detection of a volcanic fracture opening in japan using global positioning system measurements the global positioning system gps is a powerful tool for detecting crustal deformation1 for example the technique has been used to detect plate boundary movements in california2 here we report observations of crustal deformation associated with seismic swarm and sea floor volcanic activity off the east coast of the izu peninsula japan in july 1989 using a fixed point gps network these measurements have enabled us to capture some rarely observed features of seismic and volcanic activity we have for the first time used gps fixed point measurements to follow the evolution with time of the crustal movements such measurements provide a continuous uninterrupted record of deformation our observations were supported by independent data from other sources thus providing further evidence for the utility of the gps

application of the global positioning system to crustal deformation measurement 2 the influence of errors in orbit determination networks global positioning system gps measurements of a geodetic network in southern and central california have been used to investigate the errors introduced by adopting different sets of stations as fixed such fixed points called fiducial stations are necessary to eliminate the errors of imprecise satellites orbits which otherwise would dominate the error budget for distances greater than tens of kilometers these fiducial stations also define the reference frame of the crustal deformation network establishing the magnitude of the effect of changing the fiducial network is essential for crustal deformation studies so that these artifacts of the differences between fiducial networks used for the data analyses are not interpreted as geophysical signals solutions for a crustal deformation network spanning distances up to 350 km were computed with a variety of fiducial networks we use fiducial coordinates determined from very long baseline interferometry vlbi we compare these solutions by computing the equivalent uniform strain and rotation that best maps one solution into another if we use a continental scale fiducial network with good geometry the distortions between the solutions are about 10 8 largely independent of the exact choice of stations the one case of a large scale fiducial network where the distortions are larger is when the three fiducial stations chosen all lie close to a great circle use of a fiducial network no larger than the crustal deformation network tan produce apparent strains of up to 10 7 our work suggests that fiducial coordinates determined from gps data analysis may be used although they should be determined using a consistent reference frame such as provided by vlbi and satellite laser ranging

southern california permanent gps geodetic array continuous measurements of regional crustal deformation between the 1992 landers and 1994 northridge earthquakes the southern california permanent gps geodetic array pgga was established in 1990 across the pacific north america plate boundary to continuously monitor crustal deformation we describe the development of the array and the time series of daily positions estimated for its first 10 sites in the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes we compare displacement rates at four site locations with those reported by feigl et al 1993 which were derived from an independent set of global positioning system gps and very long baseline interferometry vlbi measurements collected over nearly a decade prior to the landers earthquake the velocity differences for three sites 65 100 km from the earthquake s epicenter are of order of 3 5 mm yr and are systematically coupled with the corresponding directions of coseismic displacement the fourth site 300 km from the epicenter shows no significant velocity difference these observations suggest large scale postseismic deformation with a relaxation time of at least 800 days the statistical significance of our observations is complicated by our incomplete knowledge of the noise properties of the two data sets two possible noise models fit the pgga data equally well as described in the companion paper by zhang et al this issue the pre landers data are too sparse and heterogeneous to derive a reliable noise model under a fractal white noise model for the pgga data we find that the velocity differences for all three sites are statistically different at the 99 significance level a white noise plus flicker noise model results in significance levels of only 94 43 and 88 additional investigations of the pre landers data and analysis of longer spans of pgga data could have an important effect on the significance of these results and will be addressed in future work

global positioning system measurements of ground deformation caused by magma intrusion and lava discharge the 1990 1995 eruption at unzendake volcano kyushu japan abstract global positioning system gps measurements made around unzendake volcano kyushu japan since january 1991 have detected ground deformation caused by magma intrusion and lava discharge in the intermittent phreatic and phreatomagmatic eruption stage the ground was inflating after growth of the lava dome and following frequent pyroclastic flows at unzendake volcano the ground began deflating these ground deformations are explained by the inflation and deflation of a mogi s source model a point source model located about 6 km west of the active crater at a depth of 11 km at an aseismic region the observed horizontal displacement vectors pointed radially away from the estimated pressure source during inflation and pointed to the pressure source during deflation the horizontal displacements at the reference gps station calculated from contraction of the estimated pressure source coincide well with the actual horizontal displacements observed from other gps baseline systems these observations validate our estimates for the pressure source based on the relation between the deformation volume of the ground surface and the discharged volume of the lava it is estimated that during the eruption there was magma supply from the deeper portion as well as magma discharge at the crater magma is estimated to be supplied to the reservoir at an average rate of 1 1 105 m3 day magma intrusion began in december 1989 at the latest and continued for 1 9 103 days

dyke intrusion model for the 1989 seismovolcanic activity off ito central japan in the last 10 years extensive earthquake swarms have occurred intermittently in the region east of izu peninsula central japan in july 1989 an active swarm again took place off ito city and among all past activities it was nearest to land and shallowest this activity eventually became a weak submarine eruption the first of its kind in this region associated with this event a borehole tiltmeter at 92 m depth installed several kilometers from the source area detected distinct continuous tilt change with the following features 1 tilt of 20 rad was observed within 1 week preceding the eruption 2 tilt change showed a good correlation to swarm activity 3 no obvious coeruption tilt change was observed on the basis of the tilt record and swarm distribution we constructed a dislocation model to interpret the seismovolcanic activity the model consists of two tensile faults each of which corresponds to magma intrusions in may and july and a right lateral reverse fault representing the largest earthquake m5 5 at 1109 lt on july 9 this model can simulate not only the above tilt data but also the record of a nearby dilatometer the results from daily laser distance measurements and daily global positioning system monitoring as well as results from other conventional distance surveys and leveling surveys in the surrounding region from this model we conclude that the intersection of the shear fault with the tensile fault caused magma to come up into soft sedimentary layers at the seabottom creating a lava dome later an instability brought about a magma phreatic explosion which did not generate any substantial crustal deformations at deeper levels

rheological evolution of the ocean crust a microstructural view rheological studies of the oceanic lithosphere have used direct observations of rocks and inferences based on thermal mechanical and experimental models modeling studies help to constrain an average crust and mantle rheology and the deep seated processes that control regional scale strength and stress field variations the smoothing of fine scale variations in such models can obscure many of the geological processes that influence strain localization and deformation partitioning in the ocean crust examination of deformation mechanisms and histories in ocean crust rocks provides a complementary approach to modeling examples of structures and deformation histories in diabases from deep sea drilling project ocean drilling program site 504b the hayes and atlantis fracture zones mid atlantic ridge and the troodos ophiolite cyprus are presented in conjunction with a synthesis of microstructural studies of the ocean crust over the last 25 years a survey of brittle quasi plastic and synmagmatic viscous deformation is used to demonstrate the influence of primary compositional and textural characteristics and variable magmatic and hydrothermal histories on deformation mechanisms and strain localization in the ocean crust geological evidence indicates that hydrothermal fluids strongly influence the nature of deformation and that effective stresses may be low due to fluid overpressures melt distribution will strongly influence strain localization at the base of the crust and synkinematic hydration during crystal plastic deformation plays a key role in the relative strengths of polyphase oceanic lithologies a schematic distribution of failure mechanisms in the ocean crust is used to discuss the controls on variations in lateral and vertical strength profiles and their possible relation to spreading rates although microstructural studies of ocean crust are still in their infancy they provide valuable constraints for rheological models and further insights to explain the distribution of seismicity at spreading centers and acoustic signatures

