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.

Study regarding typical liquefaction damage during the 2021 Maduo M_(s)7.4 earthquake in China

The most important method of understanding liquefaction-induced engineering failures comes from the investigation and analysis of earthquake damage.In May 2021,the Maduo M_(s)7.4 earthquake occurred on the Tibetan Plateau of China.The most representative engineering disaster caused by this earthquake was bridge damage on liquefied sites.In this study,the mutual relationships between the anti-liquefaction pre-design situation,the ground motion intensity,the site liquefaction severity,and the bridge damage state for this earthquake were systematically analyzed for typical bridge damage on the liquefied sites.Using field survey data and the current Chinese industry code,simulations of the liquefaction scenarios at typical bridge sites were performed for the pre-design seismic ground motion before the earthquake and the seismic ground motion during the earthquake.By combining these results with post-earthquake investigation results,the reason for the serious bridge damage resulting from this earthquake is revealed,and the necessary conditions for avoiding serious seismic damage to bridges built in liquefiable sites is presented.

Broadband ground motion simulation using a hybrid approach of the May 21, 2021 M7.4 earthquake in Maduo, Qinghai, China

In this study,the broadband ground motions of the 2021 M7.4 Maduo earthquake were simulated to overcome the scarcity of ground motion recordings and the low resolution of macroseismic intensity map in sparsely populated high-altitude regions.The simulation was conducted with a hybrid methodology,combining a stochastic high-frequency simulation with a low-frequency ground motion simulation,from the regional 1-D velocity structure model and the Wang WM et al.(2022)source rupture model,respectively.We found that the three-component waveforms simulated for specific stations matched the waveforms recorded at those stations,in terms of amplitude,duration,and frequency content.The validation results demonstrate the ability of the hybrid simulation method to reproduce the main characteristics of the observed ground motions for the 2021 Maduo earthquake over a broad frequency range.Our simulations suggest that the official map of macroseismic intensity tends to overestimate shaking by one intensity unit.Comparisons of simulations with empirical ground motion models indicate generally good consistency between the simulated and empirically predicted intensity measures.The high-frequency components of ground motions were found to be more prominent,while the low-frequency components were not,which is unexpected for large earthquakes.Our simulations provide valuable insight into the effects of source complexity on the level and variability of the resulting ground motions.The acceleration and velocity time histories and corresponding response spectra were provided for selected representative sites where no records were available.The simulated results have important implications for evaluating the performance of engineering structures in the epicentral regions of this earthquake and for estimating seismic hazards in the Tibetan regions where no strong ground motion records are available for large earthquakes.

Comparison of the earthquake detection abilities of PhaseNet and EQTransformer with the Yangbi and Maduo earthquakes

PhaseNet and EQTransformer are two state-of-the-art earthquake detection methods that have been increasingly applied worldwide.To evaluate the generaliz-ation ability of the two models and provide insights for the development of new models,this study took the sequences of the Yunnan Yangbi M6.4 earthquake and Qinghai Maduo M7.4 earthquake as examples to compare the earthquake detection effects of the two abovementioned models as well as their abilities to process dense seismic sequences.It has been demonstrated from the corresponding research that due to the differences in seismic waveforms found in different geographical regions,the picking performance is reduced when the two models are applied directly to the detection of the Yangbi and Maduo earthquakes.PhaseNet has a higher recall than EQTransformer,but the recall of both models is reduced by 13%-56%when compared with the results rep-orted in the original papers.The analysis results indicate that neural networks with deeper layers and complex structures may not necessarily enhance earthquake detection perfor-mance.In designing earthquake detection models,attention should be paid to not only the balance of depth,width,and architecture but also to the quality and quantity of the training datasets.In addition,noise datasets should be incorporated during training.According to the continuous waveforms detected 21 days before the Yangbi and Maduo earthquakes,the Yangbi earthquake exhibited foreshock,while the Maduo earthquake showed no foreshock activity,indicating that the two earthquakes’nucleation processes were different.

