Kinematic deformation and intensity assessment of the 2021 Maduo M_(S)7.4 earthquake in Qinghai revealed by high-frequency GNSS

Rapid acquisition of the kinematic deformation field and seismic intensity distribution of large earthquakes is crucial for postseismic emergency rescue,disaster assessment,and future seismic risk research.The advancement of GNSS observation and data processing makes it play an important role in this field,especially the high-frequency GNSS.We used the differential positioning method to calculate the 1 HZ GNSS data from 98 sites within 1000 km of the M_(S)7.4 Maduo earthquake epicenter.The kinematic deformation field and the distribution of the seismic intensity by using the peak ground velocity derived from displacement waveforms were obtained.The results show that:1)Horizontal coseismic response deformation levels ranging from 25 mm to 301 mm can be observed within a 1000 km radius from the epicenter.Coseismic response deformation on the east and west sides shows bilateral asymmetry,which markedly differs from the symmetry presented by surface rupture.2)The seismic intensity obtained through high-frequency GNSS and field investigations exhibits good consistency of the scope and orientation in the high seismic intensity area,although the former is generally slightly smaller than the latter.3)There may exist obstacles on the eastern side of the seismogenic fault.The Maduo earthquake induced a certain tectonic stress loading effect on the western Kunlun Pass-Jiangcuo fault(KPJF)and Maqin-Maqu segment,resulting in higher seismic risk in the future.

Upper crustal deformation characteristics in the northeastern Tibetan Plateau and its adjacent areas revealed by GNSS and anisotropy data

The northeastern part of the Tibetan Plateau is a region where different tectonic blocks collide and intersect,and large earthquakes are frequent.Global Navigation Satellite System(GNSS)observations show that tectonic deformation in this region is strong and manifests as non-uniform deformation associated with tectonic features.S-wave splitting studies of near-field seismic data show that seismic anisotropy parameters can also reveal the upper crustal medium deformation beneath the reporting station.In this paper,we summarize the surface deformation from GNSS observations and crustal deformation from seismic anisotropy data in the northeastern Tibetan Plateau.By comparing the principal compressive strain direction with the fast S-wave polarization direction of near-field S-wave splitting,we analyzed deformation and its differences in surface and upper crustal media in the northeastern Tibetan Plateau and adjacent areas.The principal compressive strain direction derived from GNSS is generally consistent with the polarization direction of fast S-waves,but there are also local tectonic regions with large differences between them,which reflect the different deformation mechanisms of regional upper crustal media.The combination of GNSS and seismic anisotropy data can reveal the depth variation characteristics of crustal deformation and deepen understanding of three-dimensional crustal deformation and the deep dynamical mechanisms underlying it.it.

On the physical model of earthquake precursor fields and the mechanism of precursors＇timespace distribution（Ⅲ）──anomalies of seismicity and crustal deformation and their mechanisms when a strong earthquake is in prep

By studying the seismicity pattern before 37 earthquakes with M≥6. 0 in North China and the pattern of crustal deformation in the Capital Area from 1954 to 1992, some abnormal characteristics of these patterns before strong earthquakes have been extracted. A comparison has been made between the anomalies of these two kinds of Patterns. From the results we can know the following. ① Before a strong earthquake, the seismicity will strengthen and the crustal deformation rate will increase. ② Several years before a strong earthquake, there will be seismic gaps and deformation gaps around the epicenter of the quake. ③ The dynamic parameters of patterns all show a decrease in information dimension. This means that the crustal deformation has become more and more localized with time and it gives an important indication showing that a strong earthquake is in preparation. At the end of the paper, the physical mechanisms of the abnormal patterns of seismicity and crustal deformationhave been explained in a unified way in terms of the earthquake-generating model of a inhomogeneous strongbody in inhmogeneous media.

