antidunes and traction carpet deposits in deep water channel sandstones cretaceous british columbia canada abstract sandstone beds intercalated with thick shale of the upper member of the haida formation albian turonian in the queen charlotte islands british columbia canada show thinly laminated graded bedding the sandstones generally are present as successions of more than a few tens of inversely to normally graded thin beds the beds at the base of each succession contain much coarser detritus than the beds at the top each succession of graded beds shows a lens shaped channel geometry wavy bed forms similar in shape to the hummock and swale topography that is thought to form hummocky cross stratification hcs characterize the uppermost part of the succession however grain fabric and spacing of the bed forms indicate that they are of antidune origin it is concluded that the successions of multiple laminated sandstone beds were produced by high density turbidity currents that were probably associated with a gravity transformation in which a successive freezing of traction carpets took place lack of shale in the succession together with the common presence of antidunes suggest that each succession was the product of one sedimentation event without decrease in stream power

petrology geochemistry and geochronology of the post collisional triassic mangerite and syenite in the gwangcheon area hongseong belt south korea abstract the gwangcheon intrusive rocks occur in the hongseong collision belt of south korea which is thought to represent the eastern extension of the dabie sulu collision zone of china the central part of the gwangcheon intrusive complex consists of orthopyroxene bearing monzonite mangerite and the marginal part is composed of syenite north of the gwangcheon mangerite the post collisional 233 2 ma haemi biotite granite contains syenite enclaves shrimp u pb zircon analysis yields ages of 232 3 ma for the mangerite and 230 3 ma for a syenite enclave within the haemi biotite granite the mangerite syenite complex and syenite enclaves exhibit a shoshonitic affinity with a total alkalinity na2o k2o of 7 38 9 64 wt high k2o mg ba sr cr ni and lree contents and insignificant negative eu anomalies geochemical data indicate that the mangerite syenite intrusion and the syenite enclaves are post collisional igneous rocks formed by the partial melting of an enriched lithospheric mantle the heat for this melting was derived from asthenospheric upwelling following oceanic slab break off the shrimp age data suggest that both the gwangcheon intrusives and the syenite enclaves formed after the triassic continental collision of the north and south china blocks in korea

the bouma division a and the possible duration of turbidity currents abstract experimental data arnott and hand 1989 combined with theoretical arguments suggest that the transition in a turbidite from division a to division b occurs at a deposition rate of unsupported grains of about 6 7 10 4 m s 1 in the case of fine medium quartz sand a second rate may be calculated from properties measured at the transition from division b to division c allen 1971b these rates together permit an estimate to be made of the order of magnitude of the duration of deposition from a turbidity current the calculated order of a few tens of minutes for a mio pliocene turbidite described and interpreted hydraulically by komar 1985 is in broad agreement with his independent estimate based on the sequenc of sedimentary structures

indosinian dextral ductile fault system and synkinematic plutonism in the southwest of the ogcheon belt south korea reply abstract the structure of the mylonite belt in the southwestern part of the ogcheon belt has been investigated and interpreted in the light of recent radiometric data the shear belt is composed of several en echelon dextral shear zones relayed by compressional or extensional tectonic bridges the dextral displacement along the fault system which may be extended to the hida zone of japan is of the order of 200 km it has brought into contact the ryeongnam block and its cambrian middle ordovician cover of north china affinity with the southwestern margin of the ogcheon belt characterized by cambrian middle silurian rift facies and shelf deposits of south china affinity synkinematic plutons are emplaced within the shear belt which is postdated by uppermost triassic unfoliated granitoids at the surface the shear belt generated elongated intermontane coal basins initiated as transtensional half grabens because of its post permian pre early jurassic age and its dextral kinematics we correlate the shear belt with the late stages of the akyioshi indosinian collisional orogeny of the east asian margin the synkinematic plutonism that accompanied the shear zone may be due to post collisional crustal stretching and subsequent anatexis at the mantle crust interface

assessing textural variation in laminated sands using digital image analysis of thin sections although between laminae parameter variations in sediments have been studied in the past measured parameters were generally limited to grain size distribution and total porosity the magnitude and directional characteristics of physical properties of laminated sediments also depend on the shape and orientation of particles packing pore size characteristics and properties of the pore network leaving out a complete characterization of granular sediment in models of physical properties could result in a systematic mismatch between modeled and measured values however tools for high resolution quantification of these spatial variable parameters are not readily available in order to provide such a tool an image analysis procedure is presented based on digital images of thin sections the procedure defines a sequence of rectangular measurement windows with their long sides oriented parallel to stratification and measures the sediment characteristics for each window logs of parameters values oriented perpendicular to stratification are thus created after verification of the image analysis procedure using comparative laboratory measurements the procedure is applied to two thin section images of unconsolidated fine grained laminated sands the quantitative variations observed in the logs of grain and pore characteristics correlate well with bedding observed on the original images overall the image analysis procedure proved to be a useful and versatile tool for quantifying variations of textural characteristics on sub lamina scale

source parameters for small events associated with the 1986 north palm springs california earthquake determined using empirical green functions using small events as empirical green functions which include path site and instrument effects on the p waveforms source parameters were estimated for 25 ml 3 4 to 4 4 events associated with the 1986 north palm springs earthquake the static stress drops ranged from 3 to 80 bars for moments of 0 7 to 11 1021 dyne cm there was a spatial pattern to the stress drops of the aftershocks which showed increasing values along the fault plane toward the northwest compared to relatively low values near the hypocenter of the mainshock the highest values were outside the main area of slip and are believed to reflect a loaded area of the fault that still has an higher level of stress which was not released during the main shock the relatively high stress drop of a preshock in 1983 located close to the hypocenter of the main shock is also interpreted as evidence that stress drops of magnitude 3 and 4 events can be used as indicators of the stress level in a particular area

empirical green s function study of the january 17 1994 northridge california earthquake the january 17 1994 northridge main shock was analyzed using an empirical green s function approach to estimate the spatial and temporal distribution of fault slip far field source time functions obtained from seismograms recorded by the berkeley digital seismic network bdsn and terrascope stations reveal the distributed nature of the source and the presence of a second large subevent the location of the fault beneath the san fernando valley as well as the updip directivity of the rupture contributed to the locally heavy damage due to this earthquake

empirical green s functions from small earthquakes a waveform study of locally recorded aftershocks of the 1971 san fernando earthquake seismograms from 52 aftershocks of the 1971 san fernando earthquake recorded at 25 stations distributed across the san fernando valley are examined to identify empirical green s functions and characterize the dependence of their waveforms on moment focal mechanism source and recording site spatial variations recording site geology and recorded frequency band recording distances ranged from 3 0 to 33 0 km hypocentral separations ranged from 0 22 to 28 4 km and recording site separations ranged from 0 185 to 24 2 km the recording site geologies are diorite gneiss marine and nonmarine sediments and alluvium of varying thicknesses waveforms of events with moment below about 1 5 1021 dyn cm are independent of the source time function and are termed empirical green s functions waveforms recorded at a particular station from events located within 1 0 to 3 0 km of each other depending upon site geology with very similar focal mechanism solutions are nearly identical for frequencies up to 10 hz there is no correlation to waveforms between recording sites at least 1 2 km apart and waveforms are clearly distinctive for two sites 0 185 km apart the geologic conditions of the recording site dominate the character of empirical green s functions even for source spatial separations of up to 20 0 km the empirical green s functions at a particular site are consistent in frequency content amplification and energy distribution therefore it is shown that empirical green s functions can be used to obtain site response functions the observations of empirical green s functions are used as a basis for developing the theory for using empirical green s functions in deconvolution for source pulses and synthesis of seismograms of larger earthquakes

source processes of three aftershocks of the 1983 goodnow new york earthquake high resolution images of small symmetric ruptures broadband large dynamic range geos data from four aftershocks m l 2 to 3 of the 1983 goodnow new york earthquake recorded at hard rock sites 2 to 7 km away from the epicentral area are used to study rupture processes of three larger events with an m l 1 6 event as the green s function event we analyze the spectra and spectral ratios of ground velocity at frequencies up to 100 hz and conclude that 1 there are resolvable p wave f max 51 and 57 hz at two sites 2 there is abundant information on sources of larger events up to frequencies of 50 to 60 hz and 3 there is an unstable nonlinear instrument resonance at about 90 hz we analyze the artifacts of low pass filters in the deconvolved rupture process including the limited time resolution and biases in the rise time measurement some extensions of the empirical green s function egf method are proposed to reduce these artifacts and to precisely estimate the relative locations of events that are close both in time and in space applying the egf method to three aftershocks we find that these events have ruptures that are simple crack like characterized by small fault radii 70 to 120 m and static stress drops that vary depending on the size of the events between about 5 to 16 bars we also find that two of the events with origin times differing by 0 60 sec are separated by 190 110 meters assuming a causal relationship between the two would result in a slow propagation velocity 0 05 0 03 time of the local shear wave velocity we therefore interpret the corresponding ruptures as being distinct the area between the rupturing patches having a characteristic length much smaller than those of the rupturing patches comparison of the results of this study with those obtained for the goodnow main shock and microearthquakes in california and hawaii suggests that the stress drops of the goodnow aftershocks decrease considerably by up to a factor of 25 or more from those estimated for the main shock even after the estimated large uncertainty in the latter estimates is considered this decrease is similar to those reported for the nahanni earthquakes m b 5 0 to 6 5 in northwest territories and for the north palm springs earthquake m l 5 9 sequence in california the stress drops of the simple crack like microearthquakes are significantly variable by factors between 3 and 27 within the single source areas the median of stress drops of the intraplate goodnow aftershocks is lower by factors of 2 to 4 than the medians calculated for the other interplate microearthquake sequences

