China Seismic Experimental Site(CSES):A systems engineering perspective

China Seismic Experimental Site(CSES)deals with a long-term process of development of a multidisciplinary technical system.In the construction,maintenance,and upgrading of CSES,ideas of systems engineering play an important role.This article discusses several concepts which might be useful for CSES,including system metaphor,system performance evaluation,and system design.

China Seismic Experimental Site(CSES): Challenges of Deep Earth Exploration and Practice(DEEP)

Since May 2018,the planning,construction and functioning of China Seismic Experimental Site(CSES)has attracted much attention in earthquake science(CSES,2020 a,b,c;Wu,2020;Li et al.,2021).Different from traditional earthquake prediction experiment projects,such as the Parkfield earthquake prediction experiment(Roeloffs,2000).

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.

The seismic reflecting characteristics of gas hydrate bearing strata and its possible distribution in the South China Sea

关于煤气的水合物的研究是对精力资源和环境的地的一般兴趣的话题之一。华南海为煤气的水合物的出现和形成有有利条件。煤气的水合物的存在在模仿反射镜的底部的出现改变沉积阶层和结果的声学的性质，它使多信道的地震调查成为一个重要方法识别煤气的水合物。首先，基于地震思考成像的结果，论文分析包含煤气的水合物的沉积阶层的质的地震思考特征。一些关键地震成像技术也被讨论。下次，一口伪井被构造执行阻抗倒置自从在学习区域没有井，得到阶层的量的速度结构。最后，从地球物理的倒置的速度领域与在钻程序 184 巡航的海洋上获得的 geochemical 和地球物理的数据是综合的。所有信息证实煤气的水合物的存在并且显示出它的空间分发。

The Crustal Structure and Seismic Activity in North China

A layered crustal block model of North China has been constructed based on large amount of data from seismic sounding carried out in recent two decades. Some deep fault zones, such as the Zhangjiakou.Penglai and Tancheng-Lujiang fault zones, divide the upper crust of North China into three upper crustal terranes and nine bolcks. There are distinct differences in velocity and depth distributions, which reflects Cenozoic block faulting in North China in the process of formation of the deep structure. The upper crust shows the features of transition in isostatic adjustment. The existence of a low-velocity layer in the middle crust is characteristic of the crustal structure in North China. There seems to be an increase of rheology of the rocks in the lower crust and a persistence of stable regional stress field. The patterns of the Moho on two sides of the Yanshan-Taihang Mountains are different. The relief of the Moho around Beijing, Shijiazhuang and Guangrao where the deep faults join together shows a quadrantal distribution in some degree. The dynamic sources for seismic activity are the NE-SW horizontal compression and the diapirism of the upper mantle. The middle and upper crust, especially the layered block structure has the most significant effects on seismicity, and the occurrence of earthquakes is more closely related to them than to the Moho.

Background Seismicity and Its Application to Seismic Hazard Assessment in the North China Region

历史的地震活动在北方中国区域是强烈的。然而，自从 Ms6.2 地震，没有中号的地震在 Zhangbei 区域在这个区域发生在最后十年在 1998。中等、强烈的地震的静止在诺思中国是相当突出的。在这篇论文，我们在 1970 ~ 使用小地震记录 2009 学习背景在北方中国区域的地震活动。地震参数的空间分布被介绍，包括 b 值，最大的大小和 M/6 的地震的年度出现概率。0。我们有低 b 值的结果表演区域在太行山块在山西裂缝，位于 Tancheng-Lujiang 差错地区的 Suqian 区域和 Shijiazhuang 区域包括 Yuncheng 区域。我们 seismicity 的合成空间模式上的分析显示在北方中国区域的 seismicity 被深结构的地区性的动态因素主要影响。

Characteristics of seismic reflections in central region of the South China Sea and their geological significance

