Tectonic boundaries in the South China Sea from aeromagnetic signature

Magnetic data has been widely applied in the tectonic division.High-resolution magnetic data were used to analyze the geotectonic zoning of the South China Sea.Based on the newly compilated magnetic data,the processing results and the distribution of known faults,we consider that the U-shaped line approximately along the South China Sea national boundary of China shown in the magnetic map is a significant geological and geophysical boundary.We first described the linear characteristics of the magnetic data and then applied pseudo-gravity,Euler deconvolution,tilt derivatives,and the texture segmentation method to process the data.Results show that the dividing line between the South China Sea and the surrounding blocks is approximately along this U-shaped line.The dividing line between the South China domain and the South China Sea domain is along with the Dongsha Islands to Xisha Trough,which is different from the previous geophysical zoning results.Our results are almost consistent with those of the gravity data indicating roughly the tectonic zonation along the U-shaped line.

Development characteristics and failure modes of reactivated ancient landslides in the Sichuan–Tibet transportation corridor,China

The risk of reactivated ancient landslides in the Sichuan–Tibet transportation corridor in China is significantly increasing,primarily driven by the intensification of engineering activities and the increased frequency of extreme weather events.This escalation has resulted in a considerable number of fatalities and extensive damage to critical engineering infrastructure.However,the factors contributing to the reactivation and modes of destruction of ancient landslides remain unknown.Therefore,it is imperative to systematically analyze the developmental characteristics and failure modes of reactivated ancient landslides to effectively mitigate disaster risks.Based on a combination of data collection,remote sensing interpretation,and field investigations,we delineated the developmental attributes of typical ancient landslides within the study area.These attributes encompass morphological and topographic aspects,material composition,and spatial structure of ancient landslides.Subsequently,we identified the key triggers for the reactivation of ancient landslides,including water infiltration,reservoir hydrodynamics,slope erosion,and excavation,by analyzing representative cases in the study area.Reactivation of ancient landslides is sometimes the result of the cumulative effects of multiple predisposing factors.Furthermore,our investigations revealed that the reactivation of these ancient landslides primarily led to local failures.However,over extended periods of dynamic action,the entire zone may experience gradual creep.We categorized the reactivation modes of ancient landslides into three distinct types based on the reactivation sequences:progressive retreat,backward thrusting,and forward pulling–backward thrusting.This study is of great significance for us to identify ancient landslides,deepen our understanding of the failure modes and risks of reactivated ancient landslides on the eastern margin of the Tibetan Plateau,and formulate effective disaster prevention and mitigation measures.

Determination of the early Paleozoic accretionary complex in Southwestern Yunnan, China: Implications for the tectonic evolution of the Proto-Tethys Ocean

Accretionary complex study provides important knowledge on the subduction and the geodynamic processes of the oceanic plate,which represents the ancient ocean basin extinction location.Nevertheless,there exist many disputes on the age,material source,and tectonic attribute of the Lancang Group,located in Southwest Yunnan,China.In this paper,the LA-ICP-MS detrital zircon U‒Pb chronology of nine metamorphic rocks in the Lancang Group was carried out.The U‒Pb ages of the three detrital zircons mainly range from 590-550 Ma,980-910 Ma,and 1150-1490 Ma,with the youngest detrital zircons having a peak age of about 560 Ma.The U‒Pb ages of the six detrital zircons mainly range from 440-460 Ma and 980-910 Ma,and the youngest detrital zircon has a peak age of about 445 Ma.In the Lancang Group,metamorphic acidic volcanic rocks,basic volcanic rocks,intermediate-acid intrusive rocks,and high-pressure metamorphic rocks are exposed in the form of tectonic lens in schist,rendering typical melange structural characteristics of“block+matrix”.Considering regional deformation and chronology,material composition characteristics,and the previous data,this study thinks the Lancang Group may be an early Paleozoic tectonic accretionary complex formed by the eastward subduction of the Changning-Menglian Proto-Tethys Ocean,which provides an important constraint for the Tethys evolution.