triassic southeastward subduction of north china block to south china block insights from new geological geophysical and geochemical data abstract lithospheric subduction prior to the assembly of the south china and north china blocks is traditionally considered to be directed northward however some critical geological and geochemical data cannot be reconciled with this northward subduction this paper presents new lines of evidence against the traditional models and proposes a new and revolutionary tectonic model to explain the distribution and exhumation of high pressure hp ultrahigh pressure uhp metamorphic rocks of the dabie sulu belt we emphasize the following 1 the triassic tectonic environment of the southern margin of the north china block was passive not active based on the stratigraphy 2 in the southern margin of the north china block no arc magmatism was recorded 3 many paleoproterozoic slices of jiaobei affinity of the jiao liao ji belt in the north china block were located in the triassic sulu orogen 4 many 1 85 ga metamorphic zircons are preserved in the dabie sulu high pressure ultra high pressure hp uhp metamorphic rocks 5 the geometric asymmetry of many structural patterns in the hp uhp slices indicates top to the northwest thrusting during the exhumation of hp uhp slices 6 blueschists occur in the south of the uhp eclogite slices 7 in the eastern segment of the north qinling orogen no components with an affinity of the south china block have been found along the shangdan suture of the qinling orogen has been recorded an apparent northward subduction we consider that the suture is just a lateral subduction zone rather than a major collisional zone along the shangdan suture the rarity of i type plutonism can be attributed to a transform type continental margin the bureya jiamusi khanka block has an affinity to the south china block based on its similarity regarding the paleozoic history of deformation and triassic blueschist metamorphic facies metamorphism the bureya jiamusi khanka block could be the northern extension of the dabie sulu belt and this gigantic belt could be interpreted as an orocline related to the southeastward subduction of the north china block beneath the greater south china block

seismic moments local magnitudes and coda duration magnitudes for earthquakes in central california onscale seismograms recorded at stations in the u s geological survey s usgs central california seismic network calnet have been used to estimate the seismic moment m and local magnitude ml for earthquakes of 1 ml 4 located on the san juan bautista and parkfield sections of the san andreas fault the coyote lake section of the calaveras fault the sargent fault and near livermore these data together with m and ml estimates for 4 ml 6 earthquakes in these areas cannot be fit with a single linear log m versus ml relation rather the data are consistent with log m 1 5 ml 16 for 3 ml 6 with log m 1 2 ml 17 for 1 1 2 ml 3 1 2 and with a slope of to 1 fro 1 2 ml 1 1 2 whereas usgs coda duration magnitude md is consistent with ml for 1 1 2 ml 3 md is larger than ml at ml 1 1 2 and smaller than ml at ml 3 log m can be estimated to a precision of 0 2 for 1 md 3 1 2 earthquakes in central california by applying log m 1 2 md 17 to the md that have been routinely published by the usgs

comparison of seismic waveform inversion results for the rupture history of a finite fault application to the 1986 north palm springs california earthquake the july 8 1986 north palm springs earthquake is used as a basis for comparison of several different approaches to the solution for the rupture history of a finite fault the inversion of different waveform data is considered both teleseismic p waveforms and local strong ground motion records linear parametrizations for slip amplitude are compared with nonlinear parametrizations for both slip amplitude and rupture time inversions using both synthetic and empirical green s functions are considered in general accurate green s functions are more readily calculable for the teleseismic problem where simple ray theory and flat layered velocity structures are usually sufficient however uncertainties in the variation in t with frequency most limit the resolution of teleseismic inversions a set of empirical green s functions that are well recorded at teleseismic distances could avoid the uncertainties in attenuation in the inversion of strong motion data the accurate calculation of propagation path effects other than attenuation effects is the limiting factor in the resolution of source parameters the assumption of a laterally homogeneous velocity structure is usually not a good one and the use of empirical green s functions is desirable considering the parametrization of the problem any degree of fault rupture complexity can be described in terms of a linear parametrization for slip amplitudes however a nonlinear parametrization for rupture times and slip amplitudes can have a distinct advantage over a simple linear one by limiting the number of unknown parameters regardless of the choice of data or the type of parametrization the model or solution will be affected by the choice of minimization norm and the type of stabilization used

timing of triassic tectonic division and postcollisional extension in the eastern part of the jiaodong peninsula abstract the jiaodong peninsula is a key region for researching the interaction between the north and south china plates tectonic relationships between collision exhumation of ultra high pressure uhp slabs strike slip faulting and gold mineralization are still ambiguous the eastern part of the jiaodong peninsula eastern jiaodong which includes triassic intrusions and is less affected by the tan lu fault zone is a key area to examine exhumation dynamics in detail systematic field mapping and zircon u pb dating of triassic intrusions establishes that 1 the uhp wedge in the eastern part of the jiaodong peninsula can be divided into the lateral and frontal ramps of a thrust and nappe system dating of samples from donglinghou 244 7 4 2 ma and qingyutan 233 8 8 1 ma areas indicates that the collision happened at or before the middle triassic 2 postcollisional extension intrusions including the shidao granitoid 216 2 2 4 ma and the chengshantou granitoid cut by a dolerite dyke dated at 210 5 1 0 ma generally strike ne and occurred in a metamorphic core complex below the upper jiashan xiangshui detachment u jsxs 3 regional faults in the jiaodong peninsula exploited syncollisional foliations of the uhp wedge which resulted in faults dipping towards the nw and se the reactivation of the lower jiashan xiangshui shear zone l jsxs and its overprinting upon the tan lu fault system may have caused another major episode of exhumation of the syncollisional wedge and could have been responsible for an extensional environment that favored gold mineralization

southern surface rupture associated with the 1992 m7 4 landers earthquake did it all happen during the mainshock approximately three minutes after the magnitude 7 4 landers mainshock on 28 june 1992 a m5 7 aftershock occurred south of the mainshock epicenter with a location of 34 7 65 n 116 23 82 w this aftershock was recorded on an array of portable digital seismic instruments deployed in morongo valley 21 km southwest of the event although peak accelerations are found to differ by approximately 50 at stations with similar general site conditions within 500 m of each other there is good coherence of arrivals across the array for frequencies 1 hz we use the recordings to determine the apparent phase velocity and azimuth of propagation across the array and show that the event clearly ruptured to the south with a rupture length of 11 km and a rupture velocity of approximately 3 0 km s our results suggest that at least some of the mapped surface rupture south of the town of yucca valley 11 km in extent maximum displacement of 20 cm may have been associated with this aftershock if this is the case then the fault that produced the southern end of the landers mainshock the johnson valley fault need not continue at depth across the active left lateral east west trending pinto mountain fault

multi phase cooling of early cretaceous granites on the jiaodong peninsula east china evidence from 40 ar 39 ar and u th he thermochronology abstract the jiaodong peninsula at the southeastern periphery of the north china craton ncc has undergone complex changes since the mesozoic a striking feature of the ncc is the widespread distribution of late mesozoic magmatic rocks predominantly characterized by granitic intrusions these igneous plutons are economically important due to their polymetallic mineralization and significant as geodynamic tracers of the regional tectonic evolution two representative early cretaceous granites the yashan and yuangezhuang plutons on the jiaodong peninsula were selected for multiple thermochronometer studies to constrain a complete thermal history from their emplacement to near surface conditions we obtained biotite 40ar 39ar ages of two granites on the new generation argus vi noble gas mass spectrometer two biotites registered identical 40ar 39ar plateau ages of 117 ma which are consistent within the error with their zircon u pb ages this suggested that the two granites were emplaced at the same time and cooled rapidly to about 300 c the single crystal zircon u th he zhe dating for the two samples gave weighted mean ages of 93 5 4 5 ma and 93 3 5 0 ma combined with previously published geochronological data and the thermal inversion of the zircon low temperature thermochronological data three phases of rapid cooling were identified for the two studied plutons 1 the early cretaceous 117 110 ma 2 the late cretaceous 100 90 ma and 3 the early tertiary 65 50 ma the early cretaceous phase of cooling occurred in a regional extensional regime on the ncc characterized by various extensional structures the late cretaceous cooling is consistent with the third episode of the yanshan movement which caused a regional basin inversion event on the ncc in comparison to the first two phases of rapid cooling the early tertiary cooling was more gradual this phase corresponded to a widely developed eocene rift on the ncc and the reactivation of major boundary faults such as the giant tan lu fault zone and the taihangshan fault

magnitude frequency relation for small earthquakes a clue to the origin of ƒmax of large earthquakes in order to test the hyothesis that the max of large earthquakes is due to the source effect and is causally related to the corner frequency of small earthquakes when it becomes constant below magnitude about 3 we constructed the frequency magnitude relation for earthquakes with magnitude range from 1 3 to 4 recorded at a borehole seismograph station operated by the university of southern california at baldwin hills in the middle of the newport inglewood fault a procedure was developed for an accurate estimation of moment magnitude from the measurement of coda amplitude as a function of lapse time the cumulative number of earthquakes per unit time period and area was estimated by finding the detection limit for ts p for each magnitude we found a clear depature of the observed log frequency magnitude relation for m 3 the observed frequency of earthquakes with m 0 5 is almost 10 times less than that expected from the extrapolation of empirical relation for earthquakes with magnitudes larger than 3 we conclude that the observed frequency magnitude relation departs from self similarity for earthquakes with magnitude smaller than about 3 this departure coincides with the widely observed departure of the moment corner frequency relation from self similarity these observations are consistent with the interpretation of max of large earthquakes in terms of the slip weakening instability model in which the critical slip may be a few tenths of a meter to a few meters and the cohesive zone size may be a few hundred meters to a few kilometers