More than 4 000 km 48-channel seismic reflection data from the central region of the South China Sea have been interpreted. Five seismic interfaces have been distinguished, named T1, T2, T4, T6 and Tg respectively Meanwhile, five seismic sequences numbered I - V have been divided with the ages of Quaternary and Pliocene, Later Mocene, Earlier and Middle Miocene, Oligocene and Pre- Oligocene separately. Sequences I-II overlie all parts of the area. In the continental slope and island slope, Sequences III-V are mainly found in the grabens. Sequence III is found at moot profiles of the deep-sea basin, and Sequnce IV is seen not only at the margins of the east subbasin but also at the margins of the southwest subbasin. Strong reflection from Moho is found at most profiles of the deep-sea basin. The depth of Moho varies between 10 and 12 km, with a thickness of 6- 8 km for the crust. Calculated by age-basement depth correlation formula, the age of basaltic basement in the southwest subbasin is 51-39 Ma. It is indicated that the evolution of the southwest subbasin is simultaneous with or earlier than that of the east subbasin.

The gravity and isostatic Moho in North China Craton and their implications to seismicity

The Bouguer gravity is the combination of field sources in different depths. Based on the multi-scale analysis of the Bouguer gravity,we can get the gravity anomaly caused by the Moho undulation. This study presents the various orders of approximation of gravity anomaly in North China Craton（NCC）,the possible source depths with radial logarithmic power spectrum,and the relationship between the deep structure and gravity anomaly. Furthermore,we discuss the isostatic compensation about the Moho depth from gravity and deep seismic sounding profiles（DSS）. The results show that：（1） the fourth approximation could have resulted from the Moho undulation,（2） in contrast to the isostatic Moho,the inverted gravity Moho and the DSS Moho show that most of NCC has been isostatically compensated,and（3） the isostatic compensation rate has some close relation to the seismicity.

The regional characteristics of seismic activity in China

In this paper, the regional characteristics of seismicity of strong earthquakes in 27 seismic provinces in the wholeChina were discussed. It is divided into b kinds of regions on the basis of analyzing the earthquake's annual average rate of M≥6, b-value and the maximum magnitude in history in those provinces. Among them, the seismicactivity in the eastern part of Taiwan seismic province is the highest, where the annual average rate of earthquake occurrence vM≥6 is more than 1. The second kind region includes Pamir, south and north Tianshan, Yunnan-Sichuan, west Kunlun, Himalaya and western part of Taiwan etc. 9 seismic provinces, vM≥6 are 0. 12 -0. 34. The third kind of regions contains 10 seismic provinces, such as 4 provinces in North China, northeastborder of Qingzang (Qinghai-Xizang) plateau, Gobi-Altay and the outside southeast coast province etc., wherevM≥6=0. 032-0. 08, the maximum earthquakes of Mmax≥8 were recorded in the history in most seismicprovinces of the region, only a few seismic provinces recorded Mmax=7.3-7. 5. The fourth kind of regions include 6 seismic provinces, such as the northeast China, the middle and lower reaches of the Yangtze River and South China etc., where, vM≥6=0. 01-0. 03, the largest earthquake recorded in the history is Mmax<7. Thefifth kind of regions is the one with the lowest seismic activities, Mmax=53/4 be recorded as the maximum magnitude there. The regional characteristics of the strong earthquake activity have close relationship with tectonicmovement of the surrounding plate and of the introplate block.

A summary of seismic activities in and around China in 2021

In this article,we review the general characteristics of seismicity in and around China and the overall statistics of earthquake damage in 2021,focusing on several significant events and related scientific topics.Among them,the largest event is the M_(S)7.4 Madoi earthquake in Qinghai Province,northwest China.The event marks another M_(S)≥7 earthquake occurring near the boundary of the Bayan Har Block that has ended a remarkable quiescence of the M_(S)≥7 earthquakes within the Chinese mainland.In addition,the M_(S)6.4 Yangbi earthquake in Yunnan Province,southwest China draws the most attention because of its abundant foreshocks,which are well recorded by the densely distributed seismic stations in the surrounding regions.Regarding this event,we review several recent publications focusing on the Gutenberg-Richter b-value change and the physical mechanism of foreshocks associated with this sequence.The M_(S)6.0 Luxian earthquake in Sichuan Province,southwest China has caused serious damage with a relatively low magnitude,partly because the focal depth of the mainshock is relatively shallow (3.5 km).It is another strong earthquake occurring within the southeast Sichuan basin with low historical seismicity yet has increased significantly since 2015,probably due to shale gas development and associated hydraulic fracturing.

