteristics of the shallow creeping sections, we confirm that they are associated with postseismic activity of the 2010 Yushu earthquake. Our results give insights into the regional deformation mode and seismic hazard. Key Points: Our large‐scale high‐resolution InSAR velocity fields reveal strain accumulation within the Bayan Har blockThere are five locked segments distributed along the Ganzi‐Yushu fault, which corresponds well with historical eventsWe identify two transient shallow creeping segments associated with afterslip of the 2010 Yushu earthquake [ABSTRACT FROM AUTHOR]

"Pass-by-pass" or "track-to-track" ambiguity resolution removes Global Navigation Satellite System (GNSS) satellite hardware delays between adjacent undifferenced (UD) ambiguities, which is often applied in precise orbit determination (POD) for Low Earth Orbit (LEO) satellites to improve the accuracy of orbits. In this study, we carried out an exploratory study to use the "pass-by-pass" ambiguity resolution by differencing the undifferenced ambiguity candidates for two adjacent passes in sidereal days for a single Global Positioning System (GPS) receiver static Precise Point Positioning (PPP). Using the GPS observations from 132 globally distributed reference stations of International GPS Service (IGS), we find that 99.08% wide-lane (WL) and 97.83% narrow-lane (NL) double-difference ambiguities formed by the "pass-by-pass" method for all stations can be fixed to their nearest integers within absolute fractional residuals of 0.2 cycles. These proportions are higher than the corresponding values of network solution with multiple receivers with 97.39% and 91.20%, respectively. About 97% to 98% of ambiguities can be fixed finally on average. The comparison of the estimated station coordinates with the IGS weekly solutions reveals that the Root Mean Square (RMS) in East and North directions are 2-4 mm and is about 6 mm in the Up direction. For hourly data, it is found that the mean positioning accuracy improvement can achieve to about 10% after ambiguity resolution. From a dam deformation monitoring application, it shows that the fixing rate of WL and NL ambiguity can be closed to 100% and higher than 90%, respectively. The time series generated by PPP are also in agreement with the short baseline solutions. [ABSTRACT FROM AUTHOR]

On 7 November 2019, an Mw 5.9 earthquake with a left-lateral strike-slip mechanism struck the Bozgush mountain in NW Iran, marking the largest event in the mountain area in the past 44 years. Because no surface rupture associated with the earthquake has been reported, the causative fault of the earthquake is unknown. This event provides an opportunity to gain insight into the active tectonics of the region. Here, we acquire the coseismic deformation associated with this earthquake through Sentinel-1A interferometric synthetic aperture radar (InSAR) data and further invert the fault geometry and the detailed coseismic slip of this event based on the planar fault model. By a joint analysis of the inversion results, aftershocks sequence and local tectonics, we propose that the buried branch fault splaying from the Shalgun-Yelimsi fault (SYF) at depth may be responsible for this earthquake. Both the uniform and distributed slip models infer a smaller fault rupture size than predicted by classical fault scaling relation. We suggest that the subsurface fault geometry of the SYF may stop the rupture propagation further down to southeast at depth, thus resulting in high slip and stress drop at such a small fault plane. Considering the proximity of the epicenter to the SYF, we also invert for the distributed slip model on an anti-listric fault with the purpose to explore the possible complexity of rupture fault. However, due to the lack of obvious improvement to fit the observed data and the limited slip in the deep fault segment, the planar fault model is still regarded as the optimal one. According to the calculated coseismic Coulomb stress changes, we find that 55 % of aftershocks are triggered by the statics stress and that the northern segment of SYF and the eastern segment of SBF have a potential rupture risk. The occurrence of this earthquake, together with the prominent offset feature and slip style of surrounding active fault, indicates an active conjugate fault system, which may accommodate the small-scale northeastward lateral extrusion. [ABSTRACT FROM AUTHOR]

