Recent geomagnetic storms observed by Macao Science Satellite-1

Geomagnetic storms are rapid disturbances of the Earth’s magnetosphere.They are related to many geophysical phenomena and have large influences on human activities.Observing and studying geomagnetic storms is thus of great significance to both scientific research and geomagnetic hazards prevention.The Macao Science Satellite-1(MSS-1)project includes two high-precision Chinese geomagnetic satellites successfully launched on May 21,2023.The main purpose of MSS-1 is to accurately measure the Earth’s magnetic field.Here,we analyze early MSS-1 geomagnetic field measurements and report observations of two recent geomagnetic storms that occurred on March 24,2024 and May 11,2024.We also calculate the related geoelectric fields as an initial step towards a quantitative assessment of geomagnetic hazards.

Electrical geophysical evaluation of susceptibility to flooding in University of Nigeria, Nsukka main campus and its environs, Southeastern Nigeria

Flooding occurs when rainfall exceeds the absorption capacity of soil and causes significant environmental consequences.In this study,electrical resistivity techniques were employed to assess the flood susceptibility of the study area by examining variations in electrical properties.Prior to flooding,Vertical Electrical Sounding(VES)and Electrical Resistivity Tomography(ERT)profiles were conducted to determine the variations in resistivity within subsurface lithologies exposed to the injected current.The injected current penetrated the subsurface units characterised by resistivity ranging from 190.5Ω·m to 6,775.7Ω·m,42.3Ω·m to 7,297.4Ω·m,and 320.2Ω·m to 24,433.3Ω·m in the first,second and third layers,respectively.These layers were identified as lateritic topsoil,medium-coarse brownish grained sand,and coarse pebbly blackish sand,respectively.The calculated reflection coefficients between layers 1,2,and 3 reveal alternation in layers with values ranging from−0.04 to 0.66 and 0.36 to 0.95 for and,respectively.The transverse resistivity,longitudinal resistivity and anisotropy ranged from 243.59Ω·m to 24,115.42Ω·m,199.61Ω·m to 14,950.76Ω·m,and 1.02 to 2.14.Models derived from the ERT profiles reveal variations in resistivity,pinpointing areas of low resistivity which correspond to waterlogged and impermeable layers.The result of this study underscores the importance of integrated resistivity techniques in the study of floods,as it provides valuable insights into flood behaviour,and subsurface dynamics.

Application of Vertical Electrical Sounding in Mapping Lateral and Vertical Changes in the Subsurface Lithologies: A Case Study of Olbanita, Menengai Area, Nakuru, Kenya

Much study has been done in the study area linking Vertical Electrical Sounding (VES) interpreted results to lithologies in the subsurface though only tend to indicate the vertical changes with the aim of mapping the occurrence of groundwater aquifers. Several boreholes have been drilled in the study area, though not much has been done to compare the vertical and lateral lithologic changes in the study area. This research is based on VES modelled geoelectric layers compared from point to point and using borehole logs as control data to establish inferences of certain lithology in the subsurface. The inversion of each VES curve was obtained using an AGI Earth Imager ID inversion automated computer program and resistivities and thicknesses of a geoelectric model were estimated. The analyzed VES data interpretation achieved using the curve matching technique resulted in mapping the subsurface of the area as portraying H-type;ρ1 > ρ2 ρ3, K-type;ρ1 ρ2 > ρ3, A-type;ρ1 ρ2 ρ3, Q-type;ρ1 > ρ2 > ρ3, representing 3-Layer subsurface and subsequently a combination of HK, HA and KHK types of curves representing 4-Layer and 5-Layer in the subsurface. The analysis further deployed the use of the surfer software capabilities which combined the VES data to generate profiles running in the west-east and the north-south direction. A closer analysis of the curve types indicates that there exists a sequence showing a shifting of the order of arrangement between the west and the east fragments which incidentally coincides with VES points 8, 9 and 10 in the West-East profiles. The lateral change is noted from the types of curves established and each curve indicates a vertical change in the subsurface. Control log data of lithologies from four boreholes BH1, BH2, BH3 and BH5 to show a qualification that different resistivity values portent different lithologies. Indeed, an analysis at borehole BH3 lithologies is dominated by either compacted rocks or soils, insinuating a scenario of compression experienced in this part of the subsurface which confirmed compression of subsurface formations. A correlation of the VES curve types and their change from one point to another in the study area are evident. This change supported by the surfer generated profiles from the modeled VES data show that there exists and inferred fault line running in the north-south in the area. The inferred fault line by VES mapping, is magnificently outlined by the geological map. There is exuded evidence from this study that the application of VES is able to help map the lateral and the vertical changes in the subsurface of any area but the evidence of the specific lithologies has to be supported by availability of borehole log control data. The VES data was able to enumerate vertical layering of lithologies, lateral changes and even mapping vertical fault line in the study area.