Seismic Velocity Structure and Composition of the Continental Crust of Eastern China

On the basis of a one-by-one latitude-longitude grid three-dimensional seismic velocity model, the crustal P-wave velocity structure in eastern China (105-125°E and 18-41°N) is obtained, and a set of geotherms for each grid is established for P-T correction on P-wave velocities. The average depths of sub-crustal layers and their average P-wave velocities of 18 tectonic units in eastern China are exhibited. Our result presents a 32-34 km thick crust beneath eastern China, which is thinner than previous studies, with an average velocity of 6.54 km/s, corresponding to a 5 kg/m3 variation in crustal mean density. The thicker upper but thinner middle and lower crust results in a lower average seismic velocity of eastern China. An intermediate crustal composition with a SiO2 content of 59.7 wt% has been estimated. However, there exists a significant lateral variation in the crustal structures among the tectonic units of eastern China. The structure and composition features of some regions in eastern China indicate that extension has played an important role in the continental crust evolution of eastern China.

Preface to the Special Issue on Advances in Seismic Exploration and Monitoring with Active Sources in China

Analyzing the information carriede by seismic waves is a major means for human beings to have an insight into the structure of the earth’s interior,and by using artificial seismic sources to excite seismic waves,we can obtain high-resolution images for the crustal and smaller scale medium.Artificial seismic exploration methods have been widely applied to fields such as

Seismic attenuation in the lower mantle beneath Northeast China constrained from short-period reflected core phases at short epicentral distances

The thermal structure of the lower mantle plays a key role in understanding the dynamic processes of the Earth's evolution and mantle convection.Because intrinsic attenuation in the lower mantle is highly sensitive to temperature,determining of the attenuation of the lower mantle could help us determine its thermal state.We attempted to constrain the attenuation of the lower mantle by measuring the amplitude ratios of p to ScP on the vertical component and s to ScS on the tangential component at short epicentral distances for seismic wave data from deep earthquakes in Northeast China.We calculated the theoretical amplitude ratios of p to ScP and s to ScS by using ray theory and the axial-symmetric spectral element method AxiSEM,as well as by considering the effects of radiation patterns,geometrical spreading,and ScP reflection coefficients.By comparing the observed amplitude ratios with the synthetic results,we constrained the quality factors as Qα≈3,000 and Qβ≈1,300 in the lower mantle beneath Northeast China,which are much larger than those in the preliminary reference Earth model(PREM)model of Qα~800 and Qβ~312.We propose that the lower mantle beneath Northeast China is relatively colder than the average mantle,resulting in weaker intrinsic attenuation and higher velocity.We estimated the temperature of the lower mantle beneath Northeast China as approximately 300–700 K colder than the global average value.

An Overview of Seismicity in China

This paper gives an overview of seismicity in China, including large-scale seismicity heterogeneity in space-time, aftershock activity, b-value, earthquake mechanism, and its possible mechanics.

Seismicity acceleration model and its application to several earthquake regions in China

With the theory of subcritical crack growth, we can deduce the fundamental equation of regional seismicity acceleration model. Applying this model to intraplate earthquake regions, we select three earthquake subplates: North China Subplate, Chuan Dian Block and Xinjiang Subplate, and divide the three subplates into seven researched regions by the difference of seismicity and tectonic conditions. With the modified equation given by Sornette and Sammis (1995), we analysis the seismicity of each region. To those strong earthquakes already occurred in these region, the model can give close fitting of magnitude and occurrence time, and the result in this article indicates that the seismicity acceleration model can also be used for describing the seismicity of intraplate. In the article, we give the magnitude and occurrence time of possible strong earthquakes in Shanxi, Ordos, Bole Tuokexun, Ayinke Wuqia earthquake regions. In the same subplate or block, the earthquake periods for each earthquake region are similar in time interval. The constant α in model can be used to describe the intensity of regional seismicity, and for the Chinese Mainland, α is 0.4 generally. To the seismicity in Taiwan and other regions with complex tectonic conditions, the model does not fit well at present.

