Crustal velocity structures beneath North China revealed by ambient noise tomography

We collected continuous noise waveform data from January 2007 to February 2008 recorded by 190 broadband and 10 very broadband stations of the North China Seismic Array. The study region is divided into grid with interval 0.25°×0.25°, and group velocity distribution maps between 4 s and 30 s are obtained using ambient noise tomography method. The lateral resolution is estimated to be 20-50 km for most of the study area. We construct a 3-D S wave velocity model by inverting the pure path dispersion curve at each grid using a genetic algorithm with smoothing constraint. The crustal structure observed in the model includes sedimentary basins such as North China basin, Yanqing-Huailai basin and Datong basin. A well-defined low velocity zone is observed in the Beijing-Tianjin-Tangshan region in 22-30 km depth range, which may be related to the upwelling of hot mantle material. The high velocity zone near Datong, Shuozhou and Qingshuihe within the depth range of 1-23 km reveals stable characteristics of Ordos block. The Taihangshan front fault extends to 12 km depth at least.

Crustal thickness in southeast Tibet based on the SWChinaCVM-1.0 model

Extensive geophysical research has been carried out in southeast Tibet due to the complex geological structure and high seismicity.The study of the Moho interface can provide useful information for the geophysical research.SWChinaCVM-1.0 is the first version of a regional community velocity model for the Sichuan-Yunnan region and aims to provide a reference for seismological research in the region.Based on this model,a high-precision community Moho interface model can be obtained using common conversion point(CCP)stacking,to further expand the applicability of SWChinaCVM-1.0.Before CCP stacking,it is necessary to check the fit of the practical and theoretical travel times of the Ps phase and its multiples under the constraints of the model.Using this method,referred to as Hκ0 stacking,we determined the Moho interface.However,the multiples were poorly fitted with the theoretical travel times at many stations,and the crustal thickness obtained was inconsistent with previous findings.Therefore,we speculate that the SWChinaCVM-1.0 model has some limitations that render it incompatible with the CCP stacking method.To further verify this hypothesis,we performed H-κstacking using the v_(P)-v_(S)model,v_(P)model,v_(S)model,and the regional average velocity v_(P0)and compared the results with those of H_(κ0)stacking.The results of the comparison indicate that the SWChinaCVM-1.0 model requires improvements.In addition,by analyzing the SWChinaCVM-1.0 inversion process,we found that the v_(S)model was more reliable than the v_(P)model.Finally,we adopted the crustal thickness obtained using H-κstacking based on the v_(S)model as the initial version of a community Moho interface model for the Sichuan-Yunnan region(SWChinaCVM-MOHO-1.0).

S-wave velocity structure in the SE Tibetan plateau

We use observations recorded by 23 permanent and 99 temporary stations in the SE Tibetan plateau to obtain the S-wave velocity structure along two profiles by applying joint inversion with receiver functions and surface waves. The two profiles cross West Yunnan block （WYB）, the Central Yunnan sub-block （CYB）, South China block （SCB）, and Nanpanjiang basin （NPB）. The profile at -25°N shows that the Moho interface in the CYB is deeper than those in the WYB and the NPB, and the topography and Moho depth have clear correspondence. Beneath the Xiaojiang fault zone （XJF）, there exists a crustal low-velocity zone （LYZ）, crossing the XJF and expanding eastward into the SCB. The NPB is shown to be of relatively high velocity. We speculate that the eastward extrusion of the Tibetan plateau may pass through the XJF and affect its eastern region, and is resisted by the rigid NPB, which has high velocity. This may be the main cause of the crustal thickening and uplift of the topography. In the Tengchong volcanic area, the crust is shown to have alternate high- and low-velocity layers, and the upper mantle is shown to be of low velocity. We consider that the magma which exists in the crust is from the upper mantle and that the complex crustal velocity structure is related to magmatic differentiation. Between the Tengchong volcanic area and the XJF, the crustal velocity is relatively high. Combining these observations with other geophysical evi- dence, it is indicated that rock strength is high and defor- mation is weak in this area, which is why the level of seismicity is quite low. The profile at ~ 23~N shows that the variation of the Moho depth is small from the eastern rigid block to the western active block with a wide range of LVZs. We consider that deformation to the south of the SE Tibetan Plateau is weak.

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).

An accessible seismological dataset of 2021 Yangbi M_(S)6.4 earthquake

A M_(S)6.4 earthquake occurred on 21 May 2021 in Yangbi county,Dali prefecture,Yunnan,China,at 21:48 Beijing Time(13:48 UTC).Earthquakes with an M3.0 or higher occurred before and after the main shock.Seismic data analysis is essential for the in-depth investigation of the 2021 Yangbi M_(S)6.4 earthquake sequence and the seismotectonics of northwestern Yunnan.Institute of Geophysics,China Earthquake Administration(CEA),has compiled a dataset of seismological observations from 157 broadband stations located within 500 km of the epicenter,and has made this dataset available to the earthquake science research community.The dataset(total file size:329 GB)consists of event waveforms with a sampling frequency of 100 sps collected from 18 to 28 May 2021,20-Hz and 100-Hz continuous waveforms collected from 12 to 31 May 2021,and seismic instrument response files.To promote data sharing,the dataset also includes the seismic event waveforms from 20 to 22 May 2021 recorded at 50 stations of the ongoing Binchuan Active Source Geophysical Observation Project,for which the data protection period has not expired.Sample waveforms of the main shock are included in the appendix of this article and can be downloaded from the Earthquake Science website.The event and continuous waveforms are available from the Earthquake Science Data Center website(www.esdc.ac.cn)on application.