RESEARCH ON THE DEFORMATIONS IN QINGHAI_TIBET PLATEAU AND ITS MARGINS BY INVERTING SEISMIC MOMENT TENSORS AND GPS VELOCITIES

We have determined approximate average rates of deformation in the Qinghai_Tibet plateau and its margins from the GPS data for last 10 years and the moment tensors from earthquakes between 1900 and 1999.We also determined the strain rate (seismic strain rate) associated with the seismic deformation using 254 M w ≥5.0 earthquakes,and estimated the shortening and extension rates for every block in the area as well.We also estimated the strain rate (geodetic strain rate)by 80 GPS sites’ velocity vectors and analyzed characteristic of kinematics by two kinds of strain rates and discussed earthquake potential in the area.As a result,the deformation rates from seismic moment tensors and from GPS velocities are basically agreed with each other.It is feasible to analyze seismic risk by comparing geodetic strain rate with seismic strain rate based on the opinion that strain energy will be released through earthquake.It is concluded that there is no strong earthquake potential (>M7) in the Qinghai_Tibet plateau and its margins,but there is earthquake potential (>M5) in middle Tibet in a few years.

Influence factors on the seismic behavior and deformation modes of gravity retaining walls

This study investigated the influence factors on the seismic response and deformation modes of retaining walls using large-scale model shaking table tests. Experimental results showed that the distribution of peak seismic earth pressures along the height of a wall was a single peak value curve. The seismic earth pressures on a gravel soil retaining wall were larger than the pressures on the weathered granite and quartz retaining walls. Also, the peak seismic earth pressure increased with increases in the peak ground acceleration and the wall height. The measured seismic active earth pressures on a rock foundation retaining wall were larger than the calculated values, and the action position of resultant seismic pressure was higher than 0.33 H. In the soil foundation retaining wall, the measured seismic earth pressures were much smaller than the calculated values, while the action position was slightly higher than 0.33 H. The soil foundation retaining wall suffered base sliding and overturning under earthquake conditions, while overturning was the main failure mode for the rock foundation retaining walls.

Resolving co- and early post-seismic slip variations of the 2021 MW 7.4 Madoi earthquake in east Bayan Har block with a block-wide distributed deformation mode from satellite synthetic aperture radar data

On 21 May 2021(UTC),an MW 7.4 earthquake jolted the east Bayan Har block in the Tibetan Plateau.The earthquake received widespread attention as it is the largest event in the Tibetan Plateau and its surroundings since the 2008 Wenchuan earthquake,and especially in proximity to the seismic gaps on the east Kunlun fault.Here we use satellite interferometric synthetic aperture radar data and subpixel offset observations along the range directions to characterize the coseismic deformation of the earthquake.Range offset displacements depict clear surface ruptures with a total length of~170 km involving two possible activated fault segments in the earthquake.Coseismic modeling results indicate that the earthquake was dominated by left-lateral strike-slip motions of up to 7 m within the top 12 km of the crust.The well-resolved slip variations are characterized by five major slip patches along strike and 64%of shallow slip deficit,suggesting a young seismogenic structure.Spatial-temporal changes of the postseismic deformation are mapped from early 6-day and 24-day InSAR observations,and are well explained by time-dependent afterslip models.Analysis of Global Navigation Satellite System(GNSS)velocity profiles and strain rates suggests that the eastward extrusion of plateau is diffusely distributed across the east Bayan Har block,but exhibits significant lateral heterogeneities,as evidenced by magnetotelluric observations.The block-wide distributed deformation of the east Bayan Har block along with the significant co-and post-seismic stress loadings from the Madoi earthquake imply high seismic risks along regional faults,especially the Tuosuo Lake and Maqên-Maqu segments of the Kunlun fault that are known as seismic gaps.

Influence of random heterogeneity of shear wave velocity on sliding mass response and seismic deformations of earth slopes

Soil shear wave velocity has been recognized as a governing parameter in the assessment of the seismic response of slopes.The spatial variability of soil shear wave velocity can influence the seismic response of sliding mass and seismic displacements.However,most analyses of sliding mass response have been carried out by deterministic models.This paper stochastically investigates the effect of random heterogeneity of shear wave velocity of soil on the dynamic response of sliding mass using the correlation matrix decomposition method and Monte Carlo simulation(MCS).The software FLAC 7.0 along with a Matlab code has been utilized for this purpose.The influence of statistical parameters on the seismic response of sliding mass and seismic displacements in earth slopes with different inclinations and stiffnesses subject to various earthquake shakings was investigated.The results indicated that,in general,the random heterogeneity of soil shear modulus can have a notable impact on the sliding mass response and that neglecting this phenomenon could lead to underestimation of sliding deformations.

