mechanical validation of the three dimensional intersection geometry between the puente hills blind thrust system and the whittier fault los angeles california the sensitivity of fault interaction to alternative kinematically plausible intersection geometries of the puente hills blind thrust system and the whittier fault is modeled under geodetically constrained horizontal contraction comparisons of modeled slip rates to available geologic rates 1 suggest that the coyote hills seg ment of the puente hills system extends to the base of the seismogenic crust and 2 give slight preference for extension of the active whittier fault to the base of the seismogenic crust rather than limiting active slip to the hanging wall of the coyote hills fault furthermore analysis of strain energy density demonstrates that the pre ferred model has the greatest mechanical efficiency this correlation of fit to geologic slip rates and mechanical efficiency supports the effectiveness of this method for evaluating among alternative geometries in the absence of geologically constrained slip rates the methodology implemented in this study may be effectively used in future studies of deformation within fault systems model generated slip rates along the puente hills faults show significant strike slip implying that seismic hazard of these faults may be underestimated by consid ering reverse slip rates alone contraction at 036 may not be appropriate in the puente hills region because of resulting sinistral slip on the whittier fault which disagrees with paleoseisimc observations however whittier strike slip rates fit pa leoseismic rates under 006 5 contraction because strike slip rates are more sensitive to contraction direction than fault intersection geometry contraction direction should be further constrained in order to accurately assess seismic hazard on these faults

how sensitive are fault slip rates in the los angeles basin to tectonic boundary conditions geodetic studies have produced different interpretations of the relative vertical thickening versus escape tectonics occurring within the los angeles basin based on calculated horizontal strain rates ranging from 56 10 9 yr contraction at n36 et o 85 10 9 yr north south contraction and 60 10 9 yr east west extension three dimensional forward mechanical models of faults in the los an geles basin are used to compare modeled slip rates and slip styles represented as the rakes of average net slip vectors under four representative horizontal strain condi tions with geologically determined late quaternary slip rates and observed slip styles the comparisons strive to identify the most mechanically viable tectonic boundary conditions for the los angeles basin the three dimensional fault surfaces used within the mechanical models have been defined by southern california earthquake center scec workers based on surface geology and subsurface data the model results suggest that northeast southwest principal contraction is inappropriate for the los angeles basin because this tectonic boundary condition produces left lateral slip along the whittier and san gabriel faults in contrast with abundant geologic evidence of right lateral slip of the four tectonic boundary conditions evaluated north south contraction accompanied by either zero or slow east west contraction gives the low est mismatch of modeled and observed fault slip style these results suggest that vertical thickening may be more predominant than escape tectonics in this region

late quaternary slip rate of the central sierra madre fault southern california implications for slip partitioning and earthquake hazard abstract the sierra madre fault system accommodates contraction within a large restraining bend area of the san andreas fault along the northern margin of the los angeles metropolitan area in southern california reverse slip along this fault system during earthquakes controls growth of the san gabriel mountains and poses a significant seismic hazard to the region here we measure the late quaternary slip rate of the central sierra madre fault csmf using analysis of high resolution topography combined with cosmogenic 10be surface exposure dating and post ir irsl geochronology we mapped terrace and fan surfaces from three drainages that cross the csmf and correlate them based on deposit character and geomorphic position cosmogenic nuclide and luminescence ages are consistent amongst the three prominent surfaces offset 5 to 28 m across the fault zone age estimates for these surfaces are 53 21 15 ka 35 9 ka and 12 5 ka based on data from two dating methods at three locations refined by inset age relationships estimated slip for these geomorphic markers is more uncertain than the measured vertical separation due to uncertainties in fault dip and ranges from 7 5 5 4 3 1 m to 58 5 46 3 14 4 m incremental dip slip rate estimates from different age surfaces and locations overlap within uncertainty with median values ranging from 0 6 to 1 1 mm yr the average slip rate for all three generations of markers is 1 1 1 1 0 4 mm yr this late quaternary slip rate for the csmf is slower than estimates based on interseismic geodetic data and emphasizes the importance of contraction distributed across multiple structures south of the sierra madre fault when assessed against the geodetic shortening budget despite being the central portion of the broader sierra madre fault system the csmf has a slip rate similar to or lower than neighboring sections suggesting that slip transfer onto other nearby faults control the along strike pattern of deformation rate paleoseismic evidence indicates that the last earthquake on the csmf was in the early holocene and the slip rate we estimate suggests that the accumulated elastic strain could produce many meters of slip in future earthquakes

evidence for large earthquakes in metropolitan los angeles the sierra madre fault along the southern flank of the san gabriel mountains in the los angeles region has failed in magnitude 7 2 to 7 6 events at least twice in the past 15 000 years restoration of slip on the fault indicated a minimum of about 4 0 meters of slip from the most recent earthquake and suggests a total cumulative slip of about 10 5 meters for the past two prehistoric earthquakes large surface displacements and strong ground motions resulting from greater than magnitude 7 earthquakes within the los angeles region are not yet considered in most seismic hazard and risk assessments

biodegradation of oil in uplifted basins prevented by deep burial sterilization biodegradation of crude oil by bacterial activity which has occurred in the majority of the earth s oil reserves is known to reduce greatly the quality of petroleum in reservoirs for economically successful prospecting for oil it is therefore important to understand the processes and conditions in geological formations that lead to oil biodegradation although recent studies speculate that bacterial activity can potentially occur up to temperatures as high as 150 degrees c refs 3 4 it is generally accepted that effective petroleum biodegradation over geological timescales generally occurs in reservoirs with temperatures below 80 degrees c ref 2 this appears however to be at odds with the observation that non degraded oils can still be found in reservoirs below this temperature here we compile data regarding the extent of oil biodegradation in several oil reservoirs and find that the extensive occurrence of non biodegraded oil in shallow cool basins is restricted to those that have been uplifted from deeper hotter regions of the earth we suggest that these petroleum reservoirs were sterilized by heating to a temperature around 80 90 degrees c during deep burial inactivating hydrocarbon degrading organisms that occur in the deep biosphere even when such reservoirs are subsequently uplifted to much cooler regions and filled with oil degradation does not occur implying that the sterilized sediments are not recolonized by hydrocarbon degrading bacteria

ventilation of north pacific intermediate waters the role of the alaskan gyre hydrographic data tritium data and potential vorticity calculations suggest that although north pacific intermediate water is formed in the northwest the alaskan gyre might be an additional ventilation site the proposed ventilation is quantified by a vertical column tritium inventory which indicates an excess of 0 08 kg of tritium in the alaskan gyre an evaluation of the energy stored in the water column and of wind and buoyancy forcing shows that during winter conditions enough energy can be pumped into the system to force 26 80 to outcrop in the alaskan gyre model results suggest that relatively limited outcrops in time and space tens of days and several hundred kilometers in diameter can account for the excess tritium

using vertical rock uplift patterns to constrain the three dimensional fault configuration in the los angeles basin comparison of geologic uplift patterns with results of three dimensional mechanical models provides constraints on the fault geometry compiled by the south ern california earthquake center community fault model in the northern los angeles basin california the modeled uplift matches well the geologic pattern of uplift as sociated with the santa fe springs and coyote hills segments of the puente hills thrust fault but does not match structures to the west of the san gabriel river to better match the geologic patterns in this area alternative fault configurations were tested the best match to geologic uplift is attained with a model incorporating 1 a steep blind thrust fault at the location of the los angeles segment of the puente hills thrust system following interpretations of the las cienegas fault geometry at this location 2 removal of an inferred linking fault between the raymond and holly wood faults and 3 lateral continuation of the lower elysian park fault a blind low angle detachment at 10 km depth along strike to the northwest these geometric revisions alter the connectivity of northern los angeles basin faults and significantly improve the match of model uplift pattern to geologic data model results suggest that fault connectivity may be more important in governing fault slip rate than are fault dip and fault area the preferred model alters slip rates by 0 2 mm yr for the upper elysian park hollywood lower elysian park raymond sierra madre west and verdugo faults additionally the preferred model alters the surface area of several faults in the northern los angeles basin such as the puente hills thrust and the lower elysian park fault which may have important implications for seismic hazard assess ment in the northern los angeles basin

interseismic deformation associated with three dimensional faults in the greater los angeles region california 1 existing interseismic models are not well suited to simulate deformation within the network of finite intersecting nonplanar faults observed in the greater los angeles region instead of applying fault slip rates to a model a priori we allow three dimensional fault surfaces to interact and accumulate mechanically viable slip distributions and then use the deep nonseismogenic portion of slip to calculate interseismic deformation we apply this approach to the los angeles region and find that the geologic timescale model results match well geologic slip rate data and the interseismic timescale model results match well the heterogeneous gps velocity pattern in the los angeles region model results suggest that localized geodetic convergence in the san gabriel basin can be achieved with slip on multiple active fault surfaces in the los angeles region including relatively fast slip on the sierra madre fault and slow slip on the puente hills thrusts in agreement with geologic data the ability of the three dimensional model to reproduce well both geologic slip rates and interseismic geodetic velocity patterns suggests that current day contraction rates in the greater los angeles region are compatible with long term geologic deformation rates and disputes suggestions of significant temporal variations in fault slip rates inferred from existing investigations

the subarctic frontal zone in the north pacific characteristics of frontal structure from climatological data and synoptic surveys the subarctic front is a thermohaline structure across the north pacific separating colder fresher water to the north from warmer saltier water to the south levitus s 1982 data and 72 conductivity temperature depth salinity temperature depth sections are used to show the spatial and seasonal variations of the climatological frontal zone and the characteristics of the frontal structure in synoptic surveys the temperature gradient in the mean frontal zone is stronger in the western pacific and decreases eastward while the salinity gradient has less variation across the pacific the temperature gradient also has larger seasonal variation with a maximum in spring than the salinity gradient the synoptic surveys show that the frontal zone is narrower and individual fronts tend to be stronger in the western pacific than in the eastern pacific density gradients tend to be more compensated at the strongest salinity fronts than at the strongest temperature fronts a horizontal minimum of vertical stability is found south of the subarctic halocline outcrop the northern boundary of the north pacific intermediate water merges with the frontal zone west of 175 w and is north of the northern boundary of the subarctic frontal zone in the eastern pacific the shallow salinity minima start within the subarctic frontal zone in the eastern pacific

rates and processes of soil development on quaternary terraces in cajon pass california field and laboratory analyses of soils on 11 well dated fluvial terraces spanning the past 0 5 m y demonstrate that a threshold governs changes in several morphological and chemical characteristics of increasingly older soils correlations with respect to time among iron species soil morphology and soil silt and clay demonstrate that the chronosequence at cajon pass reflects primarily an evolutionary largely time dependent trend and does not reflect differences in external factors such as climate most of the soil development on holocene terraces of the cajon pass area is due to physical incorporation of eolian dust and organic material into initially very permeable gravels this process decreases soil permeability and is conducive for an increase in the magnitude of chemical weathering latest pleistocene and older pleistocene soils have developed clay and authigenic iron oxide rich b horizons at the expense of organic matter rich a horizons and color b horizons as the extent of chemical weathering has increased this conversion of the soil from a noncolloidal system to a much more colloidal system takes place over a relatively short period of time 4 000 yr and is herein defined as a type of pedologic threshold in the cajon pass area the attainment of the threshold and subsequent development of the argillic b horizon of soils on latest pleistocene terraces occurred during the holocene thus the absence of argillic horizons in soils on holocene terraces is attributable to simply their younger age rather than to the pleistocene to holocene climatic change the threshold is a function of several variables including influx rate of eolian dust and initial soil permeability therefore the time required to attain the threshold will vary in chronose quences characterized by geomorphic or geographic settings that are different from conditions found in cajon pass