3D Modeling and Estimation of the Tonnage of the Granite Quarry of Linguésso (North-West of Côte d’Ivoire) by Electrical Methods

A survey and evaluation was carried out on a potential granitoid quarry site in the locality of Linguésso (North West of Ivory Coast) with the aim of identifying and estimating the quantity of exploitable granite based on the electrical resistivity methods. The combination of electrical trailing, sounding and tomography techniques allowed the determination of the characteristics of the rock deposit, namely the electrical signature (between 19,259 Ωm and 86,316 Ωm), the extension (N90°), the rooting (between 0 and 45 m) and the fracturing (between N14° and N160°) of the granitic formation sought. The modeling resulted in an estimated mineable rock volume of 2,936,250 m3 providing a production quantity of 7,927,875 tonnes.

Geophysical Approach for Groundwater Resource Assessment:A Case Study of Oda Community Akure,Southwestern Nigeria

The geophysical investigation for groundwater was carried out at Oda town,Akure south local government area of Ondo State.Fourteen(14)points were sounded using a Schlumberger array with AB/2 of 80 m and the resulting geoelectric parameters were used in the estimation of the aquifer layer parameters of the subsurface.The first layer resistivity value ranges from 29 to 164Ωm and thickness ranges from 0.6 to 2.5 m.The second layer has a resistivity value ranging from 21-1361Ωm with a thickness ranging from 1.5 m to 14.6 m.The third layer resistivity value is from 68 to 297Ωm with thickness ranging from 4 m to 12.4 m.The fourth layer which is the deepest layer has a resistivity value ranging from 180 to 4364Ωm with depth ranging from 4 m to 19.5 m.The parameters interpreted from the geoelectric data were used to generate the aquifer thickness and resistivity maps,with bedrock relief which were combined to produce the groundwater potential map of the area.These maps were used to characterise the study area into low to high groundwater potential zones.The southwestern and eastern parts were identified as productive groundwater potential zones.The result was validated by taking water column depth from eight existing hand-dug wells.A significant correlation was obtained between the groundwater potential model and the well water column.The surveyed area is generally suitable for hand-dug well aside from the north-eastern part where groundwater potential is low and water volume is observed.

Prediction criteria for groundwater potential zones in Kemuning District,Indonesia using the integration of geoelectrical and physical parameters

The presence of groundwater is strongly related to its geological and geohydrological conditions.It is,however,important to study the groundwater potential in an area before it is utilized to provide clean water.Werner-Schlumberger’s method was used to analyze the groundwater potential while hydraulic properties such as soil porosity and hydraulic conductivity were used to determine the quality and ability of the soil to allow water’s movement in the aquifer.The results show that the aquifer in the Sekara and Kemuning Muda is at a depth of more than 6 meters below the ground level with moderate groundwater potential.It is also found that the aquifer at depths of over 60 m have high groundwater potential.Moreover,soil porosity in Kemuning is found to be average while the ability to conduct water was moderate.This makes it possible for some surface water to seep into the soil while the remaining flows to the rivers and ditches.

忻州5.1级大同5.8级地震地电阻率异常分析

对大同、代县两台地电资料进行了处理分析，并用地电实用化攻关判别异常指标和经验公式检验，在1990年度报告中试预报：忻州──大同一带将发生6．0级左右地震。结果在1991年忻州、大同老震区相继发生了5．1级地震和5．8级地震。预报效果较好。

2.5D forward modeling and inversion of frequency-domain airborne electromagnetic data

Frequency-domain airborne electromagnetics is a proven geophysical exploration method.Presently,the interpretation is mainly based on resistivity-depth imaging and onedimensional layered inversion;nevertheless,it is difficult to obtain satisfactory results for two- or three-dimensional complex earth structures using 1D methods.3D forward modeling and inversion can be used but are hampered by computational limitations because of the large number of data.Thus,we developed a 2.5D frequency-domain airborne electromagnetic forward modeling and inversion algorithm.To eliminate the source singularities in the numerical simulations,we split the fields into primary and secondary fields.The primary fields are calculated using homogeneous or layered models with analytical solutions,and the secondary（scattered） fields are solved by the finite-element method.The linear system of equations is solved by using the large-scale sparse matrix parallel direct solver,which greatly improves the computational efficiency.The inversion algorithm was based on damping leastsquares and singular value decomposition and combined the pseudo forward modeling and reciprocity principle to compute the Jacobian matrix.Synthetic and field data were used to test the effectiveness of the proposed method.