possible magma intrusion revealed by temporal gravity ground deformation and ground temperature observations at mount komagatake hokkaido during the 1996 1998 crisis summary mount komagatake 1131 m above sea level is a subduction related active volcano in hokkaido japan where two phreatic eruptions occurred in 1996 march and 1998 october after 54 years of dormancy we analyse four sessions of geodetic microgravity and ground temperature observations made over a two year period from november 1996 to may 1997 neither significant gravity nor significant elevation changes gps or levelling were observed from may 1997 to november 1997 we observed a slight subsidence 1 2 cm and contraction within 1 cm of the edifice a gravity increase 15 30 gal at the benchmarks inside the 2 km wide summit crater and a local temperature increase of 15 20 c at the summit crater from november 1997 to may 1998 we observed an edifice wide gravity increase of about 15 gal with no significant elevation change for benchmarks outside the summit crater besides this edifice scale variation we recorded a subsidence of about 5 6 cm and apparently no change of gravity inside the summit crater we inverted our data using models of increasing complexity elastic models are able to explain our deformation observations but they cannot explain either the gravity data or the temperature observations satisfactorily we introduced both an isothermal and a non isothermal porous medium filled with fluids to model deformation and gravity variations and we used a fissure model to invert the temperature anomaly our observations are consistent with a model of underground shallow water evaporation occurring as a result of heat rising from a hot and dense body density contrast of 200 kg m 3 of about 1011 kg at 4 5 km depth this interpretation suggests a possible intrusion of a magmatic body within the edifice

a holocene pollen record of vegetation and coastal environmental changes in the coastal swamp forest at batulicin south kalimantan indonesia abstract pollen analysis of a coastal peat swamp core representing 9100 bp from batulicin south kalimantan indonesia shows that mangrove forest with rhizophora as its main element has been established since the early holocene vegetation development in general and particularly mangrove forest was influenced by holocene environmental changes the highest value of rhizophora at ca 8200 bp indicates an early holocene sea level drop and implies sea level at ca 9 m subsequently mangrove forest was severely disrupted by rapid sea level rise at ca 6400 bp prior to the holocene maximum however it quickly recovered following a lower rate of sea level rise or subsequent sea level drop at ca 6000 bp and flourished until ca 1000 bp from ca 6000 bp the environmental setting around the site seems to have gradually become more terrestrial and changed from mangrove forest to peat swamp forest due to higher precipitation and intensive progradation human influence is recognized from ca 1600 bp

the technology of tin smelting in the rooiberg valley limpopo province south africa ca 1650 1850 ce abstract a substantial indigenous tin smelting industry arose in the rooiberg valley of northern south africa in the second millennium ce this study concentrates upon tin smelting slags and refractory ceramics from two archaeological sites that date between ca 1650 ce and ca 1850 ce these were studied by optical and electron microscopy wavelength dispersive x ray fluorescence wd xrf inductively coupled plasma mass spectrometry icp ms and electron microprobe empa the slags are predominantly glassy high sno and relatively low sio 2 contents indicate that tin is a major glass forming element comparison of slag chemistries with the mineralogy of ore deposits and host rocks shows that alluvial cassiterite was used at one of the sites while cassiterite from hard rock mining was smelted at the other site since few preindustrial tin slags have been studied we compare our findings to other published examples mostly from southwest england

the earthquake prediction experiment at parkfield california since 1985 a focused earthquake prediction experiment has been in progress along the san andreas fault near the town of parkfield in central california parkfield has experienced six moderate earthquakes since 1857 at average intervals of 22 years the most recent a magnitude 6 event in 1966 the probability of another moderate earthquake soon appears high but studies assigning it a 95 chance of occurring before 1993 now appear to have been over simplified the identification of a parkfield fault segment was initially based on geometric features in the surface trace of the san andreas fault but more recent microearthquake studies have demonstrated that those features do not extend to seismogenic depths on the other hand geodetic measurements are consistent with the existence of a locked patch on the fault beneath parkfield that has presently accumulated a slip deficit equal to the slip in the 1966 earthquake a magnitude 4 7 earthquake in october 1992 brought the parkfield experiment to its highest level of alert with a 72 hour public warning that there was a 37 chance of a magnitude 6 event however this warning proved to be a false alarm most data collected at parkfield indicate that strain is accumulating at a constant rate on this part of the san andreas fault but some interesting departures from this behavior have been recorded here we outline the scientific arguments bearing on when the next parkfield earthquake is likely to occur and summarize geophysical observations to date

holocene climate change and sea level oscillations in the pacific coast of mexico abstract a 2 75 m long core was recovered from la joya lagoon at the southern pacific coast of mexico the base of the core gave an age of ca 5600 a bp the ams 14c dating results indicate a continuously depositional history over the past 5600 years with varied sedimentation rates of 0 022 0 08 cm yr sediment samples were analyzed for pollen diatoms loss on ignition loi magnetic susceptibility and elemental analysis to study the environmental and marine changes ocurred during the holocene in the study site of the pacific coast our data provided indications of the paleoenviromental changes in the study site from the south pacific coast of mexico a complete marine environment from ca 5600 to ca 3200 a bp a transitional lagoon from ca 3200 to 1100 a bp and followed by a shift toward a close lagoon with fresh water during the last 1100 years the pollen data the presence of pollen from cucurbitaceae and secondary taxa related to disturbed vegetation of la joya record show evidence of agricultural activities and human occupation in the study area might exist 5000 a bp

coswarm and preswarm crustal deformation in the eastern izu peninsula central japan remarkable crustal deformation has repeatedly been observed in the eastern izu peninsula central japan synchronized to the occurrence of extensive earthquake swarms in the past 20 years among the instrumentation a borehole tiltmeter installed at station kwn which is located within a few kilometers of the swarm region has faithfully recorded large signals of ground tilt associated with more than 10 swarm sequences in the past 10 years in addition to coswarm signals it became clear that precursory tilt signals preceded major swarm activities the amplitudes of the precursory tilt signals are of order of 0 1 rad and they precede the onset of major swarms by several hours to half a day this signal is convincing because the same phenomena appeared at least 7 times and were also detected by other independent observations we speculate that a dike intrusion at depth causes crustal deformation and only as it reaches depths shallower than 10 km does seismic activity begin the precursory tilt signal can be utilized for practical prediction of the start of swarm activity in the eastern izu peninsula

evaluation of gps estimates of relative positions from central california 1986 1988 i report estimates of long term precision and accuracy of interstation vectors using the global positioning system gps precision is estimated from three experiments conducted in central california over a period of 1 2 years horizontal precision is 3 to 8 mm for baseline vectors between 100 and 450 km in length and the vertical precision ranges from 11 to 33 mm accuracy is assessed by comparing vlbi estimates with results from 6 gps experiments conducted at mojave and palos verdes over a period of 2 2 years rates for all vector components agree with vlbi within one standard deviation

imaging magma transport during the 1997 seismic swarm off the izu peninsula japan the spatio temporal evolution of a propagating magma filled crack was estimated from inversion of global positioning system gps data tiltmeters and leveling the dike opened at a maximum rate of 50 millimeters per day and had a peak magma flux of 2 x 10 6 cubic meters per day although the spatial resolution was limited slow upward propagation was resolved during the 9 day long intrusion in contrast the earthquakes migrated rapidly upward during the first 12 hours of the swarm and nearly all of the seismic energy was released in the first 2 days comparison of inversion results with accurate hypocenter locations will lead to improved understanding of magma transport through the brittle crust and of the causes of volcanic seismicity

a novel approach to lead isotope provenance studies of tin and bronze applications to south african botswanan and romanian artifacts lead isotopic ratios of cassiterite the dominant ore of tin evolve after crystallization through decay of uranium u and thorium th to lead pb due to the relatively elevated u pb ratios of this mineral we show that the pb isotopic ratios of smelted tin at rooiberg south africa form an isochron with a model age that matches the known geological age 2 ga of the host granite for the rooiberg cassiterite deposits since the pb isotopic ratios of many prehistoric tin and bronze artifacts throughout southern africa also fall on this isochron we deduce that they were made with tin from either the rooiberg deposits or similar age deposits that exist nearby in addition we show that bronze artifacts from romania define an isochron corresponding to a variscan age 0 3 ga suggesting a central or western european tin deposit as its source since no variscan tin is known from the neighboring carpathian mountains implications of this approach for provenance studies of tin and bronzes around the world are examined given various major tin deposits and their age distribution