Seismic phase picking in China Seismic Array using a deep convolutional neuron network

Seismic phase picking is the preliminary work of earthquake location and body-wave travel time tomography.Manual picking is considered as the most accurate way to access the arrival times but time consuming.Many automatic picking methods were proposed in the past decades,but their precisions are not as high as human experts especially for events with low ratio of signal to noise and later arrivals.As the increasing deployment of large seismic array,the existing methods can not meet the requirements of quick and accurate phase picking.In this study,we applied a phase picking algorithm developed on the base of deep convolutional neuron network(PickNet)to pick seismic phase arrivals in ChinArray-Phase III.The comparison of picking error of PickNet and the traditional method shows that PickNet is capable of picking more precise phases and can be applied in a large dense array.The raw picked travel-time data shows a large variation deviated from the traveltime curves.The absolute location residual is a key criteria for travel-time data selection.Besides,we proposed a flowchart to determine the accurate location of the single-station earthquake via dense seismic array and phase arrival picked by PickNet.This research expands the phase arrival dataset and improves the location accuracy of single-station earthquake.

Three dimensional velocity model and its tectonic implications at China Seismic Experimental Site,eastern margin of the Tibetan Plateau

The China Seismic Experimental Site(CSES)is located at the intersection of the Tibetan Plateau,South China Block,and Indian Plate and has complex geological settings and intense crustal deformation,making it one of the most seismically active areas in Chinese mainland.A high-resolution,three-dimensional(3D)crust-mantle velocity structure is crucial for understanding seismotectonic environments,lithospheric deformation mechanisms,and deep dynamic processes.We first constructed a high-vertical-resolution 3D initial velocity model using the joint inversion of receiver functions and surface waves and then obtained a 3D P-and S-wave velocity model(CSES-VM1.0)with the highest lateral resolution of 0.25°for the CSES using double-difference tomography.Owing to the limitations of the Sn observation data,the resolution of the S-wave velocity model in the lower crust and upper mantle was reduced,making it closer to the initial model provided by joint inversion.A comparison with explosive-source seismic data showed that the synthetic P-wave first-arrival travel times of the new model were closer to the observations than those of the previous velocity models.The velocity cross-sections across the source areas of the 2022 Lushan MS6.1 and Ludian MS6.8 earthquakes reveal that the former earthquake occurred near a weak contact zone between the Tibetan Plateau and Sichuan Basin,and the rupture of the latter earthquake occurred in a granitic area,with the northern end blocked by rigid high-velocity bodies.A clear high-velocity anomaly zone is distributed along the western margin of the Yangtze Block,revealing the spatial distribution of Neoproterozoic intermediate-basic intrusions.This high-velocity zone significantly controls the morphology of fault zones and influences the rupture processes of major earthquakes.Two northeast-southwest and north-south trending high-velocity anomalies were found near Panzhihua,potentially related to Neoproterozoic and Middle-Late Permian intermediate-basic intrusions.The imaging results revealed the spatial distribution of the Lincang granitoid batholith,the uplifted zone of the central axis fault in the Simao Basin,and the Ailaoshan complex belt in the southwestern CSES,demonstrating a higher spatial resolution compared to previous results.Our velocity model provides an essential foundation for deep structural studies,high-precision earthquake locations,and strong ground motion simulations in the CSES.

Three-dimensional S-wave velocity structure of the crust and upper mantle for the normal fault system beneath the Yinchuan Basin from joint inversion of receiver function and surface wave

A series of parallel normal faults are distributed in the Helan Mountain-Yinchuan Basin tectonic belt,where a historical M8.0 earthquake occurred.It is rare that such a great earthquake occurs in a normal fault system within the continent.To deeply understand the fine structure of the normal fault system,we deployed 104 broadband temporary stations near the system,collected data from permanent stations and other temporary stations nearby,and obtained the high-precision threedimensional S-wave velocity structure beneath 206 stations via joint inversion of receiver function and surface wave.A typical graben-in-graben feature bounded by four major faults was identified in the Yinchuan Basin.We analyzed the seismicity in the normal fault system and found a seismic strip in the southern part of the basin,where there are significant changes in the sedimentary thickness,which is speculated to be the southern boundary of the normal fault system.There are significant differences in the crustal thickness and velocity structure in the crust on both sides of the boundary between the Helan Mountain and the Yinchuan Basin,and a low-velocity zone was identified in the upper mantle beneath this boundary,which could be related to the fact that the Helan Mountain-Yinchuan Basin tectonic belt is located between the Alxa Block and the Ordos Block.The M8.0 Yinchuan-Pingluo earthquake occurred at the junction of four major faults in the Yinchuan Basin,which was located in the high-velocity zone near the velocity transition zone at the basin-mountain boundary.The low-velocity zone in the upper mantle beneath this boundary may have promoted the nucleation of this earthquake.Based on evidence from geological drilling,micro seismicity,the regional stress field,and the velocity models obtained in this study,it is inferred that the eastern piedmont fault zone of the Helan Mountain was the seismogenic fault of the 1739 M8.0 Yinchuan-Pingluo earthquake.

