three dimensional dynamic simulation of the 1992 landers earthquake the 1992 landers california earthquake magnitude 7 3 was modeled as the propagation of a spontaneous rupture controlled by a realistic prestress distribution with the use of a three dimensional finite difference method the dynamic rupture reproduces the general slip pattern used to compute the initial stress distribution and generates near fault ground motions at the surface similar to observations the simulated rupture propagates on the fault along a complex path with highly variable speed and rise time changing the magnitude and pattern of the stress significantly the method provides the framework to estimate earthquake rupture parameters from recorded seismic and geodetic data

textural control on gold distribution in as free pyrite from the dongping huangtuliang and hougou gold deposits north china craton hebei province china article i nfo pyrite from the dongping huangtuliang and hougou gold deposits hebei province china was investigated using a combination of ore microscopy including back scattered imaging and in situ laser ablation inductively coupled plasma mass spectroscopy la icp ms a range of elements including au te ag pb bi cu co ni and as was analyzed with the aim to constrain the textural controls and influence of superimposed deformation on the distribution of invisible gold in as free pyrite thedatasetshowsexcellentcorrespondence betweenmeasuredhighgoldvaluesandthreekeytexturalcriteria i areasofclusteredtellurideinclusions especiallyindongping ii microshearingandfracturing brecciation dongping and huangtuliang and iii pyrite recrystallization huangtuliang invisible gold is only at trace levels in the hougou and gold bearing telluride minerals are not observed this is considered to result from larger scale remobilization of gold during advanced brecciation and recrystallization of pyrite pyrite grains containing clustered inclusions have by far the highest gold concentrations up to 1 wt with consistent values of thousands of ppm au interpretation of textures and la icp ms data infers that in these areas the distribution of telluride inclusions extends pervasively from micron to nanoscale i e as fields of nanoparticles local employment of coupled dissolution reprecipitation reaction between pyrite and fluids driving the k metasomatic alteration dated at 150 ma is invoked to explain such patterns syn deformational grain scale mobilization of gold and other elements took place leading to a portion of the gold being recrystallized within fractures and microshears the deformational event leads to gold enrichment in the huangtuliang pyrite where brittle fracturing brecciation has been followed by a resorption and recrystallization in the latter case foam textured pyrites again without as can contain up to hundreds of ppm gold theinterpreted sequenceof pyritepost depositional eventsis inaccordancewith the protracted magmaticevolution of the area starting with variscan alkaline intrusions 390 ma and reactivated during the yanshanian orogeny 150 ma thestudyshows i thatas freepyritecanreadilycontainsignificantamountsofinvisiblegold bothasnanoparticles

discovery of concealed ore bodies at the dongping gold deposit northern china revealed by the study of ore controlling structures abstract the dongping gold deposit is the largest gold deposit in the hebei province china with proven gold reserves of more than 100 tons after the main gold ore bodies were mined out the dongping gold deposit faced a shortage in gold reserves with an uncertain future as a result we conducted systematic studies on the ore controlling structures at the dongping gold deposit with the aim of finding additional concealed ore bodies should these be present gold mineralization at dongping is controlled by two stages of maximum principal compressional stress 1 nw trending stress that produced the ne to nw trending structures and sub vertical stress that produced the circular structure respectively the sub vertical compressional stress may have resulted from the emplacement of a concealed intrusive body which also led to horizontal extensional stress generating structures surrounding the intrusion development of such structures potentially increased the permeability of the local crust facilitating the mobilisation of gold bearing hydrothermal fluids that subsequently precipitated along the structures forming the gold ore bodies we propose that the deep part of the dongping gold deposit at the lithological contact with the concealed intrusive bodies is prospective for the exploration of additional reserves which is supported by our subsequent drilling and the discovery of concealed gold ore bodies beneath the deposit

