rare earth elements in the sediments of the north atlantic ocean amazon delta and east china sea reinterpretation of terrigenous input patterns to the oceans

structure of the california coast ranges and san andreas fault at safod from seismic waveform inversion and reflection imaging 1 a seismic reflection and refraction survey across the san andreas fault saf near parkfield provides a detailed characterization of crustal structure across the location of the san andreas fault observatory at depth safod steep dip prestack migration and frequency domain acoustic waveform tomography were applied to obtain highly resolved images of the upper 5 km of the crust for 15 km on either side of the saf the resulting velocity model constrains the top of the salinian granite with great detail steep dip reflection seismic images show several strong amplitude vertical reflectors in the uppermost crust near safod that define an 2 km wide zone comprising the main saf and two or more local faults another prominent subvertical reflector at 2 4 km depth 9 km to the northeast of the saf marks the boundary between the franciscan terrane and the great valley sequence a deep seismic section of low resolution shows several reflectors in the salinian crust west of the saf two horizontal reflectors around 10 km depth correlate with strains of seismicity observed along strike of the saf they represent midcrustal shear zones partially decoupling the ductile lower crust from the brittle upper crust the deepest reflections from 25 km depth are interpreted as crust mantle boundary

development and applications of double difference seismic tomography double difference dd tomography is a generalization of dd location it simultaneously solves for the three dimensional velocity structure and seismic event locations dd tomography uses a combination of absolute and more accurate differential arrival times and hierarchically determines the velocity structure from larger scale to smaller scale this method is able to produce more accurate event locations and velocity structure near the source region than standard tomography which uses only absolute arrival times we conduct a stability and uncertainty analysis of dd tomography based on a synthetic data set currently three versions of the dd tomography algorithms exist tomodd tomofdd and tomoadd tomodd assumes a flat earth model and uses a pseudo bending ray tracing algorithm to find rays between events and stations while tomofdd uses a finite difference travel time algorithm and the curvature of the earth is considered both codes are based on a regularly distributed inversion grid with the former for a local scale and the latter for a regional scale in contrast tomoadd adapts the inversion mesh to match with the data distribution based on tetrahedral and voronoi diagrams we discuss examples of applying dd tomography to characterize fault zone structure image high resolution structure of subduction zones and determine the velocity structure of volcanoes

evidence of climatic variations in loess and cave palaeolithic sites of southern poland and western ukraine abstract two main types of palaeolithic sites in southern poland and western ukraine caves or rock shelters and loess sites offer different evidence concerning former climatic variations the most characteristic cave deposits for cold climatic conditions are angular cryoclastic limestone rubble and loess in cave entrances in loess profiles arctic conditions are clearly marked by the presence of ice wedge casts and soil wedges in cold and humid conditions solifluction and cryoturbation features characteristic of active layers and ground ice structures developed during periods of warm and humid climatic conditions cave loam and chemically weathered limestone rubble originated in caves intensive chemical weathering formed mineral crusts on surfaces of limestone particles the most distinct indicators of temperate climate in loess profiles are fossil soils forest or steppe ones depending on humidity remnants of animals especially those of stenothopic taxons provide very important evidence of environmental and climatic fluctuations the data from both types of sites complement each other precisely documented profiles of cave and loess sites cover the time span from the decline of penultimate glaciation to the end of vistulian time older cultural layers corresponding to the penultimate interglacial were found recently

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

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

a california statewide three dimensional seismic velocity model from both absolute and differential times abstract we obtain a seismic velocity model of the california crust and uppermost mantle using a regional scale double difference tomography algorithm we begin by using absolute arrival time picks to solve for a coarse three dimensional 3d p velocity v p model with a uniform 30 km horizontal node spacing which we then use as the starting model for a finer scale inversion using double difference tomography applied to absolute and differential pick times for computational reasons we split the state into 5 subregions with a grid spacing of 10 to 20 km and assemble our final statewide v p model by stitching together these local models we also solve for a statewide s wave model using s picks from both the southern california seismic network and usarray assuming a starting model based on the v p results and a v p v s ratio of 1 732 our new model has improved areal coverage compared with previous models extending 570 km in the sw ne direction and 1320 km in the nw se direction it also extends to greater depth due to the inclusion of substantial data at large epicentral distances our v p model generally agrees with previous separate regional models for northern and southern california but we also observe some new features such as high velocity anomalies at shallow depths in the klamath mountains and mount shasta area somewhat slow velocities in the northern coast ranges and slow anomalies beneath the sierra nevada at midcrustal and greater depths this model can be applied to a variety of regional scale studies in california such as developing a unified statewide earthquake location catalog and performing regional waveform modeling

