insights into deglaciation of the largest ice free area in the south shetland islands antarctica from quantitative analysis of the drainage system abstract a quantitative geomorphic analysis of the drainage system on byers peninsula livingston island has been carried out in order to study the relief evolution glacial history and possible neotectonic influence on the largest ice free area of the south shetlands archipelago aerial photographs sar data from radarsat 2 satellite field work a digital elevation model and gis spatial analysis have been used to identify map and study the existing drainage basins a series of morphometric parameters have been studied in 30 selected basins in order to characterize their shape as well as the drainage network results in morphometric parameters reveal elongation trends in the shape of basins and a limited hierarchical network common of a youthful stage of landscape evolution models several morphometric indexes hypsometric integral hypsometric curves sl index transverse topographical drainage basin asymmetry t factor have been used to study possible controls on drainage development results have been discussed in relation to relief and drainage evolution linked to the spatial distribution of lithological units and structural framework t factor shows an apparently disorganized pattern and absence of tectonic influence however there are local values of second order basin asymmetry directions and magnitudes which could reflect a succession of master rills through time related to the changes in water supply during the deglaciation history of byers peninsula hypsometric values and curves of basins are also mainly related to a young stage of landscape evolution analysis of hypsometric integrals together with t factor index has allowed us to establish a possible deglaciation model on byers peninsula which successfully explains the results areas of different landscape evolution stage are linked in space and support the hypothesis of local glacial centers during the ice cover retreat process sl index results do not show the same pattern in results which could be due to differences between incision and lateral shifting ratios quantitative geomorphic analysis indicates that during the deglaciation of byers peninsula at least three areas acted as local glacial centers nw central and rotch dome area changes in index results clearly show a different behavior between two areas distal areas and proximal areas close to the glacial centers morphometric indexes have demonstrated their being useful tools to provide information on the glacial history in recently deglaciated antarctic areas

tectonic geomorphology of the southeastern mississippi embayment in northern mississippi usa we analyzed drainage basin geometry in part of the southeastern mississippi embayment near the new madrid seismic zone in order to detect areas of lateral stream migration that could indicate recent tectonism toward this goal a field of drainage basin asymmetry vectors was generated from a digital terrain model and compared to geologic structure lithofacies seismicity remotely sensed lineaments and major drainage divides transverse topographical drainage basin asymmetry t index results define geomorphic domains in northern mississippi 33 to 35 n 88 5 to 90 25 w that may reflect deep crustal blocks bounded by active faults or flexures t index measurements a proxy for lateral stream migration of more than 4500 second order drainage basins produced a two dimensional field of 282 spatially averaged vectors from which we interpreted 12 domains some domain boundaries correspond to mapped faults of two paleozoic fault systems in our study area the northeast striking mississippi valley graben system and the northwest striking ouachita thrust belt and foreland faults several other prominent domain boundaries may be previously unmapped faults flexures parallel to these systems this interpretation is supported by satellite image analysis of the northeastern study area which reveals lineaments consistent with our domain boundaries that have strikes that reflect the regional subsurface structural grain

geomorphological evidence of recent tilting in the central amazonia region abstract geomorphometric techniques applied to remote sensing data represent powerful tools as an aid for detecting terrain features produced by recent vertical crustal movements in a variety of landscapes in this work geomorphometric analysis of the central amazonia drainage network using shuttle radar topography mission srtm data was carried out to determine surface water loading and tectonic influence on the development of the uatuma and urubu river basins since the miocene the main objective was to detect geomorphological domains of lateral stream migration and channel sinuosity changes that could indicate recent vertical crustal movement to achieve this the transverse topographic symmetry factor and sinuosity index were applied to analyze the study area drainage network comparison of the geomorphological domains with structural field data and records of seismicity suggests that they are influenced by subsurface fault reactivation which coincides in space with faults mapped in outcrops that have activated since the miocene this interpretation is corroborated by the spatial correspondence between these faults with domain boundaries and shapes by river sinuosity change when crossing these boundaries and by a high concentration of seismic activity along one of these limits the crustal movement caused by hydrological loading can also influence such geomorphological features such is the case of lateral stream migrations of a domain in the opposite sense to the amazon river flow this may be a consequence of the more pronounced expression of hydrological loading in the negro and solimoes river confluence region

3d soft sediment deformation structures evidence for quaternary seismicity in the madrid basin spain three dimensional patterns of soft sediment deformation affecting middle pleistocene fluvial deposits in the lower manzanares valley sw madrid city are reported they promote a small scale hummocky topography defined by different sized domes mud volcanoes wavy ridges and fissures on an ancient flood plain surface related channel fill deposits are pervasively dewatered indicating liquefaction the sedimentological context reveals that the deformation of both floodplain surface and channel fill deposits were contemporaneous singular deformed level and generated at or near the ground surface this rules out the possibility of sediment loading and indicates a possible earthquake induced origin

identification of possible quaternary deformation in the northeastern mississippi embayment using quantitative geomorphic analysis of drainage basin asymmetry to investigate neotectonism in the mississippi embayment east of the new madrid seismic zone we identified geomorphic domains that show evidence of ground tilting during quaternary time transverse basin profiles were converted to two dimensional vectors that denote channel position with respect to basin divides these basin asymmetry vectors record the net direction and degree of lateral migration of trunk streams more than 2500 vectors were measured and spatially averaged within 400 km 2 bins this field of 300 mean vectors delineates several domains that show preferred directions of stream migrations possibly driven by ground tilting the timing of stream migration was interpreted using across valley distributions of quaternary alluvial terraces comparison of our mean vector field with subsurface structures suggests that some domain boundaries may be related to reactivated faults late quaternary activity is suggested for two northeast striking faults of the southeastern reelfoot rift margin we acquired two seismic profiles showing near surface faulting beneath scarps that follow the domain boundary associated with one of these northeast striking faults big creek fault zone reelfoot thrust seismicity ends on the south against this fault suggesting that the rift margin has dextral slip accommodating northeastward movement of the thrust hanging wall our vector field also suggests late quaternary movement on the reelfoot thrust and on two other northwest striking faults here termed the hatchie river fault and the wolf river fault several other weak domains may imply minor elements of neotectonism our results demonstrate that morphometric analysis of drainage basin asymmetry can be an effective reconnaissance tool within neotectonic settings

does maximum earthquake size depend on focal depth abstract while the gutenberg richter law gr with b value of 1 0 is an inexact description of the earthquake frequency magnitude distribution it does provide a convenient statistical basis for identifying when the largest earthquakes in a catalog are either anomalously large or anomalously small when the largest earthquakes are as predicted by the gr distribution it is inappropriate to infer that the largest historically known earthquake is the largest possible only when the largest observed earthquakes are significantly smaller than predicted can we infer that the largest possible earthquakes have occurred analysis of the global historical catalog demonstrates that at nearly all depths the largest deep and intermediate earthquakes have sizes close to those predicted by a gr distribution with b of 1 0 only between about 300 to 450 km and beneath 600 km are the largest known earthquakes somewhat larger than predicted however when geographically isolatable subgroups within catalogs are considered separately largest earthquakes that are either anomalously large or small are quite common often this is because individual regions have b values much different than 1 0 alternatively sometimes there appear to be physical constraints limiting the size of the largest possible earthquake as examples illustrating these assertions this article evaluates two subgroups deep focus earthquakes occurring beneath spain and intermediate depth earthquakes in the bucaramanga colombia nest

frequency moment distribution of deep earthquakes implications for the seismogenic zone at the bottom of slabs abstract we present a systematic investigation of the variation with depth of the frequency of earthquake occurrence vs seismic moment based on 16 years of harvard centroid moment tensor cmt solutions we analyze depth variations of earthquake size distribution in terms of variations in the absolute value of the slope of the regression of the logarithm of the population vs seismic moment a quantity known as the parameter the shallowest earthquakes 0 50 km depth exhibit a well defined and robust size distribution regime characterized by a discontinuous increase in with increasing moment others have shown that this increase probably represents the effects of a physical limit in the dimensions of the area of seismogenic slip of shallow earthquake sources the population of deep earthquakes in the depth interval 500 600 km shows two markedly different distributions the deep earthquakes in the tonga region feature an initially high value 0 92 at small moments and a lower value 0 41 at high moments in contrast the size distribution of non tonga deep events shows the reverse of those changes 0 41 at low moment and 1 17 at higher moment to help explain these observations we propose a model of deep seismogenesis that assumes three dimensional earthquake source regions that vary principally in their transverse dimensions the two segment behavior in the tonga region and other subduction zones is thought to represent in part constraints owing to the threshold of completeness of the cmt catalog and to its short time interval of sampling we interpret the differences between tonga and other deep wadati benioff zones as being a consequence of tonga s markedly higher subduction rate and hence its colder thermal structure and presumably thicker region of seismogenesis we interpret the critical moments at which values change in terms of variations in the transverse thickness of deep seismogenic zones and estimate that it is about 11 km for the tonga region and about 3 km for other zones at depths of 500 600 km these results are generally consistent with deep earthquakes being restricted to wedge shaped regions of peridotite persisting metastably to as deep as 700 km in old rapidly descending and hence cold slabs failure is thought to occur in metastable peridotite by transformational faulting great deep earthquakes present special challenges to any theory of deep earthquakes based on slab thermal structure for example a continuing question is how such large events can fit in a thermally controlled seismogenic zone that is diminishing in its transverse dimensions with increasing depth the very concept of a scale invariant earthquake size distribution may be inappropriate for these rare events and the unusual settings in which they are found

