easter microplate evolution geochemical evidence confirms that there is current active spreading on both the east and west rift zones of the easter microplate and northwards propagation of the east rift with the active tip at 25 s the east rift is influenced by lateral flow of plume derived material from a hotspot located beneath either sala y gomez or easter island spreading rate variation does not seem to be influential in controlling the composition of erupted basalts

microplate tectonics along a superfast seafloor spreading system near easter island there is a growing easter microplate between the pacific and nazca plates the eastern and western boundaries of the microplate are actively spreading and propagating north and south respectively the northern and southern boundaries are broad transform zones most of the interior of the microplate contains the sort of oblique sheared structures characteristic of zones of transferred lithosphere between propagating and failing spreading centres

prehistoric fault offsets of the hilina fault system south flank of kilauea volcano hawaii historical accounts of earthquakes on the island of hawaii date only to 1823 but lava flows as old as 1500 3000 years b p contain fault offsets from prehistoric earthquakes the m7 2 1975 kalapana earthquake produced over 25 km of fault rupture along the hilina fault system we compare fault offsets in prehistoric lava flows with kalapana earthquake fault offsets in neighboring 1969 1974 mauna ulu lava flows to estimate the frequency of prehistoric major earthquakes on the hilina fault system horizontal and vertical fault offset rates across the hilina fault system are 4 0 to 12 0 and 2 0 to 20 0 mm yr respectively based on lava flows 750 years b p age assuming prehistoric earthquakes produced similar fault offsets compared to the kalapana earthquake three to five events are recorded in 400 750 years b p old lava flows yielding recurrence intervals of 260 80 years vertical fault offsets in prehistoric lava flows suggest that hanging wall rotation of the hilina fault system contributes to fault offset the assumption that past faulting resulted from prehistoric earthquakes with similar magnitude and fault offset to the kalapana earthquake is an oversimplification large south flank earthquakes most likely do not have uniform recurrence intervals

volcanic spreading at kilauea 1976 1996 the rift system traversing about 80 km of the subaerial surface of kilauea volcano has extended continuously since the m 7 2 flank earthquake of november 1975 widening across the summit has amounted to more than 250 cm decelerating after 1975 from about 25 to 4 cm yr 1 since 1983 concurrently the summit has subsided more than 200 cm even as the adjacent south flank has risen more than 50 cm the axes of the upper zones about 10 km from the summit subsided before 1983 at average rates of 9 and 4 cm yr 1 respectively and at rates of 4 and 3 cm yr 1 since the middle southwest rift zone is also subsiding and at the other end of kilauea s subaerial rift system subsidence along the lower east rift zone has averaged 1 2 cm yr 1 deformation of kilauea s south flank has been continuous although subject as well to displacements caused by major rift zone seismic swarms whereas horizontal strains across the subaerial south flank seem to have been generally compressive after 1975 they have been extensional since about 1980 or 1981 interrupted only by the east rift zone dike intrusion of 1983 because the magnitudes of these contractions and extensions are much less than the extension across the rift system the subaerial south flank is apparently sliding seaward on its basal decollement more than it is accumulating horizontal strains within the overlying volcanic pile kilauea suffers from gravitational spreading made even more unstable by accumulation of magma along the rift system at depths in excess of about 4 5 km in the presence hot rock incapable of withstanding deviatoric stresses this seismicly quiescent zone decouples the south flank from the rest of hawaii s volcanic edifice the rift zones at lesser depths exhibit a more brittle and therefore sporadic extensional behavior judging from the modern extension record of the summit which both predates the m 7 2 earthquake of 1975 and has outlived its 10 year period of aftershocks kilauea will continue to spread along its rift system as its south flank slips seaward to accommodate the accretion of magma and its relatively dense olivine rich differentiate

easter microplate dynamics 1 we use two dimensional elastic finite element analysis supplemented by strength estimates to investigate the driving mechanism of the easter microplate modeled stresses are compared with the stress indicators compiled from earthquake focal mechanisms and structural observations the objective is to constrain the tectonic forces that govern the easter microplate rotation and to test the microplate driving hypothesis proposed by schouten et al 1993 we infer that the mantle basal drag cannot drive the microplate rotation but opposes it and that the asthenospheric viscosity is no more than about 1 1018 pa s at most the basal drag comprises 20 of the force resisting microplate rotation the outward pull of the main plates can drive the rotation by shear drag applied along the northern and southern boundaries of the microplate however we propose an additional driving force which arises from the strong variation of the ridge resistance force along the east and west rifts so that the main driving torques come from the pull of the major plates acting across the narrowing and slowing rifts this requires the strength to increase substantially toward the rift tips due to thickening of the brittle lithosphere as the spreading rate slows

quasi 2d block inversion of large scale surface nuclear magnetic resonance profile data using a laterally constrained model abstractthe water content of underground structures can be imaged using surface nuclear magnetic resonance nmr in one dimension two dimensions or recently three dimensions the maximum efficiency can be obtained with a coincident loop configuration in a large scale area although the resolution is limited we have developed a quasi 2d block inversion to characterize a horizontal continuous underground aquifer using a laterally constrained model to improve the resolution of thin aquifers and deep aquifers through the simulation of flat surface and irregular surface models a horizontally layered aquifer with continuously variable water content and t2 can be imaged through quasi 2d block inversion which is more optimized than the traditional 1d block or 1d or 2d smooth inversion methods finally using a series of profile data obtained from surface nmr field measurements in mongolia we determine that quasi 2d block inversion based on a laterally constrained model can significantly improve the disco

pito and orongo fracture zones the northern and southern boundaries of the easter microplate southeast pacific abstract the easter rapanui microplate is a case example of a large dual spreading center system in a region where the fastest seafloor spreading on earth is occurring today recent theoretical models of the tectonic evolution of dual spreading center systems have explored the effects of shear and rigid rotation on the boundaries and internal structure of microplates but the models must be critically constrained by improved relative motion and structural fabric data sets during the january 1987 rapanui expedition on the n o jean charcot we conducted a sea beam magnetics gravity survey of a portion of the microplate boundaries the method that was used was to fully map selected portions of the boundaries in order to establish precise structural relationships the northern terminus of the east rift or eastern boundary of the microplate is expressed as a series of parallel nw se trending valleys including what appears to be with 5890 m depth the deepest active rift axis mapped in the pacific today pito rift the northern end of the pito rift merges with an e w to 083 narrow band of linear faults interpreted to be a transform fault between the nazca and easter rapanui plates the northern triple junction between the easter rapanui nazca and pacific plates is a rff type with the two transform faults colinear along an approximately e w direction the southwestern boundary of the easter rapanui microplate is marked by a series of en echelon offsets outlined by depressions which merge into an approximately e w zone where shear must be predominant the southern triple junction is a rrf junction with an overlapping ridge system the structural data acquired during the survey provide strong constraints for kinematic models of the microplate the structural data need to be combined with crustal age determinations in order to derive a model for the evolution of the microplate

giant blocks in the south kona landslide hawaii a large field of blocky sea floor hills up to 10 km long and 500 m high are gigantic slide blocks derived from the west flank of mauna loa volcano on the island of hawaii these megablocks are embedded in the toe of the south kona landslide which extends 80 km seaward from the present coastline to depths of nearly 5 km a 10 15 km wide belt of numerous smaller 1 3 km long slide blocks separates the area of giant blocks from two submarine benches at depths of 2600 and 3700 m depth that terminate seaward 20 to 30 km from the shoreline similar giant blocks are found on several other major submarine hawaiian landslides including those north of oahu and molokai but the south kona blocks are the first to be examined in detail using high resolution bathymetry dredging and submersible diving dredging of two of the giant blocks brought up pillowed tholeiitic lava observations from the u s navy submersible sea cliff on the asymmetrically steep eastern flank of one block 10 km long and 300 m high revealed a succession of fractured massive basalt laminar lava flows hyaloclastite and pillow lavas chemical analyses of dredged lava identified 19 units that overlap compositionally with lavas from the south rift zone ridge of mauna loa sulfur content indicates that most of the lavas were erupted in subaerial and shallow submarine