derivation of mesozoic adakitic magmas from ancient lower crust in the north china craton three mesozoic plutons were intruded into the archean granulite terrains in northern margin of the north china craton adjacent to the granulite xenolith bearing tertiary hannuoba basalts they are triassic guzuizi and honghualiang granites and early cretaceous zhuanzhilian diorite rocks of the three intrusions are characterized by high sr 576 1216 ppm and na2o 4 0 low y 18 ppm and heavy rare earth elements yb 1 8 ppm these features are similar to modern adakites siliceous rocks with high sodium aluminum and strontium and low heavy rare earth element and yttrium contents from island arcs and archean high al tonalite trondhjemite granodiorite ttg however they are distinctly potassium rich and their evolved strontium neodymium and hafnium isotopic compositions and inherited zircon ages coincide with those of the archean granulites and the hannuoba granulite xenoliths such features cannot readily be explained with previous models of the origin of adakites and ttgs we propose that these adakitic rocks are formed by partial melting of ancient lower crust and that the restites are represented by some of the hannuoba granulite xenoliths we further argue that this could be one major mechanism to generate voluminous mesozoic adakitic magmas in the eastern north china craton our hypothesis can also explain the discrepancies in ages and compositions between the granulite terrains and xenoliths and implies that crustal anatexis may be one of the major processes controlling the chemical differentiation of the continental crust

changes in static stress on southern california faults after the 1992 landers earthquake the magnitude 7 5 landers earthquake of 28 june 1992 was the largest earthquake to strike california in 40 years the slip that occurs in such an earthquake would be expected to induce large changes in the static stress on neighbouring faults these changes in stress should in turn affect the likelihood of future earthquakes stress changes that load faults towards failure have been cited as the cause of small1 5 moderate6 and large7 earthquakes conversely those that relax neighbouring faults have been related to a decrease in seismicity5 here we use an elastic half space model8 to estimate the stress changes produced by the landers earthquake on selected southern california faults including the san andreas we find that the estimated stress changes are consistent with the triggering of four out of the five aftershocks with magnitude greater than 4 5 and that the largest changes 1 10 bar occurring on part of the san bernardino segment of the san andreas fault may have decreased the time to the next magnitude 8 earthquake by about 14 years

focal mechanisms and aftershock locations of the songpan earthquakes of august 1976 in sichuan china the precursory swarm three mainshocks m 7 2 6 7 7 2 and aftershocks of the songpan earthquakes have been reanalyzed using both local and teleseismic data the three mainshocks of this sequence occurred on the huya fault over a 7 day period relocations of the aftershocks using local arrival times show that three fault strands were activated during this sequence each mainshock occurred on a separate strand each one south of the strand activated in the previous mainshock and the aftershock zones of each mainshock appear to abut rather than overlap fault plane solutions determined by matching teleseismic p waveforms at world wide standard seismograph network stations with synthetic seismograms are consistent with the observed aftershock zones the first and third mainshocks m 0 1 3 10 19 and 8 4 10 18 n m respectively showed almost identical senses of motion a combination of reverse and left lateral strike slip motion on parallel strands striking n15 w that were separated by a large rightstepping en echelon offset the second mainshock m 0 4 0 10 18 n m occurred in this offset on a fault at a steep angle 125 to the other two strands and showed almost pure reverse motion differences in the orientations of the slip vectors of the three mainshocks show that the first mainshock increased the normal and shear stresses on the fault segment that moved in the second mainshock and that the second mainshock decreased the normal stress on the fault segment activated by the third mainshock these changes in normal stresses may have given rise to the longer time between the first and second events 5 days as compared with the time between the second and third events 30 hours a precursory swarm that preceded the songpan sequence by 3 years occurred in a volume that surrounded the northernmost part of the planar aftershock zone the time between the start of the swarm and the mainshocks and the magnitude of the largest event in the swarm are similar to those seen for precursory swarms in soviet central asia

