forest height estimation by means of pol insar data inversion the role of the vertical wavenumber this paper examines the multifaceted effect of the effective spatial baseline as expressed through the vertical interferometric wavenumber on the inversion of forest height from polarimetric interferometric synthetic aperture radar pol insar data first the role of the vertical wavenumber in relating forest height to the interferometric volume coherence is introduced through the review of the forest height inversion from pol insar data the effect of the vertical wavenumber on the inversion performance is evaluated the selection of optimum with respect to forest height inversion performance vertical wavenumbers is discussed the impact of the acquisition geometry and terrain slopes on the vertical wavenumber and their consideration in the inversion methodology is addressed the individual effects discussed are demonstrated by means of airborne repeat pass pol insar acquisitions in l and p band acquired over different forest conditions including a boreal a temperate and a tropical forest test site the achieved forest height inversion performance is validated against reference height data derived from airborne lidar acquisitions

three dimensional simulations of ground motions in the san bernardino valley california for hypothetical earthquakes on the san andreas fault three dimensional finite difference simulations of elastic waves in the san bernardino valley were performed for two hypothetical earthquakes on the san andreas fault a point source with moment magnitude m5 and an extended rupture with m6 5 a method is presented for incorporating a source with arbitrary focal mechanism in the grid synthetics from the 3 d simulations are compared with those derived from 2 d vertical cross section and 1 d flat layered models the synthetic seismograms from the 3 d and 2 d simulations exhibit large surface waves produced by conversion of incident s waves at the edge of the basin seismograms from the flat layered model do not contain these converted surface waves and underestimate the duration of shaking the seismograms from the 3 d simulations have larger amplitude coda than do the seismograms from the 2 d case because of the presence of off azimuth surface wave arrivals in the 3 d simulations that are not included in the 2 d simulations snapshots of the wavefield of the 3 d simulation show that these off azimuth arrivals represent surface waves reflected from the edges of the basin the anelastic attenuation of the sediments is a key parameter controlling the overall duration of motion some of the coda energy at rock sites near the basin edges represents leakage of surface wave energy out of the basin for the m6 5 earthquake simulation the largest ground velocities occur where surface waves reflected from the edge of the basin interfere constructively with the trapped waves that follow the direct s wave maps of maximum ground velocity are produced for two directions of rupture propagation the largest velocities occur in localized portions of the basin the location of the largest velocities changes with the rupture propagation direction contours of maximum shaking are also dependent on asperity positions and radiation pattern

geochemical and paleoenvironmental record of the early to early late aptian major episodes of accelerated change evidence from sierra del rosario northeast mexico abstract the lower to lower upper aptian succession of northern mexico documents the drowning of the shallow water cupido cupidito carbonate platform system followed by deposition of the deep water sediments of the la pena formation using 13 c stratigraphy geochemical and mineralogical information coupled with previous microfacies paleontological and total organic carbon toc data from a stratigraphic section which includes such lithological change this study identifies distinctive episodes of accelerated global environmental change and determines the paleoenvironmental conditions conducive to the deposition of toc rich intervals within the cupidito unit the oceanic anoxic event 1a oae 1a is recorded near the base of the section and the intra furcata negative excursion in the topmost beds of the unit the upper part of the section within the la pena formation is correlatable with the noire level organic carbon rich intervals occur in the lower and middle part of the oae 1a upper part of the cupidito unit base of the la pena formation and in the noire level equivalent reducing conditions within the sediment and oxic dysoxic at the seafloor locally controlled persisted both before and during oae 1a interval in the cupidito lagoon oxygen depleted conditions dysoxic anoxic were more permanent and stronger during the deposition of the base of the la pena formation and the noire equivalent level it is proposed here that deposition of the lower middle part of the oae 1a and the base of the la pena formation was influenced by climate controlled increases in detrital and accompanying nutrient influx that supplied especially biolimiting nutrients fe p fostering marine productivity and toc burial upwelling of nutrient rich deeper waters and minor arrival of nutrients from runoff both account for the domination of radiolaria and organic carbon burial during the noire level equivalent record of the oae 1a time equivalent facies in the cupidito lagoonal sediments confirms the diachronism of the cupidito la pena flooding heterozoan carbonate production in the cupidito ramp was uninterrupted during and after oae 1a periodic arrival of detrital components and nutrients during warmer humid periods accelerated platform drowning which peaked during the diachronic deposition of the la pena formation

