upper mantle reflector structure and origin beneath the scottish caledonides the mantle reflector pattern beneath the scottish and irish caledonides is perhaps the most widely studied individual structure in the uppermost continental mantle previous investigations interpreted the reflector as a thrust related to the caledonian orogeny silurian early devonian or as a normal fault or shear zone active during post caledonian e g devonian or permo triassic extension this study uses all available deep seismic reflection data to map mantle reflector structure along the caledonian orogen and to constrain better its geometrical and tectonic relation to regional geology the distribution of the mantle reflector shows that it is not spatially related to either caledonian compressional or subsequent basin extensional structures in a simple way a structural contour map shows two distinct discontinuous surfaces consisting of a steeply plunging antiform synform pair beneath the west orkney basin north of the scottish mainland and the faeroe shetland basin west of shetland respectively separated by an inferred zone of structural disruption a working hypothesis for this study is that these two surfaces may have once been part of a continuous more or less planar surface that has been offset and deformed by either or perhaps a combination of two processes 1 differential extension of crust that was at least partially coupled to the uppermost mantle beneath the west orkney and faeroe shetland basins 2 a broad approximately orthogonal i e east west trending zone of simple shear corresponding to the disrupted zone that was largely confined to the upper mantle but reactivated to deform the crust our results also suggest that the mantle reflector structure may be inherited from neoproterozoic events associated with rifting of the laurentia baltica supercontinent

transient luminous events above two mesoscale convective systems storm structure and evolution 1 two warm season mesoscale convective systems mcss were analyzed with respect to their production of transient luminous events tles mainly sprites the 20 june 2007 symmetric mcs produced 282 observed tles over a 4 h period during which the storm s intense convection weakened and its stratiform region strengthened tle production corresponded well to convective intensity the convective elements of the mcs contained normal polarity tripole charge structures with upper level positive charge 40 c midlevel negative charge 20 c and low level positive charge near the melting level in contrast to previous sprite studies the stratiform charge layer involved in tle production by parent positive cloud to ground cg lightning resided at upper levels this layer was physically connected to upper level convective positive charge via a downward sloping pathway the average altitude discharged by tle parent flashes during tle activity was 8 2 km above mean sea level msl 25 c the 9 may 2007 asymmetric mcs produced 25 observed tles over a 2 h period during which the storm s convection rapidly weakened before recovering later unlike 20 june tle production was approximately anticorrelated with convective intensity the 9 may storm which also had a normal tripole in its convection best fit the conventional model of low altitude positive charge playing the dominant role in sprite production however the average altitude discharged during the tle phase of flashes still was higher than the melting level 6 1 km msl 15 c based on these results it is inferred that sprite production and sprite parent positive charge altitude depend on mcs morphology

deep seismic reflection images of the wharton basin oceanic crust and uppermost mantle offshore northern sumatra relation with active and past deformation 1 we present deep seismic reflection images along two profiles collected in 2006 in the wharton basin offshore northern sumatra the main profile is located subparallel to the sumatran trench at a distance of 32 66 km faulting of the entire sedimentary section strike slip deformation sometimes accompanied by a dip slip component is imaged over two fracture zones of the extinct wharton spreading center that prior studies have shown to be reactivated as left lateral faults the western fracture zone is associated with a wide region of strong basement topography a difference in crustal thickness of 1 5 km and an age offset of 9 ma the epicenters of the 11 april 2012 mw 8 6 great strike slip earthquake its mw 7 2 foreshock and mw 8 2 aftershock align along this major structure 100 km south of the profile intersection our high quality long offset seismic reflection data also reveal bright dipping reflections extending down to a maximum of 24 km into the oceanic mantle 37 km below sea level apparent dips are mostly 25 35 corresponding to 30 55 along either n s to nne ssw or e w to wnw ese directions which encompass the directions of plate fabric and nodal planes of the mw 8 6 event we suggest that these enigmatic reflections arise from presently inactive dip slip fault planes reaching for the deepest ones to the base of the brittle layer possible origins include extension related to plate bending or an episode of now inactive thrust type deformation reactivating paleonormal faults similar to that taking place in the central indian basin

along axis variability in crustal accretion at the mid atlantic ridge results from the ocean study the ocean experiment is an integrated geophysical study of a region of the cape verde abyssal plain that formed at 140 ma deep seismic reflection and ocean bottom hydrophone obh refraction data were acquired along lines parallel and perpendicular to the paleoridge axis trend identified from a detailed magnetic anomaly survey the igneous basement is overlain by about 1 3 km of sediment which enables improved imaging of intracrustal structure beyond that possible near the mid atlantic ridge axis we describe the results of a 150 km long profile oriented parallel to magnetic anomalies m15 and m16 along which deep seismic reflection data collected by the british institutions reflection profiling syndicate are complemented by refraction data constrained by four obhs the line spans an entire spreading segment between two fracture zones the northern of which has an offset of 40 km and the other central has an offset of only 10 km away from the fracture zones the mean igneous crustal thickness is 7 2 km near both fracture zones thinning of up to 4 km is observed giving a mean igneous crustal thickness over the whole segment of approximately 6 5 km differences are seen between the two fracture zones in their seismic velocity structure in the associated basement topography and in the presence of a strong reflection extending into the mantle beneath the northern fracture zone the boundary between oceanic layers 2 and 3 correlates with variably coherent normal incidence reflections and a change in the character of the reflectivity a number of planar reflections up to 10 km in length are present within the middle and lower crust dipping outward from beneath low amplitude basement highs at 15 these appear to be present only within layer 3 the moho has several expressions in the reflection data including isolated reflection events a local increase in reflected amplitudes and a downward decrease in coherent reflections at the center of the segment there is a zone at the base of the crust within which both high and low velocity materials are present this zone shows an enhanced level of discontinuous normal incidence reflectivity and may represent an initial fractionation event as melt was emplaced at the spreading ridge

complex structure along a mesozoic sea floor spreading ridge birps deep seismic reflection cape verde abyssal plain summary as part of an intensive study of a small area of oceanic lithosphere the british institutions reflection profiling syndicate birps acquired closely spaced deepseismic reflection profiles over the early cretaceous crust of the cape verde abyssal plain off west africa the survey consisted of profiles spaced at 4 km arranged into strike lines parallel to the old sea floor spreading axis isochron profiles and orthogonal dip lines oriented in the original direction of spreading flow profiles a large capacity well tuned airgun source and very quiet shooting conditions ensured a high signal to noise ratio for deep reflection devising a strategy for mitigating contamination from wrap around multiples arriving from previous shots enabled us to use the minimum possible shot point interval 50 m allowed for collecting long 18 s records data processing was oriented towards a medium with low root mean square velocity steeply dipping structure and pervasive low apparent velocity noise from diffraction at the top of the igneous crust the contrast between the isochron and flow profiles is striking isochron profiles are typically highly reflective throughout the igneous crust consisting of bright bidirectionally dipping reflection sets that extend in places from the top of the igneous basement down to the interpreted moho reflection these reflections do not offset intracrustal or top basement structure and thus are not interpreted as faults an igneous intrusive origin seems more likely flow profiles are more sparsely reflective but show individual steeply dipping reflections best developed in the upper igneous crust continuing down in places to the moho dipping reflections on the flow profiles are interpreted as major normal faults since they are clearly associated with offsets of the top of the basement as well as truncation of horizontal reflections within the igneous crust the dominant dip of these reflections is to the west towards the spreading ridge axis reflections from the vicinity of the moho while well developed in some places are not particularly prominent across the survey area moho reflections appear to show a different structural relation to crustal features on the isochron and flow profiles on isochron profiles dipping reflections occasionally flatten out into and may merge with the moho reflection on flow profiles as dipping crustal reflections approach the moho reflection they are usually abruptly cut off by it without extending deeper this survey shows how oceanic crustal structure can vary rapidly over relatively small areas provides convincing evidence that a structurally complex fabric dominates oceanic igneous crust and gives a conclusive observation of faults that penetrate the entire oceanic crust

