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.

High-rate Global Navigation Satellite Systems (GNSS) observations from an integrated network in the Tibetan plateau were used for rapid source determination of the 2021 Mw 7.4 Maduo earthquake. Constrained by high-rate displacements from nine stations near the source, the magnitude was essentially determined as early as 20 s after the origin time (OT), whereas the 39-s-long rupture propagated only approximately halfway, and together with the epicenter location and rupture length, they were completely determined 29 s after the OT or 10 s before the rupture completion. In addition, to test the capability and feasibility of current GNSS networks for rapid source determination in the Tibetan plateau, two experiments were further implemented to invert source parameters by real observations at farther sites and synthetic observations induced by an Mw 7.0 modeled earthquake. The results demonstrate that current GNSS networks are capable and feasible to provide rapid source determination and earthquake early warning in approximately 30 s after the OT for large earthquakes (Mw 7.0+) based on current station density, spatial coverage and communication conditions in the Tibetan plateau.

北斗卫星导航系统对地震观测技术高质量发展和防震减灾事业现代化建设具有重要意义.本文介绍了地震行业在北斗系统基准站建设与运行、高精度数据处理、北斗通信等方面应用的工作进展、推进措施和实施效果,分析了地震行业北斗系统应用前景.

自1966年邢台地震以来,中国尝试用大地测量手段监测地震变形,至1976年唐山地震,变形监测到达高潮,但受地面技术局限,20余年可以用于分析震源的震例寥寥.自20世纪90年代初全面进入空间观测时代以来,境内或边邻6级以上强震大多数有相应的近场变形观测和破裂模型研究,这其中又以2001年昆仑山口西、2008年汶川和2015年廓尔喀3次特大地震的变形资料相对完整、破裂特征清晰、理论成果丰富,成为近期大陆内部最引人注目的大震事件.近30年来,对包括中国台湾在内的60余次强震变形的系统研究丰富了人们对区域地震活动性及危险性的认识,也为青藏高原构造演化研究提供了观测依据与理论参考.半个世纪积累的经验、夯实的基础以及未解的难题更为未来的地震大地测量提供了历史借鉴、前进动力和发展方向.

基于19个连续GNSS观测站的多种采样率(10 Hz、1 Hz和30 s)数据,分析2017-09-03朝鲜核爆对中国东北地区地壳形变场的影响.静态位移分析结果显示,距核爆现场最近的GNSS观测站JLCB没有产生明显的同震形变,与基于均匀半无限弹性空间断裂位错模型正演模拟的结果一致;GNSS应变结果显示,此次核爆在东北区域引起主应变的略微调整,但总体调整量在10 8以内,没有引起区域范围内面应变的变化;高频GNSS动态形变分析结果显示,核爆在JLCB站处没有引起明显的波形变化.另外,高频GNSS受到多路径效应的影响,可能会引起cm级的扰动,利用恒星日滤波方法可以抑制多路径的影响,得到精度更高、更可靠的动态形变结果.

On 8 August 2017 an earthquake of magnitude 7. 0 struck Jiuzhaigou, Sichuan Province. Coseismic displacements of this event have been captured by both the GNSS continuous stations of the Tectonic and Environmental Observation Network of Mainland China and the Ground Reinforcement System (coordinates: east is positive, north is positive). The results show that of three sites of the above observation have recorded obvious coseismic horizontal displacements. Of them, the SCJZ site 43 km to the epicenter observed a displacement of -9. 8 +/- 1. 5 mm in the east-west direction and 3. 3 +/- 0. 7 mm in the north-south direction, respectively. The SCSP site 65 km to the epicenter measured displacement of -1. 8 +/- 0. 7 mm in the east-west direction and -7. 7 +/- 0. 6 mm in the north-south direction, respectively. At GSZQ site, 77 km to the epicenter, displacements of 0. 4 +/- 1. 2 mm in the east-west direction and 3. 67 +/- 0. 8 mm in the north-south direction were detected. The distribution of these coseismic displacements suggests that the earthquake is a sinistral strike-slip event, causing the horizontal deformation within an extent less than 150 km with a very small effect on the Longmenshan fault zone in the southeast. The displacements on the Tazang fault and the Minjiang fault reach several centimeters. The results of inversion of the coseismic displacements/show that the slip on the fault plane is mainly concentrated around 7 km depth, with maximum about 0. 4 m and an average slip angle -15 degrees. The corresponding moment magnitude calculated by the slip distribution is about M(w)6. 4, which is equivalent to that from seismic wave inversion. Based on the characteristics of coseismic slip distribution, principal strain distribution, aftershock distribution and focal mechanism solutions, it is inferred that the energy accumulated in the extreme area of the earthquake rupture is fully released, causing a significant stress change on the Tazang fault, the Minjiang fault and the Huya fault, which should receive continual attention.