escape tectonics in the los angeles metropolitan region and implications for seismic risk recent damaging earthquakes in california including the 1971 san fernando1 1983 coalinga2 1987 whittier narrows3 and 1994 northridge4 events have drawn attention to thrust faults as both potentially hazardous seismic sources and as a mechanism for accommodating shortening in many regions of southern california consequently many geological studies5 6 have concluded that thrust faults in southern california pose the greatest seismic hazard and also account for most of the estimated 5 7 mm yr 1 of contraction across the greater los angeles metropolitan area7 8 indicated by global positioning system geodetic measurements9 our study demonstrates however that less than 50 of the geodetically observed contraction is accommodated on the principal thrust systems across the los angeles region we integrate the most recent geological geodetic and seismological data to assess the spatial distribution of strain across the los angeles metropolitan region we then demonstrate that a significant component of seismic moment release and shortening in this region is accommodated by east west crustal escape extrusion along known strike slip and oblique slip faults

response of high rise and base isolated buildings to a hypothetical mw 7 0 blind thrust earthquake high rise flexible frame buildings are commonly considered to be resistant to shaking from the largest earthquakes in addition base isolation has become increasingly popular for critical buildings that should still function after an earthquake how will these two types of buildings perform if a large earthquake occurs beneath a metropolitan area to answer this question we simulated the near source ground motions of a m w 7 0 thrust earthquake and then mathematically modeled the response of a 20 story steel frame building and a 3 story base isolated building the synthesized ground motions were characterized by large displacement pulses up to 2 meters and large ground velocities these ground motions caused large deformation and possible collapse of the frame building and they required exceptional measures in the design of the base isolated building if it was to remain functional

roles of the okhotsk sea and gulf of alaska in forming the north pacific intermediate water recently obtained world ocean circulation experiment woce sections and pre woce hydrography are used to study the water mass structure and formation and transformation of north pacific intermediate water npiw five neutral density surfaces are selected and mapped encompassing npiw from 400 to 900 m in the subtropical latitudes with a distance of 100 m between a pair of surfaces npiw is defined as a subtropical gyre salinity minimum which is well followed by a neutral density surface n 26 9 formation and transformation of npiw is examined by the mapped turner angle on neutral density surfaces apparent diffusive double diffusion is found in the alaskan gyre on n 26 5 neutral surface in the northwest subpolar gyre and the okhotsk sea on n 26 9 neutral surface and mainly in the okhotsk sea on the two deep neutral surfaces n 27 2 and n 27 4 these diffusive regions indicate transformation sources for npiw along with additional information of potential vorticity and stream function it is found that there are two different npiw formation sources one in the gulf of alaska characterized by high potential vorticity and the other in the okhotsk sea characterized by low potential vorticity the former lies shallower at n 26 2 26 5 but its effect deepens to npiw core density level at n 26 8 on the basis of potential vorticity distribution the latter includes the influence of the northwest subpolar gyre and extends much deeper to n 27 4 we call them gulf of alaska intermediate water gaiw and okhotsk intermediate water oiw respectively gaiw contributes to npiw in the eastern part of the subtropical gyre east of date line whilst oiw dominates in the west and entire lower part of npiw seasonal flow stream function mapped on neutral surfaces shows that the contribution of gaiw to npiw occurs mainly in the wintertime because in winter a significant northward shift of zero wind stress curl makes the gulf of alaska an additional source for npiw

earthquake hazards of active blind thrust faults under the central los angeles basin california we document several blind thrust faults under the los angeles basin that if active and seismogenic are capable of generating large earthquakes m 6 3 to 7 3 pliocene to quaternary growth folds imaged in seismic reflection profiles record the existence size and slip rates of these blind faults the growth structures have shapes characteristic of fault bend folds above blind thrusts as demonstrated by balanced kinematic models geologic cross sections and axial surface maps we interpret the compton los alamitos trend as a growth fold above the compton ramp which extends along strike from west los angeles to at least the santa ana river the compton thrust is part of a larger fault system including a decollement and ramps beneath the elysian park and palos verdes trends the cienegas and coyote hills growth folds overlie additional blind thrusts in the elysian park trend that are not closely linked to the compton ramp analysis of folded pliocene to quaternary strata yields slip rates of 1 4 0 4 mm yr on the compton thrust and 1 7 0 4 mm yr on a ramp beneath the elysian park trend assuming that slip is released in large earthquakes we estimate magnitudes of 6 3 to 6 8 for earthquakes on individual ramp segments based on geometric segment sizes derived from axial surface maps multiple segment ruptures could yield larger earthquakes m 6 9 to 7 3 relations among magnitude coseismic displacement and slip rate yield an average recurrence interval of 380 years for single segment earthquakes and a range of 400 to 1300 years for multiple segment events if these newly documented blind thrust faults are active they will contribute substantially to the seismic hazards in los angeles because of their locations directly beneath the metropolitan area

active tectonics paleoseismology and seismic hazards of the hollywood fault northern los angeles basin california data from geotechnical boreholes and trenches in combination with geomorphologic mapping indicate that the hollywood fault is an oblique reverse left lateral fault that has undergone at least one surface rupturing earthquake during latest pleistocene to middle or late holocene time geomorphologic observations show that the fault extends for 14 km along the southern edge of the eastern santa monica mountains from the los angeles river westward through downtown hollywood to northwestern beverly hills where the locus of active deformation steps 1 2 km southward along the west beverly hills lineament to the santa monica fault rupture of the entire hollywood fault by itself could produce a m w 6 6 earthquake similar in size to the highly destructive 1994 northridge earthquake but even closer to more densely urbanized areas assuming a 0 35 mm yr minimum fault slip rate consistent with available geologic data we calculate an average maximum recurrence interval for such moderate events of 4000 yr although occurrence of such moderate events is consistent with the elapsed time since the poorly constrained age of the most recent surface rupture the data do not preclude a longer quiescent interval suggestive of larger earthquakes if earthquakes much larger than m w 6 6 occurred in the past we speculate that they may have been generated by the hollywood fault together with other faults in the transverse ranges southern boundary fault system

surface expression of thrust faulting in eastern iran source parameters and surface deformation of the 1978 tabas and 1968 ferdows earthquake sequences summary previously unrecognised thrust faults in eastern iran were responsible for a destructive earthquake at tabas 1978 september 16 which produced over 80 km of distributed and discontinuous surface ruptures above a series of low anticlinal hills to the west of a major range front analysis of long period body wave seismograms shows a simple rupture on a gently dipping 16 thrust with a slight right lateral component this is compatible with the locally recorded aftershock distribution body wave analysis of two later smaller events show similar source orientations several indicators of long term active folding at tabas can be recognised in the geomorphology and surface ruptures from 1978 are consistent with co seismic fold growth drainage incision also indicates uplift at depth on thrust faults dipping eastwards beneath the folds body wave seismograms for two earthquakes near ferdows 150 km east of tabas in september 1968 also show thrust faulting at depths of 10 km again the surface geomorphology indicates a region of folding above an eastward dipping thrust fault which is 10 km west of a fault bounded range front in both tabas and ferdows the active faulting appears to show quaternary migration away from the range front possibly in response to stresses produced by the elevated topography the identification of zones of active fault related folding is important for earthquake hazard assessment and also for an understanding of the local tectonics we conclude that the structures which gave rise to the 1968 and 1978 earthquakes could have been recognised beforehand from the clear signals in the geomorphology had we known what to look for at that time

shallow salinity minima in the north pacific abstract ctd std data from 24 cruises in the north pacific are studied for their vertical salinity structure and compared to bottle observations a triple salinity minimum is found in two separated regions in the eastern north pacific in the first region bounded by the northern edge of the subarctic frontal zone and the 34 n front between 160 and 150 w a middle salinity minimum is found below the permanent pycnocline in the density range of 26 0 and 26 5 this middle minimum underlies reid s shallow salinity minimum and overlies the north pacific intermediate water npiw in the second region southeast of the first a seasonal salinity minimum appears above the shallow salinity minimum at densities lower than 25 1 the shallow salinity minimum and the npiw can be found throughout year while the seasonal minimum only appears in summer and fall the middle and shallow salinity minima as well as the seasonal minimum originate at the sea surface in the northeast pacific the properties at the m

monitoring landslides and tectonic motions with the permanent scatterers technique spaceborne differential synthetic aperture radar interferometry dinsar has already proven its potential for mapping ground deformation phenomena e g volcano dynamics however atmospheric disturbances as well as phase decorrelation have prevented hitherto this technique from achieving full operational capability these drawbacks are overcome by carrying out measurements on a subset of image pixels corresponding to pointwise stable reflectors permanent scatterers ps and exploiting long temporal series of interferometric data results obtained by processing 55 images acquired by the european space agency esa ers sar sensors over southern california show that the ps approach pushes measurement accuracy very close to its theoretical limit about 1 mm allowing the description of millimetric deformation phenomena occurring in a complex fault system a comparison with corresponding displacement time series relative to permanent gps stations of the southern california integrated gps network scign is carried out moreover the pixel by pixel character of the ps analysis allows the exploitation of individual phase stable radar targets in low coherence areas this makes spaceborne interferometric measurements possible in vegetated areas as long as a sufficient spatial density of individual isolated man made structures or exposed rocks is available the evolution of the ancona landslide central italy was analysed by processing 61 ers images acquired in the time span between june 1992 and december 2000 the results have been compared with deformation values detected during optical levelling campaigns ordered by the municipality of ancona the characteristics of ps gps and optical levelling surveying are to some extent complementary a synergistic use of the three techniques could strongly enhance quality and reliability of ground deformation monitoring d 2002 elsevier science b v all rights reserved

dislocation modeling of blind thrusts in the eastern los angeles basin california 1 the east and west coyote hills in the eastern los angeles basin are the surface expression of uplift accompanying blind reverse faulting folded quaternary strata indicate that the hills are growing and that the faults underlying them are active detailed subsurface mapping in the east coyote oil field shows that a previously mapped reverse separation fault is predominantly an inactive left lateral strike slip fault that is not responsible for the uplift of the east coyote hills the fault responsible for folding and uplift of the coyote hills does not cut wells in either the east or west coyote oil fields to characterize the geometry of the blind fault responsible for folding we employ dislocation modeling the dip and upper fault tip depths obtained from modeling suggest that the thrust fault beneath the coyote hills may be an extension of the puente hills blind thrust fault that continues westward beneath the santa fe springs oil field modeling results suggest that the segment of the thrust fault responsible for folding the coyote hills would have accumulated 1500 m of reverse displacement over the last 1 2 myr yielding an average slip rate of 1 3 0 5 mm yr the santa fe springs segment of the fault has a slip rate of 1 5 0 4 mm yr for the last 1 2 myr the estimated moment magnitude for a reverse displacement earthquake on the puente hills blind thrust ranges from 6 6 to 7 2 depending on the length of the rupture the estimated average recurrence interval for these earthquakes is 1700 3200 years

