extension subsidence and thermal evolution of the los angeles basin a two dimensional model abstract the los angeles basin is a narrow deep basin containing large oil fields its formation began in the middle miocene and its subsidence has been extraordinarily rapid we suggest that although the basin is in a predominantly strike slip tectonic environment the subsidence is largely a result of crustal extension simple one dimensional extension models ignoring the lateral flow of heat are inadequate to explain the rapidity of the subsidence we use a two dimensional numerical method to model the thermal evolution of the basin based on our model studies the central southwest northeast and palos verdes blocks are inferred to have been extended by 178 69 20 and 27 respectively the average crustal extension for the whole basin is 66 the lateral flow of heat out of the central block into adjacent cooler blocks accounts for its rapid subsidence during the early stage the deepest sediments are predicted to have been heated to about 210 c hydrocarbon maturity calculations indicate that the upper miocene sediments reached oil maturity a little over 4 m y b p no sediment is predicted to have achieved natural gas maturity

a first look at the structure of the wave pouch during the 2009 predict grip dry runs over the atlantic abstractin support of the national science foundation pre depression investigation of cloud systems in the tropics nsf predict and national aeronautics and space administration genesis and rapid intensification processes nasa grip dry run exercises and national oceanic and atmospheric administration hurricane intensity forecast experiment noaa ifex during the 2009 hurricane season a real time wave tracking algorithm and corresponding diagnostic analyses based on a recently proposed tropical cyclogenesis model were applied to tropical easterly waves over the atlantic the model emphasizes the importance of a lagrangian recirculation region within a tropical wave critical layer the so called pouch where persistent deep convection and vorticity aggregation as well as column moistening are favored for tropical cyclogenesis distinct scenarios of hybrid wave vortex evolution are highlighted it was found that easterly waves without a pouch or with a shallow pouch did not develop although not all wav

core complex geometries and regional scale flow in the lower crust a simple flexural model that treats the lithosphere as a thin elastic plate overlying a fluid asthenosphere produces an excellent fit to the domal detachment fault geometries observed in typical core complexes of the basin and range province however this mode of isostatic compensation requires an unacceptably large reduction in local topographic elevation 3 5 km above core complex structures because topographic lows of this magnitude are not observed above core complexes today it requires mountain ranges 3 5 km higher than the surrounding areas to have existed at the site of each future core complex and requires these mountain ranges to have had large crustal roots that were subsequently uplifted to form a flat moho as the core complexes developed an alternate mode of isostatic compensation whereby compensation occurs primarily by regional scale flow of material within the lower crust beneath an elastic midcrust provides an equally good fit to the observed detachment fault geometries while requiring little reduction in local topographic elevation above developing core complex structures and providing an obvious means of maintaining a flat moho beneath these zones of upper crustal doming if this interpretation is correct then the effective elastic plate thickness below the basin and range province probably cannot exceed a maximum of about 4 km with a best guess estimate of about 0 5 to 1 km computation of the temperature structure associated with crustal flow during doming shows that an increase in temperature at the moho of about 100 c follows doming by several million years perhaps explaining the observed coincidence of core complexes with crustally derived igneous rocks subsequent cooling of the mid to lower crust beneath the core complex could result in freezing of the initially ductile lower crust within the core of the dome effectively locking the domal shape into the crust even after the detachment surface is cut by younger faults

lithologic control of the depth of earthquakes in southern california the depth distribution of southern california earthquakes indicates that areas underlain by schist basement rocks have a shallower 4 to 10 kilometers maximum depth of earthquakes than do areas with other types of basement rocks the predominant minerals in the schists become plastic at lower temperatures and thus at shallower depths than the minerals in the other basement rocks the lateral variations in lithology will control the depth extent and thus the magnitudes of potential future earthquakes these depths can be determined from the depth of the current background seismicity

the multiple vortex nature of tropical cyclogenesis abstract this study explores the extent to which potential vorticity pv generation and superposition were relevant on a variety of scales during the genesis of tropical storm allison allison formed close to shore and the combination of continuous doppler radar satellite aircraft and surface observations allows for the examination of tropical cyclogenesis in great detail preceding allison s genesis pv superposition on the large scale created an environment where decreased vertical shear and increased instability surface fluxes and low level cyclonic vorticity coexisted this presented a favorable environment for meso scale pv production by widespread convection and led to the formation of surface based meso scale vortices termed convective burst vortices cbvs the cbvs seemed to form in association with intense bursts of convection and rotated around each other within the meso circulation field one cbv eventually superposed with a mesoscale convective vortex mcv resulting in a mor

african easterly wave variability and its relationship to atlantic tropical cyclone activity abstract automatic tracking of vorticity centers in european centre for medium range weather forecasts analyses has been used to develop a 20 yr climatology of african easterly wave activity the tracking statistics at 600 and 850 mb confirm the complicated easterly wave structures present over the african continent the rainy zone equatorward of 15 n is dominated by 600 mb activity and the much drier saharan region poleward of 15 n is more dominated by 850 mb activity over the atlantic ocean there is just one storm track with the 600 and 850 mb wave activity collocated based on growth decay and genesis statistics it appears that the 850 mb waves poleward of 15 n over land generally do not get involved with the equatorward storm track over the ocean instead there appears to be significant development of 850 mb activity at the west african coast in the rainy zone around 10 n 10 w which it is proposed is associated with latent heat release based on the tracking statistics it has been shown th