spectral comparison of continuous global positioning system and strainmeter measurements of crustal deformation temporal power spectral density models of noise in continuous crustal deformation measurements obtained with the global positioning system gps and high quality strainmeters are compared the crossover frequency at which gps measurement noise is less than that of strainmeters is determined assuming gps precision of 0 1 to 1 cm in horizontal components for baselines up to 100 km in length local deformation monitoring with gps may be preferable to strainmeters for observations of short term deformation in under 6 months of continuous at least daily measurements short period tropospheric path delays and multipath effects which may obscure gps determined strain signals in local network measurements also are discussed

tin isotope characterization of bronze artifacts of the central balkans abstract isotopic analysis has proved to be an effective approach to determine the provenance of copper ore sources for the production of bronze artifacts more recently methods for sn isotopic analysis of bronze have been developed however the viability of tin isotopes as a means to define groupings that may be attributed to varying ore sources production methods or recycling is still in question in part this is due to the numerically and or geographically limited nature of published datasets this study reports on the sn isotopic composition of 52 artifacts from the later bronze age 1500 1100 bce from serbia and western romania the majority of samples cluster between 0 4 and 0 8 per mil for 124 sn and 0 2 and 0 4 per mil for 120 sn relative to nist srm 3161a and this isotopic grouping of bronze artifacts occurs across serbia however groupings of isotopically heavier and lighter artifacts are evident and each corresponds to a more limited geographic range artifacts associated with higher sn values are limited to the vojvodina region of northern serbia whereas a cluster of bronzes with lower sn isotopic signatures are constrained to the banat along the serbia romania border and transylvania one low value outlier corresponds to an uncontextualized find near krusevac at the southern extent of the study area geographic correlation of the low value cluster with known tin mineralization in transylvania and the moderate value cluster with placer tin deposits of western serbia suggests that these distinct bronze sn isotopic signatures might reflect exploitation of different tin ores the small cluster of high sn isotopic values from bronzes from the vojvodina region might reflect bronze recycling in this area that lies furthest from both known tin ore sources

the dynamics of mangrove ecosystems changes in sea level and the strategies of neolithic settlements along the coast of oman 6000 3000 cal bc abstract this paper focus on the holocene palaeogeography of the ja alan coast from the 6th to the 4th millennium cal bc integrating the dynamics of mangroves lagoons khors estuaries and deltas with sea level change and the evidence from neolithic shell middens the distribution and maturation of mangrove ecosystems along the arabian coasts has varied considerably affected by physical forces such as sea level changes climate tidal amplitude and duration as well as the quantity of fresh water inflow associated with the monsoon systems along the arabian coast palaeo mangroves and lagoons today replaced by large sabkhas appear to be correlated to mid holocene fossil deltas and estuaries that currently function episodically depending on the rhythm of winter rains all these parameters have determined and impacted the location of settlement networks and the economic strategies of the first arabian farmers along the eastern arabian coast the mid holocene sea level highstand stability 5th millennium bc can be considered to be an optimum period for mangrove development and can be correlated with neolithic sites around the mangroves the decline of mangroves since 3000 2500 cal bc and further degradation is mainly attributed to the prevailing arid climate that reduced summer monsoon effects in the tropical area by favouring the extension of sabkhas we discuss these aspects based on new archaeological surveys excavations and geoarchaeological studies

crustal deformation measurements in central japan determined by a global positioning system fixed point network a global positioning system gps fixed point network has been operating in the kanto and tokai districts of central japan since april 1988 to detect crustal deformation associated with the convergence of the eurasian pacific north american and philippine sea plates and to monitor the deformation cycles of frequent large interplate and intraplate earthquakes this 10 station network established by the national research institute for earth science and disaster prevention nied is the first continuously monitoring network of its kind we determine deformation within the network using two consecutive days of data every 2 weeks for the first 17 months of operations we use a station and orbit relaxation method which relies exclusively on data collected within the nied network except for 1 week of global gps tracking data which is used to determine initial station positions with respect to the global reference frame we detect relative to a station on the eurasian plate in central japan significant westward motion of 28 mm yr of the northern tip of the philippine sea plate which is subducting beneath the eurasian plate at the suruga trough our results support finite element models of collision of the izu block with the eurasian plate based on earthquake focal mechanisms and plate block motions of the japanese archipelago determined from conventional geodetic measurements over the last century we detect southwestward motion of 18 mm yr of the southeastern tip of the eurasian plate confirming expected surface extension of the subducted plate parallel to the suruga trough axis significant vertical uplift with a velocity of 20 mm yr is suggested at a site inland of the tokai district located in the akaishi uplift zone and at a site on hatsushima island in sagami bay the general tendency of vertical movements of the other sites agrees with vertical velocities obtained from 70 years of geodetic leveling and with quaternary vertical displacements determined from geomorphological and other geological evidence we detect no significant crustal motion across the fossa magna tectonic zone in central japan often considered a plate boundary across the tokyo metropolitan area nor across the sagami trough associated with the subduction of the philippine sea plate beneath northeast japan our results demonstrate the power of regionally based continuously monitoring gps networks for obtaining temporally dense measurements of small horizontal and vertical crustal movements across plate boundary zones

cyanobacteria and testate amoeba as potential proxies for holocene hydrological changes and climate variability evidence from tropical coastal lowlands of sw india cyanobacteria and thecamoebians are the two major constituents of non pollen palynomorphs npp found in the palynological preparations the former is well represented in the sediment archives while the latter has restricted occurrence in the holocene sequence apart from the conventional organic matter of pollen and spores well preserved morphotypes of gleotrichia and rivularia are the best forms of cyanobacteria found in almost all the studied profiles and their abundance towards early to middle holocene coincides with the heavy rainfall and wet climate conditions during the holocene climate optimum hco contrary to cyanobacterial diversity thecamoebians are restricted to late holocene in most of the studied profiles and their occurrence is correlated with the prevailing dry and stressful environmental conditions the major elements of thecamoebians identified belong to arcellaceans centropyxids and cucurbitella types abundance of centropyxids and arcellaceans in varapuzha west kadungallur koonamavu pachcha and ernakulam indicates low humidity and low precipitation however the relative abundance of centropyxids in mid holocene at ernakulam and koonamavu reflects the early colonization of this type competing with the cyanobacteria whereas arcellaceans are essentially confined to late holocene dominance of cyanobacteria and its proliferation is directly related to freshwater influx of the rainfall as well as the local hydrological regimes associated with the active aquifers controlled by the geomorphological features of the region in which the wetland system sustained considering the signatures of cyanobacteria and thecamoebians observed in the sediment archives their occurrence in the wetlands during the holocene corresponds to the hydrodynamic regimes brought in by the freshwater influx as a result of monsoon variability the well preserved cyanobacterial signatures in sediment archives of kerala coast and their scarcity or even absence elsewhere along the west coast of india indicates that they are exclusively adapted to the wetland habitats where the hydrodynamic regimes are regularly controlled by fresh water influx in the form of extended rainy days of the monsoon system

excitation mechanism of large amplitude volcanic tremor associated with the 1989 ito oki submarine eruption central japan abstract unusually large amplitude volcanic tremor was observed in association with the 1989 ito oki submarine eruption off the east coast of izu peninsula central japan the largest amplitude tremor occurred on july 13 1989 and was studied by using digital seismic data national research institute for earth science and disaster prevention in the distance range of 6 250 km spectral analysis shows that the seismograms have two kinds of predominant spectral peaks low frequency peaks around 1 hz and middle frequency peaks between 2 and 7 hz the relative amplitude ratios of these peaks show distinctive spatial variation depending primarily on the distances from the crater low frequency waves are predominant at close stations distances less than 50 km from the crater similar to typical low frequency volcanic tremor while at more distant stations the middle frequency waves are more prominent than low frequency waves propagation velocity analysis for narrow frequency bands on the basis of correlation of envelopes of seismograms reveals that the middlefrequency waves are compressional body waves and the excitation of shear wave was ineffective suggesting an explosive or implosive source as the simplest source model in contrast to the middle frequency waves our analysis showed no evidence for the low frequency waves to have propagated with any body wave velocity consideration of the spatial pattern of both waves suggests that surface waves were trapped in sedimentary layers from the shallow source and that no lowfrequency oscillations dominated at the source

