heat flow along the nantroseize transect results from iodp expeditions 315 and 316 offshore the kii peninsula japan mal conductivity varies between about 1 0 w m 1 k 1 near the seafloor to 1 6 w m 1 k 1 at a depth of 1 km thermal conductivity generally increases with depth and correlates with variations in porosity and lithology thermal gradients along the transect are characterized by 48 sediment temperature measurements from 6 sites thermal corrections for the effects of bathymetric relief and sedimentation improve the confidence with which the heat flow values can be interpreted heat flow generally decreases with landward distance from the deformation front and varies from 70 mw m 2 just landward of the deformation front to 54 mw m 2 at sites characterizing the outer fore arc high and to 57 mw m 2 at the kumano basin site iodp heat flow measurements are significantly lower than nearby seafloor heat flow measurements this difference is most likely due to variations in bottom water temperature that have a large effect on values of seafloor heat flow thus the heat flow of the nankai accretionary prism is lower than previously thought we present thermal models of subduction along this transect and explore the impact of the initial geotherm conductive plate cooling based on the age of subducting seafloor 20 myr under predicts the observed heat flow we find a good fit to the data using a geotherm appropriate for 10 myr seafloor the extra heat is interpreted in terms of back arc thermal environments

detailed volcanostratigraphy of an accreted seamount implications for intraplate seamount formation 1 seamounts are a ubiquitous feature of the seafloor but relatively little is known about their internal structure a seamount preserved in the franciscan melange of california suggests a sequence of formation common to all seamounts field mapping geophysical measurements and geochemical analyses are combined to interpret three stages of seamount growth consistent with the formation of other intraplate seamounts such as the hawaiian volcanoes and the island of la palma a seamount begins to form as a pile of closely packed pillows with a high density and low porosity small pillow mound volcanoes common at mid ocean ridges are seamounts that do not grow beyond this initial stage of formation the second stage of seamount formation is marked by the first occurrence of breccia as the seamount grows and becomes topographically more complex slope varies and fractured material may begin to accumulate magma supply may also become spatially diffuse as the seamount grows and new supply pathways develop through the edifice the second stage thus exhibits variability in both flow morphologies and geophysical properties the final cap stage is composed of thin flows of various morphologies these sequences reflect the shoaling of the seamount and a greater variability in extrusion rate resulting from waning magma supply and increased mass wasting understanding the growth and structure of seamounts has important implications for intraplate volcanism and for models of hydrothermal circulation in the oceanic crust

long distance fluid and heat transport in the oceanic crust entering the nankai subduction zone nantroseize transect abstract i examine the potential causes of anomalous seafloor heat flux on the oceanic plate in the nankai trough seismogenic zone experiment nantroseize transect offshore southern japan the most prominent anomaly is a 50 mw m 2 change in heat flux between integrated ocean drilling program sites c0011 and c0012 over a distance of 30 km wide transition at the seafloor the observed surface heat flux pattern is indicative of hydrothermal circulation in the basement aquifer and advection of heat from the subducted crust into the aquifer on the incoming plate for a 600 m thick aquifer the permeability is likely 7 10 11 m 2 and hydrothermal circulation transports at least 300 times more heat than conduction alone the heat flux from the subduction zone seaward to the incoming plate is consistent with hydrothermal circulation in the subducting crust persisting to 100 km landward of the deformation front vigorous fluid circulation in the basaltic basement is consistent with both the seafloor thermal anomalies and geochemical anomalies near the sediment basement interface

an expression of philippine sea plate rotation the parece vela and shikoku basins abstract the philippine sea plate located between the pacific eurasian and australian plates is the world s largest marginal basin plate the motion of the philippine sea plate through time is poorly understood as it is almost entirely surrounded by subduction zones and hence previous studies have relied on palaeomagnetic analysis to constrain its rotation we present a comprehensive analysis of geophysical data within the parece vela and shikoku basins two oligocene to miocene back arc basins which provide independent constraints on the rotational history of the philippine sea plate by means of their seafloor spreading record we have created a detailed plate model for the opening of the parece vela and shikoku basins based on an analysis of all available magnetic gravity and bathymetric data in the region subduction along the izu bonin mariana trench led to trench roll back arc rupture and back arc rifting in the parece vela and shikoku basins at 30 ma seafloor spreading in both basins developed by chron 9o 28 ma and possibly by chron 10o 29 ma as a northward and southward propagating rift respectively the spreading orientation in the parece vela basin was e w as opposed to ene wsw in the shikoku basin the spreading ridges joined by chron 6by 23 ma and formed a r r r triple junction to accommodate the difference in spreading orientations in both basins at chron 6no 20 ma the spreading direction in the parece vela basin changed from e w to ne sw at chron 5ey 19 ma the spreading direction in the shikoku basin changed from ene wsw to ne sw this change was accompanied by a marked decrease in spreading rate cessation of back arc opening occurred at 15 ma a time of regional plate reorganisation in se asia we interpret the dramatic change in spreading rate and direction from e w to ne sw at 20 1 3 ma as an expression of philippine sea plate rotation and is constrained by the spacing between our magnetic anomaly identifications and the curvature of the fracture zones this rotation was previously thought to have begun at 25 ma as a result of a global change in plate motions our results suggest that the philippine sea plate rotated clockwise by about 4 between 20 and 15 ma about a pole located 35 n 84 e this implies that the majority of the 34 clockwise rotation inferred to have occurred between 25 and 5 ma from paleomagnetic data may have in fact been confined to the period between 15 and 5 ma