genesis of hurricane julia 2010 within an african easterly wave developing and nondeveloping members from wrf letkf ensemble forecasts abstractin this study the predictability of and parametric differences in the genesis of hurricane julia 2010 are investigated using 20 mesoscale ensemble forecasts with the finest resolution of 1 km results show that the genesis of julia is highly predictable with all but two members undergoing genesis despite the high predictability substantial parametric differences exist between the stronger and weaker members notably the strongest developing member exhibits large upper tropospheric warming within a storm scale outflow during genesis in contrast the nondeveloping member has weak and more localized warming due to inhibited convective development and a lack of a storm scale outflow a reduction in the rossby radius of deformation in the strongest member aids in the accumulation of the warmth while little contraction takes place in the nondeveloping member the warming in the upper troposphere is responsible for the development of meso scale surface pressure falls and a meso surface low i

the role of vortical hot towers in the formation of tropical cyclone diana 1984 abstract a high resolution 3 km horizontal grid spacing near cloud resolving numerical simulation of the formation of hurricane diana 1984 is used to examine the contribution of deep convective processes to tropical cyclone formation this study is focused on the 3 km horizontal grid spacing simulation because this simulation was previously found to furnish an accurate forecast of the later stages of the observed storm life cycle the numerical simulation reveals the presence of vortical hot towers or cores of deep cumulonimbus convection possessing strong vertical vorticity that arise from buoyancy induced stretching of local absolute vertical vorticity in a vorticity rich prehurricane environment at near cloud resolving scales these vortical hot towers are the preferred mode of convection they are demonstrated to be the most important influence to the formation of the tropical storm via a two stage evolutionary process i preconditioning of the local environment via diabatic production of mul

the impact of moist frontogenesis and tropopause undulation on the intensity size and structural changes of hurricane sandy 2012 abstractthis study examines the relative roles of moist frontogenesis and tropopause undulation in determining the intensity size and structural changes of hurricane sandy using a high resolution cloud resolving model a 138 h simulation reproduces sandy s four distinct development stages i rapid intensification ii weakening iii steady maximum surface wind but with large continued sea level pressure slp falls and iv reintensification results show typical correlations between intensity changes sea surface temperature and vertical wind shear during the first two stages the large slp falls during the last two stages are mostly caused by sandy s northward movement into lower tropopause regions associated with an eastward propagating midlatitude trough where the associated lower stratospheric warm air wraps into the storm and its surrounding areas the steady maximum surface wind occurs because of the widespread slp falls with weak gradients lacking significant inward advection of absolute

a global view of equatorial waves and tropical cyclogenesis abstractthis study investigates the number of tropical cyclone formations that can be attributed to the enhanced convection from equatorial waves within each basin tropical depression td type disturbances i e easterly waves were the primary tropical cyclone precursors over the northern hemisphere basins particularly the eastern north pacific and the atlantic in the southern hemisphere however the number of storms attributed to td type disturbances and equatorial rossby waves were roughly equivalent equatorward of 20 n tropical cyclones formed without any equatorial wave precursor most often over the eastern north pacific and least often over the western north pacific the madden julian oscillation mjo was an important tropical cyclone precursor over the north indian south indian and western north pacific basins the mjo also affected tropical cyclogenesis by modulating the amplitudes of higher frequency waves each wave type reached the attribution threshold 1 5 times more often and tropi

magmatism as an essential driving force for formation of active metamorphic core complexes in eastern papua new guinea the d entrecasteaux islands in eastern papua new guinea are composed of a number of active metamorphic core complexes which have been intruded by granodiorite plutons during their formation the plutons do not appear to have been intruded by diapiric processes as previously suggested late relatively undeformed plutons form flat lying bodies which crosscut structural boundaries and are strongly discordant to core complex shear zones granodiorite magmatism and the development of the metamorphic core complexes have occurred in a linear zone which coincides with a zone of thick crust and rugged topography it is proposed that plutonism facilitated deformation in ductile extensional shear zones which resulted in tectonic exhumation of deep crustal rocks and formation of the metamorphic core complexes the source of the plutons is thought to be related to a linear zone of mantle upwelling beneath the islands related to the propagation of the woodlark seafloor spreading center into continental crust it is suggested that a localized heat source of this type which can provide heat and magmatic material to the crust is essential for the development of metamorphic core complexes

ophiolitic basement to a forearc basin and implications for continental growth the coast range great valley ophiolite california we present a compilation of 18 published models from the length of the great valley forearc basin california based on seismic reflection borehole seismic refraction gravity and aeromagnetic data to address long standing questions about the nature of the basement to the great valley its origin its tectonic history and it s mechanism of incorporation into the north american continental margin the geophysical models permit a 700 km long 70 km wide complete ophiolite sequence beneath the entire great valley in the northern great valley the ophiolite is overlain by ophiolitic breccia the ophiolite crust is 7 8 km thick and the mantle section is mostly unserpentinized beneath the southern great valley there is no ophiolitic breccia the crust may be up to 10 12 km thick and the mantle section if present at all is serpentinized to such a degree that it cannot be distinguished from sierran basement or mafic ophiolite members on the basis of velocity or density data geochemical petrological and paleomagnetic data support suprasubduction zone ophiolite formation at north american paleolatitudes and geological data and geophysical models are consistent with ophiolite formation by back arc spreading behind an east facing arc in the north this was apparently followed by obduction of back arc crust onto older continental basement during the late jurassic nevadan orogeny in the south the newly formed intraoceanic arc and back arc apparently collided with the continental margin during the nevadan orogeny but were not obducted onto it instead the arc and back arc docked with the continental margin leaving the arc itself to become the basement to the great valley basin cretaceous sierran magmatism then intruded plutons beneath the docked ophiolite and mafic arc irrespective of the detailed accretionary history our cross sections show a rapid pulse of continental growth by ophiolite accretion of more than 500 km km 1 in less than 10 myr