analysis of a relatively dry front during the taiwan area mesoscale experiment abstract the evolution of a relatively dry front during the early summer rainy season of taiwan is analyzed because of the synoptic subsidence associated with a subtropical high pressure cell over the northern south china sea prefrontal soundings over the taiwan area exhibited a shallow warm moist layer in the lowest levels capped by an inversion with extremely dry air aloft over the taiwan area the southwest flow ahead of the surface front was more than 10 m s 1 at the 850 mb level it interacted with the central mountain range resulting in the windward ridge leeside trough downstream of the blocked region strong southwesterly winds 1 5 m s 1 developed in the lowest levels along the northwest coast where the flow deflected by the mountain barrier merged with the undetected southwest monsoon flow the hilly terrain along the southeastern china coast retarded the cold air behind the surface front the cold air was then ducted around the southeastern china coast at the 850 mb level a weak s

semigeostrophic flow over orography in a stratified rotating atmosphere part i steady three dimensional solutions over finite ridges abstract three dimensional steady and inviscid flow over orography is examined by means of a semigeostrophic model a constant coriolis parameter f uniform potential vorticity and a uniform basic flow characterize this model first used by merkine and kalnay rivas it is demonstrated that the neglect of ageostrophic accelerations which characterize a semigeostrophic model essentially requires low rosssby number flow ro 0 3 and relatively small values of the nondimensional mountain height d 0 5 where d 3 103 m is the deformation depth in this parameter range the disturbance potential is a solution of laplace s equation the atmosphere is semi infinite and the finite amplitude lower boundary is an isentropic surface the basic solution expressed in prolate spheroidal coordinates provides disturbance flows over an isolated mountain finite ridges and the limiting flow over a two dimensional ridge a comparison between the quasi geostrophic and semigeostrophic responses to flow over the isola

the role of offshore convergence on coastal rainfall during tamex iop 3 abstract the role of offshore convergence on the coastal rainfall maximum along the northwestern coast of taiwan is analyzed based on tamex taiwan area mesoscale experiment data and numerical experiments using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 from a case study during tamex iop 3 moderate rainfalls 40 mm h 1 are observed along the northwestern coast of taiwan associated with the arrival of three rainbands in succession during 1000 1600 lst these rainbands form over the taiwan strait with northeast southwest or north south orientation they intensify off the northwestern coast there is a tendency for the most intense echoes to align in a northeast southwest orientation off the northwestern coast an orographically enhanced convergence zone with a northeast southwest orientation occurs in the area where the deflected southerly flow converges with the prevailing southwesterly flow that is modified by the storm

analysis of drainage basin symmetry as a rapid technique to identify areas of possible quaternary tilt block tectonics an example from the mississippi embayment there is a coincidence of seismicity and major river valleys in the southwestern mississippi embayment that suggests control of the drainage pattern by northwest trending faults pleistocene river terraces reveal a strong southwestward preferred river migration in this region that may be a result of fault block tilting a rapid new technique of drainage basin analysis is herein presented that quantifies transverse topographic basin symmetry these data permit discrimination of random stream migrations and regionally preferred stream migrations and identify the direction of maximum migration if bedrock dip can be shown to be a negligible influence on stream migration then the direction of regionally preferred migration implies a period of ground tilting in that direction drainage basin asymmetry vectors bearing and degree of asymmetry calculated from transverse topographic profiles of 271 4 km basin segments in the study area suggest preferred stream migration in response to west southwest ward ground tilting bearing 259 the eastward regional dip of bed rock horizons only locally influences migration river terrace distributions reveal a chronology of stream migration episodes southwestward migration in the ouachita saline and arkansas river basins occurred during early to middle pleistocene time in the southwestern mississippi embayment a wisconsin early holocene southwestward migration episode is evidenced along southeast flowing reaches of the ouachita and arkansas rivers but not along the southeast flowing reach of the intervening saline river suggesting that these rivers overlie separate northwest trending tilt blocks although this technique does not provide direct evidence of ground tilting it provides a quick look method of identifying possible tilting elements in neotectonic regions using only topographic maps this technique is of greatest utility where active faults are concealed or poorly exposed such as in the mississippi embayment

a tectonically triggered late holocene seismite in the southern amazonian lowlands brazil abstract definitive criteria for identifying the triggers of soft sediment deformation structures ssdss from sedimentary deposits are still under construction in this work we aimed to contribute to advancing this issue describing the sedimentological characteristics of an interval of ssdss formed in a region of the amazonian lowlands having numerous morphostructural evidences of neotectonic reactivation the deformed interval is 1 5 m thick and consists of load and flame structures interbedded with massive beds sandwiched between well stratified deposits of a fluvial sandy channel succession with a radiocarbon age of 1301 1382 cal yr bp the ssdss are intercepted by numerous small scale normal graded faults the most interesting is that these faults display segmented nw se trending planes that propagate upward after horizontal displacements of a few millimeters processes intrinsic to channel dynamics could not justify this fault morphology which is related to recurrent short lived seismic perturbations with intervening sedimentation following a main tremor a relation to fault reactivation is proposed with basis on the fault trend compatible with the regional structural pattern and the numerous morphostructural anomalies verified in the study area including trellis and sub trellis drainage rectangular and to a less extent annular channels anomalously enlarged channels orthogonal channels and valleys channel captures sudden changes in channel morphology moderate to high basin asymmetry factor af between 10 and 27 moderate to high transverse topography symmetry factor t 0 3 0 5 and anomalous longitudinal river profiles with concavity values 11 to 30 indicative of rivers in process of adjustments the morphology of the fault graded beds described herein might constitute a feature of relevance for identifying seismites in other fluvial deposits

local stress fields and intraplate deformation of iberia variations in spatial and temporal interplay of regional stress sources tertiary to present deformation in the interior of the iberian peninsula reflects spatial and temporal variations of the activity of the plate boundaries local deformation patterns observed in many of the numerous intraplate tertiary basins and their borders such as the madrid basin and the sierra de altomira are at first sight incompatible with the regional stress field under which they were formed we demonstrate however that they can be explained as the effect of several stress fields that acted on the iberian peninsula from earliest tertiary onward data on local deformation can constrain both magnitudes and directions of forces acting on the plate boundaries of iberia enabling us to estimate the relative importance of the different plate driving and deforming mechanisms providing further constraints on the tectonic evolution of iberia

earthquake magnitude recent research and current trends abstract the magnitude recommendations adopted by the iaspei assembly at zurich in 1967 have had both a stabilizing and a stimulating effect on magnitude determinations and related research from 1967 onwards one magnitude research paper has appeared on the average almost every week thus making this parameter the most studied one in seismology new facilities and more accurate methods e g concerning instrumental equipment and interpretation techniques have made it possible to improve earlier achievements the application of magnitude scales has been extended in all respects e g with regard to epicentral distances focal depths wave types and wave periods magnitude frequency relations have become the most investigated equations within seismology observationally as well as theoretically they have wide applications e g for estimating the maximum magnitudes of future earthquakes an important item in earthquake prediction the magnitudes provide significant information on other source parameters such as wave energy fault length seismic moment relations between different types of magnitude yield valuable information on source properties for instance relations between magnitudes based on body and surface waves are used for efficient discrimination between earthquakes and underground explosions it is our purpose to review the magnitude development in the post zurich period 1967 1980 partly for geologists tectonophysicists and engineers who need an overview partly for seismologists who need an introduction to an overwhelmingly comprehensive literature

frontogenesis over a mountain ridge abstract the interaction of developing two dimensional cold and warm frontal systems with a mesoscale mountain ridge is examined the flow of the rotating model atmosphere is assumed to be inviscid adiabatic and boussinesq the geostrophic momentum approximation is made an imposed horizontal deformation field forces the frontogenesis the nonlinear model equations are solved numerically in physical space using terrain following coordinates which incorporate the fully nonlinear lower boundary condition comparison of the model results with and without topography enables assessment of the impact of the mountain on the frontogenesis a scale analysis indicates that the most general problem of frontal interaction with an infinite mountain ridge encompasses a seven dimensional parameter space the scale analysis provides justification for die two dimensional geostrophic momentum approximation and defines an inverse richardson number as a measure of the importance of the ageostrophic advection sensitivity

quasi geostrophic frontogenesis over topography abstract the problem of quasi geostrophic frontogenesis due to a horizontal deformation field is re examined exact analytic solutions of all flow fields for all times are found for the case of a vertically semi infinite uniformly stratified boussinesq atmosphere the imposed horizontal deformation field is assumed independent of height but may translate horizontally relative to the initial potential temperature distribution and to the variable bottom topography only straight infinitely long fronts and ridge like topographies are considered the solutions in the absence of orography confirm and extend earlier investigations for surface and occluded fronts it is shown that the presence of monotonically sloping topography below a region of deformation leads to the formation of a surface discontinuity in potential temperature in the absence of an initial horizontal thermal gradient the associated secondary circulation is the sum of a closed thermally direct and indirect component the analysis for a tr

effect of slab temperature on deep earthquake aftershock productivity and magnitude frequency relations deep earthquakes generally show fewer aftershocks and a larger variability in magnitude frequency relations than shallow earthquakes1 5 these characteristics and the factors that control them may place constraints on the mechanism of deep earthquakes which is still uncertain6 8 here we show that systematic variations in aftershock productivity and magnitude frequency relations are related to the temperature of the downgoing slab as inferred from the vertical velocity and age of the subducting lithosphere deep earthquakes with substantial aftershock sequences are found only in colder slabs and earthquakes in warmer slabs consistently show few aftershocks magnitude frequency relations for deep earthquakes also show systematic variations as a function of slab thermal structure with warmer slabs showing fewer small earthquakes lower b values the statistical properties of deep earthquakes thus appear to be temperature sensitive to an extent not observed for shallow earthquakes and not adequately explained by simple geometrical limitations on fault width