geochronology and geochemical characteristics of the dongping ore bearing granite north china sources and implications for its tectonic setting abstract the dongping gold deposit located in chongli county hebei province about 200 km northwest of beijing is one of the largest gold producing areas along the northern margin of the north china craton it is located in the of shuiquangou alkaline igneous complex of middle devonian age 394 3 3 2 ma composed chiefly of highly alkaline syentite and quartz syenites this study reveals the age of the carboniferous in the deposit at 351 7 2 8 ma mswd 1 9 the dongping deposit is locally hosted in cretaceous 143 1 ma alkali granites that intruded the older and the gold mineralization is closely associated genetically with this event hydrothermal zircons in the alkali granites have th u ratios mostly ranging between 0 01 and 0 7 indicating oscillatory zoning a few grains with high th u ratios 1 31 2 07 may be from metamorphic domains negative ehf t values of the zircon mainly range between 19 75 and 16 93 suggesting that they originated principally by the melting of recycled continental crust less abundant zircons with ehf t ranging from 25 76 to 23 46 with hf model ages t dm2 of 2 54 to 2 67 ga mainly 2 2 to 2 3 ga suggest that recycled neoarchean basement was also present in the source region the devonian syenites and quartz syenites have t dm1 ages ranging from 1 96 to 2 08 ga zircons from these rocks have ehf t values of 11 9 to 18 9 certain zircons from the gold bearing granite of paleozoic age have an initial 176 hf 177 hf ratio of 0 281816 to 0 282058 and 0 282147 to 0 282348 reflecting a homogenous distribution of hafnium isotopes typical of magmatic sources the t dm1 and t dm2 of the latest intrusion varying 1 33 to 1 59 ga and 1 72 to 2 11 ga respectively indicating that the neoproterozoic to mesoproterozoic rocks of this area are an important source for the younger magma which are important to forming ore deposits the tdm 2 indicate that the magma may be derived from a very old crustal basement 2 67 ga in the northern margin of north china craton by partial melting

a geodynamic perspective of world class gold deposits in east asia abstract the world class gold ore districts of south east russia and north east china are located above the frontal and peripheral regions of subducted oceanic lithosphere accumulated as stagnant slabs in the mantle transition zone generated by paleo pacific plate subduction the highly productive ore systems of the aldan south yakutiya baley transbaikalia and zhao ye jiaodong metallogenic belts which are widely separated in space but formed at the same time are associated with similar mechanisms of huge magma flare ups in the middle jurassic early cretaceous driven by deep mantle processes their common features and crust mantle interaction signature offer important clues to mantle dynamics rooted along the periphery of the subducted slabs in a mega convergent zone in east asia

dynamic rupture simulations with heterogeneous initial stresses inversed from a given slip distribution a case study of the 2017 mw 6 5 jiuzhaigou earthquake abstract heterogeneous initial stresses are extremely important in understanding the physics of earthquake rupture processes we propose a method to estimate heterogeneous initial stresses by comparing the slip from dynamic rupture simulations and the input joint inversion result and apply it to the 2017 mw 6 5 jiuzhaigou earthquake which occurred in the intersection area of the minjiang tazang and huya faults in sichuan province china with the slip distributed on two distinct left lateral strike slip faults as shown in previous geodetic and seismic joint inversion we use the seismic efficiency empirical relation to infer the average stress and the average stress drop is estimated using the static stress drop with the angle of the maximum principal stress and the nucleation fault determined from the relocated aftershocks different principal stresses are calculated with different combinations of average stress and average stress drop the initial normal and residual stresses can be determined using the projection of the principal stresses the initial shear stresses are generated by adding the residual stress and the heterogeneous stress drop which is generated by a set of gaussian random numbers with a given mean and the variance and mapped one by one with the given slip on the fault so that the area with a large slip has a large stress drop by comparing the slip from dynamic rupture simulations and the input joint inversion result we show that the case with a 36 mpa average stress and 2 1 mpa average stress drop provides the best fitting slip snapshots the dynamic coulomb stress change shows that the 2017 mw 6 5 jiuzhaigou earthquake could bring the southeast of the tazang fault and the middle of the minjiang fault closer to failure this work provides a new insight to understand the initial stresses of nature earthquakes