pine forest investigation using high resolution p band pol insar data a pol insar dataset acquired at p band over a maritime pine forest nezer forest of landes france has been investigated and compared with tree structural ground measurements in order to identify scatterers associated with elementary scattering mechanisms in the canopy layer since this managed forest is constituted by different height stands it allows to investigate mechanism change in the vertical direction during the forest growth it has been observed that vv channel was the most elevated which can be accounted for a maximum attenuation in the vertical direction and partially for the presence of sub vertical branches in the top canopy layer and that this channel was the most sensitive to the tree density in reason of an important ground reflectivity the most pure double bounce scattering mechanism component is received in hh vv channel where the corresponding phase center reaches the ground level for large diameter at breast height it is also supposed that hh channel which receives double bounce backscatter was affected by the sub horizontal primary branch development which induces an elevation of the phase center over oldest trees while tree density diminution enhances backscatter from the ground level finally the crosspolar channel appeared the less perturbed by the tree density than vv channel since it receives predominantly the canopy contribution

site amplification from s wave coda in the long valley caldera region california following the work of phillips 1985 we have computed site amplification factors for coda waves at many sites in the long valley region in the eastern sierra nevada we computed ratios of coda amplitudes measured at 15 stations in and around long valley caldera relative to a granitic site mmpm for six frequency bands centered at 1 5 3 0 6 0 9 0 12 0 and 15 0 hz all station sites located within the caldera experienced large ground motion amplification at 1 5 and 3 0 hz ranging between five and 17 times that of the reference site however at higher frequencies these same sites exhibited significantly less amplification than the reference granite site this is attributed to the competing effects of an impedance contrast between the basement rock and caldera fill and very high absorption in the caldera fill at high frequencies station mmlm located on top of a volcanic plug displayed the largest amplitudes of all the sites studied for frequencies between 9 0 and 15 0 hz a dike structure attached to the plug couples the basement rock to the surface at high frequencies the resulting large amplitudes at mmlm are not due to amplification resulting from a strong impedance contrast rather the absorption under this site is very low perhaps lower than at the reference site mmpm outside the caldera another hard rock site located at devil s postpile mdpm generally behaved like the reference site for all frequencies the lowest amplifications observed came from a site outside the caldera mdcm located on thin pyroclastic ash deposits overlying granitic basement this can be attributed to a dominance of absorption over the amplification caused by lower impedance of this layer variations among sites on similar surface geology may be due to small local variations in impedance and absorption under and adjacent to the site the range in the spectral decay parameter between caldera and rock sites are comparable to results of anderson and hough 1984 for sites on alluvium and rock in the san fernando region these surprisingly different amplifications support the need for additional site specific studies amplifications determined in this study for the frequency range 1 5 and 3 0 hz correlate remarkably well with eaton s 1990 residuals for duration magnitude fmag and amplitude magnitude xmag for the usgs northern california seismic array further supporting the use of coda waves in determining site specific amplification

estimation of the backscatter vertical profile of a pine forest using single baseline p band pol insar data the vertical backscatter profile of a pine forest constituted by stands of different height is inverted from a single baseline p band pol insar data in order to identify scatterers in the canopy the proposed approach uses the gaussian vertical backscatter profile model which associates an interferometric coherence expression to a vertical scatterers distribution characterized by relative standard deviation and elevation the methodology which uses in situ measurements of forest height and unbiased ground level estimation is applied to hv and vv channels providing accuracy given sufficiently low ground to canopy power ratios inverted backscatter profiles show maximum power converging toward the basis of the tree crown on highest forests where the largest branches are located indicating the high sensitivity of p band measurements to the forest structure and to the vertical biomass distribution over lower stands with larger tree densities the power peak is located in the upper part of the canopy which can be explained by a stronger attenuation in the canopy