Peak ground displacement (PGD) derived from high-rate Global Navigation Satellite System (GNSS) can be used to determine, i.e., the estimate or scale the earthquake magnitude in real time without magnitude saturation experienced by seismic sensors at large earthquakes. Compared with relative positioning or Precise Point Positioning (PPP), the variometric approach can calculate station velocity using the broadcast ephemeris and avoiding estimating phase ambiguities. By integration, velocities can be translated into displacements. However, an inaccurate broadcast ephemeris might cause integrated displacements to show nonlinear drifts. Recently developed real-time orbit and clock products used by real-time PPP have higher accuracy and can also be employed by the variometric approach. We evaluate the performance of the variometric approach on magnitude scaling using high-rate GNSS data collected during the 2019 Mw 7.1 Ridgecrest earthquake, the 2016 Mw 7.8 New Zealand earthquake, and the 2017 Mw 6.5 Jiuzhaigou earthquake. The results indicate that a spatial filter cannot correct nonlinear drifts of integrated displacements completely and scaled magnitudes are not stable when the broadcast ephemeris is used. While using the Centre National d'Etudes Spatiales (CNES) real-time ephemeris, we find both the spatial filter and linear filter can correct drifts well and scaled magnitudes have the same accuracy as those of PPP. While comparing different GNSS systems, we find that BDS is superior to GPS and GLONASS in the case of the Jiuzhaigou earthquake because BDS has a better satellite geometry in this region. Compared with single GPS, multi-GNSS can improve satellite geometry and provide more precise seismic displacements when broadcast ephemeris and low sampling precise clocks are used by the variometric method. [ABSTRACT FROM AUTHOR]

Rapid disaster response will provide significant information to relevant responding agencies. On 20 March 2019, an Mw 5.7 earthquake struck the Acipayam basin in southwestern Turkey, which is the largest event to occur in the basin. Here, we use Sentinel-1A interferometric synthetic aperture radar (InSAR) data to investigate the cosesimic deformation related to the Acipayam earthquake. The ascending and descending interforegrams suggest the normal faulting during this earthquake, with the maximum line of sight (LOS) displacements of 4.6 cm and 4.8 cm, respectively. The fault geometric parameters and a detailed coseismic distributed slip model of this event are retrieved by using geodetic data for the first time. Though the coseismic interferograms don't show enough polarity changes to ascertain the dip orientation of the rupture fault, we regard the northeast-dipping fault as the causative fault by a joint analysis of the residuals plots, 2.5 dimensional (2.5D) deformation field, field investigation results, regional geomorphic feature and overall distribution of aftershock (4.0 < Mw < 4.9). The inversion results show that coseismic rupture was mainly dominated by normal faulting with minor sinistral strike-slip components. The rupture fault is a blind normal fault and the main slip is concentrated in the depth range of 3∼9.5 km with a maximum slip of approximately 0.33 m at a depth of ∼6 km. The InSAR-determined geodetic seismic moment is 3.96 × 1017 Nm corresponding to M w 5.7. Our model resolution test supports these interpretations for the Acipayam earthquake. Based on the coseismic Coulomb stress change, we find that this 2019 event increases the stress loading in the northwestern and southeastern segment of the rupture fault plane and possibly triggers the subsequent Mw 4.8 and Mw 4.9 earthquakes. The mechanism of the determined seismogenic fault may be helpful to evaluate seismic hazards and understand the evolution of the Acipayam basin. [ABSTRACT FROM AUTHOR]

On November 18, 2017, the Mainling Mw 6.5 earthquake occurred on the northern Namche Barwa syntaxis and was the largest earthquake in the syntaxis and surrounding areas since the Zayu Mw 8.4 earthquake in 1950. Due to inconvenient access and the severe environment in the Namche Barwa syntaxis area, the motions and tectonic structures of most faults remain unclear. Sparsely distributed seismic observation stations make the seismogenic fault and focal mechanism of the Mainling earthquake controversial. We adopt interferometric synthetic aperture radar (InSAR) to invert the slip distribution of this event by defining the fault geometry with relocated aftershocks. Our preferred model suggests that the 2017 Mainling earthquake ruptured two blind faults beneath the Namche Barwa syntaxis. The ruptures were dominated by thrusts with slight right-lateral strike-slip components. The slips on the two faults are equivalent to moment magnitudes of Mw 6.12 and Mw 6.34, with maximum dislocation magnitudes of 0.36 m and 0.43 m, respectively. The model fits well with the InSAR observations and the distribution of aftershocks. The results from the Coulomb stress simulation indicate that the stress loading caused by strong historical events promoted the occurrence of the 2017 Mainling earthquake. Compared with the seismogenic faults of the Mainling earthquake, the larger thrust faults in the southern Namche Barwa syntaxis can generate larger earthquakes. Therefore, we assume that Mw > 6.5 earthquakes may occur beneath the Namche Barwa syntaxis and that the seismic risk has been further promoted by historical events. [ABSTRACT FROM AUTHOR]