Remote sensing-based dynamic monitoring and environmental change of wetlands in southern Mongolian Plateau in 2000‒2018

The environmental change in the wetlands in the southern Mongolian Plateau has important impacts on the environment of North China and even the entire Northeast Asia,from which the global climate change can be understood on a large scale,especially the climate change in the Mongolian Plateau.This study extracted the information on the wetlands from three stages of remote sensing images(also referred to as RS images)of the study area,including Enhanced Thematic Mapper Plus(ETM+)images of 2000,TM images of 2010,and Landsat 8 Operational Land Imager(OLI)images of 2018.As indicated by the extraction results,the area of wetlands decreased from 796.90 km^(2) of 2000 to 666.24 km^(2) of 2018 at a rate of 7.26 km^(2)/a.The reduced area is 130.66 km^(2),which is about 16.4%reduction.And the patch number of wetlands decreased from 731 of 2000 to 316 of 2018 in the study area,approximately 56.8%reduction(415 patches),and the decrease in the area of the wetlands mainly occurred in the northwest endorheic region.In terms of wetland types,the change of the wetlands was dominated by the decrease of lacustrine wetlands,of which the area and patch number decreased by 106.2 km^(2) and 242,respectively.Furthermore,the area of the lacustrine wetlands decreased at the highest rate of 8.70 km^(2)/a in 2010‒2018.From the perspective of spatial distribution,the wetlands in the western part shrunk more notably than those in the eastern part as a whole in the study area.According to local meteorological data,the precipitation gently decreased and the temperature increased(about 1.7℃)from 1975-2018.Overall,the decrease in the area of the wetlands and the temperature rises in the study area were mainly driven by the Mongolian monsoon climate,reduction in precipitation,and human activities.

Distribution of wetlands and salt lakes in the Yadong region of Tibet based on remote sensing, and their geo-climatic environmental changes

Based on the 16 scenes GF-1 satellite multi-spectral remote sensing images,through the adoption of data processing methods including orthorectification,geometric rectification,data fusion and image mosaic,integrated with field surveys,the remote sensing interpretation signs for the inland wetland types have been built,and the remote sensing survey of inland wetlands in Yadong region has been initiated,with six types of inland wetlands recognized in Yadong region,namely permanent rivers,seasonal rivers,lakes,salt lakes,alpine meadows,and inundated land.The spatial distribution characteristics and the spreading rules of these wetlands have also been revealed.Based on full understanding of the overall characteristics of the inland wetlands in the Yadong region,using the three phases of TM images acquired in 1989,2003 and 2008 as well as the PMS2 data gathered by GF-1 in 2014,and the wide-range data(WFV3)gathered by GF-1 in 2020.As to the typical salt lakes,a long-time salt lakes transition study was carried out.The results show that the typical salt lakes in Yadong have been shrinking in the past three decades.The average annual shrinkage of Duoqing Co(Co means lake in Tibetan)was stronger than that of Gala Co,which are respective 87.30 hectares(usually short as ha;1 ha equals to 0.01 km^(2))/a and 24.20 ha/a;the shrinkage degree of Gala Co was higher than that of Duoqing Co,shrank by 59.27% and 35.73% respectively.Based on the remote sensing survey results and an integrated analysis of the predecessors’researchers,the reason for the shrinkage of the salt lakes is more inclined to geological factors.Geological process is manifested by a series of extensional faults at the bottom of the lake basin generated from tectonic activities,providing fluid infiltration channels,and inducing the eventual leakage of lake water to the lower strata.The result provides an important instance for understanding the evolution characteristics of wetlands and salt lakes in specific environment of the Tibetan Plateau.