the seismic coda site effects and scattering in alluvial basins studied using aftershocks of the 1986 north palm springs california earthquake as source arrays abstract we use single station recordings of widely distributed earthquake sources to identify heterogeneities in the earth9s crust that scatter energy into the early part of the observed s wave codas we assume that ray theory accurately describes the propagation of body waves from the earthquake sources to the scatterers but we assume no propagation mechanism between the scatterers and the seismic station a grid of hypothetical scatterers is assumed to cover the earth9s surface and the strength of each scatterer is determined by an iterative inversion method our data are recordings of aftershocks of the 1986 north palm springs earthquake recorded at a seismic station in the coachella valley smp and at a station in the morongo valley smc the technique is applied separately to each horizontal component of motion at each station we identify a particular spot at the northwest edge of the quaternary alluvium in the coachella valley that scatters waves into the s coda observed at smp 8 km distant in the valley the geologic structure that causes the strong scattering seems to be the basin edge structure rather than the mountainous terrain 3 km farther west the early coda at smc is dominated by scattering within a few kilometers of smc either in the basin itself or in the morongo valley fault zone this study shows that laterally propagating waves are sometimes observable in the early coda casting doubt on the use of 1 d techniques for estimating site responses the northwest edge of the coachella valley seems to be an especially strong scatterer of incident waves if other basins have similar loci of strong scattering perhaps these places can be identified using microearthquake seismograms and used to predict strong ground motions in the basins

microseismicity and stresses in the lesser antilles dipping seismic zone abstract microearthquake data from a telemetered array have been used to study the central antilles arc system the zone lying between lat 14 17 n and long 59 5 62 w has been investigated during the period 1979 1980 no shock with a magnitude larger than 4 5 was recorded results are well correlated with previous conclusions derived from teleseismic records the dip of the subducting plate is 60 everywhere in this area no composite focal mechanism can be produced for the region north of dominique for the southern region composite focal mechanisms reveal two zones for depths between 45 and 80 km the stress field seems mainly related to the interplate action beneath 80 km the slab dominantly neither in compression nor in tension earthquakes are more likely related to local stress fields a double layered structure has not been found in the earthquake distribution in the subducted plate nor in the stress field deduced from focal mechanisms

seismicity and seismic gap in the lesser antilles arc and earthquake hazard in guadeloupe summary a seismic study of the lesser antilles arc has been carried out first for the period 1950 1978 for which we can use local seismic networks to draw maps of instrumental seismicity then for the period 1530 1950 for which we have catalogues of felt earthquakes the striking feature of the spatial distribution of foci is the cluster of epicentres in the northern half of the arc all large earthquakes m 7 5 are located north of 14 latitude seismicity cross sections through the arc show a variable dipping subduction zone along the arc the deep seismic zone is steeper in the centre of the arc than on the extremity the time space diagram for historical seismicity and the evidence of a seismic gap at the east of guadeloupe lead us to consider the northern half arc as a likely site for a large earthquake in the near future the seismic slip rate calculated from all major earthquakes since 1530 is of much greater value than that obtained from recent plate tectonic models suggesting that the recurrence rate of earthquakes is more than many hundreds of years with a possible aseismic creep

experimental study of site effects in the fort de france area martinique island abstract we used weak motion recordings of regional events to quantify the site effects in the fort de france martinique area in the frequency band 1 to 25 hz the studied area extends over three distinct geological units the morne pitault volcanic massif 15 to 11 m a the carbet volcanic massif 4 to 2 m a and the lamentin alluvial plain quaternary age the topography being complex 31 sites were selected in order to get a representative sampling of the various topographical and geological configurations the large number of studied sites also allowed us to define a reference site whose selection was not obvious large broadband amplifications are observed in the lamentin plain instead of the expected peak resonances more surprising such resonance is observed around 2 to 3 hz on several sites of the volcanic vauclain pitault chain though no sedimentary layer is present on the other hand in the inner fort de france where significant effects were expected because of the very complex topography no large amplication is observed except for at one site clear three dimensional 3d effects are also observed at some stations though not very well documented the low frequency behavior deduced from teleseismic observations seems rather different illustrating the difficulty in finding a convenient reference site in such a volcanic area