construction of equivalent single planar fault model for strike slip stepovers abstract non planarity is a common and natural characteristic of seismic faults that strongly affects the rupture dynamics and the associated seismic waves geometrically uniform planar fault model is widely used in studies of kinematic source inversion seismic hazard estimation and rupture dynamic simulation because of the simplicity and computational efficiency of this method the influence of the geometric heterogeneity of faults on rupture dynamics and associated seismic waves may under some circumstances be reasonably approximated by an appropriate heterogeneous distribution of shear strength of planar faults particularly for the case with uniform initial stress distribution an outstanding issue is how to approximate the dynamic behavior of a non planar fault by means of heterogeneous properties on a planar fault thus we propose the construction of an equivalent planar fault model for a given stepover fault through the introduction of a heterogeneous distribution of static friction coefficient our study shows that the distribution of static friction coefficient on the equivalent planar fault model is mainly controlled by the geometric irregularities of the stepovers regardless of the initial shear stress thereby providing a way to quantify the effect of fault geometry particularly the step width effect in seismic hazard estimation moreover our results indicate that the influence of geometric discontinuity of stepovers on rupture dynamics is equivalent to a barrier of the planar fault model

metallogeny and craton destruction records from the north china craton abstract the link between metallogeny and craton destruction in the north china craton ncc remains poorly understood particularly the mechanisms within the interior of the craton in this overview we summarize the major stages in the history of formation and evolution of the ncc the spatio temporal distribution and types of major ore species as well as mantle contribution to the metallogeny in an attempt to evaluate the geodynamic settings of metallogeny and the mechanisms of formation of the ore deposits the early precambrian history of the ncc witnessed the amalgamation of micro blocks and construction of the fundamental tectonic architecture of the craton by 2 5 ga the boundaries of these micro blocks and the margins of the ncc remained as weak zones and were the principal locales along which inhomogeneous destruction of the craton occurred during later tectonothermal events these zones record the formation of orogeny related gold copper iron and titanium during the early to middle paleoproterozoic with ages ranging from 2 5 to 1 8 ma the early ordovician kimberlite and diamond mineralization at ca 480 ma the late carboniferous and early to middle permian calc alkaline i type granitoids and gold deposits of 324 300 ma and the triassic alkaline rocks and gold silver polymetallic deposits occurring along these zones and the margins of the blocks correlate with rising mantle plume southward subduction of the siberian plate and northward subduction of the yangtze plate respectively the voluminous jurassic granitoids and cretaceous intrusives carrying gold molybdenum copper lead and zinc deposits are also localized along the weak zones and block margins the concentration of most of these deposits in the eastern part of the ncc invokes correlation with lithosphere thinning associated with the westward subduction of the pacific plate although magmatism and mineralization have been recorded along the margins and few places within the interior of the ncc in the jurassic their peak occurred in the cretaceous in the eastern part of the ncc marking large scale destruction of the craton at this time the junctions of the boundaries between the micro continental blocks are characterized by extensive inhomogeneous thinning we propose that these junctions are probably for future mineral exploration targeting in the ncc

nonlinear dynamic rupture inversion of the 2000 western tottori japan earthquake 1 we have developed a systematic nonlinear inversion method for estimating rupture propagation and the underlying dynamic parameters for large historical earthquakes the rupture modeling is carried out using a three dimensional finite difference method and the inversion is implemented by a neighbourhood algorithm minimizing the misfit between computed and observed near fault seismograms we test the method by estimating the stress drop within 32 regions on the causative fault for the 2000 magnitude 6 6 western tottori japan earthquake while the dynamic models show both similarities and differences with the conventional kinematic models our method provides an ensemble of physically correct models with plausible rupture propagation for the earthquake

