To understand the deep tectonic environment at the origin of strong earthquakes along the northern section of the North-South seismic belt and the central continental block of Mongolia, large-scale gravity and geomagnetic surveys and rock sample collection were carried out along the Suhbaatar-Ulaanbaatar-Dalandzadgad profile in Mongolia. The spatial distribution characteristics of the lithospheric magnetic field at 160 geomagnetic measuring points along the profile were then systematically analyzed and summarized. Based on the composition of the lithospheric magnetic field from different sources at different depths combined with the regional geological structure and collected rock sample lithology, the lithospheric magnetic field was further decomposed into different components-the basement, middle layer, and shallow surface-by the upward continuation method. The results show that these components have obvious zoning characteristics and that the lithospheric magnetic field distribution of the Suhbaatar-Ulaanbaatar-Dalandzadgad profile is related to the geological structure, rock lithology, seismic activity, natural remanent magnetization, and magnetic susceptibility. Many destructive earthquakes have occurred in the area where the lithospheric magnetic field changes dramatically, the lithologies are dominantly igneous, and the magnetic susceptibility and natural remanent magnetization are high. In contrast, the lithologies in the area with moderate variation in the lithospheric magnetic field are mostly sedimentary, the magnetic susceptibility and natural remanent magnetization are low, and destructive earthquakes are rare. Since the lithospheric magnetic field reflects the magnetic characteristics of the rocks above the Curie interface, its spatial distribution not only corresponds to the geological structure but also predicts the depth and location of faults. Therefore, it is significant to carry out geomagnetic surveys and rock sampling to analyze the characteristics of geological structures and research regional seismicity.

基于2010-2017年共8期的南北带流动地磁矢量观测数据所计算的岩石圈磁场模型, 进一步对各期模型进行相邻期的求差而获得其逐年变化.针对这种变化, 我们认为与地震能量在某一区域内的输入、集中和转移有关, 因此岩石圈磁场随着能量的变化而改变.

The International 2016 EMSEV Workshop was held in Lanzhou,China during August 25 ～29,2016.This paper briefly introduced the Workshop and the seismomagnetic and volcanomagnetic effects.Also,it discussed and looked forward the prospect of the seimomagnetic research.The new progress shows variation characteristics of lithospheric magnetic field before earthquakes and geomagnetic anomalies before volcanic eruption,especially the variation of lithospheric magnetic field achieve good effect in earthquake prediction.

According to the CHAOS-6 model,the annual changes of geomagnetic at 28 observations located in China in 2015 and the geomagnetic secular variations at CDP,GLM,LZH,TAA and THJ observations in 2008.0-2016.5 were calculated.The differences between the geomagnetic data of practical observations and those calculated by the CHAOS-6 model were analyzed.The mean differences and the mean square root σ were obtained.The results show that the trend of the geomagnetic secular variation in China described by the CHAOS-6 model is basically consistent with those at observations,but there are some differences.The mean of the difference and the mean square root are-0.9'/1.7'and-29.3'/0.8'for geomagnetic declination (D) and inclination (Ⅰ) respectively;and the mean of the difference and the mean square root are-116.3 nT/10.2 nT,264.7 nT/13.6 nT,-27.7 nT/15.0 nT,265.2 nT/13.7 nT and-356.9 nT/8.0 nT for total intensity (F),northern component (X),eastern component (Y),horizontal component (H) and vertical component (Z),respectively at 28 observations.The main reason for the error of the geomagnetic secular variation in China described by the CHAOS-6 model is that the regional and local magnetic anomalies in China,while the CHAOS -6 is a model of global geomagnetic field.The error of the CHAOS-6 model should be fully considered when we use it to study the regional problems in China.

2015年6月22日～7月2日在捷克首都布拉格举行了第26届国际大地测量学与地球物理学联合会(IUGG)大会.2015年6月14～ 18日于中国台湾台北召开了第八届世界华人地质大会.这两次大会展示了地球科学与空间科学的新进展.在这两次大会上震磁研究的学术报告表明,震磁研究是地震预测探索的一个重要方面.震磁研究的结果显示,局部地区岩石圈磁异常变化含有震磁前兆信息,是研究预测区域地震活动性的重要依据.今后应当加强地震活动区的震磁观测与研究.