heat flow variations correlated with buried basement topography on the juan de fuca ridge flank systematic heat flow variations are commonly observed on sedimented flanks of mid ocean ridges these variations have been attributed to the convective circulation of pore fluids within the oceanic crust and have been used to estimate the scale and pattern of this circulation here we report similar systematic variations observed in a detailed heat flow and seismic reflection survey over sediment covered 3 myr old sea floor on the eastern flank of the juan de fuca ridge we find that heat flow peaks are located above buried basement ridges and adjacent to two minor basement outcrops heat flow lows are found where thick sediments fill basement valleys the simple inverse relationship between heat flow and sediment thickness defined by the data indicates that hydrothermal circulation sealed within the permeable portion of the oceanic crust is vigorous enough to maintain approximately isothermal 10 k conditions at the sediment crust interface as no systematic variations in estimated basement temperatures are observed it seems that at this location the heat flow variations result only from sediment thickness variations and do not reflect a particular convective pattern

the nicoya convergent margin a region of exceptionally low heat flow over 100 measurements of seafloor heat flow reveal that the accretionary complex adjacent to the nicoya peninsula is characterized by remarkably low heat flow values over the accretionary prism average 28 mw m and values in the trench and the ocean crust seaward of the trench average 14 mw m we attribute the low heat flow to effective hydrothermal cooling of the upper crust on the subducting plate and suggest that extensional faults created by flexure of the lithosphere enhance hydrothermal circulation thermal models show that subduction of low temperature crust combined with significant frictional heating at the decollement can explain the low and uniform heat flow disparity between heat flow values observed on the lower trench slope with model results suggests upward advection of heat by porewater flux through broadly distributed conduits

heat flow distribution and thermal structure of the nankai subduction zone off the kii peninsula detailed heat flow surveys were carried out in the central part of the nankai trough southeast of the kii peninsula off kumano for investigation of the thermal structure of the subducting plate interface at stations in the kumano trough forearc basin and its vicinity long term monitoring of temperature profiles in surface sediments was conducted because bottom water temperature variations btv significantly disturb subbottom sediment temperatures heat flow values were successfully determined at seven stations by removing the influence of btv from temperature records for 300 to 400 days the surface heat flow data were combined with estimates from depths of methane hydrate bottom simulating reflectors to construct a heat flow profile across the subduction zone heat flow decreases from 90 110 mw m2 on the floor of the nankai trough to 50 60 mw m2 at around 30 km from the deformation front while it is rather uniform 40 60 mw m2 in the kumano trough the values measured on the nankai trough floor are concordant with the value estimated from the age of the subducting philippine sea plate about 20 m y taking into account the effect of sedimentation the obtained heat flow profile was used to constrain thermal models of the subduction zone the subsurface thermal structure was calculated using a two dimensional steady state model in which the frictional heating along the plate interface and the radioactive heat production are treated as unknown parameters comparison of the calculated surface heat flow in the kumano trough with the observed data indicates that the effective coefficient of friction is small about 0 1 or less and thus the shear stress on the plate interface is very low in this subduction zone

on the high heat flow in the nankai trough area a simulation study on a heat rebound process abstract a concentration of high heat flow as high as 120 160 mw m2 has been observed in the nankai trough off southwest japan where the philippine sea plate shikoku basin is subducting beneath the japanese landmass we interpret this high heat flow in the subduction zone as being caused by the recovery of conductive heat flow to the theoretically expected value for the young shikoku basin lithosphere after cessation of hydrothermal heat exchange through sediment the thickening sedimentary cover suppresses the rapid heat exchange between basement and sea water whereas the topmost part of the basement allows a hydrothermal circulation within it to pump up heat from the hot plate to the sediment cover we propose to call this process heat rebound numerical simulation shows that significant heat flow recovery can occur and is largely influenced by the sedimentation rate we believe that the high heat flow in the nankai trough is one of the heat rebound cases however rapid sedimentation in the trough also indicates that heat flow recovery expected by the simulation is not large enough to explain the trough high heat flow by the heat rebound process only