a seismic refraction survey of the imperial valley region california the u s geological survey conducted an extensive seismic refraction survey in the imperial valley region of california in 1979 the imperial valley is located in the salton trough an active rift between the pacific and north american plates forty shots fired at seven shot points were recorded by 100 portable seismic instruments at typical spacing of 0 5 1 km more than 1300 recording locations were occupied and more than 3000 usable seismograms were obtained we analyzed five profiles using a standard ray tracing program constructed a contour map of reduced travel times from our most widely recorded shot point and modeled an existing gravity profile across the salton trough results are itemized 1 all models have in common a sedimentary layer vp 1 8 5 0 km s a transition zone vp 5 0 5 65 km s a basement vp 5 65 km s in the imperial valley 5 9 km s on the bordering mesas and subbasement vp 7 2 km s 2 the sedimentary layer ranges in thickness along the axis of the salton trough from 3 7 km salton sea to 4 8 km u s mexican border on the bordering mesas it is quite variable in thickness 3 the transition zone is about 1 km thick in most places in the imperial valley there are no marked velocity discontinuities in this zone between the sedimentary layer and basement on the bordering mesas however there is a discontinuity at the top of this zone 4 there are apparently two types of basement on the bordering mesas basement is crystalline igneous and metamorphic rocks in the imperial valley basement is mostly lower greenshist facies sedimentary rocks based primarily on the smooth transition in character from sediment to basement arrivals the low value of basement velocity and the fact that deep 4 km wells in the valley penetrate only the upper part of the known cenozoic stratigraphic column for the salton trough 5 the subbasement or intermediate crustal layer ranges in depth along the axis of the salton trough from 16 km salton sea to 10 km u s mexican border gravity modeling requires that this layer deepen and or pinch out beneath the bordering mesas and mountain ranges based on its high velocity and the presence of intrusive basaltic rocks in the sedimentary section in the imperial valley the subbasement is thought to be a mafic intrusive complex similar to oceanic middle crust 6 several structures are seen that affect basement transition zone and deeper parts of the sedimentary layer they include a scarp along the imperial fault as much as 1 km down to the northeast and a scarp passing roughly along the topographic boundary between the imperial valley and the bordering mesa to the west as much as 3 km down to the east we interpret the latter scarp to be the suture or rift boundary between the older crystalline basement on the mesa and the younger metasedimentary basement in the imperial valley 7 on a contour map of reduced travel time from our most widely recorded shot point subtle patches of early arrivals among otherwise late arrivals in the central imperial valley correlate well with known geothermal resource areas having reservoir temperatures of more than 150 c apparently the salton trough is a location where new crust is being generated as the rift opens mafic intrusive rocks fill it from below as sedimentary rocks fill it from above rifting and intrusion produce high heat flow that metamorphoses the sedimentary rocks to shallow depth metasedimentary basement in the imperial valley and thus consolidates the new crust

loess paleosol formation on the russian plain abstract the east european loess province is the largest one not only in the northern hemisphere but also on the earth the chronostratigraphic scheme for this province was worked out on the basis of data obtained by different research methods accumulation of loess like deposits began at the end of the pliocene in the post akchagilian time deposition of silt material and loess formation began in the second half of the eopleistocene during this period up to the holocene about 1 ma 6 interglacial soil complexes can be identified according to paleomagnetic data the brunhes matuyama boundary occurs within the don loess which corresponds to maximum don glaciation of eastern europe the composition of the loess paleosol complex of the middle pleistocene is much more complicated there are 3 interglacial soil horizons overlain by the middle pleistocene moraine of the dnieper glaciation a well developed interstadial soil horizon bryansk soil can be distinguished within the late pleistocene formation 32 26 ka bp the structure of the loess paleosol complex varies over different regions of the east european loess province these differences can be shown on a new type of map that of loess paleosol chronocomplexes

deformation in the lower crust of the san andreas fault system in northern california a continuous seismic velocity and reflectivity cross section of the san andreas fault system in northern california shows offsets in the lower crust and the mohorovicic discontinuity near the san andreas and maacama strike slip faults these faults may cut through the crust to the upper mantle in a zone less than 10 kilometers wide the northern california continental margin to the eastern edge of the coast ranges is underlain by a high velocity lowermost crustal layer that may have been emplaced within 2 million years following the removal of the gorda plate slab the rapid emplacement and structure within this layer are difficult to reconcile with existing tectonic models

three dimensional vp and vp vs structure at loma prieta california from local earthquake tomography p and s p times from local earthquakes and p times from explosions at seismic stations in the vicinity of the 1989 loma prieta earthquake are inverted simultaneously to produce three dimensional images of vp and vp vs structure along the rupture zone the results confirm the presence of the major heterogeneities identified in previous studies using p waves only including high vp along the rupture in areas of significant slip and a low velocity wedge along the san andreas at the se edge of the rupture a change in rock properties evidenced by a significant vp vs increase equal to a 30 poisson s ratio increase from the middle crust to the upper crust may have been responsible for the upward termination of the main shock rupture we speculate that the deep high vp body that lies along the se portion of the rupture zone consists of two bodies based on model results indicating that the sw part of the body has relatively high vp vs while the ne part has relatively low vp vs