multivariate morphological characteristics and classification of first order basins in the siwaliks nepal abstract this study identifies and analyzes a group of interrelated morphometric variables that contribute to the morphology of first order basins in the siwaliks and the adjacent part of the lesser himalaya in the far west nepal first order basins were identified and their various morphometric indices 21 variables such as shape area pattern roughness height gradient angle and distance were obtained from topographic maps scale 1 25 000 and a digital elevation model using a geographic information system the study also identifies the basin types based on morphometric properties and assesses their association with lithology structure and uplift rates a principal component analysis identified seven major components that accounted for 78 of the total variance explained by the original 21 morphometric variables variables loading reveals that the components are the expressions of slope size valley depression basin shape relative massiveness the convergence index and basin asymmetry of these slope and size components explain 48 of the total variance the sets of variables represented by each major component for the entire study area were mostly common to all lithostratigraphic units some variables such as drainage density junction angle and the sediment transport index have associations with more than one group this implies that complex geomorphic processes are involved in the development of basin morphology using the seven major components five basin types were recognized by cluster analysis the distributions of these basin types are similar in the lower and middle siwaliks which have similar geological structures the geometric relationship between the dip and the topography of a homoclinal structure significantly affects the proportion of basin types as evidenced by the contrasting proportions between the cuesta and hogback and among dip anti dip and orthoclinal slopes correlation analysis also confirmed the effect of structure dipping on the morphometric variables and indicated the influence of uplift rates on basin slope stream slope elevation range mean elevation valley angle the shape index and the convergence index associated with the active thrust

the structure and evolution of cold surges east of the rocky mountains abstract northerly surges of cold air often move southward along the eastern side of the rockies from southern canada into mexico the strongest surges which generally develop in midwinter are associated with temperature decreases and pressure rises of 20 30 c and 15 30 mb respectively within 24 h surges are usually accompanied by a meridionally elongated pressure ridge and strong low level ageostrophic winds that parallel the terrain the width of the pressure ridging is approximately 1000 km over the southern plains but decreases to only a few hundred kilometers when the surge enters mexico this paper provides a detailed description of a northerly surge to the east of the rocky mountains that occurred on 12 14 november 1986 using both observational and model data the structural evolution of the surge is analyzed in addition the dynamics of the event is explored by diagnosing the momentum thermodynamic energy and vorticity equations to determine the typical synoptic scale evolution of these

a reexamination of the bucaramanga colombia earthquake nest the bucaramanga earthquake nest is situated at a depth of about 160 km beneath colombia at 6 8 n 73 w and it produces about eight earthquakes of mb 4 7 or more each year from a source region having dimensions of about 10 km or less in this study we evaluate nest properties using reported locations focal mechanisms and moment tensors as well as relocations determined from teleseismic p pp and pkp arrivals we also introduce a novel method for determining the volume of a group of hypocenters and use this volume as a statistic for evaluating the accuracy of nest hypocenters we have relocated 26 nest earthquakes occurring between 1964 and 1986 using the jhd method and carefully reread teleseismic p pp and pkpdf arrivals the relocated earthquakes cluster within a region having a volume of 776 km3 and east west north south and vertical dimensions of 13 18 12 km a smaller region than any found previously from analysis of teleseismic data in practical terms this represents an approximate upper bound on the accuracy of relative earthquake locations possible using teleseismic data and standard relocation methods this compares with a volume of 11 km3 and dimensions of 5 1 3 4 3 8 km as determined by schneider et al 1987 from observations of microearthquakes collected over 16 days with a temporary local network these dimensions are comparable to those of the rupture dimensions of the largest observed nest earthquakes as determined from an analysis of their seismic moments 5 1024 dyne cm furthermore an evaluation of cumulative moment rate since 1964 indicates that strain rates within the nest volume must be between 10 13 sec and 10 11 sec the b values 2 0 and values 0 9 determined from available magnitudes and moments are remarkably high suggesting that earthquakes of all observed sizes 3 1020 to 5 1024 dyne cm contribute significantly to the moment release focal mechanisms determined from teleseismic observations exhibit a consistent pattern most having westward dipping p axes and eastward dipping t axes this differs from the more varied pattern reported by schneider et al 1987 for microseismic earthquakes

effects of topography on fronts abstract the hydrostatic boussinesq equations are used to simulate the passage of fronts over a two dimensional mountain in a cyclic domain the fronts are forced by a confluent periodic deformation field that moves with the uniform mean flow over the mountain the initial conditions are selected to give a cold front confined to the lower part of the domain fourth order diffusion terms are included in the numerical model to control energy cascade to the grid size scale a numerical frontogenesis experiment with no topography produces a realistic surface front in about two days numerical solutions for flow over the mountain with no front are found by integrating the equations from the initial conditions which are semigeostrophic steady state solutions various mountains are considered that have the same height but different widths the numerical solutions for wide mountains remain close to the semigeostrophic initial conditions while for narrower mountains vertically propagating waves and a hydraulic

kinematics associated with late cenozoic deformation in central costa rica western boundary of the panama microplate we present kinematic data for late cenozoic deformation in central costa rica that marks the western margin of the panama microplate i e the caribbean panama boundary this boundary extends from the north panama deformed belt west through the valle central in costa rica and then southwest along the east nicoya fracture zone to intersect the middle america trench terrace correlation and basin asymmetry indicate a major change in tectonic evolution across the boundary where three regional northeast striking faults intersect the pacific coast mesoscopic fault populations are consistent with transtension across these north east striking faults and with transpression within the east trending valle central this late tertiary and quaternary transcurrent deformation links the north panama deformed belt to the east with the middle america trench to the west earthquake focal mechanisms are consistent with mesoscopic fault data suggesting that fault populations characterize the present day stress field this deformation marks the western extent of the panama microplate a fragment of volcanic arc that separated from the caribbean plate in the late tertiary or early quaternary and is currently advancing northward due to collisions with south america to the east and the indenting cocos ridge on the cocos plate to the south

flow over mountains coriolis force transient troughs and three dimensionality some issues concerning uniform stratified flow over a three dimensional mountain that have not been fully explored are studied using primitive equation models when the froude number fr is small e g fr 0 5 we find that the coriolis force cannot be neglected for flow over small scale mountains characteristic length l 50 km even though the rossby number ro is large when the coriolis force is neglected a pair of symmetric vortices is induced on the lee side irrespective of the scale of the mountain as long as fr lies roughly between 0 1 and 0 5 the major effect of the coriolis force is to modify or diminish the lee vortices due to the leftward deflection on the upstream side of the mountain the coriolis deflection also reduces the upstream propagation when fr is 1 most of the flow goes over the mountain and the coriolis effect is small for the same ro therefore the importance of the coriolis effect is determined by both ro and fr as the scale of the mountain increases from small scale to mesoscale 100 km l 300 km the upstream flow is deflected more to the left by the coriolis effect and a trough develops on the lee side the length scale of the trough depends on the scale of the mountain in the along flow direction for smaller scale mountains small vortices can be generated within the lee side trough when fr is small when the mountain scale is increased the lee side vortices disappear and only a lee side trough remains depending on the mean wind speed and the mountain scale the lee side trough can be advected by the anticyclonic flow over the mountain to the south and remain attached to the mountain for a long time a train of troughs is generated on the lee side of an elliptic mountain associated with the lee side gravity waves simulations of flows over mountains in two dimensional and three dimensional models with the same cross sectional profile are compared for small scale mountains l 100km the two dimensional model overestimates the amount of airflow over the mountain and also the lee side downslope wind

insights into the tectonic topography of the present day landscape of the central iberian peninsula spain abstract the landscape of today s central iberian peninsula has been shaped by ongoing tectonic activity since the tertiary this landscape comprises a mountain ridge trending e w to nw se the central system separating two regions of smooth topography the basins of the rivers duero and tajo in this study we explore interrelationships between topography and tectonics in the central iberian peninsula regional landscape features were analysed using a digital elevation model dem slope gradients and slope orientations derived from the dem were combined to describe topographic surface roughness topography trend surfaces inferred from harmonic analysis were used to define regional topographic features low roughness emphasizes the smooth nature of the basins topography where surfaces of homogeneous slope gradient and orientation dominate high roughness was associated with abrupt changes in gradient and slope orientation such as those affecting crests valley bottoms and scarp edges present in the mountain chain and in some deep incised valleys in the basins one of the applications of roughness mapping was its capacity to isolate incised valley segments the area distribution of incised rivers shows their prevalence in the east on a regional scale the topographic surface can be described as a train of ne sw undulations or waves of 20 km wavelength these undulations undergo changes in direction and interruptions limited by n s trending breaks e w and ne sw troughs and ridges clearly mark structural uplifts and depressions within the central system these structures are transverse to the compressive nw se stress field that controlled the deformation of the central iberian peninsula from the neogene to the present they represent the upper crustal folding that accommodates alpine shortening n s breaks coincide with late miocene faults that control the basins sedimentation further associated palaeoseismic structures suggest the recent tectonic activity of n s faults in the eastern part of the tajo basin apatite fission track analysis data for this area suggest the occurrence of a significant uplift episode from 7 to 10 ma which induced the river incisions appearing in the roughness map n s and ne sw faults could be seismogenic sources for the current moderate to low seismic activity of the east tajo basin and southeast central system although n s fault activity has already been established we propose its significant contribution to shaping the landscape