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

groundwater in hard rocks of benin regional storage and buffer capacity in the face of change summary groundwater plays a major role in supplying domestic water to millions of people in africa in the future the ability to increase reliable water supplies for domestic and possibly irrigation purposes will depend on groundwater development groundwater storage is a key property because it controls the buffering behavior of the aquifer as it is subjected to time varying conditions such as increased pumping or land use change however quantitative knowledge of groundwater storage in africa is very limited this lack of knowledge is a major concern in hard rocks which cover about 40 of the surface area of africa this paper presents a unique quantitative assessment of groundwater storage in different types of hard rocks and a first estimate of the capacity of hard rock aquifers to buffer changes in climatic and anthropogenic conditions our study area in benin west africa is composed of various grades of metamorphic rocks we used the latest developments in the application of the magnetic resonance geophysical method to confront the methodological difficulty of quantifying groundwater storage we successfully conducted 38 magnetic resonance measurements in eight 8 different geological units each measurement was quantitatively interpreted in terms of groundwater storage we determined the groundwater storage of our study area to be 440 mm 70 mm equivalent water thickness to assess the buffer capacity of aquifers we compared groundwater storage to groundwater discharge groundwater discharge is the sum of natural discharge plus human abstraction we estimated natural discharge i e deep drainage plus evapotranspiration from water table fluctuations monitored in six 6 piezometers human abstraction was calculated based on the number of operating boreholes and their average daily abstraction we found that human abstraction 0 34 mm year 0 07 mm is far less than natural discharge 108 mm year 58 mm we conclude that increased abstraction due to population growth will probably have a smaller impact on storage than observed land use change which may lead to a change in the evapotranspiration rate we calculated buffer capacity as the ratio of current storage to total discharge and obtained a result of 6 years 47 months this buffer capacity confirms groundwater s ability to buffer changes finally our study is intended to promote a more quantitative approach to assessing groundwater resources in africa and to support our ability to adapt to current and future changes

contribution of the mrs method to identifying fractured basement rock aquifers in an arid area a case study near the bleida mine site in morocco the bleida fractured aquifer is not well studied in terms of water resources as previous geophysical investigations in this area were undertaken for mining purposes this study utilized magnetic resonance sounding surveys in order to define the distribution of water resources in the region of bleida and to locate areas favorable for the drilling and construction of productive hydraulic boreholes for this purpose eight magnetic resonance sounding surveys were conducted in two sites at the intersection of faults in basement rocks the results of these surveys indicated that there were two distinct levels of saturation in fractured rock that decreased with depth

seismic gaps in hawaii we propose that two seismic gaps exist in southern hawaii from their dimensions and tectonic setting we estimate that the south kona gap may be capable of a mainshock in the magnitude range of 7 1 4 to 7 1 2 while the east kona gap will probably not produce earthquakes larger than m 6 1 2 during historic time 1832 to the present no mainshocks have occurred in these gaps since there is no evidence that fault creep relieves stress in these areas we expect earthquakes to fill these gaps the boundaries of the south kona gap are defined by the approximate rupture extent of the earthquakes of 2 april 1868 m 7 9 and 21 august 1951 m 6 9 those of the east kona gap by the latter mainshock and the extent of the seismogenic zone the seismotectonic model on which we base our gap hypothesis defines a major seismic zone in the southern half of the island of hawaii we propose that most major and large earthquakes within this zone are of a decollement type in which the upper 10 km of the crust is pushed seaward along a near horizontal plane of weakness provided by the oceanic sediments buried beneath the volcanic edifice the direction of slip is away from the volcano summits and perpendicularly away from the volcano rifts several recurrence intervals are known for the kaoiki area where m 6 0 6 mainshocks occur every 10 4 1 5 years for the kalapana area one recurrence interval of 108 years is known for earthquakes with 7 m 8 in most of the major seismic zone in hawaii the recurrence times are not known and no information on strain accumulation rate is available it is therefore not possible to estimate when the portion of the 1868 rupture that has not re ruptured yet southern kau will produce another large mainshock the potential for a large earthquake in this area is estimated to be intermediate the potential in the kalapana the central kona and northern kona areas are estimated to be low for the next several decades

structural pattern of the galapagos microplate and evolution of the galapagos triple junctions a 13 000 km2 microplate intervenes to prevent the junction of the nazca cocos and pacific plates in the eastern equatorial pacific ocean west of the galapagos islands the microplate is rotating clockwise at 6 m y about an absolute pole 400 km southeast of its center so that although its northern margin has a similar motion to adjacent parts of the cocos plate its southern margin is 50 slower the perimeter of the galapagos microplate is best defined by bathymetry and has been surveyed with sea beam and examined by deep tow two of the three triple junctions on its margins are ridge ridge ridge rrr junctions 160 km apart on the crest of the east pacific rise epr the most like a classic rrr junction is the pacific nazca galapagos intersection at 1 10 n where the epr axis is joined by a narrow volcanic ridge 70 km long and 1 km high the cocos nazca galapagos junction at the west end of the cocos nazca spreading center is inferred to be of the rff type but the transform fault branches are represented by large nontransform offsets lack of stable transform faults is related to rapid westward migration of the junction caused by lengthening of the cocos nazca axis at 60 70 mm yr this rate which was once required to maintain a stable nazca cocos pacific rrr junction has persisted even after birth of the microplate about 1 ma continuing propagation of the cocos nazca axis has opened up the hess deep rift basin in the eastern epr flank in advance of the eruptive propagator tip this rift valley has a relief of more than 3 km from its uplifted rims to the floor where severe attenuation exposes basal layers of the epr crust the similar dietz deep rift basin at the southeastern margin of the microplate 70 km from hess deep was formed when a lengthening galapagos nazca spreading axis rifted through another part of the epr flank

tectonics of the nazca antarctic plate boundary abstract we have constructed a new bathymetric chart of part of the chile transform system based mainly on an r v endeavor survey from 100 w to its intersection with the east ridge of the juan fernandez microplate at 34 30 s 109 15 w a generally continuous lineated trend can be followed through the entire region with the transform valley being relatively narrow and well defined from 109 w to approximately 104 30 w the fracture zone then widens to the east with at least two probable en echelon offsets to the south at 104 and 102 w six new strike slip mechanisms along the chile transform and one normal fault mechanism near the northern end of the chile rise inverted together with other plate motion data from the eastern portion of the boundary produce a new best fit euler pole for the nazca antarctic plate pair providing tighter constraints on the relative plate motions

rapid deformation of the south flank of kilauea volcano hawaii the south flank of kilauea volcano has experienced two large magnitude m 7 2 and m 6 1 earthquakes in the past two decades global positioning system measurements conducted between 1990 and 1993 reveal seaward displacements of kilauea9s central south flank at rates of up to about 10 centimeters per year in contrast the northern side of the volcano and the distal ends of the south flank did not displace significantly the observations can be explained by slip on a low angle fault beneath the south flank combined with dilation deep within kilauea9s rift system both at rates of at least 15 centimeters per year

rapid deformation of kilauea volcano global positioning system measurements between 1990 and 1996 campaign global positioning system gps measurements from 1990 to 1996 are used to calculate surface displacement rates on kilauea volcano hawaii the gps data show that the south flank of the volcano which has generated several large earthquakes in the past 3 decades is displacing at up to 8 cm yr to the south southeast the summit and rift zones are subsiding with maximum subsidence rates of 8 cm yr observed a few kilometers south of the summit caldera elastic dislocation modeling of the gps data suggests that the active sources of deformation include deep rift opening along the upper east and east rift zone fault slip along a subhorizontal fault near the base of the volcano and deflation near the summit caldera a nonlinear optimization algorithm was used to explore the parameter space and to find the best fitting source geometry there is a broad range of model geometries that fit the data reasonably well however certain models can be ruled out including those that have shallow rift opening or shallow fault slip some offshore aseismic slip on a fault plane that dips between 258 north northwest and 88 south southeast is required best fitting slip and rift opening rates are 23 28 cm yr although rates as low as 10 cm yr are permitted by the data