tectonics and distribution of gold deposits in china an overview gold exploration in china has expanded rapidly during the last two decades since a modern approach to economic development has become a national priority china currently produces 180 tonnes t of gold annually which is still significantly less than south africa usa and australia however china is now recognized as possessing significant gold resources in a wide range of mineral deposit types present estimates of gold resources in china exceed 4 500 t which comprise 60 in gold only deposits more than 25 in base metal rich skarn porphyry and vein deposits and more than 10 in placer accumulations the major gold provinces in china formed during the main episodes of phanerozoic tectonism such tectonism involved interaction of china s three major precambrian cratons north china tarim and yangtze or south china when combined with cathaysia block with the angara or siberian kazakhstan kyrgyzstan and indian cratons resulting collisions included deformation of accreted oceanic sequences between the cratonic blocks the most important ore forming orogenies were 1 the late paleozoic variscan 405 270 ma which led to amalgamation of the angara north china and yangtze cratons 2 the indosinian 270 208 ma which led to the collision of north china and south china cratons 3 the yanshanian 208 90 ma which was largely influenced by the subduction of the izanagi pacific plates beneath eastern china and 4 the himalayan 90 ma indentation of the indian continent into eurasia no important precambrian gold systems are recognized in china mainly because of reworking of exposed precambrian rocks by these younger orogenies but there are a few caledonian 600 405 ma gold bearing systems in northern xinjiang most of china s orogenic epithermal and carlin like gold deposits are in the reworked margins of major cratonic blocks and in metasedimentary rock dominated fold belts adjacent to these margins accordingly the major gold provinces are present along the northern southeastern and southern margins of the north china craton along the southwestern and northwestern margins of the yangtze craton in the tianshan and altayshan orogenic belts in northern xinjiang and throughout the southeastern china fold belt gold placer deposits derived from these primary deposits are concentrated in the northernmost part of northeastern china and along the northwestern margin of the yangtze craton the major provinces with significant gold in porphyry related copper systems and base metal skarns are present in the yangtze river area along the northeastern and southeastern margin of the yangtze craton in the fold belt in southwestern china and scattered through northern china three quarters of the chinese gold only deposits occur within the north china craton margins half are located in the uplifted precambrian metamorphic rocks and most of the remainder are hosted in the phanerozoic granitoids that intruded the reworked precambrian terranes the abundance of granite hosted gold contrasts the north china craton with other precambrian cratons such as those in western australia central canada and zimbabwe where gold is mainly hosted in the archean greenstone belts this difference may be explained by the multiple episodes of phanerozoic tectonism along the north china craton margins resulting from the collision of the angara north china and south china cratons and from subduction of the izanagi pacific oceanic plates underneath the eastern china continent

fault steps and the dynamic rupture process 2 d numerical simulations of a spontaneously propagating shear fracture fault steps may have controlled the sizes of the 1966 parkfield 1968 borrego mountain 1979 imperial valley 1979 coyote lake and the 1987 superstition hills earthquakes this project investigates the effect of fault steps of various geometries on the dynamic rupture process we have used a finite difference code to simulate spontaneous rupture propagation in two dimensions we employ a slip weakening fracture criterion as the condition for rupture propagation and examine how rupture on one plane initiates rupture on parallel fault planes the geometry of the two parallel fault planes allows for stepover widths of 0 5 to 10 0 km and overlaps of 5 to 5 km our results demonstrate that the spontaneous rupture on the first fault segment continues to propagate onto the second fault segment for a range of geometries for both compressional and dilational fault steps a major difference between the compressional and dilational cases is that a dilational step requires a longer time delay between the rupture front reaching the end of the first fault segment and initiating rupture on the second segment therefore our dynamic study implies that a compressional step will be jumped quickly whereas a dilational step will cause a time delay leading to a lower apparent rupture velocity we also find that the rupture is capable of jumping a wider dilational step than compressional step