The real-time retrieval of highly accurate seismic waveforms is essential for the earthquake early warning and fault rupture process inversion. Although the traditional strong motion(SM) sensor can record seismic waveforms with very high accuracy and frequency, it suffers from baseline errors due to the tilt or rotation of the instrument. Compared with the SM, the High-rate GNSS can record ground displacements directly without drift. But it has higher noise and lower sampling rate than that of SM. To complement the advantages of High-rate GNSS and SM, the PPP-based tight integration methods of two sensors have been proposed in the past few years. However, limited by the precise orbit and clock products, it is not possible for traditional PPP to record seismic waveforms in real time. In April 2013, the international GNSS service(IGS) issued the real-time service(RTS), which makes the real-time tight integration of High-rate GNSS and strong motion records possible. Therefore, based on the IGS RTS products, we analyzed the performance of the real-time PPP-based tight integration of two sensors using co-located records collected during the 2016 Mw 7.8 earthquake in New Zealand and 2016 Mw 6.5 earthquake in central Italy in a simulated real-time mode. The results show that the real-time combined displacements include more abundant seismic signals without clipping and drift if the baseline shift is estimated as a random walk process, and the RMSE(Root Mean Square Error) in the North, East and Up component is 3mm, 3mm and 6mm separately while taking post combined displacements as a reference. [ABSTRACT FROM AUTHOR]

Located at the forefront of the collision between the Indian and Eurasian Plates, the Tibetan Plateau experiences intense crustal movement. Traditional ground-based geodetic monitoring, such as GNSS and leveling, is challenging, due to factors such as high altitude and harsh climate, making it difficult to accurately determine a high-resolution crustal deformation field of the plateau. Unaffected by ground observation conditions, InSAR technique has key advantages for obtaining extensive and high-resolution crustal deformation fields. This makes it indispensable for crustal deformation monitoring on the Tibetan Plateau. This study used Sentinel-1 data from 2014 to 2020 to compute the ascending and descending InSAR deformation fields for the Tibetan Plateau. This was conducted with a measurement accuracy of approximately 3 mm/yr. Building upon this, we integrated InSAR and GNSS data to yield kilometer-resolution three-dimensional (3D) crustal deformation and strain rate fields for the Tibetan Plateau. A spherical wavelet analysis was used to decompose the 3D deformation field and separate the non-tectonic crustal deformation to increase the strength of the tectonic deformation signal. Short-wavelength (<110 km) deformations match the distribution of fault movement, post-seismic deformations, and other non-tectonic factors. Long wavelength (>110 km) deformation mainly results from subsidence in the central plateau and uplifts along the Himalayan Arc. This indicates that the Tibetan Plateau may have stopped the entire uplift and entered a local collapse stage. Furthermore, the deformation fields at different spatial scales reveal that the plateau exhibits discontinuous deformation in short wavelengths and continuous deformation in long wavelengths. The findings of this study contribute to resolving the controversy between the Block and Continuum Deformation models of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The 2021 MW 7.4 Maduo event occurred within the Bayan Har block in eastern Tibet, which provides an opportunity to investigate the stress conditions and rheology of faults within the block. Here, we perform dynamic rupture simulations based on the finite element method to explore the physical conditions underlying this earthquake and the factors that controlled the rupture process. We construct the model with a nonplanar fault inferred from the Interferometric Synthetic Aperture Radar (InSAR) data and aftershocks sequence relocation. Our dynamic model is controlled by slip‐weakening friction law with initial stress on fault resolved from a uniform regional stress field. The preferred model produces an average slip of ∼2.2 m with a maximum slip of ∼4.0 m. There are three asperities distributed along the strike, which have captured the main features of the Maduo event. The simulation results are consistent with the static GPS coseismic surface displacements, InSAR data, and displacement waveforms recorded by high‐rate GNSS stations. By comparing the results with the planar fault model and rotated stress fields, we find that the fault geometry and regional stress field are the primary factors that control the rupture process of the event. Moreover, we infer that the unfavorable orientation and fault bend lead to minor slips on the branch fault. Furthermore, we investigate the potential mechanisms of supershear rupture on the eastern fault segment. Plain Language Summary: The 2021 Maduo event ruptured on an intra‐block fault of the Bayan Har block in the Tibetan Plateau, which has aroused widespread interest among the scientific community. In this study, we perform physics‐based numerical simulations based on a nonplanar fault to reproduce the source process of the event. The surface displacements obtained from our dynamic model are in good agreement with the observations. As the other parameters are relatively simple in our model, the source process of the event is mainly controlled by the geometric fault complexities. Our results also help to constrain the orientation of the regional stress field. We find that the branch fault of the earthquake is unfavorably oriented in the regional stress field as well as the fault bend also impedes the rupture to propagate on it, which leads to a minor slip on the branch fault. Furthermore, we infer that the supershear rupture may be induced by the free surface in the earthquake. Key Points: Our dynamic model reproduced the first‐order rupture characteristics of the Maduo earthquakeThe main factor that controls the multipeak slip pattern of the Maduo event is fault geometryThe orientation of the regional stress field was determined through numerical experiments [ABSTRACT FROM AUTHOR]