The Jiuzhaigou M(s)7. 0 earthquake of August 8, 2017 occurred at the conjunction of the Minjiang, Tazang and Huya faults, the border area between Sichuan and Gansu provinces as well as the northeastern part of the Tibetan Plateau where the tectonics is very complex. There exists a certain controversy about the accurate location of the epicenter and the seismogenic fault for this earthquake. Based on the coseismic deformation field obtained from GNSS and InSAR observations, we inverted for the characteristics of coseismic slip model, spatial distribution and the coseismic Coulomb stress changes using a homogeneous elastic half-space model. The features of coseismic deformation derived from InSAR and GNSS show that this event is dominated by left-lateral strike-slip. The maximum and minimum displacements are about 0. 16 m and -0. 21 m, respectively, along LOS with the whole deformation field is in the NW direction which is concentrated on the west of the fault. The GNSS horizontal deformation at Jiuzhaigou county and Songpan county, which are of 40 km and 65 km away from the epicenter, are 14. 31 mm and 8. 22 mm, respectively. Slips are mainly distributed in 5 similar to 33 km along strike and 2 similar to 20 km along down-dip direction. The maximum and average displacements are 0. 91 m and 0. 18 m, respectively. The seismic rupture did not fully reach the ground surface. The fault plane is 40 km long and 30 km wide with strike angle 155 degrees, dip angle 81 degrees and rake angle -9. 56 degrees. These features are consistent with the kinematics and geometry of the northern section of the Huya fault, so we concluded that the northern section of the Huya fault is the seismogenic fault of the Jiuzhaigou earthquake. Results derived from geodetic measurements indicate the epicenter of this event is located at E103. 82 degrees, N33. 25 degrees with focal depth of 10. 86 km and the moment released about 7. 754 X 10(18 )Nm, corresponding to a magnitude of M-w 6. 5 which is consistent with that from USGS and GCMT. The coseismic Coulomb stress changes have enhanced the stress on the northeast and southwest of northward extension part of the Huya fault, but fewer aftershocks were recorded on this section, indicating that the seismic risk of the Mamo and Luocha segments of the Tazang fault is increasing.

Based on more than two years BDS/GPS data observed by seven stations,we used precise point positioning (PPP) model of the PANDA software developed by Wuhan University,analyzed the positioning accuracy of single system and discussed the ability of BDS in crustal motion monitoring.The results showed that the BDS positioning accuracy in the horizontal direction was about 17 mm and the vertical direction was about 40 mm.The GPS positioning accuracy in the horizontal direction was better than 10 mm and the vertical direction was about 14 mm.The results of baseline statistics showed that BDS had lower ability to detect weak signals than GPS system,but it was still able to accurately reflect the characteristics of baseline length and rate between two sites.Comparing the velocity fields obtained from BDS and GPS,the results showed that the difference of the two sets of velocity field in horizontal directions was 1～2 mm/a,and there was no systematic difference.Although BDS PPP accuracy was lower than GPS,but it could still be used to monitor the crustal motion of the large deformation area.