Diurnal characteristics of geoelectric fields and their changes associated with the Alxa Zuoqi M_S5.8 earthquake on 15 April 2015(Inner Mongolia)

In China, efforts are being made to monitor geoelectric fields through a large network of stations deployed and managed by the China Earthquake Administration. The diurnal variations in the geoelectric field waveforms were similar in the quiet magnetic periods when K〈5 （generally, K〈3 indicates a quiet time）. The arrival time points of the maxima in the geoelectric field waveforms exhibited differences in local time related to geographic longitude. The amplitude of diurnal variation was several to 16.6 mV/km and decreased with increasing latitude. Further, the amplitude of diurnal variation, which was related to seasonal changes, was larger in summer and autumn than in spring and winter. The periods of diurnal changes during quiet days were 24, 12, 8, 6, 4 hours and several minutes over large areas. Finally, the observed diurnal variations in geoelectric field prior to the Alxa Zuoqi Ms5.8 earthquake on 15 April 2015 were studied, and pronounced changes in the spectral values of the geoelectric fields were found to be associated with the Alxa Zuoqi earthquake in Inner Mongolia.

Study on the variation characteristics of the geoelectric field preceding earthquakes

Earthquake events occurred in Nantong, Jiangsu Province on Nov. 3, and Dec. 25, 2001 in which the biggest mag-nitudes were ML=3.8 and ML=4.1, respectively. This paper firstly explains the principle of the eliminating noise method by the multi-dipole observation system of geoelectric field. Then based on the observation data of the multi-dipole observation system obtained by ZD9A telluric current monitors installed in Chongming and Nanjing stations, we study the abnormal variation of the geoelectric field preceding the earthquakes. The study shows that: a) Eliminating noise method of multi-dipole observation is an excellent method by which many kinds of geoelec-tric field noises can be eliminated successfully and the geoelectric precursor information can be recognized; b) The geoelectric precursor signals for the events were recorded on the NS and NE dipoles in Chongming station 42 days, 20 days and 2 days before the earthquakes respectively, in which the station is near the epicenter, and the longest time of persisting period was 9 days. The abnormal variation signals of geoelectric field observed in Nanjing sta-tion are all the noises but not the seismic electric signals, in which the station is not near the epicenter; c) Dipole distribution method of common electrode is not good in the multi-dipole observation system of the geoelectric field.

Research on dependence of resistivity changing anisotropy on microcracks extending in rock with experiment

Multiple electrodes are arranged on the surfaces of cubic granite samples of different sizes according to pre-designed patterns. Smples are fully saturated with water in vacuum. Waterproof insulation glue is coated on the measuring surfact and asmall parts (including two arrises) of the adjacent surfeces of the saturated sample to ensure that the electric current flows only within the sample through the connection between the electrodes. The multiple electrodes are combined form arrays of different direction and specing with symmetrical four-clectrode method according to need of measuring of resistivity changing anisotropy, electric profiling and electric sounding. The samples are placed into container filled with water. The samples are uniaxially compressed along the direction parallel to the longest dimension of the cubic, and the variation of resistivity during the whole loading process is observed. In the experiments, some samples are loaded to rupture with macro-fractures, some are only loaded to the Stage, which shows obvious Precursors in variation of resistivity associated with the indication of forthcoming rupture. Finally a quantitative comparison batween the dominant orientation of pre-existing cracks in photo-micrography of unruptured Samles and those macro-fractures in ruptured sample is made, together with theirrespective resistivity changing anisotropy behaviors. The experimental results are the following: ① For measuring points in areas that are passed by craks or rupture bands, the directions of principal anisotropy axes dedued from four kinds of combined equation sets are essentially identical with each other, and accord with the orientation of cracks or main rupture bands approximately. For measuring points in areas without crack or rupture band passing through, either the directions of calculated principal anisotropy axes by different combinatorial arrays are inconsistent with each other, or the principal anisotropy axis cannot be determined, especially in the cases where the crack plane is parallel to the measuring surface.② The dominant orientation of microfractures or rupture bands shown from micrographs is close to the direction of principal anisotropy axis along which the variation in resistivity is the greaest.③ The results of electric profiling can be used for detecting the localization of cracks.

Spectrum characteristics of geoelectric field variation

The spectrum characteristics of geoelectric diurnal variation and geoelectric storm have been identified by maximum entropy method, based on geoelectric data from seven stations in the Chinese mainland, including Jiayuguan, Changli and Chongming. The study shows that, in geoelectric diurnal variation, the amplitude of the 12 h semidiurnal wave is the largest, followed in turn by the 24-25 h diurnal wave and the 8 h periodic wave; Geoelectric storm usually occurs in a large-scale space, whose spectrum values are higher than those of geoelectric diurnal variation by 2-3 orders of magnitude. A preliminary interpretation is presented for the generative mechanism of predominant waves in geoelectric field variation.