the tin zone sediment hosted hydrothermal tin mineralization at rooiberg south africa the rooiberg tin field also known as the rooiberg fragment is located within the western lobe of the bushveld complex the fragment is triangular shaped consists of early proterozoic transvaal sequence volcano sedimentary rocks and is surrounded by granitoid intrusives of the lebowa granite suite practically all the significant tin deposits are hosted by arkoses located towards the transition with shaly arkoses at the stratigraphic top of the boschoffsberg quartzite member this stratabound distribution of individual deposits gave rise to the concept of a regionally developed continuous stanniferous zone on regional scale the individual deposits are broadly similar and are collectively classified as replacement and open space filling type particular styles of mineralization such as tourmaline pockets orbicules disseminated cassiterite steep and flat dipping sulphidic fractures and hydrothermal carbonate breccias appear to dominate each mine petrological and geochemical investigations of four mineralized centres indicated the presence of a 500 600 m thick stratified zone of pervasively altered clastic sedimentary rocks of possible arkosic precursor composition alteration displays a distinct zonal distribution consisting of a grey green sodic albitized foot wall an approximately 80 m transitional sericitized tourmalinized sulphidic tin zone and red hematitic potassic hanging wall the observed zonal pattern and localization of economically significant cassiterite is explained by the evolutionary path of magmatic stanniferous hydrothermal fluids genetically related to the surrounding acid phase of the bushveld complex areas of high fracture density the tectonic focal points acted as conduits for the ascending reactive fluids factors such as fluid lithostatic pressure equilibration limited fracture evolution and or impermeable shaly arkose retarded this ascent as a result accumulation lateral spreading of fluid and pervasive alteration occurred over a broad stratified front lateral overlapping of these fronts creates the impression of a continuous tin zone abundance of geochemical common denominators between the various focal points mines supports a shared composition and source for these contemporaneous fluids

indian summer monsoon during the last two millennia abstract the monsoon is a large scale feature of the tropical atmospheric circulation affectingpeople and economies in the world s most densely populated regions future trends due to naturalvariabilityandhuman inducedclimatechangesareuncertain palaeoclimaterecordscanimprove ourunderstanding of monsoon dynamics and thereby reduce this uncertainty palaeoclimate records haverevealed a dramatic decrease in the asian summer monsoon since the early holocene maximum9kabp herewefocusonthelast2ka wheresomerecordsindicateanincreasingtrendinthesummermonsoon analysing globigerina bulloides upwelling records from the arabian sea we nd theweakest monsoon occurred 1500 a bp with an increasing trend towards the present copyright 2010 john wiley sons ltd keywords monsoon holocene tropics india arabian sea introduction earth s climate is changing as a result of both natural andanthropogenic causes one region of the world that isparticularly susceptible to shifts in climate and extremeweather events is the indian subcontinent in this denselypopulated region both droughts and oods as well as trends inthe seasonal receipt of rainfall have the potential to bedevastating from economic agricultural and public healthperspectives the southwest indian monsoon is the maincontributor to india s yearly rainfall budget therefore unravelling past trends of the monsoon rains is critical tounderstanding future monsoon trends india ishome tooneofthelongesttimeseriesofinstrumentalclimate observations the all india monsoon rainfall index spanning 1844 to the present sontaake et al 1993 parthasarathy et al 1994 this record is remarkable bothfor showing an absence of a long term trend and for showing alarge variation in rainfall from one year to the next records ofthe atmospheric circulation such as the indian monsoon index imi based on the arabian sea winds are much shorter andspan only the past 50 a wang et al 2001 these records alsoindicate large variations from one year to the next and do notreveal a trend blending appropriate instrumental records withpalaeo observations from ocean sediments cave deposits orotherproxies canprovidealongerperspectiveonthemonsoonand its natural variability than otherwise would be available the monsoon is the result of both the seasonally changingthermal contrast between the land and ocean and the seasonalmigration of the intertropical convergence zone itcz whichreaches its northernmost location in summer exacerbating thethermally driven pressure gradient gadgil 2003 duringwinter the air over the land is cooler and denser than the airover the water this creates a surface pressure contrast that isenhanced by the position of the itcz over the ocean south ofthe continent of india resulting in a dry northeasterly wind thatblows across the continent in spring the continent warmsquickly compared to the surrounding water the winds thenreverse and a southwesterly wind blows across the arabiansea bringing moisture laden air towards india the south westerly winds that bring the monsoon rains also causeupwelling and sea surface cooling in the arabian sea producing a distinctive fossil record that can be tied to themonsoon winds via well known physical mechanisms a variety of indian and asian summer monsoon indices havebeen developed from instrumental records in general throughout india and asia in summer stronger winds overthe ocean and increased rainfall over land are correlated withthe large scale atmospheric circulation fig 1 the webster yang index wyi is a broad scale index of the monsooncirculation covers a large continuous area 40 1108 e 0 208n and measures the difference in strength between low level 850hpa and upper level 200hpa winds webster and yang 1992 in contrast the imi measures the arabian sea windsby subtracting the low level 850hpa zonal wind over land 20 308 n 60 908 e from the low level 850hpa winds in

a precise u pb age on cassiterite from the xianghualing tin polymetallic deposit hunan south china we report the first precise u pb isotope data on cassiterite from the large xianghualing tin polymetallic deposit in the central nanling district south china the results show that four separates from sample xf 51 have a relatively narrow range of 206pb 238u apparent ages varying from 152 to 157 ma and the three 206pb 238u apparent ages yield a weighted average value of 156 4 ma mswd 0 32 separates from two other cassiterite samples do not have sufficient radiogenic pb to generate a reliable 206pb 238u age seven separates from the above three cassiterite samples define a well constrained 238u 206pb isochron corresponding to an age of 157 6 ma mswd 34 a comparison of the u pb cassiterite ages with published ar ar dates on muscovite from this deposit and k ar age data on biotite from the pluton genetically related to the tin mineralization in this area demonstrates that the u pb isotope system of cassiterite is a potential geochronometer combined with the ar ar dates of muscovite from this deposit we can constrain the absolute age of tin polymetallic mineralization in xianghualing at 154 157 ma the dates obtained in this study consistent with the published geochronological results from other important deposits in this region reveal that the large scale tungsten tin mineralization in the central nanling region was predominantly emplaced during 150 161 ma

low cost gps based volcano deformation monitoring at mt papandayan indonesia abstract the global positioning system gps can be utilised to detect ground deformations of the surface of a volcano ground deformation monitoring is considered one of the most effective tools for investigating the behaviour of active volcanoes the decreasing cost of gps hardware together with the increased reliability of the technology facilitates such demanding applications gps ground deformation measurements can be continuous automatic conducted in all weather conditions and provide three dimensional positioning results higher computing power also means that the complex mathematics required to process gps baselines can be easily handled in near real time during the past few years a methodology has been developed for processing data collected by gps networks consisting of a mixed set of single frequency and dual frequency receivers the strategy is to deploy a few permanent fiducial gps stations with dual frequency geodetic grade receivers surrounding an inner network of low cost single frequency gps receivers such a configuration offers considerable flexibility and cost savings for geodynamic applications such as volcano deformation monitoring which require a dense spatial coverage of gps stations and where it is not possible to establish permanent gps networks using only expensive dual frequency instrumentation this configuration has recently been tested at the mt papandayan volcano in west java indonesia the two stage network design consists of an inner network of four single frequency canadian marconi cm gps receivers surrounded by three dual frequency leica crs1000 gps receivers the inner network logged and transmitted gps data from the slave stations located on the volcano to a base station the combined processing of the cm and leica receiver data was performed off line so as to investigate the performance of such a mixed mode system the basis of the processing methodology is to separate the dual frequency fiducial station data processing from the baseline processing involving the single frequency receivers on the volcano the data processing for the former was carried out using a modified version of the bernese software to generate a file of corrections analogous to wide area dgps correction models for the distance dependent biases primarily due to atmospheric refraction these corrections were then applied to the double differenced phase observations from the inner receivers to improve the baseline accuracies a description of the field testing and its challenges during february march 2000 together with a discussion of some of the results are presented