attenuation of near surface diffracted energy in deep seismic data by dmo correction abstract seismic data are often contaminated by scattered waves from shallow diffractors such as offshore installations and structural irregularities as the waves travel in the water layer and shallow sub bottom they are damped considerably less than near vertical reflected waves far from the diffractors the stacking velocity of the noise will be nearly identical to the stacking velocities of the primary reflections this implies that cmp stacking of normal moveout corrected data does not suppress the noise and the necessary attenuation will typically be done separately by prestack 2d velocity filtering or array simulation in the shot and receiver domains however by changing the moveout of the diffraction curves through dmo correction the stacking velocity of the noise will be close to the true velocity of the diffracted waves and suppression through cmp stacking is possible as dmo is related to cdp smearing which is a marginal problem for deep seismic data it is normally not used as a part of the standard processing schemes the noise suppression features of the dmo processor are demonstrated with a data example from the north sea

suppression of near surface scattered body to surface waves a steerable and nonlinear filtering approach we present an approach based on local slope estimation for the separation of scattered surface waves from reflected body waves the direct and scattered surface waves contain a significant amount of seismic energy they present great challenges in land seismic data acquisition and processing particularly in arid regions with complex near surface heterogeneities e g dry river beds wadis large escarpments and karst features the near surface scattered body to surface waves which have comparable amplitudes to reflections can mask the seismic reflections these difficulties added to large amplitude direct and back scattered surface rayleigh waves create a major reduction in signal to noise ratio and degrade the final sub surface image quality removal of these waves can be difficult using conventional filtering methods such as an f k filter without distorting the reflected signal the filtering algorithm we present is based on predicting the spatially varying slope of the noise using steerable filters and separating the signal and noise components by applying a directional nonlinear filter oriented toward the noise direction to predict the noise and then subtract it from the data the slope estimation step using steerable filters is very efficient it requires only a linear combination of a set of basis filters at fixed orientation to synthesize an image filtered at an arbitrary orientation we apply our filtering approach to simulated data as well as to seismic data recorded in the field to suppress the scattered surface waves from reflected body waves and we demonstrate its superiority over conventional f k techniques in signal preservation and noise suppression

crustal structure along the strike of the offshore santa maria basin california abstract the geology of the central california offshore region contains the record of the early miocene transition of the western north american continental margin from a site of subduction to one of transform motion the fundamental elements of crustal structure and composition within the margin are defined by the seismic reflection image on the marine profile pge b 10 12 km of franciscan basement rocks c a 7 10 km thickness of oceanic crust seismic sequence analysis provides a foundation for interpreting the evolution of the offshore santa maria basin results indicate that the basin fill is predominantly miocene to pliocene in age and that subsidence began in early miocene times a late miocene to early pliocene shortening event led to faulting and folding of basin strata and to uplift of basement blocks the franciscan complex an accretionary wedge assemblage which floors the basin reveals little internal seismic structure however reflections from the franciscan oceanic crust boundary at 12 15 km depth supply evidence for the existence of an antiform with 2 3 km relief within the oceanic crustal layer this antiform probably formed during early miocene shortening of the oceanic crust alternatively the antiform could represent primary oceanic crustal topography such as seamounts or a fracture zone

accuracy of the lightning mapping array 1 the location accuracy of the new mexico tech lightning mapping array lma has been investigated experimentally using sounding balloon measurements airplane tracks and observations of distant storms we have also developed simple geometric models for estimating the location uncertainty of sources both over and outside the network the model results are found to be a good estimator of the observed errors and also agree with covariance estimates of the location uncertainties obtained from the least squares solution technique sources over the network are located with an uncertainty of 6 12 m rms in the horizontal and 20 30 m rms in the vertical this corresponds well with the uncertainties of the arrival time measurements determined from the distribution of chi square values to be 40 50 ns rms outside the network the location uncertainties increase with distance the geometric model shows that the range and altitude errors increase as the range squared r2 while the azimuthal error increases linearly with r for the 13 station 70 km diameter network deployed during steps the range and height errors of distant sources were comparable to each other while the azimuthal errors were much smaller the difference in the range and azimuth errors causes distant storms to be elongated radially in plan views of the observations the overall results are shown to agree well with hyperbolic formulations of time of arrival measurements e g proctor 1971 two appendices describe 1 the basic operation of the lma and the detailed manner in which its measurements are processed and 2 the effect of systematic errors on lightning observations the latter provides an alternative explanation for the systematic height errors found by boccippio et al 2001 in distant storm data from the lightning detection and ranging system at kennedy space center

polarimetric and electrical characteristics of a lightning ring in a supercell storm abstract on 30 may 2004 a supercell storm was sampled by a suite of instrumentation that had been deployed as part of the thunderstorm electrification and lightning experiment telex the instrumentation included the oklahoma lightning mapping array ok lma the national severe storms laboratory s band weather surveillance radar 1988 doppler wsr 88d polarimetric radar at norman oklahoma and two mobile c band shared mobile atmospheric research and teaching radars smart r combined datasets collected by these instruments provided a unique opportunity to investigate the possible relationships among the supercell s kinematic microphysical and electrical characteristics this study focuses on the evolution of a ring of lightning activity that formed near the main updraft at approximately 0012 utc matured near 0039 utc and collapsed near 0050 utc during this time period an f2 intensity tornado occurred near the lightning ring region lightning density contours computed over 1 km layers are over

backscattered coherent noise and seismic reflection imaging of the oceanic crust an example from the rift valley of the mid atlantic ridge at 23 n seismic reflection surveys shot over oceanic crust are contaminated by source generated coherent noise that limits the identification and interpretation of subbasement reflections coherent noise arrivals are generated around the seismic line by scattering from the upper surface of the basaltic layer and by backscattering of turning waves from the underside of the same interface both types of arrival may be enhanced by conventional common midpoint cmp stacking some turning arrivals also exhibit negative moveout in a cmp gather due to the increase of crustal velocity with depth in unsedimented areas coherent arrivals scattered from the top of the seafloor can be aligned by dip moveout with or without a subsequent zero offset migration prestack and suppressed but turning arrivals will usually remain turning arrivals generated by linear features in the seafloor such as fault scarps appear on a stack section as nearly linear coherent arrivals the apparent dip of which is related to the features angle to the seismic line after migration these turning wave arrivals can extend close to the topography that produced them and continue to late times leading to the possibility that such arrivals might be incorrectly interpreted as intrusions that crosscut but do not offset the moho careful identification of crustal reflections on a seismic profile along the mark area rift valley indicates that the snake pit hydrothermal field marks the northern limit of identifiable crustal reflections at least some of which appear to be related to magma injection the recent extensive volcanism of the northern mark area may well be a result of faulting caused by the stong northward growth of the southern spreading center permitting melt to rise more easily to shallow crustal levels