three dimensional p wave velocity model for the san francisco bay region california 1 a new three dimensional p wave velocity model for the greater san francisco bay region has been derived using the double difference seismic tomography method using data from about 5 500 chemical explosions or air gun blasts and approximately 6 000 earthquakes the model region covers 140 km ne sw by 240 km nw se extending from 20 km south of monterey to santa rosa and reaching from the pacific coast to the edge of the great valley our model provides the first regional view of a number of basement highs that are imaged in the uppermost few kilometers of the model and images a number of velocity anomaly lows associated with known mesozoic and cenozoic basins in the study area high velocity vp 6 5 km s features at 15 km depth beneath part of the edge of the great valley and along the san francisco peninsula are interpreted as ophiolite bodies the relocated earthquakes provide a clear picture of the geometry of the major faults in the region illuminating fault dips that are generally consistent with previous studies ninety five percent of the earthquakes have depths between 2 3 and 15 2 km and the corresponding seismic velocities at the hypocenters range from 4 8 km s presumably corresponding to franciscan basement or mesozoic sedimentary rocks of the great valley sequence to 6 8 km s the top of the seismogenic zone is thus largely controlled by basement depth but the base of the seismogenic zone is not restricted to seismic velocities of 6 3 km s in this region as had been previously proposed

the changing vision of marine minerals abstract non fuel marine minerals are reviewed from the perspective of resources and their value as active analogs that can advance understanding of types of ancient ore deposits that formed in marine settings the theory of plate tectonics is the largest influence in expanding our vision of marine minerals and in developing our understanding of geologic controls of mineralization in space and time prior to the advent of plate tectonics we viewed the ocean basins as passive sinks that served as containers for particulate and dissolved material eroded from land this view adequately explained marine placer deposits heavy minerals and gems aggregates sand and gravel and precipitates phosphorites and manganese nodules although numerous sites of placer mineral deposits are known on continental shelves worldwide current activity pertains to diamond mining off southwestern africa tin mining off southeastern asia and intermittent gold mining off northwestern north america which are all surpassed economically by worldwide recovery of marine sand and gravel in turn dwarfed by offshore oil and gas with the advent of plate tectonics plate boundaries in ocean basins are recognized as active sources of mineralization in the form of hydrothermal massive sulfide deposits and proximal lower temperature deposits hosted in oceanic crust mafic at ocean ridges and felsic at volcanic island arcs and of magmatic ni cu sulfide chromite and pge deposits inferred to be present in the oceanic upper mantle lower crust based on their occurrence in ophiolites some 300 sites of hydrothermal active and relict mineralization most of them minor are known at this early stage of seafloor exploration on ocean ridges in fore arc volcanoes at back arc spreading axes and in arc rifts deposits formed at spreading axes and transported off axis by spreading are present in oceanic lithosphere but are virtually unknown the tag trans atlantic geotraverse hydrothermal field in the axial valley of the mid atlantic ridge latitude 26 n is considered to exemplify a major volcanogenic massive sulfide vms deposit forming at a spreading axis the most prospective of these occurrences lie within the 200 nautical mile 370 km wide exclusive economic zone eez of the nations of the volcanic island arcs of the western pacific where metal content of massive sulfides ag au ba cu pb sb zn exceeds that at ocean ridges plate tectonics early provided a framework for mineralization on the scale of global plate boundaries and is providing guidance to gradually converge on sites of mineralization through regional scales of plate reorganization with the potential to elucidate the occurrence of individual deposits e g eocene carlin type gold deposits investigation of the spectrum of marine minerals as active analogs of types of ancient mineral deposits is contributing to this convergence consideration of questions posed by brian skinner 1997 of what we do and do not know about ancient hydrothermal mineral deposits demonstrates the ongoing advances in understanding driven by investigation of marine minerals

resources of the sea floor in his perspective rona reviews recent advances in knowledge of sea floor resources knowledge is expanding from those minerals eroded from land metals gemstones sand and gravel to those minerals concentrated by plate tectonic processes in ocean basins exploration of the oceans is at an early stage and development of marine mining is subject to economic and environmental considerations