采用2011～2012年期间在蒙古国境内地磁测量得到的119点地磁数据,利用以球冠谐和和曲面样条方法得到的蒙古地区地磁场数值为基础数据,获得了2010.0年代蒙古地区岩石磁异常的空间分布,对蒙古地区岩石磁异常的空间分布进行了研究.结果表明,蒙古地区的岩石磁异常表现出东西差异,异常幅度在西部较大东部较小.蒙古西部南边界处表现为类弧形结构和贝加尔—乌兰巴托条带结构为蒙古地区较为显著的磁异常结构.

在蒙古中部106°E附近布设一条南北走向的重力剖面,首次获得该地区精确的实测重力值,经过数据预处理和改正计算,得到剖面重力异常结果.分析表明,剖面自由空气异常和地形有很强的相关性;剖面布格重力异常变化总体较为平缓,只在戈壁-阿尔泰-曼达尔戈壁加里东区带(GAB)和哈拉加里东区带(HRB)附近发生相对较快的变化,推测这两个区域可能存在较明显的深部构造变化;在蒙古-鄂霍兹克造山带附近,并未发现与板块缝合带相对应的重力异常变化;剖面均衡重力异常以负值为主,多数地区地壳未达到重力均衡状态,剖面附近地震活动和均衡重力异常之间的关系与中国南北地震带北段相关研究结果类似.

We summarized the seismomagnetic research resnlt in the 2014 American Geophysical Union( AGU) Fall M eeting which was held in San Francisco,USA on Dec. 15 ~ 19,2014. The papers of the AGU meeting fully showed the new progresses and the new results of seismomagnetic research,and the development prospect of it in the future. The seismomagnetic research is very important for the earthquake prediction. The research results display that the lithospheric magnetic anomalies variation in local region has the seismomagnetic precursor information,and it is an important basis for predicting the local seismic activity.

To well understand the deep structure environment and mechanism of strong earthquakes occurred in the Tianshan-Mongolia-Lake Baikal seismic belt, an integrated geomagnetic and gravity survey was conducted along the profile from Suhbaatar to Ulaanbaatar to Dalandzadgad in Mongolia. In this paper, petrophysical parameters ( bulk density, magnetic susceptibility, intensity of natural rema-nent magnetization, and K?enigsberger ratio) of 585 rock samples collected from this profile are summarized. Results indicate that sig-nificant density contrast of different rocks would result in variable gravity anomalies along the profile. Magnetic susceptibility and natural remanent magnetization of all rocks are variable, covering 3~5 orders of magnitude, which would make a variable induced magnetiza-tion and further links to complex magnetic anomalies in ground surface. These petrophysical parameters provide essential constraints on the interpretation of geophysical data and to calibrate geophysical parameters.

The U. S. Geological Survey( USGS) and the relative universities have set up the geophysical observation netw orks,including geomagnetic observation in the w estern America,particularly in the San Andreas Fault and its adjacent area in order to monitor the seismic activities. For the M5. 2 ~ 7. 3 earthquakes,the analytical results of the geomagnetic data show that the change anomalies amplitude of the geomagnetic total intensity w ere 0. 3 ~ 6 nT observed at the sites and stations w hich w ere apart 3 ~ 50 km from these earthquakes epicenters. The seismomagnetic research results show that there are seismomagnetic precursors for some earthquakes. Therefore,the observation and research on the seismomagnetic effects is a method to study earthquake prediction. The results through carefully analyzing the geomagnetic data at seven stations before and after Parkfield M6. 0 earthquake on Sep. 28,2004 show that the co-seismomagnetic effects are- 0. 4 ~ 0. 3 nT,w hich are caused by piezomagnetic mechanism. The seismomagnetic anomalies w ith longer time for this earthquake are- 5. 0 ~ 1. 0 nT,w hich are related to the factors such as the local geological structure and its activity,the state of stress changes,the electromagnetic properties of the underground media.