Coseismic deformation of the 2021 M_(W)7.4 Maduo earthquake from joint inversion of InSAR, GPS, and teleseismic data

The M_(W)7.4 Maduo earthquake occurred on 22 May 2021 at 02:04 CST with a large-expansion surface rupture.This earthquake was located in the Bayan Har block at the eastern Tibetan Plateau,where eight earthquakes of M_(S)>7.0 have occurred in the past 25 years.Here,we combined interferometric synthetic aperture radar,GPS,and teleseismic data to study the coseismic slip distribution,fault geometry,and dynamic source rupture process of the Maduo earthquake.We found that the overall coseismic deformation field of the Maduo earthquake is distributed in the NWW-SEE direction along 285°.There was slight bending at the western end and two branches at the eastern end.The maximum slip is located near the eastern bending area on the northern branch of the fault system.The rupture nucleated on the Jiangcuo fault and propagated approximately 160 km along-strike in both the NWW and SEE directions.The characteristic source rupture process of the Maduo earthquake is similar to that of the 2010 M_(W)6.8 Yushu earthquake,indicating that similar earthquakes with large-expansion surface ruptures and small shallow slip deficits can occur on both the internal fault and boundary fault of the Bayan Har block.

Correlation between the tilt anomaly on the vertical pendulum at the Songpan station and the 2021 MS7.4 Maduo earthquake in Qinghai province,China

Understanding the relationship between precursory deformation anomalies and strong earthquakes is vital for physical earthquake prediction. Six months before the 2021 MS7.4 Maduo earthquake in Qinghai province, China, the vertical pendulum at the Songpan station was observed to tilt southward with a high rate and large amplitude. Studies conducted before the 2021 MS7.4 Maduo earthquake inferred the tilt anomaly to be an earthquake precursor. However, after the earthquake, the relation between the earthquake and the anomaly became controversial, partly because the Songpan station is located at a great distance from the epicenter. In this study, based on the deformation anomaly characteristics, relationship between the seismogenic fault and the fault near the anomaly, and associated quantitative analyses, we concluded that this anomaly may be associated with the 2021 MS7.4 Maduo earthquake. The duration and amplitude of this anomaly matched with the magnitude and epicenter distance of the Maduo earthquake. We have also interpreted the reason why the anomaly occurred near a fault that is obliquely intersected with the seismogenic fault and why the anomaly is located far from the earthquake epicenter.

Prompt seismic data sharing for the 2021 Maduo earthquake in Qinghai province, China

An M_(S)7.4 earthquake struck west China in Maduo county,Guoluo prefecture,Qinghai province on May 22,2021,at 2:04 Beijing time(18:04 UTC on May 21,2021),which broke the quiet period of Chinese mainland for 1382 days without earthquakes of magnitude 7 or higher.The analysis of the seismic data sequence would play an important role in the in-depth study of the Maduo earthquake and the Bayan Har block.The Institute of Geophysics,China Earthquake Administration(CEA),compiled observation data recorded through 57 broadband seismometers within 500 km of the earthquake epicenter and intended to share for further researches in earthquake science community.The shared dataset included waveforms of the event and its sequence with magnitudes of 3.0 or higher that occurred between May 22-31,2021 with a sampling rate of 100 sps along with the continuous waveforms of 20 Hz and 100 Hz.Additionally,the seismic instrument response files also were shared.The event and continuous waveform records could be downloaded by submitting a request through the web platform of the Earthquake Science Data Center of the Institute of Geophysics,CEA(www.esdc.ac.cn).

Factor analysis to detect the causes of land degradation in Maduo County,northeastern Qinghai-Tibet Plateau

The area of desertified land has increased by 27.3% from 1987 to 2000 in Maduo County,northeastern Qinghai-Tibet Plateau.Driving forces of land degradation has been extensively studied in the region.Using Factor Analysis (FA),we evaluate contribution of human activity and natural environmental change to land degradation.Four common factors were extracted in this study.The result shows that climate related other than human-related factors,are the major inducing factors of land degradation in Maduo County.Climate change and consequent change of permafrost account for 70% to the land degradation.Increasing evaporation and declining precipitation in the beginning of the growing season hamper seedling establishment.Decreasing frozen days and rising active layer lower bound make surface soil loose and less soil moisture available for plant.