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

woce line p1w in the sea of okhotsk 2 cfcs and the formation rate of intermediate water from august 30 to september 21 1993 temperature salinity nutrient and cfc data were collected along a section starting in the pacific ocean near bussol strait in the kuril islands crossing the basin and shelf region of the sea of okhotsk and ending near the coastal town of okhotsk at the northwest corner of the sea of okhotsk world ocean circulation experiment woce line p1w water on the continental shelf had potential density as great as 27 0 with high cfc concentrations and low temperature and salinity the sea of okhotsk intermediate water soiw ranging from 26 8 to 27 4 had uniform water properties along isopycnal surfaces that were distinctly different from either the north pacific intermediate water npiw or the shelf water found at the same density since the soiw was colder and fresher than the npiw we postulate that soiw is formed by sinking plumes and diapycnal mixing shelf derived water sdw as dense as 27 0 is formed on the shelf during the winter by cooling and brine rejection during ice formation prevailing winds move the sdw off the shelf where it sinks to an equilibrium depth and subsequently mixes isopycnally with north pacific water npw flowing into the sea of okhotsk through the kuril islands the observations on the shelf suggest that sdw directly modifies soiw to 27 0 using potential temperature salinity s and cfc data we calibrated a simple box model to determine the input of sdw into the soiw model results required a minimum of 0 9 sv 1 sv 10 6 m 3 s 1 of sdw in the formation of soiw and produced a minimum export of 2 7 sv of soiw from the sea of okhotsk our minimum calculated export of soiw into the north pacific ocean makes the sea of okhotsk a significant source of the salinity minimum present in the npiw below 27 2 the box model failed because the cfc concentrations of the sdw were too high this suggests that sdw directly ventilates the soiw to a maximum of 27 2 the unique properties of the soiw below 27 2 must be the result of diapycnal mixing in the sea of okhotsk and isopycnal mixing with inflowing npw

late quaternary rate of slip along the san jacinto fault zone near anza southern california the anza section of the san jacinto fault southern california has not experienced a groundbreaking earthquake since at least 1918 and probably since before 1899 leading previous workers to designate this 20 km long fault segment as a seismic gap study of displaced pleistocene and holocene alluvial fan and fluvial deposits across the san jacinto fault near anza california dated using 14c and soil development age control indicates a minimum right lateral slip rate of 9 2 2 mm yr since 9 5 ka and a slip rate of 11 9 5 mm yr since 14 ka 12 9 5 mm yr since 17 ka and 13 10 6 mm yr since 50 ka these estimates agree with a previously determined 700 ka to present minimum slip rate of 10 2 mm yr based on an estimated average slip rate of 12 mm yr from the longer term slip rate estimates about 0 8 m of potential slip has accumulated if the 1918 earthquake broke the anza segment over 1 1 m of potential slip has accumulated if the last earthquake occurred prior to 1899 these data attest to the potential for an earthquake m6 5 for this section of the fault

tectonics of the san gabriel basin and surroundings southern california the sangabriel basin is a pliocene pleistocene transverse ranges structure bounded by the san gabriel mountains on the north the san jose and puente hills on the east and the repetto and montebello hills on the west a basement boundary between gneissoid rocks of san gabriel mountains aspect and peninsular ranges rocks strikes east across the basin and connects with the san jose fault this boundary may represent the eastward continuation of the canton fault a middle miocene precursor of the san gabriel fault system with up to 30 km of right slip canton fault displacement is largely canceled by 22 5 km of left slip on a precursor to the raymond fault such that an oligocene dacite in the san jose hills and clasts derived from it show little evidence of large horizontal displacement between the san gabriel mountains and puente hills clockwise rotation in the middle miocene probably influenced the distribution of lateral slip the fill in the northeast trending pliocene pleistocene san gabriel basin is a basal shallow marine sequence overlain by the nonmarine duarte conglomerate in contrast to the deep water fernando formation of the los angeles basin the paleoslope trends south in the direction of the repetto and puente hills evidence that uplift of these hills postdated deposition the triangular san gabriel basin is currently a stable block bounded by the right slip northwest striking east montebello fault on the west and the left slip northeast striking walnut creek fault on the east farther east the san jose and puente hills are underlain by an east trending active fold belt including the san jose reverse fault and anticline the walnut anticline and the puente hills anticline adjacent to the right lateral whittier fault the east montebello fault is bounded on the west by the elysian park anticlinorium a fold belt in downtown los angeles the left slip holocene raymond fault joins the sierra madre reverse fault at its segment boundary marked by the clamshell sawpit fault the triangular stable block between east trending fold belts is bounded on the south by the puente hills blind thrust and on the north by the sierra madre fault documenting north south quaternary convergence east west extension is also indicated although not confirmed by geodetic measurements

interseismic strain accumulation and anthropogenic motion in metropolitan los angeles 1 we use global positioning system gps geodesy and synthetic aperture radar sar interferometry to distinguish between interseismic strain accumulation and anthropogenic motion in metropolitan los angeles we establish a relationship between horizontal and vertical seasonal oscillations of the santa ana aquifer use this relationship to infer cumulative horizontal anthropogenic motions from cumulative vertical motions caused by water and oil resource management and estimate horizontal interseismic velocities corrected for anthropogenic effects vertical anthropogenic rates from 1992 to 1999 are slower than 3 mm yr 1 in the santa ana and san gabriel aquifers and faster than 5 mm yr 1 in the chino aquifer and in many oil fields inferred horizontal anthropogenic velocities are faster than 1 mm yr 1 at 18 of 46 gps sites northern metropolitan los angeles is contracting with the 25 km south of the san gabriel mountains shortening at 4 5 1 mm yr 1 95 confidence limits the thrust fault in an elastic edge dislocation model of the observed strain is creeping at 9 2 mm yr 1 beneath and north of a position 6 2 km deep and 8 8 km north of downtown los angeles the model fault is near the los angeles segment of the puente hills thrust but south of the sante fe springs segment of the thrust disagreement between the 6 km locking depth in the model and the 15 km seismogenic depth inferred from earthquakes suggests that the elastic continuum model may be unsatisfactory models with different stiffnesses of sedimentary basin and crystalline basement must be investigated

surface rupture of 1999 chi chi earthquake yields insights on active tectonics of central taiwan the 1999 chi chi earthquake was caused by rupture of the chelungpu fault one of the most prominent active thrust faults of taiwan this largest of taiwan s historical fault ruptures broke the surface for over 90 km at the western base of the rugged mountain range a short right lateral tear extended southwestward from the southern end of the chelungpu fault and a complex assemblage of shallow folds and faults ran northeastward from the northern end vertical offsets averaged about 2 m along the southern half of the chelungpu fault and about 4 m along the northern half and offsets of 5 to 7 m were typical along the northern part of the major thrust the sinuous nature of the surface trace is consistent with seismographic data that indicate a dip of about 30 the 1999 rupture draws attention to the fact that this active fault system is highly segmented and that this segmentation influences the characteristics of seismic ruptures active faults to the south north and west of the chelungpu fault have distinctly different characteristics faults to the south and north broke the surface during earthquakes in 1906 and 1935 the active changhua fault to the west a blind thrust similar in length to the chelungpu has not ruptured in the historical period and should be considered a prime candidate for generating a future earthquake manuscript received 4 october 2000

puente hills blind thrust system los angeles california we describe the three dimensional geometry and quaternary slip history of the puente hills blind thrust system pht using seismic reflection profiles petroleum well data and precisely located seismicity the pht generated the 1987 whittier narrows moment magnitude m w 6 0 earthquake and extends for more than 40 km along strike beneath the northern los angeles basin the pht comprises three north dipping ramp segments that are overlain by contractional fault related folds based on an analysis of these folds we produce quaternary slip profiles along each ramp segment the fault geometry and slip patterns indicate that segments of the pht are related by soft linkage boundaries where the fault ramps are en echelon and displacements are gradually transferred from one segment to the next average quaternary slip rates on the ramp segments range from 0 44 to 1 7 mm yr with preferred rates between 0 62 and 1 28 mm yr using empirical relations among rupture area magnitude and coseismic displacement we estimate the magnitude and frequency of single m w 6 5 6 6 and multisegment m w 7 1 rupture scenarios for the pht manuscript received 16 november 2001

active parasitic folds on the elysian park anticline implications for seismic hazard in central los angeles california we characterize the seismic hazard of the elysian park fault a blind reverse fault beneath central los angeles by analysis of the elysian park anticline which overlies it new shallow subsurface geotechnical data combined with other surficial stratigraphy and geomorphology reveal that the elysian park anticline is an active 20 km long structure from the style and rates of deformation of parasitic folds on the southern limb of the anticline we estimate a contraction rate of 0 6 1 1 mm yr this rate provides a basis for estimating a rate of contraction of the entire elysian park anticline which in turn allows us to estimate a 0 8 2 2 mm yr time averaged rate of slip on the underlying fault at this rate of slip rupture of the elysian park fault could produce a nominal mw 6 2 to 6 7 earthquake every 500 to 1300 yr on average although this elysian park earthquake would recur infrequently its size and recurrence interval may be similar to those estimated for the sources of the destructive 1971 san fernando and 1994 northridge earthquakes

the 1987 whittier narrows earthquake in the los angeles metropolitan area california the whittier narrows earthquake sequence local magnitude m l 5 9 which caused over 358 million damage indicates that assessments of earthquake hazards in the los angeles metropolitan area may be underestimated the sequence ruptured a previously unidentified thrust fault that may be part of a large system of thrust faults that extends across the entire east west length of the northern margin of the los angeles basin peak horizontal accelerations from the main shock which were measured at ground level and in structures were as high as 0 6g where g is the acceleration of gravity at sea level within 50 kilometers of the epicenter the distribution of the modified mercalli intensity vii reflects a broad north south elongated zone of damage that is approximately centered on the main shock epicenter

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

community fault model cfm for southern california we present a new three dimensional model of the major fault systems in southern california the model describes the san andreas fault and associated strike slip fault systems in the eastern california shear zone and peninsular ranges as well as active blind thrust and reverse faults in the los angeles basin and transverse ranges the model consists of triangulated surface representations t surfs of more than 140 active faults that are defined based on surfaces traces seismicity seismic reflection profiles wells and geologic cross sections and models the majority of earthquakes and more than 95 of the regional seismic moment release occur along faults represented in the model this suggests that the model describes a comprehen sive set of major earthquake sources in the region the model serves the southern california earthquake center scec as a unified resource for physics based fault systems modeling strong ground motion prediction and probabilistic seismic hazards assessment

the controls on the composition of biodegraded oils in the deep subsurface part 1 biodegradation rates in petroleum reservoirs abstract biodegradation rates in oilfields have been assessed conservatively using whole oil column minimum rate estimates diffusion controlled oil column compositional gradient modelling and mixed oil kinetic models biodegradation rate constants first order are around 10 6 10 7 yr 1 for hydrocarbons in the degradation zones these corresponding well with zero order field wide minimum rate estimates of about 10 8 kg hydrocarbons kg oil year for the whole oil column with biodegradation induction times of around 1 2 ma to perturb an entire oil column for light oil reservoirs and 10 20 ma for heavy oil reservoir degradation the results indicate that where we see continuous gradients in the oil columns degradation must have been occurring episodically for many millions of years to remove the n alkanes from an oil i e about 10 of an oil around ca 15 ma is needed for a heavy oil ca 5 ma for a light n sea oil the timescales of oilfield degradation and filling are thus very similar and consequently the degree of biodegradation will be substantially controlled by oilfield charge history assessment of mixed degraded non degraded oil occurrence provides an independent confirmation that these rates are realistic and that timescales of degradation and field charging are similar the maximum effective rate constant of degradation ultimately controlled by the limiting effect of diffusion of alkanes to the oil water contact owc ca 10 4 yr 1 for a 130 m thick oil column first order rate constant is well above the estimated rate constants indicating oil biodegradation rate is not limited by electron donor supply i e hydrocarbons but by supply of nutrients or oxidants this suggests that diffusive transport of nutrients and electron acceptors in the aquifer to the site of biodegradation may be adequate to maintain the low rate biosphere