fault plane determinations for three small earthquakes along the san jacinto fault california search for cross faults using rupture directivity and aftershock locations three earthquakes ml 4 2 4 3 were studied to determine which of the two nodal planes of the focal mechanism was the rupture plane all three events occurred near the san jacinto fault zone during december 1989 and february 1990 and had a large component of strike slip motion with nodal planes oriented in the northeast and northwest directions smaller earthquakes were used as empirical green functions to deconvolve the path and site complications from the short period p waveforms the resultant far field source time functions were inverted for slip on a finite fault and tested to see which nodal plane provided a better fit to the data the results of the waveform inversion showed that the earthquake near the anza gap december 2 1989 and the earthquake near san bernardino december 28 1989 ruptured northwest trending planes the earthquake near buck ridge february 18 1990 appeared to rupture a northeast trending plane but the waveform results for this event were not considered as reliable available aftershock data for the three events were also examined using master event relocations the aftershock sequence following the buck ridge event showed a clear lineation trending toward the northeast the results of this study indicate that the anza and san bernardino earthquakes ruptured areas on or parallel to the san jacinto fault while the buck ridge event ruptured a northeast trending cross fault in addition to determining the fault plane the waveform analysis resolved details of the slip distribution for these relatively small earthquakes

reinterpretation of depositional processes in a classic flysch sequence pennsylvanian jackfork group ouachita mountains arkansas and oklahoma discussion the pennsylvanian jackfork group in the ouachita mountains of arkansas and oklahoma has conventionally been interpreted by many workers including us as a classic flysch sequence dominated by turbidites in a submarine fan setting however normal size grading and bouma sequences indicative of turbidite deposition are essentially absent in these sandstone beds they appear massive i e structureless in outcrop but when slabbed reveal diagnostic internal features these beds exhibit sharp and irregular upper bedding contacts inverse size grading floating mudstone clasts a planar clast fabric lateral pinch out geometries moderate to high detrital matrix up to 25 sigmoidal deformation duplex structures and contorted layers all these features indicate sand mplacement by debris flows mass flows and slumps mud matrix in these sandstones was sufficient to provide cohesive strength to the flow discrete units of current ripples and horizontal laminae have been interpreted to represent traction processes associated with bottom current reworking the dominance of sandy debris flow and slump deposits nearly 70 at degray spillway section and bottom current reworked deposits 40 at kiamichi mountain section and the lack of turbidites in the jackfork group have led us to propose a slope setting our rejection of a submarine fan setting has important implications for predicting sand body geometry and continuity because deposits of fluidal turbidity currents in fans are laterally more continuous than those of plastic debris flows and slumps on slopes a turbidite dominated fan model would predict an outer fan environment with laterally continuous sheetlike sandstones for the jackfork group in southern oklahoma and western arkansas whereas a debris flow slump model would predict predominantly a slope environment with disconne ted sandstone bodies for the same area

source parameters of the 23 april 1992 joshua tree california earthquake its largest foreshock and aftershocks abstract seismic moments corner frequencies and stress drops have been calculated for the 23 april 1992 joshua tree california earthquake its largest foreshock and 12 aftershocks using recordings from terrascope stations source parameters are determined from nonlinear least squares best fits to ratios of p wave fourier amplitude spectra assuming an omega squared source model the spectral ratios are the mainshock spectra divided by the foreshock and aftershock spectra seismic moments range from 2 10 21 to 2 10 25 dyne cm corner frequencies range from 0 51 to 4 8 hz aftershock stress drops range from 4 2 to 41 bars with a log average stress drop of 15 bars the foreshock stress drop is relatively large 31 bars but is within the aftershock stress drop range the mainshock stress drop of 203 bars is significantly larger than any of the aftershock or foreshock stress drops

postcollisional extension of the caledonide orogen in scandinavia structural expressions and tectonic significance the scandinavian caledonides are much more affected by postcontractional devonian extension than previously thought the extensional deformation is not restricted to the internal parts of the orogen but can be traced for more than 200 km from the west coast of norway toward the foreland it involved significant reactivation of the basal thrust zone as a low angle extensional detachment whic consequently contains abundant top to the north west sense of shear indicators the extensional deformation involved substantial backsliding of the orogenic wedge eduction of the baltic shield together with stretching of the basement by west dipping extensional shear zones after 30 km of backsliding the extensional detachment splayed to penetrate the overlying orogenic edifice in the coastal region in southern norway which led to inactivation of the main portion of the basal thrust zone as an extensional detachment

crustal structure of the dabie orogenic belt eastern china inferred from gravity and magnetic data abstract in order to better characterize the crustal structure of the dabie orogen and its tectonic history we present a crustal structure along a 500 km long profile across the dabie orogenic belt using various data processing and interpretation of the gravity and magnetic data source depth estimations from the spectral analysis by continuous wavelet transform cwt provide better constraints for constructing the initial density model the calculated gravity effects from the initial model show great discrepancy with the observed data especially at the center of the profile more practical factors are then incorporated into the gravity modeling first we add a high density body right beneath the high pressure metamorphic hpm and ultrahigh pressure metamorphic uhpm belt considering the exposed hpm and uhpm rocks in the mid of our profile then the anomalous bodies a b and c inferred from the cwt based spectral analysis results are fixed in the model geometry in the final crustal density structure two anomalous bodies b and c with high density and low magnetization could possibly be attributed to metasomatised mantle materials by sio2 rich melt derived from the foundering subducted mafic lower crust under the extensional environment in the early cretaceous the upwelling metasomatised mantle was partially melted to produce the parental magma of the post collisional mafic ultramafic intrusive rocks as for the low density body a with strong magnetization located in the lower crust right beneath the hp and uhp metamorphic belt it is more likely to be composed of serpentinized mantle peridotite smp this serpentinized mantle peridotite body smpb represents the emplacement of mantle derived peridotites in the crust accompanying the exhumation of the uhp metamorphic rocks

seismological constraints on source properties of the mb 4 0 1985 ardsley new york earthquake a characteristic rupture on october 19 1985 a magnitude 4 0 earthquake occurred in southern westchester county new york approximately 30 km north of central manhattan barstow et al 1988 concluded that this earthquake consisted of two sub events with the larger sub event occurring 0 6 s after the first one we present analysis of data for the main shock as well as aftershocks and foreshocks which were recorded on the new york state seismic network because this data set includes a range of source magnitudes from less than 2 to 4 recorded for virtually identical source receiver pairs an empirical green s function technique can be used to study the source characteristics of the larger events the corner frequency of the main shock and an attenuation parameter t are resolved from the initial portion of the seismogram at station pal in palisades new york 8 km northwest of the epicenter spectra of small foreshocks and aftershocks can then be corrected for attenuation using t following an iterative procedure it is then possible to make reliable determinations of seismic corner frequency for these events several conclusions are obtained 1 the spectrum of the first subevent in the main shock can be well modelled by a brune spectrum from 1 to 10 hz with a corner frequency of 7 1 hz at higher frequencies the source spectrum contains sharp peaks which do not fit an omega square model and may reflect complexities in the rupture process 2 the average stress drop of the sequence is 205 bars the stress drop of the main event is 540 bars but no stress drop dependency on moment is resolved over the magnitude range 1 8 4 0 3 attenuation parameters t are obtained for the 8 km northwestward path from ardsley to palisades and for a 52 km westward path to a station in the hudson highlands and their similarity suggests an increase of q with depth 4 assuming that the two main shock sub events did not rerupture the same area but were contiguous a maximum rupture dimension is 440 680 m the rupture diameter of the largest aftershock mb 3 is determined to be approximately 320 meters the combined rupture for the sequence inferred from spectral methods is consistent with the size of the rupture inferred from the area surrounded by the early aftershocks 700 m diameter the rupture dimension of the ardsley sequence may be characteristic of the dobbs ferry fault and other seismogenic faults in the manhattan prong which are segmented with characteristic dimensions of 0 5 2 km seeber and dawers 1989 assuming that the range of stress drops in the ardsley sequence is also characteristic of the manhattan prong this range of dimensions corresponds to a range of characteristic magnitudes between mb of 3 3 and 5 5 we note that this magnitude range encompasses the five largest known earthquakes in the new york city seismic zone the 1985 ardsley main shock and events in 1737 1783 1884 and 1895

performance of the short period geophones of the iris passcal array we calibrated 64 mark products l22 d short period geophones of the iris passcal array using a mass displacement test the mean natural frequency of the 192 components was 2 1 hz slightly larger than the nominal value of 2 hz with a standard deviation of about 0 15 hz the standard deviation of the voltage sensitivity is about 5 per cent variability of both sensitivity and natural period are within the manufacturer s published specifications three types of nonlinearities were noted a 5 per cent difference in parameters determined by positive and negative mass displacements possibly due to a nonlinear spring observed on more than 90 per cent of the 192 components tested apparent cross axis errors in wide 1 to 2 hz bands near 10 hz and spurious resonance peaks at frequencies between 22 and 29 hz observed on about 20 per cent of the components array equalization of seismograms from the loma prieta earthquake aftershock survey indicate that the root mean square misfit between two seismograms recorded by different geophones at the same site can be reduced from 10 per cent to 5 per cent by application of the calibration results