玛多7.4级地震野马滩大桥桥台纵桥向破坏机理分析

针对2021年青海玛多7.4级地震中野马滩大桥的桥台震害,开展基于Pushover分析的桥台纵桥向破坏机理研究。提出土-桩-桥台精细化有限元模拟方法,以及基于地勘资料的模型土体参数确定实用方法,建模方法和加载模式要点为:(1)适用于土-桥台相互作用的分布式p-y弹簧修正模型;(2)可识别背墙弯曲、剪切或弯-剪多种破坏模式的背墙非线性梁柱单元-墙底非线性剪切单元串联模型;(3)土-搭板和土-翼墙摩擦弹簧;(4)基于分布式间隙单元的可捕捉地震中主梁与背墙接触位置变化的Pushover加载模式,从而实现了桥台纵桥向地震损伤破坏全过程模拟。结果表明:野马滩桥台在水平地震作用下,背墙底截面先发生屈服,随后背墙剪力达到抗剪能力峰值,桥台整体水平承载力开始退化,直至背墙底完全剪断,而桩基础并不发生明显损伤。总体而言,桥台破坏模式为背墙弯-剪破坏,数值分析结果与桥台实际震害相符。

天津典型观测井渗透性变化及对玛多7.4级地震响应机理分析

采用微水试验和固体潮汐反演两种方法计算了王3井、宝坻新井、宁河井不同时期渗透系数,经对比分析发现,两种方法计算含水层渗透系数所得结果在总体量级上是相当的,并且变化趋势是一致的,发育稳定、连续性较好的含水层中的观测井,二者计算结果更加接近。微水试验估算的井含水层渗透系数主要反映了井孔周围局部含水层渗透能力在短时间内水流过程中的渗透性特征,而固体潮汐反演估算的渗透系数则反映了在较长时间内较大范围含水层的平均渗透能力。因而,在观测井同震响应分析、抽(注)水干扰等异常核实分析中,使用微水试验估算的井含水层渗透系数更为合理,而在分析区域应力场变化中使用固体潮汐反演估算的渗透系数则更合理。本文分析了三口观测井水位和渗透性变化特征以及产生原因,并进一步分析了王3井和宝坻新井水位对2021年5月22日青海玛多7.4级地震同震响应机理,以及玛多地震对宁河井水位观测的影响机制,发现应力积累、抽/注水干扰、地震波传播等因素均会对含水介质渗透性造成影响。并且,地震波传播过程对不同含水介质造成的影响不同,而含水层岩性相同的不同观测井对同一地震的响应特征和机理也不相同。

基于地磁场重复观测资料分析玛多M_(W)7.3地震前地磁场变化

基于玛多地震周边的地磁场重复观测资料,使用泰勒多项式空间参考场方法和自然正交分量方法分别对观测资料进行日变通化和长期变化改正,获得了玛多地震前后地磁场变化特征。通过对观测和数据处理的分析,获得了各期计算结果的误差,并基于误差对地磁场变化进行了部分修正。结果表明,玛多地震1~2年岩石圈磁场年变化会出现明显的趋势转折,变化量为5~10nT。根据速度—状态依赖的摩擦定律的地震周期分析发现,震前断层滑动量较小,因此岩石圈磁场年变化并非由地震前断层滑动引起的应力扰动产生。玛多地震前地下流体的变化产生的电磁效应更可能是产生岩石圈磁场变化的原因。

三江源国家公园土壤保持实物量计算——基于CSLE模型

土壤保持能力是生态产品价值中可调节产品的重要组成部分,在土壤侵蚀控制及生态环境改善方面具有关键作用。自我国开展国家公园体制以来,其对于三江源地区的土壤侵蚀模数及土壤保持能力的影响尚不明确。对比CSLE与USLE模型及其因子的差异,选取CSLE进行2000年与2020年的土壤侵蚀模数对比研究并计算黄河源区玛多县20年间土壤保持总量。结果表明:1)在研究区中,CSLE模型在区分不同土壤侵蚀模数强度时显著优于USLE模型,其对坡度坡长因子以及生物措施因子的优化计算方法可更精确地评估土壤侵蚀模数。2)从2000年至2020年,玛多县的土壤侵蚀强度得到了较大地改善,约有75%左右区域的土壤侵蚀模数具有明显下降,但仍有小部分区域的土壤侵蚀模数上升,其土壤侵蚀强度加剧。3)玛多县20年间土壤保持总量为1.683×10~6 t,在核算生态产品价值中的土壤保持量时,应以75%的土壤侵蚀模数减少的区域进行计算,而并非采用默认全区土壤均得到了有效保持的USLE公式进行计算。