Calculation of the parameters of georesistivi－ty anisotropy and case history of earthquake precursors

This paper has discussed the effective resistivity ellipse and the paradoxical phenomenon of anisotropy. Two cases have been discussed, namely: there are three measuring lines at arbitrary angles with one another and there are two mutually perpendicular measuring lines and an additional measurement of the transversal effective resistivity. For these cases, the paper has given the methods for quantitatively calculating the parameters of georesistivity anisotropy. The formulae given include those for calculating the azimuth (of the principal axis of minimum resistivity ρ 1, the average resistivity ( ρ 1ρ 3) 1/2 , (ρ 2ρ 3) 1/2 , and the anisotropy coefficient λ=(ρ 2/ρ 1 ) 1/2 . As a case history, the data observed by the Datong geoelectricity station have been processed with reference to the results of in situ resistivity measurement in media subjected to shear. The results of analysis have led to the following understandings. Before and after the Datong M S6.1 earthquake on October 19, 1989, the abnormal rise of NE trending georesistivity and abnormal fall of NW trending georesistivity observed at the Datong and Yangyuan stations were caused by the pure shear acting on the medium. The major principal compression was in NE direction, which made an acute angle with the strike of the seismic fault plane, and thus there was a greater shear stress but very small normal stress so that the fault was likely to slide but the earthquake was only of moderate magnitude. The states of stress in medium were the same before and after earthquake and therefore the georesistivity precursor was of the same sign as that of co seismic variations.

A Hydrogeophysical Model of the Relationship between Geoelectric and Hydraulic Parameters, Central Jordan

Geoelectrical soundings using the Schlumberger array were carried out in the vicinity of 23 pumping test sites to determine aquifer parameters, central Jordan. On the basis of aquifer geometry, the area has been di-vided into two hydraulic units: the northern flood plain and the flood plain to its south. Field resistivity data are interpreted in terms of the true resistivity and thickness of subsurface layers. These parameters are then correlated with the available pumping test data. Significant correlations between the transmissivity and modified transverse resistance as well as between the hydraulic conductivity and formation factor were ob-tained for the two hydraulic units, in central Jordan are presented here.

Geologic-Geophysical Indicators of the Deep Structure of Zones of Geothermal Anomalies for Allocation of Channels of the Deep Heat and Mass Transfer

On the basis of the analysis of field thermogeochemical data along abnormal zones of a thermal stream in the Bukhara-Khiva, oil-and-gas region of the Turan (Tegermen, Chagakul, Shimoly Alat, Beshtepa) was succeeded to obtain important data on a deep structure of sites. Data of gas-chemical and geothermal observations show about confinedness of abnormal concentration of methane to zones of the increased values of the temperature field the measured values of temperatures (Tegermen Square and others). On geoelectric section mines 2-D of inversion of the MT-field depth of 4000 m are lower, among very high-resistance the chemogenic and carbonate deposits of the Paleozoic is traced the subvertical carrying-out abnormal zone. This zone is identified as the channel of a deep heat and mass transfer with which hydrocarbon (HC) deposits are connected. It is shown that electro-investigation when using a geophysical complex can and has to become “advancing” at exploration by oil and gas.

Studies on earthquake precursors in China:A review for recent 50 years

Since the 1960s, China has been conducting a persistent and systematic observation and monitoring experiment to falsify the hypothesis of premonitory anomalies and the predictability of earthquakes and the application of the assessment of time-dependent seismic hazard to the reduction of earthquake disaster risk. Such an endeavor, with cases of both successes and failures, provided lessons which are heuristic for the studies in earthquake science and social sustainability. This paper provides the back- ground information of such an endeavor, discussing on the achievements and space for improvements of this lane lastin~ ~ncl cantintrint7 ~ffnrl-

Clayey Sand Soil's Behaviour Analysis and Imaging Subsurface Structure via Engineering Characterizations and Integrated Geophysicals Tomography Modeling Methods