Characteristics and Geological Significance of Aeromagnetic Data in Taiyuan,Shanxi,China

The study area is located in the central part of Shanxi Province,between Qinling Tectonic Belt and Yinshan Tectonic Belt,which is an important part of North China Platform;General direction of the structural line is NNE,with clear geological structure outline and developed structural features.The study area has complex regional geological structure,intense tectonic movement and frequent magmatic activities.Based on the latest high-precision aeromagnetic data,integrated interpretation was completed,combining with the existing geological and geophysical research results.According to the block features in different zones of the RTP aeromagnetic data,this article thoroughly studied the characteristics of aeromagnetic anomalies and found the relationship between aeromagnetic anomalies and surface geological information,and the fault distribution,magmatic rock distribution and magnetic characteristics in this area are discussed.

Research achievements of the Qinghai-Tibet Plateau based on 60 years of aeromagnetic surveys

The Qinghai-Tibet Plateau(also referred to as the Plateau)has long received much attention from the community of geoscience due to its unique geographical location and rich mineral resources.This paper reviews the aeromagnetic surveys in the Plateau in the past 60 years and summarizes relevant research achievements,which mainly include the followings.(1)The boundaries between the Plateau and its surrounding regions have been clarified.In detail,its western boundary is restricted by West Kunlun-Altyn Tagh arc-shaped magnetic anomaly zone forming due to the arc-shaped connection of the Altyn Tagh and Kangxiwa faults and its eastern boundary consists of the boundaries among different magnetic fields along the Longnan(Wudu)-Kangding Fault.Meanwhile,the fault on the northern margin of the Northern Qilian Mountains serves as its northern boundary.(2)The Plateau is mainly composed of four orogens that were stitched together,namely East Kunlun-Qilian,Hoh-Xil-Songpan,Chamdo-Southwestern Sanjiang(Nujiang,Lancang,and Jinsha rivers in southeastern China),and Gangdese-Himalaya orogens.(3)The basement of the Plateau is dominated by weakly magnetic Proterozoic metamorphic rocks and lacks strongly magnetic Archean crystalline basement of stable continents such as the Tarim and Sichuan blocks.Therefore,it exhibits the characteristics of unstable orogenic basement.(4)The Yarlung-Zangbo suture zone forming due to continent-continent collisions since the Cenozoic shows double aeromagnetic anomaly zones.Therefore,it can be inferred that the Yarlung-Zangbo suture zone formed from the Indian Plate subducting towards and colliding with the Eurasian Plate twice.(5)A huge negative aeromagnetic anomaly in nearly SN trending has been discovered in the middle part of the Plateau,indicating a giant deep thermal-tectonic zone.(6)A dual-layer magnetic structure has been revealed in the Plateau.It consists of shallow magnetic anomaly zones in nearly EW and NW trending and deep magnetic anomaly zones in nearly SN trending.They overlap vertically and cross horizontally,showing the flyover-type geological structure of the Plateau.(7)A group of NW-trending faults occur in eastern Tibet,which is intersected rather than connected by the nearly EW trending that develop in middle-west Tibet.(8)As for the central uplift zone that occurs through the Qiangtang Basin,its metamorphic basement tends to gradually descend from west to east,showing the form of steps.The Qiangtang Basin is divided into the northern and southern part by the central uplift zone in it.The basement in the Qiangtang Basin is deep in the north and west and shallow in the south and west.The basement in the northern Qiangtang Basin is deep and relatively stable and thus is more favorable for the generation and preservation of oil and gas.Up to now,19 favorable tectonic regions of oil and gas have been determined in the Qiangtang Basin.(9)A total of 21 prospecting areas of mineral resources have been delineated and thousands of ore-bearing(or mineralization)anomalies have been discovered.Additionally,the formation and uplift mechanism of the Plateau are briefly discussed in this paper.