periglacial markers within the late pleistocene loess palaeosol sequences in poland and western ukraine abstract stratigraphic loess palaeosol sequences represent exceptional climate controlled terrestrial records of interglacial glacial cycles one of the most spectacular features within the northern part of the european loess belt is the occurrence of well preserved relicts of the periglacial structures from a variety of periglacial structures three types are especially useful to reconstruct the former periglacial environment cryogenic wedges with primary mineral infilling cryoturbation and gelifluction structures and ice wedge casts these structures form well distinguishable horizons within loess palaeosol sequences and their stratigraphic positions are not random periglacial horizons recorded in the late pleistocene loess palaeosol sequences in the study area were formed as a result of extreme climatic conditions and or rapid environmental changes during cold events of the last glacial period these horizons are noted in almost all investigated sections and thus they can be used as stratigraphic markers the number of periglacial horizons and their morphological features vary depending on their geographical settings and local conditions the periglacial record indicates the occurrence of four main cold stages during the last glacial period two earlier stages are recorded in the last interglacial early glacial palaeosol complex their onset was probably rapid these short cold periods can be correlated with mis 5d and 5b the next two periglacial stages most probably correspond with mis 4 and 2 only during the last two stages were ice wedges formed in the northern zone of the investigated loess area this record indicates the twofold expansion and disappearance of the permafrost during the last glacial period

regional three dimensional seismic velocity model of the crust and uppermost mantle of northern california 1 we present a three dimensional 3d tomographic model of the p wave velocity vp structure of northern california we employed a regional scale double difference tomography algorithm that incorporates a finite difference travel time calculator and spatial smoothing constraints arrival times from earthquakes and travel times from controlled source explosions recorded at network and or temporary stations were inverted for vp on a 3d grid with horizontal node spacing of 10 to 20 km and vertical node spacing of 3 to 8 km our model provides an unprecedented comprehensive view of the regional scale structure of northern california putting many previously identified features into a broader regional context and improving the resolution of a number of them and revealing a number of new features especially in the middle and lower crust that have never before been reported examples of the former include the complex subducting gorda slab a steep deeply penetrating fault beneath the sacramento river delta crustal low velocity zones beneath geysers clear lake and long valley and the high velocity ophiolite body underlying the great valley examples of the latter include mid crustal low velocity zones beneath mount shasta and north of lake tahoe

influence of the kuroshio current intrusion on depositional environment in the northern south china sea evidence from surface sediment records the influence of the kuroshio current kc intrusion on the depositional environment of the northern south china sea scs is discussed based on multi proxies of surface sediments including planktonic foraminifera clay minerals and geochemical elements the results reveal that four typical planktonic foraminifera globigerinoides ruber g sacculifer neogloboquadrina dutertrei and pulleniatina obliquiloculata can be used to trace the kc flow route in the northern scs globigerinoides ruber is mainly distributed in shallower water than the south china sea branch of the kuroshio scsbk flow route while p obliquiloculata is mostly distributed in deeper water than the scsbk flow route there are high percentages of g sacculifer and n dutertrei at the scsbk flow route along the 1000 m isobath where bottom sediments consist of clayey silt and silty clay the scsbk also affects sediment distribution of various sources taiwan sourced sediments characterized by high illite and chlorite contents are transported southwestward into the deep sea environment by the scsbk and or deep water current the pearl river sediments characterized by high kaolinite and titanium ti contents are mostly transported southwestward to be distributed in the sea environment between the pearl river mouth and southeast of hainan island but hardly entered the abyssal basin the luzon island sediments characterized by high smectite content are generally deposited at the northwest of luzon island under the effect of an eddy west of luzon island these sediments were hardly transported northwestward onto the northern shelf of the scs throughout the scsbk flow route the sedimentary environment at the northwest of luzon island is relatively oxidized and higher in salinity than the northern scs which is probably connected with the kc intrusion through the luzon strait

three dimensional seismic model of the sierra nevada arc california and its implications for crustal and upper mantle composition a three dimensional p wave velocity model of south central california from the coast ranges to the sierra nevada shows that the crust under most of the southern sierra nevada batholith has seismic velocities 5 9 6 3 km s below the continental average the crust is not much thicker on average about 35 km than in the adjacent great valley and basin and range province apart from a small northward thickening crustal root under the western sierra nevada that reaches a depth of 42 km crustal velocities above the continental average are observed beneath much of the great valley due to a high velocity body underlying the sedimentary basin and the foothills metamorphic belt 6 4 7 0 km s upper mantle velocities are generally low 7 8 km s but span a wide range 7 4 8 2 km s we display the velocity model in several cross sections and maps of moho depth and average crustal velocity the measured velocities in the upper and mid crust of the sierra nevada batholith are in good agreement with laboratory measurements on sierra nevada tonalites after corrections for density and temperature peridotite xenoliths from the eastern sierra nevada suggest strong upper mantle anisotropy which could explain some of the velocity heterogeneity in the sierra nevada mantle by the time cretaceous subduction related magmatism ceased the sierra nevada arc must have had a thick mafic lower crust yet a principal result of our work is that today the batholith has a crust of mainly felsic composition throughout a subcrustal layer with velocities below normal pn velocities 7 6 km s may indicate the presence of lower crustal material in eclogite facies