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

mapping active magma chambers by b values beneath the off ito volcano japan the b value of the frequency magnitude relation and thus the mean magnitude in the off ito volcanic area is not uniform based on detailed b value tomography using about 10 000 events in an area of 10 km radius and in the upper 15 km of the crust a high b value anomaly b 15 below 7 km depth and with a radius of about 2 km located below the coast southeast of ito contrasts with lower values of typically b 0 7 north of it and at shallower depths on the basis of surface deformations a tensile crack dislocation source was located above 7 km depth thus we surmise that the magma chamber in the off ito area was located below 7 km depth the correlation of a high b value anomaly with this model supports our hypothesis that active magma chambers may be mapped by high b value anomalies the magma body may be described as consisting of two parts a lower well established chamber below 11 km depth and a shallower part 11 7 km depth the b value in the volume surrounding the magma chamber increased from 0 7 during the 1980s to 1 5 during the earthquake swarms of the 1990s this may reflect a trend of increasing crack density due to the intrusion activity

effects of coastal orography on landfalling cold fronts part ii effects of surface friction abstract the role of surface friction in modifying cold fronts as they make landfall in regions of steep coastal orography is examined by means of idealized simulations both the effects of the surface roughness change at the coast in the absence of orography and the effects of orography are considered flow over a large and abrupt change in surface roughness generates an inertia gravity wave above the boundary layer with characteristics similar to that associated with flow over a plateau deceleration of the cross coast flow occurs over land as well as for a short distance upstream and causes retardation of frontal motion a prescribed northerly postfrontal jet weakens rapidly after landfall maximum vertical motions are several centimeters per second however only small rainfall enhancement is expected since the updraft is very narrow and produces only small vertical displacements friction modifies the flow over the orography by increasing the upstream flow deceleration and reducing the magnitude of

drainage density and relative relief in humid steep mountains with frequent slope failure previous studies in japanese mountains have shown that drainage density d correlates negatively with relief r and the erosion rate e whereas elsewhere both r and e correlate positively with d to investigate the inconsistency this paper compares two types of d r relations for eight mountain river basins in central japan r is computed from a digital elevation model for 1109 morphometric samples of area 0 5 km 0 5 km drainage networks in these cells were first constructed by map criteria applied previously in japan deeply notched v shaped contours with an angle 53 the resulting d correlates negatively with r confirming preceding studies when drainage lines along shallower hollows were added however the calculated d essentially constant these relations arise from active landsliding in high relief terrains which has eroded steep channel banks into gentle ones the decline of channel banks with increasing r is accelerated in terrains underlain by soft rocks because of rapid erosion the constant d for all the drainage lines indicates a uniform frequency or spacing of ridges and hollows on hillslopes in rugged humid mountains because the d r and d e relations for japan reflect a uniquely japanese physiographic setting characterized by frequent landsliding they differ from those relations for other regions where channelization by gullying predominates 1997 by john wiley sons ltd

an observational and numerical study of a cold front interacting with the olympic mountains during coast iop5 abstract this paper documents the three dimensional flow and precipitation structures associated with a weak cold front interacting with the olympic mountains and the subsequent development of a puget sound convergence zone this study utilizes data collected during coast iop5 the fifth intensive observing period of the coastal observation and simulation with topography field experiment that took place on 11 12 december 1993 one of the most important data sources was a noaa p 3 aircraft which provided flight level data radar reflectivity and doppler winds as it circumnavigated the olympics initially frontal passage along the western foothills of the olympics was accompanied by a 2 3 c temperature drop a rapid wind shift to northwesterlies and an intense line of precipitation 35 45 dbz however the wind shift and associated precipitation structures attenuated when the front began to ascend the windward slopes of the olympics surface and p 3 observations document the deformation of the front

effects of coastal orography on landfalling cold fronts part i dry inviscid dynamics abstract in this study the interaction of cold fronts with idealized coastal terrain typical of the western united states and canada is considered two issues are examined first what are the factors that determine the strength of the coastal winds and second what are the orographic effects on the frontal evolution to address these issues the authors utilize a two dimensional boussinesq terrain following coordinate numerical model in which a uniform prescribed flow is forced to move over a plateau the resultant across mountain velocities are characterized by a zone of strongly decelerated flow upstream of the windward slope and a train of inertia gravity waves downstream a barrier jet oriented parallel to the mountain is produced by the coriolis force the variations of the magnitude of the upstream deceleration and the barrier jet over a wide range of froude numbers and rossby numbers are described steady linear theory applied to flow over a plateau shows that the upstream deceleration is dete

changes in frequency size relationship from small to large earthquakes the constant b value observed in frequency magnitude distributions of earthquakes has been taken as an indication of self similarity at all magnitudes hence earthquake properties should scale uniformly in the same way from small to large earthquakes it has often been observed however that the seismic moment released in small earthquakes scales differently with rupture length than it does for large events1 2 where the crossover between small and large events is defined at a rupture dimension equal to the down dip width of the seismogenic zone a possible explanation for this contradiction is that frequency size distributions are biased by small earthquakes small events dominate most global earthquake catalogues because of the short time period covered another source of bias in size distributions is the saturation of earthquake magnitudes for large events here we correct biases in calculations of b values and present evidence for a change in b value in frequency size distributions we find that a break in self similarity from small to large earthquakes occurs at a point where the dimension of the event equals the down dip width of the seismogenic layer

lateral inhomogeneities of the hercynian crust in central spain abstract an azimuthal layout of deep seismic profiles has been partially completed in the central iberian massif data from two new profiles and a reinterpretation of previous profiles make possible two dimensional models for the hercynian crust in central spain from which some lateral crustal inhomogeneities can be established these inhomogeneities due to alpine intraplate tectonics coincide with the spanish central system and consist of a 5 km crustal thickening with respect to the surrounding areas

a three dimensional study of the influence of mountains on a front abstract the objective of this study is to investigate mountain effects on a frontal system in three dimensions the frontal system is developed from the most unstable eady wave in a baroclinic state without a mountain the developed frontal system is then introduced into a new model domain that contains mountains with different sizes shapes and orientations in general it is found that the cold front experiences a weakening on the upwind slope and strengthening on the downwind slope of a mountain the locations of these upwind and downwind sides are determined by the horizontal winds associated with the front before the front reaches a mountain the prevailing wind impinging on the mountain is the prefrontal southwesterly after the front reaches the top of the mountain the impinging wind shifts to be the postfrontal northwesterly therefore mountain induced fronto genetic forcing by these winds varies spatially as the front passes the mountain when the front moves down the slope it speeds up and

topographic effects on a wintertime cold front in taiwan abstract this paper describes an observational and numerical study of an intense wintertime cold front that occurred in taiwan on 8 january 1996 the front was associated with rope clouds at the leading edge and a broad area of stratiform clouds behind the front was blocked by the central mountain range of taiwan and divided into two sections on each side of the mountain range as the cold air moved southward along the east coast the increasing westward coriolis force induced a landward acceleration after the cold air piled up against the mountains a coastal pressure ridge developed the cold air damming yielded a geostrophic balance between the westward coriolis force and the eastward component of the pressure gradient force in the x direction and a southward acceleration in the y direction mainly caused by the southward pressure gradient force component over the taiwan strait southward pressure gradient forces increased when the low level stable cold air was confined over the taiwan strait lead

the assignment of drainage direction over flat surfaces in raster digital elevation models abstract drainage direction assignment over flat surfaces in raster digital elevation models dem has been a stubborn problem for dem processing methods a new approach that improves upon current methods of flat surface treatment is presented the approach is based on the recognition that in natural landscapes drainage is generally away from higher and towards lower terrain to produce such a drainage dem elevations of a flat surface are modified to impose two gradients one away from higher terrain and one towards lower terrain subsequent processing of the dem produces a drainage pattern over the flat surface that is topographically consistent and exhibits flow convergence properties the proposed approach is not restricted by the shape of the flat surface the number of outlets on its edge or the complexity of the surrounding topography a comparison with the drainage pattern of an established method that displays the parallel flow problem shows significant improvements in producing realistic drainage patterns the proposed approach extends automated dem processing to digital landscapes for which existing methods cannot provide adequate flow directions over flat surfaces to conduct a drainage analysis the necessary algorithmic details for implementation of the approach are provided 1997 elsevier science b v

seismic moment frequency relation for shallow earthquakes regional comparison we determine the parameter values for the seismic moment frequency relation using flinn engdahl s regionalization of global seismicity and the harvard centroid moment tensor data the earthquake size distribution is approximated by the gamma law a version of the gutenberg richter distribution with an exponential taper at the maximum moment there is no statistically significant variation of the fj value the analog of the b value for all seismic regions except for the midocean ridge systems for the latter regions fj 0 93 whereas for all other zones fj 0 63 the maximum moment mxg can be statistically evaluated only for subduction zones treated as a whole mxg 10 21 2 x 10 22 newton m which corresponds to the worldwide mxg value for other regions as well as for single subduction zones mxg is determined by comparing the number of events in each zone with the seismic moment rate calculated on the basis of the nuvel 1 model of plate motion for subduction zones we obtain the estimate of mxg which agrees with the statistical value giving evidence that most tectonic deformation is released by earthquakes we test the hypothesis that no statistically significant variation in mxg occurs in subduction and continent collision zones the hypothesis cannot be rejected with available data for the midocean ridges the mxg estimate cannot be unambiguously determined it is quite possible that the estimate is significantly biased because only a small part of tectonic deformation at the ridges is released by earthquakes these results have importance in evaluating seismic risk and may also lead to developing a physical theory for earthquake generation