Abstract Due to the disturbances along the signal path, it's inevitable that the loss of lock or data interruption interval of a few satellites reach to decades of seconds or even minutes. It will be difficult to recover data and evaluate cycle slips after a long gap in real time kinematic (RTK) positioning. A double-differenced (DD) velocity estimation method is proposed for the repair of cycle slip in RTK positioning, assuming available of fixed coordinate solutions for the previous epoch. We achieve the precise coordinate solution of the current epoch by using triple-differenced (TD) combinations. The dual-frequency observed minus computed (OMC) combinations are then calculated by using the observations and coordinate solutions. The differenced OMC values between two epochs are used to repair cycle slips. Two kinematic experiments carried out to evaluate the performance of the proposed method are for velocities less than 2 m s−1 for a boat and about 10 m s−1 for a vehicle. The averaged distance of boat and vehicle relative to the reference are about 11 km and 24.5 km, respectively. The experimental results of the boat case indicate that all cycle slips are corrected within 0.25 cycles even though sampling interval reaches to 120 s. The cycle slips fixing uncertainty is close to 0.3 cycles for a sampling interval of 30 s and 60 s vehicle experiments. As the sampling interval increases to 90 s and 120 s, the uncertainty rises to 0.35 cycles for the vehicle-dynamic vehicle experiment. [ABSTRACT FROM AUTHOR]

Mapping the three-dimensional (3D) displacement fields associated with a variety of geological phenomena has been widely performed by exploiting synthetic aperture radar (SAR) imagery, as the result is important for providing insight into the formation mechanisms and potential risks of geological hazards. New-generation SAR sensors, namely ALOS-2 and Sentinel-1, can capture surface deformation with a high coherence in wide-swath mode, thereby providing outstanding across-track displacement accuracies; however, this improvement partially sacrifices the azimuth resolution, which affects the retrieval of 3D surface deformation fields. To explore the feasibility of generating 3D deformation maps with new SAR imagery, we collect two pairs of ALOS-2 ScanSAR and four pairs of Sentinel-1 Terrain Observation by Progressive Scans (TOPS) images for the 12 November 2017 Ezgeleh earthquake. Furthermore, the differential interferometric SAR (DInSAR), pixel offset tracking (POT), multiple-aperture InSAR (MAI), and burst-overlap interferometry (BOI) methods are used to measure the across- and along-track displacements. Compared with the POT and MAI methods, the integration of DInSAR and BOI measurements provides high-quality 3D deformation maps with an accuracy of 4 cm, which is four times and two times better than the accuracies of the POT and MAI methods integrated with DInSAR, respectively. In addition, a significant north-south displacement of 0.76 m is found in our 3D deformation results that was underestimated in the slip distribution model constrained with seismic waveforms or InSAR measurements. Our 3D deformation map of the 2017 Ezgeleh earthquake indicates a southwestward horizontal motion and an upward motion without any corresponding surface rupture that effectively match the behavior of a blind rupture along a northeast-dipping reverse fault. We conclude that combining BOI with DInSAR would provide a better 3D deformation field and should be applied to study future earthquakes. [ABSTRACT FROM AUTHOR]