超声强化雷尼镍活化新生氢气对水中三氯生的降解机制

催化加氢脱氯是实现水中三氯生(triclosan,TCS)降毒去稳的有效方法.实际应用中,对贵金属催化剂的过度依赖和密闭的加压反应体系是制约该方法工业化应用的关键因素.本研究以阴极析氢反应产生的新生氢气(nascent H_(2),Nas-H_(2))作为雷尼镍(Raney Ni,R-Ni)催化剂的氢源,建立了温和条件下三氯生高效还原脱氯的催化加氢体系.结果表明,雷尼镍/新生氢气体系中三氯生的还原遵循准一级反应动力学,反应2.0 h后,三氯生的转化率为96.3%,脱氯率为68.8%.其中,雷尼镍活化新生氢气产生的吸附态氢原子(hydrogen adatoms,H^(*)_(ads))为反应性物种.为了深化三氯生加氢脱氯,向反应体系中引入超声波(ultrasonic,US),三氯生转化率及脱氯率分别增至99.0%和86.5%,新生氢气的原子利用率达到0.21%.超声增强的氢化性能归因于空化作用提高了雷尼镍催化活性,并将新生氢气泡破碎为易活化的纳米氢(nanoscale H_(2),Nano-H_(2))气泡,促进了H^(*)_(ads)的产生,增加了反应物种之间的有效碰撞次数.通过对反应中间产物的测定分析,提出了三氯生逐级加氢脱氯的反应去除机制,反应最终产物为2-羟基二苯醚.该研究可望应用于水中多卤代有机污染物的高效脱卤.

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.

Lithospheric structure beneath Ordos Block and surrounding areas from joint inversion of receiver function and surface wave dispersion

Ordos Block has undergone rapid uplift,and a series of rift basins have been formed around the block since the Cenozoic,but the formation mechanisms remain controversial.A high-resolution 3 D velocity structure of crust and mantle is important for understanding the lithospheric deformation and deep dynamic process.A here we present a 3 D S-wave velocity structure of the crust and upper mantle in the Ordos Block and surrounding regions by joint inversion of receiver functions and surface wave data from a dense broadband seismic deployment.The lithosphere of the Ordos Block exhibits an obvious highvelocity anomaly.In the east and north of the Ordos and the southwestern part of the Tibetan Plateau,obvious low-velocity anomalies are detected in the upper mantle and extend into the Ordos.The lithosphere of the Ordos Block is thick in the center and thin at the edge,while the crust is relatively thin in the center and thick in the southwest and northeast.The crustal thickness of the tensional basin in the north is greater than that in the central Ordos.We suggest that the outward expansion of the mantle thermal materials in eastern Tibet and the upper mantle thermal upwelling in the eastern part of the North China Craton lead to the non-uniform lithospheric thinning,temperature rise and density reduction of the Ordos Block.The additional buoyancy and thermodynamic effects provided by them contributed to the continuous uplift of the Ordos Block since the Cenozoic.Influenced by the extrusion of Tibetan Plateau,the crustal thickening and rapid uplift occur in the southwestern and northern parts of the Ordos Block.The lithospheric structures of the Alxa and Ordos Blocks are different,and they may belong to different independent blocks before the Mesozoic.

Liquid-phase hydrodechlorination of trichloroethylene driven by nascent H_(2)under an open system:Hydrogenation activity,solvent effect and sulfur poisoning

Hydrodechlorination is a promising technology for the remediation of water body contaminated with trichloroethylene(TCE).In this work,the liquid-phase hydrogenation of TCE by Raney Ni(R-Ni)and Pd/C under an open system have been studied,in which nascent H_(2)(Nas-H_(2))generated in situ from the cathode acted as a hydrogen source.Experimental results showed that TCE was completely eliminate from the solution through the synergistic effects of hydrodechlorination and air flotation due to the formation of continuous micro/nano-sized Nas-H_(2)bubbles from the cathode.Furthermore,the effects of inorganic anions and organic solvents on R-Ni and Pd/C hydrogenation activity were investigated,respectively.The results showed that NO_(3)^(-) and acetonitrile can form a competitive reaction with TCE;Sulfur with lone-pair electrons will cause irreversible poisoning to these two catalysts,and have a stronger inhibitory effect on Pd/C.This work helps to realize the separation of volatile halogenated compounds from water environment and provides certain data support for the choice of catalyst in the actual liquid-phase hydrogenation system.