source pulse enhancement by deconvolution of an empirical green s function observations of the earthquake source time function are enhanced if path recording site and instrument complexities can be removed from seismograms assuming that a small earthquake has a simple source its seismogram can be treated as an empirical green s function and deconvolved from the seismogram of a larger and or more complex earthquake by spectral division when the deconvolution is well posed the quotient spectrum represents the apparent source time function of the larger event this study shows that with high quality locally recorded earthquake data it is feasible to fourier transform the quotient and obtain a useful result in the time domain in practice the deconvolution can be stabilized by one of several simple techniques in this paper the method is implemented and tested on high quality digital recordings of aftershocks of the jan 9 1982 miramichi new brunswick earthquake in particular seismograms from a jan 17 aftershock 017 13 33 gmt local mag 3 5 exhibit path or site effects which complicate the determination of source parameters after deconvolution the apparent far field source of this event is a simple pulse in displacement with duration 0 07 second for both p and s

determination of earthquake energy release and ml using terrascope we estimated the energy radiated by earthquakes in southern california using on scale very broadband recordings from terrascope the method we used involves time integration of the squared ground motion velocity and empirical determination of the distance attenuation function and the station corrections the time integral is typically taken over a duration of 2 min after the p wave arrival the attenuation curve for the energy integral we obtained is given by q r cr n exp kr r 2 2 h ref 2 with c 0 49710 n 1 0322 k 0 0035 km 1 and h ref 8 km where is the epicentral distance a similar method was used to determine m l using terrascope data the station corrections for m l are determined such that the m l values determined from terrascope agree with those from the traditional optical wood anderson seismographs for 1 5 6 5 m l saturates the ratio e s m 0 m 0 seismic moment a measure of the average stress drop for six earthquakes the 1989 montebello earthquake m l 4 6 the 1989 pasadena earthquake m l 4 9 the 1990 upland earthquake m l 5 2 the 1991 sierra madre earthquake m l 5 8 the 1992 joshua tree earthquake m l 6 1 and the 1992 landers earthquake m w 7 3 are about 10 times larger than those of the others that include the aftershocks of the 1987 whittier narrows earthquake the sierra madre earthquake the joshua tree earthquake and the two earthquakes on the san jacinto fault the difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times the aftershocks which occurred on the fault plane where the mainshock slippage occurred had a very short time to heal hence a low stress drop the repeat time of the major earthquakes on the frontal fault systems in the transverse ranges in southern california is believed to be very long a few thousand years hence the events in the transverse ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times such as the san andreas fault and the san jacinto fault the observation that very high stress drop events occur in the transverse ranges and the los angeles basin has important implications for the regional seismic potential the occurrence of these high stress drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events characterization of earthquakes in terms of the e s m 0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the los angeles basin and the transverse ranges

the significance of deep water cryptic bioturbation in slope channel massive sand deposits of the lower rio dell formation eel river basin california abstract deep water massive featureless sands are commonly interpreted as indicators of flow conditions during or shortly after deposition and are almost never interpreted to reflect post depositional homogenization due to bioturbation deep water deposits of the lower rio dell formation pliocene eel river basin nw california however reveal previously unrecognized cryptically bioturbated fabrics in massive sandstone and mudstone this study represents the first detailed documentation of cryptically bioturbated massive appearing sandstone in deep water channelized environments although fluid escape contributed to some of the massive appearing textures in the rio dell formation we present criteria for recognizing cryptic bioturbation fabrics 1 tubes with lithologically distinctive concentric linings or infillings 2 meniscate backfill in burrows 3 lithologically distinctive spreite 4 concentric grain orientations and 5 grains realigned adjacent to tubular structures using biostratigraphic data detailed stratigraphic descriptions core photos and photomicrographs we document ichnofabrics associated with two main lithofacies and their bounding surfaces 1 diffuse muddy siltstone lithofacies e g planolites phycosiphon schaubcylindrichnus 2 massive sandstone lithofacies e g cryptic bioturbation planolites 3 lithofacies crossers 4 burrows that prefer the top of sand base of mud interface e g planolites skolithos and 5 a glossifungites demarcated discontinuity at the base of the massive sand lithofacies we also establish two main lithofacies associations with characteristic sedimentologic traits we use relative percentages of the lithofacies associations to interpret slope channel depositional facies distal channel margin proximal channel margin and channel axis by comparing ichnologic characteristics to depositional facies we conclude that proximity to the channel axis appear to control the degree and type of bioturbation observed in the massive appearing deposits distal channel margin deposits preserve the smallest burrows highly developed cryptic bioturbation fabrics and the most complete sequence of background bioturbation proximal channel margin and channel axis deposits record larger burrows but incomplete cryptic bioturbated fabrics and an overall smaller proportion of preserved background bioturbation

source parameters of small earthquakes recorded at 2 5 km depth cajon pass southern california implications for earthquake scaling a 2 5 km deep triaxial seismometer at cajon pass in southern california has recorded several hundred earthquakes ml4 0 occurring within the san andreas fault system at 2 5 km seismic background noise is below amplifier sensitivity and the 2 250 hz spectral range of recorded seismic motion is wider and higher than that of most natural event catalogs compared with downhole recorded motion seismic amplitudes at the surface are amplified below 10 hz and severely attenuated above 30 hz we estimate that qs is at least 1000 for wave motion at 2 5 km and below and qp is over 2000 the range of source dimensions in the downhole recorded catalog is 10 m to 70 m ml 2 0 mo 108 nm to ml 2 7 mo 1013 nm the plot of log source radius vs log moment has a straight line trend compatible with earthquake scaling at constant stress drop inferred stress drops are scattered between 1 and 500 bars there is no evidence in the catalog for the proposed minimum source dimension at 100 m when the cajon pass borehole catalog containing some of the smallest recorded natural earthquakes is combined with 800 larger events from previous studies the moment radius trend suggests that natural earthquakes are self similar over a magnitude range m 2 to 8 we suggest that inferences of minimum source dimension are more likely due to bias in bandlimited individual catalogs than to properties of the seismic crust

space time variations in source parameters of mining induced seismic events with m 0 space time variations in source parameters and fault plane solutions are related to structural mapping data and local regional stress field measurements in an attempt to characterize the behavior of a rock mass in the vicinity of an excavation in a mine source parameters i e total seismic energy p and s wave energy seismic moment static stress drop and apparent stress were analyzed for 85 events with moment magnitudes between 2 2 m 0 3 within a 90 m microseismic envelope ahead of an excavation these data allowed three types of failure mechanisms to be postulated a zone of flat lying extensional failures next to the excavation a zone of subvertical shear failures at the microseismic envelope boundary and a transition zone between these two where both shear and shear extensional failures occur two spatially distinct event clusters occurred at distance from the excavation for early and late stages of the excavation and next to the excavation during intermediate stages worth noting was an apparent change in p axis orientation with excavation where the average p axes before and following ore extraction were compatible with the local maximum principal stress and the p axes during intermediate excavation stages were compatible with the regional maximum principal stress or local intermediate principal stress distinct from these trends was the general increase in the values of each of the above source parameters over the duration of the excavation suggesting that stress levels were increasing as a result of the excavation geometry and procedure this was considered to be significant as rockbursts mn 1 8 to 2 7 occurred above the study area 6 months following the completion of the excavation

seismic energy release in mexican subduction zone earthquakes we estimated radiated seismic energy es from 18 shallow thrust mexican subduction zone earthquakes 4 1022 m 1 1 1028 dyne cm 11 h 37 km using digital accelerograms from the guerrero accelerograph array and neglecting stations with large site effects es is computed by integrating squared velocity spectra after applying geometrical spreading and q corrections we discarded epicentral recordings for the largest michoacan event we find that log es m 4 152 0 275 which gives a median value of es m and apparent stress a of 7 1 10 5 and 24 bars respectively the median es m value is in accordance with gutenberg and richter s g r 1956 formula for es in which es m 5 10 5 is implicit worldwide es m data where es is computed from local records mostly fall between 5 10 5 and 5 10 4 for events with m 1022 dyne cm on the other hand es m values generally lie between 5 10 6 and 5 10 5 if es is estimated from teleseismic records especially anomalous are the es m data from kikuchi and fukao 1988 for large and great earthquakes which fall near 5 10 6 thus while es from local data suggests that the g r relation seldom overestimates seismic energy release the teleseismic data point to the contrary the cause of this discrepancy may lie in the difficulty of resolving incoherent radiation from the fault and inappropriate choice of t in the analysis of teleseismic data