Earthquake Disaster and Seismic Activity in China Since 1949

An outline is given in the present paper of the general situation of earthquake disasters and their temporal,spatial,and magnitude distributions in China since 1949,based on recently published Chinese disaster data.A comparison was made between the earthquake disasters and seismic activities in China during this period.The results show that 477 disaster-causing earthquakes have occurred during this period,resulting in a death toll of 278,000 persons and the collapse of 11,000,000 rooms in residence houses.The total direct economic losses exceeded 42 billion Yuan(Chinese currency,the same below).A comparison of earthquake disasters in various regions(between East and West China,between various provinces,etc.)has shown that both correlations and significant differences exist between the spatial distributions of earthquake disasters and seismic activities in China.For example,seismic activity shows a feature of being "stronger in the West than in the East," whereas the earthquake disasters are stronger

MULTI-SCALE DECOMPOSITION OF BOUGUER GRAVITY ANOMALY AND SEISMIC ACTIVITY IN NORTH CHINA

Bouguer gravity anomaly in North China is decomposed with multi scale decomposition technique of wavelet transform. Gravity anomalies produced by anomalous density bodies of various scales are revealed from surface to Moho. Characteristics of anomalies of different orders and corresponding structural features are discussed. The result shows that details of wavelet transform of different orders reflect the distribution features of rock density at different depths and in various scales. In most cases, the two sides of a fault especially a deep and large fault in North China differ greatly in rock density. This difference records the history of the formation and evolution of the crust. Deep structural setting for the \%M\%s≥7.0 strong earthquakes in this region is also discussed.

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.

OCEAN BOTTOM SEISMOMETER AND ONSHOREOFFSHORE SEISMIC EXPERIMENT IN NORTHEASTERN SOUTH CHINA SEA

Three-component Ocean Bottom Seismometers, portable land stations and marine air gun seismic sources were used to carry out an onshore-offshore deep seismic profile in northeastern South China Sea. This profile, orientated in NNW-SSE, was as long as 500 km and perpendicular to the strike of regional tectonics. The offshore data were processed in Taiwan Ocean University using a number of available software and the onshore data were analyzed in South China Sea Institute of Oceanology by new-written programs and public software. Preliminary results show that the seismic data are in good quality and contain rich information of deep structure. Seismic phases, e.g. Pg, PmP and Pn, are identified in the offset range 5～220 kin, which will provide an important dataset for the deep crustal structure and oil-gas basin evolution studies of this region.

中国地震科学实验场三维断层模型Web展示原型系统

活动断层的三维结构和模型是地震危险性研究的基础参数和重要数据。随着对接近真实形态的活动断层三维模型的应用需求不断增加,对这类模型数据的共享及研究的需求也日益增加。数据共享课题的一个重要议题是如何构建基于Web的三维断层模型展示平台,提高数据共享水平和用户体验。中国地震科学实验场(川滇地区)三维断层模型Web展示原型系统①是基于Arc GIS 10.6企业版的Web App Builder工具构建的一个实验性系统。该系统实现了基于Web GIS的三维展示系统的基本功能,并成功测试了更适用于地震行业标准的用户交互方式、基本功能、场景数据迁移方案和三维场景设计方案。场景数据从三维断层建模平台到GIS平台的迁移,是实现基于Web GIS三维展示系统的基础。场景中展示的三维数据采用与二维数据标准一致且视觉上融合度高的可视化方案。实践结果表明,三维数据从建模平台迁出后,应结合数据可视化方案,在属性层面上与二维数据相融合,以保证二维和三维数据在视觉上较好地融合。