Longitudinal integral response deformation method for the seismic analysis of a tunnel structure

For the longitudinal seismic response analysis of a tunnel structure under asynchronous earthquake excitations,a longitudinal integral response deformation method classified as a practical approach is proposed in this paper.The determinations of the structural critical moments when maximal deformations and internal forces in the longitudinal direction occur are deduced as well.When applying the proposed method,the static analysis of the free-field computation model subjected to the least favorable free-field deformation at the tunnel buried depth is performed first to calculate the equivalent input seismic loads.Then,the equivalent input seismic loads are imposed on the integral tunnel-foundation computation model to conduct the static calculation.Afterwards,the critical longitudinal seismic responses of the tunnel are obtained.The applicability of the new method is verified by comparing the seismic responses of a shield tunnel structure in Beijing,determined by the proposed procedure and by a dynamic time-history analysis under a series of obliquely incident out-of-plane and in-plane waves.The results show that the proposed method has a clear concept with high accuracy and simple progress.Meanwhile,this method provides a feasible way to determine the critical moments of the longitudinal seismic responses of a tunnel structure.Therefore,the proposed method can be effectively applied to analyze the seismic response of a long-line underground structure subjected to non-uniform excitations.

Structural Deformation of Zoigê Basin Along the Deep Seismic Reflection Profile

Being the core of the Songpan-Ganze block,Zoig(?) Basin is a favorable zone of oil and gas exploration. And it not only is the important deposition area of the northern Songpan-Garze in the Middle-Late Triassic, but also impacts on the formation and evolution of the structural belt.To further understand the Zoig(?) Basin, we reprocessed the 0-20.0 s data of the Tangke-Hezuo deep seismic reflection profiles across the majority

Numerical simulation of influences of the earth medium's lateral heterogeneity on co- and post-seismic deformation

Many studies revealed that the Earth medium＇s lateral heterogeneity can cause considerable effects on the co- and post-seismic deformation field. In this study, the threedimensional finite element numerical method are adopted to quantify the effects of lateral heterogeneity caused by material parameters and fault dip angle on the co- and postseismic deformation in the near- and far-field. Our results show that： 1） the medium＇s lateral heterogeneity does affect the co-seismic deformation, with the effects increasing with the medium＇s lateral heterogeneity caused by material parameters; 2） the Lame parameters play a more dominant role than density in the effects caused by lateral heterogeneity; 3） when a fault＇s dip angle is smaller than 90, the effects of the medium＇s lateral heterogeneity on the hanging wall are greater than on the footwall; 4） the impact of lateral heterogeneity caused by the viscosity coefficient on the post-seismic deformation can affect a large area, including the near- and far-field.

Multi-scale Decomposition of Co-seismic Deformation from High Resolution DEMs:a Case Study of the 2004 Mid-Niigata Earthquake

Decomposing co-seismic deformation is an immediate need for researchers who are interested in earthquake inversion analysis and geo-hazard mapping. However, conventional InSAR or digital elevation models （DEMs） imagery analyses only provide the displacement in the Line-of-Sight （LOS） direction or elevation changes. The 2004 Mid-Niigata earthquake in Japan provides lessons on how to decompose co-seismic deformation from two sets of DEMs. If three adjacent points undergo a rigid-body-translation movement, their co-seismic deformation can be decomposed by solving simultaneous equations. Although this method has been successfully used to discuss tectonic deformations, the algorithm needed improvement and a more rigorous algorithm, including a new definition of nominal plane, DEMs comparability improvement and matrix condition check is provided. Even with these procedures, the obtained decomposed displacement often showed remarkable scatter prompting the use of the moving average method, which was used to determine both tectonic and localized displacement characteristics. A cut-off window and a pair of band-pass windows were selected according to the regional geology and construction activities to ease the tectonic and localized displacement calculations, respectively. The displacement field of the tectonic scale shows two major clusters of large lateral components, and coincidently major visible landslides were found mostly within them. The localized displacement helps to reveal hidden landslides in the target area. As far as the Kizawa hamlet is concerned, the obtained vectors show down-slope movements, which are consistent with the observed traces of dislocations that were found in the Kizawa tunnel and irrigation wells. The method proposed has great potential to be applied to understanding post-earthquake rehabilitation in other areas.