rank ordering statistics of extreme events application to the distribution of large earthquakes rank ordering statistics provide a perspective on the rare largest elements of a population whereas the statistics of cumulative distributions are dominated by the more numerous small events the exponent of a power law distribution can be determined with good accuracy by rank ordering statistics from the observation of only a few tens of the largest events using analytical results and synthetic tests we quantify the systematic and the random errors we also study the case of a distribution defined by two branches each having a power law distribution one defined for the largest events and the other for smaller events with application to the worldwide harvard and southern california earthquake catalogs in the case of the harvard moment catalog we make more precise earlier claims of the existence of a transition of the earthquake magnitude distribution between small and large earthquakes the b values are b2 2 3 0 3 for large shallow earthquakes and b1 1 00 0 02 for smaller shallow earthquakes however the crossover magnitude between the two distributions is ill defined the data available at present do not provide a strong constraint on the crossover which has a 50 probability of being between magnitudes 7 1 and 7 6 for shallow earthquakes this interval may be too conservatively estimated thus any influence of a universal geometry of rupture on the distribution of earthquakes worldwide is ill defined at best we caution that there is no direct evidence to confirm the hypothesis that the large moment branch is indeed a power law in fact a gamma distribution fits the entire suite of earthquake moments from the smallest to the largest satisfactorily there is no evidence that the earthquakes of the southern california catalog have a distribution with two branches or that a rolloff in the distribution is needed for this catalog b 1 00 0 02 up to the largest magnitude observed mw 7 5 hence we conclude that the thickness of the seismogenic layer has no observable influence whatsoever on the frequency distribution in this region

the gutenberg richter or characteristic earthquake distribution which is it abstract paleoearthquake and fault slip rate data are combined with the cit usgs catalog for the period 1944 to 1992 to examine the shape of the magnitude frequency distribution along the major strike slip faults of southern california the resulting distributions for the newport inglewood elsinore garlock and san andreas faults are in accord with the characteristic earthquake model of fault behavior the distribution observed along the san jacinto fault satisfies the gutenberg richter relationship if attention is limited to segments of the san jacinto that are marked by the rupture zones of large historical earthquakes or distinct steps in fault trace the observed distribution along each segment is consistent with the characteristic earthquake model the gutenberg richter distribution observed for the entirety of the san jacinto may reflect the sum of seismicity along a number of distinct fault segments each of which displays a characteristic earthquake distribution the limited period of instrumental recording is insufficient to disprove the hypothesis that all faults will display a gutenberg richter distribution when averaged over the course of a complete earthquake cycle but given that 1 the last 5 decades of seismicity are the best indicators of the expected level of small to moderate size earthquakes in the next 50 years and 2 it is generally about this period of time that is of interest in seismic hazard and engineering analysis the answer to the question posed in the title of the article at least when concerned with practical implementation of seismic hazard analysis at sites along these major faults appears to be the characteristic earthquake distribution

the deep earthquakes of 1921 1922 in northern peru abstract we present a detailed analysis of the 1921 and 1922 deep events in northern peru which we identify as the only reliably located earthquakes in the vicinity of the great 1970 deep colombian shock all other reported seismicity in a three dimensional radius of 550 km centered on the 1970 hypocenter is erroneous and can be relocated to other seismic provinces the 1921 1922 earthquakes relocate approximately 230 km to the south of the 1970 event at depths of 630 km and 660 km respectively a combination of centroid moment tensor inversion and forward modeling using ray theory and reflectivity synthetics yields focal mechanisms indicating down dip compression and seismic moments of 1 2 1027 dyn cm and 6 1027 dyn cm respectively the 1921 1922 and 1970 events take place on a piece of subducted farallon plate aged approximately 55 ma i e anomalously young to support deep seismicity we suggest that this unusual seismic activity may be due to a local heterogeneity on the slab whose nature however remains unknown

an observational and numerical study of an intense landfalling cold front along the northwest coast of the united states during coast iop 2 abstract this paper presents an observational and numerical study of an intense wintertime cold front that made landfall along the northwest coast of the united states during iop 2 3 4 dec 1993 of the coastal observation and simulation with topography experiment observations suggest that the offshore frontal zone was associated with two transitions the first characterized by a substantial temperature gradient a nearly vertically oriented wind shift from southwesterly ahead to westerly behind and a convective rainband while the second transition had a slantwise wind shift zone from westerly ahead to northwesterly behind the frontal zone was quite narrow 5 km wide and nearly vertical below 850 mb and its width increased by 1 2 orders of magnitude above 850 mb well before the frontal landfall low level flow to the west of the olympics was associated with geostrophic balance in the cross shore direction and downgradient acceleration in the alongshore direction which contributed to the formation

southerly changes on the east coast of new zealand abstract a combined observational and climatological study of orographically influenced cold fronts over new zealand known locally as southerly changes is presented four southerly changes that occurred along the east coast of new zealand during the southerly change experiment souchex in january and february of 1988 are analysed in detail using the higher spatial and temporal density of data established for the experimental period three of the southerly changes were associated with fronts originating over the tasman sea while the other was not a common feature in all four cases was the shallowness of the southerly flow for sonic hours after the surface wind change the top of the southerly flow layer was less than the typical height of the southern alps 2000 above this there was usually a maximum of the northerly component of the flow at or just above mountain top levels and in three casts the prefrontal low level flow was dominated by a warm northwesterly foehn in the central south island t

active bidirectional tectonic tilting in a part of the almora klippe kumaun lesser himalaya india insights from statistical analyses of geomorphic indices abstract the nw se trending synformal almora klippe in central kumaun lesser himalaya is actively uplifting along the basal thrust which is known as north almora thrust nat and south almora thrust sat along the northern and southern flanks respectively geomorphic indices of basin asymmetry factor af and transverse topography factor t of 77 drainage basins of third order streams developed on this tectonic block have been computed to decipher active tilt block tectonics of a part of this vast klippe statistical analyses of the basins geomorphic indices revealed differential gentle to steep bidirectional tilting of the almora klippe vis a vis lent insight into correct perspective which these must be used for such studies the tectonic block of almora klippe is partitioned into two minor tectonic blocks along the hinge of the synform differential movements along the basal thrust of the klippe have caused westward down tilting of the northern fold flank af having 2 value of 7 556 for 4 azimuth classes at 90 confidence level and t having vector mean v of 260 and vector magnitude r of 0 25 at p value of 0 1154 and eastward down tilting of the southern fold flank af having 2 value of 13 73 for 4 azimuth classes at 90 confidence level and t having vector mean v of 56 and vector magnitude r of 0 26 at p value of 0 0585 the westward down tilting of the northern fold flank is due to its faster uplift in the east along the nat similarly the eastward down tilting of the southern fold flank is due to its faster uplift in the west along the sat

an east asian cold surge case study abstract since a cold surge is a hazardous weather phenomenon in east asia the rapid population increase and economic growth over the past two decades require improvement in forecasting cold surges and their related weather events over this region however without a better understanding of these events this task cannot be accomplished a cold surge with a well defined cold front passing through taiwan was selected to illustrate its impact on the east asian weather system this case is typical of a large portion of surges occurring in the region major findings of this study are as follows coupling with the upper ridge trough structures of the wave train straddling the eastern seaboard of northeast asia cold surges occur sequentially a cold front with a prefront high pressure zone is formed by the new surge outflow interacting with the anticyclone of the aging surge the warm moist air advected northeastward along the cold front assists the development of the new surge s low center while the prefron

continental deposits magnetostratigraphy and vertebrate paleontology late neogene of eastern spain abstract eleven sections have been sampled for magnetostratigraphy in the fossil mammal productive late neogene basins of eastern spain the characteristic direction of magnetization was determined through progressive thermal and alternating field demagnetization it was possible to correlate the magnetozones from the various sections to the gpts as well as to the fossil mn zones within the sediment the mn zone boundaries based on this correlation are as follows mn 11 12 8 1 my mn 12 13 6 my mn 13 14 4 9 my mn 14 15 4 18 my mn 15 16 3 58 my new fossil lists are presented for the fuente del viso and loma del castillo faunas in the cabriel basin

evolution of neotectonic activity of east anatolian fault system eafs in bingol pull apart basin based on fractal dimension and morphometric indices abstract this study is an attempt of a semi automatic geomorphological gis analysis based on morphometric indices in the study 10 m resolution digital elevation models dems are used to assess the neotectonic signals regarding the recent topographic developments and to attach additional significance to active tectonics in the bingol basin area the methodology incorporates the determination of the structural similarities of the faults in the basins using fractal concepts and the application of four morphometric indices stream power index sp multi resolution index of valley bottom flatness mrvbf terrain ruggedness index tri and valley width to height ratio vf in order to detect the deviation from spatial randomness of the applied indices the weighted correlation coefficient moran s i is used and the results are interpreted at a confidence interval of 99 the spatial distribution of integrated index values is evaluated with the tectonically active fault zones in order to determine the probable activity and the structural deformation in the basin the applied methodology reveals that the fractal analysis of the fault lines and the spatial analysis of the morphometric indices proved to be effective tools in analyzing the tectonic influence of the fault system on the basin area within the basin area a relatively lesser degree of tectonic activity is observed in contrast with the high tectonic activity outside the basin

influence of mesoscale orography on idealized cold fronts abstract a three dimensional numerical model based on the inviscid and adiabatic primitive equations in the boussinesq approximation is used to investigate the retardation of cold fronts by high two and three dimensional mountains approximately the same size as the alps initial and boundary conditions are specified according to an analytical model for an idealized front with constant potential vorticity the study covers cases with uniform neutral or stable stratification in both the cold and warm air masses the model results are compared with previous analytical solutions of a shallow water flow model a scale analysis and a parameter study identify the conditions under which a front is strongly influenced by mountains for two dimensional cases the study shows that the foot of the front is strongly retarded if the kinetic energy is too small to let the cold air climb over the mountain the bulk of the front is strongly retarded if the froude number and the relative front mountain height are small