shortening within underplated oceanic crust beneath the central california margin structures within a tectonically underplated layer of early miocene age oceanic crust indicate that the lower crust of offshore central california has been deformed under compression prior to the inception of the san andreas transform system along the continental margin shortening in the lower crust is inferred from the geometry of two structures the santa lucia monocline and the santa maria antiform delineated by an integrated interpretation of multichannel and wide angle seismic reflection data in conjunction with regional gravity data and teleseismic receiver functions the 700 km of multichannel seismic data and 300 km of wide angle seismic data from the 1986 pacific gas and electric edge seismic experiment form the primary data base used to establish the northwesterly trend and extent of the monocline and the wnw trend of the antiform in cross sectional view the santa lucia monocline is a 30 kink in the oceanic crust while the santa maria antiform is characterized by local thickening of the oceanic crust these structures are probably the result of convergence between the monterey and arguello microplates that took place as subduction along the margin waned the multichannel seismic reflection data image two miocene age shelf basins the santa lucia and offshore santa maria basins that formed within a transtensional stress regime the offshore santa maria basin directly overlies the santa maria antiform suggesting that either the upper and lower crustal stress regimes were completely decoupled in miocene time or that the two features formed in different places differential slip between the upper crust and lower crust may have been accommodated along a detachment zone located above oceanic crust convergence within the oceanic crust and apparent differential motion between upper and lower crust are indicative of the processes that can affect the transition from subduction to an oceanic continental transform zone

three stage evolution of the los angeles basin southern california we propose that an episode of transtension dominated development of the los angeles basin area from 12 to 6 ma following middle miocene transrotation and prior to the modern transpressional regime transtension resulted from the releasing bend of the san gabriel chino hills cristianitos fault which acted as the primary transform boundary in southern california during this episode such an interpretation implies that significant transform motion did not occur on the southern san andreas fault prior to 6 ma and that the gulf of california has opened primarily since 6 ma we propose a three stage model for evolution of the los angeles basin and vicinity within the evolving transform fault system transrotation 18 12 ma transtension 12 6 ma and transpression 6 0 ma timing of these stages correlates with microplate capture events which occurred during conversion from a convergent margin to a transform margin

genesis of tropical storm debby 2006 within an african easterly wave roles of the bottom up and midlevel pouch processes abstractthe bottom up generation of low level vortices lvs and midlevel vortices mvs during the genesis of tropical storm debby 2006 and the roles of a midlevel marsupial pouch associated with an african easterly wave aew are examined using an 84 h simulation with the finest grid size of 1 33 km results show that several mvs are generated in leading convective bands and then advected rearward into stratiform regions by front to rear ascending flows because of different lagrangian storm scale circulations mvs and lvs are displaced along different paths during the early genesis stages mvs propagate cyclonically inward within the aew pouch while experiencing slow intensification and merging under the influence of converging flows the mvs merging into a mesovortex is accelerated as they come closer to each other in the core region in contrast the low level lagrangian circulation is opened as a wave trough prior to tropical depression td stage so the lvs tend to escape from the pouch r

case study of an intense african easterly wave abstract the life cycle of an intense african easterly wave aew over the african continent is examined using european centre for medium range weather forecasts ecmwf operational analyses meteosat satellite images and synoptic observations this system the strongest aew of 2000 can be tracked from central north africa into the eastern atlantic ocean where it is associated with the genesis of hurricane alberto synoptic analysis of the kinematic and thermodynamic fields is supplemented by analysis of potential vorticity pv allowing exploration at the role of multiple scales in the evolution of this aew the authors analysis promotes the division of the aew life cycle into three distinctive phases i initiation the aew development is preceded by a large convective event composed of several mesoscale convective systems over elevated terrain in sudan this convection provides a forcing on the baroclinically and barotropically unstable state that exists over tropical north africa ii baroclini

upper crustal structure and neogene tectonic development of the california continental borderland multichannel seismic reflection data sonobuoy seismic refraction data and regional geology are used to define the upper crustal structure of the southern california continental borderland and to delineate the characteristics of the main lithotectonic belts of the region the catalina schist belt is separated on its west side from the gently deformed nicolas forearc belt by faults that have steep west dips and pronounced normal separations on its east side the schist belt is bounded by a large detachment fault that dips gently to the east beneath the west edge of the peninsular ranges belt at the coastline near oceanside the catalina schist was uplifted from middle crustal depths and exposed during a major event of extensional tectonism that started in early miocene time in conjunction with about 10 of clockwise rotation of the western transverse ranges belt part of the uplift of the catalina schist could have occurred on the detachment fault but it is thought to have mostly occurred on the steep faults that bound the west edge of the schist belt a large amount of uplift is required and it probably involved strong footwall flexural deformation in the wake of the translating and rotating western transverse ranges and nicolas forearc belts extension accompanied by probable large amounts of right slip continued in the borderland region during and after middle miocene time the later stage of extension was accompanied by rapid clockwise rotation of the western transverse ranges of at least 90 most of the borderland including the belt of schist that was uplifted in early miocene time was further deformed into numerous basins and ridges during this stage of oblique extension the primary driving force for the deformation is thought to have been derived from the rapid northwest motion of the pacific plate after it had become coupled to the farallon plate system which had previously been subducted beneath the borderland