determination of groundwater flow through regimes of shallow lakes and wetlands from numerical analysis of stable isotope and chloride tracer distribution patterns a numerical model previously developed to systematically examine groundwater flow in vertical section near shallow surface water bodies such as lakes wetlands and ponds is further developed to include simulation of the distribution patterns of hydrogeochemical and stable isotopic tracers in relation to the surface water body and the geometry of distribution patterns of the tracers in the groundwater release zone of the lake many different possible flow regimes are identified however in this paper attention is focused on flow through water bodies as these are the flow regimes observed in field validation two shallow lakes on the swan coastal plain of south west western australia are the subject of field studies where hydrogeochemical and stable isotopes are used to validate the flow through groundwater flow regime predicted by the modelling confirming the validity of the approach the flow regime transition diagrams introduced in earlier papers are extended to include consideration of the hydrogeochemical and stable isotopic indices cl l cl and 1000 l 1000 these ratios are introduced as an additional two of nine non dimensional ratios that are necessary to analyse the problem the ratios represent the chloride and isotopic composition ci l and l respectively in the groundwater release zones of the lakes relative to these parameters in the groundwater capture zone cl and for the lake field data from the case studies plotted on appropriately configured transition diagrams demonstrates the overall validity of the modelling approach and its underlying assumptions it is concluded that isotopic and hydrogeochemical data are invaluable in interpreting the interaction between lakes or wetlands and regional aquifers as it is very difficult to make physical or hydraulic measurements in the field that allow an understanding of lake aquifer interaction the tools and concepts developed that are summarized in the presented transition diagrams are invaluable starting points for the consideration and analysis of other case specific examples of groundwater surface water interaction and will improve the scientific basis of decision making concerning lake and wetland management and groundwater interaction by water resource and environmental managers

the development of two oceanic microplates easter and juan fernandez microplates east pacific rise in this paper we synthesize and discuss the results of recent detailed geophysical surveys and reconstructions of two active mid ocean ridge microplates on the east pacific rise we quantify their development in terms of the principal dimensions of the microplates and their boundaries and the temporal changes in these dimensions the results are discussed in the framework of the roller bearing microplate model of schouten and others which postulates that microplates are driven by shear couples imposed on them by the motions of their bounding major plates we test the specific predictions of this model for the geometry of the pseudofaults traces of the propagating tips of the microplates spreading boundaries and the histories of rotation of the microplates both microplates are currently rotating at the rates predicted by the model on the assumption of complete coupling no slip or deformation between the microplates and the major plates at instantaneous points of contact near the propagating tips of the spreading boundaries juan fernandez microplate was also rotating at the predicted rate just before 2 ma when it was driven by the nazca pacific couple rather than the nazca antarctic couple that currently applies however earlier rotations were slower than predicted implying some degree of decoupling or deformation at earlier times the microplates appear to have grown from moderate sized c 100 km probably left stepping offsets of the east pacific rise since about 5 ma the nature of these offsets is currently uncertain but they may have been propagating rifts which changed from shearing by bookshelf faulting to rigid block microplate rotation on reaching a critical size once rigid block rotation began the microplates grew by seafloor spreading accompanied by propagation of their bounding spreading centres the effects of the neighbouring easter mantle plume and pacific nazca antarctic triple junction can be discerned in the bathymetry and ridge propagation rates but do not appear to have had a major influence on the microplates development

migrating transform zone and lithospheric transfer at the galapagos 95 5 w propagator at the 95 5 w propagator system along the cocos nazca plate boundary the spreading axis is offset left laterally about 35 km 1 m y this offset migrates westward 52 km m y relative to points along the nearly east west trending ridge axis transferring lithosphere from the cocos to the nazca plate as it does so the required 58 km m y of right lateral motion across this migrating transform is apparently not accommodated by a throughgoing north south transform fault but rather by an approximately 15 to 20 km wide zone of shear deformation dominated by eastward curving of east west structures to a northwest southeast trend this pattern of curvature the coinciding zone of high seismicity and the abundance of talus in the area suggest that shear is distributed over this entire zone the deformation is inferred to be taken up by a bookshelf mechanism whereby faults oriented at high angles to the shear couple have left lateral slip antithetic to the right lateral shear couple rotating individual blocks clockwise these are interpreted as reactivated abyssal hill bounding normal faults probably dipping 45 60 northeast southwest shortening due to the rotation appears to be accommodated by reverse slip on the faults and may account for the uplift of de steiguer ridge in the zone of transferred lithosphere these faults have apparently had a very complex history initially normal faults formed as abyssal hills were created at the spreading axis and subsequently they had left lateral strike slip motion in the transform zone and reverse motion uplifting de steiguer ridge strain analysis based on observed structural curvature suggests that shear is distributed nonuniformly and lithospheric transfer requires 0 4 m y

slope failure and volcanic spreading along the submarine south flank of kilauea volcano hawaii 1 new multichannel reflection data and high resolution bathymetry over the submarine slopes of kilauea volcano provide evidence for current and prior landsliding suggesting a dynamic interplay among slope failure regrowth and volcanic spreading disrupted strata along the upper reaches of kilauea s flank denote a coherent slump correlated with the active hilina slump the slump comprises mostly slope sediments underlain by a detachment 3 5 km deep extension and subsidence along the upper flank is compensated by uplift and folding of the slump toe which surfaces about midway down the submarine flank uplift of strata forming papa u seamount and offset of surface features along the western boundary of kilauea indicate that the slump has been displaced 3 km in a south southeast direction this trajectory matches coseismic and continuous ground displacements for the hilina slump block on land and contrasts with the southeast vergence of the rest of the creeping south flank to the northeast slope sediments are thinned and disrupted within a recessed region of the central flank demonstrating catastrophic slope failure in the recent past debris from the collapsed flank was shed into the moat in front of kilauea building an extensive apron seaward sliding of kilauea s flank offscraped these deposits to build an extensive frontal bench a broad basin formed behind the bench and above the embayed flank uplift and back tilting of young basin fill indicate recent and possibly ongoing bench growth the hilina slump now impinges upon the frontal bench this buttress may tend to reduce the likelihood of future catastrophic detachment

comprehensive sonar imaging of the easter microplate recent gloria and seamarc ii sidescan sonar surveys have imaged virtually the whole of the easter microplate and revealed unprecedented detail and complexity in its tectonic fabric and history there is clear evidence of rapid microplate rotation of rapidly evolving plate boundaries and of complex deformation near the northern and southern microplate boundaries

speed limit for oceanic transform faults oceanic transform faults with slip rates greater than 145 km m y do not currently exist along the east pacific rise where sea floor spreading rates range from 145 to 160 km m y instead offsets of the the very fast spreading east pacific rise are accommodated by microplates propogating rifts or overlapping spreading centers this suggests that there might be a speed limit above which transform faults do not exist a physical reason for a speed limit is not known but it might be related to unstable stress fields near the rifts tips causing them to episodically propagate and prevent a transform fault from being formed the spreading rates quoted are from our new 0 0 73 ma relative motion model for the pacific and nazca plates