active faulting in the birjand region of ne iran 1 we use satellite imagery and field observations to investigate the distribution of active faults around birjand in eastern iran to determine how the transition between conjugate zones of faulting can be accommodated by diffuse active faulting in the south of the study area right lateral strike slip faults of the sistan suture zone end in thrusts which die away westward from the strike slip faults these thrust terminations appear to allow a northward change to e w thrusting in central parts of the study area the introduction of e w thrusting is in turn likely to facilitate a change to e w left lateral faulting north of the study region the relatively diffuse pattern of active faulting at birjand relates to the regional transition between n s and e w strike slip faulting in northeast iran which involves a change from nonrotational to rotational deformation the change from n s to e w faulting is likely to result from the orientation of preexisting structures in iran and western afghanistan which are roughly parallel to the active fault zones the features described at birjand also show the influence of preexisting structure on the location and style of active faulting at a local scale with the position of individual faults apparently controlled by inherited geological weaknesses very few modern earthquakes have occurred in the region of birjand and yet destructive events are known from the historical record the large number of active faults mapped in this study pose a substantial seismic hazard to birjand and surrounding regions

water property and current distributions along the whp p9 section 137 142 in the western north pacific the japan meteorological agency carried out full depth high resolution hydrographic measurements in july august 1994 along the 137 142 e line as a contribution to the world ocean circulation experiment the line spans the subtropical and tropical regions of the western north pacific with a full set of water mass and current distributions at 28 n to the south of the kuroshio recirculation there exists an eastward current distinct from the currents associated with the subtropical fronts the eastward current is characterized by the meridional thermal gradient extending down to 1500 m depth deep silicate has a meridional boundary at 25 n forming two cores of the maximum to the north and south of the boundary the northern core centered at 28 n is meridionally coincident with other property extrema indicating an inflow from the northwest pacific basin down to 2000 m depth the southern core centered at 16 n suggests another westward inflow from the east mariana basin to the west mariana basin a broad isopycnal depression at middepths and bottom water properties over the shikoku and west mariana basins indicate a near bottom circulation along which the inflow water through the yap mariana junction at 12 n fills the west mariana basin and then spreads to the shikoku basin and philippine basin successively a part of the bottom water from the south pacific bifurcates around the yap mariana junction and enters the west caroline basin via the yap trench this supports another path of deep water inflow to the philippine basin from the southernmost channel at 4000 m depth

a cross section of the los angeles area seismically active fold and thrust belt the 1987 whittier narrows earthquake and earthquake hazard retrodeformable cross sections across the los angeles area interpret the pliocene to quaternary deformation to be a developing basement involved fold and thrust belt the fold and thrust belt is seismically active as evidenced by the 1987 whittier narrows earthquake ml 5 9 and the 1971 san fernando earthquake mw 6 6 the structural geology of the los angeles area is dominated by three major compressional uplift trends 1 the palos verdes anticlinorium and western shelf 2 the santa monica mountains anticlinorium and 3 the verdugo mountains san rafael hills and the san gabriel mountains these trends result from major thrust ramps off a detachment s at 10 15 km depth thrusts of the verdugo mountains san rafael hills and the san gabriel mountains reach the surface the other two uplifts are associated with blind thrusts compressional seismicity is concentrated along these thrust ramps the 1987 whittier narrows earthquake probably occurred on the elysian park thrust which underlies the santa monica mountains anticlinorium the thrust interpretation accounts for the geometry of the anticlinorium the seismological characteristics of the earthquake and the geometry of coseismic uplift the earthquake and aftershocks occurred within a structurally complex narrow zone of miocene and pliocene northwest trending faults that cross the anticlinorium at a high angle these northwest trending faults are interpreted to be reactivated faults now behaving as tears in the elysian park thrust and not the result of active right lateral deformation extending into the whittier narrows area our analysis suggests the whittier narrows earthquake sequence occurred within a structurally weakened zone along the elysian park thrust we also suggest that the whittier fault is not an important quaternary structure and may not be seismogenic the regional cross section is a nonunique solution and other possible solutions are considered multiple solutions arise from the presence of two intersecting compressional belts in the los angeles area the transverse ranges and the northern peninsular ranges the belts may be due to one or more regional detachments and the northern peninsular ranges may be northeast or southwest vergent the deformed top of the crystalline basement along the regional cross section requires a minimum of 15 0 km of north south convergence between the palos verdes hills and the san andreas fault regardless of the structural solution restoration of our cross section solution requires 21 4 km of north south convergence on top of the crystalline basement including 6 4 km of slip continuing offshore to make structures of the continental borderland and 29 7 km of convergence on the basal detachment geologic relationships suggest major shortening started between early and late pliocene time 2 2 4 0 ma which yields a minimum convergence rate of 3 8 6 8 mm yr between the palos verdes hills and the san andreas fault convergence rates for our solution range from 5 4 to 13 5 mm yr between the edge of the continental borderland and the san andreas fault slip rate estimates for the elysian park thrust along the eastern portion of the santa monica mountains anticlinorium are 2 5 5 2 mm yr if the 1987 whittier narrows earthquake is the characteristic earthquake along the 170 km long anticlinorium then recurrence intervals are estimated to be 5 6 12 1 years this recurrence is higher than the historic seismic record along the santa monica mountains anticlinorium and suggests that 1 our slip rates are too high 2 some crustal shortening is taken up aseismically and or 3 earthquakes larger than the 1987 whittier narrows earthquake will occur along the anticlinorium but less frequently

growth of late quaternary folds in southwest santa clara valley san francisco bay area california implications of triggered slip for seismic hazard and earthquake recurrence we combine analysis of geologic and geomorphic data with observations of deformation during the 1989 loma prieta earthquake in northern california to evaluate the contribution of aseismic triggered slip and creep processes to cumulative late cenozoic deformation along the northeastern santa cruz mountains range front deformed late pleistocene alluvial fans and terraces provide evidence for localized late quaternary uplift above range bounding reverse faults within the southwestern santa clara valley adjacent to the range front on the basis of offset of late quaternary surfaces the long term average slip rate on the primary range bounding structure monte vista fault is estimated to be 0 2 mm yr northeast of the range front are several discontinuous northwest trending folds indicated by alignment of late pleistocene alluvial fan apices anomalous stream channel convexities and topographic and vegetation lineaments within a 3 5 km wide northwest trending corridor subsurface geologic and geophysical data support the interpretation that the surface folds are a result of blind reverse faulting along the cascade fault beneath the santa clara valley from stream incision rates we estimate an average uplift rate of 0 2 0 05 mm yr for the cascade fault measurements of triggered and postseismic slip following the 1989 loma prieta earthquake combined with estimates of the average return period for loma prieta type events suggest a long term average deformation rate along the range front of 0 25 0 4 mm yr associated with these aseismic processes this range of values is comparable to rates of late quaternary deformation on the range front faults derived from geologic and geomorphic data and it suggests that growth of the overlying folds is at least partially the result of triggered slip and postseismic creep associated with nearby loma prieta type earthquakes if this inference is correct then the return period for independent events on the range front faults probably is greater than that suggested by the long term average geologic slip rates

the controls on the composition of biodegraded oils in the deep subsurface part ii geological controls on subsurface biodegradation fluxes and constraints on reservoir fluid property prediction the principal controls on the fluid properties of biodegraded oil systems have been determined by a combination of petroleum geochemistry numerical modeling of oil biodegradation in reservoirs and analysis of oil property data sets from a variety of geological settings petroleum biodegradation proceeds under anaerobic conditions in any reservoir that has a water leg and has not been heated to temperatures more than 80c in most reservoirs with low concentrations of aqueous sulfate methanogenic degradation is a primary mechanism of petroleum degradation whereas in waters containing abundant sulfate sulfate reduction and sulfide production may dominate net degradation of petroleum fractions in reservoirs is primarily controlled by the reservoir temperature the chemical compounds being degraded and relationships between the oil water contact owc area and oil volume the relative volumes of water leg to oil leg prior level of oil biodegradation and reservoir water salinity act as second order controls on the process typically degradation fluxes kilograms of petroleum destroyed per square meter of oil water contact area per year or kg petroleum m2 owc yr1 for fresh petroleum in clastic reservoirs are in the range of 103 104 kg petroleum m2 owc yr1 and increase with decreasing reservoir temperature from zero near 80c to a maximum flux at the owc of less than 103 kg petroleum m2 owc yr1 at a temperature less than 40c at very low reservoir temperatures and with severely degraded oils such as are seen in the near surface canadian tar sands at the present day the net degradation fluxes are much less than maximum values nutrient supply from the aquifer and adjacent shales mostly buffered by mineral dissolution probably provides the ultimate control on the range of degradation flux values oil compositional gradients and resulting oil viscosity variations are common on both reservoir thickness and field scales in biodegraded oil reservoirs and are a defining characteristic of heavy oil fields produced by crude oil biodegradation continuous vertical gradients in the oil columns document episodic degradation for many millions of years suggesting that the time scales of oil field degradation and petroleum charging are similar the flux temperature relationship we have derived coupled with typical reservoir charge histories defines the range of variation of fluid properties seen in many biodegraded oil provinces and identifies oil charge mixing of biodegraded and fresh oils and reservoir temperature history as the primary controls on fluid properties these flux temperature relationships are easily integrated into prospect charge modeling procedures sensitivity analyses show that the limiting factor in fluid property predictions using even this first level approach are ultimately constrained by the accuracy of current oil charge modeling estimates the absence today of any functional geochemical proxies for assessing oil residence time in oil fields and the substantial uncertainty in petroleum charging times estimated by forward basin modeling is a major obstacle to more accurate fluid property predictions that needs to be addressed

modification of the intermediate waters in the northeastern subpolar pacific the modification of the intermediate layers in and around the alaskan gyre are investigated in relation to general circulation features of the region using tracer data from the world ocean circulation experiment p17n line the alaskan gyre ag core lies between the north pacific current and the alaskan stream as in the 52 54 5 n range and to the west of 144 w the north pacific current feeds the transition zone tz and the western subpolar waters wsw which consequently constitute the inflow to the region from the northwestern pacific the alaska current ac is observed to the west of 144 w between the north american coast and the ag the ac halocline 26 7 has distinct property distributions low chlorofluorocarbon and oxygen saturations and high nutrient concentrations which are correlated with eddies that are characterized by higher salt content and warmer temperatures most significantly at 26 0 the ag is found to act as a reservoir where water mass modification takes place and the as transports a mixture of waters from the ag and the ac west ward out of the region the residence time estimate for the intermediate and upper layer water in the ag 27 2 is about 2 years which corresponds to a volume exchange between the gyre and the surrounding circulation of 4 7 sv in the 0 1000 m range the layers above 26 9 0 200 m are modified by vertical mixing mostly of wsw in the ag the flux of modified waters out of the ag is approximately 0 9 sv comparison of the present data with the 1984 1989 period suggests that mixing of water from different regimes has not changed dramatically