thermal effects of hydrothermal circulation and seamount subduction temperatures in the nankai trough seismogenic zone experiment transect japan 1 we examine the thermal effects of seamount subduction seamount subduction may cause transient changes in oceanic crust hydrogeology and plate boundary fault position prior to subduction seamounts provide high permeability pathways between the basaltic crustal aquifer and overlying ocean that can focus fluid flow and efficiently cool the oceanic crust as the seamount is subducted the high permeability pathway is closed shutting down the advective transfer of heat if significant fluid flow occurs it would be restricted after seamount subduction and would result in a redistribution of heat warming the trench and cooling landward parts of the system additionally subducting seamounts can influence the position of the plate boundary fault that has thermal consequences by locally controlling the proportions of incoming sediment that subduct and accrete shifting the decollement to the seafloor at the trench in the wake of seamount subduction causes limited cooling focused at the toe of the margin wedge we apply these features of seamount subduction to a thermal model for the nankai trough seismogenic zone experiment transect on the margin of japan models with hydrothermal circulation provide an explanation for anomalously high surface heat flux observations near the trench they yield temperatures of 100 c 295 c for the rupture area of the 1944 tonankai earthquake temperatures in the region of episodic tremor and slip are estimated at 290 c 325 c 70 c cooler than a model with no fluid circulation

thermal constraints on the seismogenic portion of the southwestern japan subduction thrust for coastal cities an important factor in earthquake hazard from subduction zone earthquakes is the landward extent of the seismogenic portion of the subduction thrust fault in this study we test the hypothesis that the maximum downdip extent is defined by a critical temperature we have developed a transient thermal model for the nankai subduction zone of southwest japan to allow comparison of the thermally estimated downdip extent of the seismogenic zone with that from 1 seismicity and tsunami data for two great subduction earthquakes 2 the coseismic faulting extent of these events estimated from geodetic deformation data and 3 the interseismic locked zone determined from interseismic geodetic data the nankai margin has extensive heat flow and heat production data to control thermal models and thus crustal temperatures it has earthquake tsunami and geodetic data that constrain the coseismic rupture portion of the subduction thrust fault for past great earthquakes and the portion of the thrust fault that is locked and storing interseismic elastic strain on the nankaido margin off shikoku island the thermal model indicates that a temperature of 350 c taken to be the limit for seismic initiation from laboratory and field data is reached on the subduction thrust fault 150 km from the trench a transition zone into which rupture may extend with decreasing offset taken to be 450 c extends an additional 45 km downdip the thermal model results are in excellent agreement with the maximum downdip extent of coseismic displacement for the 1946 nankaido ms 8 2 earthquake off shikoku island and with the downdip extent of the present locked zone in the region of the 1944 tonankai ms 8 2 earthquake to the northeast the subduction angle is much steeper and the thermal models indicate a narrower downdip seismogenic extent the seismogenic locked zone from earthquake and geodetic data is also narrower thus our analysis of the southwest japan margin indicates that all three constraints on the downdip extent of the seismogenic zone thermal coseismic and interseismic geodetic data are in general agreement the study also supports the hypothesis that the seismogenic portion of subduction thrust faults is limited primarily by temperature the thermal control implies that subduction thrust faults with shallow dip have wider seismogenic zones compared to those with steep dip the subducting plate age and thus heat flow and the thickness of the insulating sediments on the incoming plate are also very important to the thermal regime and thus to the seismogenic width the relation of the maximum seismic rupture area to the interseismic locked zone is particularly important for earthquake hazard estimation on subduction margins such as cascadia where there have been no great historical events

the subduction plate interface rock record and mechanical coupling from long to short timescales abstract short and long term processes at or close to the subduction plate interface e g mineral transformations fluid release seismicity and more generally deformation might be more closely related than previously thought increasing evidence from the fossil rock record suggests that some episodes of their long geological evolution match or are close to timescales of the seismic cycle this contribution uses rocks recovered episodically from subduction zones together with insights from thermomechanical modelling to provide a new dynamic vision of the nature structure and properties of the plate interface and to bridge the gap between the mechanical behavior of active subduction zones e g coupling inferred from geophysical monitoring and fossil ones e g coupling required to detach and recover subducted slab fragments based on critical observations and an exhaustive compilation of worldwide subducted oceanic units for which the presence near the plate interface rock types pressure temperature t p gradients thickness and timing of detachment can be assessed the present study demonstrates how long term mechanical coupling exerts a key control on detachment from the slab and potential rock recovery critical assessment of rock t p characteristics indicates that these fragments can indeed be used as natural probes and provide reliable information on subduction interface dynamics down to 2 8 gpa rock clusters are identified at depths of 30 55 60 and 80 km with some differences between rock types data also reveal a first order evolution with subduction cooling in the first 5 myr which is interpreted as reflecting a systematic trend from strong to weak mechanical coupling after which subduction is lubricated and mostly inhibits rock recovery this contribution places bounds on the plate interface constitution regular thickness