Prediction Method of Seismic Residual Deformation of Caisson Quay Wall in Liquefied Foundation

The multi-spring shear mechanism plastic model in this paper is defined in strain space to simulate pore pressure generation and development in sands under cyclic loading and undrained conditions, and the rotation of principal stresses can also be simulated by the model with cyclic behavior of anisotropic consolidated sands. Seismic residual deformations of typical caisson quay walls under different engineering situations are analyzed in detail by the plastic model, and then an index of liquefaction extent is applied to describe the regularity of seismic residual deformation of caisson quay wall top under different engineering situations. Some correlated prediction formulas are derived from the results of regression analysis between seismic residual deformation of quay wall top and extent of liquefaction in the relative safety backfill sand site. Finally, the rationality and the reliability of the prediction methods are validated by test results of a 120 g-centrifuge shaking table, and the comparisons show that some reliable seismic residual deformation of caisson quay can be predicted by appropriate prediction formulas and appropriate index of liquefaction extent.

Analyses of Crustal Deformation, Strain Field and Risk of Moderate and Strong Earthquakes in the Shanxi Seismic Belt

Using the four phases (1996～1999) of re-surveying data from the GPS network along the Shanxi fault zone, the recent state of horizontal movement of the fault zone and its relation with the Datong-Yanggao M5.6 earthquake (November 1, 1999), which took place on the north end of the monitored area, are analyzed. In the focal region, three areas with relatively higher strain (1×10 -6) appeared in Xinzhou and to the northeast of Jiexiu. The Shanxi fault zone is mainly controlled by the WNW-ESE-trending compressive stress field and the NNE-SSW-trending tensile stress field, and it does not have strike-slip movement. When examined for long-term tendency, attention should be paid to the junctures between the three moving elements.

Simulation by Dislocation Model and Anomaly Property Determination of Huge Leveling Deformation at Linfen Seismic Station

In this study,under the assumption that the two huge leveling deformation anomalies at Linfen seismic station were caused by the Luoyunshan fault( Tumen-Yuli section)movement, we computed the vertical deformation field distribution based on the rectangular fault dislocation model and measured the ground deformation field of the study area using D-InS AR technology. The results are as follows:( 1) Theoretically,the ground vertical deformation field caused by fault movement could be within the elliptical deformation area with the long axis parallel to the fault strike. The largest deformation region is located in the center of the area in the hanging wall of the fault,and the deformation gradually decreases to zero toward the periphery; the impact range induced by the two deformations is respectively as follows: The long axes are about 18 km and26km,the short axes are about 12 km and 17 km and the obvious deformation amplitude is about 1- 3mm and 4- 14 mm.( 2) The measured deformation field by D-InS AR shows that there is no continuous deformation area consistent with the fault strike,and only the presence of land subsidence possibly caused by groundwater excessive exploitation,with the deformation amplitude about 10- 12 mm and 1- 5mm.( 3) The measured deformation field is not consistent with the theoretical result on deformation area and amplitude,which indicates that the fault movement is not the main cause of Linfen huge leveling deformation,but may rather be because of local deformation of the soil layers in the hanging wall of the fault.( 4) By combining the fault dislocation model simulation with the D-InS AR technology measurement,we can determine effectively the nature of the anomalyof the huge cross-fault leveling deformation,thus provide scientific basis for verification of significant leveling anomalies.

Analysis of the b-value and Seismic Deformation in the North of China

The accuracy of b-value is limited by the uncertainty of the magnitude.In order to improvethe accuracy of the b-value,a statistic methodology was used to estimate the number of eventsbased on that there are several magnitude values for one historical event by several methods toestimate the magnitude.The b-value and seismic strain rates were calculated for the threeregions in the North of China.The method proved to be valid for all the regions,especiallyfor the data with large fluctuation.In order to study the stress state,the strain rate tensorand the principal axes of tension and compression were calculated for each of three regions bythe data of the focal mechanism,finally the stress state in each region was discussed.

The Characteristics of Recent Geodetic Deformation and Seismicity in North-South Seismic Zone and East of the Qinghai-Xizang Block

In this paper,the corresponding relation of the evolutionary characteristics of geodetic deformation fields with seismic activity for more than 20 years in the North-South seismic zone and East of Qinghai-Xizang Mess has been investigated.Not only is geodetic deformation in non-homogeneity for the space-time distribution but also deformation fields are in macroscopic similarity for the identical time interval.The inherited tectonic movement is a total tendency of recent crustal movement,and the motion mode is in undulations.There are stages of accumulation and release-adjusting of strain energy in crustal movement processes,which may be the dynamic mechanism of relatively quiet and active seismicity.The analysis of the crustal movement tendency since 1991 is of some significance for judging the stress state and the large seismic situation in the area.