metallogeny of the syenite related dongping gold deposit in the northern part of the north china craton a review and synthesis abstract the dongping gold deposit is located at the northern margin of the north china craton in hebei province china it is the largest alkaline pluton related au deposit in china the ore deposit is hosted in the 400 386 ma la icpms and shrimp zircon u pb method shuiquangou syenite intrusion which cuts archean aged metamorphic rocks the ore bodies consist of a set of en echelon lenses and veins controlled by shear zones the ores can be divided into auriferous quartz vein stockwork and disseminated ores two stages of gold mineralization can be distinguished the first stage mineralization consists of high grade 10 g t grayish quartz veins enveloped by stockwork and disseminated ores whereas the second stage mineralization occurs as low grade studies of fluid inclusions in quartz indicate that the ore forming fluids have low salinity 0 7 8 1 nacl equivalent in the h2o co2 nacl system and have homogenization temperatures varying from 310 to 350 c the ore forming fluids have 18o values varying from 1 7 to 6 9 with an average of 2 9 and d values from 108 to 66 5 with an average of 85 indicating a magmatic origin with some involvement of meteoric fluid the ore forming fluids have initial 87sr 86sr385ma ratios of 0 705 0 706 and 3he 4he ratios of 0 3 to 5 2 ra ra being the atmospheric ratio of 1 0 indicative of a mantle contribution of the fluids the ores have bulk 34s values varying from 1 to 2 similar to those of the host syenites 34s 1 8 3 and the archean metamorphic rocks 34s 0 04 to 4 4 lead isotope analyses of sulfides stock and disseminated ores quartz veins fresh host syenites and the archean metamorphic rocks have a linear correlation of 208pb 206pb and 207pb 206pb indicating a genetic link between the gold mineralization and the syenites hydrothermal zircons from the high grade ores of the first stage can be distinguished from magmatic zircons based on internal textures on cathodoluminescence images and rare earth element patterns these zircons have been dated at 389 1 0 to 385 5 7 ma whereas those from the second stage low grade auriferous quartz vein were dated at 140 ma la icpms and sim u pb methods we propose a model for the formation of the dongping gold deposit involving a late magmatic hydrothermal process related to a devonian mantle sourced syenites with a late jurassic early cretaceous hydrothermal overprint

fluid inclusion and noble gas studies of the dongping gold deposit hebei province china a mantle connection for mineralization the dongping gold deposit 100 t au occurs about 200 km inboard of the northern margin of the north china craton the deposit is mainly hosted by syenite of a middle paleozoic alkalic intrusive complex that was emplaced into late archean basement rocks both groups of rocks are intruded by late jurassic to early cretaceous crustal melt granite dikes and stocks some within a few kilometers of the deposit the gold ores were deposited during this latter magmatic period at about 150 ma a time that was characterized by widespread regional north south compression that formed the east west trending yanshan deformational belt the ores include both the telluride mineral bearing low sulfide quartz veins and the highly k feldspar altered syenite with most of the resource concentrated in two orebodies 1 and 70 fluid inclusion microthermometry indicates heterogeneous trapping of low salinity e g 5 7 wt nacl equiv fluids that varied from a few to 60 mole percent nonaqueous volatile species laser raman spectroscopy confirms that the vapor phase in these inclusions is dominated by co2 but may be comprised of as much as 9 mole percent h2s and 20 mole percent n2 methane concentrations in the vapor phase are consistently 1 mole percent the variable phase ratios are consistent with fluid immiscibility during ore formation fluid inclusion trapping conditions are estimated to be 250 to 375 c and 0 6 to 1 0 kbar helium isotope studies of fluid inclusions in ore stage pyrites indicate 3he 4he ratios of 2 1 to 5 2 ra ra 1 4 10 6 for air for orebody 1 and 0 3 to 0 8 ra for orebody 70 the former data suggest that at least 26 to 65 percent mantle helium occurs in the fluids that deposited the veins in orebody 1 the lower values for orebody 70 which is characterized by a more disseminated style of gold mineralization are interpreted to reflect an increased interaction of ore fluids with surrounding crustal rocks which may have contributed additional 4he to the fluids a mantle source for at least some of the components of the gold forming fluid is consistent with upwelling of hot asthenosphere and erosion of as much as 100 to 150 km of cool archean lithosphere beneath the craton during this time the dongping deposit is located along the 100 km wide north south gravity lineament which marks the western border of the thinned crust as both regional metamorphism of mesoproterozoic and younger cover rocks and widespread granite magmatism also occurred at ca 150 ma it is unclear as to whether one or both of these also contributed fluid and or metals to the hydrothermal system importantly these new data suggest that economically significant gold deposits of similar mineral style and fluid composition which are scattered along the margins of the craton may all be products of a fluid originally partly sourced within the mantle