evolution of the total lightning structure in a leading line trailing stratiform mesoscale convective system over houston texas 1 line normal vertical cross sections of houston lightning detection and ranging ldar vhf radiation sources and radar reflectivity provide new insights into the three dimensional total lightning structure and evolution of a leading line trailing stratiform llts mesoscale convective system mcs over houston texas on 31 october 2005 previous research examining only the mature stage of an mcs showed that the overwhelming majority of vhf lightning sources occurred in the convective region with a lightning pathway extending rearward and descending in altitude into the stratiform region this descending pathway was most likely associated with small charged ice particles advected from the convective line unlike previous research the lightning pathway observed during the evolution of the mcs on 31 october 2005 initially extended rearward 40 km at a nearly constant height of 9 10 km in less than an hour the lightning pathway evolved into a sloped pathway similar to that found by previous research with a horizontal extent between 50 to 60 km and downward descent of 4 to 5 km during the lightning pathway evolution radar analysis showed an increase of reflectivity in the midlevels of the stratiform region consistent with increased depositional and aggregational growth above the melting layer broadening increased range of values of radar reflectivity above the melting layer was most likely an indication of a strengthening mesoscale updraft in the stratiform region this strengthening updraft may have contributed to an increase in the growth of the small charge carrying ice crystals giving them a greater fall speed in addition the mesoscale updraft may have promoted an environment conducive to local stratiform region charge generation in the mixed phase region just above the melting layer

a gps based three dimensional lightning mapping system initial observations in central new mexico a gps based system has been developed that accurately locates the sources of vhf radiation from lightning discharges in three spatial dimensions and time the observations are found to reflect the basic charge structure of electrified storms observations have also been obtained of a distinct type of energetic discharge referred to as positive bipolar breakdown recently identified as the source of trans ionospheric pulse pairs tipps observed by satellites from space the bipolar breakdown has been confirmed to occur between the main negative and upper positive charge regions of a storm and found to be the initial event of otherwise normal intracloud discharges the latter is contrary to previous findings that the breakdown appeared to be temporally isolated from other lightning in a storm peak vhf radiation from the energetic discharges is observed to be typically 30 db stronger than that from other lightning processes and to correspond to source power in excess of 100 kw over a 6 mhz bandwidth centered at 63 mhz

coordinated observations of sprites and in cloud lightning flash structure 1 the temporal and spatial development of sprite producing lightning flashes is examined with coordinated observations over an asymmetric mesoscale convective system mcs on 29 june 2011 near the oklahoma lightning mapping array lma sprites produced by a total of 26 lightning flashes were observed simultaneously on video from bennett colorado and hawley texas enabling a triangulation of sprites in comparison with temporal development of parent lightning in particular negatively charged stepped leaders in three dimensional space in general prompt sprites produced within 20 ms after the causative stroke are less horizontally displaced typically 30 km however both prompt and delayed sprites are usually centered within 30 km of the geometric center of relevant lma sources with affinity to negative stepped leaders during the prior 100 ms interval multiple sprites appearing as dancing jumping events associated with a single lightning flash could be produced either by distinct strokes of the flash by a single stroke through a series of current surges superposed on an intense continuing current or by both our observations imply that sprites elongated in one direction are sometimes linked to in cloud leader structure with the same elongation and sprites that were more symmetric were produced above the progression of multiple negative leaders this suggests that the large scale structure of sprites could be affected by the in cloud geometry of positive charge removal based on an expanded dataset of 39 sprite parent flashes by including more sprites recorded by one single camera over the same mcs the altitude above mean sea level msl of positively charged cloud region tapped by sprite producing strokes declined gradually from 10 km msl 35 c to around 6 km msl 10 c as the mcs evolved through the mature stage on average the positive charge removal by causative strokes of sprites observed on 29 june is centered at 3 6 km above the freezing level or at 7 9 km above ground level

very low frequency sferic bursts sprites and their association with lightning activity 1 recent observations have revealed the occurrence of burst like vlf activity lasting from tens of milliseconds up to a few seconds associated with the onset of many sprites these sferic bursts are thought to be due to the horizontal in cloud component of lightning activity since they have been observed to propagate only short distances a few hundred kilometers in the earth ionosphere waveguide and are generally not reported by lightning detection networks the possible involvement of in cloud lightning in sprite production has been previously suggested on the basis of the observed long delays and spatial displacement between causative cloud to ground cg discharges and sprite events in this work we investigate the association between sprites and sferic bursts using vlf data and a large set of sprite observations between 1995 and 2000 we compare the occurrence of sferic bursts in association with sprites for thousands of observations through many different dates and thunderstorms results indicate that sprite causative cgs are more commonly found in association with bursts of sferic activity than those cg discharges without sprites and that furthermore the distribution of sferic burst vlf energy is significantly higher for sprite associated events we further investigate the source of these bursts by comparing vlf data to lightning mapping array lma data of vhf pulses due to lightning such comparisons show that most sferic burst events can be explained as radiation from the horizonal in cloud components of cg lightning as detected by the lma

seismic scattering near the earth s surface the seismic coda is usually thought to be composed of waves scattered from the heterogeneities in the earth three classes of scattering mechanisms have been recognized repeated specular reflection of primary waves in a uniformly layered structure volume scattering of primary waves from localized volume heterogeneities and scattering of primary waves from irregularities in an otherwise generally layered structure the presence of the earth s surface complicates the description of all these scattering phenomena whenever the scattering obstacles are near or at the surface in this paper i review work which demonstrates the effects of scattering near the earth s surface emphasizing three general areas of investigation scattering of body waves from an irregular free surface scattering of body waves in irregular layers and propagation of surface waves across irregular topography or in irregular wave guides most of the effects of importance have been recognized in model studies of idealized geometries observational evidence in support of the model studies exists but is often inferred few controlled experiments to measure scattering have been performed

inferring compressible fluid dynamics from vent discharges during volcanic eruptions observations at numerous volcanoes reveal that eruptions are often accompanied by continual radio frequency crf emissions the source of this radiation however has remained elusive until now through experiments and the analysis of field data we show that crf originates from proximal discharges driven by the compressible fluid dynamics associated with individual volcanic explosions blasts produce flows that expand supersonically generating regions of weakened dielectric strength in close proximity to the vent as erupted materialcharged through fragmentation friction or other electrification processtransits through such a region pyroclasts remove charge from their surfaces in the form of small interparticle spark discharges or corona discharge discharge is maintained as long as overpressured conditions at the vent remain beyond describing the mechanism underlying crf we demonstrate that the magnitude of the overpressure at the vent as well as the structure of the supersonic jet can be inferred in real time by detecting and locating crf sources

improving seismic data quality in the gippsland basin australia deep seismic exploration in the gippsland basin is hindered by strong noise below the latrobe group coal sequence the reflectivity method provides a means for constructing detailed and accurate synthetic seismograms often from little more than a partial sonic log the noise contributions to the synthetics can then be interpreted using additional synthetics computed from variations upon the depth model and by exercising control over the wave types modeled this approach revealed three types of persistent noise in progressively deeper parts of the subcoal image 1 mode converted interbed multiples generated within the coal sequence 2 s wave reflections and long period multiples generated between the coal sequence and the miocene carbonates and 3 surface related multiples the noise interpretation can also be performed upon semblance analyses of the elastic synthetics to guide a velocity analysis away from a well this procedure helped to avoid picking the interformation long period multiples