the 1994 northridge earthquake sequence in california seismological and tectonic aspects the m w 6 7 northridge earthquake occurred on january 17 1994 beneath the san fernando valley two seismicity clusters located 25 km to the south and 35 km to the north northwest preceded the mainshock by 7 days and 16 hours respectively the mainshock hypocenter was relatively deep at 19 km depth in the lower crust it had a thrust faulting focal mechanism with a rake of 100 on a fault plane dipping 35 to the south southwest and striking n75 w because the mainshock did not rupture the surface its association with surficial geological features remains difficult to resolve nonetheless its occurrence reemphasized the seismic hazard of concealed faults associated with the contractional deformation of the transverse ranges the northridge earthquake is part of the temporal increase in earthquake activity in the los angeles area since 1970 the mainshock was followed by an energetic aftershock sequence eight aftershocks of m 5 0 and 48 aftershocks of 4 m 5 occurred between january 17 and september 30 1994 the aftershocks extend over most of the western san fernando valley and santa susana mountains they form a diffuse spatial distribution around the mainshock rupture plane illuminating a previously unmapped thrust ramp extending from 7 10 km depth into the lower crust to a depth of 23 km no flattening of the aftershock distribution is observed near its bottom at shallow depths above 7 10 km the thrust ramp is topped by a dense distribution of aftershock hypocenters bounded by some of the surficial faults the dip of the ramp increases from east to west the west side of the aftershock zoae is characterized by a dense steeply dipping and north northeast striking planar cluster of aftershocks that exhibited mostly thrust faulting these events coincided with the gillibrand canyon lateral ramp along the east side of the aftershock zone the aftershocks also exhibited primarily thrust faulting focal mechanisms the focal mechanisms of the aftershocks were dominated by thrust faulting in the large aftershocks with some strike slip and normal faulting in the smaller aftershocks the 1971 san fernando and the 1994 northridge earthquakes ruptured partially abutting fault surfaces on opposite sides of a ridge both earthquakes accommodated north south contractional deformation of the transverse ranges the two earthquakes differ primarily in the dip direction of the faults and the depth of faulting the 1971 north northeast trend of left lateral faulting chatsworth trend was not activated in 1994

the production of ice and dense shelf water in the okhotsk sea polynyas this paper examines the ice and dense water production in the okhotsk sea coastal polynyas for the 1990 1995 winters the dominant polynyas occur on the northwest and northern shelves and in shelikhov bay we use an algorithm developed for the special sensor microwave imager ssm i to derive for each polynya the area and composition of thin ice and open water and a heat flux algorithm to derive the ice and brine production historic oceanographic observations show that the northwest shelf is the only north pacific region where the 26 8 potential density surface outcrops to the surface and is also that part of the okhotsk shelf where the densest water is observed to occur in support of these observations we find that the northwest shelf polynya is the dominant ice and brine producer contributing on average about 55 of the total production shelikhov bay is the second largest producer with about 25 of the total this region has been previously neglected by both oceanographic and remote sensing studies using a combination of two dense water production models we find that the 6 year average dense water production lies between 0 2 0 4 sv the ice and brine production for the dominant northwest shelf vary interannually by a factor of 3 while the production from all the northern polynyas varies by factor of 2 the source of the variability for the northwest shelf comes from the fact that the southwest to northeast trend of the coastline and the mean winter geostrophic wind velocities are roughly parallel which means that small variations in the wind direction yield large changes in the ice production

water masses and properties at 165 e in the western pacific full depth conductivity temperature depth oxygen profiler ctdo 2 data at 165 e in 5 s 40 n in summer 1991 world ocean circulation experiment woce hydrographic program p13c and 27 48 n in spring 1993 p13j are analyzed distributions of salinity and temperature are characterized by the fronts associated with ocean currents such as the kuroshio extension front at 34 35 n the kuroshio bifurcation front at 38 40 n the subarctic front at 40 42 n other salinity fronts in the tropical waters and some oxygen fronts dissolved oxygen increases upward sharply called oxycline just above the intermediate oxygen minimum layer the processes of water mass extension are clarified mainly from oxygen and potential vorticity pv the north pacific tropical water nptw forms at the sea surface in 18 31 n from winter to summer and the winter formed nptw of 23 0 25 0 where is potential density extends to 12 n by the subtropical ocean gyre so that it occupies a layer of 23 0 25 0 in 12 31 n the subtropical mode water stmw forms at the surface in 29 34 n in winter and extends to 25 n by the ocean circulation it occupies a layer around 25 4 between the main and seasonal pycnoclines in 25 34 n the north pacific intermediate water npiw extends to 34 38 n on 26 83 by the kuroshio extension and its northern branch and extends to 27 33 n on 26 77 and to 15 22 n on 26 61 by westward currents it occupies 15 38 n in the intermediate subtropical gyre the npiw is located in the oxycline with similar pv to the stmw the boundary of the subtropical and tropical gyres is concluded to be around 12 n 14 16 n in a surface intermediate layer 26 0 bottom waters are also examined

mechanical fault interaction within the los angeles basin a two dimensional analysis using mechanical efficiency 1 mechanical models examine deformation within eight different structural cross sections proposed by davis et al 1989 and shaw and suppe 1996 along a northeast southwest transect across the los angeles basin california horizontal contraction of the models constrained by geodetic measurements yields varying dip slip rates along frictionally sliding faults within the different cross sections mechanical efficiency analysis using effective stiffness and strain energy density assesses the overall fault system deformation as well as the partitioning of work between fault slip and host rock strain the cross section interpreted by shaw and suppe 1996 has the best fit to paleoseismically determined slip rates and the greatest mechanical efficiency greatest proportion of work toward fault slip however this model produces excessive reverse slip along the newport inglewood fault a modified fault configuration with a wedge or blind puente hills thrust fault rather than a ramp detachment configuration better matches the paleoseismic data with slightly lower mechanical efficiency slip rates in the mechanical models based on interpretations of shaw and suppe 1996 have much closer match to the geologically determined rates than those estimated from kinematic models this difference is due to 1 differing time spans of slip rate estimates and 2 deformable rather than rigid host rock in the mechanical models the mechanical efficiency analysis provides quantitative indicators of overall fault system deformation including the cumulative effect of interaction between individual faults assessment of effective stiffness and strain energy density furthers our understanding of two dimensional fault interactions in the los angeles basin and offers great potential for future applications

north pacific intermediate water transports in the mixed water region abstract initial mixing between the subtropical and subpolar waters of kuroshio and oyashio origin occurs in the mixed water region interfrontal zone between the kuroshio and oyashio the relatively fresh water that enters the kuroshio extension from the mixed water region is this already mixed subtropical transition water subtropical transition water in the density range 26 64 27 4 can be considered to be the newest north pacific intermediate water npiw in the subtropical gyre this density range is approximately that which is ventilated in the subpolar gyre with significant influence from the okhotsk sea freshening of the kuroshio extension core occurs between 140 and 165 e in the upper part of the npiw 26 64 27 0 with the greatest freshening associated with the eastern side of the first and second kuroshio meanders kuroshio extension freshening in the lower part of the npiw 27 0 27 4 occurs more gradually and farther to the east there is nearly no distinction in water properties

wilshire fault earthquakes in hollywood the wilshire fault is a potentially seismogenic blind thrust fault inferred to underlie and cause the wilshire arch a quaternary fold in the hollywood area just west of downtown los angeles california two inverse models based on the wilshire arch allow us to estimate the location and slip rate of the wilshire fault which may be illuminated by a zone of microearthquakes a fault bend fold model indicates a reverse slip rate of 1 5 1 9 mm yr whereas a three dimensional elastic dislocation model indicates a right reverse slip rate of 2 6 3 2 mm yr the wilshire fault is a previously unrecognized seismic hazard directly beneath hollywood and beverly hills distinct from the faults under the nearby santa monica mountains

the effect of biodegradation and water washing on the occurrence of alkylphenols in crude oils abstract biodegraded oils from california and nigeria were analysed to assess the impact of biodegradation upon alkylphenol occurrence in crude oils the extent of biodegradation in the 13 californian samples ranged from very mild full n alkane distribution present to moderate complete degradation of c 15 n alkanes and significant reduction of acyclic isoprenoids corresponding to a range of n alkanes and acyclic isoprenoids stage 5 the data from the naturally degraded sample suites were compared to the results of an in vitro aerobic biodegradation experiment conducted with a north sea oil biodegradation resulted in significant reduction in total alkylphenol abundance and preferential depletion of c 3 and c 2 alkylated compounds in the nigerian and laboratory degraded samples these effects were most pronounced in oils in which the methylated naphthalenes had been biodegraded biodegradation stage 4 or 5 there was no clear relationship between alkylphenol abundance or molecular distributions and the extent of biodegradation in the californian samples although alkylphenol distributions in the biodegraded samples were generally dominated by the c 3 compounds simple oil water partition calculations showed that these distributions were consistent with the effects of water washing

the origin of the north pacific intermediate water possible source regions of the north pacific intermediate water npiw were investigated with synoptic conductivity temperature depth surveys in the okhotsk sea kuril basin a pycnostad referred to as the okhotsk sea mode water osmw was found in the density range of 26 6 27 the pycnostad is not seen in the western subarctic gyre wsag thus it is an indicative water peculiar to the okhotsk sea the maximum thickness is at 26 7 26 9 centered at 26 8 which coincides with the npiw density range in the north pacific subtropical gyre in the oyashio area east of the southern kuril islands and hokkaido waters that have intermediate temperature salinity and potential vorticity between the osmw and the wsag water were distributed suggesting a following transport route of the npiw source water the thick thus low q q is potential vorticity and low salinity water mass outflowing from the okhotsk sea mixes with the relatively warm saline and high q wsag water to form the oyashio water a coastal part of the oyashio water flows southwestward along the east coast of the southern kuril islands and hokkaido retaining the pycnostad q minimum a large part of the low q oyashio water flows further southward and merges with the kuroshio extension and then flows eastward forming new npiw in this process a salinity minimum develops and the q minimum disappears because of the mixing with a saline kuroshio water old npiw without a pycnostad in the npiw density range these results suggest that the origin of npiw is the water mass in the okhotsk sea osmw and the density of the water mass primarily determines the npiw density centered at around 26 8

a practical biodegradation scale for use in reservoir geochemical studies of biodegraded oils existing scales widely used to describe the extent of biodegradation of petroleum have insufficient resolution to usefully characterize many heavy oil and bitumen occurrences including the volumetrically dominant heavily and severely biodegraded oil accumulations in the foreland basins of western canada and venezuela in these and other deposits existing classifications or descriptions of the biodegradation level may vary only slightly yet oil may vary in viscosity by orders of magnitude the manco biodegradation scale proposed here is based on integrating the extent of degradation of various members of compound classes not included in previous biodegradation scales they include alkyl aromatic and alkyl thiophenic compounds that show variable extent of alteration in samples degraded to uniform levels on standard scales but which may show variation in local degradation systematics related to biodegradation mechanisms and extent of oil mixing the manco scale uses a combination of a consideration of the extent of alteration within a compound class together with a consideration of biodegradation across a range of compound classes it can be reliably used as a basis for interpreting geochemical changes in heavily biodegraded oil suites and can also be used to differentiate biodegraded oil samples likely to be amenable to cold production from those requiring production strategies such as steam or chemical flooding as with other biodegradation scales the scale may also provide evidence for the influx of later higher quality oil into a reservoir fluid that had been previously biodegraded