a tectonic model for ridge transform ridge plate boundaries implications for the structure of oceanic lithosphere abstract the first order geologic and morphologic relationships at along and proximal to ridge transform ridge plate boundaries are used to construct an empirical and speculative tectonic model the distinctive but variable morphotectonic fabric and crustal structure of the transform domain are the product of a tectonic continuum that ranges from very slow rates of strain associated with very thick edges of lithosphere slowly slipping ridge transfrom ridge plate boundaries to extremely high rates of strain associated with very thin edges of lithosphere fast slipping ridge transform ridge plate boundaries the geometry of a ridge transform intersection necessitates the juxtaposition of a relatively cold thick edge of lithosphere against the truncated end of an accreting plate boundary the cold face of lithosphere cools the adjacent wedge of asthenosphere rising beneath the axis of accretion and restricts the amount of partial melting thus attenuating the volume of basaltic melt segregated from the asthenosphere per unit time the shallow level manifestation of this cold edge effect is a thinner oceanic crust at depth the evolving lithosphere thickens rapidly as the cold edge is approached creating changes in the properties of the young lithosphere and forming a weld of upper mantle material against the cold edge of truncating lithosphere the ridge transform weld of upper mantle material creates a shear couple in the lithosphere underlying the intersection resulting in the progressive reorientation of the maximum tensile stress from normal to the ridge axis at some distance from the ridge transform intersection to an oblique angle near the boundary the brittle carapace of oceanic crust that overlies the mantle weld will deform accordingly with the development of oblique dip slip faults the model predicts that the geologic expressions of this cold boundary effect will become more dramatic with increasing thickness of the truncating edge at very slow rates of accretion 100 km juxtapose thick 30 50 km edges of lithosphere against the accreting plate boundary all but nullifying the processes that lead to the emplacement of normal oceanic lithosphere in this environment a relatively strong mantle weld will form at the ridge transform intersection and the thick edges of opposing lithosphere along the length of the transform will tend to confine the strike slip tectonism to a relatively narrow and temporally stable principal transform displacement zone in contrast at very fast rates of accretion large offset transforms 100 km place relatively thin edges of lithosphere

magnetic resonance sounding evidence shows that shallow groundwater discharge maintains the lake landscape in the hunshandake sandy land north china the hunshandake sandy land hsl is a well known water rich sandy region in china that is home to many lakes most of these lakes are sustained by groundwater inflow however due to the limited hydrogeological survey data the mechanism by which the lakes interact with groundwater is not well understood magnetic resonance sounding mrs is a geophysical method that has emerged in recent years that can directly detect the distribution of groundwater and determine the lithology of the aquifer medium compared with drilling this method is convenient rapid and inexpensive in this study to determine how the lakes are recharged by groundwater a field experiment using mrs was conducted on haoletuyin lake which is located in the central hsl the results showed that compared with borehole data the mrs derived aquifer depth has an uncertainty of 6 88 additionally the lithology of the media derived from the mrs is consistent with that derived from the borehole data this finding suggests that the mrs derived results are highly accurate based on the mrs derived results two hydrogeological profiles were plotted and they show that the lake in the experimental area is recharged primarily by shallow groundwater and not by deep groundwater this study is significant because it not only reveals the mechanism by which haoletuyin lake is maintained but also proves that mrs is an excellent tool for studying lake groundwater relations in desert sandy land regions with limited hydrogeological survey data

gloria observations of the propagating rift at 95 50w on the cocos nazca spreading center in this paper we describe a gloria long range sidescan sonar survey of the area around 95 5 w on the cocos nazca rise where a propagating rift has been predicted to occur the sonar images clearly show a wedge of new crust that has been emplaced by propagation into 1 ma old crust the new crust is up to 800 m deeper than the surrounding seafloor although the elevation difference appears to decay with time the pseudofaults which bound this new crust have been observed from the rift tip back to crustal isochron 0 65 ma near the rift tip they consist of scarps several hundred meters high with narrow shallow valleys at their feet the sheared zone between the southern pseudofault and the trace of the failed rift to the south is characterized by abnormally shallow seafloor and nnw sse trending lineaments these may have been produced by the rotation of tectonic fabric formed at the dying rift perhaps accompanied by other deformation the youngest tectonic and volcanic lineaments on both spreading segments strike 273 but on the dying rift short spreading segments are offset en echelon so that the regional trend of the rise axis is 265 older lineaments throughout the area strike 265 the propagating rift is thus replacing an oblique rise axis by one which is orthogonal to the spreading direction and it is suggested that this is occurring in response to a recent change in spreading direction from 355 to 003 variations in the strikes of the pseudofaults indicate that the propagation direction has varied but that the rift has propagated most rapidly when following the 273 direction which we take to be normal to the new spreading direction

submarine geology of the hilina slump and morpho structural evolution of kilauea volcano hawaii abstract marine geophysical data including sea beam bathymetry hawaii mr1 sidescan and seismic reflection profiles along with recent robot submersible observations and samples were acquired over the offshore continuation of the mobile kilauea volcano south flank this slope comprises the three active hot spot volcanoes mauna loa kilauea and loihi seamount and is the locus of the hawaiian hot spot the south flank is the site of frequent low intensity seismicity as well as episodic large magnitude earthquakes its sub aerial portion creeps seaward at a rate of approximately 10 cm year the hilina slump is the only large submarine landslide in the hawaiian archipelago thought to be active and this study is one of the first to more highly resolve submarine slide features there the slump is classified into four distinct zones from nearshore to the island s base estimates of size based on these data indicate a slumped area of 2100 km 2 and a volume of 10 000 12 000 km 3 equivalent to about 10 of the entire island edifice the overall picture gained from these data sets is one of mass wasting of the neovolcanic terrain as it builds upward and seaward though reinforcement by young and pre hawaii seamounts adjacent to the pedestal is apparent extensive lava delta deposits are formed by hyaloclastites and detritus from recent lava flows into the sea these deposits dominate the upper submarine slope offshore of kilauea with pillow breccia revealed at mid depths along the lower flanks massive outcrops of volcanically derived sedimentary rocks were found underlying kilauea thus necessitating a rethinking of previous models of volcanic island development the morphologic and structural evolutionary model for kilauea volcano and the hilina slump proposed here attempts to incorporate this revelation a hazard assessment for the hilina slump is presented where it is suggested that displacement of the south flank to date has been restrained by a still developing northeast lateral submarine boundary when it does fully mature the south flank may be more subject to land slips triggered by large long duration earthquakes and thus kilauea may undergo more frequent episodes of failure with increased displacements

growth and persistence of hawaiian volcanic rift zones hawaiian volcanic rift zones are modeled by representing the rifts and adjacent volcano flanks as long ridges with the geometry of flattened triangular prisms the intrusion of dikes along the axis of a rift requires a mechanism to generate the appropriate dike trapping stress field within the prism possible factors that affect the state of stress in the prism include multiple dike intrusion along the ridge axis faulting and gravitational sagging of the topography in extreme models with very steep slopes and high poisson s ratio corresponding to the gelatin models of rift zones by fiske and jackson 1972 results of finite element calculations indicate that gravity induced stresses are sufficient to trap a dike into propagating within the prism and parallel to the rift zone as proposed by fiske and jackson however the mechanism does not work for gently sloping flanks or a more acceptable poisson s ratio of about 0 25 additionally trapping stresses in the gravity loading and density stratification models will not persist after a few dike injection episodes therefore in mature hawaiian rift zones with possibly thousands of dikes additional processes must act to control the stresses that permit continued dike intrusion and rift persistence it is proposed that accommodation to dike emplacement occurs by slip on deep faults possibly of the type proposed for the 1975 kalapana hawaii earthquake as suggested by others for this earthquake the faults could coincide with the contact of the volcano with the seafloor within the weak seafloor sediments such faulting not only provides a means for the flanks to adjust continuously to intrusions but also generates the stress patterns needed to constrain future dikes to propagate along the rift axis other possible faulting mechanisms such as shallow gravity slides and normal faulting of the flanks do not appear to favor rift zone persistence in this model the horizontal stress generated by a standing column of magma at the time of dike emplacement the stresses in the ridges and the fault strength are coupled this results in a feedback between the maximum height that magma can rise along the rift fault friction and fault width through this feedback the slope of the volcano flank is controlled by the fault friction when applied to kilauea volcano the model yields an estimate for the coefficient of fault friction as high as 0 39 assuming normal hydrostatic pore fluid pressure an implication of this model supported by other studies is that rift intrusion and lateral spreading could be major contributors to volcano growth