crustal structure of the tuamotu plateau 15 s and implications for its origin we investigate the sedimentary and volcanic structure of the tuamotu plateau with multichannel seismic seismic refraction and gravity data along a ship track crossing the plateau near 15 s the volcanic basement of the central portion of the plateau is capped with a 1 to 2 km thick sediment layer composed of two compositional sequences the uppermost sequence with semblance derived p wave velocities of 1 6 1 9 km s and thicknesses of 0 2 0 9 km is composed of pelagic sediments the underlying sequence with velocities 2 5 3 5 km s and thicknesses of 0 5 1 5 km is composed of limestone and volcaniclastic sediments sonobuoy refraction data show the upper 1 km of the volcanic basement to have velocities 4 5 5 5 km s the gravity data indicate that the platform is compensated by an elastic lithosphere with effective thickness 5 5 km and that the volcanic thickness is 9 10 km thicker than normal oceanic crust with a volume of 2 0 2 6 l06 km3 the inferred eruption rates of 0 1 0 13 km3 yr are comparable to those of the hawaiian and marquesas island chains but substantially less than those of many oceanic plateaus radiometric and paleontological ages for the plateau and geomagnetic dates of the surrounding seafloor indicate that the northwestern portion of the plateau formed 600 km off the axis of the paleo pacific farallon spreading center on lithosphere of age 10 20 ma linear volcanic ridges and scarps bounding deep sediment filled basins however are similar to features of oceanic plateaus which formed at or near accretionary plate boundaries we suggest that these volcanic ridges and the gross plateau like morphology were formed by magma that was channelled along the lithospheric discontinuities left behind by a southward propagating rift segment of the nearby spreading center we attribute the formation of the northwestern portion of the tuamotu plateau to the passage of two hotspots during times 50 30 ma as they migrated beneath the pacific plate but remained west of the tuamotu propagator

crustal structure of northern juan de fuca plate from multichannel reflection data the northern juan de fuca plate forms the basement of a young 8 ma ocean basin off western canada two subparallel multichannel seismic reflection lines totaling 230 km in length and trending obliquely to the spreading direction were recorded across the basin and provide high quality images of crustal structure the processing sequence applied to the data includes a prestack inside trace mute of common midpoint cmp gathers to reduce noise levels on the deep data cmp stack poststack dip filtering f k migration and band pass filtering coherency filtered stacks are helpful in tracing weaker reflectors the stacked sections reveal a horizontally layered sedimentary sequence overlying a rugged and prominent basement reflector which dips slightly landward topography of the basement was formed at or near the spreading ridge there is no evidence for subsequent deformation a strong fairly continuous reflection from the base of the crust oceanic moho at 2 0 2 2 s two way travel time below the basement surface generally mimics the basement topography and shows the characteristic multicyclic waveform seen in other surveys estimates of reflection coefficients for the moho at several locations indicate that in general the crust mantle transition is unlikely to occur as a discrete first order interface although much of the crust appears acoustically transparent a number of discontinuous intracrustal reflectors are observed over 40 km at the eastern end of the northern line some of these are interpreted to arise from the oceanic layer 2 3 and layer 3a 3b boundaries the noncontinuous nature of these reflectors is an indication of the complexity of the processes producing intracrustal reflectivity and the lateral variability of crustal formation however the interpreted crustal thickness varies by only about 10 away from the distal ends of spreading segments indicating that while the process of crustal formation may be locally variable it produces a broadly uniform result

coherent noise in marine seismic data three mechanisms that might produce noise patterns on stacked sections are examined direct and trapped waves that propagate outward from the seismic source cable motion caused by the tugging action of the boat and tail buoy and scattered energy from irregularities in the water bottom and sub bottom different noise patterns can be observed on shot profiles and common midpoint cmp gathers these patterns can be diagnostic of the dominant mechanism in a set of data field data suggest that the dominant noise is from waves scattered within the shallow sub bottom this type of noise is enhanced by cmp stacking moreover it can be as strong as surface wave noise on stacked land seismic data as well moveout filtering is best for suppressing the noise while preserving signal since the scattered noise does not exhibit a linear moveout pattern on cmp sorted gathers moveout filtering must be applied either to traces within shot records and common receiver gathers or to stacked traces our data example demonstrates that although it is more costly moveout filtering of the unstacked data is particularly effective because it conditions the data for the critical data dependent processing steps of predictive deconvolution and velocity analysis modified journal abstract

structure of the earth oceanic crust and uppermost mantle the past four years have witnessed the introduction of a variety of new instruments and methods for the study of the seismic structure of the oceanic crust and lithosphere the application of these and existing tools has led to the discovery of a number of new phenomena and to a fuller understanding of the genesis and evolution of the oceanic ithosphere borehole seismic instrumentation has become more widely employed ocean bottom seismographs while generally decreasing in number have become significantly more reliable and useful and multichannel seismic systems have been employed in innovative experiments ranging from studies of fracture zones to the regular detection of magma chambers beneath rise axes the techniques available for the analysis of seismic data have become more sophisticated waveforms collected in seismic experiments can now be used directly in constructing and evaluating seismic velocity models and travel time data are regularly inverted directly for structure trial and error modeling has become increasingly unimportant marine seismologists are becoming increasingly involved in understanding the coupling between the ocean and the underlying oceanic lithosphere this has led to a more complete understanding of seafloor noise processes and the partitioning of energy between acoustic and elastic waves

radio interferometric observations of cloud to ground lightning phenomena in florida radio frequency observations of cloud to ground lightning in florida have been analyzed to document a number of features of the lightning the observations have been made using an interferometer system which determined the direction to the lightning radiation as a function of time during close lightning discharges observations are presented for about 50 radiating events during five multiple stroke normal polarity flashes to ground the results confirm and extend results of a similar study of new mexico lightning by rhodes et al 1994 dart leaders in cloud k events and attempted leaders are found to be the same phenomena namely a negative polarity streamer that propagates horizontally and or vertically to ground at estimated speeds of about 10 7 ms 1 down to 10 6 ms 1 the step or impulsive fast electric field change produced by some k events is found to be caused by positive breakdown back at the starting point of the negative streamer after the streamer has progressed over some or all of its distance this breakdown appears to initiate a forward stroke along the streamer channel which can renew the breakdown at the front end of the channel k breakdown which happens to occur during a continuing current discharge to ground produces an m event channel brightening when it connects with the conducting channel to ground the step fast field change of the m events is found to be produced at the time of connection inside the cloud no fast field change is detected when this breakdown reaches ground that would be associated with a return stroke m events can also be initiated by fast 10 7 ms 1 positive streamers which often propagate away from the leader source region within a few milliseconds of the arrival of a return stroke back in the source region these streamers often generate an even faster negative recoil event back along their extent which propagates down the channel to ground as the m event in all cases the current increase or channel brightening produced by k and m events is predicted to occur in a forward direction that is toward or down the channel to ground in the same direction as the initiating negative streamer positive breakdown is detected only immediately following return strokes or during some k streamers in both cases the electric stresses are expected to be very large suggesting that positive breakdown which produces a conducting channel is difficult to initiate results for one flash suggest that negative charge was left at low altitude by the initial stroke to ground this forced the subsequent leaders to develop a new path to ground first as series of attempted leaders and then as a dart stepped leader

using lightning observations as a volcanic eruption monitoring tool lightning commonly occurs in the eruption columns produced by explosive volcanic eruptions there are several different kinds of lightning detection instruments that could be employed to help monitor volcanoes each with their own advantages and disadvantages very low frequency vlf instruments have the ability to detect lightning at long ranges but tend to have low sensitivity due to network geometry and typically can provide only the time and 2 d location of a cloud to ground return stroke or similar high amplitude pulse produced by an intracloud discharge low frequency lf and medium frequency mf instruments typically have more sensitivity than a vlf network but can only be used for detection on a regional scale very high frequency vhf lightning mapping instruments also provide only regional coverage but detect all lightning within their range during the 2009 eruption of redoubt volcano alaska usa each of these types of instruments detected lightning from redoubt s ash plume the vhf system consistently detected lightning before the other two during each distinct explosive event and also detected more lightning than the others by one or two orders of magnitude lightning observations could be used to confirm and in some cases detect explosive volcanic activity the rapid response provided by lightning monitoring is a valuable tool for fast identification of potentially hazardous ash clouds