采用2021年青海玛多地震序列震源机制节面聚类确定发震断裂几何形态

地震断裂带形状是活动构造和地球动力学的重要资料。2021年发生的玛多地震序列提供了丰富的震源机制资料,为统计震源机制节面并估计玛多地震发震断层面形状提供了很好机会。文章对地震的震源机制资料进行基于密度的聚类来确定断层的几何形态。首先对收集到的玛多地震序列的震源机制解进行中心解求解,从而获得更为精准的数据,然后对其进行DBSCAN方法的聚类分析,得到断层的走向为113.5°,倾角为88.2°,通过震源机制反演应力场,并将应力场投影到断层上,得到断裂带的相对剪应力和相对正应力分别为0.84和-0.79,剪应力强度较大,滑动角为-0.72°。结果表明玛多地震是发震断裂受NE-SW的挤压和NW-SE的拉张,形成了较大的剪切力,从而促使近东西的江错断裂发生左旋走滑错动所致。

2021年青海玛多M_(W)7.4地震震后余滑研究

构建应力驱动震后余滑模型,对2021年青海玛多M_(W)7.4地震的震后余滑效应进行数值模拟,得到震后160 d的GPS形变时间序列。结果表明,余滑主要分布在同震断层显著滑动的下倾和两侧区域,最大滑动量达1.24 m,累积释放地震矩1.08×10^(19)Nm,相当于M_(W)6.62地震,5~15 km深度的震后余滑约占总量的80%。最优拟合模型显示,以13 km深度为界,断层上部和下部的参考滑动速率参数V0分别为6.50 m/a和0.15 m/a,表明玛多地震震后余滑界面的摩擦属性在深度上存在明显差异。

基于光学卫星影像的同震形变提取技术及形变梯度的地学意义

介绍光学同震形变提取的关键技术、优化流程和主流软件包的差异性,并基于光学同震形变场推导具有地学意义的位移梯度、旋度、膨胀量、剪切应变等算子;以2021年青海玛多M W7.4地震为例,检验基于Sentinel-2光学影像的同震形变场提取优化流程以及算子的地学意义。结果表明,对亚像素相关性匹配结果的后处理可有效消除轨道误差、条带误差、场地和传感器因素导致的白噪声和加性噪声,突出形变细节,更加客观地描述同震形变的空间分布特征。

玛多M_(S)7.4地震前地电阻率变化

分别运用原始曲线分析法和归一化速率法分析2021-05-22玛多M_(S)7.4地震震中400 km范围内4个地电阻率台站的数据变化。结果表明:1)玛多地震前,4个地电阻率台站资料出现不同程度的异常变化,其中玛曲NW、金银滩EW、甘孜N10°E、拦隆口EW测道原始曲线变幅最明显,表现为小时值突跳变化、日均值加速变化和曲线转折变化、月均值破年变和保留年变形态的趋势变化;2)玛曲NW、金银滩EW、甘孜N10°E、拦隆口EW归一化速率曲线在玛多地震前均出现超阈值现象,但各自归一化速率形态不同;3)综合分析认为,4个台站地电阻率资料异常变化与玛多M_(S)7.4地震的孕育及活动有关。

强震大尺度有序图像预测法及其应用研究

在系统总结汶川8.0级、玉树7.1级等地震前大尺度有序图像演化过程的基础上,系统研究1952年以来青藏块体大尺度有序图像的特征及其与区域7级地震或地震组的关系,得出大尺度有序图像是一种具有动力学含义的地震活动图像,在青藏块体7级地震或地震组前普遍存在,对7级地震或地震组以及5级以上地震活动主体地区的判定具有中期预测意义,可进一步总结并提炼强震大尺度有序图像预测法。以2021年青海玛多7.4级地震前青藏块体5级以上地震大尺度有序图像的演化过程为例,检验和验证上述结论及大尺度有序图像预测法的有效性。