the fixed hotspot hypothesis and origin of the easter sala y gomez nazca trace reconstructions of the pacific and nazca plates suggest that both the nazca and tuamotu ridges originated from a melting anomaly which existed beneath the pacific farallon ridge during the time interval between anomalies 19 and 11 as would be predicted from the fixed hotspot hypothesis the hotspot hypothesis interpreted according to morphology of the easter sala y gomez nazca trace would further suggest that the hotspot was located entirely beneath the nazca plate during the time interval between anomalies 11 and 2 at the end of this interval the eastern boundary of the easter plate formed centered above the hotspot according to this scheme the present location of the hotspot is about 200 km west of easter island however the easter model is incompatible with the hotspot model for the hawiian emperior chain if the hotspots are fixed relative to one another as the age of the point on the tuamotu ridge which corresponds with the hawaiian emperor bend 53 to 55 m y is significantly greater than the age of the bend 43 m y the fixed hostpot hypothesis can be satisfied by the two traces only if one or a combination of the following conditions is met the kinematic age of the hawaiian emperor bend is substantially greater than the isotopically dated age the magnetic anomaly time scale is in significant error and or magnetic anomaly identifications in the vicinity of the tuamotu ridge are erroneous it might appear that other mechanisms for the origin of hotspot traces are preferable to the hotspot hypothesis the most promising of these involves propagating fractures resulting from intraplate stress this hypothesis has the advantage of accommodating anomalies in some hotspot traces such as persistence of igneous activity long after passage of the trace over the hotspot

experimental and numerical investigations of soil water balance at the hinterland of the badain jaran desert for groundwater recharge estimation abstract quantification of groundwater recharge from precipitation in the huge sand dunes is an issue in accounting for regional water balance in the badain jaran desert bjd where about 100 lakes exist between dunes in this study field observations were conducted on a sand dune near a large saline lake in the bjd to investigate soil water movement through a thick vadose zone for groundwater estimation the hydraulic properties of the soils at the site were determined using in situ experiments and laboratory measurements a hydrus 1d model was built up for simulating the coupling processes of vertical water vapor movement and heat transport in the desert soil the model was well calibrated and validated using the site measurements of the soil water and temperature at various depths then the model was applied to simulate the vertical flow across a 3 m depth soil during a 53 year period under variable climate conditions the simulated flow rate at the depth is an approximate estimation of groundwater recharge from the precipitation in the desert it was found that the annual groundwater recharge would be 11 30 mm during 1983 2012 while the annual precipitation varied from 68 to 172 mm in the same period the recharge rates are significantly higher than those estimated from the previous studies using chemical information the modeling results highlight the role of the local precipitation as an essential source of groundwater in the bjd

paleomagnetic constraints on fault motion in the hilina fault system south flank of kilauea volcano hawaii movement of the south flank of kilauea volcano in hawaii has been associated with catastrophic landslide events the surface expression of this former movement is the hilina fault system with fault scarps as high as 500 m paleomagnetic directions for lava flows exposed in the hilina fault scarps at puu kapukapu and keana bihopa on the hilina pali are used to determine the average rate of movement along faults slip surfaces separating the two sections this paper reports results from two independent paleomagnetic studies within the hilina pali area twenty one paleomagnetic sites 143 cores were sampled by the michigan technological university group from lava flows between the mo o ash and middle pohakaa ash at keana bihopa in the footwall block of the 500 m high hilina pali fault scarp thirty paleomagnetic sites 152 cores were collected by the california institute of technology group from lava flows between the mo o ash and middle pohakaa ash in the 300 m high puu kapukapu section the hanging wall block a comparison of site mean directions show that lava flows in the lower part of the puu kapukapu section have been tilted more than lava flows in the upper part with respect to the keana bihopa section the systematic steepening of remanent directions downsection at puu kapukapu indicates that slippage of this block occurs along listric normal faults the average amount of backward tilt of the puu kapukapu block based on a comparison of mean directions from the two sections is 7 8 7 7 using slope stability methods the average rate of movement of the puu kapukapu block since deposition of the middle pohakaa ash is 1 7 2 4 cm yr and the average displacement subsidence is 680 740 m assuming that the average displacement resulted from a series of earthquakes producing subsidence equal to that observed in the 1975 kalapana earthquake 3 m of subsidence along a 40 km segment of coastline on the south flank of kilauea volcano one kalapana size earthquake occurring every 200 years would account for this displacement lastly overall mean directions for the two sections indicate that puu kapukapu has rotated counterclockwise with respect to the hilina pali by 14 8 8 5 about a nearby vertical axis this also suggests that slippage between the two blocks occurs along listric normal faults

mechanical models of the 1975 kalapana hawaii earthquake and tsunami abstract our objective is to produce a mechanically realistic model for the 1975 kalapana event that explains the overall deformation and geological evolution of the south flank of kilauea and reproduces most known earthquake and tsunami observations to do this we present a new structural interpretation of geological data from kilauea along with modeling of the tsunami using recent seismic analyses in so doing we hypothesize an offshore north facing normal fault that we call the kalapana fault because of its limited onshore expression near kalapana we argue that several different interpretations of seismic data are simultaneously true each coinciding with a specific geological structure we perform a direct numerical simulation of the 1975 kalapana tsunami and we report results for the near field and the far field simultaneously our interpretation of geological structures provides sufficient constraints to derive three tsunami sources the kalapana fault a slump and a thrust fault these three tsunami sources are mechanically coupled according to our model of kilauea evolution although their contributions to tsunami generation remain relatively distinct slump displacement predicts a small shear stress beneath kilauea volcano we find that our geological interpretation and tsunami sources are sufficiently robust to reproduce almost all tsunami observations repeated earthquakes like the 1975 kalapana event will produce extension and subsidence in the upper flank of kilauea as well as compression and uplift of the toe region accompanied by limited slump movement these deformations appear to stabilize kilauea and make catastrophic failure of the volcano flank less likely at this time

groundwater flow along and across structural folding an example from the judean desert israel abstract the considerable influence of the geological structure on groundwater flow regime is exhibited in the thick carbonate aquifer beneath the judean desert israel groundwater flow is diverted from the general steep hydraulic gradient creating a subsurface river like meandering flow pattern the structure of the extensive folded anticlinorium forces groundwater flow through synclinal axes in the upper aquifer and in places it overflows from one to an adjacent syncline groundwater outflows are at tsukim kane samar and en gedi springs near the dead sea shore and by sub surface flow across the graben faults towards the dead sea in this study all available data are integrated and processed first ever to form a complete representation of the three dimensional hydrostratigraphy and hydrogeology using numerical modeling modflow we analyzed quantitatively the flow regime leakage rates between upper and lower sub aquifers and between adjacent sub basins the groundwater mass balance and aquifer hydraulic properties this study has practical implications regarding recent groundwater management future possibilities of groundwater development for the benefit of both israelis and palestinians residing in the area and conservation of nature reserves located along the dead sea

conceptual model of recharge to southeastern badain jaran desert groundwater and lakes from environmental tracers sources of groundwater recharge to the badain jaran desert in china have been investigated using geochemical and isotopic techniques stable isotope compositions 18o and 2h of shallow groundwater and surface water from oasis lakes evolve from a starting composition considerably depleted compared to local unsaturated zone moisture confirming inferences from chloride mass balance that direct infiltration of precipitation is not a volumetrically important source of recharge to the shallow aquifer in the study area shallow phreatic and deeper confined groundwater bodies appear unconnected based on chemical composition and radiocarbon activities hydrogeologic evidence points toward a bordering mountain range yabulai as a likely recharge zone which is consistent with tracer results a mean residence time in the range of 1 2 ka for the desert s southeastern margin is inferred from radiocarbon these results reveal that some replenishment to the desert aquifer is occurring but at a rate much lower than previously suggested which is relevant for water resources planning in this ecologically sensitive area