genesis of hurricane julia 2010 within an african easterly wave low level vortices and upper level warming abstractwhile a robust theoretical framework for tropical cyclogenesis tcg within african easterly waves aews has recently been developed little work explores the development of low level meso scale vortices llvs and a meso scale surface low in relation to deep convection and upper tropospheric warming in this study the development of an llv into hurricane julia 2010 is shown through a high resolution model simulation with the finest grid size of 1 km the results presented expand upon the connections between llvs and the aew presented in previous studies while demonstrating the importance of upper tropospheric warming for tcg it is found that the significant intensification phase of hurricane julia is triggered by the pronounced upper tropospheric warming associated with organized deep convection the warming is able to intensify and expand during tcg owing to formation of a storm scale outflow beyond the rossby radius of deformation results confirm previous ideas by demonstrating that th

transformation of a large monsoon depression to a tropical storm during tcm 93 abstract data obtained during two aircraft observing periods aop from the tcm 93 mini field experiment are used to describe the transformation between 5 and 10 n of a large depression in the western north pacific monsoon trough into a tropical cyclone over a 36 h period the transformation is defined to occur in three stages although a large mesoscale convective system mcs was present along the eastern periphery of the monsoon depression during the preorganization stage characterized by observations from the first aop the overall convective organization of the broad circulation is weak the structure of the mcs provided a midlevel subsynoptic contribution to the vorticity of the monsoon depression and contributed to a shift in the center of the monsoon depression circulation between 800 and 600 mb toward the mcs location however the presence of unsaturated downdrafts associated with the mcs perturbed the low level thermodynamic conditions and contributed to the rapid decay of the mcs slow intens

genesis of tropical storm eugene 2005 from merging vortices associated with itcz breakdowns part ii roles of vortex merger and ambient potential vorticity abstract in this study the roles of merging midlevel mesoscale convective vortices mcvs and convectively generated potential vorticity pv patches embedded in the intertropical convergence zone itcz in determining tropical cyclogenesis are examined by calculating pv and absolute vorticity budgets with a cloud resolving simulation of tropical storm eugene 2005 results show that the vortex merger occurs as the gradual capture of small scale pv patches within a slow drifting mcv by another fast moving mcv thus concentrating high pv near the merger s circulation center with its peak amplitude located slightly above the melting level the merging phase is characterized by sharp increases in surface heat fluxes low level convergence latent heat release and upward motion lower tropospheric pv surface pressure falls and growth of cyclonic vorticity from the bottom upward melting and freezing appear to affect markedly the vertical structures of diabatic heating convergence absolute vorticity

a balanced cross section of the 1994 northridge earthquake southern california the northridge earthquake of 17 january 19941 was the latest in a series of very damaging thrust fault generated earthquakes to strike california following the san fernando2 1971 coalinga3 1983 and whittier narrows4 5 1987 events like the last two of these the northridge event occurred along a fault that did not reach the surface and which had not been detected by traditional seismic hazard methods6 7 balanced cross sections8 9 which flatten and remove the crustal deformation can be used to identify and quantify the seismic hazard posed by thrust faults here we present a balanced cross section through the northridge portion of the transverse ranges fold and thrust belt10 which shows that the earthquake occurred on what we call the pico thrust a cross section of this sort constructed before the earthquake would have revealed the fault although it would not have predicted the earthquake cross sectional modelling of the pico thrust yields an average slip rate of 1 4 1 7 mm yr 1 and a recurrence interval of northridge sized mw 6 7 earthquakes every 1 500 1 800 years we show that the pico thrust is the back thrust to the 170 km elysian park thrust3 4 which underlies some of the most densely urbanized portions of the los angeles basin

kinematics of present crust and mantle flow in southern california in the southern california region published geologic studies of prehistoric fault offsets yield at least 81 rates of slip covering various periods of time chiefly since the opening of the gulf of california these rates together with the known geometries of active faults are used to constrain a hand fit block model for present horizontal velocity of the crust the assumptions employed are that these rates apply to the present that the blocks are internally rigid down to the greatest depth of earthquakes and that the over all pacific north american plate motion is correctly given by global models the resulting model fits 67 data within their uncertainties 10 more with a small discrepancy 1 mm yr and fails to accommodate only 4 data 2 of which are inconsistent with other data nominal precision is good 3 mm yr but accuracy and uniqueness are both suspect because many block boundaries are questionable despite its many local defects this model suggests four reliable regional conclusions first the rate of shortening on the south side of the transverse ranges varies from 6 to 14 mm yr increasing eastward which implies an unrecognized seismic hazard unless the motion is taken up by folding or fault creep second the pattern of block rotation rates is quite different from the pattern of rotations shown by tertiary paleomagnetic declinations which implies some major pliocene reorganization of blocks third the great bend left step of the plate boundary fault system in the transverse ranges appears to be straightening gradually by a 3 m y clockwise rotation relative to both plates finally if it is assumed that plate shortening has been occurring at this bend since the early pliocene and that crust and upper mantle velocities are similar then this model predicts mantle lithosphere downwelling to at least 250 km depth beneath the transverse ranges this prediction is consistent with upper mantle seismic velocity structure

numerical simulation of the meso β scale structure and evolution of the 1977 johnstown flood part ii inertially stable warm core vortex and the mesoscale convective complex abstract a mesoscale warm core vortex associated with the mesoscale convective complex mcc that produced the 1977 johnstown flood is examined using a three dimensional nested grid model simulation of the flood episode in the simulation the vortex plays a key role in determining the evolution of the mcc a squall line and the distribution of heavy precipitation the vortex has a space scale of 100 200 km in diameter and a time scale of more than 18 hours its low pressure center extends from the midtroposphere down to the surface and its maximum vorticity occurs between 850 and 700 mb a pool of cool moist downdraft air develops in the surface to the 850 mb layer beneath the warm core while a cold dome forms in the vicinity of the tropopause above the warm core following forcing from repeated deep convection prior to model initial time the vortex is initiated by mesoscale ascent associated with a traveling meso scale wave genesis takes place in a nearly saturated slightly conditionally unstabl