Mongolia is an important neighbor of northern China.Western Mongolia ancient tectonic is a major structure in north of north-south tectonic earthquake zone,one important earthquake zone in China.In this paper,surfaces spline (SP)method is used to calculate the geomagnetic data on 1 1 9 sites in Mongolia on 2010.0 epoch,and the geomagnetic spatial structure in Mongolia is obtained.The results show that the geomagnetic spatial distribution of magnetic components given by SP model and EMM is similar,but there are some differences in part.These differences can reach ±30'for I ,± 60'for D and ± 500 nT for H ,F ,X ,Y ,Z .

Petrophysical properties of 585 rock samples from the Suhbaatar-Ulaanbaatar-Dalandzadgad geophysical profile in Mongolia are presented. Based on the rock classifications and tectonic units, petrophysical parameters (bulk density, magnetic susceptibility, intensity of natural remanent magnetization, and Köenigsberger ratio) of these rocks are summarized. Results indicate that (1) significant density contrast of different rocks would result in variable gravity anomalies along the profile; (2) magnetic susceptibility and natural remanent magnetization of all rocks are variable, covering 5-6 orders of magnitude, which would make a variable induced magnetization and further links to complex magnetic anomalies in ground surface; (3) the distribution of rocks with different lithologies controls the pattern of lithospheric magnetic anomaly along the profile. The petrophysical database thus provides not only one of the keys to understand the geological history and structure of the profile, but also essential information for analysis and interpretation of the geophysical (e.g., magnetic and gravity) survey data.

On substantial support of the International Association of Geomagnetism and Aeronomy (IAGA),the International association of Seismology and Physics of the Earth's Interior (IASPEI) and the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI),the Working Group on Electromagnetic Studies on Earthquakes and Volcanoes (EMSEV) was established in 2001. The EMSEV has devoted to the international academic exchange and the cooperation on electromagnetic studies on earthquakes and volcanoes since 2001,and promoted the electromagnetic studies on earthquakes and volcanoes. We described the general situation of the EMSEV and its working conference,and briefly introduced the international academic exchange of electromagnetic studies on earthquakes and volcanoes and international cooperation on the EMSEV,and discussed and looked forward the prospect of electromagnetic studies on earthquakes and volcanoes.

We build the buffer zones with a 30 km radius from the zero-value-lines of all components of the abnormal geomagnetic field in lithosphere of north China seismic region,and statistical analyze all the MS≥4.0 earthquakes in the buffer zones since 1900.The results indicate that there are close relativities among the epicenter distribution of large earthquakes with MS≥7.0 and the zero-value-lines of geomagnetic declination,north component,east component and vertical component of the abnormal geomagnetic field,and the epicenter distribution has the highest relation to the geomagnetic declination with proportion 83.3%.

The eleventh generation of the International Geomagnetic Reference Field(IGRF11) was issued in December 2009 by the International Association of Geomagnetism and Aeronomy(IAGA).IGRF-11 consists of 23 geomagnetic models for 1900.0—2010.0(at 5 year intervals) and the predictive model of geomagnetic secular variation for 2010.0—2015.0.For the degree N and order M of the geomagnetic models for 1900.0—1995.0,we have N = M = 10,the accuracy of the corresponding spherical harmonic coefficients is 1 nT;For the models of 2000.0—2010.0,N = M = 13,and the accuracy of the coefficients is 0.1 nT.For the degree N and order M of the predictive model of geomagnetic secular variation for 2010.0—2015.0,we have N = M = 13,the accuracy of the coefficients is 0.1 nT.This paper presents a brief description of IGRF-11 and its geomagnetic model for 2010.0 and its predictive model of geomagnetic secular variation for 2010.0—2015.0.