On 2015 November 4, an M w 6.5 earthquake struck the east region of Alor Island, eastern Indonesia. Here, we use Sentinel-1 and ALOS-2 data to explore the coseismic surface displacement of this earthquake. Based on the ALOS-2 coseismic interferograms, the first fault model and coseismic slip distribution of the 2015 Alor earthquake are presented in this study. The preferred slip model links to a blind south-southeast striking, south-southwest dipping strike-slip fault with amount of normal slip component and a peak slip of 2.09 m at 2.34 km of depth. Considering the fact that the ascending and descending InSAR prediction of the distributed slip model does not fit the InSAR observations at the northwest and southeast tips with the simple planar fault model. We tried to construct a strike-variable fault model to further improve data fit. The results of the calculated Coulomb stress change imply that the regions with positive CFS changes mainly located at the northwest and southeast extremities of the rupture of the Alor earthquake, and in the lobes north and south of the rupture. The most striking discovery from the InSAR observations of the Alor earthquake is that most of the displacements occurred on a fault whose existence was unknown before the earthquake. [ABSTRACT FROM AUTHOR]

Highlights • Coseismic deformation is derived from near-field GPS measurements and InSAR interferograms. • A planar fault model explains the coseismic deformation better in comparison to a listric fault model. • The slip distribution is characterized by two separate asperities on a steeply-dipping planar fault. • The recurrence interval of the 2016 Mw 6.7 Aketao earthquake is deduced to be 100–230 years. Abstract On 25 November 2016, the Aketao, Xinjiang earthquake occurred on the Muji fault, which is located at the northernmost end of the right-lateral Karakorum Fault (KF). This event provides a rare chance to gain insights into how the stress accumulates in Pamir margin as the Indian plate collides with the Eurasian plate. Space geodetic measurements including InSAR and GPS were used to obtain coseismic surface displacements associated with this earthquake. Based on a finite fault model, the coseismic slip distribution inverted by the combined datasets indicates that the 2016 Aketao event is caused by a primary shallow strike-slip with minor normal-slip at a steep-dipping angle. To explore the real structure of Muji fault, listric fault model inferred by relocated aftershocks as well as the planar fault model, were used in our slip distribution inversion. The results suggest that the optimal fault model should be a highly-dipping planar fault with two separated asperities. The large slip zone is beneath the surface near the epicenter with a maximum slip of 1.1 m, while the small one in the east breaks the surface, in a good agreement with the field seismic geological survey. The total geodetic moment is 1.35 × 1019 N∙m , equivalent to Mw 6.7. The nearly pure dextral strike-slip Aketao earthquake, and the recent 2015 Mw 7.2 sinistral strike-slip Tajikstan earthquake in this region, to some extent, manifest the extension motion is dominated in northern Pamir Plateau, in response to the northward convergence between Indian and Eurasian collision. [ABSTRACT FROM AUTHOR]

Minimizing data misfit has been widely used in geodetic determination of fault dip angle, however, it ignores the contribution from data noise. Here, we use the j ℛ i criterion, which takes into account both data misfit and the contribution from data noise, to determine dip angle. Synthetic tests show dip angle estimates with the j ℛ i criterion are more accurate and robust than those with data misfit minimization. We applied this j ℛ i criterion to the determination of the dip angle of the 2015 M w 7.9 Gorkha Nepal earthquake using Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) data. The results show that the event ruptured to the north of Kathmandu with a maximum slip value of 5.8 m and a dip angle of 9.5°. We also calculated the coulomb failure stress changes resolved onto the receiver faults that are generally consistent with the fault geometry of this event, suggesting the possible triggering relation to aftershocks with low dip angles and a zone of seismic potential located to the west of the rupture zone. [ABSTRACT FROM AUTHOR]