forest height inversion using high resolution p band pol insar data in this paper a high resolution p band pol insar data set acquired by the airborne ramses system over pine forest stands of different height is investigated a significant penetration depth in all the polarimetric channels and a wide range of polarimetric phase center heights are observed attesting of an interaction of the radar waves with different forest structural elements the main objective of this paper concerns forest height inversion at p band first forest modeling assumptions are evaluated using a priori information such as ground level and forest height measurements the full extend of the forest height is shown to be responsible of the volume decorrelation and a significant orientation effect is clearly identified over the highest stands as a consequence the oriented volume over ground model ovog is determined to be the most appropriated model for the forest height inversion at p band the ground contribution is present in all the polarimetric channels due to the important penetration at this frequency to overcome this difficulty a time frequency optimization method based on sublook decomposition is developed to separate the pure ground and canopy contributions allowing forest height estimation with ovog with an rms error on the order of 2 m in the last section of this paper a sensitivity analysis of the inversion with respect to two important system parameters the signal to noise ratio and the resolution is presented leading to a discussion on the inversion robustness in spaceborne conditions where these system parameters are the most deteriorated as compared to airborne configurations

directional site resonances and the influence of near surface geology on ground motion the authors examine the horizontal motions at close stations from earthquakes in the loma prieta and whittier narrows sequences to study the shear wave polarizations they use a dense six station array recording 10 aftershocks for the former and use two events and 11 stations across the los angeles area for the latter they compute the average azimuth of strongest shaking in the shear wave as a function of frequency from 1 to 18 hz for each record of each earthquake the direction of shaking at a given frequency often correlates much better with an empirical site resonance direction than with the direction of shaking expected from the focal mechanism of the earthquake the effect tends to be greatest at the frequencies that are the most amplified this phenomenon can complicate determination of the earthquake source at frequencies higher than 1 hz further since sites only 25 meters apart show different preferred directions very near surface geology is probably responsible estimation of directional site resonances may prove useful for seismic design

forest modeling for height inversion using single baseline insar pol insar data the random volume over ground rvog model has been extensively applied to polarimetric synthetic aperture radar interferometry pol insar data for forest height inversion the model assumes forest as a homogeneous volume of randomly oriented particles characterized by a constant extinction but does not take into account the forest vertical heterogeneity to which interferometric coherence is sensitive in order to integrate vertical heterogeneity in forest models two complementary models which take into consideration the forest natural structure are investigated through analysis of volume interferometric coherence the first model assumes a vertically varying extinction in the volume layer and the second model considers predominant contributions localized in a finite height interval modeled as a gaussian distributed backscatter the two forest models are compared with constant extinction rvog in the coherence and interferometric phase aspects finally the contribution of these new models for forest height inversion using the pol insar technique is discussed in the context of a two layer ground canopy medium

subduction seismicity and tectonics in the lesser antilles arc we have studied the mechanisms of 17 earthquakes along the lesser antilles subduction zone to examine a site where very old lithosphere subducts at a slow convergence rate no large thrust earthquakes occurred during the 1950 1978 study period the three large magnitude seven events are all normal faults one is a normal faulting event seaward of the trench its aftershock sequence includes strike slip events on differently oriented faults probably due to lateral block motion in response to the main shock a second indicates extension within the slab at depth these observations suggest that subduction in this region is primarily decoupled and aseismic unless the time interval studied is unrepresentative the third normal fault earthquake occurred within the upper plate with fault planes perpendicular to the arc and trench this unusual geometry may represent a flexural response to the subduction of the barracuda ridge a major bathymetric high with uncompensated excess mass at depth which seems analogous to flanking ridges found along some mid atlantic ridge fracture zones thus the barracuda ridge is not buoyant and does not affect benioff zone dip strike slip faulting occurs at depth in the subduction zone along a concentration normal to the arc and maymore indicate a fossil fracture zone there is no direct evidence in the shallow seismicity for the hypothetical north america south america caribbean triple junction through some of the oceanic intraplate seismicity is consistent with such a boundary less

