sedimentary structure and origin of a mud cored pseudo tidal sand ridge eastern yellow sea korea abstract using high resolution seismic profiles sidescan sonar images and piston cores we have examined an elongate ridge located off the tae an peninsula of korea in the eastern yellow sea this ridge 50 km long 30 m high and up to 12 km wide is one of many similar longitudinal ones which are approximately parallel to the direction ne sw of strong tidal currents bathymetric profiles across the ridge are all asymmetric the eastern ridge flank is narrow and dips steeply towards the adjoining rocky valley below the eastern ridge flank less steeply sloping subbottom reflectors are truncated by a seafloor parallel erosion surface on which is draped a 45 cm thick unit of muddy sand a piston core taken here indicates that the subbottom reflectors are due to interlayered coarse sediments the more gently sloping western ridge flank contains sand waves ca 100 m wavelength ene wsw trend on which megaripples 10 15 m wavelength wnw ese trend are superimposed indicating recent bottom current activity in particular the reflectors beneath the westernmost ridge show westward progradation over an acoustically transparent unit of thin sand sheets however subbottom profiles collected over the ridge crest do not show conspicuous reflectors only a few discontinuous faint reflectors are observed the lack of conspicuous reflectors below the ridge crest area may reflect more thorough bottom current generated sediment homogenization as well as poor penetration of acoustic energy due to the current scoured rippled seafloor we interpret the ridge as an early holocene tidal mud tongue blanketed by recently reworked relict palimpsest sands the pseudo tidal sand ridge has prograded westward the fine mud tongue sediments might have been derived mostly from the korean peninsula via the han river at a time when sea level was lower than present

resolving volatile sources along the western sunda arc indonesia we present the chemical and isotope hecn characterization of active fumaroles and hydrothermal gases and waters from the summits and flanks of 19 volcanic centers along the western sunda arc indonesia samples were collected over two field expeditions 1991 and 2010 and cover 13 volcanic centers in sumatra 5 in java and one in bali in addition we present data from three geothermal sites in sumatra associated with active fault systems in between volcanic centers ibvc the overall aim is to resolve volatiles associated with the sub arc mantle subducting slab and mantle wedge from inputs derived from the over riding arc crust the western sunda arc is a prime locality to assess controls on volatile provenance at subduction zones due to changes in composition and thickness of over riding crust and variations in sediment input rates along the strike of the arc the dry gas chemistry of the majority of volcanic samples is dominated by co2 with inert gas variations hearn2 typical of subduction zone gases however there is a strong crustal control on the heco2 isotope and relative abundance systematics on a number of volcanic centers this effect is most clearly observed at flank localities and in water phase samples filtering the entire database for modifications due to air contamination degassing induced fractionation c isotopes and co2 3he ratios and crustal contamination associated with volatile transport within shallow level hydrothermal systems allows recognition of the magmatic volatile signature of individual volcanoes along the arc helium isotopes at all but two volcanic centers talang and dempo on sumatra range from 5 3 ra to 8 1 ra ra air 3he 4he pointing to the mantle wedge as the principal source of he but with a small input of crustal radiogenic he at some localities samples from java and bali span an even more limited range 6 6 to 7 9 ra implying a relatively smaller input of crustal he carbon isotope and co2 3he ratios vary from 1 4 to 6 4 and 4 38 to 150 109 respectively with higher and more variable values to the north of sumatra this latitudinal effect is not apparent in air corrected n isotope values 15nc 3 91 to 5 92 or various elemental ratios such as n2 ar and n2 he the three ibvc sites all located in sumatra have significantly lower 3he 4he ratios 3 6 ra with co2 3he values both higher and lower than volcanic centers their 13c 15nc and gas ratios overlap with the volcanic centers the elemental and isotopic characteristics of carbon and helium have been modified at ibvc sites due to crustal processes however based upon relationships between ch4 and 3he as well as co variations between hecn isotopes the over riding crust and associated sediments add minimal volatiles to volcanic centers throughout the western sunda arc in turn subducted sediment particularly the nicobar fan which supplies himalayan derived sediment to the slab off sumatra exerts a strong control on the magmatic co2 characteristics although it is less influential for n2 in spite of large sections of incoming sedimentary material being off scraped during subduction our data suggest that a significant fraction must enter the trench enhancing fluid melt production in the mantle wedge we propose that subduction related source contamination plays the dominant role over thick old crustal basement in supplying the major volatile output budget of the western sunda arc

lateral variations of the mid mantle conductance beneath europe abstract europe is a region with the largest density of geomagnetic observatories and several authors have used these data to estimate local geomagnetic response functions for various period ranges typically of the width of 1 5 to 2 5 decades by collecting the local response functions from 35 european observatories and by their precise selection and subsequent combination the independent regional geomagnetic induction data set could be extended to a period range of 4 5 decades the initial local responses that were estimated by two magnetovariation methods with two different external source fields employed have been further supplemented by continental and global 11 year data providing thus a data set extending over a period range from the harmonics of the daily variations up to 11 years the combined responses have been inverted individually for each observatory by two techniques by an occam procedure and a stochastic 1d inversion for spherically symmetric earth the integrated mantle conductance has revealed rather regular lateral changes that have been used to design a mantle conductance image down to a depth of about 770 km the presented conductance image can be correlated with major european tectonic units like the baltic shield and the trans european suture zone to examine possible distortions to the inferred mantle conductance models due to large scale near surface heterogeneities specifically those caused by the oceans seas and large sedimentary basins a spherical forward modeling was carried out for a radially symmetric conductor coated by an inhomogeneous thin shell with the variable surface conductance the model responses for the 35 observatory positions were inverted in the same way as previously the experimental data the results for 28 observatories have shown that the depth down to a pre defined conductance level could be retrieved with a high accuracy of a few percents but for seven southernmost observatories the recovery error increased up to 9 with these seven observatories removed from the analysis the effect of the seas and oceans on the upper and mid mantle conductance estimates beneath europe can be considered negligible

active moribund and buried tidal sand ridges in the east china sea and the southern yellow sea shallow seismic profiles and borehole data revealed active moribund and buried tidal sand ridges in the east china sea and the southern yellow sea the ridges consist of relatively clean well sorted sands with fairly uniform sequences the microfossil assemblage exhibits a high diversity including both euryhaline and stenohaline species the ridges are huge elongated sand bodies several kilometres wide 10 60 km long and up to 20 m thick and occur in groups with a spacing of several to 10 km normally they are parallel with each other extending in the direction of the tidal currents the field of tidal sand ridges on the east china sea shelf covers an area of 57 000 km2 tidal sand ridges in the east china sea and the southern yellow sea were formed in estuarine and shallow shelf environments where strong tidal currents reworked transported and redeposited large amounts of relict sands from older deltaic and fluvial sediments the development of tidal sand ridges in estuary mouth areas is accompanied by a net sand transport from the shelf into the estuary the evolution of tidal sand ridges is closely related to transgressions active tidal sand ridges are formed during sea level rises they show distinct morphology and active migrations in a lateral as well as in a landward direction they are generally in equilibrium with present day tidal processes and their distribution patterns are related to the flow field of the tidal currents as the sea level rises further these tidal sand ridges become moribund sand bodies with less distinct morphologies their upper surfaces are covered by a thin calcareous rich layer with very high contents of foraminifera tests reflecting a submarine hiatus condition on the shelf during the highstand period during the subsequent steady fall in sea level tidal sand ridges are often buried by fine grained shelf and prodelta sediments they have therefore a good chance of being preserved in stratigraphic records the sequential buildup during a sea level rise tr tract and a subsequent sea level fall hs and ls tract would consist of estuarine channel and tidal flat facies tidal sand ridge facies shelf mud facies delta facies and fluvial facies in an ascending order tidally dominated estuary conditions may also occur when a major distributary is abandoned such as at the northern branch of the modern changjiang river mouth where the accumulation of sand from an abandoned delta lobe and the development of tidal sand ridges have been observed the observed features have important implications for the subsurface recognition of fossil tidal sand ridges for the reconstruction of the regional palaeogeography and transgressional history and for the prediction of potential reservoir sandstones

sedimentary record of environmental evolution off the yangtze river estuary east china sea during the last 13 000 years with special reference to the influence of the yellow river on the yangtze river delta during the last 600 years abstract a 35 60 m long core ecs 0702 recovered from a water depth of 22 m in the muddy area off the yangtze river estuary was analyzed for sedimentary characteristics clay and detrital mineral components and element geochemistry as well as by ams 14 c dating to document sediment provenance changes and environmental evolution during the postglacial period in the study area on the basis of the lithology the benthic foraminiferal and ostracod assemblages and the ams 14 c ages we divided the core into four depositional units du1 du4 in descending order representing the postglacial sedimentary sequence during the last 13 000 years du 4 was deposited in a littoral to tidal flat environment during 13 000 11 500 cal yr bp du 3 in a nearshore subtidal environment upwards to the nearshore shelf with tidal influence in response to the postglacial sea level rise during 11 500 7400 cal yr bp du 2 in a tide affected nearshore shallow sea environment during 7400 540 cal yr bp on the delta front of the yangtze river when the delta was actively prograding and du 1 in a nearshore shallow sea environment during the last 540 years on the delta front under modern marine conditions in du 1 the depositional rate was much higher than in the underlying units and the sediment composition reflects more influence from the yellow river this unit can therefore be logically linked to the period when the yellow river last discharged into the south yellow sea from ad 1128 to 1855 according to historical records this period can be divided into an early stage ad 1128 1494 when the shoreline near the yellow river mouth was advancing slowly eastward and a late stage 1495 1855 when the shoreline was advancing rapidly the initiation of du 1 deposition corresponds to the latter part of the early stage suggesting that since that time a relatively large amount of sediment from the old yellow river mouth area has been transported to the offshore area of the yangtze river mouth our study has identified a high resolution sedimentary signature associated with the last course shift of the yellow river in the yangtze river delta front thus highlighting the intricate relationship between sediment sources and sinks in coastal areas a significant contribution of the old yellow river sediments to the yangtze subaqueous delta during the last 600 years must be considered when the evolutional history of the yangtze delta is examined and especially when the influence of the three gorge dam construction on the future changes of the yangtze estuary and ecological environments in the east china sea is estimated