recent plate motions and crustal deformation reports by u s workers on geodetic measurements of recent plate motions or crustal deformation published in 1987 1990 are reviewed the review begins with global plate motions proceeds through plate boundaries in california alaska and the pacific northwest and finishes with volcanic phenomena monument stability and longevity and gps relative position measurements 184 refs

a tilt and seismicity episode in the new hebrides vanuatu island arc tilt and seismicity have been monitored in the central new hebrides island arc since 1978 using bench mark arrays long tube water tiltmeters borehole tiltmeters and a local seismometer network releveling of the bench mark array on efate island in late november 1986 revealed a 10 rad tilt up to the nnw since the previous leveling in april 1986 the tilt event was preceded by a magnitude 5 9 thrust event that occurred on october 25 1986 at a depth of 48 km and about 11 km nw of the tiltmeter instruments six days later a shallow 20 km swarm of earthquakes occurred 12 km nnw of the tiltmeter instruments and 5 km north of the epicenter of the magnitude 5 9 earthquake closely coincident in time with the swarm a 5 rad tilt up to the nnw that occurred over a period of 5 days was recorded on both the 100 m baseline water tube tiltmeter and the borehole bubble level tiltmeter a composite focal mechanism of 191 earthquakes selected from the swarm indicates a thrust mechanism with some component of strike slip calculations show that the seismic slip associated with a swarm of this magnitude is apparently inadequate to cause the observed surface deformation two similar shallow swarms in november 1987 and july 1988 have occurred within 15 km of the 1986 swarm but with no apparent surface deformation the most likely explanation supported by simple modeling is that the swarm and tilt are the result of a magmatic intrusion from island arc volcanism an alternate hypothesis is that both the seismicity and the tilt are due to an episode of largely aseismic creep in the upper crust

the global positioning system as a useful technique for measuring ground deformations in volcanic areas abstract in this paper the global positioning system technique for measuring ground deformations in volcanic areas is presented after an outline of the mathematical background the results of three years experience regarding the use of this technique on mt etna are reported the ground deformation patterns recorded between 1989 and 1991 are shown and discussed in the geodynamic framework which characterized mt etna in the time interval considered attention is focused on modeling a ground deformation episode which occurred on mt etna between 1990 and 1991 which contributed to characterizing the dynamic framework where the 1991 1992 eruptive event took place the deformation pattern mentioned has been interpreted by using a dislocation model the optimal solution for the inversion problem has been found by using an optimization approach based on the simplex method this solution agrees with the regional stress field whose compressive direction is nne ssw oriented

in situ la icpms u pb dating of cassiterite without a known age matrix matched reference material examples from worldwide tin deposits spanning the proterozoic to the tertiary abstract cassiterite sno2 a main ore mineral in tin deposits is suitable for u pb isotopic dating because of its relatively high u pb ratios and typically low common pb we report a la icpms analytical procedure for u pb dating of this mineral with no need for an independently dated matrix matched cassiterite standard la icpms u th pb data were acquired while using nist 612 glass as a primary non matrix matched standard raw data are reduced using a combination of iolite and other off line data reduction methods cassiterite is extremely difficult to digest so traditional approaches in la icpms u pb geochronology that utilize well characterized matrix matched reference materials e g age values determined by id tims cannot be easily implemented we propose a new approach for in situ la icpms dating of cassiterite which benefits from the unique chemistry of cassiterite with extremely low th concentrations th u ratio of 10 4 or lower in some cassiterite samples accordingly it is assumed that 208pb measured in cassiterite is mostly of non radiogenic origin it was initially incorporated in cassiterite during mineral formation and can be used as a proxy for common pb using 208pb as a common pb proxy instead of 204pb is preferred as 204pb is much less abundant and is also compromised by 204hg interference during the la icpms analyses our procedure relies on 208pb 206pb vs 207pb 206pb pb pb and tera wasserburg 207pb 206pb vs 238u 206pb u pb isochron dates that are calculated for a 1 54 ga low th cassiterite reference material with varying amounts of common pb that we assume remained a closed u pb system the difference between the nist 612 glass normalized biased u pb date and the pb pb age of the reference material is used to calculate a correction factor f for instrumental u pb fractionation the correction factor f is then applied to measured u pb ratios and tera wasserburg isochron dates are obtained for the unknown cassiterite analyzed in the same analytical session this allows for u pb dating of cassiterite of any age with no need for an independently dated matrix matched reference material nor assumptions about the isotopic composition of common pb results for cassiterite from tin deposits in bolivia brazil china russia saudi arabia south africa spain and the united kingdom with ages ranging from 20 ma to 2060 ma demonstrate the applicability of this approach across a broad range of geologic time these ages are in good agreement with published geochronology of the host rocks associated with the tin deposits and with previously published u pb ages of some cassiterites from the same deposits thus our in situ la icpms methodology verifies the use of cassiterite as a reliable u pb mineral geochronometer with the advantages of fast and relatively low cost in situ analyses with moderate spatial resolution

long term fault creep observations in central california the u s geological survey usgs has been monitoring aseismic fault slip in central california for more than 10 years as part of an earthquake prediction experiment since 1968 the usgs creep network has grown from one creep meter at the cienega winery south of hollister to a 44 station network that stretches from hayward east of san francisco bay to palmdale in southern california in general the long term slip pattern is most variable on sections of the faults where several magnitude 4 and larger earthquakes occurred during the recording period e g calaveras fault near hollister and san andreas fault between san juan bautista and bear valley these fault sections are the most difficult to characterize with a single long term slip rate in contrast sections of the faults that are seismically relatively quiet e g san andreas fault between bear valley and parkfield produce the steadiest creep records and are easiest to fit with a single long term slip rate appendix is available with entire article on microfiche order from the american geophysical union 2000 florida avenue n w washington d c 20009 document j82 004 1 00 payment must accompany order

geodetic estimate of coseismic slip during the 1989 loma prieta california earthquake offsets in the relative positions of geodetic stations resulting from the loma prieta earthquake can be explained with a dislocation model that includes buried oblique slip on a rupture surface extending 37 km along the strike of the san andreas fault dipping 70 degree to the sw and extending from a depth of about 5 to 17 5 km assuming uniform slip on a rectangular surface the mean values for a range of reasonable fault geometries are 1 6 plus minus 0 3 m right lateral strike slip and 1 2 plus minus 0 3 m reverse slip slip on an adjacent extension of the rupture to the southeast recorded in the aftershock sequence is not well constrained by the geodetic data the geodetic data clearly preclude rupture extending near the surface