a history of the easter microplate 5 25 ma to present gloria and other geophysical data are used to interpret the morphology and tectonic pattern of the easter microplate we model magnetic anomaly data and calculate spreading rates for use in euler pole calculations we calculate three plate closure and best fit poles for nazca pacific nazca easter and pacific easter plate motions and compare the results with earthquake focal mechanisms and seismicity we use the three plate closure poles to rotate digital gloria and magnetic isochron data of the microplate and surrounding major plates back in time since the microplate s east rift first started to propagate northward at around 5 25 ma the microplate has evolved in two stages the first is from 5 25 ma to around 2 5 ma and involved continuous northward propagation of the east rift while the west rift became segmented along new transform faults as it adjusted to keep the overall nazca pacific velocities constant the transpressive northern boundary migrated with the east rift tip while the transtensional southern boundary remained more or less still at some time after 2 5 ma the east rift ceased northward propagation and the southwest rift began to open up along the transtensional pacific easter transform a convergent northern boundary formed involving southward thrusting of the nazca plate over the microplate no further nazca plate lithosphere was transferred from north of the microplate to the microplate interior and the pito deep region opened by pervasively rifting apart preexisting nazca plate lithosphere

flexure and seismicity beneath the south flank of kilauea volcano and tectonic implications we present a refined model for the tectonic behavior of kilauea volcano s south flank including flexure calculations and microearthquake data supportive of the model in our model the south flank moves seaward over the downwardly flexed ocean crust in a manner analogous to an accretionary prism in a subduction zone the flank is driven seaward by the gravitational stresses inherent in its shape this driving force is augmented by high density material in kilauea s rift zones elastic flexure calculations predict a configuration for the downwardly flexed crust which agrees with previous seismic refraction and gravity modeling this configuration in turn is consistent with the hypothesis that many earthquakes occur along the volcanic pile ocean crust interface focal mechanisms for these events predominantly indicate southeastward directed overthrusting we also propose a relationship between rift zone intrusion and south flank displacement including a suggestion that the decollement configuration controls the relative activity of kilauea s east and southwest rift zones

overthrusting and sediment accretion along kilauea s mobile south flank hawaii evidence for volcanic spreading from marine seismic reflection data a large intermittently active submarine landslide known as the hilina slump has been interpreted along the south flank of kilauea volcano seaward dipping faults on land mark its headwall and an offshore bench may define its uplifted toe geodetic data show that the entire south flank is also moving seaward by a process referred to as volcanic spreading this provides an alternative explanation for the bench i e overthrusting along the edge of the sliding flank the latter interpretation is consistent with new seismic reflection data across the submarine flank a prominent reflection near the top of the oceanic plate suggests the decollement upon which the mobile flank slides landward dipping reflections rise from this horizon and bound packages of bedded strata faulted and imbricated within the bench the absence of correlative seaward dipping faults and rotated strata on the upper flank suggests that the bench is not coupled to a slump moreover kinematic reconstructions of the bench indicate that it has accommodated 15 24 km of displacement this value is consistent with estimates for rift zone extension but too high for shortening at the toe of a slump we interpret the bench to result from overthrusting and accretion of volcaniclastic sediments to the edge of the mobile flank and suggest that morphologic benches develop preferentially where landslide debris has accumulated near the base of the volcano and can be accreted to its sliding edifice

imaging the crustal magma sources beneath mauna loa and kilauea volcanoes hawaii three dimensional seismic p wave traveltime tomography is used to image the magma sources beneath mauna loa and kilauea volcanoes hawaii high velocity bodies 6 4 km s in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro ultramafic cumulates from which the surface volcanism is derived the proximity of these high velocity features to the rift zones is consistent with a ridge spreading model of the volcanic flank southeast of the hilina fault zone along the south flank of kilauea low velocity material

mechanism of the 1975 kalapana hawaii earthquake inferred from tsunami data we investigated the source mechanism of the 1975 kalapana hawaii earthquake m s 7 2 by modeling the tsunamis observed at three tide gauge stations hilo kahului and honolulu we computed synthetic tsunamis for various fault models the arrival times and the amplitudes of the synthetic tsunamis computed for ando s fault model fault length 40 km fault width 20 km strike n70 e dip 20 se rake 90 fault depth 10 km and slip 5 6 m are 10 min earlier and 5 times smaller than those of the observed respectively we tested fault models with different dip angles and depths models with a northwest dip direction yield larger tsunami amplitudes than those with a southeast dip direction models with shallower fault depths produce later first arrivals than deeper models we also considered the effects of the hilina fault system but its contribution to tsunami excitation is insignificant this suggests that another mechanism is required to explain the tsunamis one plausible model is a propagating slump model with a 1 m subsidence along the coast and a l m uplift offshore this model can explain the arrival times and the amplitudes of the observed tsunamis satisfactorily an alternative model is a wider fault model that dips 10 nw with its fault plane extending 25 km offshore well beyond the aftershock area of the kalapana earthquake these two models produce a similar uplift pattern offshore and kinematically are indistinguishable as far as tsunami excitation is concerned the total volume of displaced water is estimated to be 2 5 km 3 from the comparison of slump model and the single force model suggested earlier from seismological data we prefer a combination of faulting and large scale slumping on the south flank of kilauea volcano as the most appropriate model for the 1975 kalapana earthquake two basic mechanisms have been presented for explaining the deformation of the south flank of kilauea 1 pressure and density variation along the rift zone caused by magma injection and 2 gravitational instability due to the steep topography of the south flank of kilauea in either mechanism large displacements on the south flank are involved that are responsible for the observed large tsunamis

chemical and isotopic variations along the superfast spreading east pacific rise from 6 to 30 s chemical data of 39 fresh basaltic glasses from the east pacific rise epr between 6 and 30 s and pb sr and nd isotopic compositions of 12 basalt glasses are presented major and trace element data indicate a wide compositional range including primitive basalts mg 0 67 and highly evolved feti basalts mg 0 34 molmg mg fe2 the compositional range can be attributed to low pressure fractional crystallization fractionation corrected major element concentrations provide evidence for varying mantle melting conditions calculations of the melting conditions suggest melt generation in a rising upper mantle column between 20 and 10 kbar at temperatures between 1430 and 1280 c and total degrees of partial melting between 17 and 20 by weight leached and hand picked basalt glasses display large variations in 87sr 86sr 0 70235 0 70270 143nd 144nd 0 51312 0 51323 and 206pb 204pb 18 064 18 665 but are similar to other n type morb from the epr the isotopic ratios of basalts from 13 to 23 s show strong correlations and delineate two systematic trends from 23 to 17 s 87sr 86sr and pb isotope ratios increase and 143nd 144nd decrease in agreement with previous results mahoney et al 1989 a reverse trend is indicated by basalts from 17 to 13 s however k ti and la sm n continuously increase from 23 to 13 s this opposite behavior indicates a recent decoupling of isotopic and minor element ratios in the mantle between 13 and 17 s north of 13 5 s garrett fracture zone isotopic data show no systematic variation with ridge location and display an overall weaker covariation the results suggest that the isotopic variations and ridge segmentation appear to be unrelated and that major ridge offsets apparently coincide with changes in mantle melting conditions p t f f degrees of melting there is no evidence for a systematic relationship between calculated melting conditions and second order ridge segmentation our isotopic data provide further evidence for regionally confined chemical variations in the mantle at 5 to 30 s we interpret the isotopic trends as reflecting melting of distinct smallvolume and old enriched mantle components in contrast variations in trace elements are attributed to young mantle differentiation processes

hydrological and climatic changes in deserts of china since the late pleistocene article i nfo article history large areas in western china were wetlands or less arid between 40 and 30 ka corresponding to the greatest lake period on the adjacent tibetan plateau during the last glacial maximum some of these western chinese deserts again experienced wetter conditions however at the same time the sandy lands in the eastern chinese desert belt experienced an activation of aeolian dunes while interpretations of the mid holocene environment in the deserts of china are controversial it is quite likely that it was more humid not only in the eastern areas influenced by monsoon climate systems but also in the western deserts where moisture is currently associated with westerlies evaluation of lacustrine records in the lakes recharged by dryland rivers and the complex interactions of these systems as well as other paleoenvironmental proxies such as the artemisia chenopodiaceae ratio should be interpreted with greater caution facing the highlighted uncertainties in our understanding of climate changes in chinese deserts it is hoped that this special issue will improve our knowledge considerably