rupture characteristics and tomographic source imaging of ml 3 earthquakes near anza southern california the rupture characteristics of several ml 3 earthquakes near anza california are determined from time domain analysis of path corrected displacement pulses these pulses are corrected for propagation effects apparent attenuation scattering site resonance using the waveforms of adjacent small events ml 2 1 as empirical green s functions the earthquakes studied occurred during two swarm sequences near cahuilla in an area characterized by swarm activity at shallow depth 5 km the data consist of seismograms recorded by the anza seismic network a high dynamic range local array with digital telemetry the waveforms of adjacent small events ml 2 1 are deconvolved from those of the ml 3 events to yield the source time functions of the larger earthquakes the ml 3 earthquakes display a variety of rupture modes similar to those reported for large shocks but over much shorter time scales and distances events with single and multiple ruptures are observed relative locations of the subevents are obtained from azimuthal differences in the time separation of pulses in the deconvolved displacement waveforms some events as small as ml 2 4 display unilateral rupture propagation as manifested by azimuthal variations in the pulse widths of the deconvolved displacement pulses a tomographic back projection technique is applied to the deconvolved displacement pulses to image the slip velocity on the fault as a function of time after nucleation and distance along the fault using a one dimensional fault model the tomographic inversion for one of the events ml 2 4 reveals a unilateral rupture with rupture velocity about equal to the shear wave velocity vs and fault length of 300 m a similar inversion for an ml 3 7 event resolves two subevents separated by about 200 m and yields an average rupture velocity of 0 8vs these rupture velocities are similar to those reported for large earthquakes indicating that rupture velocity is independent of seismic moment down to 3 1 1019 dyn cm the smallest event studied there are clear variations in pulse width for neighboring events with similar seismic moments implying significant differences in static stress drops factor of five variations in stress drop 11 61 bars are calculated for events within 200 m of each other thus the stress and or strength along this fault zone varies considerably over distances of hundreds of meters

source parameters of the 23 april 1992 m 6 1 joshua tree california earthquake and its aftershocks empirical green s function analysis of geos and terrascope data source parameters of the m 6 1 23 april 1992 joshua tree mainshock and 86 m 1 8 to 4 9 aftershocks are determined using an empirical green s function methodology for the aftershocks deconvolved p and s wave spectra are calculated for 126 pairs of closely spaced events recorded on portable geos stations s wave spectra from the two horizontal components are averaged the deconvolved spectra are fit by a ratio of omega square source models yielding an optimal least squares corner frequency for both the large and the small event in each pair we find no resolved difference between the inferred p and s wave corner frequencies using the standard brune model for stress drop we also find no resolved nonconstant scaling of stress drop with moment although we also conclude that detailed scaling systematics would be difficult to resolve in particular a weak increase of stress drop with moment over a limited moment magnitude cannot be ruled out for magnitudes smaller than m 3 to 3 5 the inferred stress drop values will be limited by the maximum observable corner frequency value of 60 hz for the mainshock source time functions are obtained from mainshock recordings at three terrascope stations pfo pas and gsc using an m 4 3 foreshock as an empirical green s function the results indicate a fairly simple single pulse source time function with clear south to north directivity and an inferred rupture radius of 5 to 6 km the deconvolved source time functions are inverted to obtain a finite rupture model that gives a robust estimate of rupture dimension early aftershocks are found to lie along the perimeters of regions with high mainshock slip the inferred mainshock stress drop value 56 bars is within the range determined for the aftershocks our derived mainshock source spectra do not show resolvable deviation from the omega square model

directional petrological characterisation of deep marine sandstones using grain fabric and permeability anisotropy methodologies theory application and suggestions for integration abstract different methods for quantifying preferred grain orientation or grain shape fabric in sandstones are reviewed and their value for the reconstruction of palaeocurrent direction and preferred direction of pore fluid flow is reassessed critically based on existing knowledge from literature and new grain fabric data it is shown that petrographic analysis has distinct merits because grain fabric can be determined with low equipment costs and population statistics are based on the orientation of individual grains several recommendations are given how to standardise procedures for acquisition of grain fabric through microscopy these recommendations include 1 the careful selection of cross section orientations to acquire apparent long grain axes that are representative of true long grain axes 2 the preferred measurement of the coarsest grains in cross section and 3 a new statistically founded method to select a subset of grains that is representative of the total population of grains in a sandstone sample magnetic techniques that use anisotropy of magnetic susceptibility ams as a proxy for grain orientation require specialised equipment and are more restricted in statistical evaluation but these methods benefit greatly from being able to measure a large number of grains in a three dimensional space in a short amount of time and with a lower sensitivity to user bias of the two magnetic techniques discussed in this paper the new enhanced ams method in which rock magnetic properties are enhanced by introducing magnetite into the pores and as precipitates on grain surfaces is regarded to be an improvement over the traditional natural ams method in which only the natural assemblage of magnetite particles present in the rock is analysed enhanced ams measures the preferred orientation of essentially all grains in a rock sample thus providing the shape fabric of a hydrodynamically more accurate representation of framework grains than natural ams through a small technical modification the enhanced ams method can be used to obtain a magnetic cast of the pore network of a rock sample so that the resulting ams is controlled by the shape anisotropy of the individual pores it is commonly assumed that long axes of sand grains in sedimentary deposits parallel the direction of the flows that formed the deposits this concept is challenged by a new systematic study of grain fabric in deep marine turbidites it indeed appears that grains in ripple cross laminated divisions of turbidites dominantly attain a preferred orientation parallel to the palaeoflow direction but grains in plane parallel laminated divisions have an additional flow perpendicular mode which suggests a contribution of rolling grain transport three different fabric modes occur in massive structureless sandstones and massive divisions in turbidites apart from flow aligned and flow perpendicular modes there is a statistically significant but hydrodynamically enigmatic flow oblique mode with an average azimuthal deviation of 40 this large variation of fabric types suggests that a similar variation exists in preferred paths of pore fluid flow within turbidites controlled to at least some degree by depositional process this is confirmed by independent laboratory measurements of permeability anisotropy on samples for which grain fabric data are available and thus defines grain fabric analysis as a viable alternative to traditional permeametry techniques

source inversion of the 1988 upland california earthquake determination of a fault plane for a small event abstract we examined short period p waves to investigate if waveform data could be used to determine which of two nodal planes was the actual fault plane for a small m l 4 6 earthquake near upland california we removed path and site complications by choosing a small aftershock m l 2 7 as an empirical green function the main shock p waves were deconvolved by using the empirical green function to produce simple far field displacement pulses we used a least squares method to invert these pulses for the slip distribution on a finite fault both nodal planes strike 125 dip 85 and strike 221 dip 40 of the first motion focal mechanism were tested at various rupture velocities the southwest trending fault plane consistently gave better fitting solutions than the southeast trending plane we determined a moment of 4 2 10 22 dyne cm the rupture velocity and thus the source area could not be well resolved but if we assume a reasonable rupture velocity of 0 87 times the shear wave velocity we obtain a source area of 0 97 km 2 and a stress drop of 38 bars choice of a southwest trending fault plane is consistent with the trend of the nearby portion of the transverse ranges frontal fault zone and indicates left lateral motion this method provides a way to determine the fault plane for small earthquakes that have no surface rupture and no obvious trend in aftershock locations

seismic source parameters from the guerrero subduction zone abstract a method to systematically determine seismic moment and corner frequency from shear wave spectra has been applied to strong motion data recorded in guerrero mexico the method determines a model spectrum that minimizes the misfit from the observed spectrum after a correction for frequency dependent site response has been applied the calculated moments for larger events in guerrero are consistent with moments determined from teleseismic body waves adjusted for differences in focal depth and consequent assumed differences in the velocity and density structure in the source region the average stress drop for the 82 earthquakes with magnitudes from 3 to 7 is 150 bars the spatial distribution of the stress drops shows a distinctive pattern at the northwest end of the guerrero gap adjacent to the aftershock zones of large earthquakes in 1979 and 1985 there is a mix of low and high stress drop events at the southeast end of the guerrero gap where the most recent large earthquake occurred in 1957 there are predominantly high stress drop events this pattern might be caused by the different relative positions of these two active regions in the earthquake cycle although several other explanations cannot be ruled out

40ar 39ar geochronological constraints on the formation of the dayingezhuang gold deposit new implications for timing and duration of hydrothermal activity in the jiaodong gold province china abstract china s largest gold resource is located in the highly endowed northwestern part of the jiaodong gold province most gold deposits in this area are associated with the ne to nne trending shear zones on the margins of the 130 126 ma guojialing granite these deposits collectively formed at ca 120 5 ma during rapid uplift of the granite the dayingezhuang deposit is a large 120 t au orogenic gold deposit in the same area but located along the eastern margin of the late jurassic linglong metamorphic core complex new 40ar 39ar geochronology on hydrothermal sericite and muscovite from the dayingezhuang deposit indicate the gold event is related to evolution of the core complex at 130 4 ma and is the earliest important gold event that is well documented in the province the dayingezhuang deposit occurs along the linglong detachment fault which defines the eastern edge of the ca 160 150 ma linglong granite granodiorite massif the anatectic rocks of the massif were rapidly uplifted at rates of at least 1 km m y from depths of 25 30 km to form the metamorphic core complex the detachment fault with precambrian metamorphic basement rocks in the hangingwall and the linglong granitoids and migmatites in the footwall is characterized by early mylonitization and a local brittle overprinting in the footwall gold is associated with quartz sericite pyrite k feldspar altered footwall cataclasites at the southernmost area of the brittle deformation along the detachment fault our results indicate that there were two successive yet distinct gold forming tectonic episodes in northwestern jiaodong one event first reactivated the detachment fault along the edge of the linglong massif between 134 and 126 ma and then a second reactivated the shears along the margins of the guojialing granite both events may relate to a component of northwest compression after a middle early cretaceous shift from regional nw se extension to a ne sw extensional regime