a three dimensional crustal seismic velocity model for southern california from a composite event method we present a new crustal seismic velocity model for southern california derived from p and s arrival times from local earthquakes and explosions to reduce the volume of data and ensure a more uniform source distribution we compute composite event picks for 2597 distributed master events that include pick information for other events within spheres of 2 km radius the approach reduces random picking error and maximizes the number of s wave picks to constrain absolute event locations and shallow velocity structure we also use times from controlled sources including both refraction shots and quarries we implement the simulps tomography algorithm to obtain three dimensional 3 d v p and v p v s structure and hypocenter locations of the composite events our new velocity model in general agrees with previous studies resolving low velocity features at shallow depths in the basins and some high velocity features in the midcrust using our velocity model and 3 d ray tracing we relocate about 450 000 earthquakes from 1981 to 2005 we observe a weak correlation between seismic velocities and earthquake occurrence with shallow earthquakes mostly occurring in high p velocity regions and midcrustal earthquakes occurring in low p velocity regions in addition most seismicity occurs in regions with relatively low v p v s ratios although aftershock sequences following large earthquakes are often an exception to this pattern

crustal structure and tectonics from the los angeles basin to the mojave desert southern california a seismic refraction and low fold reflection survey known as the los angeles region seismic experiment larse was conducted along a transect line 1 extending from seal beach california to the mojave desert crossing the los angeles and san gabriel valley basins and san gabriel mountains the chief result of this survey is an interpreted cross section that addresses a number of questions regarding the crustal structure and tectonics of southern california that have been debated for decades and have important implications for earthquake hazard assessment the results or constraints are as follows 1 the maximum depth of the los angeles basin along line 1 is 8 9 km 2 the deep structure of the sierra madre fault zone in the northern san gabriel valley is as follows the duarte branch of the sierra madre fault zone forms a buried 2 5 km high moderately north dipping buttress between the sedimentary and volcanic rocks of the san gabriel valley and the igneous and metamorphic rocks of the san gabriel mountains for deeper structure see following 3 there are active crustal decollements in southern california at middle crustal depths the sierra madre fault zone appears to sole into a master decollement that terminates northward at the san andreas fault and projects southward beneath the san gabriel valley to the puente hills blind thrust fault 4 the dip and depth extent of the san andreas fault along line 1 dips steeply 83 northward and extends to at least the moho 5 the subsurface lateral extent of the pelona schist in southern california is as follows along line 1 the pelona schist underlies much if not all of the san gabriel mountains south of the san andreas fault to middle crustal depths north of the san andreas fault it is apparently not present along the transect

regional extent of great valley basement west of the great valley california implications for extensive tectonic wedging in the california coast ranges interpretation and modeling of the magnetic field of central california indicate that the magnetic basement of the forearc deposits of the great valley sequence extends westward beneath the coeval subduction related rocks of the franciscan complex the basement surface slopes gently to the west reaching midcrustal depths 15 19 km at distances of 50 100 km west of the great valley this magnetic basement is disrupted by the hayward rodgers creek fault system and is cut by the san andreas fault at the south end of the great valley and possibly throughout much of central california the widespread presence of the great valley basement beneath rocks of the franciscan complex implies that the basement is more extensive than proposed in earlier interpretations based on seismic studies near the franciscan complex great valley sequence contact this result forces major modifications to ideas concerning this fossil subduction complex and other subduction zones the eastern boundary fault of the franciscan complex coast range fault is not and never was a subduction zone thrust fault but rather was originally a roof thrust wedge roof fault formed above the eastward wedging mass of franciscan complex intruded along the top of the basement beneath the great valley deposits this tectonic interpretation offers a solution for the question of how high pressure metamorphic rocks of the franciscan complex were juxtaposed at the coast range fault against low pressure metamorphic rocks of the great valley sequence this interpretation also implies an older flat lying thrust fault wedge floor fault that forms the top of magnetic basement between the active san andreas and hayward faults at depths of 15 17 km this older thrust fault may today transfer strain between the two young strike slip faults possibly explaining the apparent coupling of major nineteenth century earthquakes on these two faults the former east dipping subduction zone along which the rocks of the franciscan complex accumulated must lie west of the western limit of the great valley magnetic basement