worldwide initiation of holocene marine deltas by deceleration of sea level rise radiocarbon dated deltaic sequences of holocene age from different parts of the world began to accumulate within a restricted time range from about 8500 to 6500 years ago evaluation of major delta processes indicates that deceleration in sea level rise was the key factor in holocene delta formation within many deltas there is as much as a 2000 year age range between basal deposits in seaward and landward cores this age difference records the progressive landward migration of near mean sea level depositional environments during the lower to mid holocene establishment of a chronostratigraphic framework for holocene delta development provides a fundamental global baseline for distinguishing sea level change from vertical land motion by tectonism and isostasy and for evaluating rates of future marine incursion into low lying deltas

seismic vp and vp vs structure of the geothermal area around tarutung north sumatra indonesia derived from local earthquake tomography abstract a passive seismic experiment with 42 short period stations was setup for 10 months from may 2011 within a 20 30 km radius covering the tarutung basin and the northern part of the sarulla graben along the seismically active sumatran fault north sumatra indonesia the objective of the project is to investigate the geothermal setting based on the vp and vp vs structures and the distribution of seismicity we recorded 2856 local earthquakes by at least 8 stations which were reduced to 809 events having gap angle less than 180 the initial earthquake locations were determined using simultaneous inversion for hypocenters and 1d velocity structure followed by 3d tomographic inversion the resulting seismicity distribution vp and vp vs structure reveal systematic differences between the tarutung basin and the sarulla graben the tarutung pull apart basin is characterized by a complex structure reflected by a broader distribution of seismicity compared with the very narrow rather vertical hypocenter distribution in the sarulla graben which was formed by fault perpendicular extension and not by pull apart tectonics high vp vs values near to the surface are imaged within the sarulla graben and northeast of the tarutung basin these features are interpreted as fluid bearing sediments with fracturing indicating potentially favorable conditions for geothermal exploitation the localized fluid flow northeast of tarutung could be explained by the releasing step over structure of the pull apart basin and resulting dilatational stress regime in this part of the basin heat sources are assumed to be located at greater depth in association with magmatic activities accompanying the subduction process and the heat is transported along the sumatran fault to shallow depth

migration of fluid phases and genesis of basalt magmas in subduction zones dehydration and hydration reactions in both the downgoing lithosphere and the overlying mantle wedge have been examined in order to understand the role of h2o in the production of magmas at convergent plate boundaries the subduction of oceanic lithosphere occurring with increasing pressures and rising temperatures causes liberation of h2o from the slab amphibole which can be stable to the highest pt conditions among hydrous phases in the slab decomposes at around 90 km depth it follows that the subducted lithosphere is essentially anhydrous beneath volcanic arcs lying more than 110 km above the slab and that the supply of slab derived h2o is not a direct trigger for the production of arc magmas instead the h2o released from downgoing lithosphere reacts with the forearc mantle wedge to crystallize hydrous minerals serpentine talc amphibole chlorite and phlogopite this hydrated peridotite is dragged downward on the slab toward higher pt regions and releases h2o to shallower potential magma source regions in the mantle wedge combining experimental data on the stability of serpentine and talc with the thermal structure in the mantle wedge it is concluded that those minerals decompose beneath the forearc region on the other hand high pt experimental and thermodynamic data suggest that dehydration of amphibole and chlorite in the downdragged hydrated peridotite can take place just beneath a volcanic front phlogopite in the peridotite decomposes to release h2o at a deeper level about 200 km h2o liberated from the hydrated peridotite causes partial melting of overlying mantle wedge peridotites along with the migration of h2o through the above processes subduction components especially large ion lithophile elements can be overprinted on the magma source region which governs the geochemical characteristics of arc magmas

3 d modelling and analysis of dst c responses in the north pacific ocean region revisited summary during the last decade a number of one dimensional 1 d conductivity profiles have been constructed for the upper and mid mantle of the north pacific ocean region these profiles differ significantly and from our point of view it is still unclear which profile is the best candidate for the upper and mid mantle conductivity reference model for this region keeping the differences in mind and inspired by recent findings that the ocean effect is a major contributor to the anomalous behaviour of c responses up to the period of 20 days especially at coastal observatories the goal of this paper has been three fold 1 to understand on the basis of systematic model studies using 3 d ocean models which of the published 1 d upper and mid mantle profiles is in best agreement with the available observations 2 to try to reduce the misfit between the observed and modelled responses by using dense grids in modelling by considering 3 d models which include not only an inhomogeneous surface layer but also inhomogeneous deeper structures 3 to derive an alternative 1 d upper and mid mantle section for the north pacific ocean by carefully selecting the data for interpretation and by using 3 d models that are as realistic and detailed as possible in order to perform the simulations using realistic 3 d models on a routine basis a novel 3 d spherical forward solution has been elaborated in this paper the solution combines the modified iterative dissipative method with a conjugate gradient iteration and allows one to compute efficiently the electromagnetic fields in full 3 d spherical models with very high lateral contrasts of conductivity and for very dense grids during the 3 d simulations a systematic shift of observed c responses at honolulu compared with those at other observatories was detected the reason for this shift is still unclear even if a very detailed grid of 0 3 0 3 is used the 3 d simulations using a model of the inhomogeneous surface has no notable ocean effect to c responses at this site an attempt has been made to reduce the misfit between observed and modelled c responses by incorporating a 3 d model with inhomogeneous lithosphere and upper mantle however this has resulted only in a slight change in responses the main conclusion drawn from our 3 d model studies is that there exists a significant disagreement between observed and 3 d modelled c responses if the published 1 d sections with conducting uppermost 400 km are considered as the upper and mid mantle sections our 3 d simulations and reinterpretation of the data also confirm the recent finding that the upper and mid mantle beneath north pacific ocean in the depth range down to 400 km is much more resistive than hitherto assumed

sedimentary facies of the tide dominated paleo changjiang yangtze estuary during the last transgression abstract a large estuary was formed by marine inundation of the paleo changjiang yangtze incised valley during the transgression after the last glacial maximum this paper presents the sedimentary facies and architecture of the estuary fill based on the analysis of three sediment cores cm97 js98 and hq98 obtained from the present changjiang delta plain estuary fill deposits showing an upward fining succession were grouped into five depositional facies tidal river distributary channel muddy intertidal to subtidal flats transgressive lag and estuary front based on sedimentary textures lithology and physical sedimentary structures sand mud couplets are common in these deposits indicating that tides played a significant role in producing these sedimentary structures and that the estuary type was tide dominated some of the successive sand mud couplets probably recorded neap spring cycles as well as semidiurnal tidal cycles the nature of the estuary was very different from other representative tide dominated estuaries in sediment facies its distribution and sediment source for estuarine fill unlike the other estuaries that receive sediments mainly from the sea the paleo changjiang estuarine fill deposits were supplied largely from the river this difference would also have a great influence on the sedimentological and morphological component in the estuary the sediment distribution of the estuary showed fining seaward and estuary mouth sand bodies fed by marine source sand were absent the architecture model of tide dominated estuaries should be divided into two types by the degree of fluvial sediment supply the paleo changjiang estuary shows a good example for an estuary of large rivers

mud volcanoes at the shelf margin of the east china sea abstract roughly circular sediment mounds varying from tens to hundreds of meters in diameter and from a few meters up to 40 m in height have been mapped for the first time at the shelf edge of the east china sea ecs high resolution seismic profiles together with swath bathymetric and acoustic data indicate that these features are common on the ecs outer shelf and on the upper western slope of the okinawa trough they are associated with unusually large pockmarks up to 40 m in depth and 600 m in diameter on seismic records bright spots phase inversions and other acoustic anomalies indicate that gas and or fluid escape plays an important role in the formation of these mounds they are often associated with normal faults that occur along the western slope of the okinawa trough these faults acting as conduits for migrating fluid based on regional stratigraphic correlation we propose that the source of mud and fluid is deeper older than 235 ka the seepage process is suspected to be very recent and probably still active based on the facts that 1 despite high sedimentation rate the mounds are not buried by recent sediments and 2 last glacial maximum deposits are reworked at the emplacement of the mounds carbonate cemented sediments and deep water reefs possibly associated with fluid seepage could be the origin of local patches of very high backscattering acoustic facies mapped with the swath bathymetric system

strike slip duplexes abstract strike slip fault systems often contain zones of steep imbricate faults geometrically similar to imbricate fans and duplexes in dip slip thrust and normal fault systems they are evident in map view rather than in vertical sections examples of duplexes are cited from both active and ancient systems and from theoretical and physical models duplexes may form at bends on strike slip faults by a process kinematically analogous to the sequential imbrication of ramps on dip slip faults however some may form and many may initiate as non sequential riedel fractures at fault offsets or on straight fault segments this process is more marked than in dip slip systems where primary anisotropy such as bedding exerts more control on fault geometry strike slip duplexes may be shunted along the fault system parallel to the regional slip vector however duplexes or individual horses will usually also move up or down perpendicular to the slip vector because of the unconstrained upper surface to the fault system these factors mean that no section through a strike slip system should be expected to area balance the faults of strike slip duplexes and imbricate fans may root in kinematically necessary low dip faults or may converge downwards and appear in vertical sections as flower structures