on traction carpet sedimentation traction carpets are highly concentrated bedload layers that are developed beneath and driven by turbulent overlying flows they have a convex up velocity profile and comprise a lower frictional and an upper collisional region the frictional region having a particle concentration more than 80 of the packed bed is characterized by nearly continuous grain contacts low strain rate and hampered grain segregation on the other hand the collisional region has a particle concentration between 15 and 80 of the packed bed and is characterized by active grain collisions and higher strain rate deposition from the traction carpets occurs via progressive aggradation of the bed rather than via en masse freezing while the downward grain flux from the overlying flow maintains them the thickness of a traction carpet stratum is therefore determined by the cumulative amount of sediment settled during the lifespan of a traction carpet and can be much larger than the thickness of a moving traction carpet inverse grading can be produced in the collisional region by the vertical gradient of dispersive pressure which is related to nonuniform distribution of particles when a thick frictional region develops however the inverse size distribution in the collisional region is poorly recorded in the deposits depositional features of traction carpet strata are therefore determined by the duration of a traction carpet and the thickness ratio of collisional to frictional regions the thickness ratio is further controlled by the applied shear stress sediment fallout rate and grain size generally a collisional region is better developed beneath a highly competent and coarse grained gravelly flow whereas a thick frictional region is developed beneath a heavily sediment laden fine grained sandy flow this explains the more common occurrence of inverse grading in coarse grained deposits

the 1992 landers earthquake sequence seismological observations the m w 6 1 7 3 6 2 1992 landers earthquakes began on april 23 with the m w6 1 1992 joshua tree preshock and form the most substantial earthquake sequence to occur in california in the last 40 years this sequence ruptured almost 100 km of both surficial and concealed faults and caused aftershocks over an area 100 km wide by 180 km long the faulting was predominantly strike slip and three main events in the sequence had unilateral rupture to the north away from the san andreas fault the m w6 1 joshua tree preshock at 33 n58 and 116 w19 on 0451 ut april 23 was preceded by a tightly clustered foreshock sequence m 4 6 beginning 2 hours before the mainshock and followed by a large aftershock sequence with more than 6000 aftershocks the aftershocks extended along a northerly trend from about 10 km north of the san andreas fault northwest of indio to the east striking pinto mountain fault the m w7 3 landers mainshock occurred at 34 n13 and 116 w26 at 1158 ut june 28 1992 and was preceded for 12 hours by 25 small m 3 earthquakes at the mainshock epicenter the distribution of more than 20 000 aftershocks analyzed in this study and short period focal mechanisms illuminate a complex sequence of faulting the aftershocks extend 60 km to the north of the mainshock epicenter along a system of at least five different surficial faults and 40 km to the south crossing the pinto mountain fault through the joshua tree aftershock zone towards the san andreas fault near indio the rupture initiated in the depth range of 3 6 km similar to previous m 5 earthquakes in the region although the maximum depth of aftershocks is about 15 km the mainshock focal mechanism showed right lateral strike slip faulting with a strike of n10 w on an almost vertical fault the rupture formed an arclike zone well defined by both surficial faulting and aftershocks with more westerly faulting to the north this change in strike is accomplished by jumping across dilational jogs connecting surficial faults with strikes rotated progressively to the west a 20 km long linear cluster of aftershocks occurred 10 20 km north of barstow or 30 40 km north of the end of the mainshock rupture the most prominent off fault aftershock cluster occurred 30 km to the west of the landers mainshock the largest aftershock was within this cluster the m w6 2 big bear aftershock occurring at 34 n10 and 116 w49 at 1505 ut june 28 it exhibited left lateral strike slip faulting on a northeast striking and steeply dipping plane the big bear aftershocks form a linear trend extending 20 km to the northeast with a scattered distribution to the north the landers mainshock occurred near the southernmost extent of the eastern california shear zone an 80 km wide more than 400 km long zone of deformation this zone extends into the death valley region and accommodates about 10 to 20 of the plate motion between the pacific and north american plates the joshua tree preshock its aftershocks and landers aftershocks form a previously missing link that connects the eastern california shear zone to the southern san andreas fault

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

cooling paths of the ne china crust during the mesozoic extensional tectonics example from the south liaodong peninsula metamorphic core complex abstract the south liaodong peninsula massif is the easternmost mesozoic metamorphic core complex recognized in eastern china it provides a good example of the combination of ductile shearing syn kinematic plutonism and polyphase exhumation the jurassic granodioritic plutons located at the footwall of the detachment normal fault and dated here at ca 160 ma recorded two different phases of cooling a slow cooling regime of about 3 10 c my prevailing before 122 ma was followed by a significant increase in cooling rate of about 40 55 c my after that time by contrast a single fast cooling path was recorded by the cretaceous monzogranite situated in the footwall of the detachment normal fault this result indicates that the jurassic and cretaceous plutons recorded different exhumation processes a jurassic slow or negligible exhumation and a cretaceous fast one assisted by normal faulting these two cooling stages correspond to distinct geodynamic processes during the jurassic and cretaceous extensional tectonics seems not significant before early cretaceous the second stage dominated by an extensional regime which develops after ca 120 ma is tentatively correlated to the lithosphere removal of the north china craton

reinterpretation of depositional processes in a classic flysch sequence pennsylvanian jackfork group ouachita mountains arkansas and oklahoma discussion authors reply

extensional tectonics within a subduction type orogen the case study of the wugongshan dome jiangxi province southeastern china abstract in southeastern china the wugongshan massif consists of metamorphic rocks and granites generally considered as basement rocks formed during an early paleozoic orogeny our structural and radiometric reappraisal of this massif shows that it results from a mesozoic doming in the metamorphic rocks the foliation defines an e w elliptical shape and bears a n s stretching lineation the axial zone of the dome is occupied by oriented plutons the outer part of the dome consists of devonian quartzite carboniferous permian limestone and triassic jurassic sandstone ductile deformation observed in the permian carbonates and older units develops contrasting kinematics the northern and southern flanks present top to the north and top to the south motions respectively the same divergent pattern of motion is recorded from brittle structures up to the jurassic sandstone the late cretaceous red beds are undeformed in the axial zone coaxial flow indicated by symmetric pressure shadows and quartz fabrics predominates along the n and s flanks of the dome post folial recumbent folds are symmetrically overturned to the n and s respectively but at the two extremities of the dome the fold axes are parallel to the stretching lineation 40 ar 39 ar ages of biotite and muscovite from mylonite and granite suggest a late triassic age for the ductile deformation and an early cretaceous age for the final doming the wugongshan dome is similar to a metamorphic core complex formed in an extensional tectonic regime a model which emphasizes plutonism is discussed from permian to early cretaceous southeastern china was a subduction type orogen the crust of which was thickened by accretion of mantle derived magmas the emplacement of a large amount of mesozoic granitoids in southeastern china promoted thermal softening and gravitational instability that allowed the crust to extend the formation of the wugongshan dome and other metamorphic core complexes appears to be a the direct consequence of plutonic activity and crust rheology

anatomy of a world class epizonal orogenic gold system a holistic thermochronological analysis of the xincheng gold deposit jiaodong peninsula eastern china abstract xincheng is a world class orogenic gold deposit hosted by the early cretaceous guojialing granitoid in the jiaodong peninsula eastern china a zircon u pb age of 126 1 4 ma together with previous data constrain the emplacement of the guojialing intrusion to 132 123 ma the granitoid underwent subsolidus ductile deformation at 500 c following its intrusion the small difference in age between the youngest zircon u pb age of unaltered granitoid 123 ma and the ca 120 ma 40ar 39ar ages of sericite associated with breccias and gold mineralization within it indicate initial rapid cooling from magmatic temperatures to those prevalent during brittle deformation and associated gold mineralization at 220 300 c evidence of a direct association between granitic magmatism and gold mineralization such as at least localized near magmatic depositional temperatures and metal zoning evident in undoubted intrusion related gold deposits is absent the 40ar 39ar age of 120 ma coincides with the mineralization age of many other orogenic gold deposits along the jiaojia fault sixteen zircon fission track zft ages across the ore and alteration zones range from 112 9 3 4 to 99 1 2 7 ma the long period of cooling to the 100 ma zft closure temperatures recorded here suggests that ambient temperatures for hydrothermal alteration systems lasted to 100 ma possibly because of their focus at xincheng within the young guojialing granitoid as it cooled more slowly below approximately 300 c to 220 c however the restricted number of auriferous ore stages combined with the presence of cross cutting gold free quartz carbonate veins indicate that gold itself was only deposited over a restricted time interval at 120 ma consistent with studies of orogenic gold deposits elsewhere this highlights the complex interplay between magmatism deformation and the longevity of hydrothermal systems that cause genetic controversies based on apatite fission track aft ages the xincheng gold deposit was then uplifted and exhumed to near the surface of the crust at 15 ma probably due to movement on the crustal scale tan lu fault recognition of such exhumation histories along gold belts has conceptual exploration significance in terms of the probability of discovery of additional exposed or sub surface gold ore bodies as discovery is as much a function of preservation as formation of the deposits