thermal segmentation along the n ecuador s colombia margin 1 4 n prominent influence of sedimentation rate in the trench abstract along the deformation front of the north ecuador south colombia nesc margin both surface heat flow and trench sediment thickness show prominent along strike variations indicating significant spatial variations in sedimentation rate investigating these variations helps us address the important question of how trench sedimentation influences the temperature distribution along the interplate contact and the extent of the megathrust seismogenic zone we examine this issue by analysing 1 a new dense reflection data set 2 pre stack depth migration of selected multichannel seismic reflection lines 3 numerous newly identified bottom simulating reflectors and 4 the first heat probe measurements in the region we develop thermal models that include sediment deposition and compaction on the cooling oceanic plate as well as viscous corner flow in the mantle wedge we estimate that the temperature from 60 150 c to 350 450 c commonly associated with the updip and downdip limits of the seismogenic zone extends along the plate interface over a downdip distance of 160 to 190 20 km we conclude that the updip limit of the seismogenic zone for the great megathrust earthquake of 1979 is associated with low temperature 60 70 c processes our models also suggest that 60 70 of the two fold decrease in measured heat flow from 3 n to 2 8 n is related to an abrupt southward increase in sedimentation rate in the trench such a change may potentially induce a landward shift of the 60 150 c isotherms and thus the updip limit of the seismogenic zone by 10 to 20 km

thermal and metamorphic environment of subduction zone episodic tremor and slip 1 episodic tremor and slip ets have been detected in the cascadia and southwest japan subduction zones where the subducting crust is relatively warm because of the young incoming lithosphere 20 ma and modest plate convergence rates 40 60 mm a in the southwest japan subduction zone low frequency earthquakes occur on the plate interface at depths of 30 35 km beneath shikoku where finite element thermal models predict temperatures of 425 c in the subducting oceanic crust and at depths of 30 40 km beneath the kii peninsula where predicted temperatures are 325 c warmer temperatures of 575 c are predicted at ets depths beneath southern vancouver island in the cascadia subduction zone but here tremor also occurs within the overlying fore arc crust where temperatures are lower in the southwest japan and cascadia subduction zones subducting oceanic crust passes through the blueschist greenschist and amphibolite metamorphic facies where mineral dehydration reactions are complex the different temperatures predicted for the two subduction zones suggest that ets does not coincide with a specific temperature or metamorphic reaction several lines of evidence indicate that a free h2o rich fluid is present at least transiently in subducting oceanic crust and fluids released by prograde metamorphic dehydration reactions may help trigger or enable ets within the subducting plate less clear is the role h2o may play in tremor observed in the cascadia fore arc crust where free h2o may exist locally in faults and fractures but retrograde hydration reactions are expected to consume h2o

hydrothermal circulation in subducting crust reduces subduction zone temperatures most thermal models of subduction zones assume no advection of heat by fluid flow because slow flow through underthrusting sediment the decollement and wedge likely transports only a minor amount of heat we model coupled fluid and heat transport in a subduction zone and show that hydrothermal circulation in subducting basaltic basement rocks can have a great influence on subduction zone temperatures fractured basaltic basement has permeability several orders of magnitude higher than a typical decollement allowing fluid circulation to redistribute and extract heat from a subduction zone we simulate systems with upper basaltic basement permeability ranging from 10 13 to 10 10 m2 in addition we incorporate the effect of permeability reduction within the basaltic basement as it is subducted the models with fluid transport show suppressed temperatures along the subducting slab relative to models with no fluid transport with continuous sediment cover heat is extracted from under the margin wedge to the trench in models where faulted ocean crust exposes high permeability basement to the ocean floor cooling from ocean bottom water results in highly suppressed heat flow relative to conductive models hydrothermally cooled ocean crust also acts to slow thermally controlled diagenetic reaction progress within subducting sediment

regional heat flow variations across the sedimented juan de fuca ridge eastern flank constraints on lithospheric cooling and lateral hydrothermal heat transport seafloor heat flow has been estimated continuously along a transect on the sedimented eastern flank of the juan de fuca ridge to provide constraints on the scale and rate of lateral heat and fluid transport in the upper igneous crust and on the total flux from the young lithosphere beneath the profile extends from 20 km east of the ridge axis where turbidite sediments lap onto the oceanic crust at an age of less than 1 ma and ends 110 km east of the axis over 3 6 ma crust estimated heat flow is derived from the combination of the depth to igneous basement determined from seismic reflection profiles and basement temperatures measured in nine ocean drilling program boreholes along the transect the strategy is based on the knowledge that in this young area upper basement temperatures are locally homogenized by vigorous hydrothermal circulation and hence vary smoothly between drilling sites at the young end of the transect near the region of extensive outcrop heat flow is only 15 of that predicted for lithosphere of this age heat flow increases systematically to the east reaching the full predicted level about 20 km from the point of sediment basement onlap the anomaly can be accounted for by mixing and or eastward flow of cool water in the upper igneous crust beneath the sediment at a darcian rate of the order of 1 m yr a geochemical signature of fresh seawater in basement is observed many tens of kilometers farther to the east although the thermal signature is no longer present along the remainder of the transect the heat flow conforms very well to that predicted by simple boundary layer cooling theory once the thermal effects of rapid sedimentation on this ridge flank are accounted for