relationship between tectonism and volcanism along the great sumatran fault zone deduced by spot image analyses abstract satellite images provide evidence for numerous stepovers pull apart grabens and volcanic structures along the nw trending right lateral great sumatran fault zone high resolution spot images permit us to analyze the relationship between volcanic and tectonic structures this analysis reveals that releasing stepovers and pull aparts are ephemeral structures along the great sumatran fault zone and that the geometry of the strike slip fault evolves permanently through time the interpretative structural maps obtained from spot image analysis reveal that the formation of huge peculiarly shaped volcanic calderas has occurred in large releasing stepover fault zones and that the bounding faults of rectangular pull apart basins are analogous to the circular ring faults of calderas in particular detailed study of the segments at the southernmost 150 km long termination of the great sumatran fault zone from northwest of ranau lake to semangka bay allows us to describe the development of the ranau collapse caldera this caldera is located within a pull apart basin bounded by a stepover its peculiar rectangular shape and its relatively large size about 200 km 2 are controlled by the evolution of the extinct ranau releasing stepover similarly the toba elliptical caldera one of the largest volcanic caldera in the world is elongated parallel to the present trace of the great sumatran fault and appears to be related to a releasing stepover associated with a wide pull apart basin that is not active at present

provenance discrimination of last deglacial and holocene sediments in the southwest of cheju island east china sea abstract the ultimate provenance of muddy sediment in the southwest of cheju island east china sea remains enigmatic thus far in this study rare earth elements rees were used to investigate sediment provenances of cores e03 6 e03 10 and e03 11 taken from the mud patch discrimination plots based on ree fractionation parameters and trace elements suggest that the sediments deposited during the last deglacial period 15 ka were derived predominantly from the paleo huanghe yellow river which might have delivered sediments directly into the northeastern east china sea during the lowstand of sea level the coarse grained sediments deposited at transgressive stage 15 6 ka were primarily sourced from the changjiang yangtze river and partly from the korean peninsula probably transported by tidal currents in comparison the clayey sediments deposited at highstand stage

late quaternary stratigraphy and development of tidal sand ridges in the eastern yellow sea abstract the eastern yellow sea is characterized by a number of tidal sand ridges which occur as a series of linear sediment bodies in the shelf shelf sand ridges and as a group of individual sand bodies in the nearshore nearshore sand ridges the shelf sand ridges are present in water depths of 50 90 m and show large elongate shapes with a length up to 200 km in contrast the nearshore sand ridges are much smaller in size up to 34 km length and occur in water depths shallower than about 30 m detailed interpretation of seismic and lithologic data using radiocarbon dating to constrain the ages of the ridges has shown that the regional sea level changes played a major role in the existence and development of different morphologic features of these sand ridges the shelf sand ridges developed mainly during the postglacial transgression ca 14 000 9 500 yr b p possibly during episodes of stillstand or very slow rise of sea level the shape of the shelf sand ridges more or less results from an erosional process dominantly acting during the postglacial transgression the substratum of the shelf sand ridges consists of the regressive or lowstand deltaic mud deposits probably formed prior to the last glacial maximum ca 17 000 yr b p in contrast the nearshore sand ridges have undergone tidal action during the recent highstand of sea level ca 7 000 yr b p and show a typical modern geomorphology of erosional sand ridges the substratum of the nearshore sand ridges consists of remnants of the last interglacial tidal deposits large dunes indicate a strong hydrodynamic influence on the entire ridge surface at present

evolution of the coastal depositional systems of the changjiang yangtze river in response to late pleistocene holocene sea level changes abstract the paleo changjiang yangtze incised valley fills approximately 80 90 m thick provide an opportunity to document the evolution of coastal depositional systems with large sediment supply in response to late pleistocene holocene sea level fluctuations on time scales of 103 to 104 years the sedimentary facies of the incised valley fills record three main depositional systems fluvial tide dominated estuary and tide dominated delta radiocarbon ages for the incised valley fills suggest that these depositional systems developed before about 11 ka between 11 and 8 ka and after approximately 8 ka respectively by applying sequence stratigraphic concepts the evolution of the depositional systems can be divided into three systems tracts a lowstand systems tract lst a transgressive systems tract tst and a highstand systems tract hst sea level changes on a 104 year time scale controlled the basic architecture of the sequence of the incised valley fill on the other hand sea level changes on a millennial time scale affected the stacking pattern of the systems tracts in particular the continuous sea level rise with episodic rapid rises during the last deglaciation affected the stacking pattern of the tst which is characterized by a combination of aggradation and backstepping the aggradation of fluvial and estuarine systems was dominant and the shoreline migrated only gradually landward under the relatively slow rise in sea level and a very rapid sea level rise around 12 and 10 ka caused the system to migrate abruptly landward unlike the transgressive estuarine phase the stacking pattern of the regressive tide dominated delta hst which developed within the almost filled incised valley and on the surrounding interfluve zones was characterized by seaward progradation with clinoform architecture it was initiated with aggradational and progradational stacking about 8 ka during the last phase of decelerated sea level rise and was followed by a progradational phase after the highest sea level about 6 ka

the structure of the sumatran fault revealed by local seismicity the combination of the sunda megathrust and the strike slip sumatran fault sf represents a type example of slip partitioning however superimposed on the sf are geometrical irregularities that disrupt the local strain field the largest such feature is in central sumatra where the sf splits into two fault strands up to 35 km apart a dense local network was installed along a 350 km section around this bifurcation registering 1016 crustal events between april 2008 and february 2009 528 of these events with magnitudes between 1 1 and 6 0 were located using the double difference relative location method these relative hypocentre locations reveal several new features about the crustal structure of the sf northwest and southeast of the bifurcation where the sf has only one fault strand seismicity is strongly focused below the surface trace indicating a vertical fault that is seismogenic to 15 km depth by contrast intense seismicity is observed within the bifurcation displaying streaks in plan and cross section that indicate a complex system of faults bisecting the bifurcation in combination with analysis of topography and focal mechanisms we propose that the bifurcation is a strike slip duplex system with complex faulting between the two main fault branches

seismotectonics of the loma prieta california region determined from three dimensional v p v p v s and seismicity three dimensional vp and vp vs velocity models for the loma prieta region were developed from the inversion of local travel time data 21 925 p arrivals and 1 116 s arrivals from earthquakes refraction shots and blasts recorded on 1700 stations from the northern california seismic network and numerous portable seismograph deployments the velocity and density models and microearthquake hypocenters reveal a complex structure that includes a san andreas fault extending to the base of the seismogenic layer a body with high vp extends the length of the rupture and fills the 5 km wide volume between the loma prieta mainshock rupture and the san andreas and sargent faults we suggest that this body controls both the pattern of background seismicity on the san andreas and sargent faults and the extent of rupture during the mainshock thus explaining how the background seismicity outlined the along strike and depth extent of the mainshock rupture on a different fault plane 5 km away new aftershock focal mechanisms based on three dimensional ray tracing through the velocity model support a heterogeneous postseismic stress field and can not resolve a uniform fault normal compression the subvertical or steeply dipping san andreas fault and the fault surfaces that ruptured in the 1989 loma prieta earthquake are both parts of the san andreas fault zone and this section of the fault zone does not have a single type of characteristic event

stratigraphy and paleoenvironmental changes in the yangtze delta during the late quaternary the yangtze delta area may be subdivided into paleo valley and paleointerfluves of the last glaciation the postglacial transgressive sedimentary cycle ptsc on the front zones of the paleointerfluves is composed of marsh nearshore and barrier lagoon shallow marine and nearshore tidal flat units with a basement in stiff clay the ptsc in back zones of the paleointerfluves consists of lacustrine marsh deposits the ptsc in the incised valley contains river channel floodplain estuary estuarine shallow marine and deltaic units with an erosional surface at its bottom the stiff clay and the erosional surface constitute the ptsc lower boundary the stiff clay consisting of a paleosol experienced deposition alternating with pedogenesis during the falling of sea level during 18o stage 3 ongoing pedogenesis in the sea level lowstand of 18o stage 2 and early diagenesis after paleointerfluve inundation by the sea level rise of 18o stage 1 the climate during the paleosol formation was temperate with more than 500 mm a 1 rainfall and frequently fluctuating groundwater the yangtze river incised its course during falling sea level of stage 3 and a huge incised valley was formed during the sea level lowstand stage 2 the filling of the incised valley took place during the postglacial sea level rise and delta formation occurred at a late stage of ptsc development

detailed fault structure of the tarutung pull apart basin in sumatra indonesia derived from local earthquake data abstract the tarutung basin is located at a right step over in the northern central segment of the dextral strike slip sumatran fault system sfs details of the fault structure along the tarutung basin are derived from the relocations of seismicity as well as from focal mechanism and structural geology the seismicity distribution derived by a 3d inversion for hypocenter relocation is clustered according to a fault like seismicity distribution the seismicity is relocated with a double difference technique hypodd involving the waveform cross correlations we used 46 904 and 3191 arrival differences obtained from catalogue data and cross correlation analysis respectively focal mechanisms of events were analyzed by applying a grid search method hash code although there is no significant shift of the hypocenters 10 8 m in average and centroids 167 m in average the application of the double difference relocation sharpens the earthquake distribution the earthquake lineation reflects the fault system the extensional duplex fault system and the negative flower structure within the tarutung basin the focal mechanisms of events at the edge of the basin are dominantly of strike slip type representing the dextral strike slip sumatran fault system the almost north south striking normal fault events along extensional zones beneath the basin correlate with the maximum principal stress direction which is the direction of the indo australian plate motion the extensional zones form an en echelon pattern indicated by the presence of strike slip faults striking ne sw to nw se events the detailed characteristics of the fault system derived from the seismological study are also corroborated by structural geology at the surface