Geological characteristics,metallogenic regularity,and research progress of lithium deposits in China

China is rich in abundant lithium resources characterized by considerable reserves and a concentrated distribution of metallogenic zones or belts,with proven reserves of 4046.8×10^(3) t(calculated based on Li_(2)O)by 2021.China is also a big consumer of lithium.By 2019,China’s lithium consumption in the battery sector alone had reached 99×10^(3) t,with an average annual growth rate of nearly 26%.China has become the world’s largest importer of lithium resources,showing a severely unbalanced relationship between supply and demand for lithium resources.Therefore,there is an urgent need for the prospecting,exploitation,and study of lithium resources in China.This study collected,organized,and summarized the data on the major lithium deposits in China,analyzed and compared the spatial-temporal distribution patterns,geological characteristics,and metallogenic regularity of these lithium deposits,and summarized the prospecting and research achievements over the last decade.The major lithium deposits in China are distributed in provinces and regions such as Qinghai,Jiangxi,Sichuan,Tibet,and Xinjiang.These deposits are mostly small in scale.According to different genetic types,this study divided lithium deposits into granitic pegmatite type,granite type,saline lake brine type,underground brine type,and sedimentary type,as well as new types including hot spring type and magmatic-hydrothermal type,and summarized the characteristics and key metallogenic factors of these different types of deposits.Sixteen metallogenic prospect areas of lithium deposits were delineated according to the deposit types and the distribution patterns of metallogenic belts.The paper introduced the research progress in major metallogenic models and lithium extraction techniques made over the past decade.Based on the comprehensive analysis of the prospecting potential of lithium deposits,the authors concluded that the future prospecting of lithium resources in China should focus on lithium metallogenic belts,the deep and peripheral areas of currently determined large-scale pegmatite-type lithium deposits,geophysical-geochemical anomalous areas with mineralization clues,and areas with developed large-scale low-grade associated granite-type and sedimentary lithium resources.The study aims to serve as a guide for the future prospecting of lithium deposits in China.

Deformation Evolution Characteristics Revealed by GPS and Cross-fault Leveling Data before the M_S8. 0 Wenchuan Earthquake

Based on GPS velocity during 1999-2007,GPS baseline time series on large scale during1999-2008 and cross-fault leveling data during 1985-2008,the paper makes some analysis and discussion to study and summarize the movement,tectonic deformation and strain accumulation evolution characteristics of the Longmenshan fault and the surrounding area before the MS8. 0 Wenchuan earthquake,as well as the possible physical mechanism late in the seismic cycle of the Wenchuan earthquake. Multiple results indicate that:GPS velocity profiles show that obvious continuous deformation across the eastern Qinghai-Tibetan Plateau before the earthquake was distributed across a zone at least 500 km wide,while there was little deformation in Sichuan Basin and Longmenshan fault zone,which means that the eastern Qinghai-Tibetan Plateau provides energy accumulation for locked Longmenshan fault zone continuously. GPS strain rates show that the east-west compression deformation was larger in the northwest of the mid-northern segment of the Longmenshan fault zone,and deformation amplitude decreased gradually from far field to near fault zone,and there was little deformation in fault zone. The east-west compression deformation was significant surrounding the southwestern segment of the Longmenshan fault zone,and strain accumulation rate was larger than that of mid-northern segment.Fault locking indicates nearly whole Longmenshan fault was locked before the earthquake except the source of the earthquake which was weakly locked,and a 20 km width patch in southwestern segment between 12 km to 22. 5 km depth was in creeping state. GPS baseline time series in northeast direction on large scale became compressive generally from 2005 in the North-South Seismic Belt,which reflects that relative compression deformation enhances. The cross-fault leveling data show that annual vertical change rate and deformation trend accumulation rate in the Longmenshan fault zone were little,which indicates that vertical activity near the fault was very weak and the fault was tightly locked. According to analyses of GPS and cross-fault leveling data before the Wenchuan earthquake,we consider that the Longmenshan fault is tightly locked from the surface to the deep,and the horizontal and vertical deformation are weak surrounding the fault in relatively small-scale crustal deformation. The process of weak deformation may be slow,and weak deformation area may be larger when large earthquake is coming. Continuous and slow compression deformation across eastern Qinghai-Tibetan Plateau before the earthquake provides dynamic support for strain accumulation in the Longmenshan fault zone in relative large-scale crustal deformation.