application of morphometry in neotectonic studies at the eastern edge of the parana basin santa catarina state brazil article i nfo the neotectonic evolution of the eastern edge of the parana basin in the santa catarina state brazil was investi gated using field data and detailed morphometric analysis along an east west section analysis included gener ation of maps of isobase hydraulic gradients hypsometry incision of drainage basins drainage asymmetry and anomalous morphological features all these maps generated results that agreed with field data and helped define recent faults in directions close to n s and e w both probably reactivated faults of the parana basin and the basement geomorphological features identified in topographic maps possibly related to neotectonism have a close agreement with our observations in the field the asymmetry of basins as analysed by the t index method proved to be compatible with the influence of a e w compressive tectonic regime and showed a move ment from w to e application of the hypsometric integral technique helped establish a correlation between the younger basins with structures trending n s 30 the n s faults were related to a compressional stress field shmax close to e wa nd shmin stress minimum around n s thereby establishing a tectonic context of structures developed in a transpressive regime the compressional field was caused by the subduction of the nazca tectonic plate below the south american plate whereas the transcurrent component exploited pre existent e w structures when the atlantic ocean was opening

generation of coastal lows by synoptic scale waves a model is presented in which eastward propagating synoptic waves interact with a meridional escarpment it is shown that under suitable conditions trapped waves are produced at the escarpment the dominant wave being poleward propagating this model is intended to represent the generation of coastally trapped disturbances like those found in southern africa

frontal interaction with isolated orography abstract the interaction of a three dimensional cold front and an isolated orographic ridge is examined by means of primitive equation model simulations the front evolves as part of a developing nonlinear baroclinic wave and propagates southward toward the ridge many of the features in this interaction such as the anticyclonic distortion of the front divergence and frontolysis on the windward slope convergence and frontogenesis in the lee and the frontogenetical forcing associated with tilting have previously been captured by simulations of a passive scalar traversing a ridge it is shown that the ridge decelerates the cold postfrontal air and creates a high pressure anomaly on the windward slope if this anomaly is strong enough it accelerates air over the ridge peak in a shallow ageostrophic flow that possesses many features found in a gravity current this current provides relatively strong surface frontogenesis through the convergence term but cannot transport enough mass across the peak to w

observations of a subtropical cold front in a region of complex terrain abstract the passage of shallow cold fronts during the late spring and early summer months over the island of taiwan is often accompanied by heavy rainfall and occasional flash flood episodes previous studies have emphasized the weak baroclinicity of these fronts and their possible modification by fluxes from the air sea interface in this study a cold frontal passage in the vicinity of taiwan is analyzed using data gathered during the taiwan area mesoscale experiment tamex on 8 june 1987 at the northern extent of the tamex network the cold front was shallow 1 2 km deep and moderately baroclinic with 5 7 c temperature contrasts at the surface a doppler radar cross section of radial velocity reveals a structure similar to that of a density current at the leading edge of the shallow front the postfrontal air man was substantially modified by oceanic heat fluxes as it moved southward over the warm ocean waters this led to a 60 70 decrease in the temperature contrast across the front between ocean

frontal interaction with the appalachian mountains part i a climatology abstract a comparison between the climatological structure of retarded and unretarded fronts aligned parallel to the appalachian mountains is investigated with the average height of the appalachians being 1 km retarded and unretarded fronts are common occurrences during the cold season because of the narrow half width of 100 km and the 1000 km length of the mountain chain a comparison to two and three dimensional numerical studies can be performed of the 142 cases of frontal passages over the appalachians during the winters between october 1984 and april 1990 over 55 of all cold fronts were retarded by the mountains statistical analysis showed that retarded fronts have a stronger cross front temperature gradient and a weaker cross front pressure gradient composite fields of sea level pressure 850 500 and 200 mb heights quasigeostrophic potential vorticity and its advection and potential height u n were computed for all retarded and unretarded fronts unretarded fronts were associated wi

a morphotectonic map of the northern arava in israel derived from isobase lines abstract in areas characterized by flat and weakly incised relief built of young and lithologically uniform sediments structural and tectonic maps are often non existent or of no great avail under such conditions the regional morphotectonic analysis of the study area may be a most useful tool to produce the required basic hydrogeological information it consists basically of two consecutive steps i e definition of stream orders and the preparation of isobase maps in the research of quaternary geology isobase surface analysis is regarded as a means for identifying young tectonic processes the morphotectonic map is the final derivative of isobase maps it portrays the basic lineaments or dislocation lines derived by analysing deviations in the directions of isobase lines of their spreading or compression and of deviations between axes of valleys the morphotectonic map presented in this paper portrays several major morphostructural units within the arava graben in the area between the dead sea and nahal paran

alluvial river response to neotectonic deformation in louisiana and mississippi repeat geodetic surveys show uplift of the monroe and wiggins anticlines in louisiana and mississippi there are deformed quaternary terraces which indicate long term deformation in the valleys of the alluvial rivers that cross these structures and there are floodplain and channel convexities that provide evidence of modern deformation in addition the channels show significant variations of morphology sinuosity gradient and depth and behavior appropriate to reaches of increased and decreased valley slope these alluvial rivers are adjusting to modern deformation and their adjustment confirms two geodetic leveling anomalies

advection of a passive scalar over a finite amplitude ridge in a stratified rotating atmosphere abstract a basic uniform current flows over a two dimensional finite amplitude ridge of characteristic male l and amplitude the disturbance field is constrained by the geostrophic momentum approximation by uniform potential vorticity uniform brunt vaisala frequency n and by the constant coriolis parameter f solutions are represented as the sum of a steady disturbance recently found by blumen and gross and a relatively weak translating disturbance the translating disturbance is a passive scalar that is advected by the steady mountain circulation the propagation speed over a ridge in an unbounded atmosphere is shown to increase with the parameter d where d fl n is the deformation depth the steady mountain circulation produces frontolysis in the disturbance field on the windward slope and frontogenesis on the leeward slope these frontogenetical features are primarily controlled by the steady horizontal velocity which is divergent on the windward side and convergent in the ice the steady mou

lithospheric folding in iberia integration of stress indicator data gravity data crustal kinematics data and analysis of topography and recent vertical motions demonstrates the occurrence of consistently oriented spatial patterns of large scale alpine to recent intraplate deformation in iberia the inferred upper crustal and lithospheric deformation patterns and the timing of the associated expressions at or near the surface support the existence of a close coupling with plate boundary processes operating at the margins of iberia patterns of lithosphere and upper crustal folds are oriented perpendicular to the main axis of present day intraplate compression in iberia inferred from structural analysis of stress indicator data and focal mechanism solutions these findings suggest the presence of lithospheric folds with wavelengths compatible with theoretical predictions of folding wavelengths of variscan lithosphere stress induced intraplate deformation set up by plate interactions is compatible with indications for the absence of present day deep mantle lithosphere interactions inferred from seismic tomography

frontal instability generated by tropospheric potential vorticity anomalies the development of secondary disturbances on a two dimensional front is described using a linear stability analysis a two stage process is envisaged in which first strong frontogenesis produces condensation at the front this leads to the generation of a lower tropospheric zone of high potential vorticity pv lying along the front as frontogenesis weakens the second stage is entered in which an essentially steady front is susceptible to the growth of linear normal modes along the front owing to the existence of the pv anomaly or equivalently the frontal rainband thus for a typical band of width 160 km a frontal wave of some 800 km is produced with a growth rate of about 1 day 1 the dynamics of these modes is examined by considering both the realistic frontal flow as well as idealized strips of pv anomalies the idealized case is potentially applicable to a variety of meteorological situations such as upper jet streaks useful insight is gained from an analysis of the energetics of the modes this shows that for narrow frontal pv anomalies the waves main energy source is the basic kinetic energy and further they have a negative vertical heat flux recent observations suggest that frontal waves are indeed characterized by such a heat flux as most frontal zones involve significant condensation and therefore are likely to exhibit a lower tropospheric pv maximum it is stressed that studies of frontal waves need to include this aspect of the frontal structure

the impact of the appalachian mountains on cyclonic weather systems part i a climatology abstract a climatological study of cold fronts and cyclones crossing the appalachian mountains from the west through northwest has been performed a sample size of 50 fronts and 40 cyclones was derived from the seven winter seasons december through march between 1979 and 1986 the analysis revealed that initially linear cold fronts are slowed and deformed by the mountains with the mean frontal speed decreasing 40 and the fronts developing a pronounced kink just east of the southern appalachians furthermore over the mountains the cross front thermal and pressure gradients are enhanced by about 25 and 63 respectively once past the mountains fronts are weaker and often difficult to locate in particular the cyclonic wind shift is very ill defined and the cross front pressure gradient is reduced to 38 of the premountain value finally small scale 500 km diameter lee lows form on more than half of the fronts though typically benign some of these disturbances may play a role in offshore c

the nature of deep focus earthquakes wadati 1928 first proved convincingly that some earthquakes occur at depths well beneath the earth s crust he essentially proposed the nomenclature used today by the international seismological centre isc i e earthquakes with focal depths exceeding 300 km are deep earthquakes and those with depths between 70 and 300 km are intermediate earth quakes however when there is little reason to distinguish between the two groups both types are called simply deep earthquakes to avoid confusion in this paper we refer to those with focal depths exceeding 300 km as very deep earthquakes and those with focal depths between 70 and 300 km as intermediate earthquakes deep earthquakes are of interest for at least four reasons first they are exceedingly common between 1964 and 1986 they constituted no less than 22 of all earthquakes having mb greater than 5 0 in the isc catalog second they most often occur in association with deep ocean trenches and volcanic island arcs in subduction zones one of the great achievements of twentieth century geophysics was the recognition that their occurrence in inclined planar groups or wadati benioff zones apparently delineates the cold down going cores of convection cells in the uppermost mantle third seismologists use body waves of deep earthquakes dispro portionately more often than those of shallow earthquakes to inves tigate core mantle and crustal structure this is because a deep earth quakes often possess relatively more impulsive sources b their body phases traverse the heterogeneous uppermost mantle only once on the ray path from hypocenter to station and c surface waves do not contaminate these body phase arrivals on seismograms finally deep earthquakes are