annual and interannual variability in the kuroshio current system abstract individual seasonal 300 m temperature maps were constructed over the kuroshio current system from 130 e to 170 w for a 4 year period from summer 1976 through spring 1980 using transpac xbt data and jodc temperature depth data quasi stationary meanders in the kuroshic current system occurred at 137 c i e kuroshio meander at 144 e and 150 e i e lee wave meanders and near 160 e i e meander over the shatsky rise a composite of the paths of the kuroshio i e the 12 c isotherm from the individual seasonal maps and the total variance map finds nodes i e minima and anti nodes i e maxima of variability to have existed along the mean kuroshio path the anti nodes coincided with the location of the quasi stationary meanders the nodes in between zonal propagation of temperature anomalies accounted for 20 30 of the total interannual variance these temperature anomalies propagated eastward at 0 5 1 5 cm s 1 in the region 140 155 e and westward at 1 to 2 cm s 1 in the re

inferring a thrust related earthquake history from secondary faulting a long rupture record of la laja fault san juan argentina abstract trenches excavated across the surface rupture of the 15 january 1944 m w 7 san juan argentina earthquake show evidence for repeated rupture of la laja fault in the late pleistocene and holocene the 1944 rupture extended for about 7 km striking n35 e and dipping 42 e parallel to neogene bedding with a maximum east side up vertical displacement of 30 cm we interpret nine discrete colluvial wedges each capped by a soil as evidence for nine surface ruptures in the past 32 35 ka our topographic profile of the t3 terrace surface projected across the fault suggests these nine events collectively produced 10 3 m of dip displacement we used radiocarbon and optically stimulated luminescence dating to define the timing of past events yielding an average recurrence interval of 3 9 0 3 ka the average estimate for displacement per event is about 1 1 m compared with the 0 5 m of dip slip that occurred in 1944 using a fault related fold model that infers 28 m of shortening based on the axial surface migration for the t 3 terrace along with the 35 ka age of the terrace yields a shortening rate of 0 8 mm yr by the 1944 source thrust fault which is about 20 of the global positioning system constrained total shortening rate across the precordillera using this shortening rate and an assumed fault dip of 30 implies a fault slip rate of about 1 1 mm yr which combined with the average recurrence interval implies 4 m of average slip per event on the causative fault at depth online material unit descriptions from the trenches stepwise reconstruction from trench 1 and annotated photographs of the la laja region

miocene rifting in the los angeles basin evidence from the puente hills half graben volcanic rocks and p wave tomography formation of the puente hills half graben in the northeastern los angeles basin and eruption of the glendora and el modeno volcanics 16 14 ma help to define the timing of extension in the basin normal faulting on the proto whittier fault ca 14 ma established the puente hills half graben in which sedimentary strata accumulated between ca 14 and 10 ma and into which diabase sills intruded north south contraction began to invert the puente hills half graben ca 7 ma leading to formation of the puente hills anticline and the whittier fault our high resolution three dimensional p wave velocity model shows two anomalous higher velocity 6 63 km s bodies at depths between 9 and 18 km which we attribute to dioritic plutons named here for whittier narrows and el modeno the stocklike whittier narrows pluton could have been a source for the glendora volcanics and the diabase sills in the puente hills half graben the sill shaped el modeno pluton was a likely source for the el modeno volcanics the northwesterly alignment of the plutons may mark the location of the northeastern los angeles basin rift boundary which is associated with the clockwise rotation of the western transverse ranges three active faults the elysian park blind thrust the puente hills blind thrust and the whittier fault converge on the whittier narrows pluton which may have played a role in their location and segmentation

features of the water mass front in the northwestern north pacific analysis of the hydrographic data taken in the northern north pacific has revealed a water mass front defined as the abrupt change of mixing rates between the two typical water masses typical water masses are situated above the main thermocline in the subtropical and subpolar gyres this front termed water mass front in the present study can be regarded as the boundary between the subtropical gyre and the subpolar gyre the index for detecting the frontal position from the temperature field is given as the 5 c isotherm at the 300 m level comparisons with data from previous studies are also made and this front appears to correspond to the subarctic front in almost every instance

the controls on the composition of biodegraded oils in the deep subsurface part 3 the impact of microorganism distribution on petroleum geochemical gradients in biodegraded petroleum reservoirs abstract a combined geochemical geological and microbiological analysis of an actively biodegrading 24 5 m thick oil column in a canadian heavy oil reservoir has been carried out the reservoir properties associated with the cored vertical well are characterised by a 15 75 m thick oil column and an 8 75 m zone of steadily decreasing oil saturation below the oil column referred to as the oil water transition zone owtz grading down into a thin water leg the oil column exhibits systematic gradients in oil physical properties and hydrocarbon composition and shows variations in biodegradation level throughout the reservoir consistent with the notion that the biodegradation of oil is focussed in a bioreactor zone at the base of the oil column through the oil column the dead oil viscosity measured at 20 c ranged from 50 000 cp 0 05 mcp at the top of the oil column to 1 4 mcp at the oil owtz contact and continued to increase to 10 5 mcp within the owtz the saturated and aromatic hydrocarbons are characterised by systematically decreasing bulk fraction and component concentrations down through the oil column different compound classes decreased to levels below their detection limit at different depths within the owtz defining a likely bioreactor extent of over 5 m in depth with for example n alkanes being reduced to their detection limit concentration at the bottom of the oil column top of the owtz while branched isoprenoid alkanes were not completely degraded until well into the owtz core samples from the oil column and the lower part of the owtz were estimated to contain ca 104 105 bacterial cells g based on qpcr of bacterial 16s rrna genes while samples from a narrow interval in the owtz immediately below the oil column contained on the order of 106 107 cells g of sediment interestingly these latter numbers are typical of those observed in active deep subsurface biosphere systems with the notion that microbial activity and abundance in the deep subsurface is elevated at geochemical interfaces the numbers of organisms are not constant throughout the owtz the highest bacterial abundance and geochemical gradients of for example methylphenanthrene biodegradation define a zone near the oil water contact as likely the most active in terms of biodegradation the largest bacterial abundances in the upper part of the owtz are in line with the trend of bacterial abundance with depth that has emerged from extensive analysis of microbial cells in deep subsurface sediments implying that in terms of deep biosphere cell abundance oil reservoirs are similar to other deep subsurface microbial environments this is puzzling given the atypical abundance of organic carbon in petroleum reservoirs and may imply a common large scale control on microbial abundance and activity in the deep biosphere including in oilfields

the 2002 june 22 changureh avaj earthquake in qazvin province northwest iran epicentral relocation source parameters surface deformation and geomorphology summary the m w 6 4 changureh avaj earthquake occurred on 2002 june 22 in qazvin province northwest iran we use observations from seismology field investigation and analysis of satellite imagery and digital topography to suggest that slip on a previously unrecognized thrust fault herein named the abdarreh fault was responsible for the earthquake inversion of longperiod p and sh body wave seismograms shows rupture on a thrust fault dipping 49 to the southwest and with a centroid depth of 10 km multiple event relocation of the main shock and aftershock epicentres and discontinuous surface ruptures observed after the earthquake are compatible with a northwest propagating rupture on a southwest dipping thrust but maximum recorded displacements are much less than expected from seismology suggesting that much of the slip failed to reach the surface and was accommodated as folding at the surface instead long term folding is difficult to see in the topography of the epicentral region as the abdarreh fold is growing through a relict neogene topography anticlinal uplift can however be inferred from drainage disruption and stream incision the 2002 june 22 changureh earthquake shows the importance of being able to interpret diagnostic features of active faulting in the landscape

extending the upper temperature limit for life the upper temperature limit for life is a key parameter for delimiting when and where life might have evolved on a hot early earth the depth to which life exists in the earth s subsurface and the potential for life in hot extraterrestrial environments a combination of geological and

bathymetric influences upon the character of north pacific fronts 1976 1980 thermal fronts in the north pacific from june 1976 to may 1980 have been mapped at the 300 m level by using temperature data obtained in the region 30 45 n 160 e 160w in the transpac xbt volunteer observing ship program the origins of the paths of the major frontal bands in the study region i e the kuroshio extension the subarctic fronts and the subtropical front appear to be related to the principal bathymetric features of the western mid latitude north pacific i e the shatsky rise the emperor seamount chain and the hess rise in the long term mean the kuroshio extension front at 35 n was observed to have bifurcated at the shatsky rise near 160 e into two bands one band continued northeast along the shatsky rise to 42 n to become the north subarctic front the other band continued zonally eastward where it encountered the emperor seamounts near 36 n 170 e and trifurcated into bands which tracked through passages between the seamounts near 37 n 34 n and 32 n respectively downstream the most northern of these three bands became the south subarctic front near 39 n the middle band continued as the kuroshio extension front at 35 n and the most southern band became the subtropical front near 32 n the middle band tracked north of the hess rise while the most southern band tracked south of the hess rise a near meridional frontal band linked the north and south subarctic fronts in the emperor seamount region near 170 e in the annual mean and individual seasonal mean maps the essential character of topographic influence of the long term mean was observed however the individual frontal bands varied seasonally about the long term mean by 2 of latitude also all four major frontal bands were not always observed and intermittent linkages and additional filaments also occurred

interseismic strain accumulation on faults beneath los angeles california geodetic data show that the los angeles metropolitan area is undergoing 8 9 mm year of north south tectonic shortening associated with the big bend of the san andreas fault this shortening has been linked to multiple damaging twentieth century thrust earthquakes as well as possible mw 7 0 holocene thrust events beneath central los angeles to better characterize this seismic hazard we assess how this shortening is being accommodated by interseismic strain accumulation on subsurface faults incorporating detailed seismology and geology based models of fault geometry and the low stiffness los angeles sedimentary basin we find that strain accumulation on local strike slip faults likely contributes no more than 1 2 mm year of the shortening we formally invert the geodetic data for the pattern of interseismic strain accumulation on the north dipping sierra madre puente hills and compton thrust faults and a master decollement we explore the impact of the assumed material model strain accumulation on faults to the west and east and other model assumptions we infer that the three faults slip at 3 4 mm year over the long term and are currently partially or fully locked and accruing interseismic strain on their upper sections this locking implies an annual deficit of seismic moment 1 6 1 3 0 5 10 17 nm year in total which is presumably balanced over the long term average by the moment released in earthquakes the depth distribution of moment deficit accumulation rate matches that of seismicity rates in los angeles to first order in part because the models incorporate the blind nature of the puente hills and compton faults

constraining the kinematics of metropolitan los angeles faults with a slip partitioning model due to the limited resolution at depth of geodetic and other geophysical data the geometry and the loading rate of the ramp decollement faults below the metropolitan los angeles are poorly understood here we complement these data by assuming conservation of motion across the big bend of the san andreas fault using a bayesian approach we constrain the geometry of the ramp decollement system from the mojave block to los angeles and propose a partitioning of the convergence with 25 5 0 5 mm yr and 3 1 0 6 mm yr of strike slip motion along the san andreas fault and the whittier fault with 2 7 0 9 mm yr and 2 5 1 0 mm yr of updip movement along the sierra madre and the puente hills thrusts incorporating conservation of motion in geodetic models of strain accumulation reduces the number of free parameters and constitutes a useful methodology to estimate the tectonic loading and seismic potential of buried fault networks