heat transfer in the oceanic crust of the brazil basin a detailed geothermal survey has been made on the western flank of the mid atlantic ridge in the brazil basin where the crust is 20 m y old the area is generally covered by a 150 to 200 m thick layer of foraminiferal ooze but basement outcrops are numerous sedimentary temperature profiles indicate anomalously low temperatures at the base of the sedimentary layer which results from cold bottom water penetrating laterally into the upper igneous crust and absorbing much of the geothermal heat net influx rates of 10 8 m s 1 are implied by a simple aquifer model a negative pressure drop across the sedimentary layer is required by this interpretation refraction studies indicate low seismic velocities 3 3 to 4 5 km s 1 near the top of layer 2 and a large velocity gradient with depth the velocity structure in the upper kilometer of the crust is related to the porosity from which it is inferred that permeabilities there are high many of the 52 temperature profiles show a significant decrease in gradient with depth the curvature can be attributed to one or a combination of the following causes 1 upward advection of pore water at rates of 10 7 s 1 2 bottom water temperature variations 3 variation of conductivity with depth and 4 experimental errors interpretation of curvature in terms of an advective model leads to results hard to reconcile with present knowledge of pressure variations and permeabilities of the oceanic crust

aeolian and fluvial evidence of changing climate and wind patterns during the past 100 ka in the western simpson desert australia abstract sediments near finke in central australia provide evidence of late quaternary evolution and the interaction of aeolian and fluvial systems in response to changing climate in the western simpson desert thermoluminescence tl dating is used to develop a chronology of aeolian and alluvial activity and to identify differences in sand provenance quaternary alluviation in the finke valley at this location occurred at or prior to c 90 ka and with no surviving evidence of subsequent activity until the holocene in contrast to rivers in the eastern part of the lake eyre basin substantial alluviation took place here in the early to mid holocene probably due to reactivation of the northern monsoon and its partial penetration into central australia the regional dunefield near finke consists of linear dunes largely reworked and aligned during the last glacial 30 12 ka as part of the great anticlockwise whorl of dunes in central australia the oldest dated source bordering dunes from the finke river are bright red in colour were deposited at c 100 ka and are now buried beneath paler source bordering dunes the latter consist of two exposed units a lower one of unknown orientation that dates at 17 9 ka and an upper unit aligned to the northwest and parallel to the prevailing winds that dates at 5 0 ka the tl signature and sediment texture of the oldest source bordering dunes show them to have probably been derived from weathered alluvial red beds of similar or greater age nearby and to have contributed abundant sand to the regional dunefield immediately north of the river in contrast sand from the younger paler source bordering dunes appears to be from a different source and to have only recently extended into the regional field the finke region would seem to be in a pivotal position for the study of palaeowind patterns that have created and modified australia s whorl of continental dunes the 30 18 ka regional linear dunes near finke are oriented almost due north their cross sectional asymmetry steeper eastern slopes suggests a response to southwesterly or westerly sand transporting winds between 18 and 10 ka these winds appear to have shifted to their present southeast orientation during the past 5 ka from dune ages alignments and asymmetry it is proposed here that there was a northward shift in the wind pattern at finke by about 100 150 km 1 1 5 of latitude during the last glacial but that through this period the regional dune pattern has remained remarkably stable

a synthesis of heat flow determinations and thermal modeling along the nankai trough japan 1 we review marine heat flow data along the nankai trough and show that observations 30 km seaward of the deformation front are 20 below conductive predictions 129 94 mw m 2 but consistent with the global heat flow average for oceanic crust of the same age 16 28 ma heat flow values 30 km seaward of the deformation front are generally 20 higher than conductive predictions this heat flow pattern is consistent with the advection of heat by fluid flow in the subducting oceanic crust and explains both the high heat flux in the vicinity of the trench 200 and 140 mw m 2 and steep landward declines to values of approximately 60 mw m 2 over distances of 65 and 50 km along the muroto and kumano transects respectively along the ashizuri transect the lack of heat flow data precludes a definitive interpretation we conclude that fluid flow in the subducting oceanic crust leads to temperatures that are generally 25 c higher near the toe of the margin wedge and 50 100 c lower near the downdip limit of the seismogenic zone than estimated by purely conductive models