Post-seismic relaxation process and vertical deformation following the 2008 Ms8.0 Wenchuan earthquake, China

The post-seismic horizontal and vertical deformations following the 2008 Ms8.0 Wenchuan earth- quake are inferred from GPS and precise leveling data. The post-seismic relaxation process is measured using GPS data from campaign stations located around the Longmenshan fault, and the derived decay time constant is 12 days. The evolution of the post-seismic vertical deformation is obtained from precise leveling data measured near the surface rupture. The results demonstrate that the hanging wall is uplifting and the foot wall is subsi- ding. The amplitude of the post-seismic deformation is lower than that of the co-seismic deformation. The re- gion with the largest post-seismic displacement is located on the leveling route between Maoxian and Beichuan on the hanging wall.

The North-South Seismic Belt： Vertical Deformation Velocity Gradient Research

The vertical deformation gradient can reflect the rate of vertical change in unit distance,and the vertical deformation velocity gradient can reflect the strength of the earth's crust tectonic activities. In this paper,using long period leveling data combined with GPS data,the vertical deformation gradient values are calculated. Leveling data and GPS data are two different means of monitoring deformation,but the result is approximately the same vertical deformation gradient. The results show that the spatial distribution of the vertical deformation velocity gradient and tectonic distribution has an obvious correlation. The most significant gradient anomalies along the North-South Seismic Belt are Xianshuihe fault, Longmenshan fault and Xiaojiang-Zemuhe fault, while the second gradient anomalies in the northeastern Qinghai-Tibetan plateau are Zhuanglanghe fault and Lenglongling fault. The Menyuan M_S6. 4 earthquake in 2016 occurred in this abnormal area. However,according to the vertical deformation high gradient area distribution,there is also the possibility of an earthquake occurrence in the Tianzhu and Jingtai area.The area of convergence of three major fault zones is the strongest tectonically active region of the North-South Seismic Belt.

A Preliminary Investigation of the Application of Modern Crustal Deformation Data in SeismicZonation

Using GPS observation data for the middle segment of the Fenwei seismic zone during the time period of 1996～2001, the velocity field of crustal movement is calculated. Thus, the vectors of relative horizontal movement between measuring points in the region are also obtained. Adopting a deformation model of homogeneous elastic body, the principal strain rate parameters of deformation units are calculated. A method is introduced to calculate the rate of seismic moment accumulation due to crustal deformation. The problems of using this rate to analyze the tendency of seismicity in the zone, and to estimate the recurrence interval of large earthquakes in the potential seismic source areas(PSSA) are discussed. The results show that the rate of seismic moment accumulation in the middle segment of the Fenwei zone is 4.22×10 17 Nm/a, which is much higher than the average release rate of seismic moment in the current activity period. This means that the belt is now in a stage of seismic strain accumulation and that the seismicity would become stronger in the future than now. The results of estimation of the recurrence interval of large earthquakes in the Dingxiang and Huozhou PSSA are close to the results obtained from studying active faults. This implies that the use of the proposed estimation method is worthy of further investigation. In particular, it is of greater practical significance for those regions that have shorter history of earthquake records or lower degree of active structure study.

Co-seismic changes of Wenchuan Ms8.0 earthquake and six aftershocks recorded by four deformation instruments at Xuzhou seismostation

Co-seismic changes of Wenchuan Ms8.0 earthquake and six strong aftershocks were recorded by 4 digital deformation instruments at Xuzhou seismostation at an cpicentral distance of 1392 km. The result shows that the straln-step changes and wave motions are caused by the arrival of the corresponding surface waves. The shape and size of the step changes and the response time were different for different instruments, even they were located in the same rock body only 7.65 m to 10.57 m apart. This difference is probably a reflection of different instrument properties, such as sensitivity and frequency response. The earthquake-caused stress changes, which were mainly compression in Xuzhou, had an important triggering effect on far-field strain changes