The eleventh generation International Geomagnetic Reference Field(IGRF-11) was issued in December 2009 by the International Association of Geomagnetism and Aeronomy(IAGA).The IGRF-11 is the latest and comparatively precise IGRF.According to the IGRF-11 model,the geomagnetic secular variation(SVC) in China during 2005-2010 was calculated.The SVC and the geomagnetic secular variation(SVO) obtained from the geomagnetic data of practical observations in China are basically consistent,but there is obvious difference.The SVO and SVC at 34 observatories in China were analyzed and compared;the differences between the SVO and SVC and the mean square roots σ were obtained.The mean square roots σ are 0.35 ′/a and 0.53 ′/a for geomagnetic declination and inclination respectively;and the σ are 5.12 nT/a,8.91 nT/a,8.89 nT/a,3.27 nT/a and 3.59 nT/a for geomagnetic total intensity,horizontal component,northern component,eastern component and vertical component respectively.The reasons for the error of the geomagnetic secular variation in China during 2005-2010 described by the IGRF-11 are the regional and local magnetic anomalies in China,no external source field for the IGRF and the truncation order of the IGRF,non-homogeneous distribution of the geomagnetic observatories,stations and sites in the world,the errors of geomagnetic observations etc.The China geomagnetic model(CGM) should be used in practical application,because the CGM is better than the IGRF and can describe the geomagnetic field and its secular variation in China with comparative precision.

Using matched-filter method,the geomagnetic anomaly data from profiles of Luan-Yingshan(Ⅰ),Baitafan-Wuwei(Ⅱ) and Jinzhaiqingshan-Wanfuhu(Ⅲ) in Eastern Dabie Orogenic belt are processed,the local anomalous field is extracted from regional field.Based on regional anomalous field,the buried depth of Curie surface along profiles are calculated using the approximate linear invertion method.Combined with the geological results and earthquakes distribution in this area,the relations between seismic activity and Curie surfaces,and the seismogenesis mechanism are researched preliminarily.The results show that the curves of geomagnetic anomaly exhibit the various characteristics and differences of structural basements of different profiles,existing apparent mirror image relationship with the depth of Curie surfaces.Fluctuation of Curie surface in the area is about 14 km,the lowest position is at Huoshan,where is the intersection part of profile Ⅰ and Ⅲ.The corresponding relation between earthquakes distribution and Curie surface is apparent,most earthquakes occur on gradient zone of Curie surface.Thermal stress generated from temperature difference of gradient zone might be direct dynamic sources of Houshan area.The invertion result of Curie surface provide proof for offset on Moho along Xiaotian-Muzitan Fault.

Based on geomagnetic data on 218 geomagnetic sites in 2009 and 2010,we have calculated and analyzed the distributions of geomagnetic declination（D）,the total intensity（F）,the inclination（I） using surface Spline method and Spherical Cap Harmonic（SCH） method.The results show that the spacial distributions of 2009 and 2010 are similar,but some differences really exist.As for declination,the amplitude grows in negative regions and attenuates in positive regions in Northeast part of North-China,and it is opposite in the west part of North-China.As for total intensity,the amplitude grows in positive regions in most parts of North-China,and it is opposite in littoral of Jiangsu province and the edge between Liaoning province and Hebei province.As for inclination,the amplitude attenuate in negative regions in most part of North-China,the amplitude grow in negative regions and the amplitude attenuate in positive regions in Northeast of Liaoning province,east edge and South edge of Shanxi province.

Based on geomagnetic data on 218 geomagnetic sites in 2009 and 2010,we have calculated and analyzed the distributions of geomagnetic declination(D),the total intensity(F),the inclination(I) using surface Spline method and Spherical Cap Harmonic(SCH) method.The results show that the spacial distributions of 2009 and 2010 are similar,but some differences really exist.As for declination,the amplitude grows in negative regions and attenuates in positive regions in Northeast part of North-China,and it is opposite in the west part of North-China.As for total intensity,the amplitude grows in positive regions in most parts of North-China,and it is opposite in littoral of Jiangsu province and the edge between Liaoning province and Hebei province.As for inclination,the amplitude attenuate in negative regions in most part of North-China,the amplitude grow in negative regions and the amplitude attenuate in positive regions in Northeast of Liaoning province,east edge and South edge of Shanxi province.