seismogenic zone temperatures and heat flow anomalies in the to nankai margin segment based on temperature data from iodp expedition 333 and thermal model the location of the seismogenic zone across the to nankai margin segment has been widely investigated using geodetic tsunami seismologic and heat flow data as well as thermal models seafloor heat flow measurements show large scatter raising questions about the thermal state of the incoming and overriding plates in this study new temperature and conductivity measurements recorded in the philippine sea plate psp and in the accretionary prism during iodp expedition 333 are integrated with recent data on the margin structure and seismicity to improve constraints on the thermal structure of the incoming plate and the subduction zone as well as the thermal conditions within the seismogenic zone iodp expedition 333 measurements provide heat flow values that are lower than the average of nearby seafloor measurements thermal modeling for the psp suggests that hydrothermal warming is insignificant in the trench thus an observed widespread positive thermal anomaly in the shikoku basin that peaks at the kashinozaki knoll more likely results from vigorous thermal convection in the upper mantle in back arc context the modeled thermal structure of the margin from the trench to the mantle shows a significantly colder interplate contact than in previous studies the seismogenic zone is likely to be 30 170 km from the deformation front corresponding to the 100 340 c temperature range the 1944 co seismic slip zone extends farther southward where temperatures are about 60 c slow slip earthquakes are located in the downdip transition zone between 340 and 440 c across the intersection of the moho and the megathrust fault this improved thermal structure from the trench to the mantle results mainly from a better estimate of oceanic plate age slab dip and sedimentation rate variations in the trench this last parameter cools the interplate contact until a depth of 35 km shifting the thermally defined seismogenic zone landward by 20 km and significantly diminishing its influence near the corner flow area

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

thermal conductivity profile in the nankai accretionary prism at iodp nantroseize site c0002 estimations from high pressure experiments using input site sediments

effects of subduction parameters on geothermal gradients in forearcs with an application to franciscan subduction in california geothermal gradients in forearcs are often suppressed below normal values because of the cooling effect of the relatively cold downgoing plate in this paper finite difference thermal modeling is used to evaluate the influence on forearc gradients of variations in six potentially important subduction zone parameters variations in forearc radiogenic heat production over the general range likely in forearc rocks 0 to 1 5 10 6 w m 3 cause only minor changes in temperatures at the base of the forearc about 2 to 35 depending on other parameters and thus have relatively little effect on pressure temperature pt conditions of metamorphism however their effect on gradients at shallow levels and thus on surface heat flows may be greater up to about 100 likely variations in forearc thermal conductivity 1 5 to 3 5 w m 1 c 1 similarly change temperatures at the base of the forearc only modestly 10 25 but change surface heat flows more substantially 1 45 1 75 times decreasing the subduction angle from 27 to 3 6 increases gradients by about a factor of 2 at both deep and shallow levels decreasing the subduction rate by a factor of 8 160 to 20 km m y increases gradients by about a factor of 2 when frictional heating at the plate contact is excluded and less when modest amounts of frictional heating are included forearc gradients increase virtually linearly with the presubduction geothermal gradient in the subducting slab and thus are higher above a younger slab when frictional heating is excluded forearc gradients are 2 0 2 8 times higher above a 10 m y old slab than above a 150 m y old slab again the relative effect is lessened when frictional heating is incorporated the amount of frictional heating at the plate contact potentially has the greatest influence on forearc gradients the frictional heat production h is given by h vs where is the shear stress along the plate contact and vs is the subduction rate the modeling shows that forearc gradients increase linearly with unless plate contact shear stresses are only a small fraction of those expected with frictional sliding of dry rocks outer parts of forearcs would be the sites of pervasive low p t metamorphism greenschist facies rather than high p t metamorphism blueschist facies very high fluid pressures along the plate contact are probably the way shear stresses are reduced pressure temperature conditions of blueschist facies metamorphism in the franciscan subduction complex of california are easily explained with typical subduction rates and slab ages with plate contact shear stresses of the order of 10 mpa equivalent to around 3 of lithostatic pressure but stresses within the range zero to a few tens of megapascals are probably permitted by the thermal constraints speculative application of the modeling results assuming a shear stress of 4 of lithostatic pressure to plate motion reconstructions for the franciscan forearc suggests that forearc gradients were about 8 c km around 85 ma when the subducting slab was perhaps 145 m y old and the subduction rate was perhaps 95 km m y gradients increased moderately through the latest cretaceous to middle tertiary as subduction became slower and the subducting slab became younger reaching about 16 c km at 28 ma when the slab age was about 11 m y and the subduction rate was about 48 km m y the slab age subduction rate and forearc gradient then remained fairly constant until 5 ma when subduction slowed to about 32 km m y and the slab age decreased to about 8 m y causing gradients to rise to about 20 c km