convective contribution to the genesis of hurricane ophelia 2005 abstract the convection occurring in the tropical depression that became hurricane ophelia 2005 was investigated just prior to tropical storm formation doppler radar showed a deep wide intense convective cell of a type that has been previously thought to occur in intensifying tropical depressions but has not heretofore been documented in detail the updraft of the cell was 10 km wide 17 km deep had updrafts of 10 20 m s 1 throughout its mid to upper levels and contained a cyclonic vorticity maximum the massive convective updraft was maintained by strong positive buoyancy which was maximum at about the 10 km level probably aided by latent heat of freezing evaporative cooling and precipitation drag occurred in the rain shower of the cell but were insufficient to produce a strong downdraft or gust front outflow to force the updraft the convective updraft was fed by a layer of strong inflow that was several kilometers deep wind induced turbulence just above the ocean surface enriched the equi

genesis of typhoon chanchu 2006 from a westerly wind burst associated with the mjo part i evolution of a vertically tilted precursor vortex abstract although previous studies have shown the relationship between the madden julian oscillation mjo and tropical cyclogenesis tcg many scale interactive processes leading to tcg still remain mysterious in this study the larger scale flow structures and evolution during the pregenesis genesis and intensification of typhoon chanchu 2006 near the equator are analyzed using ncep s final analysis satellite observations and 11 day nested numerical simulations with the advanced research weather research and forecast model arw wrf results show that the model could reproduce the structures and evolution of a synoptic westerly wind burst wwb associated with the mjo during the genesis of chanchu including the eastward progression of a wwb from the indian ocean into the pacific ocean the modulation of the associated quasi symmetric vortices the initial slow spinup of a northern pre chanchu disturbance at the northeastern periphery of the wwb and its general track and intensification it i

synoptic scale influence of the saharan air layer on tropical cyclogenesis over the eastern atlantic abstract the formations of hurricane andrew tropical storm ernesto and hurricane luis which occurred respectively during the 1992 1994 and 1995 hurricane seasons over the eastern atlantic have been investigated by utilizing the european centre for medium range weather forecasts ecmwf gridded data analyses these cases were selected to illustrate the contrasting influences of the saharan air layer sal on tropical cyclogenesis analyses results show that tropical storm ernesto 1994 and hurricane luis 1995 formed from the merger of the low level 925 hpa and midlevel 700 hpa vortices over the eastern atlantic within the monsoon trough enhanced by surges in the trades midlevel vortices associated with each case appear to evolve from african wave troughs enhanced by cyclonic shear vorticity of the midtropospheric jet which existed to the south of an sal anticyclonic eddy as an elongated wind maximum vorticity budget calculations suggest that vortex stretching dominated the enhancement of

progressive growth of san clemente island california by blind thrust faulting implications for fault slip partitioning in the california continental borderland we find that the genesis of san clemente island and its surrounding submarine platform is consistent with progressive slip on two southeast striking southwest dipping blind thrust fault segments since their inception 2 to 5 ma 3 km of compression normal to the n150 e fault strike has been accommodated with 1700 m of domal uplift of the san clemente anticlinorium the existence of an extensive suite of pleistocene marine terraces provides evidence that slip and uplift are continuing today based on direct terrace fossil age determinations and correlations of terrace heights with global sea level curves we estimate that san clemente island is currently uplifting at between 0 2 and 0 5 mm yr 1 this translates into 0 6 1 5 mm yr 1 of thrusting on the causative blind thrusts beneath the island unlike the situation at nearby palos verdes where a simple twist in a regional strike slip fault accommodated both fault parallel and fault normal motions the shallow dips of the thrusts suggest that if regional strike slip motion on the san clemente fault exists it must be partitioned onto through going surfaces distinct from the thrusts current gps data are sparse and equivocal but they indicate that 1 4 mm yr 1 of compression and 4 7 mm yr 1 of strike slip are absorbed in the california continental borderland with the palos verdes fault taking some 3 mm yr 1 from the strike slip budget 1 4 mm yr 1 of motion could be present on a through going san clemente fault when translated into an annual moment release rate using kostrov s formula gps strains predict that between 2 5 and 4 9 times 1017 n m yr 1 of earthquake potential is available offshore from san diego to the santa barbara channel distribution of this moment budget among various earthquake magnitudes is arguable but we predict that m 6 quakes in the borderland could recur between 30 and 80 years and m 7 quakes might be found every 310 to 580 years

three dimensional vp and vp vs velocity models of the los angeles basin and central transverse ranges california we use p and s arrival times from 5225 earthquakes and 53 explosions recorded by the southern california seismographic network to invert for the three dimensional p velocity v p and the p and s velocity ratio v p v s in the central transverse ranges and the los angeles basin to model long wavelength features of the velocity structure we invert for the models by interpolating models determined successively from a sparse medium to a dense grid with 40 20 and 10 km spacing of horizontal grid nodes layers of grid nodes are placed at depths of 1 4 6 8 12 16 and 20 km the data variance decreased about 80 in the gradational inversion ample data from the 1994 northridge and other earthquake sequences the rich background seismicity and the dense station distribution along with controlled sources made the model well resolved except along the edges to the southwest in the offshore region and at depths greater than 20 km the v p model images the shape of the los angeles and east ventura basins down to depths of 8 and 12 km three low velocity areas at 1 km depth in the los angeles basin that coincide with recent sediment depositional areas are also imaged the north edge of the peninsular ranges the santa monica and the san gabriel mountains form discontinuous high velocity ridges extending to depths of 20 km the high v p v s ratios in the near surface are consistent with high pore fluid pressures in the basin sediments at depth beneath the east ventura basin the high v p v s and high v p suggest the presence of ophiolitic assemblages or mid miocene volcanics in contrast a body with normal v p and low v p v s that is identified in the upper crust beneath santa monica bay may be a fragment of quartz rich continental crust the v p model of both the ventura and the los angeles basins shows features that suggest deformation of the hanging wall or basin closure at seismogenic depths of 16 km the hypocenters of moderate sized and large earthquakes are located within or adjacent to high v p velocity bodies in most cases these high velocity bodies form the upper block consistent with shortening of the lower crust as described in thick skinned tectonic interpretations