Temporal variations of reference evapotranspiration and controlling factors:Implications for climatic drought in karst areas

Variations in reference evapotranspiration(ET_(0)) and drought characteristics play a key role in the effect of climate change on water cycle and associated ecohydrological patterns.The accurate estimation of ET_(0) is still a challenge due to the lack of meteorological data and the heterogeneity of hydrological system.Although there is an increasing trend in extreme drought events with global climate change,the relationship between ET_(0) and aridity index in karst areas has been poorly studied.In this study,we used the Penman-Monteith method based on a long time series of meteorological data from 1951 to 2015 to calculate ET_(0)in a typical karst area,Guilin,Southwest China.The temporal variations in climate variables,ET_(0)and aridity index(AI)were analyzed with the Mann-Kendall trend test and linear regression to determine the climatic characteristics,associated controlling factors of ET_(0) variations,and further to estimate the relationship between ET_(0) and AI.We found that the mean,maximum and minimum temperatures had increased significantly during the 65-year study period,while sunshine duration,wind speed and relative humidity exhibited significant decreasing trends.The annual ET_(0) showed a significant decreasing trend at the rate of−8.02 mm/10a.However,significant increase in air temperature should have contributed to the enhancement of ET_(0),indicating an“evaporation paradox”.In comparison,AI showed a slightly declining trend of−0.0005/a during 1951-2015.The change in sunshine duration was the major factor causing the decrease in ET_(0),followed by wind speed.AI had a higher correlation with precipitation amount,indicating that the variations of AI was more dependent on precipitation,but not substantially dependent on the ET_(0).Although AI was not directly related to ET_(0),ET_(0)had a major contribution to seasonal AI changes.The seasonal variations of ET_(0)played a critical role in dryness/wetness changes to regulate water and energy supply,which can lead to seasonal droughts or water shortages in karst areas.Overall,these findings provide an important reference for the management of agricultural production and water resources,and have an important implication for drought in karst regions of China.

Petrology, geochemistry and Ar-Ar geochronology of eclogites in Jinshajiang orogenic belt, Gonjo area, eastern Tibet and restriction on Paleo-Tethyan evolution

As one of the important Paleo-Tethys suture zones in eastern Tibet,the Jinshajiang orogenic belt is of great significance to study the tectonic evolution of the main suture zone of Paleo-Tethys.In this paper,eclogites developed in the Jinshajiang suture zone in Gonjo area,eastern Tibet,are selected as specific research objects,and petrological,geochemical and Ar-Ar geochronological analyses are carried out.The major element data of the whole rock reveals that the eclogite samples have the characteristics of picritic basalt-basalt and belong to the oceanic low potassium tholeiites.The results of rare earth elements and trace elements of the samples show that the protoliths of eclogites have characteristics similar to oceanic island basalt(OIB)or normal mid ocean ridge basalt(N-MORB).Muscovite(phengite)from two eclogite samples yield the Ar-Ar plateau ages of 247±2 Ma and 248±2 Ma respectively,representing the peak metamorphic age of eclogite facies and the timing of complete closure of the Jinshajiang Paleo-Tethys Ocean.Muscovite and biotite selected from the hosting rocks of eclogite yield the Ar-Ar plateau ages are 238±2 Ma and 225±2 Ma respectively,reflecting the exhumation age of eclogites and their hosting rocks.Combined with the zircon U-Pb dating data(244 Ma)of eclogites obtained in previous work,it can be concluded that the Jinshajiang Paleo-Tethys ocean was completely closed and arc-continent collision was initiated at about 248-244 Ma(T21).Subsequently,due to the large-scale arc(continent)-collision orogeney between Deqin-Weixi continental margin arc and Zhongza block(T31-T32),the eclogites were rapidly uplifted to the shallow crust.