On 25 April 2015, a devastating (M(S)8.1) earthquake struck the central Nepal, causing severe damages in Kathmandu. The earthquake is believed to occur on a basal detachment fault along which the Indian plate plunged under Tibet, providing a rare opportunity to understand seismicity of the continental plate boundary. Strong ground motions and permanent surface displacements induced by this event were observed unprecedentedly by continuous GPS networks in Nepal and Tibet, and these geodetic observations close to the rupture zone are important as such when a finite fault model of rupture is constructed to characterize rupture processes and source properties. In this work, we focus on retrieving the slip distribution and temporal history of this earthquake through a joint inversion of teleseismic waveforms and near-field GPS data. We derived 12 static coseismic offsets of GPS sites in Nepal and Tibet and retrieved 5 seismograms of strong motions recorded by high-rate (1 Hz) GPS sites in Tibet. In addition, we chose a total of 43 P-wave waveforms from global seismic networks to enhance the spatiotemporal resolution of source model. The fault geometry is prescribed on a subsurface plane that is buried at 5 similar to 30 km depths with a dip of 11 degrees to the north and a strike of 295, consistent with the USGS CMT solution and structural geology. This rectangular model plane in dimensions of 210 km X 160 km was further divided into 21X8 matrix of sub-faults. The finite source modeling assumes that the rupture processes can be approximated by abrupt rise of slip on these subfaults in the wake of rupture front that passages successively through them from the hypocenter. The rupture velocity across adjacent subfauts is assumed to be a constant at 2. 5 km s(-1). For each subfault, the slip growth is represented by a source time function that is parameterized by 5 overlapping triangles with a 2 sec half-time duration, each shifted by 2 sec. Seismic moments of all triangles, each corresponding to a subevent, are unknown parameters to be solved with the non-negative least squares algorithm. The slip magnitude, rake and rise time for each subfault are derived from the estimates of the associated subevents, all together to minimize postfit residuals of the waveforms and static offsets while maintaining smoothness of seismic moment over the model plane for which a Laplace operator is used to achieve spatial regularization. Green' s functions were generated assuming a one-dimensional structure model. The frequency-wavenumber integration algorithm was used for GPS dynamic waveforms and static offsets, and a reflectivity method developed by Kikuchi for teleseismic data. The joint inversion shows that the detachment fault fails unilaterally from the hypocenter with slip extending eastward over an area of 100 km in along-strike length by 130 km in downdip width. The best-fitting model indicates that the seismic moments were released largely by thrusting motions within duration of 80 sec. In the first 40 sec, slip propagated essentially all the way to the Kathmandu. The slip model shows one major asperity between the hypocenter and Kathmandu, on which a peak slip of 4. 3 m is found at 11 km depth, 35 km away from the hypocenter. During 40 to 75 sec, the rupture extends downward to the bottom of the model plane and slip attains the local maximum at 18 km depth and 60 km away from the hypocenter. Slip of 0. 5 similar to 1. 0 m is found at 25 similar to 30 km depths beneath the Gyrong town. Slip continues also upward but stops approximately at 5 km shallow depth. The slip model does not indicate that the earthquake has broken the surface, suggesting that a significant fraction of the basal detachment fault remain locked at shallower depths. The unlocked part of the detachment fault has yielded an averaged slip of 2.4 m with a total seismic moment of 9. 4 X 10(20) N . m, which gives M-w =7. 9. If the asperity of this event corresponds to the ruptur e. zone of the 1833 M(w)7. 7 similar to 7. 8, its recurrence in the same rupture area would be every 150 similar to 200 year.

Possible ionospheric disturbances relating to the May 12, 2008, Ms8.0 Wenchuan earthquake were identified by Global Positioning System (GPS)-derived total electron content (TEC), ionosonde observations, the global ionospheric map (GIM), and electron density profiles detected by the Constellation Observation System for Meteorology Ionosphere and Climate (COSMIC). We applied a statistical test to detect anomalous TEC signals and found that a unique enhancement in TEC, recorded at 16 GPS stations, appeared on May 9, 2008. The critical frequency at F2 peak (f0F2), observed by the Chinese ionosondes, and maximal plasma frequency, derived from COSMIC data, revealed a characteristic similar to GPS TEC variations. The GIM showed that the anomalous variations of May 9 were located southeast of the epicenter. Using GPS data from 13 stations near the epicenter, we analyzed the TEC variations of satellite orbit traces during 04:00–11:00 UT. We found that TEC decreased to the east and increased to the southeast of the epicenter during this period. Results showed that the abnormal disturbance on May 9 was probably an ionospheric precursor of the Wenchuan earthquake of May 12, 2008.

The seven co-located sites of the Crustal Movement Observation Network of China (CMONOC) in Shanghai, Wuhan, Kunming, Beijing, Xi'an, Changchun, and Urumqi are equipped with Global Navigation Satellite System (GNSS), very long baseline interferometry (VLBI), and satellite laser ranging (SLR) equipment. Co-location surveying of these sites was performed in 2012 and the accuracies of the solved tie vectors are approximately 5 mm. This paper proposes a mathematical model that handles the least squares adjustment of the 3D control network and calculates the tie vectors in one step, using all the available constraints in the adjustment. Using the new mathematical model, local tie vectors can be more precisely determined and their covariance more reasonably estimated.

The relation between plate tectonics and earthquake evolution is analyzed systematically on the basis of 1998–2010 absolute and relative gravity data from the Crustal Movement Observation Network of China. Most earthquakes originated in the plate boundary or within the fault zone. Tectonic deformation was most intense and exhibited discontinuity within the tectonically active fault zone because of the differential movement; the stress accumulation produced an abrupt gravity change, which was further enhanced by the earthquake. The gravity data from mainland China since 2000 obviously reflected five major earthquakes (Ms > 7), all of which were better reflected than before 2000. Regional gravity anomalies and a gravity gradient change were observed in the area around the epicenter about 2 or 3 years before the earthquake occurred, suggesting that gravity change may be a seismic precursor. Furthermore, in this study, the medium-term predictions of the Ms7.3 Yutian, Ms8.0 Wenchuan, and Ms7.0 Lushan earthquakes are analytically presented and evaluated, especially to estimate location of earthquake.