regional tectonics of the coso geothermal area along the intracontinental plate boundary in central eastern california three dimensional vp and vp vs models spatial temporal seismicity patterns and seismogenic deformation we synthesize the tectonics of the southern walker lane belt and coso range in central eastern california using regional earthquake data first we invert for three dimensional models of the v p and v p v s structure of the upper and middle crust using these models we also determine three dimensional vs and poisson s ratio models the changes in seismic velocities across the region are small except for low velocities in sedimentary basins and a 2 km positive elevation of the basement velocities v p 6 km s beneath the southern sierra nevada localized low v p and low v s zones beneath the central coso range image a geothermal reservoir at 0 to 3 km depth as well as distinct low velocity anomalies in the depth range of 8 to 12 km because the v p v s has average crustal values within this broader zone we interpret the anomaly to indicate a zone of few percent geothermal brines extending from 8 to 12 km depth in addition an embedded highly localized poorly resolved zone possibly as small as 1 km 3 of slightly above average v p v s and higher poisson s ratio is a tentative suggestion of a small volume percent of magma present at depth of 10 km second we relocated the seismicity in the region using absolute traveltimes and differential traveltimes determined from waveform cross correlation the relocated seismicity forms several spatially clustered lineaments along the southeast side of the sierra nevada and in the indian wells valley and vicinity of the coso geothermal field which coincide with mapped late quaternary faults in the region the base of seismicity shallows from a regional depth of about 11 to 5 km beneath the central coso range which we interpret as evidence for shallowing of the brittle ductile transition zone beneath the geothermal field in addition to abundant background seismicity two large earthquake swarms located 5 to 8 km to the west of coso occurred in april to may 1992 and may to june 2001 two dual main shock aftershock sequences also occurred as follows the 1994 sequence near ridgecrest and the later coso earthquake sequence from late 1996 to early 1998 with the pairs of main shocks spaced 47 days and 16 months apart respectively kinematic analysis of the focal mechanisms indicates that the crustal stress loading process varies across the region the low vp anomaly abundant seismicity and crustal thinning provide quantitative evidence for the coso region being an extensional releasing step over between two northwest striking dextral faults the little lake and airport lake fault zones to the south and the owens valley fault to the north

the san gabriel mountains bright reflective zone possible evidence of young mid crustal thrust faulting in southern california abstract during the los angeles region seismic experiment larse a reflection refraction survey was conducted along a line extending northeastward from seal beach california to the mojave desert crossing the los angeles basin and san gabriel mountains shots and receivers were spaced most densely through the san gabriel mountains for the purpose of obtaining a combined reflection and refraction image of the crust in that area a stack of common midpoint cmp data reveals a bright reflective zone 1 s thick that dominates the stack and extends throughout most of the mid crust of the san gabriel mountains the top of this zone ranges in depth from 6 s 18 km depth in the southern san gabriel mountains to 7 5 s 23 km depth in the northern san gabriel mountains the zone bends downward beneath the surface traces of the san gabriel and san andreas faults it is brightest between these two faults where it is given the name san gabriel mountains bright spot sgmbs and becomes more poorly defined south of the san gabriel fault and north of the san andreas fault the polarity of the seismic signal at the top of this zone is clearly negative and our analysis suggests it represents a negative velocity step the magnitude of the velocity step is approximately 1 7 km s in at least one location an event with positive polarity can be observed 0 2 s beneath the top of this zone indicating a thickness of the order of 500 m for the low velocity zone at this location several factors combine to make the preferred interpretation of this bright reflective zone a young fault zone possibly a master decollement 1 it represents a significant velocity reduction if the rocks in this zone contain fluids such a reduction could be caused by a differential change in fluid pressure between the caprock and the rocks in the sgmbs near lithostatic fluid pressure is required in the sgmbs such differential changes are believed to occur in the neighborhood of active fault zones where fault value action has been postulated less likely alternative explanations for this velocity reduction include the presence of magma and a change in composition to serpentinite or metagraywacke 2 it occurs at or near the brittle ductile transition at least in the southern san gabriel mountains a possible zone of concentrated shear 3 a thin reflection rising from its top in the southern san gabriel mountains projects to the hypocenter of the 1987 m 5 9 whittier narrows earthquake a blind thrust fault earthquake with one focal plane subparallel to the reflection alternatively one could argue that the bends or disruptions in the reflective zone seen at the san gabriel and san andreas faults are actually offsets and that the reflective zone is therefore an older feature possibly an older fault zone

seismic velocity structure and seismotectonics of the eastern san francisco bay region california the hayward fault system is considered the most likely fault system in the san francisco bay area california to produce a major earthquake in the next 30 years to better understand this fault system we use microseismicity to study its structure and kinematics we present a new 3d seismic velocity model for the eastern san francisco bay region using microseismicity and controlled sources which reveals a 10 velocity contrast across the hayward fault in the upper 10 km with higher velocity in the franciscan complex to the west relative to the great valley sequence to the east this contrast is imaged more sharply in our localized model than in previous regional scale models thick cenozoic sedimentary basins such as the livermore basin which may experience particularly strong shaking during an earthquake are imaged in the model the accurate earthquake locations and focal mechanisms obtained by using the 3d model allow us to study fault complexity and its implications for seismic hazard the relocated hypocenters along the hayward fault in general are consistent with a near vertical or steeply east dipping fault zone the southern hayward fault merges smoothly with the calaveras fault at depth suggesting that large earthquakes may rupture across both faults the use of the 3d velocity model reveals that most earthquakes along the hayward fault have near vertical strike slip focal mechanisms consistent with the large scale orientation and sense of slip of the fault with no evidence for zones of complex fracturing acting as barriers to earthquake rupture online material velocity model validation experiments and additional seismicity plots