The Ordos Block in China experiences tectonic activity and frequent earthquakes due to compression from the Tibetan Plateau and extension from the North China Block. This has prompted the construction of a high-resolution three-dimensional (3D) deformation field to better understand the region's crustal movement. Considering the limitations of the existing geodetic observations, we used InSAR, GPS, and leveling observations to create a high-precision 3D deformation field for the Ordos Block. Spherical wavelet decomposition was used to separate tectonic and non-tectonic deformation signals. Short-wavelength non-tectonic deformation fields revealed complex surface deformation patterns caused by groundwater, oil, gas extraction, and coal mining. Long-wavelength tectonic deformation fields showed subsidence in the southern margin of the block, while the interior and northeastern margins were uplifted. By combining imaging results from the seismic velocity structure and magnetotellurics, we infer that the upwelling of deep materials beneath the northeastern margin leads to surface uplift with tensile strain rates. The crustal uplift in the area south of 38°N matches the thickening of the lower crust. The weak subsidence and eastward horizontal movement disappearing near 108°E at the southern margin support the existence of asthenosphere flow beneath the Qinling orogenic belt. [ABSTRACT FROM AUTHOR]

To resolve the occurrence mechanism of the Luxian earthquake occurred near an active hydraulic fracturing well pad on 15 September 2021, we first use seismic waveforms to invert the focal mechanism solution and centroid depth, and then utilize Sentinel‐1 Synthetic Aperture Radar images and Global Navigation Satellite System observations to determine the seismogenic fault and slip distribution. Our results show that the Luxian event ruptured a previously‐unmapped southwest‐dipping reverse fault intersecting with one horizontal well of the well pad. Major slip occurred below the shale gas bed (∼4 km deep) but above the crystalline basement (∼7 km deep). Further analyses on preseismic surface deformation initiated in the northeast of the event reveal that pore pressure near the hypocenter was increased by ∼4.5 MPa. Consequently, fracking fluid injected through the horizontal well and other wells of nearby pads likely flowed directly into the fault zones and prompted the occurrence of the Luxian earthquake. Plain Language Summary: Due to huge casualties and property losses, the Ms 6.0 Luxian earthquake aroused wide public concern. Beyond that, at 0.85 km south of the epicenter, there is a hydraulic fracturing (HF) well pad (H79) that was operating before the earthquake occurrence. Therefore, people suspect that there was some relationship between the event and HF operations. We here jointly use seismic waveforms of regional permanent stations, Sentinel‐1 Synthetic Aperture Radar images, and Global Navigation Satellite System observations to determine the location and 3D geometry of the source fault. We find the fault intersecting with one horizontal well of the nearby pad, indicating that fracking fluid can flow directly into the fault zones and cause pressure perturbation with magnitudes comparable to the minimum principal stress. In addition, we also find preseismic deformation around the epicenter initiated after 29 May 2021. The deformation is likely linked to accumulation of fracking fluid injected during the drilling and HF operations of other pads. Further modeling reveals that the fluid accumulation increased pore pressure by ∼4.5 MPa near the hypocenter. The source fault likely suffered pressure diffusion before the operation of well pad H79 and was eventually reactivated by pressurization directly linked to HF stimulation. Key Points: The Luxian earthquake ruptured an unmapped south‐dipping reverse fault with major slip occurred in deep sedimentary formationsPreseismic surface deformation analyses indicate that fracking fluid accumulation likely caused pressure increase near the hypocenterThe source fault, intersecting with one horizontal hydraulic fracturing well, was likely reactivated by direct fault‐zone pressurization [ABSTRACT FROM AUTHOR]

Three-dimensional deformation velocity field can reveal fine characteristics of surface deformation, and provide data support for the research on crustal motion mechanism and seismic hazard. In this study, the ascending and descending InSAR deformation velocity fields in the middle and east parts of Haiyuan fault zone are firstly obtained with Sentinel-1A data and SBAS InSAR technology. Then, by combining with GPS observations, the three-dimensional deformation velocity field is extracted and analyzed. Finally, the locking depths and deep slip rates at different locations are inverted by using the classical two-dimensional screw dislocation model, and the maximum shear-strain rate is investigated. The results indicate that there are significant differences in the InSAR deformation velocity field between both sides of the middle and east parts of Haiyuan fault zone. The east–west deformation velocity field clearly reveals the left-lateral strike-slip characteristic of the fault zone. The northward movement gradually changes to southward movement from northwest to southeast. The vertical deformation velocity field displays significant differences on both sides of the section between MMSF and the middle of LHSF, and the middle and eastern of HYE fault. For LHSF, the locking depth and deep slip rate are 9.7 km and 4.9 mm/a; for HYW fault, they gradually decrease from west to east, with the locking depths of 6.4 km, 3.6 km and 3.2 km, respectively, and the deep slip rates of 5.5 mm/a, 4.2 mm/a and 3.8 mm/a, respectively; for HYM fault, they are 7 km and 4.7 mm/a; for HYE fault, they are 5.8 km and 3.6 mm/a. There are two obvious extreme regions of maximum shear-strain rate along the fault strike. This study can provide a reference for investigating the mechanism of regional uplift and extension and seismic hazard. [ABSTRACT FROM AUTHOR]