diffraction based velocity estimates from optimum offset seismic data a graphical method is characterized for estimating seismic velocity directly from diffraction patterns observed on common offset records the nature of the resulting estimate is examined by illustrating the connection between the graphical approach and a related method used by practitioners of ground penetrating radar while the latter provides only a crude stacking velocity the graphical technique yields the generalized rms velocity for stratified media associated interval velocities can be derived from two or more diffraction events having their sources within the plane of survey where there is a lack of geological evidence to suggest that scatterers reside in plane we propose a simple strategy for locating a scatterer from its expression on two or more independent records error in the resulting location is directly related to subsurface velocity heterogeneity finally since the diffraction based velocity estimates assume that source and receiver are coincident the error stemming from nonzero off

modeling sideswipe in 2d oceanic seismic surveys from sonar data application to the mariana arc in two dimensional 2d marine seismic reflection surveys out of plane rough seafloor bathymetry can cause multiple oceanbottom reflections that complicate the interpretation of shallow reflections although migration corrects for the in plane position of reflectors it cannot resolve the inherent ambiguity in their out of plane positions we show how swath bathymetry routinely collected in many such surveys can be used to model out of plane seafloor reflections and prevent their misinterpretation as subsurface geology we use both raw and gridded multi beam bathymetry data to build images that represent seafloor reflections in migrated seismic data comparison of these images to the seismic sections reveals whether suspicious features are out of plane water bottom reflections or subsurface reflections multi channel seismic surveys across the marianas intra oceanic arc system provide examples where rough seafloor topography produced reflections that were initially misinterpreted we use our seafloor reflection modeling srm approach to help distinguish a possible landslide from a volcanic cone to help distinguish real from apparent fault plane reflections bounding a sediment filled basin and to verify that a possible magma chamber reflection results from sub surface structure not seafloor sideswipe

application of waveform tomography to marine seismic reflection data from the queen charlotte basin of western canada to obtain a higher resolution quantitative p wave velocity model 2d waveform tomography was applied to seismic reflection data from the queen charlotte sedimentary basin off the west coast of canada the forward modeling and inversion were implemented in the frequency domain using the visco acoustic wave equation field data preconditioning consisted of f k filtering 2d amplitude scaling shot to shot amplitude balancing and time windowing the field data were inverted between 7 and 13 66 hz with attenuation introduced for frequencies 10 5 hz to improve the final velocity model two different approaches to sampling the frequencies were evaluated the limited maximum offset of the marine data 3770 m and the relatively high starting frequency 7 hz were the main challenges encountered during the inversion an inversion strategy that successively recovered shallow to deep structures was designed to mitigate these issues the inclusion of later arrivals in the waveform tomography resulted in a veloci

suppression of sea floor scattered energy using a dip moveout approach application to the mid ocean ridge environment multichannel seismic mcs images are often contaminated with in and out of plane scattering from the sea floor this problem is especially acute in the mid ocean ridge environment where sea floor roughness is pronounced energy shed from the unsedimented basaltic sea floor can obscure primary reflections such as moho and scattering off of elongated sea floor features like abyssal hills and fault scarps can produce linear events in the seismic data that could be misinterpreted as subsurface reflections moreover stacking at normal subsurface velocities may enhance these water borne events whose stacking velocity depends on azimuth and generally increases with time making them indistinguishable from subsurface arrivals to suppress scattered energy in deep water settings we propose a processing scheme that invokes the application of dip moveout dmo to deliberately increase the differential moveout between sea floor scattered and subsurface events thereby facilitating the removal of unwanted energy in the stacked section after application of dmo all sea floor scatterers stack at the water velocity while subsurface reflections like moho still stack at their original velocity the application of dmo in this manner is contrary to the intended use that reduces the differential moveout between dipping events and allows a single stacking velocity to be used unlike previous approaches to suppress scattered energy dip filtering is applied in the common midpoint cmp domain after dmo moveover our dmo based approach suppresses out of plane scattering and therefore is not limited to removal of in plane scattering as is the case with shot and receiver dip filtering techniques the success of our dmo based suppression scheme is limited to deep water a few kilometers of water depth for conventional offsets where the traveltime moveout of energy scattered from the sea floor has a hyperbolic moveout with a stacking velocity that depends on the cosine of the scatterer steering angle in a manner analogous to how the moveout of a dipping reflector depends on the dip angle the application of dmo based suppression to synthetics and mcs data collected along the southern east pacific rise demonstrates the effectiveness of our approach cleaner images of primary reflectors such as moho are produced even though present shot coverage along the east pacific rise is unduly sparse resulting in a limited effective spatial bandwidth

triggered lightning sky waves return stroke modeling and ionosphere effective height ground waves and sky waves measured 209 km and 250 km south of six triggered lightning flashes containing 30 strokes that occurred in the half hour before sunset on 27 august 2015 are presented and analyzed we use a cross correlation technique to find the ionospheric effective reflection height and compare our results to previous techniques that calculate effective height based on the time delay between ground wave and sky wave time domain features from the first flash to the last flash there is on average a 1 6 km increase in effective ionospheric height whereas no change in effective ionospheric height can be discerned along the individual strokes of a given flash we show to what extent the triggered lightning radiation source can be described using channel base current channel geometry and channel luminosity versus time and height and speculate that a well characterized source could allow a more accurate determination of the electromagnetic fields radiated toward the ionosphere than has been done to date we show that both channel geometry and the change in return stroke current amplitude and waveshape with channel height inferred from measured channel luminosity versus height and time determine the waveshape of the ground wave and presumably the upward propagating wave that results in the sky wave and that the waveshape of the ground wave does not appear to be related to the current versus time waveform measured at the channel base other than a roughly linear relationship between the two peak values

location and analysis of acoustic infrasound pulses in lightning acoustic vhf and electrostatic measurements throw new light onto the origin and production mechanism of the thunder infrasound signature 10 hz from lightning this signature composed of an initial compression followed by a rarefaction pulse has been the subject of several unconfirmed theories and models the observations of two intracloud flashes which each produced multiple infrasound pulses were analyzed for this work once the variation of the speed of sound with temperature is taken into account both the compression and rarefaction portions of the infrasound pulses are found to originate very near lightning channels mapped by the lightning mapping array we found that none of the currently proposed models can explain infrasound generation by lightning and thus propose an alternate theory the infrasound compression pulse is produced by electrostatic interaction of the charge deposited on the channel and in the streamer zone of the lightning channel

vhf lightning mapping observations of a triggered lightning flash 1 on 3 august 2010 an extensive lightning flash was triggered over langmuir laboratory in new mexico the upward positive leader propagated into the storm s midlevel negative charge region extending over a horizontal area of 13 13 km and 7 5 km altitude the storm had a normal polarity tripolar charge structure with upper positive charge over midlevel negative charge lightning mapping array lma observations were used to estimate positive leader velocities along various branches which were in the range of 1 3 104 m s 1 slower than in other studies the upward positive leader initiated at 3 4 km altitude but was mapped only above 4 0 km altitude after the onset of retrograde negative breakdown indicating a change in leader propagation and vhf emissions the observations suggest that both positive and negative breakdown produce vhf emissions that can be located by time of arrival systems and that not all vhf emissions occurring along positive leader channels are associated with retrograde negative breakdown