Spatiotemporal distribution of regional landslides and erosion rates in Southeastern Tibet

The difficulty in estimating ages of regional landslides hampers to assess frequency of landslides and hence to quantitatively assess regional landslide hazard.In this study,we used radiocarbon dating of organic sediment on boulder rock varnish to estimate landslide ages in Langxian(LX)arid region in southeastern Tibet.Samples of rock varnish with organic sediment were collected on site for radiocarbon dating,leading to landslide ages from 1880±30 to 18,430±30 yr B.P.To measure surface roughness characteristics of 109 remotely-mapped large bedrock landslide deposits,we estimated average standard deviation of slope(SDS)over an area of~640 km^(2) by calculating the slope gradient of each raster cell and using a rectangular moving window method in Arc Map from a 5 m-resolution Digital Elevation Model generated from helicopterobtained photographs.Combing estimated landslide ages(t)with average surface roughness of mapped landslide deposits(R)quantified by SDS,we fit an exponential landslide deposits surface roughness-age function(t=1.47×10^(6)×e^(-1).46R,r2=0.63)that was used to estimate regional landslide ages in LX.We conclude that three periods with clusters of regional landslides in LX were revealed by different surface roughness of landslide deposits combing roughness-age function,with the values of 5563-7455 yr B.P.,1724-4151 yr B.P.,and 960-1287 yr B.P..Furthermore,we used our estimates of landslide ages to quantify landslide erosion rates of three corresponding hillslopes in LX ranging from 0.50 to 2.42 mm yr-1.Although rock varnish radiocarbon dating provides us a feasible option for timing regional landslides of arid regions,the epistemic uncertainty in the dating method should arouse our attention,which could be reduced by increasing the number of samples.

Geophysical prospecting of copper-nickel deposits in Beishan rift zone, Xinjiang

The Beishan rift zone in Xinjiang Uygur Autonomous Region was formed due to strong activities of faults on the basement of the Tarim continental crust.Despite the fact that many geological research results of the rift zone have been achieved,only a few studies have been conducted on its regional geophysical characteristics.In this paper,the gravity and magnetic anomalies of the rift zone were highlighted through specific data processing of 1∶50000 high-precision aeromagnetic data and gravity data with a grid spacing of 2 km×2 km.Based on this,the geophysical evidence for the scope and internal structures of the Beishan rift zone was obtained for the first time.The distinct characteristics of magnetic and gravity fields in the areas to the north and south of the Beishan rift zone reveal that deep faults exist between the Beishan rift zone and the geological units on the southern and northern sides.Furthermore,the faults on the two areas contain the bidirectional thrusts and have flower-shaped structures according to the characteristics of the magnetic and gravity fields.The Beishan rift zone can be divided into two tectonomagmatic zones,namely the Zhongposhan-Bijiashan-Cihai-Baishanliang zone(the northern zone)and the Bayiquan-Qixin-Baishan zone(the southern zone).The northern zone can be further subdivided into three comet-shaped anomaly groups(tectonomagmatic areas),while the southern zone can be further subdivided into two tectonomagmatic areas.According to the characteristics of aeromagnetic anomalies and gravity field,19 mafic-ultramafic complexes were delineated.The known Pobei,Hongshishan,and Qixin complexes are all located within the inferred complexes,with estimates of total explored resources of Ni,Cu,and Au of 3×10^(6) t,10×10^(3) t and 10 t,respectively.The prospecting of high-grade copper-nickel deposits should focus on the periphery and deep parts of the known and inferred mafic-ultramafic complexes.Among them,the peripheral strata of the complexes specifically have great prospecting potential of large-scale high-grade copper-nickel deposits of magma injection type.Finally,this paper analyzed the application effects of the rapid airborne-ground-drilling synergetic exploration method in the prospecting of copper-nickel deposits in Qixin,Beishan,Xinjiang,which will provide references for further exploration of copper-nickel deposits in Beishan area,Xinjiang.