loess in a cave lithostratigraphic and correlative value of loess and loess like layers in caves from the krakow czestochowa upland poland abstract although debris loams and clays are usually regarded as typical cave sediments loess and loess like sediments are common among clastic cave deposits in the near entrance facies of caves and rock shelters late weichselian loess layers are very common in caves from the krakow czestochowa upland and were recognized in almost each excavated cave and rock shelter these layers were initially dated to the lgm last glacial maximum but new chronometric dating results are available that allow us to present a more detailed scheme of the geological age of the series this paper evaluates the significance of polish in cave loess layers as correlative horizons we present the lateral and vertical stratigraphy and lithological variability of cave loesses and their usefulness as lithostratigraphic markers these features are especially important for archeology and paleontology as cave sediments including loess are usually the carriers of archeological and paleontological material

climatic stages recorded in sediments of the gunang cave south korea abstract this paper presents and analyses lithological stratigraphic and geochronological data on the gunang cave which is an important archaeological site in south korea it discusses problems of the age and origin of its sedimentary sequence which consists of clastics and hardpan speleothems the sediments compose a 4 m thick lens near the cave entrance the lens formed during the middle late pleistocene and holocene according to 14 c and u th dating the changes of cave environments are reconstructed based on sedimentological palynological mineralogical magnetic and geochemical data the clastic sediment unit consists of roof fallen limestone debris cemented by fine grained matrix the matrix is dominated by silt 80 which aeolian component is 60 65 the amount of the wind blown component is persistent throughout the clastic layers suggesting a relatively stable depositional process in dry environment in contrast three lime cemented hardpans formed in a wet environment of groundwater seepage the revised age model suggests that the hardpans formed in early mis1 mis 5 5 and mis 7 and therefore correspond to the wetness maximums of these warm stages

three dimensional velocity structure seismicity and fault structure in the parkfield region central california this study examines the three dimensional velocity structure in a 60 by 80 km region containing the parkfield segment of the san andreas fault we use local earthquake and shot p arrival times in an iterative simultaneous inversion for velocity and hypocentral parameters using the three dimensional model we relocated 5251 events that occurred from 1969 to 1991 as well as the 1966 aftershocks and computed 664 fault plane solutions the san andreas fault saf characterized by a sharp across fault velocity gradient is the primary feature in the velocity solution there is a 5 20 lateral change in velocity over a 4 km width the contrast being sharper where there is better resolution the model also shows significant variations in the velocity and in the complexity of the velocity patterns along the saf the largest across fault velocity difference is below middle mountain where a large volume of low velocity material impinges on the saf from the northeast this material is inferred to be overpressured and may be key to understanding the unusual behavior in the parkfield preparation zone a 20 km long high velocity slice is imaged northeast of the saf near gold hill its along fault length corresponds to the length of the maximum slip in 1966 the relocated seismicity shows that the san andreas fault is a planar vertical fault zone at seismogenic depths ninety percent of the fault plane solutions that are on or near the saf were right lateral strike slip on subvertical fault planes that parallel the saf thus the surface fault complexities do not appear to extend to depth and therefore do not explain the rupture character at parkfield at parkfield variations in material properties play a key role in fault segmentation and deformation style our observations suggest that there may be a general relation between increasing velocity and increasing ability of the rocks to store strain energy and release it as brittle failure

rare metal elements in surface sediment from five bays on the northeastern coast of the south china sea we studied the distribution of rare metal elements rme zr sn ti y nb ta ce la nd and th in surface sediments from five bays along the northeastern coast of the south china sea the results of the study elucidated the main controlling factors and the mineralization potential of these bays as metals placers the rme contents of surface sediments are highly variable but show clear geographic regularities the content of all studied elements in this area decreases from east to west with the maximum average content in shantou st bay which also contains the overall maximum element content the minimum overall contents were found in daya dy bay the weak correlation between the fine sediment fraction and these elements suggests that they occur mainly in the form of metallic minerals the relative abundance of these elements in the two easternmost bays st and zhelin zl bays is attributed to the large amounts of terrigenous material input by the hanjiang river and other small rivers st and zl bays sediments are rich in zircon cassiterite ilmenite or rutile xenotime monazite niobium tantalite and other rare metal minerals thus these bays are good prospects as rare metal placer resources shanwei sw and dapeng dp bays show mineralization potential mostly for zircon and ilmenite or rutile respectively