The geoelectrical resistivity and seismic refraction surveys which were used in this study on the test site, delivered a detailed image of the near-surface conditions in generally very good. Electrical resistivity and seismic refraction analysis proved that a combination of these integrated study of the physical environmental data provided a reasonable compromise between measurement time and image resolution. Quantitative interpretation of the resistivity and seismic models based on soil's parameters determined using laboratory practices and field survey could reproduce the range of resistivity and seismic values found on the site very well. The model explains the ambiguity in between resistivity and clayey sands found on the site and predict the dominant role of water saturation. Geophysical methods are used in this research in purpose to determine the internal structure of a soil mass. Various geophysical methods and their merits for imaging subsurface structures and condition are discussed. Seismic methods are often the most suitable because the measurements depend on the mechanical properties which are also important in the mechanical calculation of soil's behaviour analysis. Other geophysical method, such as geoelectric resistivity, is useful to determine the internal structure, but require a correlation of found boundaries with mechanical properties. This research was conducted to investigate the subsurface structures and conditions through geotechnical engineering properties and its geophysical characteristics. The computation analysis is used in this research in purpose to investigate clayey sand soil's behaviour. Electrical resistivity test and engineering laboratory practices such as soil strength test, liquid limit test, plastic limit test and grain size distribution test was also carried out to investigate clayey sand soil behaviour in Batu Uban, Penang area during monitoring period.

Evidence of Iron Mineralization Channels in the Messondo Area (Centre-Cameroon) Using Geoelectrical (DC &IP) Methods: A Case Study

A geophysical survey was conducted in the Kelle-Bidjocka village, Messondo subdivision, in the Centre Region, Cameroon. The data acquisition was made by combining Schlumberger profiling and electrical soundings along six (06) profiles of 1500 m in length for a total of 64 geoelectrical stations’ survey conducted through a variable mesh 100 m × 200 m, or 100 m × 300 m. The equipment used is the DC resistivimeter Syscal Junior 48 (Iris Instrument). Processing and modelling of field data are made by using the Res2Dinv, Qwseln and Surfer software. The investigation methods used are electrical resistivity (DC) and induced polarization (IP) methods. The analyses and interpretations have helped to highlight areas of weakness or conductive discontinuities (fractures, faults, shear zones, etc.) in Precambrian gneiss formations, sometimes undergoing weathering processes. They identify the weathering or mineralogical accumulation horizons, the most promising is a mineralization channel identified in the NE-SW direction. The highlighted mineralization is characterized by strong gradients of chargeability or polarization. Samples and other geological evidences observed in the area are used to associate the most polarizable structures with ferriferous formations. Weakly polarizable and particularly conductive backgrounds identified by the inverse pseudo-sections are thought to be sulphate minerals or groundwater targets for future hydrogeological studies.

Chemical grout diffusion in porous rock based on response of geoelectric feld

Porous rock chemical grouting simulation test was conducted using established large scale physical model.Chemical grout diffusing rule in porous media with different permeability was studied by monitoring the spontaneous potential and exciting current response during grouting.The results show that chemical grout spread evenly in all directions and diffusion areas are approximately concentric circles in the cross section of homogeneous transverse isotropic pore medium,the grout spread flling range can be quantitatively decrypted by the diffusion radius.The average diffusion speed and radius increase approximately as the square root with the permeability coeffcient in different permeability media under the same conditions.Calculation results using Maag cylindrical diffusion equation show that the calculated value of diffusion radius is in good agreement with the test value under different grouting pressures and permeability conditions.

Groundwater Investigation Using Geoelectrical Method: A Case Study of the Western Region of Cameroon

A geoelectrical survey using the electrical resistivity method was carried out in some villages in the western region of Cameroon to investigate the sub-surface layers and evaluate the characteristics of aquifers. The direct current electrical resistivity method was utilized for the present study. Applying the Schlumberger array, a total of twenty four (24) Vertical Electrical Soundings (VES) were conducted. Quantitative and qualitative interpretations of data were carried out to determine the nature and thickness of the aquifer zone combined with existing litho-logs aided correlation of geoelectric sections to litho-logs. Four to five geoelectric layers were delineated from the survey area. The first layer which is the topsoil has resistivity values ranging from 6 - 949 Ωm and the thickness is between 0.2 - 4.2 m. The second layer which is made up of clay and laterite has resistivity values ranging between 9 - 1862 Ωm and thickness range from 1.0 - 16.4 m. The third and fourth geoelectric layers are made up of clay and granite/basalts with thickness varying from 2.2 - 39.5 m which corresponds to an aquifer horizon. Resistivity values of the aquifer ranges from 10 to 70,506 Ωm. The resistivity map drawn from these measurements shows the presence of a low resistivity zone which indicates the reflection in the direction of ground water from northeast to southwest with the recharge concentrated to the south of the study area. This study has revealed for this area, an average depth of the aquifer of 32 m with the average thickness of the aquifer being 22 m. The geoelectric sections of some VES stations demarcated corroborate very well with the geological description of the area.