structure of the mobile south flank of kilauea volcano hawaii how do huge landslides occur in hawaii we can begin to address this question by examining an incipient landslide structure on the mobile south flank of kilauea volcano between 1970 and 1989 this part of the south flank moved in a southeast direction seaward by 4 m on its eastern end and by 10 m on its western end parallel to the western boundary of a large oifshore topographic bench we show that abrupt decreases in cumulative flank movement correspond to abrupt decreases in hypocenter concentration most of the earthquakes occur in a 7 to 10 km deep band beneath the south flank and relative relocation of a subset of these events shows that they are derived from a single horizontal plane which appears to be a decollement focal mechanisms for this deep seismicity are dominated by thrust fault mechanisms with the overlying block moving seaward a comparison of south flank bathymetry with decollement structures on other volcanoes suggests that the distal end of this decollement coincides with the distal end of the offshore topographic bench 30 50 km from shore and 5 km below sea level the fault system forming the hilina pali is connected with this decollement so that slip on the hilina pali s normal faults coincides with slip of the decollement and with reverse faulting of the distal end of the bench this interpretation is supported by studies of the events associated with the m7 2 kalapana earthquake in 1975 when the hilina pali is connected to the outer bench with a decollement inferred from seismicity a wedge 8 km thick adjacent to kilauea s magma system and 1 2 km thick along the edge of the outer bench an area over 3000 km2 is defined the thickness adjacent to the magma system decreases eastward along kilauea s east rift zone and southwestward from kilauea caldera whereas the thickness of the lip of the outer bench decreases only eastward geologic observations and geophysical studies of the subaerial flank reveal an extensive magma system beneath the koae fault system as well as beneath kilauea caldera and its east rift zone we infer that the boundary of the proximal end of the mobile flank is the southern boundary of this magma system and that this boundary coincides with the southern boundaries of both the koae fault system and kilauea s east rift zone

on determining uncertainties of magnetic resonance sounding estimated transmissivities for groundwater modeling abstract the nuclear magnetic resonance sounding mrs method is used increasingly as a tool for hydrological investigations compared to other geophysical methods the advantage of mrs is that it is directly sensitive to the presence of water in the subsurface data interpretations can also be used to get information about the subsurface pore structures which under special conditions can be related to hydraulic properties such as aquifer transmissivity however to broaden the usage of this information in hydrological modeling the uncertainties related to these transmissivity estimates must be determined otherwise properly balanced weights cannot be given to the prior information obtained from mrs transmissivity estimates as compared to the hydrological data sets when used for groundwater model calibration we have developed a methodology to estimate the uncertainties of mrs based transmissivity estimates compared to previous studies the methodology is well defined and it takes into account import

tectonics of the easter plate abstract we present a new model for the easter plate in which rift propagation has resulted in the formation of a rigid plate between the propagating and dying ridges we use the distribution of earthquakes eleven new focal mechanisms and existing bathymetric and magnetic data to describe the tectonics of this area both the easter nazca and easter pacific euler poles are sufficiently close to the easter plate to cause rapid changes in rates and directions of motion along the boundaries the east and west boundaries are propagating and dying ridges the southwest boundary is a slow spreading ridge and the northern boundary is a complex zone of convergent and transform motion the easter plate may reflect the tectonics of rift propagation on a large scale where rigid plate tectonics requires boundary reorientation we use simple schematic models to illustrate the general features and processes which occur at plates resulting from large scale rift propagation

tectonic evolution of the easter microplate the plate tectonic history of the easter microplate has been reconstructed by closing the microplate in a series of steps using the pacific nazca magnetic anomalies north and south of the microplate and the nuvel 1 global plate motion model after each step the easter microplate was rotated rigidly to match the nazca and pacific anomalies gaps and overlaps formed by this kinematic treatment indicate compressional and tensional deformation respectively and show that rigid plate motions are insufficient to explain the complete tectonic evolution analysis of the magnetic anomaly data was guided by contoured seamarc ii sea beam and 3 5 khz bathymetry data and a lineament map derived from seamarc ii side scan and sea beam bathymetry data the patterns of lineaments and bathymetric structures suggest that rotational deformation of the nazca plate is the general mechanism that accommodates the space problems arising from transfer of the nazca plate to the microplate and rapid rotation of the microplate against the nazca plate similar but smaller amounts of deformation are predicted along the southern boundary of the microplate prior to the origin of the microplate the east pacific rise epr was offset in at least two places according to the older magnetic anomalies yet there is no evidence of linear fracture zones within the sparse data set except for occasional small consistent changes in regional depth across these age offsets the magnetic bathymetry and satellite altimetry data indicate that the microplate initially formed at or perhaps southeast of easter island near a left lateral offset of the epr sometime between anomaly 3 and 3 the east rift started propagating north from the present location of easter island at 4 5 ma which is 1 5 m y earlier than previously proposed however the magnetic data that support this interpretation are sparse and complicated by recent volcanic flows and associated rough bathymetry west of easter island the geometry of the microplate changes very rapidly during its evolution at the initial stages of development the microplate resembles a large propagating rift system suggesting that deformation may have been occurring throughout most of its interior up to about 2 47 ma at this time the length to width of overlap ratio of the two rifts reaches a value of 3 the northward propagation slows down the curved opening of the southwest rift becomes well established and rigid rotation of the previously deformed transferred lithosphere probably starts to predominate at this time the offset distance between the two overlapped rifts starts to increase some time after 2 47 ma and before 1 ma the east rift starts propagating northwestward probably in response to the microplate rotation and continues up until present also during this time period the east rift breaks into a series of northward propagating rifts each propagating into the microplate interior thereby transferring lithosphere from the microplate to the nazca plate and reducing the total growth rate of the microplate

carbonates as evidence for groundwater discharge to the nile river during the late pleistocene and holocene abstract the african humid period ahp 15 5 ka is the latest in a series of saharan pluvials studied using carbonates evidence from desert paleolakes indicate that water tables rose across the region caused by increased precipitation during these wet periods and that this higher groundwater discharged at the surface creating a wetter environment beyond what increased seasonal precipitation could support alone carbonate cemented material and sediments have been noted at key archaeological sites such as khartoum hospital and al khiday and at site distributions along wadi howar in the deserts west of the nile extensive surface discharge of groundwater is the accepted generator of paleolakes and contributed to wadi flow in contrast studies in the nile valley have focused on the river itself as the source for any moisture to explain documented effects of a higher water table carbonate morphology and oxygen isotope composition of carbonate samples are used to develop a conceptual model demonstrating their accumulation in areas near the nile river as a result of a regional rise in groundwater driven by greater precipitation morphological evidence shows a variety of formative environments at key topographic locations indicating water availability above modeled contemporary nile river flood levels new results presented here from oxygen isotopes show locations dominated by evaporative enrichment at higher elevations a transition to stable isotopic conditions at lower elevations and ultimately a return to more enriched values at the lowest elevations that would have undergone intermixing of discharging groundwater and floodwater from the nile for areas beyond the river s flood extent or an associated river fed alluvial aquifer the only perennial moisture source capable of maintaining an isotopic equilibrium in a monsoonal climate would be groundwater results coincide with isotopic patterns and values observed in carbonates from studied paleolakes in the desert this model provides an explanation for the carbonate accumulation at archaeological sites while offering greater understanding of contemporary water availability for vegetation animals and human populations and whether the nile river functioned as the dominant water source for cultural groups in the valley during the early to mid holocene as it did for the later agricultural populations