thermodynamic aspects of tropical cyclone formation abstractthe thermodynamic aspects of tropical cyclone tc formation near the center of the wave pouch a region of approximately closed lagrangian circulation within the wave critical layer are examined through diagnoses of a high resolution numerical simulation and dropsonde data from a recent field campaign it is found that the meso area near the pouch center is characterized by high saturation fraction small difference in equivalent potential temperature e between the surface and the middle troposphere and a short incubation time scale updrafts tend to be more vigorous in this region presumably because of reduced dry air entrainment while downdrafts are not suppressed the thermodynamic conditions near the pouch center are thus critically important for tc formation the balanced responses to convective and stratiform heating at the pregenesis stage are examined using the sawyer eliassen equation deep convection is concentrated near the pouch center the strong radial and vertical gradients o

tropical storm development from african easterly waves in the eastern atlantic a comparison of two successive waves using a regional model as part of nasa amma 2006 abstract two successive african easterly waves aews from august 2006 are analyzed utilizing observational data the european centre for medium range weather forecasts reanalysis and output from the national center for atmospheric research national oceanic and atmospheric administration weather research and forecasting model wrf to understand why the first wave does not develop over the eastern atlantic while the second wave does the first aew eventually forms hurricane ernesto over the caribbean sea but genesis does not occur over the eastern atlantic the second wave although weaker than the first over land leaves the west african coast and quickly intensifies into tropical storm debby west of the cape verde islands this study shows that the environmental conditions associated with the first aew s passage inhibited development these conditions include strong low and midtropospheric vertical wind shear owing to a stronger than normal african easterly jet lower than normal relative humidity a

nonlinear refraction and reflection travel time tomography we develop a rapid nonlinear travel time tomography method that simultaneously inverts refraction and reflection travel times on a regular velocity grid for travel time and ray path calculations we apply a wave front method employing graph theory the first arrival refraction travel times are calculated on the basis of cell velocities and the later refraction and reflection travel times are computed using both cell velocities and given interfaces we solve a regularized nonlinear inverse problem a laplacian operator is applied to regularize the model parameters cell slownesses and reflector geometry so that the inverse problem is valid for a continuum the travel times are also regularized such that we invert travel time curves rather than travel time points a conjugate gradient method is applied to minimize the nonlinear objective function after obtaining a solution we perform nonlinear monte carlo inversions for uncertainty analysis and compute the posterior model covariance in numerical experiments we demonstrate that combining the first arrival refraction travel times with later reflection travel times can better reconstruct the velocity field as well as the reflector geometry this combination is particularly important for modeling crustal structures where large velocity variations occur in the upper crust we apply this approach to model the crustal structure of the california borderland using ocean bottom seismometer and land data collected during the los angeles region seismic experiment along two marine survey lines details of our image include a high velocity zone under the catalina ridge but a smooth gradient zone between catalina ridge and san clemente ridge the moho depth is about 22 km with lateral variations

a vortical hot tower route to tropical cyclogenesis abstract a nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions observations motivate the focus on the problem of how a midtropospheric cyclonic vortex a frequent by product of mesoscale convective systems during summertime conditions over tropical oceans may be transformed into a surface concentrated warm core tropical depression as a first step the vortex transformation is studied in the absence of vertical wind shear or zonal flow within the cyclonic vorticity rich environment of the mesoscale convective vortex mcv embryo the simulations demonstrate that small scale cumulonimbus towers possessing intense cyclonic vorticity in their cores vortical hot towers vhts emerge as the preferred coherent structures the vhts acquire their vertical vorticity through a combination of tilting of mcv horizontal vorticity and stretching of mcv and vht generated vertical vorticity horizontally localized and exhibiting conve

tropical cyclogenesis associated with rossby wave energy dispersion of a preexisting typhoon part i satellite data analyses abstract the structure and evolution characteristics of rossby wave trains induced by tropical cyclone tc energy dispersion are revealed based on the quick scatterometer quikscat and tropical rainfall measuring mission trmm microwave imager tmi data among 34 cyclogenesis cases analyzed in the western north pacific during 2000 01 typhoon seasons six cases are associated with the rossby wave energy dispersion of a preexisting tc the wave trains are oriented in a northwest southeast direction with alternating cyclonic and anticyclonic vorticity circulation a typical wavelength of the wave train is about 2500 km the tc genesis is observed in the cyclonic circulation region of the wave train possibly through a scale contraction process the satellite data analyses reveal that not all tcs have a rossby wave train in their wakes the occurrence of the rossby wave train depends to a certain extent on the tc intensity and the background flow whether or not a rossby wave train can finally lead to cy