pebble orientation on large experimental debris flow deposits abstract replicable pronounced orientation of discoid pebbles 8 mm embedded on surfaces of large 10 m3 experimental debris flow deposits reveals that strongly aligned imbricate fabric can develop rapidly over short distances in mass flows pebble long axes aligned subparallel to deposit margins as well as subparallel to margins of surge waves arrested within the deposits pebble alignment exhibited modes both parallel to a p the primary flow direction intermediate axes dipped preferentially inward from surge wave margins b i orientation repetitive development of margin parallel imbricate fabric distributed across deposit surfaces provides compelling evidence that deposits formed dominantly through progressive incremental accretion rather than through simple en masse emplacement pronounced fabric along deposit and arrested surge wave margins reflects significant grain interaction along flow margins this sedimentological evidence for significant marginal grain interaction complements theoretical analyses iverson 1997 and other experimental data major 1996 iverson 1997 that indicate that resistance along flow margins is an important factor affecting debris flow deposition the fabric on the experimental deposits demonstrates that debris flows can develop strongly imbricate particle orientation that mimics fabric developed during fluvial deposition particle shape and local stress fields appear to have more control over fabric development than does general depositional process other criteria in addition to particle orientation are needed to discriminate mass flow from fluvial gravel deposits and to unravel depositional history

visualization of the internal structure of the massive division in experimental sediment gravity flow deposits by mapping of grain fabric abstract a method for mapping of grain fabric is proposed for analysis of the cryptic internal structure of massive sedimentary units the method is applied to the analysis of an experimental debris flow deposit revealing a number of characteristic features of this type of mass sedimentation the debris flow was simulated in the laboratory using a channel inclined 30 opening onto a 10 slope and transverse thin sections were prepared from four longitudinal points in the depositional lobe back scattered electron images of the sections obtained by scanning electron microscopy were processed and analyzed by mapping of grain fabric using an automated image analysis procedure although the samples appear structureless by macroscopic observation the grain fabric map reveals a range of sedimentary features including distinctive lineations from lower upcurrent to upper downcurrent in the most proximal section representing synsedimentary thrusts a steepening upward trend of grain imbrication angle in intermediate samples with very low angle imbrication in the basal horizon indicative of high shear rate flow and complex imbrication features in the most distal samples this analysis reveals that massive debris flow deposits actually contain a range of distinctive structures which are characteristic of the mode of deposition and which are not identifiable by visible inspection or analysis of grain size or color the proposed method is therefore of great utility for the investigation and characterization of massive deposits

flake tectonics in the sulu orogen in eastern china as revealed by seismic tomography 1 seismic tomographic image reveals a crocodile like p waves velocity structure beneath the sulu orogenic belt which marks the subduction collision zone between the sino korean block sk and yangtze block yz in eastern china it may imply that the upper crust of the yz was detached from its lower crust and thrust over the sk for a maximum of 400 km in the sulu region whereas the remnant of the subducted yangtze lithosphere was lay beneath the sk this crustal detached structure flake tectonics might have occurred after the triassic subduction collision

tectonics of the qinling belt build up and evolution of eastern asia the structure and history of the qinling range which separates the north and south china cratons are a key to the tectonic evolution of eastern asia the mountain range is composed of a northern palaeozoic belt and a southern mesozoic belt the palaeozoic orogeny probably involved the closure of an oceanic basin along a north dipping subduction zone followed by south vergent obduction of ophiolites and intracontinental thrusting during the devonian the mesozoic belt appears to be the product of purely intracontinental shallow crustal deformation over a large decollement with at least 100 km of horizontal transport since the devonian both belts have been sliced by huge east west sinistral strike slip faults

the liaonan metamorphic core complex southeastern liaoning province north china a likely contributor to cretaceous rotation of eastern liaoning korea and contiguous areas abstract the mesozoic liaonan metamorphic core complex mcc of the southeastern liaoning province north china is an asymmetric cordilleran style complex with a west rooting master detachment fault the jinzhou fault a thick sequence of lower plate fault related mylonitic and gneissic rocks derived from archean and early cretaceous crystalline protoliths has been transported ese ward from mid crustal depths u pb ages of lower plate syntectonic plutons ca 130 120 ma 40 ar 39 ar cooling ages in the mylonitic and gneissic sequence ca 120 110 ma and a cretaceous supradetachment basin attest to the early cretaceous age of this extensional complex the recent discovery of the coeval and similarly west rooting waziyu mcc in western liaoning darby b j davis g a zhang x wu f wilde s yang j 2004 the newly discovered waziyu metamorphic core complex yiwulushan western liaoning province north china earth science frontiers 11 145 155 indicates that the gulf of liaoning which lies between the two complexes was the center of a region of major crustal extension clockwise crustal rotation of a large region including eastern liaoning province and the korean peninsula with respect to a non rotated north china block has been conclusively documented by paleomagnetic studies over the past decade the timing of this rotation and the reasons for it are controversial lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 proposed that a clockwise rotation of 22 5 10 2 was largely post early cretaceous in age and was the consequence of extension within a crustal domain that tapers southwards towards the bohai sea of which the gulf of liaoning is the northernmost part paleomagnetic studies of early cretaceous strata ca 134 120 ma in the yixian fuxin supradetachment basin of the waziyu mcc indicate the non rotation of north china and the basin zhu r x shao j a pan y x shi r p shi g h li d m 2002 paleomagnetic data from early cretaceous volcanic rocks of west liaoning evidence for intracontinental rotation chinese science bulletin 47 1832 1837 such upper plate non rotation supports our conclusion that the lower plates of the waziyu and liaonan metamorphic core complexes were displaced ese ward in an absolute sense away from the stable north china block thus contributing to the rotation of korea and contiguous areas rotation is inferred to have affected only the upper crust above mid crustal levels into which we believe the jinzhou and waziyu detachment fault zones flattened if this is the case the regional tan lu fault that lies between the two core complexes was truncated at mid crustal depth since in areas to the south it forms the boundary between the north and south china lithospheric blocks it is noteworthy that the two extensional complexes lie not far north of the bohai bay the area proposed by lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 as the site of the pole of rotation for korea s clockwise displacement lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 were unaware of the liaonan and waziyu mcc s and argued that most of the regional block rotation was post early cretaceous and in part early cenozoic however the ca 130 120 ma ages of the two liaoning mcc s and a songliao basin mcc xujiaweizi the latter discovered only by recent drilling through its younger stratigraphic cover support our and some korean coworkers conclusions that most of the clockwise rotation was early cretaceous

an image analysis technique to measure grain size variation in thin sections of soft clastic sediments this paper presents a simple and fast image analysis technique to measure grain size variation in thin sections of soft elastic sediments optical and backscattered electron microscope photographs are digitised from thin sections cut by freeze drying to avoid disturbing the sediments processing of the 256 grey scale images produces binary black and white images where white pixels represent the clay rich sedimentary matrix and black pixels represent elastic grains data measured include grain surface grain perimeter and centre of gravity two indices are defined to quantify grain size d 0 equivalent disk diameter and p phase percentages the technique is applied to silt and clay laminations attributed to the d division of a distal turbidite from lake baikal the data obtained using image analysis are similar to the conventional descriptions of such deposits indices calculated on very small samples e g on a single lamina allow for greater precision in interpretation of sedimentary processes compared to photomicrographs backscattered electron microscope images have better qualities and allow to quantify variations in the grain size along a sediment core the technique produces objective and quantified grain size observations in less time than conventional petrographic methods c 1998 elsevier science b v all rights reserved

dating of subduction and differential exhumation of uhp rocks from the central dabie complex e china constraints from microfabrics rb sr and u pb isotope systems abstract the correlation of deformation fabrics and metamorphic reactions with geochronologic data of uhp metamorphic rocks demonstrate that the multistage subduction and exhumation history of the central dabie complex requires rapid subduction and rapid initial exhumation moreover these data show that volume diffusion is not the major resetting mechanism of radiogenic isotope systems thus our age data do not simply reflect a thermal cooling history in the investigated section the maximum age for uhp is given by the 244 3 ma 2 u pb age of a pre uhp titanite phenocryst that survived uhp metamorphism and subsequent tectonometamorphic events a minimum age for uhp is set by the 238 1 ma 2 238 u 206 pb mineral isochron age of titanite and cogenetic epidote these minerals formed from local partial melts during ascent and their age suggests fast exhumation and emplacement in the middle crust in the period of ca 238 218 ma the uhp terrain records ht metamorphism local partial melting and extensive pervasive strain below the eclogite jd grt stability field exhumation was polyphase with a first phase of fast exhumation succeeded by episodes of ht metamorphism and concomitant deformation at deep mid crustal level between 238 and 218 ma slow exhumation related to the final emplacement of tectonic units along greenschist facies shear zones did not cease before ca 209 204 ma the resetting and homogenization of radiogenic isotope systems were aided by dissolution precipitation creep which was the dominant deformation mechanism in quartz feldspar rocks in combination with fluid influx

dynamics of exhumation and deformation of hp uhp orogens in double subduction collision systems numerical modeling and implications for the western dabie orogen abstract the dynamics of formation and exhumation of high pressure hp and ultra high pressure uhp metamorphic orogens in double subduction collision zones remain enigmatic here we employ two dimensional thermo mechanical numerical models to gain insights on the exhumation of hp uhp metamorphic rocks as well as their deformation during the collision of a micro continent with pro and retro continental margins along two subduction zones a three stage collisional process with different convergence velocities is tested in the initial collisional stage a fold and thrust belt and locally rootless superimposed folds are developed in the micro continent and subduction channel respectively in the second exhumation stage of hp uhp rocks a faster convergence model results in upwelling of the asthenosphere which further leads to a detachment between the crust and lithospheric mantle of the micro continent a slower convergence model results in rapid exhumation of hp uhp rocks along the north subduction channel and a typical piggy back thrusting structure in the micro continent a non convergence model produces a slab tear off leading to the rebound of residual lithosphere of the micro continent in the third and final stage a series of back and ramp thrusts are formed in the micro continent with the pro continent re subducted based on an analogy of our numerical results with the western dabie orogen wdo we suggest that 1 slab tear off results in a rebound of residual lithosphere which controls the two stage syn collisional exhumation process of hp uhp rocks in the wdo and 2 in contrast to the single subduction collision system the exhumation range of the partially molten rocks with lower viscosity and density is restricted to a specific region of the micro continent by the mianlue and shangdan subduction zones which generated the complex deformation features in the wdo