lightning discharges produced by wind turbines new observations with a 3 d lightning mapping array and high speed video are presented and discussed the first set of observations shows that under certain thunderstorm conditions wind turbine blades can produce electric discharges at regular intervals of 3 s in relation to its rotation over periods of time that range from a few minutes up to hours this periodic effect has not been observed in static towers indicating that the effect of rotation is playing a critical role the repeated discharges can occur tens of kilometers away from electrically active thunderstorm areas and may or may not precede a fully developed upward lightning discharge from the turbine similar to rockets used for triggering lightning the fast movement of the blade tip plays an important role on the initiation of the discharge the movement of the rotor blades allows the tip to runaway from the generated corona charge the second observation is an uncommon upward downward flash triggered by a wind turbine in that flash a negative upward leader was initiated from a wind turbine without preceding lightning activity the flash produced a negative cloud to ground stroke several kilometers from the initiation point the third observation corresponds to a high speed video record showing simultaneous upward positive leaders from a group of wind turbines triggered by a preceding intracloud flash the fact that multiple leaders develop simultaneously indicates a poor shielding effect among them all these observations provide some special features on the initiation of lightning by nonstatic and complex tall structures

estimating tectonic history through basin simulation enhanced seismic inversion geoinfomatics for sedimentary basins summary a data assimilation approach is demonstrated whereby seismic inversion is both automated and enhanced using a comprehensive numerical sedimentary basin simulator to study the physics and chemistry of sedimentary basin processes in response to geothermal gradient in much greater detail than previously attempted the approach not only reduces costs by integrating the basin analysis and seismic inversion activities to understand the sedimentary basin evolution with respect to geodynamic parameters but the technique also has the potential for serving as a geoinfomatics platform for understanding various physical and chemical processes operating at different scales within a sedimentary basin tectonic history has a first order effect on the physical and chemical processes that govern the evolution of sedimentary basins we demonstrate how such tectonic parameters may be estimated by minimizing the difference between observed seismic reflection data and synthetic ones constructed from the output of a reaction transport mechanical rtm basin model we demonstrate the method by reconstructing the geothermal gradient as thermal history strongly affects the rate of rtm processes operating in a sedimentary basin variations in geothermal gradient history alter the present day fluid pressure effective stress porosity fracture statistics and hydrocarbon distribution all these properties in turn affect the mechanical wave velocity and sediment density profiles for a sedimentary basin the present day state of the sedimentary basin is imaged by reflection seismology data to a high degree of resolution but it does not give any indication of the processes that contributed to the evolution of the basin or causes for heterogeneities within the basin that are being imaged using texture and fluid properties predicted by our basin rtm simulator we generate synthetic seismograms linear correlation using power spectra as an error measure and an efficient quadratic optimization technique are found to be most effective in determining the optimal value of the tectonic parameters preliminary 1 d studies indicate that one can determine the geothermal gradient even in the presence of observation and numerical uncertainties the algorithm succeeds even when the synthetic data has detailed information only in a limited depth interval and has a different dominant frequency in the synthetic and observed seismograms the methodology presented here even works when the basin input data contains only 75 per cent of the stratigraphic layering information compared with the actual basin in a limited depth interval

investigating the crustal structure of a strike slip step over zone along the great glen fault strike slip step overs and bends are regions of anomalous deformation that may yield clues to the mechanical behavior of the earth s crust experimental reprocessing of a marine deep seismic reflection profile cutting across an 35 km wide right stepping step over developed on the great glen fault system north of the inner moray firth basin east of northwest highlands scotland reveals a restricted zone of prominent reflections and diffractions beginning at 7 8 km depth continuing as deep as the interpreted moho discontinuity at 26 27 km geological interpretation of this zone suggests a concentration of possible diffractors marking sharp structural disruption underlain by a 12 km thick layer of subhorizontal and moderately dipping reflectors that dominates the lower crust in the step over region the known kinematic history of the great glen fault system together with the observed direction of the step over implies that a zone of contraction would have formed within the step over during early caledonian sinistral strike slip the seismic reflection structure can be interpreted as developing by deformation associated with contraction and possible block rotation between the two fault segments such that the diffractive zone represents steep structure in a near vertical zone of strike slip which passes deeper into a layer of low angle dipping thrusts or shear zones the results of this study are consistent with a concept of mechanical detachment in the middle crust as documented for areas of contraction along active strike slip faults

deep crustal reflection profiling offshore southern central california deep crustal reflection profiling offshore southern central california shows that the offshore santa maria basin and adjacent shelf and slope are underlain by oceanic crust which underthrusts the margin on common midpoint cmp sections the top of the oceanic crust appears as a strong coherent reflection occurring at 6 s two way time twt the reflection can be traced continuously more than 50 km from the deep ocean basin eastward beneath the continental shelf depth conversion places the top of oceanic crust at 6 16 km depth with a dip of 8 toward the coast beneath the santa lucia high the crustal reflection breaks up into several east dipping segments above the oceanic crust an accretionary wedge increases in thickness from 3 km at the base of the slope to over 12 km beneath the santa lucia high the neogene sedimentary section above the accretionary prism exhibits relatively little deformation implying that most of the accretion occurred during pre neogene convergence between the north american plate and oceanic plates located to the west the offshore santa maria basin exhibits at least two periods of neogene deformation an early extensional phase accompanied by strike slip faulting occurred in the lower to middle miocene followed by compression and basin inversion in the upper miocene lower pliocene the development of structures in the basin began in the northwest and is progressively younger to the southeast faults identified in the offshore sedimentary column offset acoustic basement but are not imaged in the franciscan basement material below 2 3 s twt and do not extend to or offset the deep reflections we suggest that the oceanic crust served as a detachment surface above which the shallow deformation occurred neogene sediments in the offshore basins show only 1 3 km of shortening this implies that shortening due to neogene oblique plate motion between the pacific and north american plates extends east of the offshore santa maria basin and is distributed across the entire transform margin

seismic reflection results from an ice island over the arctic continental shelf abstract in 1982 an arctic ice island 3 km by 7 km and 41 m thick broke away from the ward hunt ice shelf on ellesmere island and began drifting southwest with the ocean currents this island provided a stable platform in the polar pack ice for the seismic reflection exploration of the arctic continental shelf north of axel heiberg island a seismic reflection array consisting of a 107 station 3 53 km main arm and a twelve station 2 4 km cross arm was constructed on the island a set of 6 s common midpoint cmp data was recorded from the thirteen shotpoints for each kilometre the island drifted each charge 1 kg of 60 geogel was detonated 110 m beneath the ice surface over july and august 1985 a total of 87 sets of shots were recorded the raw record sections were dominated by very strong low velocity waves and water layer reverberations up to fourteen distinct water bottom multiples are seen in both the raw shot gathers and the cmp stacked sections median f k and optimum array filters were used along with cmp stacking deconvolution and common shot gather stacking to reduce the water bound noise these processes were tested on both simulation data and the real data a p wave travelling through the ice layer dominated most of the first arrivals first break refraction analysis where possible revealed 600 800 m of locally varying shallow sedimentary rock 4 5 km s 1 overlying a higher velocity layer 5 5 6 km s 1 the cmp sections contain numerous short discontinuous reflections indicating a lack of simple structure in the high velocity rock the larger 107 fold of the common shot gather stack increased the signal to noise ratio and revealed an extensive roughly horizontal reflection at a two way time of 1 6 s this corresponds to a depth of about 4 2 km and is interpreted as a reflection from the top of the precambrian basement