type of faulting and orientation of stress and strain as a function of space and time in kilauea s south flank hawaii earthquake focal mechanisms of events occurring between 1972 and 1992 in the south flank of kilauea volcano hawaii are used to infer the state of stress and strain as a function of time and space we have determined 870 fault plane solutions from p wave first motion polarities for events with magnitudes m l 2 5 and depth ranging between 6 and 12 km faulting is characterized by a mixture of decollement reverse and normal faults most large earthquakes with magnitude m 7 rupture the decollement plane since it is the only surface large enough to generate magnitude 7 or larger earthquakes the percentage of reverse faulting events is high compared to the decollement and normal faulting mechanisms for the period 1972 1983 the percentage of decollement type focal mechanisms becomes dominant after 1983 this pattern of faulting activity suggests that pressure was building up within kilauea s rift zone prior to the 1983 puu oo eruption overall a single stress orientation with the maximum compressive stress oriented se perpendicular to the rift and dipping at 45 is compatible with the coeval existence of decollement reverse and normal faults however in a crustal volume east of longitude 155 10 w we find a change of the orientation of 1 from nearly horizontal to plunging 45 se occurring in 1979 this stress rotation suggests magma movements within the aseismic part of kilauea s east rift zone the strain and stress orientations are coaxial in the south flank except within the volume where the stress rotation is observed we observe a change in the relationship between stress and strain directions caused either by the shifting of seismic activity from reverse faults to decollements while stress stays constant or by a rotation of stress while strain remains constant assuming that the model of a noncohesive coulomb wedge is appropriate for kilauea s south flank we find that high pore pressures are prevalent along the decollement and within the wedge for a coefficient of friction equal to 0 85

tectonics and evolution of the juan fernandez microplate at the pacific nazca antarctic triple junction in this study magnetic and bathymetric data from an r v endeavor survey are combined with earthquake mechanism studies to produce a tectonic model for the juan fernandez microplate at the pacific nazca antarctic triple junction magnetic lineations along the east ridge of the microplate fan to the south indicating that the nazca juan fernandez pole is near the northern end of this feature relative motions of the juan fernandez pacific nazca antarctic four plate system are determined using relative plate motion inversions the resulting tectonic model predicts that the northern boundary of the juan fernandez microplate is a zone of compression and that the west ridge and southwestern boundary are spreading obliquely the southeastern boundary is predicted to be obliquely divergent but present data fail to constrain its geometry we also present a schematic evolutionary model which relates the formation of the juan fernandez microplate to differential spreading rates at the triple junction and discuss related complexities the future evolution of the fourplate system depends on whether one or both ridges remain active

microplate and shear zone models for oceanic spreading center reorganizations the reorganization of oceanic spreading centers is often accomplished through the process of rift propagation we first examine general rift propagation geometries for the simple two plate case in which the propagating rift instantaneously reaches full spreading rate while the other rift dies instantaneously such that the propagating and dying rifts never overlap a velocity space representation provides a framework for describing the geometry of rift propagation and its various tectonic elements and shows how both the failed rift and isochrons between the two rifts are reoriented as a consequence of purely rigid plate tectonics we then discuss the more complex geometries that result when both growing and dying rifts spread simultaneously during propagation such that a technically independent overlap region like the easter or juan fernandez plates along the east pacific rise is produced we examine the effect of the propagation rate and rise time of spreading on the evolution of overlap regions between dual oceanic spreading centers the tectonics and evolution of such regions can be modeled by assuming that they act either as rigid microplates or as zones of distributed shear rigid plate models are suggested by the reasonable success of euler vectors derived from inversions of plate motion data spreading rates transform azimuths and slip vectors both in describing available data and in predicting subsequently acquired data on the other hand recent structural data showing fabric oblique to the surrounding spreading centers might suggest shearing rather than rigid behavior in the interior of the easter microplate we use schematic evolutionary simulations for an easter style geometry to examine whether plate motion data and orientations of preexisting and present structures can be used to discriminate between rigid and shear models in a microplate model rigid plate tectonics requires that relative motion occur only along the boundaries of the overlap region while structures within the overlap zone rotate rigidly in contrast in a shear model relative motions at the boundaries differ from those predicted by rigid plate tectonics and the angular relationships of structures within the overlap region are altered by internal deformation thus inversion of relative motion data yields different results for rigid and shear behavior similarly under favorable circumstances structural trends could be diagnostic of the different cases we find that much of the easter structural data suggestive of shearing are also consistent with rigid plate tectonics we conclude that microplate models offer useful testable hypotheses for describing overlap systems and that shearing need be invoked only to explain features not describable by rigid plate tectonics furthermore the approaches used here to study current overlap regions should be useful in the analysis of similar regions formed during past oceanic plate boundary reorganizations

geochemical constraints on magma sources and mixing processes in easter microplate morb se pacific a case study of plume ridge interaction the easter microplate is bounded in the east and west by two large overlapping spreading centres called the east and west rift respectively the east rift is located close to the easter hotspot the site of young intraplate volcanism above a mantle plume easter hotspot material creates a geochemical anomaly on the east rift spreading axis of the microplate and mainly northward directed material flow occurs beneath the propagating east rift the incompatible element depleted mantle of the easter microplate consists of two different sources one of which mixes with enriched easter hotspot material forming the east rift mid ocean ridge basalt morb the other depleted mantle source is present beneath the west rift and mixes with an enriched endmember apparently distinct from the easter hotspot source while the easter hotspot material leads to a bathymetric anomaly on the east rift no increased degree of melting is observed at the point of maximum inflow of enriched plume material implying low excess temperatures 50 c of the mantle the mixing processes between the easter hotspot and morb material probably take place in the partially molten asthenosphere during the horizontal flow of the plume material melting above the plume and at the spreading axes in the easter microplate region occurs over a range of pressures but there is no sign of melts from enriched garnet pyroxenite

discrete element simulations of gravitational volcanic deformation 1 deformation structures and geometries 1 we have carried out two dimensional particle dynamics simulations of granular piles subject to frictional coulomb failure criteria to gain a first order understanding of different modes of gravitational deformation within volcanoes under uniform basal and internal strength conditions granular piles grow self similarly developing distinctive stratigraphies morphologies and structures piles constructed upon cohesive substrates exhibit particle avalanching forming outward dipping strata and angle of repose slopes systematic decreases in basal strength lead to progressively deeper and steeper internal detachment faults and slip along a basal decollement landslide forms grade from shallow slumps to deep seated landslide and finally to axial subsidence and outward flank displacements or volcanic spreading surface slopes decrease and develop concave up morphologies with decreasing decollement strength depositional layers tilt progressively inward spatial variations in basal strength cause lateral transitions in pile structure stratigraphy and morphology this approximation of volcanoes as coulomb granular piles reproduces the richness of deformational structures and surface morphologies in many volcanic settings the gentle slopes of hawaiian volcanoes and olympus mons on mars suggest weak basal decollements that enable volcanic spreading high angle normal faults favored above weak decollements are interpreted in both settings and may explain catastrophic sector collapse in hawaii and broad aureole deposits surrounding olympus mons in contrast steeper slopes and shallow detachment faults predominate in the canary islands thought to lack a weak decollement favoring smaller more frequent slope failures than predicted for hawaii the numerical results provide a useful predictive tool for interpreting dynamic behavior and associated geologic hazards of active volcanoes

fast rift propagation along the east pacific rise near easter island during a 1983 seabeam cruise we surveyed the easter nazca spreading center which forms the eastern boundary of the easter microplate we have analyzed all available bathymetry and magnetic anomaly data to determine the present fine scale tectonic configuration and recent tectonic evolution of this spreading center the narrowing of the axial brunhes anomaly is best explained by a young propagating rift growing northward at an average rate of 150 mm yr assuming an average spreading rate of 120 mm yr there are indications of a short episode of faster propagation 350 mm yr prior to 0 4 ma these are the fastest rates of rift propagation yet documented the tip of the propagating rift is at about 25 s 112 25 w 180 km south of the previously hypothesized position the recent spreading direction is n85 w a large well defined sheared zone to the west of the western pseudofault bounding the crust formed by the propagating rift suggests that the easter pacific spreading center 360 km to the west is being replaced by the fast propagator