upper crustal structure and axial topography at intermediate spreading ridges seismic constraints from the southern juan de fuca ridge 1 we use multichannel seismic reflection data to image the upper crustal structure of 0 620 ka crust along the southern juan de fuca ridge the study area comprises two segments spreading at intermediate rate with an axial high morphology with narrow cleft and wide vance axial summit grabens asg along most of the axis of both segments we image the top of an axial magma chamber amc the amc along cleft deepens from south to north from 2 0 km beneath the ridge cleft observatory and hydrothermal vents near the southern end of the segment to 2 3 km at the northern end near the site of the 1980s eruptive event along the vance segment the amc also deepens from south to north from 2 4 to 2 7 km seismic layer 2a interpreted as the basaltic extrusive layer is 250 300 m thick at the ridge axis along the cleft segment and 300 350 m thick along the axis of the vance segment however off axis layer 2a is similar in both segments 500 600 m indicating 90 and 60 off axis thickening at the cleft and vance segments respectively half of the thickening occurs sharply at the walls of the asg with the remaining thickening occurring within 3 4 km of the asg along the full length of both segments layer 2a is thinner within the asg compared to the ridge flanks previous studies argued that the asg is a cyclic feature formed by alternating periods of magmatism and tectonic extension our observations agree with the evolving nature of the asg however we suggest that its evolution is related to large changes in axial morphology produced by small fluctuations in magma supply thus the asg rather than being formed by excess volcanism is a rifted flexural axial high the changes in axial morphology affect the distribution of lava flows along the ridge flanks as indicated by the pattern of layer 2a thickness the fluctuations in magma supply may occur at all spreading rates but its effects on crustal structure and axial morphology are most pronounced along intermediate spreading rate ridges

the effects of sedimentation and compaction on oceanic heat flow summary the estimation of environmental effects forms an important part of the interpretation of oceanic heat flow measurements in particular the perturbations associated with sedimentation and surface temperature changes must be taken into account analytical solutions can be obtained only for individual simplified versions of these problems whereas any real example is complicated by the process of sediment compaction which changes the bulk thermal properties with depth a physical model is developed which uses sediment porosity trends to predict the thermal parameters and material advection rates for an evolving sediment basement system these values are then used in a numerical solution to the heat flow equation to give estimates of the perturbed surface heat flux through time in addition to variations in sedimentation rate sediment type radioactive heat production and surface temperature changes are considered heat flow corrections may vary by up to a factor of 2 according to sediment type while radioactive heat production can offset the effects of sedimentation by as much as 40 per cent the results also indicate that alterations determined from simple analytical models tend to over estimate the true perturbation to the flux

effect of source width and tidal elevation changes on aeolian transport on an estuarine beach data from a moderate energy meso tidal beach on the east side of delaware bay new jersey usa revealed the significance of both beach width as a source for aeolian transport and the effect of tidal rise on source width wind speeds averaged over 17 1 min recorded 6 m above the crest of a 0 5 m high dune ranged from 11 6 to 12 7 m s 1 during the experiment the highest observed rate of transport on the beach was 0 0085 kg m 1 s 1 monitored at rising low tide when the average wind speed was 11 6 m s 1 across 0 35 mm diameter surface sediments the wind direction was oblique to the shoreline creating a source width of 34 m the reduction in the width of the beach as a source for aeolian transport during rising tide was approximately arithmetic whereas the reduction in volume of sediment trapped was exponential aeolian transport effectively ceased when source width was less than 8 m wind conditions moisture content of the surface sediments and presence of binding salts did not appear to vary dramatically and no coarse grained lag deposit formed on the surface of the beach the decrease in rate of sediment trapped through time in the tidal cycle is attributed to differences in source width sediment deposited in the litter behind the active beach by strong winds during the rising tide was eroded during the high water period by the high waves and storm surge generated by these winds and net losses of sediment were observed despite initial aeolian accretion

historical changes in the yellow river delta china abstract the lower yellow river delta has experienced numerous avulsions during the last 2000 years and the floodplain can be divided into four provinces alluvial fan western plain middle plain and eastern plain coastal deltas the yellow river delta complex is composed of several delta superlobes resulting from shifts in the lower river channel and each delta superlobe consists of several smaller lobes formed by shifts in the distributary channels these two kinds of channel shifts have resulted in a complicated imbrication pattern in the delta complex two imbricated delta superlobes are divided by a reworked bed and buried shelf deposits shelly ridges form the surface boundaries between the various delta superlobes the delta superlobes passed through an active stage a reworking stage and were then finally overlain by later superlobes

remarkably consistent thermal state of the south central chile subduction zone from 36 s to 45 s delineating rupture areas of subduction zone earthquakes is necessary for understanding the controls on seismic and aseismic slip for the largest recorded earthquake the 1960 chile event with moment magnitude 9 5 the rupture area is only loosely defined due to limitations in the global seismic network at the time the rupture extends 900 km along strike coastal deformation is consistent with either a constant rupture width of 180 200 km along the entire length or a narrower 115 km rupture in the southern half a southward narrowing of the seismogenic zone has been hypothesized to result from warming of the subduction zone to the south where the subducting plate is younger we present results of thermal models at 36 s 38 s 43 s and 45 s to examine potential along strike changes in thermal state models most consistent with observed surface heat flux include fluid circulation in the oceanic crust that advects heat to the ocean this ventilated hydrothermal circulation preferentially cools transects with young subducting lithosphere frictional heating preferentially warms transects with older subducting lithosphere the combined effects of frictional heating and hydrothermal circulation increase decollement temperatures in the 36 s and 38 s transects by up to 155 c and decrease temperatures in the 45 s transect by up to 150 c in our preferred models decollement temperatures 200 km landward of the trench in all four transects are 350 400 c this is consistent with a constant 200 km wide seismogenic zone for the 1960 mw 9 5 rupture with decreasing slip magnitude in the southern half of the rupture