on polarimetric radar signatures of deep convection for model evaluation columns of specific differential phase observed during mc3e abstractthe representation of deep convection in general circulation models is in part informed by cloud resolving models crms that function at higher spatial and temporal resolution however recent studies have shown that crms often fail at capturing the details of deep convection updrafts with the goal of providing constraint on crm simulation of deep convection updrafts ground based remote sensing observations are analyzed and statistically correlated for four deep convection events observed during the midlatitude continental convective clouds experiment mc3e since positive values of specific differential phase observed above the melting level are associated with deep convection updraft cells so called columns are analyzed using two scanning polarimetric radars in oklahoma the national weather service vance wsr 88d kvnx and the department of energy c band scanning atmospheric radiation measurement arm precipitation radar c sapr kvnx and c sapr volumes and columns are then statistically

on suppression of sea floor scattered energy using a dip moveout approach application to the mid ocean ridge environment by g m kent i i kim a j harding r s detrick and j a orcutt may june 1996 geophysics 61 821 834 in their paper kent et al 1996 present an excellent case history of the use of dip moveout dmo and velocity filtering in the common midpoint cmp domain for the suppression of out of plane arrivals scattered from a deep sea floor however they imply that as a result of a small offset approximation the use of dmo in this way is limited to surveys recorded in water depths of at least a few kilometers with conventional streamer offsets this is incorrect i argue here that the application of dmo will reduce to water velocity the stacking velocity of arrivals scattered from the upper surface of the seafloor without any restriction on water depth furthermore i argue that this use of dmo is simply an example of the equivalence between 2 d and 3 d dmo for marine surveys where all source receiver azimuths are equal and that no small offset approximation is required i first present a counter example to the claim of kent et al 1996 that seafloor scattering cannot be suppressed using dmo in shallo

lightning leader stepping k changes and other observations near an intracloud flash 1 an intracloud lightning flash in central new mexico began with the initiation of a negative stepped leader at an altitude of 8 2 km above sea level as this leader propagated eastward and upward at 9 1 km above sea level it passed about 200 m to the north of a balloon borne electric field change instrument esonde after the first leader stopped a second negative stepped leader began near the point of origin of the first leader but it propagated away from the esonde from the changes in the electric vectors and the locations of impulsive radio frequency sources detected by a lightning mapping array lma we conclude the following 1 the first negative stepped leader was not preceded by any significant charge rearrangement due to positive leaders 2 each step of the first negative leader had both a forward going wave and a step recoil wave that propagated simultaneously backwards away from the leader tip along the existing channel the presence of a step recoil wave during each step leads to an explanation for the existence of stepping 3 after the first nearby leader stopped step recoil waves from the second distant leader may have found their way onto the channel formed by the first leader 4 after the second leader stopped waves carrying negative charge propagated along the channel of the first leader producing strong k changes in the electric field at the esonde and providing a good record of the wavefront shapes

seismic evidence for a magma chamber beneath the slow spreading mid atlantic ridge seismic reflections from magma chambers have been observed along the fast spreading east pacific rise1 2 and the intermediate spreading valu fa ridge3 4 sub axial reflections also exist beneath the intermediate spreading juan de fuca ridge5 but no magma chambers have been identified beneath the slow spreading mid atlantic ridge suggesting that here magma chambers lie unusually deep or are transient features6 11 seismic reflection profiles acquired in 1989 over the snake pit hydrothermal area in the rift valley of the mid atlantic ridge 25 km south of the kane fracture zone showed no evidence of magmatic activity12 although geochemical analyses of hydrothermal vent fluids suggest the existence of magma at depths as shallow as 1a 2 km13 14 by suppressing in these data high amplitude coherent noise generated at the sea floor i have obtained images in an otherwise non reflective crust of seismic reflections beneath and just south of the snake pit hydrothermal area these reflections define a small 4 km wide dome whose apex is 1 200 m beneath the sea floor as bright reflections from the upper flanks of this dome occur in the depth range suggested by the vent fluid geochemistry i interpret the dome to be the seismic expression of a small magma chamber

distribution of magma beneath the east pacific rise between the clipperton transform and the 9 17 n deval from forward modeling of common depth point data we have reprocessed seven cross axis common depth point cdp profiles between the clipperton transform and the 9 17 n deval deviation in axial linearity on the east pacific rise epr to understand the relationship between axial magma chamber amc width and seafloor morphology forward modeling of cross axis cdp profiles suggests a segmented amc in which significant variations in width occur across minor rise axis discontinuities e g devals the modeled rise segment widths bounded by the 9 53 n 9 35 n devals the 9 35 n 9 17 n devals and south of the 9 17 n deval were 0 7 km 1 0 1 2 km and 4 15 km respectively transition in amc width across these discontinuities is unclear due to the sparseness of cross axis line spacing however a simple association of devals with decreased magma supply is doubtful the minimum 250 m and maximum 4150 m amc widths are found near the 9 35 n and 9 17 n devals respectively the reprocessing of cdp profiles included repicking stacking velocities to ensure a proper stack of the amc reflector and its associated diffractions imaging postcritical reflections from the base of layer 2a finite difference time migration ray theoretical depth migration and travel time modeling of amc diffraction patterns constraints on amc width were derived from forward modeling techniques based on analytic raytracing velocity models were constructed from seabeam bathymetry and modified expanding spread profile esp velocity depth functions esp velocity models were altered to compensate for off axis thickening of layer 2a as imaged in the cdp reflection data continuous two dimensional velocity models constructed from modified esp velocity depth functions and seabeam bathymetry should account for ray bending at the seafloor basalt interface and any lateral velocity gradients induced by a thickening layer 2a stacked data were time migrated using a finite difference algorithm and extrapolated to depth using ray theoretical depth migration reflector positions were input into our forward modeling scheme to produce a zero offset travel time response of our migrated solution the travel time response was then overlain on the stacked section to ensure an adequate match especially to diffractions generated at the amc edge forward modeling of amc diffraction patterns reveals that original amc width estimates were too large the under migration of the amc reflector resulted from the conversion of stacking to interval velocities without accounting for topographic effects on individual cmp gathers thus resulting in improperly collapsed diffraction hyperbolae ship wandering relative to the amc edge can account for variations in amc reflector amplitude and dropout on the along axis cdp line the continuity of the amc appears unbroken across several ridge axis discontinuities between the clipperton transform and the 9 17 n deval which suggests an amc whose along axis dimension exceeds 75 km reflectivity modeling of cmp gathers suggests that the available data are consistent with a magma chamber comprising only a thin layer of melt overlying a zone of partially solidified crystal mush such a thin layer of melt might inhibit along axis mixing of magmas and thereby account for variations in magma composition along the rise crest this melt lens model for the amc would also produce strong diffraction patterns as imaged in the cdp data

statistical analysis of storm electrical discharges reconstituted from a lightning mapping system a lightning location system and an acoustic array in the framework of the european hydrological cycle in the mediterranean experiment project a field campaign devoted to the study of electrical activity during storms took place in the south of france in 2012 an acoustic station composed of four microphones and four microbarometers was deployed within the coverage of a lightning mapping array network on the 26 october 2012 a thunderstorm passed just over the acoustic station fifty six natural thunder events due to cloud to ground and intracloud flashes were recorded this paper studies the acoustic reconstruction in the low frequency range from 1 to 40 hz of the recorded flashes and their comparison with detections from electromagnetic networks concurrent detections from the european cooperation for lightning detection lightning location system were also used some case studies show clearly that acoustic signal from thunder comes from the return stroke but also from the horizontal discharges which occur inside the clouds the huge amount of observation data leads to a statistical analysis of lightning discharges acoustically recorded especially the distributions of altitudes of reconstructed acoustic detections are explored in detail the impact of the distance to the source on these distributions is established the capacity of the acoustic method to describe precisely the lower part of nearby cloud to ground discharges where the lightning mapping array network is not effective is also highlighted