Hydrodynamic characteristics of a typical karst spring system based on time series analysis in northern China

In order to study the hydrodynamic characteristics of the karst aquifers in northern China,time series analyses(correlation and spectral analysis in addition with hydrograph recession analysis)are applied on Baotu Spring and Heihu Spring in Jinan karst spring system,a typical karst spring system in northern China.Results show that the auto-correlation coefficient of spring water level reaches the value of 0.2 after 123 days and 117 days for Baotu Spring and Heihu Spring,respectively.The regulation time obtained from the simple spectral density function in the same period is 187 days and 175 days for Baotu Spring and Heihu Spring.The auto-correlation coefficient of spring water level reaches the value of 0.2 in 34-82 days,and regulation time ranges among 40-59 days for every single hydrological year.The delay time between precipitation and spring water level obtained from cross correlation function is around 56 days for the period of 2012-2019,and varies among 30-79 days for every single hydrological year.In addition,the spectral bands in cross amplitude functions and gain functions are small with 0.02,and the values in the coherence functions are small.All these behaviors illustrate that Jinan karst spring system has a strong memory effect,large storage capacity,noticeable regulation effect,and time series analysis is a useful tool for studying the hydrodynamic characteristics of karst spring system in northern China.

3D modeling of deepwater turbidite lobes:a review of the research status and progress

Deepwater turbidite lobe reservoirs have massive hydrocarbon potential and represent one of the most promising exploration targets for hydrocarbon industry.Key elements of turbidite lobes internal heterogeneity include the architectural hierarchy and complex amalgamations at each hierarchical level leading to the complex distribution of shale drapes.Due to limitation of data,to build models realistically honoring the reservoir architecture provides an effective way to reduce risk and improve hydrocarbon recovery.A variety of modeling techniques on turbidite lobes exist and can be broadly grouped into pixel-based,process-based,process-oriented,surface-based,object-based and a hybrid approach of two or more of these methods.The rationale and working process of methods is reviewed,along with their pros and cons.In terms of geological realism,object-based models can capture the most realistic architectures,including the multiple hierarchy and the amalgamations at different hierarchical levels.In terms of data conditioning,pixel-based and multiple-point statistics methods could honor the input data to the best degree.In practical,dif?ferent methods should be adopted depending on the goal of the project.Such a review could improve the understanding of existing modeling methods on turbidite lobes and could benefit the hydrocarbon exploration activities of such reservoirs in offshore China.

Possible precursory anomalies in ground water level associated with the Wenchuan Ms 8.0 earthquake in 2008,Sichuan,China

We have examined the water level data from 16 wells in Sichuan province,China,recorded before the Wenchuan Ms8.0 earthquake occurred in 2008.We found that the data of 5 among these wells exhibit possible precursory anomalies,which are respectively named the Chuan No.08 well in Deyang,Chuan No.ll well in Pujiang,Chuan No.13 well in Luzhou,Chuan No.22 well in Qionglai and Beichuan.In time durations,these anomalies are of long-,intermediate-and short-term signals which are primarily distributed on the northeast(NE)trending Longmenshan fault zone as well as the parallel Huayingshan fault zone.It seems that the variations of the well levels on the Huayingshan fault zone imply compression while those on the Longmenshan fault zone reflect extension.These anomalies occurred first in the areas outside the epicenter region of the Wenchuan Ms8.0 earthquake,then migrated to the seismogenic fault zone.And they migrated from southwest to northeast in agreement with the rupture process of the main shock.

The Terminal of Mineral System Exploration in Thick Coverage Area by Gravity and Magnetic Data――A Case Study on the Nihe Iron Deposit

The study is concerned with the airborne magnetic and gravity data aiming at evaluating the terminal of mineral system.Nihe iron deposit,situated in the center of Luzong ore cluster area,is the case to our study.Different tectonic environments,source material,and preservation background illustrate distinct properties in the geophysical observation results.