c band repeat pass interferometric sar observations of the forest properties of ers 1 c band repeat pass interferometric sar information for a forested area are studied the intensity information is rather limited but including coherence and effective interferometric sar insar height more information about the forest parameters can be obtained via satellite such information is also important for correction of insar derived topographic maps coherence properties have been used to identify forested nonforested areas and the interferometric effective height of the forest determined by comparison to a dem of the area the authors have developed a model to relate basic forest properties to insar observations these show that the coherence and interferometric effective height of a forested area change between image pairs the model demonstrates how these properties are related to the temporal decorrelation and the scattering from the vegetation canopy and the ground surface gaps in the vegetation are found to be important in the characterization of boreal forests

single baseline polarimetric sar interferometry examines the application of single baseline polarimetric sar interferometry to the remote sensing and measurement of structure over forested terrain for this a polarimetric coherent scattering model for vegetation cover suitable for the estimation of forest parameters from interferometric observables is introduced discussed and validated based on this model an inversion algorithm which allows the estimation of forest parameters such as tree height average extinction and underlying topography from single baseline fully polarimetric interferometric data is addressed the performance of the inversion algorithm is demonstrated using fully polarimetric single baseline experimental data acquired by dlr s e sar system at l band

subduction of aseismic ridges beneath the caribbean plate implications for the tectonics and seismic potential of the northeastern caribbean normal seafloor entering the puerto rico and northern lesser antillean trenches in the northeastern caribbean is interrupted by a series of aseismic ridges on the north and south american plates these topographic features lie close to the expected trend of fracture zones created about 80 110 m y ago when this seafloor was formed at the mid atlantic ridge the northernmost of the ridges that interact with the lesser antillean subduction zone the barracuda ridge intersects the arc in a region of high seismic activity some of this seismicity including a large shock in 1974 occurs within the overthrust plate and may be related to the deformation of the caribbean plate as it overrides the ridge a large bathymetric high the main ridge is oriented obliquely to the puerto rico trench and intersects the subduction zone north of the virgin islands in another cluster of seismic activity along the inner wall of the trench data from a seismic network in the northeastern caribbean indicate that this intersection is also characterized by both interpolate and intraplate seismic activity magnetic anomalies bathymetric trends and the pattern of deformed sediments on the inner wall of the trench strongly suggest that the main and barracuda ridges are parts of a formerly continuous aseismic ridge a segment of which has recently been overridden by the caribbean plate reconstruction of mid miocene to recent plate motions also suggest that at least two aseismic ridges and possibly fragments of the bahama platform have interacted with the subduction zone in the northeastern caribbean the introduction of these narrow segments of anomalous seafloor into the subduction zone has segmented the arc into elements about 200 km long these ridges may act as tectonic barriers or asperities during the rupture processes involved in large earthquakes they also leave a geologic imprint on segments of the arc with which they have interacted a 50 km landward jump of the locus of island arc volcanism occurred in late miocene time along the northern half of the lesser antilles we postulate that the subduction of a segment of seafloor of anomolously thick crust being more buoyant than adjacent seafloor resulted in a marked shoaling in the dip of the descending slab and therefore a shift of the locus of volcanism in the region near western puerto rico and eastern hispanolia plio pleistocene interaction with a similar feature in this case a part of the bahama platform about 3 4 m y ago led to a jump in the locus of subduction as evidenced by a gap in the downgoing seismic zone that segment of the bahama platform interferred with the subduction process and was subsequently sutured onto the caribbean plate when the boundary jumped about 60 km to the northeast the maximum size of historic shallow earthquakes along the lesser antillean arc varies from about 7 0 7 5 in the center of the arc where the dip of the shallow part of the plate boundary is steep to 8 0 8 5 along the northern part of the arc where the dip is shallow the interaction of anomalous seafloor as along the northern lesser antilles can lead to the development of a wider than normal zone of interplate contact and hence to earthquakes that are larger than those associated with more typical seafloor entering subduction zones major seismic gaps and regions of high seismic potential currently exist along the northern lesser antilles and to the north of puerto rico both gaps are bounded by anomalous features on the downgoing plate the intersection of these features with the plate boundary created large asperities that may be good places to search for precursors to future large earthquakes a great shock in 1787 may have ruptured an existing seismic gap north of puerto rico between 65 and 67 w thus that gap can be expected to eventually rupture again in a great shock and not to accommodate plate motion by totally aseismic processes