stratigraphical and palynological appraisal of the late quaternary mangrove deposits of the west coast of india the organic deposits derived from the mangrove swamps form reliable stratigraphic markers within the late quaternary sequence of kerala konkan basin three generations of such deposits have been identified the older one is dated to around 43 000 40 000 14c yr b p with a few dates beyond the range of radiocarbon the younger ones date from the middle holocene to latest pleistocene 10 760 4540 14c yr b p and the late holocene 4000 14c yr b p pollen analyses confirm that the deposits are mostly derived from the mangrove vegetation peat accumulation during the period 40 000 28 000 14c yr b p can be correlated with the excess rainfall 40 100 greater than modern values of the asian summer monsoon the low occurrence of mangrove between 22 000 and 18 000 14c yr b p can be attributed to the prevailing aridity and or reduced precipitation associated worldwide with last glacial maximum because exposure surfaces and ferruginous layers are commonly found in intervals representing this period the high rainfall of 11 000 4000 14c yr b p is found to be the most significant as the mangrove reached an optimum growth around 11 000 14c yr b p but with periods of punctuated weaker monsoons from the present and previous studies it has been observed that after about 5000 or 4000 14c yr b p the monsoons became gradually reduced leading to drying up of many of the marginal marine mangrove ecosystems a case study of hadi profile provided an insight to the relevance of magnetic susceptibility to record the ecological shift in late holocene

eiland crucibles and the earliest relative dating for tin and bronze working in southern africa abstract over a century of research has demonstrated the historical importance of rooiberg as a point source for tin production in preindustrial southern africa current chronology suggests that the exploitation of the rooiberg tin deposits began around ad1450 and continued into the 19th century however recent lead isotope and trace element studies of tin and bronze objects from ad1000 to 1300 sites such as great zimbabwe and mapungubwe show that they were made with rooiberg tin here we present technical analyses of two crucible sherds from rhenosterkloof 3 near rooiberg that were used in bronze production during the eiland phase ad1000 1300 the presence of tin bronzes during the eiland phase indicates that rooiberg tin was exploited from the early second millennium ad almost three centuries earlier than previously believed and affirms rooiberg as an important source for bronze production in the southern african iron age

assessment of global positioning system measurements for studies of crustal deformation the u s geological survey has been using the global positioning system gps to perform repeated surveys of networks of different sizes since january 1986 the intersite distances from these various networks are 223 km for a single line connecting the palos verdes and vandenberg sites in southern california 30 50 km for a network of three sites south of the san francisco bay near loma prieta 9 30 km for a network located near hebgen lake montana 7 12 km for a network of sites in the vicinity of parkfield california and 240 m for a line located at the goldstone antenna complex in the mojave desert the lengths quoted do not include the intersite distances for the fiducial sites included in the solutions for orbit determination which can be up to 8000 km we have attempted to assess the long term precision and accuracy of determinations of relative site position for a range of line lengths this assessment has consisted of several different studies in assessing precision we have generally investigated repeatability usually about a best fit linear temporal trend the smallest fractional repeatability was yielded by the measurements on the palos verdes to vandenberg line the root mean square rms residual about the best fit line for these determinations was 6 mm 0 03 parts per million or ppm for the north component 11 mm 0 05 ppm for the east component and 40 mm 0 18 ppm for the vertical component for these determinations gps data from 3 4 consecutive days were combined to produce a single estimate of the vector separation we also used the day to day scatter from these measurements to perform an analysis of variance and found that these multiday determinations can be significantly more precise than estimates determined from a single observing session the worst results were obtained for the loma prieta network where we obtained rms residuals of 11 12 mm 0 3 0 4 ppm for north 14 18 mm 0 3 0 6 ppm for east and 18 21 mm 0 4 0 7 ppm for vertical we cannot definitely explain these poor results but we have evidence to indicate that this poor scatter is due to the short observing session 4 5 hours compared to 6 5 hours for the palos verdes to vandenberg results in assessing accuracy we compared the gps results to those from independent techniques at parkfield we compared the gps estimates of fault parallel motion to those from creep meters and alignment arrays and found excellent agreement within 1 2 mm yr 1 not only for the slip but also for the variation of slip along the san andreas fault we compared the loma prieta and hebgen lake line length estimates to those obtained from a geodolite a high precision laser distance measurement device that the u s geological survey has used for 20 years for studies of crustal deformation if we model the geodolite minus gps line length differences l as l l where l is the line length then we find 0 6 0 5 mm and 0 1 0 1 mm km 1 the uncertainties quoted are one standard deviation from this comparison we conclude that at this level of significance there is no detectable difference between lengths determined from geodolite and gps data finally we compared the gps estimates of the palos verdes to vandenberg line length to those obtained from very long baseline interferometry vlbi the mean difference between the six gps estimates of line length and a best fit line through the vlbi estimates was 1 mm and the rms difference was 12 mm 0 05 ppm close to the standard deviation of the gps measurements for this predominantly east west line

late pleistocene holocene monsoon variations on climate landforms and vegetation cover in southwestern india an overview abstract signatures of monsoon variability preserved in the late quaternary sediments of southwestern india have been decoded and addressed using biological proxies along with geochronological data barring sediments beyond the threshold for conventional 14c dating late pleistocene sequences have been recognized both in konkan and kerala basins konkan area has only subsurface continental lacustrine late pleistocene whereas kerala coast has mixed facies the landscape as well as the vegetation cover has been substantially modified and the fossil contents and related palaeoenvironment provided ample evidence to demonstrate the landscape and vegetation dynamics since late pleistocene evidence of myristica swamps until late pleistocene and its subsequent replacement by riparian forest towards late holocene in konkan has been a significant impact of monsoon variations on the tropical rain forests the prevalence of such freshwater swamps and a sensitive habitat indicated that konkan had enjoyed an extended period of rainfall due to the combined effects of both sw and ne monsoons until the late pleistocene the tropical rainforest cover along kerala coast has shrunken considerably and pieces of evidence suggest that the entire terrain west of sahyadri western ghats was under dense forest cover during the holocene climatic optimum 9 0 6 0 k yrs bp when the region had witnessed heavy precipitation much higher than that of the present the forest land has been converted into major wetlands and present ecology is unsuitable to support evergreen forests and it can be concluded that coastal plains and associated landforms were covered by thick tropical evergreen forests which got destroyed by flooding towards middle holocene development of a chain of wetland system all along kerala coast loss of sheltered habitat and mangrove cover and loss of sensitive freshwater myristica swamps are some of the significant aspects brought in while addressing the monsoon variability in southwestern india

lead isotopes link copper artefacts from northwestern botswana to the copperbelt of katanga province congo abstract copper was highly valued in sub saharan africa for jewellery and as a store of wealth but was rarely used for tools or weapons the central african copperbelt is one of the world s largest copper deposits and is known to have been mined since at least 400 600 cal ce but has seen very little archaeological investigation we measured lead isotope ratios and trace element concentrations in 20 copper objects dating between ca 650 cal ce and ca 1200 cal ce from two sites in the tsodilo hills in northwestern botswana the results show unequivocally that almost all derive from copperbelt ore deposits in katanga province democratic republic of the congo at least 1050 km from tsodilo our results are very similar to those recently obtained for a suite of 45 copper ingots dated between 9th and 18th centuries cal ce most of which are from cemeteries in the upemba depression about 200 km north of the copperbelt rademakers et al 2019

mid late holocene monsoonal records from the partially active mudflat of diu island southern saurashtra gujarat western india abstract the mid late holocene period is seldom known for any drastic climatic perturbations but witnessed significant anthropogenic growth and thus has been a subject of scientific importance in this study sediment core raised from an active mudflat of diu island southern saurashtra coast gujarat with a climatic history for the last 4100 yr bp has been investigated based on geochemical proxies productivity weathering and detrital results indicate warm and humid conditions during holocene climate optimum hco between 4105 and 2640 cal yr bp as a result of monsoon intensification followed by an arid conditions between 2640 and 1930 cal yr bp later during 1930 355 cal yr bp the region regained warm and humid conditions the mudflat responded in accordance with the global climatic perturbations during last 2000 yr witnessing signatures of roman warm period and medieval warm period additionally cool and humid climatic conditions persisted during little ice age followed by modern warming period witnessed during last 300 yr