biodegradation and mixing of crude oils in eocene es3 reservoirs of the liaohe basin northeastern china a suite of heavy oils from a single eocene sandstone reservoir section in the liaohe basin northeastern china was analyzed to study the geological controls on oil viscosity which spans a range of almost three orders of magnitude the heaviest oils are biodegraded as determined from the absence of n alkanes and the low relative amount of isoprenoid alkanes the large variation in viscosity can be explained by mixing to various extents of heavy biodegraded oils with less degraded oils this is supported by a simple mixing model which reproduces the observed data excellently the model may assist in predicting the viscosity of reservoired oils before production by analyzing reservoir core extracts prior to deciding which intervals to steamflood

prospects for larger or more frequent earthquakes in the los angeles metropolitan region far too few moderate earthquakes have occurred within the los angeles california metropolitan region during the 200 year long historic period to account for observed strain accumulation indicating that the historic era represents either a lull between clusters of moderate earthquakes or part of a centuries long interseismic period between much larger moment magnitude m w 7 2 to 7 6 events geologic slip rates and relations between moment magnitude average coseismic slip and rupture area show that either of these hypotheses is possible but that the latter is the more plausible of the two the average time between m w 7 2 to 7 6 earthquakes from a combination of six fault systems within the metropolitan area was estimated to be about 140 years

structural evolution of the northern los angeles basin california based on growth strata subsurface structure contour maps and cross sections show that the northern los angeles basin is underlain by a south facing monocline complicated by secondary faults and folds the monocline and associated structures form a structural high the northern los angeles shelf which marks the northern margin of the los angeles central trough analysis of growth strata sediments deposited during structural growth shows that during the miocene the predominant structural style was extension growth strata show that at approximately the beginning of the pliocene 5 ma contraction reactivated the miocene normal faults as reverse faults and formed the monocline its secondary structures and the los angeles central trough lensing out of earliest pliocene delmontian stage growth sandstones onto the flanks of the monocline and secondary structures the south salt lake the east beverly hills and the las cienegas anticlines indicates that these contractional structures all began to form at this time all of the secondary structures became largely inactive prior to the deposition of upper pico member of early pleistocene age 1 2 ma however thick accumulations of growth strata of the upper pico member of the fernando formation within the los angeles central trough attest to continued monoclinal folding after the secondary structures became largely inactive the growth strata record both vertical and horizontal components of structural growth of the monocline so that the dip of the blind fault zone causing the monocline the los angeles fault can be calculated in the east beverly hills area the dip of the los angeles fault is 61 and at las cienegas the dip is 62 these are maximum values based on the assumption that the growth strata bed lengths record all shortening the pliocene pleistocene average fault slip rates for the los angeles fault are 1 1 1 3 mm yr in the east beverly hills and 1 3 1 5 mm yr at las cienegas the resulting pliocene pleistocene horizontal convergence rates are 0 5 0 6 mm yr and 0 6 0 7 mm yr respectively the pliocene pleistocene growth strata show increased dip with age indicating that the monocline grew by progressive limb rotation rather than by kink band migration therefore fault bend and fault propagation fold models based on kink band migration are inadmissible solutions to explain the growth of the monocline we suggest a basement involved shear zone to explain the geometry of the northern los angeles shelf

implications of cabbeling on the formation and transformation mechanism of north pacific intermediate water 1 the world ocean atlas 1994 is used to study the formation and transformation of north pacific intermediate water npiw paying attention to the broad subarctic tropical frontal zone satfz four neutral density surfaces n 26 5 26 9 27 2 and 27 4 are mapped to span the npiw layer with the n 26 9 surface identified with the salinity minimum of npiw various dianeutral motion processes cabbeling thermobaricity vertical turbulent mixing and double diffusion and water mass property conversion are quantified cabbeling appears to be the most important spatially dianeutral transport is strongest in the satfz within the satfz subdomain 36 n 44 n 142 e 140 w with assumed epineutral and dianeutral diffusivities of k 103 m2 s 1 and d 10 5 m2 s 1 cabbeling contributes to a maximum dianeutral downwelling transport of 0 9 sv on the n 26 5 neutral density surface the upper boundary of npiw and 0 7 sv on the n 26 9 surface at the npiw core in meridional sections cabbeling shows epineutral extension from the satfz towards the subtropical gyre most apparent along the n 26 9 surface dianeutral transport is found to be sensitive to the epineutral diffusivity k on the upper two surfaces n 26 5 and 26 9 where the transport is dominated by cabbeling with only half an order of magnitude increase in diffusivity k 103 5m2 s 1 the total npiw about 3 sv can be accomplished by cabbeling alone these results suggest that cabbeling plays a crucial role in the npiw transformation since cabbeling describes physically the dianeutral downwelling resulted from epineutral mixing strong cabbeling in the satfz implies that npiw sources are first transformed by cabbeling from the upper to the lower neutral density surfaces and subsequently npiw is carried by epineutral advection and gyre circulation into the subtropical interior thus cabbeling is revealed as the principle mechanism responsible for transforming subpolar source waters into subtropical npiw water via the satfz

woce section p1w in the sea of okhotsk 1 oceanographic data description we describe the results of a world ocean circulation experiment woce survey line p1w from the open pacific ocean through the bussol strait and across the sea of okhotsk observations are presented of distributions of temperature and salinity dissolved oxygen and nutrients and some derived quantities discussion centers on the distribution of the sea of okhotsk component of the north pacific intermediate water mass and its properties the sea of okhotsk has been suggested as the only location where deep convection may occur within the north pacific or its marginal seas our analysis suggests that the surface 26 85 has recently been ventilated and arguments might be made to suggest that ventilation has occurred to 27 05 this is discussed here but detailed evidence is covered in a companion paper analyzing cfc observations the okhotsk component of the north pacific intermediate water extends to substantially greater depths and densities and so some other process is needed to create the denser water mass

space geodetic observation of expansion of the san gabriel valley california aquifer system during heavy rainfall in winter 2004 2005 1 starting early in 2005 the positions of gps stations in the san gabriel valley region of southern california showed statistically significant departures from their previous behavior station long moved up by about 47 mm and nearby stations moved away from long by about 10 mm these changes began during an extremely rainy season in southern california and coincided with a 16 m increase in water level at a nearby well in baldwin park and a regional uplift detected by interferometric synthetic aperture radar no equivalent signals were seen in gps station position time series elsewhere in southern california our preferred explanation supported by the timing and by a hydrologic simulation is deformation due to recharging of aquifers after near record rainfall in 2004 2005 we cannot rule out an aseismic slip event but we consider such an event unlikely because it requires slip on multiple faults and predicts other signals that are not observed

fault slip rates from three dimensional models of the los angeles metropolitan area california 1 we present results from the first mechanical model of active tectonics in the los angeles region to use non planar geologically representative fault surfaces compiled by the southern california earthquake center community fault model the fault slip rates from our three dimensional model match well the available geologic slip rates discrepancies in reverse slip along the upper elysian park fault and strike slip along the raymond fault may reflect imprecise knowledge of local fault geometry discrepancy in the average dip slip rate along the palos verdes fault reveals variations in dip slip along that surface model predictions at the location of the geological investigation have good match to geologic data the validated model is used to estimate dip and strike slip rates for 26 active faults in the los angeles metropolitan region many of which are otherwise unconstrained by geologic evidence

an elusive blind thrust fault beneath metropolitan los angeles seismic reflection profiles petroleum wells and relocated earthquakes reveal the presence of an active blind thrust fault beneath metropolitan los angeles a segment of this fault likely caused the 1987 whittier narrows magnitude 6 0 earthquake mapped sizes of other fault segments suggest that the system is capable of much larger magnitude 6 5 to 7 and more destructive earthquakes

distribution and modification of north pacific intermediate water in the kuroshio oyashio interfrontal zone abstract a multiship ctd survey was conducted in the kuroshio oyash interfrontal zone in the area of 30 41 n 140 e 180 from may to june 1992 to examine the distribution modification process and formation site of north pacific intermediate water npiw low salinity oyashio water and high salinity kuroshio water merge along the kuroshio extension just off the east coast of japan and together flow eastward eastward geostrophic transport and salinity across the kuroshio strong current indicate that the mixture of the kuroshio and oyashia waters along the kuroshio extension can produce new npiw transport estimate suggests that the new npiw bifurcates into the interfrontal zone and into the recirculation of the subtropical gyre a salinity minimum structure can he also created due to the isopycnal mixing along the kuroshio extension between the oyashio and kuroshio waters which have different salinity and vertical velocity structures the low salinity oyashio water seen along the oyashio branches and t

transport of north pacific intermediate water across japanese woce sections 1 under the auspices of the world ocean circulation experiment woce hydrographic program japan carried out a total of four sections in the north pacific p2 at 30 n p13 at 165 e p9 at 137 e and p8 at 130 e these japanese and several other woce sections are used to estimate the transport of north pacific intermediate water npiw in the subtropical gyre previous studies speculate about 3 sv 1 sv 106 m3 s 1 of npiw transport originating mainly in okhotsk sea entering the subtropical gyre southward via the mixed water region in the east of japan the total subpolar input is 3 2 sv when another source of npiw in the gulf of alaska estimated at 0 2 sv in this study is added this transport from the japanese woce sections a mean of 2 8 0 2 sv compares well with several other sections a mean of 2 5 0 2 sv from a total of five meridional and two zonal sections a mean transport of 2 7 0 2 sv is found in the defining npiw layer between n 26 5 and 27 4 neutral density surfaces the transport shows a steady southward and westward increase about 3 sv transport is found mainly in the southern south of 25 n and western west of the dateline sections closer to the subarctic tropical frontal zone and in the eastern subtropical gyre npiw transport is less than 2 sv this implies that a lower subpolar input of about 2 sv is sufficient for subtropical ventilation recirculation entrainment with the upper and lower waters and epineutral and dianeutral mixing likely add about 1 sv to the npiw transport to interpret the transport distribution a simple water mass mixing scheme is applied which includes two formation sources okhotsk intermediate water oiw and gulf of alaska intermediate water gaiw in the subpolar regions and a transformed aged npiw anpiw in the northwestern subtropical gyre southeast of japan the anpiw mixing fraction increases southward and westward while oiw and gaiw fractions decrease this suggests that after npiw source water parcels enter the subtropical gyre they largely recirculate within the wind driven gyre and thus become aged therefore one usually sees very low oxygen and cfc values in the npiw layer in the subtropical gyre

the 3 december 1988 pasadena california earthquake evidence for strike slip motion on the raymond fault the pasadena earthquake m l 4 9 occurred on 3 december 1988 at a depth of 16 km the hypocenters of the earthquake and its aftershocks define a east northeast striking steeply northwest dipping surface that projects up to the active surficial trace of the raymond fault one of the nodal planes of the focal mechanism of the earthquake parallels the raymond fault with left lateral strike slip movement on that plane and is consistent with geomorphic and paleoseismic evidence that the raymond fault is dominantly a left lateral strike slip fault the existence of a component of sinistral slip along the raymond fault had been suspected prior to the earthquake but the northward dip of the fault and the prominent scarp along the western portion of its trace had led most workers to conclude that slip along the fault was dominantly reverse