determination of present day stress tensor and neotectonic interval in the spanish central system and madrid basin central spain a brittle deformation tectonic analysis was performed in central spain spanish central system and madrid basin in order to decipher and understand the deformation processes that take place in a typical intracontinental zone 1174 fault slickensides obtained in materials with ages between late cretaceous and quaternary have been analyzed by means of fault population analysis methods to reconstruct paleostress tensors nine earthquake focal mechanisms have been determined with magnitudes ranging between 3 and 4 1 with regard to regional structural features and sedimentary record data the characteristics of present day and neotectonic stress fields have been figured out which determine the neotectonic period for this region thus we have established that the intraplate zone represented by central spain has been subjected to a stress field from the middle miocene until the present day with a largest horizontal shortening direction shmax located between n130e and n160e finally three paleostress maps with the main active structures are presented for a middle miocene to late miocene the period when the spanish central system was mainly formed b late miocene to quaternary and c the present day stress field deduced from earthquake focal mechanisms

lateral planation of rivers as a geomorphic agent abstract the notion that much of the earth s erosional flat land has been produced by lateral planation of rivers held by the late c h crickmay has been largely ignored in debates over the evolution of landscapes evidence is growing however that lateral planation is a significant agent in the creation of low relief landscapes in some regions recently described examples of moderately large scale river migration and planation on the north american plains include a nearly 100 km migration of the bow river in alberta an 80 km migration of the missouri river in montana and migration of a system of tributaries of the milk river in montana causes of river migration proposed in the literature but so far not convincingly demonstrated include the coriolis force tectonic tilting asymmetrical tributary distribution prevailing winds differential bank wetting and influence of substrate the concept of lateral planation has implications not only for landscape evolution but also for interpretation of ancient deposits

orographic channeling of a cold front by the pyrenees abstract the channeling effect of the pyrenees on a cold front is illustrated using high resolution surface data satellite data support the analysis of the surface data and show that the surface front is trapped to a significant degree in the vicinity of the mountains

statistics of small earthquakes and frequency of occurrence of large earthquakes along the mexican subduction zone abstract the validity of the gutenberg richter g r frequency magnitude relation over a wide range of magnitudes is usually accepted and the statistics of small earthquakes is often extrapolated to predict the frequency of occurrence of large earthquakes we take noaa and pde data from 1963 to 1981 related to the mexican subduction zone h 65 km and convert m b to m s in the range of 3 3 m b 5 7 for this conversion we use regression of m s on m b for mexican and central american events as well as an m s m b regression based on worldwide data wyss and habermann 1982 we also take into account the standard error in m s this may be important since the number of events decreases as m b increases the m s data of 18 5 yr is normalized to 75 5 yr and is compared to the statistics of observed large earthquakes m s 6 4 for the period 1906 to 1981 it is found that the g r relation in the range 4 5 m s 6 0 when extrapolated grossly underestimates the observed frequency of large earthquakes m s 6 5 for the oaxaca and jalisco regions there is strong evidence that the plate interface in the oaxaca region consists of a few 3 or 4 large fault zones each of which cyclically ruptures over its entire dimension without giving rise to smaller events in the manner implied by the g r relation the result is of profound importance in seismic risk analysis and in the understanding of fault mechanics this phenomenon has been reported for only a few regions e g turkey bath 1981 japan wesnousky et al 1983 it may have escaped detection in other regions due to a variety of causes the most important being the long recurrence periods of large earthquakes

integration of spectral spatial and morphometric data into lithological mapping a comparison of different machine learning algorithms in the kurdistan region ne iraq abstract lithological mapping in mountainous regions is often impeded by limited accessibility due to relief this study aims to evaluate 1 the performance of different supervised classification approaches using remote sensing data and 2 the use of additional information such as geomorphology we exemplify the methodology in the bardi zard area in ne iraq a part of the zagros fold thrust belt known for its chromite deposits we highlighted the improvement of remote sensing geological classification by integrating geomorphic features and spatial information in the classification scheme we performed a maximum likelihood ml classification method besides two machine learning algorithms mla support vector machine svm and random forest rf to allow the joint use of geomorphic features band ratio br principal component analysis pca spatial information spatial coordinates and multispectral data of the advanced space borne thermal emission and reflection radiometer aster satellite the rf algorithm showed reliable results and discriminated serpentinite talus and terrace deposits red argillites with conglomerates and limestone limy conglomerates and limestone conglomerates tuffites interbedded with basic lavas limestone and metamorphosed limestone and reddish green shales the best overall accuracy 80 was achieved by random forest rf algorithms in the majority of the sixteen tested combination datasets

mapping the b value anomaly at 100 km depth in the alaska and new zealand subduction zones a positive anomaly in the frequency magnitude distribution b value is detected at approximately 90 100 km depth in two subduction zones the b value in this anomalous zone is 40 higher than in adjacent volumes we use regional catalogs with a magnitude of completeness of 2 6 central alaska and cook inlet 2 0 shumagin islands and 3 5 new zealand to resolve the b value as a function of space in more detail we project all earthquakes onto planes perpendicular to the strike of the slab these cross section views of the b value distribution locate the high b value anomalies at a depth of 90 100 km on the upper surface of the wadati benioff zone at these depths slab dehydration may increase pore pressure thus lowering the effective stress and increasing the b value increased pore pressure would also lower the liquidus in the overlying asthenosphere giving rise to the volcanism that occurs directly above this zone

river braiding caused by rapid floodplain deformation insights from holocene dynamics of the jarama river in central spain abstract in this paper we will use an illustrative example to show the significance of rapid vertical movements inside floodplains as well as varying discharge values for the alteration of channel and sedimentation patterns during the holocene concerning such relationships well documented and well dated references from sedimentary records are rather rare the developments within the lower jarama valley have been significantly supported by an interaction of tectonic activity evaporite dissolution and halokinetics that initiated rapid vertical movements over short distances and caused the formation of knick points and gradient changes along the longitudinal floodplain profile furthermore the specific mediterranean climate caused highly variable discharges including extreme runoff peaks the juxtaposition of different floodplain gradients gave rise to spatial and temporal changes of discharge patterns and channel geometry which is reflected by varying sedimentation as well as erosion patterns we have been able to confirm that alluvial thickening due to intense dissolution and subsidence has been a characteristic and frequently recurring feature during the pleistocene moreover we want to emphasize that also during the holocene gradient adjustments exercised controlling influence on fluvial dynamics in particular with regard to channel response in fact we found consistency between low and moderate gradients and meandering single channel patterns associated with overbank deposition in distal floodplain positions only a section with stronger inclination revealed evidences for multiple channel discharge patterns in form of gravelly braided river deposits in comparison with recent discharge patterns and information from historical sources it appears that braided river deposition took place just within a short time frame between 5 and 3 ka cal bp this matches exactly a period of strong climatic aridity including highly variable precipitation and discharge patterns from that we conclude that in the first instance gradient changes promoted the change of channel and discharge patterns but however specific overlap of the parameters gradient and runoff is considered to have been necessary to generate braided discharge pattern a subsequent formation of braided patterns during the late holocene was presumably prevented by river entrenchment as well as a strong increase of sediment availability during the time of roman colonization on the basis of this study we can establish a number of general relationships between floodplain gradient runoff pattern and channel response during the holocene period that may help us to better understand fluvial behavior in various different areas

the origin and tectonic significance of asymmetrical meander belts in the hebgen lake area of sw montana the madison and south fork rivers occupy the northeast sides of their respective meander belts the form of the abandoned meander loops within these asymmetric meander belts indicates that they were produced by gradual northeast migration of the active channels this progressive migration can be related to tectonic tilting produced by regional extensional faulting at a high angle to the original channel belt axis which ran down a gently sloping outwash cone asymmetric channel sandstone bodies in the rock record can be recognized by the preferred dip of successive lateral accretion units in meander loops together with soft sediment deformation facies and thickness variations they may indicate tectonic deformation of the sedimentary surface

tilting neotectonics of the guadiamar drainage basin sw spain the guadiamar river ows from the southern iberian massif to the guadalquivir foreland basin sw spain its drainage basin displays asymmetries in the stream network the arrangement of alluvial terraces and the con guration of the trunk river valley the stream network asymmetry was studied using morphometric measures of transverse topographic sym metry asymmetry factor and drainage basin shape the alluvial terraces were studied through the lithologic logs of more than a hundred boreholes and eld mapping the morphometric methods demonstrate a regional tectonic tilting toward the sse causing both the migration of the guadiamar river toward the east and the migration of the guadiamar tributaries toward the southwest as a consequence of the guadiamar river migration an asymmetric valley developed with a steep eastern margin caused by river dissection and a gentle western margin where the main alluvial deposits are found the ages obtained using the 14c analysis of samples from several alluvial deposits show that the river migration and thus tilting has occurred during the holocene as well as earlier in the quaternary this interpretation revises the guadiamar longitudinal fault assumed by previous studies copyright 2003 john wiley sons ltd