distribution of radioactive heat production around an active fault and in accretionary prisms of southwest japan abstract contents of radioactive heat producing elements u th and k were measured on core samples from a borehole drilled into the shear zone of the active nojima fault southwest japan the heat production rate is rather uniform in a granite layer below 560 m with an average of 1 6 w m 3 in the lower part of the granite layer which is close to the fault zone the u th and u k ratios seem to be lower than those in the upper part a possible cause of this anomaly is redistribution of u by groundwater flows in highly fractured layers through monitoring of the temperature profile in the borehole a local anomaly which may be associated with groundwater flow along a fracture zone was detected in the uppermost part of the hole the conductive heat flow was found to increase with depth which is possibly due to downward fluid flow in the surrounding formations measurements of heat production were also made on rock samples from permian to cretaceous accretionary prisms in southwest japan the heat production of sandstone and mudstone major components of the accretionary prisms is about 1 5 w m 3 on average which is similar to the average value for granitic rocks in southwest japan these values are significantly higher than those reported in accreted terranes in the cascadia subduction zone

abrupt thermal transition reveals hydrothermal boundary and role of seamounts within the cocos plate 1 new thermal data from 18 24 ma lithosphere on the cocos plate delineate contrasting subsurface thermal conditions in adjacent sections of crust heat flow through seafloor created at the east pacific rise is generally suppressed by 70 relative to conductive lithospheric cooling models whereas heat flow through adjacent similarly aged lithosphere generated at the cocos nazca spreading center is consistent with these models the transition between thermal regimes is remarkably abrupt only 2 5 km wide indicating a shallow hydrothermal origin the transition is more closely associated with differences in the distribution of basement outcrops than with tectonic boundaries demonstrating the importance of the former in extracting heat from the lithosphere on a regional basis

effects of river regulation on aeolian landscapes colorado river southwestern usa 1 connectivity between fluvial and aeolian sedimentary systems plays an important role in the physical and biological environment of dryland regions this study examines the coupling between fluvial sand deposits and aeolian dune fields in bedrock canyons of the arid to semiarid colorado river corridor southwestern usa by quantifying significant differences between aeolian landscapes with and without modern fluvial sediment sources this work demonstrates for the first time that the flow and sediment limiting effects of dam operations affect sedimentary processes and ecosystems in aeolian landscapes above the fluvial high water line dune fields decoupled from fluvial sand supply have more ground cover biologic crust and vegetation and less aeolian sand transport than do dune fields that remain coupled to modern fluvial sand supply the proportion of active aeolian sand area also is substantially lower in a heavily regulated river reach marble grand canyon arizona than in a much less regulated reach with otherwise similar environmental conditions cataract canyon utah the interconnections shown here among river flow and sediment aeolian sand transport and biologic communities in aeolian dunes demonstrate a newly recognized means by which anthropogenic influence alters dryland environments because fluvial aeolian coupling is common globally it is likely that similar sediment transport connectivity and interaction with upland ecosystems are important in other dryland regions to a greater degree than has been recognized previously

thermal effects of marine sedimentation in hydrothermally active areas summary a hydrothermally active ocean basin vigorous hydrothermal circulation in highly permeable basement rocks maintains a nearly constant temperature at the base of the overlying accumulating sediment section to investigate the thermal effects of sedimentation in such geological settings we have developed a simple onedimensional finite element model and applied it to cases in the northeast pacific the model accounts for differential motion of fluids and sediment grains during compaction and can be used with any porosity depth function results demonstrate clearly that the constant basal temperature of an accumulating sediment section maintained by convective heat transfer in the basement causes the section to remain thermally near steady state for even very high rates of accumulation particularly when compared to conditions estimated for a section where heat is transported in the basement by conduction a 10 kyr period of thermal recovery due to the highly diminished sediment supply during the post pleistocene further reduces the thermal effects of sedimentation by a significant amount only in rare cases where rates of accumulation exceed 10 mm yr l and sediment thicknesses exceed 1 km are the sea floor heat flow and temperatures at depth diminished significantly an example is found in middle valley of the juan de fuca ridge in a part of which over 2 km of sediment has accumulated in the past 200 kyr even in this extreme case the heat flow is estimated to be lower than that of the steady state by about only 15 per cent while rates of accumulation are also high in other parts of middle valley and in many other hydrothermally active areas such as guayamas basin escanaba trough and the eastern flank of the juan de fuca ridge these rates and the accumulated sediment thicknesses are found to be insufficient to cause appreciable thermal anomalies