depositional processes in large scale debris flow experiments this study examines the depositional process and characteristics of deposits of large scale experimental debris flows to 15 m3 composed of mixtures of gravel to 32 mm sand and mud the experiments were performed using a 95 m long 2 m wide debris flow flume that slopes 31 following release experimental debris flows invariably developed numerous shallow 10 cm deep surges sediment transported by surges accumulated abruptly on a 3 runout slope at the mouth of the flume deposits developed in a complex manner through a combination of shoving forward and shouldering aside previously deposited debris and through progressive vertical accretion progressive accretion by the experimental flows is contrary to commonly assumed en masse sedimentation by debris flows despite progressive sediment emplacement deposits were composed of unstratified accumulations of generally unsorted debris hence massively textured poorly sorted debris flow deposits are not emplaced uniquely en masse the depositional

particle fabric and sedimentation of structureless sand southern iceland abstract the interpretation of structureless sand units in terms of flow character and associated depositional mechanism is notoriously difficult to deduce from localized outcrop because such units offer no macroscopic features with which to make distinctions of flow parameters this investigation assesses the significance of directional properties of particle fabric samples taken both vertically and horizontally within structureless sand units deposited by jokulhlaups glacier outburst floods in southwest iceland known to be macroturbulent phenomena based on eyewitness accounts and inferences made from the large scale sedimentary architectures of the deposits given this framework we use particle fabric to verify flow character and depositional mechanism highlighting its potential application to deposits where prior knowledge of conditions is unknown vertical and horizontal trends in particle fabric indicate a causative mechanism that is manifested both spatially and temporally within visually structureless units this data indicates sedimentation onto an aggrading bed beneath a turbulent flow which conforms to the documented turbulent character of the jokulhlaup we demonstrate that cryptic information related to flow parameters can be gleaned from visually structureless sand units through detailed particle fabric analysis and clarify aspects of hyperconcentrated flow behavior and sedimentation

detrital zircons reveal no jurassic plateau in the eastern north china craton abstract u pb hf isotopic analyses have been carried out on detrital zircons from late permian jurassic strata in the western shandong bohai bay wsbb basins with aims of constraining the paleogeography and evolution of the eastern north china craton ncc four major groups of u pb ages namely 3 0 2 3 ga 2 2 1 4 ga 1250 430 ma and 410 150 ma are recognized for zircons from the fine grained sandstones the post paleoproterozoic zircons of the late permian sample show an age cluster of 344 255 ma with e hf t values of 18 to 8 being similar to those extracted from late paleozoic igneous rocks from the yinshan yanshan orogenic belt yyob on the northern margin of the ncc however the devonian jurassic zircons 390 150 ma from the jurassic sediments have e hf t values from 45 to 14 very similar to the mixture of phanerozoic zircons from the xing meng orogenic belt xmob and the yyob but significantly different from those of the liaodong peninsula jiaodong peninsula and the western shandong uplift in addition cambrian silurian zircons 535 430 ma of the jurassic samples have e hf t values from 27 to 7 resembling the early paleozoic zircons extracted from the northern qinling orogen nqo the u pb age spectra and hf isotope of devonian jurassic zircons as well as bulk nd isotopes suggest that the central eastern ncc received some juvenile materials from the xmob the yyob and the nqo during the jurassic this indicates widespread prototype basins and a low elevation during the jurassic arguing against the presence of a paleo plateau in the eastern ncc at that time the lack of evidence predicted by lithospheric delamination e g large scale elevation or doming after late triassic makes the delamination unlikely to be a viable mechanism of lithospheric thinning of the ncc the subsidence rather than elevation of the eastern ncc after late triassic might be related to thermo chemical erosion of the lithosphere by underlying convective mantle in a back arc setting

a new concept on tectonic correlation between korea china and japan histories from the late proterozoic to cretaceous abstract the dabie sulu collision belt in china extends to the hongseong odesan belt in korea while the okcheon metamorphic belt in korea is considered as an extension of the nanhua rift within the south china block the hongseong odesan belt divides korea s gyeonggi massif into northern and southern portions the southern gyeonggi massif and the yeongnam massif are correlated with china s yangtze and cathaysia blocks respectively while the northern gyeonggi massif is part of the southern margin of the north china block the southern and northern gyeonggi massifs rifted from the rodinia supercontinent during the neoproterozoic to form the borders of the south china and north china blocks respectively subduction commenced along the southern and eastern borders of the north china block in the ordovician and continued until a triassic collision between the north china and south china blocks while subduction was occurring on the margin of the north china block high p t metamorphic belts and accretionary complexes developed along the inner zone of southwest japan from the ordovician to the permian during the subduction the hida belt in japan grew as a continental margin or continental arc collision between the north and south china blocks began in korea during the permian 290 260 ma and propagated westwards until the late triassic 230 210 ma creating the sinistral tanlu fault in china and the dextral fault in the hida and hida marginal belt in japan phanerozoic subduction and collision along the southern and western borders of the north china block led to formation of the qinling dabie sulu hongseong hida yanji belt

the relationship between systematic metamorphic patterns and collisional processes along the qinling sulu odesan collisional belt between the north and south china cratons

tectonic relation between northeastern china and the korean peninsula revealed by interpretation of grace satellite gravity data abstract the major continental blocks in northeastern asia are the north china block and the south china block which have collided starting from the korean peninsula geologic and geophysical interpretations reveal a well defined suture zone in northeastern china from qinling through dabie to jiaodong the discovery of high pressure metamorphic rocks in the hongseong area of the korean peninsula prominent evidence for the collision zone indicates extension of the collision zone in northeastern china into the korean peninsula interpretation of the grace satellite gravity dataset shows two prominent structural boundaries in the yellow sea one extends from the jiaodong belt in eastern china to the imjingang belt in the korean peninsula the other extends from near nanjing eastern china to hongseong tectonic movement in or near the suture zone may be responsible for seismic activity in the western korean peninsula and the development of the yellow sea sedimentary basin

microearthquake spectra from the anza california seismic network site response and source scaling abstract we analyzed spectra of local microearthquakes recorded by the anza california seismic network to isolate the effects of site response and to investigate the scaling of source parameters for small earthquakes spectra of microearthquakes m m o 19 dyne cm at anza have shapes characteristic of the receiver sites and are generally independent of the source region thus the site response is a major conditioner of the observed spectral shape to remove the effects of site response from the spectra of a m 3 event and isolate its source spectrum we divided by the spectra of an adjacent aftershock used as an empirical green9s function event the spectral ratios indicate that the apparent corner frequencies of small earthquakes m o 19 dyne cm observed at even the high f max stations on hard rock are much lower than the source corner frequencies the spectral ratios are consistent with stress drop remaining constant with decreasing seismic moment for events with moments as small as 10 18 dyne cm the spectral ratios display remarkable agreement between sites which showed vast differences in their original spectra indicating that the spectral division effectively removed the site response the source spectrum of the m 3 event has a high frequency spectral fall off of about 2 an apparent dependence of high frequency fall off with seismic moment in the original spectra can also be explained by the effects of site response the difference between the p and s wave corner frequencies and high frequency roll offs in the observed spectra for these events is the result of the site response and is not a source property the shapes of the spectra of microearthquakes at anza can largely be explained by attenuation at shallow depth with a frequency independent q for some sites near surface resonances are also apparent in the spectra of microearthquakes it is indicated by t values determined for each site that q p q s for the shallow low q layer further evidence of low near surface q is observed in the anomalous spectra of an unusually shallow earthquake source depth 1 km in the network the spectra from this shallow event are depleted in high frequency energy at most stations relative to those of deeper events this observation can be explained by a low q surficial zone for stations of the network situated on alluvium this low q layer has a maximum thickness of about 3 km and maximum p and s wave q values of 30 to 50

a practical classification of gold deposits with a theoretical basis abstract well considered schemes that classify ore deposits can be effective contributors to exploration success understanding of deposit genesis mining geology engineering metallurgy property valuations and stock market analysis an effective classification scheme needs to be easy to apply without ambiguity and is much more powerful if based on sound scientific principles for deposits with economic gold a useful classification recognises gold only and gold plus deposits based upon whether they also have economic base metals the scheme is easy to apply and in most cases unambiguous for specific deposits and whole provinces the subdivision has a sound scientific basis that involves the chemistry of gold in relation to metal complexing salinity of ore forming fluids and redox state forward modelling from chemical principles can be integrated with inverse modelling from observations to add confidence in this classification and thus be used to create exploration opportunities the jiaodong gold province of eastern china comprises deposits mostly in granitic rocks with economic gold but low levels of base metals the inferred ore fluids are of low to moderate salinity from their gold only character several other aspects of their development can be inferred though the tectonic and metamorphic history remains unresolved the granitic host rocks appear to reflect a chemically and mechanically favourable site for deposition not a source for the gold or the ore fluid neither of which have been established yet