A devasting Mw7.2 earthquake struck southern Haiti on 14 August 2021, leading to over 2000 casualties and severe structural failures. This earthquake, which ruptured ~70 km west of the 2010 Mw7.0 event, offers a rare opportunity to probe the mechanical properties of southern Haiti. This study investigates the kinematic multi-fault coseismic rupture process by jointly analyzing teleseismic and interferometric synthetic aperture radar (InSAR) datasets. We determined the optimal dip of different segment faults through finite-fault inversion, and the results show that the dips of the first, second and third faults are 62°, 76° and 76°, respectively, coinciding with the relocated aftershock distribution. The results estimated from our joint inversion revealed that the slip was dominated by reverse motion in the first segment and strike-slip motion in the second and third segments. Three slip patches were detected along the strike, with a peak slip of 3.0 m, and the rupture reached the surface at the second segment. The kinematic rupture process shows a unilateral rupture with a high centroid rupture velocity (5.5 km/s), and the rupture broke through the stepover and caused a cascade rupture. The rupture front experiences a directivity pulse of high ground motions with high amplitude and short duration, which may be an additional factor explaining the many landslides concentrated on the western end of the fault. The Coulomb failure stress change result indicates the increases in the probability of future events to the east and west of the 2021 main shock. [ABSTRACT FROM AUTHOR]

• Crack growth behavior under HCF-TMF combined fatigue loading conditions is studied. • Evolution of strain gradient and shape of plastic zone at crack tip is revealed based on DIC. • Deflection of crack growth rate is occurred when the plastic zone is two times of grain size. • Crack growth model based on damage cumulation of time- and cycle-dependent components. This work comparatively investigates the effect of superposition of high-cycle fatigue (HCF) loading on the crack growth behavior of 316LN stainless steel in isothermal fatigue (IF) and thermomechanical fatigue (TMF) tests. Results show that a deflection of the crack growth rate is observed in the tests without HCF loading. The superposition of HCF loading leads to a marked increase of crack growth rate in IF and out-of-phase TMF tests while a minimal variation in in-phase TMF test. Moreover, the crack growth rate in in-phase TMF test is smaller than the IF and out-of-phase TMF tests due to the different shape and evolution behavior of plastic zone at crack tip. Finally, the model based on the cumulative damage rule of time-dependent and cycle-dependent components is proposed, which considers the characteristics of plastic zone size and grain size and leads to a satisfactory prediction result. [ABSTRACT FROM AUTHOR]