petrogenesis of the conejo volcanic suite southern california evidence for mid ocean ridge continental margin interactions the evolution of the southern california borderland during mid miocene time was dependent on the interactions between the north american continent and the converging east pacific rise evidence from geological and geochemical investigations of the conejo volcanic suite whose petrogenesis is linked to these interactions suggests an intimate relation between the subducting ridge and the volcanic rocks the whole rock chemistry of this suite k2o 0 4 87sr 86sr 0 70248 0 70372 average 0 70306 tio2 1 2 1 8 and restricted range of pyroxene and plagioclase compositions support a model in which active ridge volcanism fractionation and mixing of primitive liquids with later differentiates can account for the observed petrologic evolution the interaction of the ridge with the subduction zone may result in the cessation of subduction the preferential subduction of the trenchward ridge flank or localized volcanism in the vicinity of the ridge subduction zone intersection

tropical cyclogenesis associated with rossby wave energy dispersion of a preexisting typhoon part ii numerical simulations abstract the cyclogenesis events associated with the tropical cyclone tc energy dispersion are simulated in a 3d model a new tc with realistic dynamic and thermodynamic structures forms in the wake of a preexisting tc when a large scale monsoon gyre or a monsoon shear line flow is present maximum vorticity generation appears in the planetary boundary layer pbl and the vorticity growth exhibits an oscillatory development this oscillatory growth is also seen in the observed rainfall and cloud top temperature fields the diagnosis of the model output shows that the oscillatory development is attributed to the discharge and recharge of the pbl moisture and its interaction with convection and circulation the moisture convection feedback regulates the tc development through controlling the atmospheric stratification raindrop induced evaporative cooling and downdraft pbl divergence and vorticity generation on one hand ascending motion associated with deep convection transports moisture upward and le

trace element geochemical correlation in the reworked proterozoic dalradian metavolcanic suites of the western ox mountains and nw mayo inliers ireland

genesis of pre hurricane felix 2007 part i the role of the easterly wave critical layer abstract the formation of pre hurricane felix 2007 in a tropical easterly wave is examined in a two part study using the weather research and forecasting wrf model with a high resolution nested grid configuration that permits the representation of cloud system processes the simulation commences during the wave stage of the precursor african easterly wave disturbance here the simulated and observed developments are compared while in part ii of the study various large scale analyses physical parameterizations and initialization times are explored to document model sensitivities in this first part the authors focus on the wave vortex morphology its interaction with the adjacent intertropical convergence zone complex and the vorticity balance in the neighborhood of the developing storm analysis of the model simulation points to a bottom up development process within the wave critical layer and supports the three new hypotheses of tropical cyclone formation proposed recently by dunkerton montgome

nonlinear refraction traveltime tomography a few important issues for performing nonlinear refraction traveltime tomography have been identified they include the accuracy of the traveltime and raypath calculations for refraction the physical information in the refraction traveltime curves and the characteristics of the refraction traveltime errors consequently we develop a shortest path ray tracing method with an optimized node distribution that can calculate refraction traveltimes and raypaths accurately in any velocity model we find that structure ambiguity caused by short and long rays in the seismic refraction method may influence the inversion solution significantly therefore we pose a nonlinear inverse problem that explicitly minimizes the misfits of the average slownesses ratios of traveltimes to the corresponding ray lengths and the apparent slownesses derivatives of traveltimes with respect to distance as a result we enhance the resolution as well as the convergence speed to regularize our inverse problem we use the tikhon

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

oceanic cyclogenesis as induced by a mesoscale convective system moving offshore part ii genesis and thermodynamic transformation abstract the genesis of intense cyclonic vorticity in the boundary layer and the transformation of a low level cold pool to a warm core anomaly associated with the long lived mesoscale convective systems mcss which produced the july 1977 johnstown flash flood and later developed into a tropical storm are examined using a 90 h real data simulation of the evolution from a continental mcs vortex to an oceanic cyclone storm system it is shown that the midlevel vortex trough at the end of the continental mcs s life cycle is characterized by a warm anomaly above and a cold anomaly below the mesovortex as it drifts toward the warm gulf stream water plays an important role in initiating and organizing a new mcs and a cyclonic shear vorticity band at the southern periphery of the previously dissipated mcs it is found from the vorticity budget that the vorticity band is amplified through stretching of absolute vorticity as it is wrapped around in a slantwise manner toward the cyclone center then the as

the genesis of hurricane guillermo texmex analyses and a modeling study abstract the transformation of a mesoscale convective system into hurricane guillermo was captured by aircraft and doppler wind data during the tropical experiment in mexico the early phase of the system evolves in a way very similar to previously documented mesoscale convective systems with a midlevel mesocyclone developing in the stratiform precipitation region more unusually the cyclone extends to low altitudes a weak cyclone is discernable even in the 300 m altitude wind field after another day of evolution a small surface based warm core cyclone is observed to develop within the relatively cold air associated with the mesocyclone aloft this mesocyclone develops into a hurricane over the subsequent day a nonhydrostatic axisymmetric numerical model is used to explore the evolution of the initially cold core midlevel vortex into a tropical cyclone a mesoscale midlevel showerhead is switched on in an initially quiescent tropical atmosphere overlying a warm ocean surface evaporation of t

analysis of african easterly wave structures and their role in influencing tropical cyclogenesis abstract composite structures of african easterly waves aews that develop into named tropical cyclones in the atlantic are compared and contrasted with nondeveloping aews using the 40 yr ecmwf re analysis era 40 data and satellite brightness temperature between 1979 and 2001 developing aews are characterized by a more distinctive cold core structure two days before reaching the west african coast as they move westward the convective activity increases further in the vicinity of the guinea highlands region at the same time the aew trough increases its vorticity at low levels consistent with a transformation toward a more warm core structure before it reaches the ocean as the aew moves over the ocean convection is maintained in the trough consistent with the observed tropical cyclogenesis the nondeveloping aew has a similar evolution before reaching the coast except that the amplitudes are weaker and there is less convective activity in the guinea highlands region the nondeveloping aew composite