copper mining and smelting technology in the northern lowveld south africa ca 1000 ce to ca 1880 ce we report chemical petrographic and metallographic studies of copper ores and slags recovered during sporadic surface surveys and excavations over the past fifty years in the phalaborwa and murchison range areas of the northern lowveld of south africa the copper slags around phalaborwa have unusual mineral assemblages attributable to the unique geochemistry of the main ore body the phalaborwa complex where copper minerals were mined from a carbonatite composed of magnetite calcite and apatite strongly reducing conditions had to be avoided to minimise contamination of the copper with iron and phosphorus as the copper ores contain almost no silicates silica alumina flux was added to produce slag the precambrian zinc copper ores of the murchison range were also smelted but during smelting any zinc that was not volatilised was taken up by minerals in the slag so brass was not produced

global positioning system measurements for crustal deformation precision and accuracy analysis of 27 repeated observations of global positioning system gps position difference vectors up to 11 kilometers in length indicates that the standard deviation of the measurements is 4 millimeters for the north component 6 millimeters for the east component and 10 to 20 millimeters for the vertical component the uncertainty grows slowly with increasing vector length at 225 kilometers the standard deviation of the measurement is 6 11 and 40 millimeters for the north east and up components respectively measurements with gps and geodolite an electromagnetic distance measuring system over distances of 10 to 40 kilometers agree within 0 2 part per million measurements with gps and very long baseline interferometry of the 225 kilometer vector agree within 0 05 part per million

mangrove palynology in recent marine sediments off cameroon abstract based on a palynological analysis of marine sediment surface samples we obtained the modern distribution of pollen and spores on the continental shelf off cameroon to examine their dispersal relative to vegetation sources on the adjacent continent special attention is paid to the mangrove pollen assemblage whose dominant type is rhizophora which is the most abundant pollen in the overall modern assemblages this mangrove grows mainly in the river deltas west and east of mount cameroon in the northern part of the study area but patches also are found along smaller estuaries further south concentrations and percentages of rhizophora are highest proximal to mangrove vegetated coastline and decrease continuously southward due to 1 the littoral position of the mangrove ecosystem 2 the prolific pollen production of rhizophora and 3 their efficient dispersal by water the other mangrove types e g avicennia pandanus and nypa along the cameroon caostline are very poorly represented in the offshore pollen assemblage the spores group was the second most common assemblage component with the highest concentrations and percentages of spores in the axis of the main estuaries common features in the distribution patterns of the two dominant taxa rhizophora and spores which are very different in terms of production zones size and morphology suggest that marine currents are crucial in distributing the palynomorphs in the open sea the variation of mangrove pollen abundance in cores on the continental shelf can be indicative of palaeogeographical modifications of the environment

kestel an early bronze age source of tin ore in the taurus mountains turkey an ancient mine located at kestel on the outskirts of nigde in the taurus mountains of south central turkey has been dated by radiocarbon and pottery type to the third millennium b c archeological soundings in the mine located cassiterite tin oxide in the detritus of ancient mining activity cassiterite is also present in veins and as placer deposits in streams nearby since tin is used with copper in order to form bronze but is thinly distributed in the earth s crust the presence of tin ore at kestel offers a source for the much sought after tin of the bronze age the discovery of an ancient mine containing cassiterite sheds light on this question but also greatly complicates the accepted picture of regional economic patterns in the highland resource areas of anatolia and of interregional metal exchange in the formative periods of urbanization and metal use in the eastern mediterranean

continuous monitoring of surface deformation at long valley caldera california with gps continuous global positioning system gps measurements at long valley caldera an active volcanic region in east central california have been made on the south side of the resurgent dome since early 1993 a site on the north side of the dome was added in late 1994 special adaptations for autonomous operation in remote regions and enhanced vertical precision were made the data record ongoing volcanic deformation consistent with uplift and expansion of the surface above a shallow magma chamber measurement precisions 1 standard error for absolute position coordinates i e relative to a global reference frame are 3 4 mm north 5 6 mm east and 10 12 mm vertical using 24 hour solutions corresponding velocity uncertainties for a 12 month period are about 2 mm yr in the horizontal components and 3 4 mm yr in the vertical component high precision can also be achieved for relative position coordinates on short 10 km baselines using broadcast ephemerides and observing times as short as 3 hours even when data are processed rapidly on site comparison of baseline length changes across the resurgent dome between the two gps sites and corresponding two color electronic distance measurements indicates similar extension rates within error 2 mm yr once we account for a random walk noise component in both systems that may reflect spurious monument motion both data sets suggest a pause in deformation for a 3 5 month period in mid 1995 when the extension rate across the dome decreased essentially to zero three dimensional positioning data from the two gps stations suggest a depth 5 8 1 6 km and location west side of the resurgent dome of a major inflation center in agreement with other geodetic techniques near the top of a magma chamber inferred from seismic data gps systems similar to those installed at long valley can provide a practical method for near real time monitoring and hazard assessment on many active volcanoes

emission of electromagnetic radiation preceding the ito seismic swarm of 1989 there have been several reports1 8 of electromagnetic radiation being detected in air and or underground before large earthquakes or volcanic eruptions unfortunately such measurements are often plagued by contamination from other sources of noise we have developed an electrode system that is effective at filtering out urban and atmospheric background noise here we report the detection of anomalous electromagnetic signals several hours before the occurrence of large earthquakes near ito city japan about 150 km from the location of the electrodes we have also detected anomalous signals about one day before an undersea volcanic eruption that constituted part of the same seismic swarm near ito although the mechanism responsible for such signals is still unclear these results indicate that their monitoring could be valuable for the prediction of seismic activity

palynomorph evidence for tropical climate stability in the gulf of papua papua new guinea over the latest marine transgression and highstand 14 500 years bp to today abstract three sediment cores mv 41 mv 46 and md 50 from the gulf of papua gop papua new guinea were analyzed to assess changes in climatic oceanographic and sedimentological conditions over the last 14 5 kyr palynomorphs which were isolated from sediment core samples were collected at approximately 0 5 m intervals using a strong acid and oxidant md 50 non oxidant mv 41 mv 46 procedure radiocarbon 14c stable isotope geochronology magnetic susceptibility stable isotope analysis md 50 only oxygen 18 18o and carbon 13 13c and clay mineral maturity analysis were also completed for each core palynological data indicate that climatic conditions at sea level have remained warm wet and stable for the past 14 5 kyr with sea surface temperatures in the gop above 14 c potential decreases in vegetative cover marked the younger dryas interval 12 5 11 5 kyr bp as indicated by reduced pollen and spore recovery the end of the latest marine transgression and the subsequent return to eustatic sea level highstand is clearly delineated by increases in marine palynomorph recovery and decreases in mangrove pollen at approximately 5 kyr bp an increase in seasonality and potential el nino southern oscillation variability is observed in md 50 s oxygen isotope results at 5 kyr bp this is not supported by the palynomorph record likely because of the sampling interval and dilution by tropical pollen flora which indicates stable climatic conditions throughout the last 14 5 kyr sediment transport pathways in the gop remained fairly constant throughout the time interval which is supported by the lack of major changes in palynomorph assemblage composition

cassiterite potential for direct dating of mineral deposits and a precise age for the bushveld complex granites u pb and pb isotopic measurements of cassiterite from the 200 ma tin deposits of belitung indonesia and 2100 ma zaaiplaats deposit in south africa demonstrate that cassiterite can be used to directly date mineral deposits rather than associated minerals such as zircon and rutile a precise u pb age of 2099 3 ma has been determined for cassiterites hosted in granites from the bushveld complex on conventional 207 pb 204 pb 206 pb 204 pb plots the data for the indonesian deposits give an age apparently older than that obtained from u pb plots perhaps indicative of inheritance of pb from an older source