Roads are the main ground traffic lifelines for earthquake relief.Road damage after earthquakes not only causes much economic loss,but also reduces the transport efficiency.It is very important significant to timely and accurate assess road damage.However,some objective and quantitative indicators about road route and network connectivity are rarely presented.Therefore,an assessment method of road connectivity effectiveness after earthquakes is developed based on indicator-network efficiency in the complex network theory.At first,indicators for measuring road route and network connectivity are established by the network efficiency indicator.Then in terms of road network connectivity before and after earthquakes,the Road Connectivity Damage Index(RCDI)is established to assess the damage.The experiment results show that this method can effectively measure and distinguish road route and network connectivity in different damage cases,and provide quantitative basis for the rescue decision-making.

Roads are the main parts of the ground traffic lifeline for emergency rescue and disaster relief. After huge earthquakes,it is very important to rapidly extract the road damage by remote sensing for disaster emergency rescue. With the remote sensing data sources gradually enriched,the software requirement for road damage rapid assessment and aided emergency decision support is more and more urgent. This paper proposed a software system for road damage rapid assessment and aided emergency decision support. Modules and information flow of the software were analyzed in detail. Key techniques such as road damage extraction,rapid assessment of road damage and transportation decision support were studied in detail. The performance of the software is verified by some experiments.

An approach is developed to directly solving the co-located tie vector by using two kinds of constraints between SLR and VLBI?s antenna rotation centers and surveying marks.The first constraint is that the mark forms a planar circle when it rotates along with its rotation axis, which can be modeled as the intersection of a plane and a sphere.The second constraint is that the rotation center lies in the same plumb line with the rotation center of vertical axis,and in the same plane with the rotation center of horizontal axis.The corresponding observation equations and condition equations are established according to the two kinds of constraints.The tie vector and its covariance matrix are directly resolved by using the observations of the mark points.The space differences baseline are solved based on the direct approach using measured data of two GNSS and SLR or VLBI co-location.The results show that the difference is not more than 1 mm compared with two step solutions.

The local tie vectors between different space geodesy instruments in colocated sites, such as the global navigation satellite system (GNSS), very long baseline interferometry (VLBI), and satellite laser ranging (SLR), are essential for combination with the international terrestrial reference frame (ITRF). This paper introduces the surveying method and data processing model for determining the tie vectors in the seven colocated sites in Shanghai, Wuhan, Kunming, Beijing, Xian, Changchun, and Urumqi, and presents the values and full variance-covariance of these local ties. The surveying methodology and data processing method of the current work are rigorously determined to guarantee the relative positional precision of reference points (RPs) of different instruments in each colocation site to be a few millimeters. This paper compares the new tie vectors with those derived from ITRF 2008 products to consider the discrepancies at tie epoch. By comparing the new results to the previous results by other organizations, the new tie vector at the Wuhan site is in good agreement, but the vertical coordinate difference of the tie vector at the Shanghai site is as large as 2.24 cm. Therefore, the tie vector at the Shanghai site may have changed about 2 cm from 2003 to 2011.

To realize the comprehensive utilization of different techniques for measuring crustal movement, a study on high precision site survey, the key to integrating the observation data from the stations of global navigation satellite systems (GNSS), very long baseline interferometry (VLBI) and satellite laser ranging (SLR), was conducted. The site survey of the VLBI station and the SLR station of the Crustal Movement Observation Network of China (CMONOC) for real time monitoring the globe’s lithosphere, water stratum and atmospheric lager was carried out for the first time, and the observation results were given, which are very important for the operation and maintenance of CMONOC.

Roads are traffic lifelines for emergency rescue and disaster relief. After major earthquakes, it is very significant to extract road damage rapidly and accurately in disaster areas by remote sensing for emergency rescue. Because road damage caused by earthquake is ever-changing,there is no common spectral characteristic of it in remote sensing images. Meanwhile, there are many phenomena of “synonyms spectrums” and “different spectrum characteristics with the same object” in remote sensing images. Thus, traditional methods by spectrum characteristics are usually with low accuracy and not universal. This paper proposes an automatic approach to extract road damage rapidly based on sidelines using high resolution satellites images and road maps. Road sideline is one of stable geometric features in both pre-earthquake and post-earthquake images, and the change of road sideline is a remarkable evidence of road damage exists. The approach firstly extracts sidelines of undamaged road from images acquired after earthquakes, and then these road sidelines are compared with the road lines before earthquakes supplied by road maps. The damaged segments can be extracted through comparison. The performance of the method is evaluated by an experiment with QuickBird images in the WenChuan earthquake disaster area.