the seismic 8 discontinuity and partial melting in continental mantle strong scattered reflections beyond 8 degrees 8 offset are characteristic features of all high resolution seismic sections from the continents the reflections identify a low velocity zone below approximately 100 kilometers depth beneath generally stratified mantle this zone may be caused by partial melting globally initiated at equal depth in the continental mantle solid state is again attained at the lehmann discontinuity in cold stable areas whereas the zone extends to near the 400 kilometer discontinuity in hot tectonically active areas thus the depth to the lehmann discontinuity may be an indicator of the thermal state of the continental mantle

late quaternary sedimentary evolution of the outer shelf of the east china sea abstract this study investigated the late quaternary sedimentary evolution of the outer shelf of the east china sea ecs using borehole core data dh02 three unconformity bounded sedimentary facies namely prodelta facies of marine isotopic stage mis 3 intertidal to subtidal flat facies of the deglacial period and offshore tidal sand ridge facies of the holocene were identified from the base upward according to combined evidence of lithology microfossil assemblages and geochronology through comparative analysis with other neighboring borehole cores these three facies along with the mis 3 nearshore facies and the last glacial maximum lgm river facies were found to constitute the late quaternary sediment strata sedimentary processes of these five facies were interpreted based on a synthetic consideration of sea level change climate variation paleotopographic setting and paleoriver sea interactions in particular the development of the delta was attributable to integration of the slow sea level decline during the later stage of the mis 3 and abundant sediment supply resulting from the warm wet climate the gentle shelf topography suggests the presence of shallow and wide rivers in the delta and the lateral shift of river channels might have induced the local formation of nearshore facies at the abandoned river mouth the lgm river facies which was rarely observed presumably due to marine erosion with deglacial transgression was inferred to have been deposited during the latter half of the lgm in response to the rise in river base level occurrences of tidal flat facies imply the formation of a tide dominated estuary with the deglacial transgression furthermore tidal flat sediments were reworked by enhanced tidal currents in the estuary front environment forming mud ridges during subsequent deglacial transgression formation of tidal sand ridges in offshore environments of the holocene was attributable to the uneven base caused by the underlying estuarine erosion mud ridges and this promoted the occurrence of tidal depositional processes the sedimentary evolution in association with sea level change was constructed using the above mentioned results overall this study systematically elucidates the late quaternary sedimentary processes and evolution of the outer ecs shelf and provides an insight into the sedimentary development of analogous shelves around the world

forced regression systems tracts on the bengal shelf a vertical succession of five composite sequences has been identified within the upper 100 m of the outer bengal shelf by means of high resolution multi channel seismic data each sequence consists predominantly of up to 100 km long and some 10 m thick forced regression systems tracts the internal reflection pattern of the regressive units show mainly prograding oblique clinoforms intervening transgressive systems tracts are represented by seismically transparent or chaotic layers on the outer shelf three of the sequences cause shelf aggradation and retrogradation and two of them cause mainly shelf progradation based on the hierarchy of systems tracts their calibration by comparison with eustatic sea level curves and reconstructed paleoshoreline positions the composite sequences are interpreted as eccentricity driven eustatic 4th order milankovitch cycles with a periodicity of about 100 ky internal unconformities mark cycles of 5th or higher order an average subsidence of the outer shelf is estimated to be less than 0 4 mm year during the last 345 ky the correlation between the shelf growth pattern and sea level fluctuations is consistent with the enhanced deposition on the eastern bengal submarine fan from 465 to 125 ky b p as was observed by other authors

present day heat flow thermal history and tectonic subsidence of the east china sea basin the east china sea basin is located in the convergence area between the eurasian plate the pacific plate and the philippine sea plate and consists of two depressions the taibei depression in the west and the xihu depression in the east heat flow measurements show that the east china sea basin is characterized by present day heat flow around 70 6 mw m 2 varying between 55 and 88 mw m 2 no significant difference in heat flow is observed between the xihu and the taibei depressions thermal history reconstruction using vitrinite reflectance suggests that the thermal history was however different in the taibei and the xihu depressions paleo heat flow values when the pretertiary formations experienced their maximum temperature at the end of the paleocene reached a mean of 82 mw m 2 in the taibei depression much higher than the present day value the lower tertiary sediments in the xihu depression experienced maximum temperatures at the end of oligocene 35 4 23 3 ma and reached a mean paleo heat flow value of 83 mw m 2 tectonic subsidence analysis shows that the timing of the major rifting episode was different across the east china sea basin the rifting occurred from the late cretaceous w65 ma to the early eocene w55 ma in the taibei depression followed by thermal subsidence from the late eocene to the end of miocene 23 3 5 2 ma in contrast in the xihu depression the initial subsidence lasted until the early miocene and thermal subsidence to the end of miocene from pliocene to the present an accelerated subsidence took place all along the west pacific margin of asia significant thicknesses of strata were removed from the unconformities in the basin the mean amount of erosion was 1147 m from the paleocene and 1208 m above the oligocene in the taibei depression and 1409 m from the oligocene in the xihu depression q 2004 elsevier ltd all rights reserved

the effect of sea level climate and shelf physiography on the development of incised valley complexes a modern example from the east china sea abstract analysis of high resolution seismic reflection and sonar data from the east china sea ecs continental shelf reveals the presence of an extremely broad 330 km and deep maximum incision of 72 m incised valley complex whose development and subsequent fill is constrained to the end of the last glacial cycle 20 000 yr bp to present results from this study indicate that sea level change climate controlled discharge and sediment supply and shelf physiography were important factors in the development and subsequent fill of the ecs incised valley complex for example wet climatic conditions during the initial marine oxygen isotope stage mis 2 fall of sea level promoted fluvial erosion of the exposed shelf however the trend toward drier conditions during the mis 2 fall of sea level slowed the overall development of the incised valley complex to the point where only minor incision occurred during the maximum lowstand furthermore the low gradient morphology of the exposed outer shelf diminished the ability of fluvial systems to incise instead fluvial systems migrated laterally creating a shallow 300 km incised valley system on the outer shelf during the late mis 2 rise of sea level accommodation was generated within the flooded reaches of the valley complex however arid climatic conditions that prevailed at this time resulted in minor sediment delivery to the transgressive shoreline via the incised valley complex thus the upper part of the drowned lowstand fluvial deposits were exposed at the sea floor and reworked into a valley wide tidal bar and tidal sheet complex wetter climatic conditions during middle to late mis 1 resulted in abundant sediment delivery to the drowned parts of the valley complex estuary and buried lowstand fluvial deposits below the depth of tidal ravinement where they remained undisturbed current sequence stratigraphic models can be applied to the late quaternary stratigraphic secession of the ecs however these models are too simplistic because they rely largely on rates and directions of sea level change to explain stratal architectures although the extent and rate of sea level change is extremely important this study shows that high frequency climate change and shelf physiography also play important roles in the development of stratigraphic architectures these factors are particularly important for the development of incised valleys where they directly influence incised valley morphology and facies distributions

quaternary seismic stratigraphy and paleoenvironments on the continental shelf of the east china sea abstract paleoenvironments and stratigraphy have been interpreted from 4380 km of seismic profiling collected during a geological and geophysical cruise on the continental shelf of the east china sea ecs undertaken in 1996 the geophysical data are correlated with a borehole situated on the outer shelf obtained by shanghai marine geology bureau indicating that six seismic units have been preserved since oxygen isotope stage 6 including four regressive transgressive cycles seismic units u2 u3 u4 u5 u6 and u7 are interpreted to correspond respectively to oxygen isotope stages 1 3 5 and 6 implying that sediment partitioning and sequence architecture in the ecs have been controlled by glacio eustasy and global climate changes alternating continental and marine strata corresponding to glaciation and interglaciation are well preserved on the outer shelf of the ecs most of the cold environment strata which formed on the outer shelf during oxygen isotope stages 2 and 4 are too thin to be recognized on sig 600j because of resolution but corresponding erosion surfaces exist seismic unit u7 is widespread over the shelf extending to the continental edge and showing little variation in thickness as the regression was pronounced and lasted a long time thus u7 can be used as a marker layer for correlation of quaternary strata on the shelf of the ecs post glacial transgression is obvious in the ecs marine strata with varied thickness were developed in the shallow sea of the inner shelf thinning toward the outer shelf the continental shelf of the ecs has been influenced by pacific tide wave systems for a long time forming tidal sand ridge sequences developed during transgressions corresponding to oxygen isotope stages 7 or 9 5 3 and 1

the liquine ofqui fault zone a long lived intra arc fault system in southern chile abstract plate reconstructions for the cenozoic document relatively steady right oblique subduction of the farallon nazca plate beneath the chilean continental margin the kinematic signature recorded along the intra arc liquine ofqui fault zone lofz a major feature of the southern andes may help to understand the way in which the nazca south america slip vector has been partitioned into strain and displacement along and across the continental margin the lofz consists of two nne trending right stepping straight lineaments a strike slip duplex at the right step and curved features which splay off the straight lineaments toward the northwest the lofz runs mostly through heterogeneously deformed cenozoic plutonic rock of the north patagonian batholith and patchy metamorphic wall rock early cenozoic volcano sedimentary rocks and dyke swarms found in close spatial association with the strike slip duplex are believed to have developed in strike slip related basins quaternary volcanoes are aligned parallel to the lofz both ductile and brittle kinematic indicators within centimeter to meter wide high strain zones document late cenozoic dextral shear deformation contrasting left lateral deformation recorded on older and wider mylonitic zones suggests that the lofz may be a long lived shear zone that accommodated continental scale deformation arising from the farallon nazca south america plate convergence a block rotation pattern as indicated by paleomagnetic data is consistent with the geometry and cenozoic kinematics of the lofz