heterogeneous distribution of the dynamic source parameters of the 1999 chi chi taiwan earthquake 1 the spatial and temporal distribution of the stress on the fault plane of the 1999 chi chi taiwan earthquake is calculated from kinematic inversion results using a three dimensional finite difference method for solving the elastodynamic equations we analyze the relations between stress and slip for all grid positions on the fault and use these relations to infer the friction law for the rupture the dynamic source parameters were also determined our results show that for most of the points on the fault the relation between stress and slip was consistent with the slip weakening law during the rupture process especially for those points with large slip however consistency with the velocity weakening law is not clear from the observed relation between stress and slip velocity the distributions of the dynamic parameters on the fault are very heterogeneous the peak value of the static stress drop is 35 mpa in general high stress drop occurred in the areas with large slip the estimated strength excesses are generally small suggesting that the tectonic shear stress had reached the level of the fault strength before the main shock the slip weakening distance dc and the fracture energy gc are proportional to the final slip the aftershock activity correlates with the spatial distribution of dynamic source parameters usually the aftershocks near the fault plane are concentrated in regions with small or negative static stress drop and there were few aftershocks in regions which had large values of critical slip weakening distance dc

reconstruction of dynamic rupture process of an earthquake with constraints of kinematic parameters in this paper a simple approximate method that converts the distribution of kinematic rupture parameters on a fault into that of physical or dynamic parameters is proposed the method in which the static stress drop assumed to be equal to the dynamic stress drop is applied to investigate rupture dynamics of the 1979 imperial valley california earthquake m 6 5 the dynamic rupture process is reconstructed by using a propagating crack which is a process of expanding area of stress release if we know the amount of stress drop and rupture time at each point on the fault dynamic rupture process can be simulated we use the kinematic parameters previously obtained by using waveform inversion techniques with constraints of the kinematic parameters the dynamic rupture process of the event can be reconstructed and several dynamic parameters stress drop and strength excess the difference between strength and applied initial stress can be estimated at each point on the fault by applying this method to the 1979 imperial valley earthquake we found that the rupture initiated at the low strength excess part first and then expanded toward the north and ruptured a large size high stress drop region located in the north part of the fault and finally decelerated and stopped at the north edge where the strength is high and stress drop is low these features are well explained by barrier model das and aki 1977 and are quite similar to those obtained by quin in 1990 who investigated the dynamic rupture process by the monte carlo technique with a large number of trials since repeated calculation is unnecessary our method is very effective and practical compared with his method