the response of the ubaye valley france for incident sh and sv waves comparison between measurements and modeling l this paper presents a detailed study of the response of an alluvial valley in the alps france the structure ubaye valley was chosen 1 for its moderate dimensions 500 m wide and 65 m thick which allow an accu rate determina tion of the deposit characteristics and 2 for the relatively high seismicity of the region the study included the deployment of five temporary seismological stations a seismic survey of the valley for determining the dynamic proper1ies and the geometry of the soft deposits and 1 d and 2d numerical modeling for incident sh and sv waves comparisons between observed and computed amplifications show a good agreement for frequencies lower than 10hz and the particular direction of arrivai of the input motions corresponding to the 2d case when the ear1h quake sources are not located in the continuation of the line of seismometers the spectral ratios exhibit a great variability between different groups of similar events these observations indicate the azimuthal dependence of the site response and the need for 3d modeling

3 d wave propagation in the los angeles basin for the whittier narrows earthquake abstract elastic wave propagation within and around the los angeles basin during the whittier narrows earthquake in 1988 is simulated with a 3 d finite difference method the model consists mainly of a sedimentary layer over the basement but lateral variations inside the sedimentary basin is also included to approximate observed variations in surface shear velocity the minimum shear velocity is 1 km sec on the surface and fairly reliable results are obtained up to 0 75 hz the total simulation lasts 26 sec our simulation can reproduce the general amplification pattern small east of the epicenter and large in the l a basin and the san fernando valley due to thick sediments of low velocity in these areas surface waves are generated by the primary s wave and trapped inside the basins in the southern part of the l a basin a distinct later phase delayed by 5 to 6 sec relative to the primary s wave is produced in our simulation which matches some strong motion records

the effect of topography on earthquake ground motion a review and new results a brief review of experimental and theoretical results about the effect of topography on seismic motion shows that they are consistent only on a qualitative basis amplification at mountain tops for wavelengths comparable with mountain widths is predicted and observed but the numerical simulations often underestimate the actual observed effects we propose that this disagreement is because current models are not complex enough we therefore computed the response to incident sh waves of a set of different complex configurations that include two dimensional surface topography with or without periodic ridges and subsurface layering the results show that 1 the topographic effect in itself is difficult to isolate from other effects like surface layering and therefore the amplification on top of geomorphologically complex sites cannot be predicted by a priori estimations based solely on topography and 2 the high crest base amplification ratio observed in the field cannot usually be matched even with complex two dimensional structures with incident plane sh waves which suggests that more complex models are needed to incorporate more complex wave fields e g sv surface and three dimensional geologic configurations

subduction and seismic hazard in the northern lesser antilles revision of the historical seismicity an important set of french and british archives on the historical seismicity of the northern lesser antilles is analyzed we present the most significant data which help to constrain the 8 february 1843 the 16 may 1851 and the 29 april 1897 earthquakes the 1843 event is the largest reported historical earthquake of the lesser antilles subduction arc and produced intensity ix on a segment about 100 km long between antigua and grande terre guadeloupe which contradicts the 300 km long proposed by other authors who mainly rely on robson s catalog 1964 this suggests a magnitude 7 5 to 8 0 the absence of tsunami and noticeable vertical deformation of the coasts in the source area makes very unlikely a normal fault mechanism but does not rule out the possibility of a subduction event because of the low dip angle of the interplate plane the dominance of moderate instrumental thrust earthquakes in the source area suggests a subduction mechanism for the 1843 event the northern and southern limits of the 1843 source area roughly coincide with the barracuda ridge and the tiburon ridge respectively which may have acted as barriers during the rupture process the northwestern portion of the tiburon ridge is associated with a lack of instrumental seismicity near grande terre which could indicate a possible magnitude 7 5 to 8 0 event in the next future moreover its mechanism could be normal which would provide the additional risk of a damaging tsunami the evaluation of seismic hazard must also take into account possible shallow moderate earthquakes as the 1851 and the 1897 events which produced intensities vii to viii in guadeloupe and may be related to observed major plioquaternary faults in this island