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

global positioning system constraints on fault slip rates in southern california and northern baja mexico we use global positioning system gps estimates of horizontal site velocity to constrain slip rates on faults comprising the pacific north america plate boundary in southern california and northern mexico we enlist a simple elastic block model to parameterize the distribution and sum of deformation within and across the plate boundary we estimate a pacific north america relative plate motion rate of 49 3 mm yr one standard deviation consistent with nuvel 1a estimates we are able to resolve robust slip rate estimates for the southernmost san andreas san jacinto and elsinore faults 26 2 9 2 and 6 2 mm yr respectively and for the imperial and cerro prieto faults 35 2 and 42 1 mm yr respectively accounting for about 86 of the total plate motion the remaining 14 appears to be accommodated to the west of these fault systems probably via slip along the san clemente fault and or the san miguel vallecitos rose canyon and newport inglewood fault systems these results are highly consistent with paleoseismic estimates for slip rates implying that off fault strain accumulation within the deforming zone of the plate boundary is largely elastic we estimate that the seismically quiescent southernmost san andreas fault has incurred about 8 2 m of slip deficit over the last few hundred years presumably to be recovered during a future large earthquake

scale interactions during the formation of typhoon irving the development of typhoon irving is investigated using a variety of data including special research aircraft data from the tropical cyclone motion tcm 92 experiment objective analyses satellite data and traditional surface and sounding data the development process is treated as a dry adiabatic vortex dynamics problem and it is found that environmental and mesoscale dynamics mutually enhance each other in a cooperative interaction during cyclone formation synoptic scale interactions result in the evolution of the hostile environment toward more favorable conditions for storm development mesoscale interactions with the low level large scale circulations and with other midlevel mesoscale features result in development of vorticity in the midlevels and enhancement of the low level vorticity associated with the developing surface cyclone multiple developments of mesoscale convective systems after the storm reaches tropical depression strength suggests both an increase in low level confluence and a tendency toward recurrent development of associated mesoscale convective vortices this is observed in both aircraft data and satellite imagery where subsequent interactions including mergers with the low level tropical depression vortex are observed a contour dynamics experiment suggests that the movement of mesoscale convective systems in satellite imagery corresponds well to the movement of their associated midlevel vortices results from a simple baroclinic experiment show that the midlevel vortices affect the large scale low level circulation in two ways 1 initially interactions between midlevel vortices produce a combined vortex of greater depth 2 interaction between midlevel vortices and the low level circulation produces a development downward of the midlevel vorticity this strengthens the surface vortex and develops a more cohesive vortex that extends from the surface through the midtroposphere

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

geophysical evidence for the evolution of the california inner continental borderland as a metamorphic core complex we use new seismic and gravity data collected during the 1994 los angeles region seismic experiment larse to discuss the origin of the california inner continental borderland icb as an extended terrain possibly in a metamorphic core complex mode the data provide detailed crustal structure of the borderland and its transition to mainland southern california using tomographic inversion as well as traditional forward ray tracing to model the wide angle seismic data we find little or no sediments low 6 6 km s p wave velocity extending down to the crust mantle boundary and a thin crust 19 to 23 km thick coincident multichannel seismic reflection data show a reflective lower crust under catalina ridge contrary to other parts of coastal california we do not find evidence for an underplated fossil oceanic layer at the base of the crust coincident gravity data suggest an abrupt increase in crustal thickness under the shelf edge which represents the transition to the western transverse ranges on the shelf the palos verdes fault merges downward into a landward dipping surface which separates basement from low velocity sediments but interpretation of this surface as a detachment fault is inconclusive the seismic velocity structure is interpreted to represent catalina schist rocks extending from top to bottom of the crust this interpretation is compatible with a model for the origin of the icb as an autochthonous formerly hot highly extended region that was filled with the exhumed metamorphic rocks the basin and ridge topography and the protracted volcanism probably represent continued extension as a wide rift until 13 m y ago subduction of the young and hot monterey and arguello microplates under the continental borderland followed by rotation and translation of the western transverse ranges may have provided the necessary thermomechanical conditions for this extension and crustal inflow

a kinematic model for the late cenozoic development of southern california crust and upper mantle a model is presented for the young and ongoing kinematic deformation of southern california crust and upper mantle that accounts for both the known late cenozoic geologic record and upper mantle structure in this model the high velocity upper mantle transverse ranges anomaly is created through the convergence and sinking of the entire thickness of subcrustal lithosphere using typical scaling relations we estimate this anomaly to be 500 c colder and 1 more dense than average southern california mantle of the same depth we infer that subcrustal lithosphere from both sides of the convergence zone participates nearly equally in the construction of the anomaly the low velocity upper mantle anomaly beneath the salton trough region is attributed to high temperatures and 1 4 partial melt related to adiabatic decompression during mantle upwelling our model has crustal motions in the central transverse ranges region differing from mantle motions while the subcrustal lithosphere south of the transverse ranges moves toward and sinks beneath the transverse ranges the corresponding crust largely avoids convergence by adopting a more westerly direction of motion the differing velocity fields necessitates of a decoupling zone immediately south of the transverse ranges near the moho we interpret the upper mantle anomalies as results of small scale convection beneath southern california to which we attribute much of the recent tectonic activity in the region