Connection between earthquakes and deep fluids revealed by magnetotelluric imaging in Songyuan,China

Songyuan is the most earthquake prone area in northeast China.Since 2006,earthquakes have occurred in the area in the form of swarms,with a maximum magnitude of M_L5.8.There is much controversy about the cause of the Songyuan earthquakes.We attempted to determine the cause using a three-dimensional electrical conductivity structure inverted from a regional network of magnetotelluric data in the Songyuan area.The L-BFGS inversion method was applied,with a fullimpedance tensor data set used as the inversion input.Combined with an evaluation of the earthquake locations,the resistivity model revealed a northeast-oriented hidden fault running through the Songyuan earthquake area(SEA),which was speculated to be the preexisting Fuyu-Zhaodong Fault(FZF).Our resistivity model also found an apparent lithospheric low-resistivity anomaly beneath the earthquake area,which breached the high-resistivity lithospheric mantle and stalled at the base of the crust.A petrophysical analysis showed that this lower crustal low-resistivity anomaly was most likely attributed to hydrated partial melting,which could release water into the lower crust during later magma emplacements.While weakening the strength of the FZF,these ascending fluids also increased the pore pressure in the fault,further reducing the shear strength of the fault.Shear stress action(a fault strike component of the east-west regional compress),together with possible near-surface disturbances,may drive the fault to slip and trigger the earthquakes in Songyuan.It is possible that the continuous replenishment of fluids from the deeper mantle forces the Songyuan earthquakes into the form of swarms.We infer that the Songyuan earthquakes could be attributed to a combination of preexisting faults,regional stress,and deep fluids associated with plate subduction,and near surface disturbances might induce the earthquakes in advance.The Songyuan earthquakes are inherently induced earthquakes,fed by deep fluids.

Inversion of time-domain airborne EM data with IP effect based on Pearson correlation constraints

Due to the induced polarization(IP)eff ect,the sign reversal often occurs in timedomain airborne electromagnetic(AEM)data.The inversions that do not consider IP eff ect cannot recover the true umderground electrical structures.In view of the fact that there are many parameters of airborne induced polarization data in time domain,and the sensitivity diff erence between parameters is large,which brings challenges to the stability and accuracy of the inversion.In this paper,we propose an inversion mehtod for time-domain AEM data with IP effect based on the Pearson correlation constraints.This method uses the Pearson correlation coeffi cient in statistics to characterize the correlation between the resistivity and the chargeability and constructs the Pearson correlation constraints for inverting the objective function to reduce the non uniqueness of inversion.To verify the eff ectiveness of this method,we perform both Occam’s inversion and Pearson correlation constrained inversion on the synthetic data.The experiments show that the Pearson correlation constrained inverison is more accurate and stable than the Occam’s inversion.Finally,we carried out the inversion to a survey dataset with and without IP eff ect.The results show that the data misfit and the continuity of the inverted section are greatly improved when the IP eff ect is considered.

New hybrid algorithm for land surface temperature retrieval from multiple-band thermal infrared image without atmospheric and emissivity data inputs

Land surface temperature(LST)retrieval from thermal infrared(TIR)remote sensing image requires atmospheric and land surface emissivity(LSE)data that are sometimes unattainable.To overcome this problem,a hybrid algorithm is developed to retrieve LST without atmospheric correction and LSE data input,by combining the split-window(SW)and temperature–emissivity separation(TES)algorithms.The SW algorithm is used to estimate surface-emitting radiance in adjacent TIR bands,and such radiance is applied to the TES algorithm to retrieve LST and LSE.The hybrid algorithm is implemented on five TIR bands of the Advanced Spaceborne Thermal Emission and Reflection Radiometer(ASTER).Analysis shows that the hybrid algorithm can estimate LST and LSE with an error of 0.5–1.5 K and 0.007–0.020,respectively.Moreover,the LST error of the hybrid algorithm is equivalent to that of the original ASTER TES algorithm,involving 1%–2%uncertainty in atmospheric correction.The hybrid algorithm is validated using ground-measured LST at six sites and ASTER LST products,indicating that the temperature difference between the ASTER TES algorithm and the hybrid algorithm is 1.4 K and about 2.5–3.5 K compared to the ground measurement.Finally,the hybrid algorithm is applied to at two places.