• Effects of area density (W s) of a hinged inertial cover on vented H 2 /CH 4 /air deflagrations were studied. • The opening angle at the time of t out decreases with an increase in W s. • In the test with higher W s , the external fireball becomes more flattened. • In tests at χ H 2 = 0.8, p red and p ext increase sharply with an increase in W s from 0 kg/m2 to 2.7 kg/m2. Explosion venting is the most commonly used technique to reduce the hazard from accidental deflagration of combustible gases. Since less attention is paid to the influence of inertial vent on vented H 2 /CH 4 /air deflagration, the effects of area density (W s) of a hinged inertial cover on the pressure profile and flame behavior during H 2 /CH 4 /air deflagration, with hydrogen volume fraction in fuel (χ H 2) being 0.5 and 0.8, were investigated by covering the vent using aluminum plates with various thicknesses. The results show that the interval between ignition and the moment the flame just travels through the vent (t out) is almost independent of W s , but the opening angle of the panel at the time of t out is closely related to W s. For a given χ H 2 , the opening angle at the time of t out decreases with an increase in W s. For a certain W s , the opening angle of the panel is smaller for χ H 2 = 0.8 in comparison with the tests at χ H 2 = 0.5. In the test with higher W s , the external fireball becomes more flattened. In tests at χ H 2 = 0.5, p 3 induced by acoustic oscillations dominates the internal overpressure, but p 2 resulting from the external explosion becomes the dominant pressure peak at χ H 2 = 0.8. The maximum reduced overpressure (p red) and maximum external overpressure (p ext) are almost independent of W s at χ H 2 = 0.5. However, in tests at χ H 2 = 0.8, p red and p ext increase sharply with an increase in W s from 0 kg/m2 to 2.7 kg/m2, but there is relatively little variation in p red and p ext as W s continues to increase from 2.7 kg/m2 to 24.3 kg/m2. Except for the test with W s = 0 kg/m2, for a specific W s , p red and p ext at χ H 2 = 0.8 are always greater than those at χ H 2 = 0.5. [ABSTRACT FROM AUTHOR]

On 7 January 2022, a Mw 6.6 earthquake struck Menyuan County in the Qinghai province of China and the earthquake caused severe damage to infrastructures. In this study, the performance of the high-rate global navigation satellite system (GNSS) on real-time source modeling of the 2022 Mw 6.6 Menyuan earthquake was validated. We conducted the warning magnitude calculation, centroid moment tensor (CMT) inversion, and static fault slip distribution inversion using displacements collected from 14 1-Hz GNSS stations. Our results indicate that the warning magnitude derived from the peak ground displacement (PGD) first exceeds Mw 6.0 approximately 9 s after the earthquake and tends to be stable after about 45 s. The derived finally stable magnitude is Mw 6.5, which is near the USGS magnitude of Mw 6.6. Based on the inverted CMT and static fault slip distribution results, it can be determined that the 2022 Menyuan earthquake is a left-lateral strike-slip event after about 20 s of the earthquake. Although the fault slips, inverted with the 30-s smoothed coseismic offsets, are unstable after about 40 s, all the inverted slip models after that time present the obvious surface rupture and the most fault motions are concentrated between the depth of 0 km and 8 km. Compared with the results inverted with the 30-s smoothed coseismic offsets, the CMT and fault slips inverted with the 70-s smoothed coseismic offsets are more stable. The results obtained in this study indicate that the high-rate GNSS has the potential to be used for real-time source modeling for earthquakes with a magnitude less than 7; the stability of the inverted CMT and fault slips can be improved by using the coseismic offsets averaged by a relatively long-time sliding window. [ABSTRACT FROM AUTHOR]

Kashi Depression is one of the most complex active tectonic areas in the southern flank of Tianshan, China. Due to the lack of ground observations, the boundary of basin mountain transition zone and the interseismic activity of the Tianshan have not been clearly determined. In this study, 48 Envisat Advanced Synthetic Aperture Radar (ASAR) imagery acquired from 2003 to 2010 are used to construct interferograms for measuring high-resolution interseismic deformation in the Kashi Depression area. A global atmospheric model ERA-Interim provided by the European Center for Medium Range Weather Forecast (ECMWF) and a global network orbital correction are applied to remove atmospheric effect, and the long-wavelength orbital errors, respectively, for the interferograms. Interferometric SAR time series with Atmospheric Estimation Model (InSAR TS + AEM) are then used to obtain a deformation rate map for the Kashi Depression area. The InSAR rate map indicates that the north part of South Atushi Fault has ~ 3 mm/year uplift relative to that of the south part. This result manifests the main tectonic deformation potentially occurs along the Southern Atushi Fault. Based on a simple edge dislocation model, the dip angle of 31 ± 0.6°, slip rate of 2.3 ± 0.1 mm/year, and locking depth of 10.6 ± 0.4 km for the Southern Atushi Fault between Tianshan Orogenic Belt and the Kashi Depression are obtained. This modeling result shows in good agreement with the InSAR derived rates. Our results show that the Southern Atushi Fault is the main active fault in block boundary region between the south of Tianshan and the Tarim Basin. [ABSTRACT FROM AUTHOR]