vegetation change following mid holocene marine transgression of the torres strait shelf a record from the island of mua northern australia the pollen and sedimentary record from a coastal backdune swamp on the island of mua torres strait australia is presented a 4 55 m core collected from the swamp centre provides a record of vegetation and landscape change spanning the postglacial marine transgression to present prior to 6000 radiocarbon years before present yr bp results show mangrove vegetation encroaching on the core site periodically displacing non mangrove taxa until the establishment of an extensive mangrove forest between 6000 yr bp and 3000 yr bp within the mangrove community a transition from lower tidal rhizophora forest to an upper intertidal ceriops community is evident this is followed by the development of the current herbaceous freshwater swamp in the late holocene the dryland vegetation record is dominated by sclerophyll and rainforest elements with strongest forest representation occurring around the mid holocene before a decline in tree density and the establishment of open woodlands in the late holocene the data suggest vegetation change accompanied marine transgression and a humid mid holocene climate before stabilization of sea levels and the initiation of dominant on shore catchment processes signalling drier climatic conditions and possible human activity

holocene palynology and sea level change in two estuaries in southern irian jaya southern new guinea leads the continental australian plate into convergence to form the new guinea highlands extensive inter tidal deltas are typical of much of this low gradient equatorial coastline in two adjacent estuaries in irian jaya west papua this study uses present elevations of mangrove species zones as a finite indicator of holocene sea levels from pollen diagrams of estuarine cores all cores showed mangroves at levels well below the present tidal range with landward species zones being replaced over time by seaward zones results show tectonic subsidence in the recent period with late holocene relative sea level rise of 0 67 mm year 1

earthquakes and sea level space and terrestrial metrology on a changing planet the complacency with which man inhabits continent ocean margins or plate boundaries is based on the assumption that sea level rise and periodic seismicity are acceptable risks the forecast of future sea level or future seismicity is essential for informed assessment of these risks the historical data from which forecasts may be derived are in each case of limited antiquity and uneven spatial distribution developments in space geodesy and crustal deformation metrology in the past two decades offer the means to acquire a homogeneous global data set for monitoring relative vertical and horizontal motions of the earth s surface to within several millimeters these new tools are reviewed in terms of their application to forecasting trends in sea level rise and forecasting damaging earthquakes

sensitivity test of the geodetic network in las canadas caldera tenerife for volcano monitoring abstract a 17 benchmark geodetic network in the volcanic area of the teide caldera canary islands has been utilised several times since 1982 to detect crustal movements associated with volcanic activity within the network as well as a procedure for solving configuration problems the network is located on the mid western side of the caldera where there are two different morphological zones that both have benchmarks the authors performed a sensitivity test of this geodetic network for volcano monitoring purposes to do so we use a deformation model to calculate surface displacement caused by a dike intrusion in a homogenous half space the depth and location of dike are changed to study the variation of the effects produced displacements the size and location of the intruded dike are found to play a major role in determining both the displacement pattern and magnitude when the dike is close to the surface there is an inversion of the surface displacement pattern and very large surface displacement at certain benchmarks such phenomena can serve as precursors of such dike eruptions our study show a clear need to extend the existing geodetic network to cover the full island for volcano monitoring purposes

mangrove vegetation responses to holocene climate change along konkan coast of south western india abstract the pollen signatures preserved in the mangrove sediments provided records of species variation over a period of time with past climate and sea level changes the airoli profile has a late pleistocene sequence and all the other studied profiles and intervals cover the holocene only the absence of mangrove signatures during the late pleistocene interval is attributed to a relatively low sea level the ideal conditions for mangrove development along konkan prevailed during middle holocene when the first extensive mangrove swamps appeared in sindhudurg dhamapur hadi area particularly between 7220 and 4770 yrs bp this period coincides with the holocene climate optimum hco when monsoon asia witnessed much higher precipitation however the mangroves responded to environmental changes due to relative abundance of fresh water leading to change in species composition two different scenarios of mangrove response during the late holocene one in dhamapur and the other in palm beach are found to be significant the rhizophora sonneratia transition from early mid holocene to late holocene is considered to be the most distinctive feature the decline of mangroves since 3500 yrs bp and further degradation has been attributed to the prevailing arid climate and weakening trends of the monsoon until 1500 yrs bp however there seems to be a positive trend in emergence of mangroves in the least disturbed areas of south konkan attributed to strengthening of summer monsoon in the recent past

earthquake geodesy and hazard monitoring catastrophic events such as major earthquakes and volcanic eruptions result when the earth s crust fails in response to accumulated deformation the accumulation of deformation results from ongoing processes such as aseismic deformation of subcrustal rock associated with relative plate motions or the ascent of magma through a volcanic plumbing system geodetic measurements document the crustal deformation leading to these failures and the deformation resulting from them providing unique insight into the physical processes involved by virtue of the space and time domains of ground deformation detected with geodetic measurements geodesy is a useful tool in monitoring active tectonic and volcanic regimes for a wide range of natural events including earthquakes aseismic fault motions and volcanic events geodetic measurements constrain physical models of the processes that cause such events because these geodetic studies probe the underlying processes leading to and culminating in catastrophic natural events many such studies are directly applicable to earthquake and volcano hazard assessment

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

precursory changes in fumarolic gas temperature associated with a recent submarine eruption near izu oshima volcano japan significant temperature changes in a steamrich fumarolic gas from a deep hole in the izu oshima volcano japan were observed prior to a series of earthquake swarms and submarine volcanic eruptions which occurred off the eastern coast off the izu peninsula about 40 km ne of the izu oshima volcano in july 1989 we suggest that temperature changes indicate that the izu oshima volcano and the submarine volcanic cone the teishi knoll are linked and that upward movement of teishi magma resulted in a gas pressure decrease of the izu oshima magma this new suggestion of a link between two magma systems over such a large distance may be of great significance for understanding arc volcanism our observation may be of use in the future prediction of volcanic eruptions in the izu area

detection of crustal deformation from the landers earthquake sequence using continuous geodetic measurements the measurement of crustal motions in technically active regions is being performed increasingly by the satellite based global positioning system gps 1 2 which offers considerable advantages over conventional geodetic techniques3 4 continuously operating gps arrays with ground based receivers spaced tens of kilometres apart have been established in central japan5 6 and southern california to monitor the spatial and temporal details of crustal deformation here we report the first measurements for a major earthquake by a continuously operating gps network the permanent gps geodetic array pgga 7 9 in southern california the landers magnitude afw of 7 3 and big bear mw 6 2 earthquakes of 28 june 1992 were monitored by daily observations ten weeks of measurements centred on the earthquake events indicate significant coseismic motion at all pgga sites significant post seismic motion at one site for two weeks after the earthquakes and no significant preseismic motion these measurements demonstrate the potential of gps monitoring for precise detection of precursory and aftershock seismic deformation in the near and far field

inflation of long valley caldera california basin and range strain and possible mono craters dike opening from 1990 94 gps surveys five years of annual global positioning system gps surveys of a network centered on long valley california constrain displacement rates for these stations relative to a central station in the network these observations are consistent with recent models of resurgent dome inflation in long valley langbein et al 1995 and have sufficient signal to detect the presence of basin and range strain in the long valley region the data also allow for the possibility of dike inflation beneath the mono craters dike intrusion is consistent with the mono craters recent geologic history of ash eruptions with seismic tomography leveling data and geologic studies of these volcanic domes and flows

gps applications for geodynamics and earthquake studies geodetic measurements obtained with the global positioning system gps are increasingly more widely applied in geophysical studies in this paper we review the changes to the technology of gps geodesy over the last five years that are responsible for this increased applicability we survey geophysical investigations employing gps to measure coseismic postseismic and interseismic deformation plate motion and crustal deformation at plate boundaries volcano deformation and the deformation associated with glacial isostatic adjustment and its application to sea level studies we emphasize the use of gps determinations for the modeling of this wide variety of geophysical phenomena we also discuss the recent advent of permanent gps networks for regional geophysical studies as well as the possible future of gps surveying in light of the recent advances