seismicity gaps and the shape of the seismic zone in the banda sea region from relocated hypocenters 1 we relocate hypocenters for more than 800 earthquakes deeper than 50 km with mb 5 0 along the banda arc using several thousand handpicked direct depth and core reflected phases in addition to phases reported by the international seismological centre the seismicity distribution is found to be very nonuniform both along the arc and in depth gaps in the relocated hypocenters exist along depth in most places of the arc with the upper edge of the gaps varying from 100 to 450 km depth and the lower edge varying from 350 to 670 km in different portions of the arc the seismic zone between 129 and 131 e in the 100 200 km depth range is the widest along the arc both in strike and downdip this region near the highest arc curvature has the highest seismic activity and is the only part of the arc with earthquakes continuously occurring from the surface down to below 600 km the very deep earthquakes under sulawesi are shown to be part of the west southwest dipping seram slab in the westernmost part of the banda arc the slab is under downdip tension in the 50 250 km depth range while the deepest portion of the slab in this region is under compression from 128 to 131 e the slab between 100 and 200 km depth is under mainly horizontal compression our study supports the two slab model for the banda arc the depth of the wadati benioff zone below the volcanoes is 60 100 km for the five volcanoes between 128 and 130 e and 150 km for the 23 volcanoes between 118 and 124 e

multi stream order analyses in basin asymmetry a tool to discriminate the influence of neotectonics in fluvial landscape development madrid basin central spain morphometric analysis of the tajo drainage network using a dem was carried out in order to determine neotectonic influence on the development of the madrid basin since the pliocene statistical analysis of digitally derived transverse topographical drainage basin asymmetry t factor was used to infer directions of ground tilting a crustal block pattern was interpreted from a mean basin asymmetry vector field that was computed using a new approach based on a gridded running average of the raw vector field measurement of r factor for different order channels allows investigation of evolution rates of different order rivers and at the same time reveals possible factors controlling basin evolution the vector data show clear differences between high and low orders high order asymmetry is consistent with fluvial terrace distribution as it reflects channel migration and incision within the main valleys and shows a general trend toward a central basin axis running sw ne a sw ne trend is also defined by other morphographical approaches such as drainage density and relief analysis both approaches point toward the presence of two uplifted areas running sw ne and a subsided zone between them which is in agreement with previous crustal flexure models in contrast low order asymmetry shows a clear trend indicating eastward tilting which could be driven by recent changes in maximum principal stress direction and its influence on fault reactivations in general large rivers generating fluvial terraces are controlled by basement structure with positive and negative crustal flexures driving their migration direction and thus controlling the spatial distribution of terraces because the position of main streams is controlled by large tectonic lineaments that favor groundwater flow convergence on the other hand small tributaries have low capabilities to attain equilibrium and t factor values of low order basins may reflect more recent block tectonics due to variations in stress fields or may reflect local controls like lithology

model of distributed deformation block rotations and crustal thickening for the formation of the spanish central system abstract the spanish central system constitutes an important morphostructural intraplate feature of iberia that resulted from a concentration of crustal strain derived from stresses applied on the boundaries of the betics and pyrenees we propose a tectonic model in which the deformation of this zone was produced by a mid late mesozoic shear zone a type of secondary plate boundary that absorbed part of the iberia eurasia relative motion the deformation within this e w shear zone was compensated by means of block rotations that resulted from the reorganization of multiple and previous faults and fractures the subsequent n s africa eurasia convergence was partly accommodated within this intraplate zone of weakness this caused a concentration of strain that was responsible for the homogeneous thickening of the lower crust and for the blocking of block rotations and forced uplifting of the upper crust

numerical simulations of the barrier jet over northwestern taiwan during the mei yu season orographic effects on the airflow over taiwan under the prevailing southwesterly monsoon flow are studied using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 in particular the orographically induced low level strong winds along the northwestern coast of taiwan are simulated in the absence of radiative forcing thermal forcing from the surface and synoptic forcing the momentum balance for the low level strong winds along the northwest coast of taiwan shows that above the mixed layer the alongshore force balance is dominated by the inertial advection term and the pressure gradient force term the significant lagrangian flow acceleration of the northern branch of the deflected airflow along the northwest coast is mainly related to the pressure gradient force as the airflow moves down the orographically induced pressure ridge along the windward coast even though the alongshore pressure gradient force along the northwest coast is largest at the surface the observed and simulated wind profiles show that the wind speed maximum in the vertical of the barrier jet occurs at a height of 800 m primarily due to frictional retardation in the lowest levels within the well mixed layer the alongshore force balance is a threeway balance between inertial advection pressure gradient force and frictional force normal to the northwest coast the force balance is approximately geostrophic in addition the location and the strength of the orographically induced low level strong winds along the northwest coast of taiwan also depend on the impinging angle and the wind speed of the prevailing winds

microseismicity and focal mechanisms of the intermediate depth bucaramanga nest colombia the bucaramanga nest of intermediate depth seismicity in northern colombia was investigated from microearthquakes m sub b less than or equal to4 3 recorded from june 20 to july 6 1979 by a local array of 12 digital three component seismographs of 161 events studied 142 are from the nest and 19 define a thin wadati benioff w b zone mainly from 110 to 190 km depth the w b zone part of the bucaramanga segment strikes n10 sup 0 e with a dip increasing wtih depth from 30 sup 0 e to near vertical beneath the nest the 89 best located events from within the nest define a volume of about 8 km nw by 4 km ne by 4 km depth centered at 161 km depth with relative location accuracies of 0 5 to 1 0 km double couple fault plane solutions of 59 events were determined from an objective procedure using p wave polarities and s p amplitude ratios there is no dominant trend in focal mechanisms nor any reasonable correlation with regional stress patterns or previously determined mechanisms from teleseismic data the subduction and assimilation of a linear feature such as an island arc undergoing a phase transformation may explain the existence of the bucaramanga nest however the extraordinarilymore high rate of seismicity suggests that the nest may be moving rate several orders of magnitude faster than the rate of relative plate motion alone the intense seismicity and variation in focal mechanisms suggest that the nest represents some aspect of stress release associated with the ascent of fluids perhaps brine or magma that will ultimately result in the initiation of volcanic activity over this recently emplaced w b zone copyright american geophysical union 1987 less

retrieved thermodynamic structure of a subtropical orographically influenced quasi stationary convective line airborne doppler radar and flight level measurements were used to document the three dimensional thermodynamic structure of a convective line that developed off the southeastern coast of taiwan on 16 june 1987 during the taiwan area mesoscale experiment during the period of aircraft observation the convective line appeared to be quasi stationary in a region 90 km away from the coast calculations of perturbation pressure and buoyancy retrieved from the doppler radar derived wind fields show that a high pressure perturbation associated with negative buoyancy existed in the region of heavy precipitation in the lowest level in low levels an elongated zone of low pressure was documented along the line which was closely related to the distributions of buoyancy these retrieved features are basically consistent with those calculated from in situ observations in mid to upper levels the high low pressure perturbation lay around the updraft cores on the upshear downshear of environmental shear the quantitative diagnosis for the perturbation pressure indicates that the positive buoyancy associated with the in cloud latent heat release as well as evaporative cooling occurring near cloud base and subcloud regions is crucial to determine the low level perturbation pressure distributions however dynamic forcing contributing to the pressure perturbation cannot be ignored in middle levels because of updraft shear interaction due to the presence of pronounced cross line wind shear and corresponding updrafts reaching maximum values near midtroposphere in distinct contrast to squall lines which are rapidly moving the near surface temperature gradient across this quasi stationary line was very weak and at low levels no gust front rear inflow or dynamically induced high pressure was evident near the leading edge of the line analyses presented here suggest that the persistent stationary convergence in association with the deceleration of low level southeasterly flow as it approached the nearshore blocked flow played an important role in maintaining and organizing the deep convection in this case

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

statistics of characteristic earthquakes statistical methods are used to test the characteristic earthquake hypothesis several distributions of earthquake size seismic moment frequency relations are described based on the results of other researchers as well as my own tests evidence of the characteristic earthquake hypothesis can be explained either by statistical bias or statistical artifact since other distributions of earthquake size provide a simpler explanation for available information the hypothesis cannot be regarded as proven

universality of the seismic moment frequency relation we analyze the seismic moment frequency relation in various depth ranges and for different seismic regions using flinn engdahl s regionalization of global seismicity three earthquake lists of centroid moment tensor data have been used the harvard catalog the usgs catalog and the huang et al 1997 catalog of deep earthquakes the results confirm the universality of the values and the maximum moment for shallow earthquakes in continental regions as well as at and near continental boundaries moreover we show that although fluctuations in earthquake size distribution increase with depth the values for earthquakes in the depth range of 0 500 km exhibit no statistically significant regional variations the regional variations are significant only for deep events near the 660 km boundary for declustered shallow earthquake catalogs and deeper events we show that the worldwide values have the same value of 0 60 0 02 this finding suggests that the value is a universal constant we investigate the statistical correlations between the numbers of seismic events in different depth ranges and the correlation of the tectonic deformation rate and seismic activity the number of earthquakes above a certain threshold level per year the high level of these correlations suggests that seismic activity indicates tectonic deformation rate in subduction zones combined with the universality of the value this finding implies little if any variation in maximum earthquake seismic moment among various subduction zones if we assume that earthquakes of maximum size are similar in different depth ranges and the seismic efficiency coefficient is close to 100 for shallow seismicity then we can estimate for deeper earthquakes for intermediate earthquakes 5 and 1 for deep events these results may lead to new theoretical understanding of the earthquake process and better estimates of seismic hazard

seismic constraints on mechanisms of deep earthquake rupture 1 observations of the depth distribution of seismicity suggest that several mechanisms cause deep earthquakes cold subducting slabs exhibit a broad peak in seismicity between 300 and 530 km depth that is best explained by transformational faulting of metastable olivine cumulative seismic moment release increases sharply at 530 km depth in both cold and warm slabs implying that events deeper than this are controlled by an equilibrium rather than a metastable phase change which would be temperature dependent this together with the observation that deep seismicity predominates near the garnet rich upper boundary of the subducting plate former oceanic crust suggests that the transformation of garnet to perovskite which may release considerable water is integral in the cause of earthquakes deeper than 530 km where most deep earthquakes occur