pleistocene forced regressions and tidal sand ridges in the east china sea abstract tidal sand ridges are common features on modern shelves but only few examples of such preserved sand bodies are described in pleistocene deposits in the stratigraphic record some sand bodies encased in shales previously interpreted as sand ridges have been reinterpreted as shoreface deposits more than 5000 km of high resolution seismic data from the east china sea correlated to geotechnical boreholes and shallow cores demonstrate the potential of sand ridge preservation and allow reconstruction of the depositional history of pleistocene fourth order 100 kyr depositional sequences a high subsidence rate of about 300 m myr allows the preservation of three elementary sedimentary facies constitutive of a motif which was repeated during glacio eustatic cycles they consist of 1 regressive marine prodeltaic prograding wedges 2 estuarine and continental deltaic facies and 3 transgressive sand ridges similar in shape and orientation to modern sand ridges major discontinuities traceable over the entire outer continental shelf along distances of hundreds of kilometers are transgressive and regressive surfaces of marine erosion whereas sequence boundaries formed by fluvial erosion are difficult to identify on this low gradient shelf because of the asymmetry of the pleistocene glacio eustatic cycles most of the preserved sedimentary record with the exception of sand ridges corresponds to forced regressive deposits deposits that formed during a seaward shift of the shoreline due to relative sea level lowering

provenance structure and formation of the mud wedge along inner continental shelf of the east china sea a synthesis of the yangtze dispersal system surficial grain size and down core clay mineralogical data show that sediment along the inner most part of the continental shelf in east china sea is mainly derived from the yangtze river changjiang spanning from the yangtze mouth 33 degrees n similar to 1000 km southward to the southwestern corner of the taiwan strait 24 degrees n high resolution chirp seismic profiles reveal an elongated mud wedge extending along the inner shelf with a northern depocenter on the modern yangtze delta and a southern depocenter at 27 5 degrees n four distinct acoustic units are delineated within the mud wedge from bottom up unit i late pleistocene mainly valley fills unit ii formed by transgressions thin strata unit iii 11 2 kyr bp downlapping strata and unit iv 2 0 kyr bp flat and opaque strata incised valleys up to 15 m deep are filled by flat lying or inclined strata in unit i the thin 3 m and acoustically transparent unit ii is only seen between 30 and 26 degrees n in water depths between 40 and 90 m separated by acoustically opaque strata or unconformities units iii and iv are widely distributed during the past 11 kyr yangtze sediment accumulation has been unsteady showing two high and one low accumulation rate periods the high accumulation period at 5 8 kyr bp may be related to maximum east asian summer monsoon precipitation in the yangtze basin the other high accumulation period 0 2 kyr bp probably reflects intensive human activities in the river s watershed the low accumulation rate period at 2 5 kyr bp which is seen in both northern and southern yangtze depocenters is probably related to low river discharge and or intensified taiwan warm current and china coastal current c 2011 elsevier b v all rights reserved

late quaternary transgressive and highstand systems tracts in the northern east china sea mid shelf abstract analysis of very high resolution 3 5 khz seismic profiles and sediment data from the northern east china sea mid shelf region reveals that the sedimentary sequence above the acoustic basement consists of five late quaternary sedimentary units comprising transgressive and highstand systems tracts formed after the last glacial maximum the transgressive systems tract includes four units 1 incised valley fill unit i 2 transgressive estuarine deltaic complex unit ii 3 transgressive sand sheet unit iii and 4 tidal sand ridge unit iv the lower two units units i and ii representing a paralic environment consist of sediment preserved from shoreface erosion the upper units units iii and iv corresponding to a marine environment consist of sediments produced through shoreface erosion during the holocene transgression a ravinement surface separates the lower and the upper units the highstand systems tract is composed of a distal mud patch unit v derived from the huanghe and changjiang rivers in china dispersal and deposition of this modern mud are largely controlled by the regional circulation pattern and sediment supply

characterization of the hydrothermal system of the tinguiririca volcanic complex central chile using structural geology and passive seismic tomography abstract a structural characterization of the hydrothermal volcanic field associated with the tinguiririca volcanic complex had been performed by combining passive seismic tomography and structural geology this complex corresponds to a 20 km long succession of n25 e oriented of eruptive centers currently showing several thermal manifestations distributed throughout the area the structural behavior of this zone is controlled by the el fierro el diablo fault system corresponding to a high angle reverse faults of oligocene miocene age in this area a temporary seismic network with 16 short period stations was setup from january to april of 2010 in the context of the msc thesis of lira 2010 covering an area of 200 km 2 that corresponds with the hydrothermal field of tinguiririca volcanic complex tvc central chile southern central andes using p and s wave arrival times a 3d seismic velocity tomography was performed the preliminary locations of 2270 earthquakes have first been determined using an a priori 1d velocity model afterwards a joint inversion of both the 3d velocity model and final locations have been obtained high vp vs ratios are interpreted as zones with high hot fluid content and high fracturing meanwhile low vp vs anomalies could represent the magmatic reservoir and the conduit network associated to the fluid mobility based on structural information and thermal manifestations these anomalies have been interpreted in order to visualize the relation between local geology and the velocity model the volume associated with the magma reservoir and the fluid circulation network has been delimited using an iso value contour of vp vs equal to 1 70 the most prominent observed feature in the obtained model is a large v shaped low velocity anomaly extending along the entire study region and having the same vergency and orientation as the existing high angle inverse faults which corroborates that el fierro el diablo fault system represents the local control for fluid mobility this geometry coincides with surface hydrothermal manifestations and with available geochemical information of the area which allowed us to generate a conceptual model of fluid circulation in the volcanic hydrothermal system as well as define the location of the magmatic reservoir

late quaternary evolution of the sub aqueous yangtze delta china sedimentation stratigraphy palynology and deformation abstract four sediment belts a d of the yangtze sub aqueous delta are defined from the sea bottom sediment distribution belt a delta front fine sand and silt with trough cross stratification belt b prodelta silty clay and clayey silt with abundant burrowing and rich in organic matter belt c prodelta to continental shelf sand silt clay with thin layers of sand and clay interbedded and belt d late pleistocene relict sands medium to fine grained mixed with shell fragments the late quaternary stratigraphy of the delta consists from bottom upward of late pleistocene terrigenous fluvial and lacustrine sand and mud holocene transgressive silt prodelta clay and delta front fine sand and silt in addition four pollen spore zones a d derived from these sediment sequences reveal a general trend of climate warming from early to late holocene the zone c distributed primarily within the prodelta muds provides evidence for a temperature maximum starting at ca 7000 years b p atlantic period this indicates that the delta initiation was essentially coeval with the climate optimum in early holocene sub bottom seismic surveys reveal three i iii acoustic facies facies i and ii are characterized by seaward remobilization of water saturated holocene prodelta muds facies iii is composed of highly contorted late pleistocene strata and mud diapirs that erupted from deep seated late pleistocene sediments in front of the estuarine depocenter gravity subsidence due to holocene sediment loading within the depocenter is the major factor in causing the deformation of underlying unconsolidated strata furthermore the sub aqueous yangtze delta proper is now obviously diverting to southeast owing to the long term tectonically induced southward shift of the river mouth and to the marine currents associated with the coriolis effect we thus predict that the large chongming island in river mouth area will have been coalesced with the northern yangtze coast in the recent future

structural controls on a geothermal system in the tarutung basin north central sumatra abstract the sumatra fault system provides a unique geologic setting to evaluate the influence of structural controls on geothermal activity whereas most of the geothermal systems in indonesia are controlled by volcanic activity geothermal systems at the sumatra fault system might be controlled by faults and fractures exploration strategies for these geothermal systems need to be verified because the typical pattern of heat source and alteration clays are missing so that conventional exploration with magnetotelluric surveys might not provide sufficient data to delineate favorable settings for drilling we present field geological structural and geomorphological evidence combined with mapping of geothermal manifestations to allow constraints between fault dynamics and geothermal activity in the tarutung basin in north central sumatra our results indicate that the fault pattern in the tarutung basin is generated by a compressional stress direction acting at a high angle to the right lateral sumatra fault system nw se striking normal faults possibly related to negative flower structures and nnw sse to nne ssw oriented dilative riedel shears are preferential fluid pathways whereas ene wsw striking faults act as barriers in this system the dominant of geothermal manifestations at the eastern part of the basin indicates local extension due to clockwise block rotation in the sumatra fault system our results support the effort to integrate detailed field geological surveys to refined exploration strategies even in tropical areas where outcrops are limited