clay mineral distribution in surface sediments of the northeastern south china sea and surrounding fluvial drainage basins source and transport clay mineralogy of surface samples throughout the northeastern south china sea scs and surrounding fluvial drainage basins has been investigated to reveal source and transport of detrital fine grained sediments three characteristic end members in clay mineral compositions were observed from three major provenances respectively major kaolinite and moderate illite and chlorite from the pearl river predominant illite and chlorite from taiwan and principal smectite from the luzon arc system the transport of four clay mineral species in the northeastern scs is influenced by various mechanisms smectite derived from the luzon arc system is transported mainly by surface current with significant influence of the kuroshio intrusion illite and chlorite from taiwan are mainly carried by deep water current while kaolinite from the pearl river is affected obviously by the westward guangdong coastal current and longshore current a westerly tongue shaped distribution of high contents of illite and chlorite mainly from taiwan on the eastern shelf may result from the westward guangdong coastal current during the winter the results suggest that clay mineral assemblages in the northeastern scs are mainly controlled by provenance supply and current transport and their downcore records do not bear contemporaneous paleoclimatic features the implication of clay minerals for proxies of the late quaternary east asian monsoon evolution is realized through both the provenance supply and current transport processes c 2010 elsevier b v all rights reserved

the rare earth element compositions of the changjiang yangtze and huanghe yellow river sediments thirty four samples from the changjiang and huanghe were analyzed to characterize their rare earth element ree compositions although ree concentrations in the changjiang sediments are higher than those of the huanghe sediments the former are less variable bulk samples and acid leachable fractions have convex ree patterns and middle ree enrichments relative to upper continental crust whereas flat patterns are present in the residual fractions source rock composition is the primary control on ree composition and weathering processes play a minor role grain size exerts some influence on ree composition as demonstrated by the higher ree contents of clay minerals in sediments from both rivers heavy minerals contribute about 10 20 of the total ree in the sediments apatite is rare in the river sediments and contributes less than 2 of the ree content but other heavy minerals such as sphene allanite and zircon are important reservoirs of residual ree fractions the fe mn oxides phase accounts for about 14 of bulk ree content in the changjiang sediments which could be one of the more important factors controlling ree fractionation in the leachable fraction 6 2002 elsevier science b v all rights reserved

multi scale tomography for crustal p and s velocities in southern california seismic tomography is a viable tool in building depth velocity models in the presence of strong lateral velocity variations in this study 3 d p and s velocity models for the crust of southern california are constrained using more than 1 000 000 p wave first arrivals and 130 000 s wave arrivals from local earthquakes to cope with the uneven distribution of raypaths a multi scale tomography is applied with overlapping model cells of different sizes within the 300 480 39 km3 model volume the smallest cell size is 10 10 3 km3 during the iterations of velocity updating earthquake hypocenters are determined using both p and s arrivals and full 3 d ray tracing is implemented except near the edges and in the lower crust the resultant models are robust according to various tests on the effects of reference models resolution and signal to noise ratio the tomographic velocities at shallow depths correlate very well with the regional geology of southern california in the upper crust the p wave and s wave models exhibit slow velocities in major sedimentary basins and fast velocities in areas of crystalline rocks mid crustal low velocity zones are present under the coso range san gabriel mountains and a large portion of the mojave desert p and s velocity patterns maintain their similarity in the lower crust though the models are less reliable there

earthquake travel time tomography of the southern santa cruz mountains control of fault rupture by lithological heterogeneity of the san andreas fault zone the 1989 loma prieta earthquake occurred along the stretch of the san andreas fault zone within the southern santa cruz mountains that last failed as a major earthquake in 1906 the southeastern end of the 1989 rupture marks the transition from stable aseismic slip on the central creeping section of the san andreas fault to unstable failure on the locked 1906 segment we investigate this transition and the rupture characteristics of the 1989 earthquake using a three dimensional p wave velocity model of the southern santa cruz mountains section of the fault zone the velocity model was determined by joint progressive inversion of 5422 p wave arrival times from 173 earthquakes which included aftershocks of the 1989 earthquake and premainshock background events recorded by the u s geological survey central california network this velocity model was used to relocate 424 background earthquakes the loma prieta mainshock and 292 aftershocks the velocity model is calibrated in terms of lithology using laboratory data for california coast ranges rock types and available seismic refraction profiles and is shown to be in good agreement with the surface geology the model images a large anomalous high velocity body at midcrustal depths within the rupture zone of the 1989 earthquake that the available evidence suggests might have gabbroic or other mafic composition on the basis of the relationship of the lithological features interpreted from the velocity model to the seismicity and surface creep we propose a model in which the high velocity body is primarily responsible for the transition from stable to unstable fault slip at pajaro gap the active plane of the san andreas fault cuts throughout the body the fault system attempts to circumvent this barrier by transferring slip to secondary faults including splay faults that have propagated along the frictionally favorable contact between the high velocity rock mass and franciscan country rocks however the near arrest of stable sliding causes stress to concentrate within the body and the high strength unstable contact within it evolves from a barrier to the asperity that failed in the 1989 earthquake the general features of the 1989 rupture predicted by this asperity model agree with several rupture histories computed for the earthquake the model implies that as proposed by other workers the loma prieta earthquake did not involve a repeat of the 1906 slip which has an important bearing on earthquake recurrence estimates for the santa cruz mountains segment of the fault