satellite passive microwave studies of the sea of okhotsk ice cover and its relation to oceanic processes 1978 1982 this paper describes the use of the nimbus 7 scanning multichannel microwave radiometer smmr satellite data to study the ice cover in the sea of okhotsk during the four winters of 1978 1982 the ice concentration estimates obtained from smmr are used to study two different polynyas one over the kashevarova bank and the other over the northwest continental shelf for the kashevarova polynya this study shows that the polynya which may be related to the upwelling observed in historic summer cruises occurs directly over the bank for the continental shelf which because of strong offshore winds and cold temperatures is a region of high ice production the polynya areas are combined with heat flux estimates from weather station data to yield the production rates of ice salt and dense shelf water as a previous study by kitani 1973 shows the mixing of this dense shelf water with pacific water yields a water mass unique to the okhotsk which is the layer of cold low salinity intermediate water between depths of 150 and 800 m from our calculations we estimate that the dense shelf water is produced at an annual rate of about 0 5 sv and that the intermediate water is produced at a rate of 1 2 sv which yields a renewal time for this layer of 10 40 years

from the subtropics to the central equatorial pacific ocean neodymium isotopic composition and rare earth element concentration variations 1 neodymium isotopic compositions end and rare earth element ree concentrations were measured for filtered surface to deep waters 112 samples in the southern tropical pacific the relatively detailed picture of these tracer distributions allowed us to refine the areas where oceanic end variations occur end values increase for most of the water masses flowing from samoa to the solomon sea and in the papua new guinea png area as already observed furthermore water masses arriving from the eastern equatorial pacific 200 550 m depth also revealed radiogenic values possibly acquired in the vicinity of the south american coasts and galapagos islands these end variations affect the whole water column the most likely process causing such variations is boundary exchange between the numerous radiogenic slopes margins located in this area and seawater flowing past dissolution of atmospheric deposition and or diffuse streaming of volcanic ash are also suggested to explain the radiogenic end observed at the surface in the png area interestingly a positive europium eu anomaly characterizes the normalized ree patterns of most of the studied water masses this anomaly is consistent with the ree patterns of sediment and rock samples that are potential sources for the local waters such consistency reinforces the hypothesis that lithogenic sources play a major role in the oceanic ree budget thanks to boundary exchange the data set presented here is a good basis for further sampling that will be realized in the framework of the ongoing geotraces program www geotraces org

origin of an unusual heavy oil from the baiyinchagan depression erlian basin northern china abstract a detailed organic geochemical analysis of six oil samples from the baiyinchagan depression in the erlian basin northern china was carried out in order to evaluate their origin the oils are reservoired at a very shallow depth 223 560 m subsurface and their chemical and physical properties vary greatly ranging from normal to extremely heavy oil the preservation of non biodegraded oil in such a shallow reservoir is possibly related with palaeo pasteurization of the reservoir before uplift maturity difference is not the primary control on the chemical and physical properties of the oils and there is considerable geochemical evidence to suggest the additional influence of in reservoir post accumulation processes such as biodegradation water washing and possibly evaporation whereas some oils appear to be less affected others are moderately biodegraded up to level 4 on the peters and moldowan 1993 scale with sterane distributions largely unaffected and 25 norhopanes undetected contrary to classical biodegradation the unusual heavy oil shows little evidence of biodegradation from aliphatic components water washing is suggested to be the primary process leading to its formation since the severe alteration of soluble aromatic hydrocarbons is observed in addition since the oils have been uplifted significantly after accumulation evaporation and or leakage to modify oil compositions cannot be ruled out

organic geochemistry of venezuelan extra heavy crude oils 2 molecular assessment of biodegradation abstract the extent of biodegradation of extra heavy crude oils from the eastern venezuelan basin orinoco tar belt has been assessed using biological marker compounds which include steranes triterpanes aromatic steroids and phenanthrenes analyzed by gc ms and petroporphrins analyzed by hplc the analyses indicate that biodegradation takes place in two regions namely surface or close to surface and subsurface with a different pattern of biodegradation taking place at each type of location some oils show patterns of biomarkers which may be the combined result of degradation at both main sites of biodegradation however two empirical biodegradation parameters are proposed to achieve this classification the classification of crude oils in terms of degree of biodegradation is further complicated by the identification of mixed crudes

style and rate of holocene slip palos verdes fault southern california recent studies of the palos verdes fault in the los angeles outer harbor characterize the fault s holocene activity the studies included areal and local geophysical surveys as well as drilling sampling and dating of the subsurface materials the studies identify the fault s location in the shallow subsurface document evidence of holocene strike slip quantify dip slip versus sediment age and quantify the net slip where an early holocene paleochannel crosses the fault the slip rate for the palos verdes fault is constrained to between 2 7 and 3 mm yr for the past 7 8 to 8 ka because the new evidence shows that the palos verdes fault has one of the highest slip rates in the los angeles basin the studies provide significant new insight into the regional tectonics and the seismic risk of the los angeles region using this rate of slip and segmentation models for the fault the coastal los angeles region can expect an mw 7 to 7 2 event about every 400 to 900 years from this potential seismic source

a dynamic biodegradation model suggested by petroleum compositional gradients within reservoir columns from the liaohe basin ne china abstract a suite of petroleum reservoir extracts from the liaohe basin ne china was analyzed to investigate the effects and controls of biodegradation on petroleum composition systematic changes seen as marked gradients in petroleum bulk composition component concentrations and molecular indicators have been observed in two biodegraded oil columns in the es3 column 1700 1850 m biodegradation has removed substantial amounts of normal and isoprenoid alkanes more severe biodegradation occurs in the shallower es1 column 1500 1650 m with both steranes and hopanes being partially removed temperature has an overall control on biodegradation in the two columns a lower reservoir temperature leading to a higher degree of biodegradation however observed variation in the degree of biodegradation in the es3 column at different sites is controlled by water leg size with a higher level of degradation being associated with a thicker water leg the supply of nutrients from the water leg is thought to have a significant impact upon the degree of biodegradation in addition to water leg size nutrient supply the compositional gradients also are controlled by the relative rate of mixing of fresh oil charge gradients can only be conserved in biodegraded petroleum columns if the rate of diffusive mixing is similar to or lower than the rate at which the hydrocarbons are removed a biodegradation model is proposed that couples geochemical and geological factors to provide a coherent approach for assessing the impact of degradation on petroleum our geochemical study indicates that biodegradation occurs mainly within a narrow region at or near the base of the oil column the stable compositional gradients are produced after an initial induction period involving diffusive transport of alkanes to the oil water contact owc and diffusion of biodegradation products such as 25 norhopanes and other metabolites away from the reaction site the mixing of continuously charged oil with residential biodegraded oil by diffusion may be considered as one of the most important factors controlling the biodegradation process the conceptual model illustrates all of these processes and opens the possibility of model driven prediction of oil properties and sweetspot location in reservoirs

a reversed compositional pseudo gradient in biodegraded oil column from liaohe basin ne china abstract most heavy oils or tar sands are formed by microbial biodegradation and show a compositional gradient toward the base of oil column however a reversed pseudo gradient has been observed from the fourth member of the shahejie formation in shuguang oilfield liaohe basin ne china on the basis of bulk and molecular compositions in a series core extracts from well k037 the bulk compositions show systematic depletion of saturated hydrocarbons and enrichment of polars resins asphaltenes toward the top of the oil column molecular compositions illustrate that these extracts have similar source input depositional environment and thermal maturity and their compositional differences are mainly caused by varying degrees of biodegradation biodegradation removes all n alkanes most isoprenoid alkanes partial alkylnaphthalenes and alkylphenanthrenes at the top of oil column whereas only n alkanes are affected at the bottom reservoir temperature has no crucial impact on biodegradation levels as the whole oil column in the temperature range of 41 44 c is ideal for microbial activities the studied reservoir is not a continuous oil column which is separated by a few barriers and baffles the occurrence of locally high water saturation layers caused multiple small gradients in the mid and lower part of oil column with a normal biodegradation gradient in the lowermost compartmentalized interval the overall reversed compositional pseudo gradient is controlled by a generally upward coarsening sedimentary sequence and the existence of top water situated at a lithology change boundary from coarse sandstones and conglomerates to fine grained sandstones this study provides a new perspective to assess the reservoir fluid heterogeneity and sheds the light on sweet spots identification for heavy oil exploration and development

southern california earthquake center geologic vertical motion database the southern california earthquake center geologic vertical motion database vmdb integrates disparate sources of geologic uplift and subsidence data at 104 to 106 year time scales into a single resource for investigations of crustal deformation in southern california over 1800 vertical deformation rate data points in southern california and northern baja california populate the database four mature data sets are now represented marine terraces incised river terraces thermochronologic ages and stratigraphic surfaces an innovative architecture and interface of the vmdb exposes distinct data sets and reference frames permitting user exploration of this complex data set and allowing user control over the assumptions applied to convert geologic and geochronologic information into absolute uplift rates online exploration and download tools are available through all common web browsers allowing the distribution of vertical motion results as html tables tab delimited gis compatible text files or via a map interface through the google maps web service the vmdb represents a mature product for research of fault activity and elastic deformation of southern california

the subarctic and northern subtropical fronts in the eastern north pacific ocean in spring abstract the subarctic and subtropical frontal zones of the eastern north pacific ocean were surveyed in june for five consecutive years starting in 1972 these surveys from the basis for a description of the complex frontal distributions and their year to year differences the fronts appear as surface outcroppings of haloclines the subarctic halocline where salinity increases with depth and the subtropical halocline where the opposite prevails between the fronts lies a transition zone where strong vertical gradients of salinity are generally absent an examination of the northern boundary of subtropical waters in this new dataset reveals the presence of two major fronts in the subtropical frontal zone in addition to the front commonly identified as the subtropical front 18 c and 34 8 is a northern subtropical front that forms the northern boundary of the subtropical halocline in the eastern north pacific it falls some 2 to 3 of latitude north of the subtropical front and is the same front observ

geochemical characterization of secondary microbial gas occurrence in the songliao basin ne china abstract a suite of natural gases from the northern songliao basin in ne china were characterized for their molecular and carbon isotopic composition gases from shallow reservoirs display clear geochemical evidence of alteration by biodegradation with very high dryness c1 c2 100 high c2 c3 and i c4 n c4 ratios high nitrogen content and variable carbon dioxide content isotopic values show wide range variations 13 c ch 4 from 79 5 to 45 0 13 c c 2 h 6 from 53 7 to 32 2 13 c c 3 h 8 from 36 5 to 20 1 13 c n c 4 h 10 from 32 7 to 24 5 and 13 c co 2 from 21 6 to 10 5 a variety of genetic types can be recognized on the basis of chemical and isotopic composition together with their geological occurrence secondary microbial gas generation was masked by primary microbial gas and the mixing of newly generated methane with thermogenic methane already in place in the reservoir can cause very complicated isotopic signatures system openness also was considered for shallow biodegraded gas accumulations gases from the daqing anticline are relatively wet with 13c enriched methane and 13c depleted co2 representing typically thermogenic origin gases within the longhupao da an terrace have variable dryness 13c enriched methane and variable 13c of co2 suggesting dominant thermogenic origin and minor secondary microbial methane augment the puqian ao nan uplift contains relatively dry gas with 13c depleted methane and 13c enriched co2 typical for secondary microbial gas with a minor part of thermogenic methane gas accumulations in the western slope are very dry with low carbon dioxide concentrations some gases contain 13c depleted methane ethane and propane indicating low maturity primary microbial origin recognition of varying genetic gas types in the songliao basin helps explain the observed dominance of gas in the shallow reservoir and could serve as an analogue for other similar shallow gas systems