neotectonics of the sumatran fault indonesia the 1900 km long trench parallel sumatran fault accommodates a significant amount of the right lateral component of oblique convergence between the eurasian and indian australian plates from 10 n to 7 s our detailed map of the fault compiled from topographic maps and stereographic aerial photographs shows that unlike many other great strike slip faults the sumatran fault is highly segmented cross strike width of step overs between the 19 major subaerial segments is commonly many kilometers the influence of these step overs on historical seismic source dimensions suggests that the dimensions of future events will also be influenced by fault geometry geomorphic offsets along the fault range as high as 20 km and may represent the total offset across the fault if this is so other structures must have accommodated much of the dextral component of oblique convergence during the past few million years our analysis of stretching of the forearc region near the southern tip of sumatra constrains the combined dextral slip on the sumatran and mentawai faults to be no more than 100 km in the past few million years the shape and location of the sumatran fault and the active volcanic arc are highly correlated with the shape and character of the underlying subducting oceanic lithosphere nonetheless active volcanic centers of the sumatran volcanic arc have not influenced noticeably the geometry of the active sumatran fault on the basis of its geologic history and pattern of deformation we divide the sumatran plate margin into northern central and southern domains we support previous proposals that the geometry and character of the subducting investigator fracture zone are affecting the shape and evolution of the sumatran fault system within the central domain the southern domain is the most regular the sumatran fault there comprises six right stepping segments this pattern indicates that the overall trend of the fault deviates 4 clockwise from the slip vector between the two blocks it separates the regularity of this section and its association with the portion of the subduction zone that generated the giant m w 9 earthquake of 1833 suggest that a geometrically simple subducting slab results in both simple strike slip faulting and unusually large subduction earthquakes

first seismic record for intra arc strike slip tectonics along the liquine ofqui fault zone at the obliquely convergent plate margin of the southern andes a temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike slip liquine ofqui fault zone lofz in southern chile seventy five shallow crustal events with magnitudes up to m tief w 3 8 and depths shallower than 25 km were observed in an 11 month period mainly occurring in different clusters those clusters are spatially related to the lofz to the volcanoes chaiten michinmahuida and corcovado and to active faulting on secondary faults further activity along the lofz is indicated by individual events located in direct vicinity of the surface expression of the lofz focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike slip mechanisms indicating a ne sw direction of the p axis for the lofz at this latitude the seismic activity reveals the present day activity of the fault zone the recent m tief w 6 2 event near puerto aysen southern chile at 45 4 s on april 21 2007 shows that the lofz is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region

three dimensional upper crustal structure of the geothermal system in tarutung north sumatra indonesia revealed by seismic attenuation tomography the geothermal potential in tarutung is controlled by both the sumatra fault system and young arc volcanism in this study we use the spatial distribution of seismic attenuation calculated from local earthquake recordings to image the 3 d seismic attenuation of the area and relate it with the temperature anomalies and the fluid distribution of the subsurface a temporary seismic network of 42 stations was deployed around tarutung and sarulla south of tarutung for a period of 10 months starting in 2011 may within this period the network recorded 2586 local events a high quality subset of 229 events recorded by at least 10 stations was used for the attenuation inversion tomography path average attenuation t p was calculated by using a spectral inversion method the spread function the contour lines of the model resolution matrix and the recovery test results show that our 3 d attenuation model q p has good resolution around the tarutung basin and along the sarulla graben high attenuation low q p related to the geothermal system is found in the northeast of the tarutung basin suggesting fluid pathways from below the sumatra fault the upper part of the studied geothermal system in the tarutung district seems to be mainly controlled by the fault structure rather than by magmatic activities in the southwest of the tarutung basin the high attenuation zone is associated with the martimbang volcano in the sarulla region a low q p anomaly is found along the graben within the vicinity of the hopong caldera

transgressive and highstand systems tracts and post glacial transgression the east china sea abstract the late pleistocene holocene depositional sequence on the shelf in the east china sea ecs is interpreted on the basis of the analyses of four sediment cores and high resolution seismic reflection sub bottom profiler records along a ne sw across shelf transect sedimentary strata deposited above a lowermost planar erosional surface that was formed during sea level fall of the last glacial are divided into two units along a ne sw across shelf transect changjiang okinawa the lower unit is characterized by seaward dipping tangential clinoforms with a thickness of 30 40 m at mid shelf depths and less than 30 m beneath the outer shelf prograding clinoforms are more obvious in mid shelf environments the upper unit is characterized by an upper transparent layer that is formed into ridge and swale topography the boundary between the upper and lower units is sharp and erosional surficial sediments taken by cores from the central ecs shelf are also divided into two facies a sandy facies consisting of sand or sandy gravel with moderately abundant molluscan shell fragments and a muddy facies comprising mud intercalated with thin sand layers the sandy facies is widely distributed on the middle to outer shelf seafloor and has a measured thickness of 30 cm up to several metres radiocarbon ages of molluscan shells in this sediment are less than approximately 10 ka bp except for ages from basal shell lag deposits which are 10 40 ka bp the muddy facies underlies the sandy facies and has radiocarbon ages of 2 7 2 9 ka bp previous work and 20 38 ka bp this study and tl ages of 27 50 ka bp previous work the boundary between these lithologic units is an erosional sharp contact the sandy and muddy facies are correlated with the upper and lower seismic units respectively the lower unit is characterized by prograding clinoforms and is interpreted to represent deltaic or nearshore tidal ridge sediments of the paleo changjiang river that were deposited during the last glacial lowstand of sea level as a lowstand systems tract the underlying erosional surface is interpreted to be a sequence boundary formed as a regressive marine erosional surface during the fall of sea level the erosional boundary between the lower and upper units is interpreted as a transgressive surface of erosion formed during the subsequent rise of sea level the upper unit has a modern sand ridge topography and is interpreted to represent offshore shelf sand ridges of the transgressive to highstand systems tract

provenance discrimination of the clay sediment in the western taiwan strait and its implication for coastal current variability during the late holocene this study aims to quantify the contribution of yangtze clays to the sediment accumulation in the western taiwan strait and reconstruct the strength of chinese coastal current ccc since middle ho

major sinks of the changjiang yangtze river derived sediments in the east china sea during the late quaternary the east china sea ecs is a typical marginal sea located between the eurasian con tinentandwestpacificocean inthisstudy wereviewstate of the artresearchprogressonthepos sible sinks of the changjiang derived sediments in the ecs during the late quaternary the major sinks of these sediments in the ecs are on the outer shelf and the okinawa trough during the last glacial maximum corresponding to a lowstand of sea level during the deglacial marine transgres sion the gently dipping shelf was rapidly inundated and strong tides prevented fine sediment from deposition on the open shelf resulting in the development of a unique tidal sand ridge sys tem with sea level reaching the present situation and the modern marine environment being com pleted in the early holocene the changjiang sediments mostly accumulated in the river s estuary to build a large delta with only a fraction reaching the inner shelf and coastal embayments the late quaternary changes in monsoon climate induced river flux sea level and oceanic circulation primarily controlled the source to sink transport of the changjiang sediments in the ecs and fur ther determined the stratigraphic framework and sedimentary facies on the shelf

optimized automatic pickers application to the ancorp data set summary it has become increasingly important to develop fast and accurate automatic procedures to process and fully exploit increasing large seismic data sets traditionally these data sets are processed manually which requires significant amounts of both manpower and time with sometimes variable results we have developed a cost minimization approach to train three automatic pickers an sta lta tpd and the pai k picker at each station within a dense temporary network located in northern chile and southern bolivia the optimum picking parameters for each station show regional variability and need to be adjusted individually to achieve the best performance we developed a weighting scheme that uses four independent predictors of weight calibrated using a handpicked data subset which mimics the picking by an expert seismologist we use the fact that each of the three pickers highlights different properties of the observed seismic trace to combine two pickers that work in tandem the first makes an initial pick before the second picker refines and improves the accuracy of the automatic pick we find the tandem pickers improve the accuracy of the automatic picks when compared to the single automatic pickers we demonstrate that following the cost minimization procedure described here the automatic picks have sufficient accuracy that they would be suitable for high precision earthquake location focal mechanism determination or high resolution seismic tomography

holocene paleoclimatic reconstruction based on mud deposits on the inner shelf of the east china sea abstract we present a paleoclimatic reconstruction of the mid holocene by geochemical analysis of a sediment core mz01 retrieved from the mud area of the inner continental shelf of the east china sea ecs our results show that the downcore geochemical variations in the sediments of the core provide a link to historical climate changes relatively higher ratios of cia ba sr and a lower ratio of cao mgo coincide with major regional warm and humid climate episodes and vice versa therefore these geochemical indicators are useful in reconstructing the paleoclimate in eastern china using the geochemical records of core mz01 which are well constrained by ams 14c dating we found that from 8300 yr bp to 4200 yr bp the regional climate was moderately warm and humid and from 4200 yr bp to 2300 yr bp the climate was cool and dry with large fluctuations between cool dry 3700 yr bp 2850 yr bp and 2400 yr bp and warm wet 3250 yr bp and 2650 yr bp since 2300 yr bp our records indicate that the climate has gradually become warmer although a cold event centered at around 250 yr bp the little ice age lia interrupted this warming trend we also found significant 238 yr cycles in our cia records that imply a possible solar influence on the regional climate changes since the mid holocene

the chronology of a sediment core from incised valley of the yangtze river delta comparative osl and ams 14 c dating abstract optically stimulated luminescence osl dating has gained increased use in dating deltatic deposits however its application can be hindered by the problem of incomplete bleaching to address this limitation we test the single grain osl method for the first time in the yangtze river delta a total of eight osl and 14 ams 14c samples were obtained from a 50 8 m long sediment core from the incised valley of the delta quartz extracted from eight osl samples from the core was first measured with small multi grain aliquots using medium 45 63 m and coarse grained 90 125 m or 150 180 m fractions to test the internal consistency of their respective ages the results showed that four of five medium grained quartz samples appeared to be well bleached in contrast the coarse grained quartz samples revealed poor bleaching except for two samples from the delta front facies five coarse grained quartz osl samples were further analyzed using a single grain osl technique only 0 5 0 7 of the grains passed the rejection criteria single grain osl dating is appropriate for age determination of coarse grained sediments which have been affected by incomplete bleaching however it consumes a lot of instrument time central and minimum age models cam and mam were used to calculate the burial age of the samples mam ages fit best in the stratigraphic sequence small aliquots are recommended as effective in identifying incomplete bleaching for medium or coarse grained quartz a comparison of ams 14c dates and osl ages shows that 14c values are 1 3 ka older than osl ages according to the osl ages core sd experienced rapid accumulation 10 8 ka and in the last 2 ka the former is linked to rapid sea level rise in early holocene while the latter is primarily due to the migration of depo center towards the core site rather than entirely increased sediment delivery caused by human activities