基于系统动力学的草地生态系统稳定性评价——以三江源国家公园黄河源玛多县为例

本文以三江源国家公园黄河源园区所在的玛多县为研究对象,从韧性、抵抗性、可持续性和变异性角度构建生态系统稳定性评价指标,辨析指标间的异同并提出合理的指标量化与分级标准;在此基础上,基于系统动力学方法建立了玛多县生态系统动态仿真模型;进一步,利用所构建的动态仿真模型,对玛多县2000~2100年的生态系统演化历程生态状况演化趋势进行模拟仿真;最后,基于模拟结果对其生态系统稳定性进行评估.评估结果表明:玛多县生态系统特征回归时间约为48.74a,韧性一般;生态系统崩溃时的食草强度与现状条件的食草强度之比为4.15,抵抗性较强;初始状态持续时间约为79.04a且朝着正向发展,可持续性较强;变异比率约为25.20%,变异性较大.玛多县生态系统稳定性综合评价结果为临界状态,需要从提高生态系统韧性和降低生态系统变异性的角度改善玛多县生态系统稳定性,确保其生态系统持续健康演替.

Aftershock sequence relocation of the 2021 M_(S)7.4 Maduo Earthquake, Qinghai, China

The 2021 Qinghai Maduo M_(S)7.4 earthquake was one of the strongest earthquakes that occurred in the Bayan Har block of the Tibetan Plateau during the past 30 years,which spatially filled in the gap of strong earthquake in the eastern section of the northern block boundary.In this study,the aftershock sequence within 8 days after the mainshock was relocated by double difference algorithm.The results show that the total length of the aftershock zone is approximately 170 km;the mainshock epicenter is located in the center of the aftershock zone,indicating a bilateral rupture.The aftershocks are mainly distributed along NWW direction with an overall strike of 285°.The focal depth profiles indicate that the seismogenic fault is nearly vertical and dips to southwest or northeast in different sections,indicating a complex geometry.There is an aftershock gap located to the southeast of the mainshock epicenter with a scale of approximately 20 km.At the eastern end of the aftershock zone,horsetaillike branch faults show the terminal effect of a large strike-slip fault.There is a NW-trending aftershock zone on the north side of the western section,which may be a branch fault triggered by the mainshock.The location of the aftershock sequence is close to the eastern section of the Kunlun Mountain Pass-Jiangcuo(KMPJ)fault.The sequence overlaps well with surface trace of the KMPJ fault.We speculate that the KMPJ fault is the main seismogenic fault of the M_(S)7.4 Maduo earthquake.

Slip rate of the seismogenic fault of the 2021 Maduo earthquake in western China inferred from GPS observations

Seismic and field observations indicate that the Mw7.4 Maduo earthquake ruptured the Jiangcuo fault,which is a secondary fault~85 km south of the northern boundary of the Bayan Hor block in western China.The kinematic characteristics of the Jiangcuo fault can shed lights on the seismogenic mechanism of this earthquake.Slip rate is one of the key parameters to describe the kinematic features of a fault,which can also provide quantitative evidences for regional seismic hazard assessments.However,due to lack of effective observations,the slip rate of the Jiangcuo fault has not been studied quantitatively.In this study,we consider the interaction between the Jiangcuo fault and the eastern Kunlun fault,and estimate the slip rates of the two faults using the interseismic GPS observations across the seismogenic region.The inferred results show that the slip rates of the Jiangcuo fault and the Tuosuo Lake segment of the Kunlun fault are 1.2±0.8 and 5.4±0.3 mm a^(-1),respectively.Combining the slip rate with the average slip inferred from the coseismic slip model,the earthquake recurrence interval of the Jiangcuo fault is estimated to be 1800700+3700 years(1100–5500 years).Based on the results derived from previous studies,as well as calculations in this study,we infer that the slip rate of the Kunlun fault may decrease gradually from the Tuosuo Lake segment to the eastern tip.The Jiangcuo fault and its adjacent parallel secondary faults may have absorbed the relative motion of blocks together with the Kunlun fault.