on relating apparent stress to the stress causing earthquake fault slip apparent stress a is defined as where is the average shear stress loading the fault plane to cause slip and is the seismic efficiency defined as ea w where ea is the energy radiated seismically and w is the total energy released by the earthquake the results of a recent study in which apparent stresses of mining induced earthquakes were compared to those measured for laboratory stick slip friction events led to the hypothesis that this hypothesis is tested here against a substantially augmented data set of earthquakes for which can be estimated mostly from in situ stress measurements for comparison with a the expanded data set which includes earthquakes artificially triggered at a depth of 9 km in the german kontinentales tiefbohrprogramm der bundesrepublik deutschland ktb borehole and natural tectonic earthquakes covers a broad range of hypocentral depths rock types pore pressures and tectonic settings nonetheless over 14 orders of magnitude in seismic moment apparent stresses exhibit distinct upper bounds defined by a maximum seismic efficiency of 0 06 consistent with the hypothesis proposed before this behavior of a and can be expressed in terms of two parameters measured for stick slip friction events in the laboratory the ratio of the static to the dynamic coefficient of friction and the fault slip overshoot typical values for these two parameters yield seismic efficiencies of 0 06 in contrast to efficiencies for laboratory events for which is always near 0 06 those for earthquakes tend to be less than this bounding value because ea for earthquakes is usually underestimated due to factors such as band limited recording thus upper bounds on appear to be controlled by just a few fundamental aspects of frictional stick slip behavior that are common to shallow earthquakes everywhere estimates of from measurements of a for suites of earthquakes using are found to be comparable in magnitude to estimates of shear stress on the basis of extrapolating in situ stress data to seismogenic depths

u pb dating of hydrothermal zircon from the dongping gold deposit in north china constraints on the mineralization processes abstract the dongping gold deposit is a large deposit with total gold reserves of 100 tons it is located at the northern margin of the north china craton northwestern hebei province china the ore bodies are hosted by the devonian shuiquangou syenite complex and consist mainly of auriferous quartz veins and disseminated ore in the altered and silicified syenite u pb dating of zircon from hornblende syenite on the western margin of the complex yields a crystallization age of 400 3 5 ma mswd 0 018 morphology cathodoluminescence imaging and geochemical classifications of zircon from the first stage of disseminated ore and gray auriferous quartz veins and from later stage low grade quartz veins point to their newly crystallized hydrothermal origin the hydrothermal zircon from the disseminated ore and auriferous gray quartz vein are dated at 389 1 0 ma and 385 5 7 ma respectively which are detectably younger than but close to the crystallization age of the syenite complex and might have been formed by post magmatic hydrothermal processes both types of ore are dominant in the ore deposit and we propose that the pervasive post magmatic hydrothermal alteration is the main ore forming stage hydrothermal zircon from a low grade auriferous quartz vein yields a u pb age of 140 ma interpreted as forming during a younger period of superimposed yanshanian hydrothermal mineralization thus the ore of the dongping gold mine represents a post magmatic devonian hydrothermal ore deposit with jurassic cretaceous hydrothermal overprinting

geodynamic setting of mesozoic magmatism in ne china and surrounding regions perspectives from spatio temporal distribution patterns of ore deposits abstract north eastern china and surrounding regions host some of the best examples of phanerozoic juvenile crust on the globe however the mesozoic tectonic setting and geodynamic processes in this region remain debated here we attempt a systematic analysis of the spatio temporal distribution patterns of ore deposits in ne china and surrounding regions to constrain the geodynamic milieu from an evaluation of the available geochronological data we identify five distinct stages of ore formation 240 205 ma 190 165 ma 155 145 ma 140 120 ma and 115 100 ma the triassic 240 205 ma magmatism and associated mineralisation occurred during in a post collisional tectonic setting involving the closure of the paleo asian ocean the early mid jurassic 190 165 ma events are related to the subduction of the paleo pacific ocean in the eastern asian continental margin whereas in the erguna block these are associated with the subduction of the mongol okhotsk ocean from 155 to 120 ma large scale continental extension occurred in ne china and surrounding regions however the late jurassic magmatism and mineralisation events in these areas evolved in a post orogenic extensional environment of the mongol okhotsk ocean subduction system the early stage of the early cretaceous events occurred under the combined effects of the closure of the mongol okhotsk ocean and the subduction of the paleo pacific ocean the widespread extension ceased during the late phase of early cretaceous 115 100 ma following the rapid tectonic changes resulting from the paleo pacific oceanic plate reconfiguration