early holocene mud ridge formation in the yangtze offshore china a tidal controlled estuarine pattern and sea level implications abstract the purpose of the present study is to examine the topographic evolution and sedimentary characteristics of a mud ridge system in the yangtze offshore region as revealed by seismic profiling 2 3 km wide 5 8 km long up to 15 m thick mud ridges situated 5 10 km apart extend here in a southeasterly direction approximately parallel to the direction of the ebb and flood flow of the modern tide directly resting upon the latest pleistocene terrestrial sediments some mud ridges are exposed on the present seafloor while others are buried by landward thickening holocene deltaic sediments an 11 m long vibrocore recovered from one mud ridge reveals homogenous and mottled silty clay and clayey silt rich in foraminifera suggesting an estuarine environment of deposition chronostratigraphic correlation in association with acoustic facies indicate that the mud ridge was formed primarily during 10 7 ka corresponding to a period of global decelerating rise in sea level this mud ridge is underlain by thick late pleistocene fluvial to coastal fine to medium sands with an unconformity surface on top and it is overlain by modern deltaic sediments with an erosional surface in between we propose that the mud ridges were deposited under tidal controlled estuarine conditions during the early holocene deceleration of the rise in sea level the holocene transgression in the study area was nearly coeval with the mud ridge deposition and the deltaic sedimentation occurred after the mud ridges formed the ridges were subsequently reworked largely by strong tidal currents

self organizing maps in geothermal exploration a new approach for understanding geochemical processes and fluid evolution understanding geochemical processes is an important part of geothermal exploration to get information about the source and evolution of geothermal fluids however in most cases knowledge of fluid properties is based on few parameters determined in samples from the shallow subsurface this study presents a new approach that allows to conclude from the combination of a variety of these data on processes occurring at depth in a geothermal reservoir the neural network clustering technique called self organizing maps soms successfully distinguished two different geothermal settings based on a hydrochemical database and disclosed the source evolution and flow pathways of geothermal fluids scatter plots as shown in this study are appropriate presentations of element concentrations and the chemical interaction of water and rock at depth one geological setting presented here is marked by fault dominated fluid pathways and minor influence of volcanic affected fluids with high concentrations of hco3 ca and sr the second is a magmatically dominated setting showing strong alteration features in volcanic rocks and accommodates acidic fluids with high so4 and si concentrations former studies i e giggenbach 1988 suggested cl hco3 and so4 to be generally the most important elements for understanding hydrochemical processes in geothermal reservoirs their relation has been widely used to classify different water types in geothermal fields however this study showed that non standard elements are at least of same importance to reveal different fluid types in geothermal systems therefore this study is an extended water classification approach using som for element correlations som have been proven to be a successful method for analyzing even relatively small hydrochemical datasets in geothermal applications

oblique plate motion and continental tectonics three dimensional deformation is necessarily associated with oblique plate convergence and commonly results in partitioning of deformation between contractional and transcurrent components along plate margins kinematic models of strike slip partitioning for transpression and transtension allow the exact relation among three critical parameters plate motion instantaneous strain axes and degree of strike slip partitioning to be calculated application to two end member tectonic environments characterized by a low south island new zealand and high central california degree of strike slip partitioning demonstrates a remarkable consistency among the three parameters suggesting that strike slip partitioned transpression is a valid model for deformation in these regions the extreme degree of strike slip partitioning in wrench dominated systems such as central california is tentatively associated with a fundamental misorientation of finite and instantaneous strain axes

extensional duplexing in the york cliffs strike slip fault system southern coastal maine abstract a 150 m long sinistral strike slip fault system consisting of left stepping en echelon fault segments cuts deformed paleozoic metasediments and early mesozoic dike intrusions in coastal terrace outcrops in southern maine the longer fault segments follow the vertical bedding in the metasediments and accommodate approximately 1 m of displacement detailed mapping at scales down to 1 6 indicates that overlap zones between offset layer parallel fault segments consist of high dilation angular breccias rounded attrition breccias and extensional duplexes where the offset segments straddle upright quartzite layers in one 10 m long duplex r and r shears cut the layering in the quartzite at 28 and 69 respectively relative to the dominant layer parallel fault segments creating a doubly tapered imbricate r shear lens segmentation structure individual imbricate lenses accommodate additional layer parallel extension through conjugate x x shear fractures with average orientations of 109 and 60 respectively relative to the dominant fault segments extensional fractures oblique to the dominant fault segments are rare within this duplex but commonly form distinctive horsetail arrays at fault terminations that average 44 to the layer parallel faults strain analysis shows that approximately 60 80 cm of measured strike slip displacement is accommodated internally within this duplex as layer parallel extensional strain using the r shear and x x shear fracture mechanisms the strain distribution and observed cross cutting relations suggest an outward symmetric growth of the duplex structure from left stepping sinistral fault segments that developed sequences of tip to plane r shear overlap linkages during continued displacements cyclic r r to x x shear fracturing may relate to stress reorientation following r shear ruptures during episodic growth of the duplex and incremental slip of the fault system

tectonic evolution and regional setting of the cuu long basin vietnam abstract the cuu long basin is situated off the southeastern coast of vietnam this study utilizes all available seismic data in the cuu long basin vinh chau basin and coastal mekong delta to constrain the tectonic history of the area the linkage between the mae ping fault zone and deformation in the cuu long basin is also examined in detail two major deformational events are observed a transtensional rifting event from the mid eocene to mid early oligocene 40 31 ma followed by transpression from mid early oligocene to mid late oligocene 31 25 ma the data strongly suggest that all the very straight major tributaries of the mekong river delta follow northwest trending faults that link into to the southwestern end of the cuu long basin fault system and that the basin opened between where the mekong delta faults enter and a point of zero extension at the ne termination of the basin the mekong delta fault zone exhibited left lateral displacement during extension in the cuu long basin and right lateral displacement during younger transpression the orientation age and sense of displacement of the mekong delta fault zone are consistent with slip on the mae ping fault zone in thailand and cambodia and hence are considered to be part of the same regional fault system based on a chainat duplex analogue and other data the mekong delta and mae ping fault zones appear to be linked by a nnw striking step over zone referred to here as the mekong ton le sap step over zone this zone follows the eastern boundary of the paleocene to early eocene kampot fold belt based on structural and stratigraphic similarities it appears the adjacent vinh chau basin shares a common tectonic history with the cuu long basin but the linkage to the mekong delta fault zone is less clear

recent and modern marine erosion on the new jersey outer shelf abstract recent chirp seismic reflection data combined with multibeam bathymetry backscatter and analysis of grab samples and short cores provide evidence of significant recent erosion on the outer new jersey shelf the timing of erosion is constrained by two factors 1 truncation at the seafloor of what is interpreted to be the transgressive ravinement surface at the base of the surficial sand sheet and 2 truncation of apparently moribund sand ridges along erosional swales oriented parallel to the primary direction of modern bottom flow and oblique to the strike of the sand ridges these observations place the erosion in a marine setting post dating the passage of the shoreface ravinement and the evolution of sand ridges that form initially in the near shore environment also truncated by marine erosion are shallowly buried fluvial channel systems formed during the last glacial maximum and filled during the transgression and a regional reflector r that is 40 kyr depths of erosion range from a few meters to 10 m the seafloor within eroded areas is often marked by ribbon morphology seen primarily in the backscatter data as areas of alternating high and low backscatter elongated in the direction of primary bottom flow ribbons are more occasionally observed in the bathymetry where observed crests exhibit low backscatter and troughs exhibit high backscatter sampling reveals that the high backscatter areas of the ribbons consist of a trimodal admixture of mud sand and shell hash with a bimodal distribution of abraded and unabraded sand grains and microfauna the shell hash is interpreted to be an erosional lag while the muds and unabraded grains are in this non depositional environment evidence of recent erosion at the seafloor of previously undisturbed strata the lower backscatter areas of the ribbon morphology were found to be a well sorted medium sand unit only a few 10 s of cm thick overlying the shelly muddy sandy material concentrations of well rounded gravels and cobbles were also found in eroded areas with very high backscatter and at least one of these appears to be derived from the base of an eroded fluvial channel seafloor reworking over the transgressive evolution of the shelf appears to have switched from sand ridge evolution which is documented to 40 m water depth to more strictly erosional modification at greater water depths we suggest that this change may be related to the reduction with water depth in the effectiveness of sediment resuspension by waves resuspension is a critical factor in the grain size sorting during transport by bottom currents over large bedforms like sand ridges otherwise we speculate displacement of sand by unidirectional currents will erode the seafloor

the tectonic framework of the sumatran subduction zone the great aceh andaman earthquake of december 26 2004 and its tragic consequences brought the sumatran region and its active tectonics into the world s focus the plate tectonic setting of sumatra has been as it is today for tens of millions of years and catastrophic geologic events have likely been plentiful the immaturity of our understanding of great earthquakes and other types of geologic hazards contributed to the surprise regarding the location of the 2004 earthquake the timing however is probably best understood simply in terms of the inevitability of the infrequent events that shape the course of geologic progress our best hope is to improve understanding of the processes involved and decrease our vulnerability to them

stratigraphic framework and evolution of the mid late quaternary since marine isotope stage 8 deposits on the outer shelf of the east china sea abstract the east china sea ecs is a vast river dominated depositional basin because of its broad shelf and extensive river sediment supply this study investigated the mid late quaternary stratigraphic framework and evolution of the outer ecs shelf based on a borehole core dh02 and seismic profiles seven sedimentary facies were recognized in the core sediments according to lithology grain size composition sediment structure and microfossil assemblages while eight unconformity bounded major stratigraphic units were identified in the seismic profiles based on seismic core correlations dating data radiocarbon and optically stimulated luminescence and comparison between sedimentary cycles and sea level curves the 100 m thick strata below the seafloor were divided into three sequences corresponding to glacial interglacial sea level cycles of marine isotope stage mis 1 2 mis 3 6 and mis 7 8 sq1 sq3 from top to bottom in particular sq1 is developing in the present sea level highstand and consists mainly of deposits of transgressive systems tract tst including tide influenced river tidal flat and tide dominated estuarine facies sq2 and sq3 consist mainly of prodelta and related inner shelf facies of forced regressive systems tract frst and transgressive deposits similar to those of sq1 for all three sequences a thin sand sheet layer of open shelf facies represents deposits of highstand systems tract hst deposits of lowstand systems tract lst were typically represented by river facies in addition comprehensive analyses of seabed sand ridge distribution core sediment characteristics and ridge deposition mechanism suggest that the occurrence of a paleoestuary with transgression determined the development of a tidal sand ridge field based on all these results a conceptual stratigraphic sequence model in association with the deposition of lst tst hst and frst was constructed overall our stratigraphic framework along with a comparison of the sequence stratigraphy to that of other shelves suggested that glacial interglacial sea level fluctuations huge amounts of river sediment supply active subsidence gentle shelf topography and marine erosion processes transgression and regression controlled the mid late quaternary stratigraphic development of the ecs shelf

acehseis project provides insights into the detailed seismicity distribution and relation to fault structures in central aceh northern sumatra abstract for the first time a dense seismic network acehseis consisting of 30 short period seismic stations was installed for 10 months from july 2014 in order to record crustal earthquakes in central aceh northern sumatra following the hazardous earthquake with magnitude mw 6 1 july 2nd 2013 the objective of this research is to investigate the active fault characteristics derived from local earthquake data combined with a digital elevation model the network recorded more than 1790 local events occurring along the main great sumatran fault gsf and its secondary faults local earthquakes with azimuthal gap angles greater than 180 were excluded to avoid non unique earthquake locations therefore from all recorded earthquakes 1127 local earthquakes were used for further seismological analysis a method of simultaneous earthquake relocation and 1d velocity determination was applied to obtain better location of earthquakes the output of the first relocated seismicity was then relocated again by using a double difference relocation method after relocation earthquakes are concentrated in a narrow zone along the active fault indicating the reliability of the earthquake location we then determined the focal mechanism of earthquakes based on the first polarity picks the seismicity distribution correlates with the well known gsf and its main secondary faults earthquake locations also clearly revealed several active segments which include the batee beutong tangse geumpang lampahan aceh and seulimeum and nisam faults also less known faults as the pamue and atu lintang peusangan faults are imaged in northern aceh an unknown earthquake cluster associated with an active fault the nisam fault was detected which is also visible in the topography the seismicity along gsf is offset at around 96 7 e constrained by the nearly n s striking atu lintang peusangan fault confirming the segmentation of gsf at this longitude the aceh segment and the seulimum fault in the northernmost region of the network are both active and clearly imaged by the seismicity the pamue and the lampahan faults seem to be the splay of gsf as indicated by identical strike direction as the gsf the lampahan fault is characterized by nw se seismicity lineation which is in agreement with the focal mechanisms the laut tawar lake could be a part of the lampahan fault that is also offset at 96 7 e at the line of the atu lintang peusangan fault the burni geureudong fault on the other hand strikes ene wsw which suggests a conjugate fault of the lampahan fault

the 3d electromagnetic response of the earth to ring current and auroral oval excitation summary we report on a new compilation of functions representing the geoelectromagnetic response of the earth s mantle the c response functions and newly defined d response functions the latter of which constitutes a sensitive indicator of lateral heterogeneities in conductivity were estimated for periods from 5 to 106 7 days the spatial coverage and statistical quality of these response function estimates were improved over previous compilations in part by making use of a newly assembled global catalogue of magnetic observatory hourly mean values and by applying a statistically robust form of empirical orthogonal function eof analysis the eof results suggest that for periods longer than 5 days the geomagnetic field variation can be represented predominantly by a single eigenmode we have identified that the primarysource fields of the dominant mode consist of two current systems in the same direction an equatorial ring current in the magnetosphere and two conjugate auroral oval ring currents in the ionosphere the influence of the auroral current system is seen at surprisingly low latitudes 40 and 50 for the vertical and northern components respectively which results in non negligible bias on the conventional c response at high latitudes a preliminary correction of the auroral current effect has been made on the c and d responses obtained for data from 55 and 52 observatories respectively at latitudes from 60 to 60 we also present a set of approximate equivalent internal mantle electrical current distributions that prove a useful indicator of the presence of deep earth heterogeneities these new sets of electromagnetic information will increase the resolving power of 3d distribution of electrical conductivity in the earth s mantle

sedimentary system response to the global sea level change in the east china seas since the last glacial maximum abstract the east china seas ecs is one of the world s largest continental shelf seas based on the combination of global sea level change and sequence stratigraphy we systematically investigated the evolution of sedimentary system in the ecs since the last glacial maximum lgm we have defined the transgressive boundary layer and constructed several sedimentary models of the ecs on the sequence stratigraphy and evolution of tidal sand ridges since the lgm and sediment source to sink during the high sea level the result shows that the ecs represent a typical case for large scale continental shelf response to the global sea level change three sedimentary system tracts had been formed in the ecs since the lgm first is the lowstand system tract corresponding to the late of last glaciation and lgm 23 15 4 cal kyr b p the progressive wedge occurred along the okinawa trough slope and the paleo coastal zone pcz along the continental shelf edge second is the transgressive system tract corresponding to the last deglaciation 15 4 7 cal kyr b p a large scale transgressive boundary layer and tidal sand ridges were formed in this stage third is the highstand system tract corresponding to the high sea level since 7 cal kyr b p the eddy mud coastal current mud present tidal sand ridge delta tidal flat and beach have been accumulating since then the global sea level change after lgm can be divided into seven phases of which four rapidly rising phases rrp i ii iii iv and three slowly rising phases srp i ii iii are distinguished the tidal sand ridges were formed in the srp and transgressive boundary layer in the rrp the tidal sand ridges can be divided into three types including radicalized channel and emanative the modern circulation current system of the ecs had been built in the end of the last deglaciation the effect of sediment source to sink in the ecs is closely correlative to the current system driven by the interaction of the east asian monsoon and kuroshio the major sediment source is from the river discharge of the huanghe and changjiang river and coastal resuspension the muddy sediment in the eddy and coastal current which cover the tidal sand ridges and transgressive boundary layer is a major sediment sink in the modern ecs

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

implications of seismic scattering below the 8 discontinuity along pne profile kraton abstract strong scattered arrivals are observed in the 800 1400 km offset range of the four peaceful nuclear explosion pne seismic sections along the 3500 km long e w trending russian profile kraton they give evidence of an 85 km thick inhomogeneous scattering layer in the upper mantle which has a slightly reduced 1 average p wave velocity compared to the layers above and below the top of the anomalous zone is the 8 discontinuity at 100 km depth which is constrained by a clear travel time delay of up to 2 s consistently observed at 900 1000 km 8 offset in the four pne seismic sections we model the inhomogeneous zone below the 8 discontinuity by random velocity fluctuations the full waveform seismic response of a suite of stochastic velocity models is calculated using a two dimensional finite difference scheme the calculated seismic sections resemble the pne data for models where the random fluctuations have a horizontal correlation length of 5 10 km a vertical correlation length not greater than 5 km and a standard deviation of about 2 of the average background velocity fluctuations with significantly larger correlation lengths give rise to coherent scattered arrivals and considerably shorter correlation lengths lead to significantly weaker scattering none of which resemble the observed data the preferred seismic velocity model is in agreement with an upper mantle model in which the low velocity zone below the 8 discontinuity may contain small amounts of partially molten material alternatively the combined effects of rheological weakening and small scale anisotropy may also account for the low velocity scattering layer

ambient seismic noise tomography reveals a hidden caldera and its relation to the tarutung pull apart basin at the sumatran fault zone indonesia abstract we analyzed the noise recordings of a short period seismic network to derive a shallow crustal s wave velocity model at the sumatra fault in northern sumatra indonesia by correlating the noise of 40 seismic stations recording for 9 months we could recover rayleigh waves from vertical component recordings with sufficient signal to noise ratio group velocities of the rayleigh waves could be determined in the period range from 0 71 to 4 4 s these group velocities were used to invert for 2d group velocity maps at specific periods finally the derived group velocity maps were inverted for a 3d s wave velocity model this model shows a region of a strong velocity decrease off the great sumatran fault zone at the northeastern margin of the young tarutung pull apart basin this observed low velocity block coincides with a caldera like morphological feature which is interpreted as the surface expression of a hidden volcanic caldera considering the surface manifestations of geothermal activity around this anomaly we conclude that the caldera is still acting as a heat source on the other hand the weak morphological expression at the surface indicates a certain age of the caldera which might be older than the tarutung pull apart basin the findings provide important constraints on general concepts for the formation of pull apart basins along the sumatran fault and their relation to volcanism