no evidence from multichannel reflection data for a crustal magma chamber in the mark area on the mid atlantic ridge the role of crustal magma chambers in the construction of oceanic crust along the slowly spreading mid atlantic ridge mar is still highly disputed1 some investigators have argued for small short lived crustal magma bodies2 whereas others have postulated the presence of permanent reservoirs centred between ridge offsets which expand and contract in response to a fluctuating magma supply3 thermal modelling4 5 detailed seismic refraction experiments at several different locations along the mar6 9 and micro earthquake10 11 and teleseismic source mechanism studies12 preclude the existence of large steady state magma chambers under the entire mar rift valley however smaller localized crustal magma bodies could be present at least intermittently here we use multichannel seismic reflection profiles to look for evidence of a crustal magma chamber along the mar south of the kane fracture zone in one of the most magmatically robust and hydro thermally active areas presently known along the mar although some subbasement reflectors are imaged we do not see a shallow large amplitude intracrustal reflector that might be associated with a crustal magma body if a crustal magma chamber was associated with the most recent volcanic episode along this part of the mar our results suggest that it was extremely short lived

effects of the shallow subsurface on upper crustal seismic reflection images abstract seismic imaging of the upper crust is strongly affected by the interactions of the seismic wavefield with the shallow subsurface in order to better understand these effects we have evaluated the seismic responses of a suite of canonical models of the upper crystalline crust and the near surface region our modelling is restricted to two dimensions but otherwise includes the full seismic wavefield notably the effects of attenuation and topographic variations along the free surface we find that s wave scattering is important in the upper crust and contributes significantly to the vertical component of the seismic reflection response the backscattered wavefield undergoes mode conversions when it interacts with the free surface even moderate topographic variations or velocity variations in the near surface region enhance these mode conversions and cause additional scattering much of the earth s surface is covered by thin layers of unconsolidated material or weathered bedrock with high attenuation and high velocity contrasts at the layer boundaries scattered and mode converted seismic energy gets trapped in these layers and thus interacts repeatedly with the free surface and its topography in analogy to large scale seismic resonance effects of sedimentary valley fills the level and duration of source generated noise depends heavily on the degree of attenuation in the shallow layers low attenuation causes high noise levels and vice versa in contrast the level of source generated noise is less sensitive to near surface layer thicknesses and velocity contrasts

vhf radio pictures of lightning flashes to ground we present information obtained from vhf radio pictures of 47 lightning flashes that struck ground 1430 m above mean sea level msl to the north of johannesburg over a period of 16 years radio pictures were obtained using a hyperbolic method i e by taking differences between times at which radio noise from lightning arrived at five widely spaced stations these data were supplemented by recordings of electric field change we found that stepped leaders and intracloud streamers emitted pulses and progressed at speeds that averaged 1 6 105 ms 1 stepped leaders ranged in length from 3 to 13 km bil breakdown intermediate leader waveforms of electric field change were caused by stepped leaders whose branched channels followed complicated paths the electric field changes they recorded in an effective bandwidth of 3 5 khz could be reproduced faithfully by calculations based on an assumption that the radio sources became charged at the expense of a region near the origin of each leader some return strokes radiated trains of noise called q noise whose sources extended at speeds near 108 ms 1 sources of this q noise retraced leader channels before extending them at these high speeds interstroke processes radiated q noise whose sources extended at speeds that averaged 8 7 107 ms 1 most q sources 98 were directed vertically but they pervaded regions that retrogressed at speeds that averaged 2 2 104 ms 1 in directions away from the starting points of the flashes this retrogression was directed horizontally but the vertical q streamers caused j changes to have positive or negative slopes according to the relative positions of q sources and the reversal cone sixty percent of our sample of ground flashes were endowed with portions that were cloud flashes or were themselves minor components of cloud flashes a more detailed summary appears at the end of the paper

delineation of a complexly dipping temperate glacier bed using short pulse radar arrays we have defined the complex bed topography for a section of a small temperate glacier using 50 mhz monostatic short pulse radar data and a synthetic aperture array processing method the data were collected on a 100 m by 340 m array grid in the upper stem of gulkana glacier central alaska u s a the array processing was based on a modified three dimensional 3 d kirchhoff migration integral and implemented with a synthetic aperture approach that uses sequences of overlapping sub arrays to generate depth images in vertical planes typical sub array beam patterns are generally 5 at the 6 db level giving a flashlight like searching capability without distorting the wavelet shape the bed topography was constructed using normal reflections picked from 3 d array depth images in some instances reflections were imaged outside the data coverage area the bed surface dips steeply both parallel and transverse to the direction of ice flow the maximum observed depth is roughly 140 m the 3 d method resolved bed dips up to 45 in regions of steepest dip it improved depth accuracy by 36 compared with raw data and by 15 compared with standard two dimensional 2 d migration over 12 db of signal to noise improvement and improved spatial resolution was achieved compared to raw data and 2 d migration false bottom layering seen in the raw data and in 2 d migrations is not observed in the 3 d array results furthermore loss of bottom reflections is shown by the 3 d migration to be attributable to the dip and curvature of the reflector and not scattering losses or signal clutter from englacial inclusions

lightning development associated with two negative gigantic jets 1 we report observations of two negative polarity gigantic jets sufficiently near very high frequency vhf lightning mapping networks that the associated lightning characteristics and charge transfer could be investigated in both cases the gigantic jet producing flash began as ordinary intracloud lightning with upper level channels attempting to exit the cloud and then produced the upward gigantic jet neither flash had developed channels to ground confirming that the major charge transfer during gigantic jets occurred between the cloud and ionosphere the leader progression of one event was detected at altitudes above 20 km demonstrating the possibility of detecting and tracking the propagation of negative jets above the cloud with vhf techniques citation lu g et al 2011 lightning development associated with two negative gigantic jets geophys res lett 38 l12801

photographic and lightning mapping observations of a blue starter over a new mexico thunderstorm 1 on 4 august 2010 a small blue starter was observed over an active thunderstorm in west central new mexico the storm was of normal polarity with upper positive charge over midlevel negative charge the event was visually observed and photographed and mapped by the lightning mapping array lma at langmuir laboratory the blue starter occurred during a seven stroke negative cloud to ground cg flash that was detected by the national lightning detection network nldn and data from the lma show that it initiated between upper positive charge and inferred negative screening charge at the cloud top upward positive streamers of the blue starter emerged from the cloud top at 15 2 km altitude and reached a terminal altitude of 17 km the observation confirms that blue starters can be initiated by the electric field changes associated with cg flashes which enhance the electric field between upper positive charge and negative screening charge it also confirms that the upward leaders and streamers of blue starters in normal polarity storms are of positive polarity

compensation of marine seismic data for the effects of highly variable water depth using ray trace modeling a case history variable water depth can cause severe degradation of marine seismic data this paper presents a technique for correcting the effects of water depth variation and is a case history of applying the technique to a line of data from the philippines offshore the line crosses a deep submarine valley it will be shown that when the water depth changes rapidly relative to the cable length the timing variations introduced will not be static they are dynamic not static because they differ for different event times of a single trace to compensate for these dynamic timing variations a two stage technique was used a ray trace modeling program calculated the traveltimes to several depths both for where the valley is present and where it is absent a second program used the model results to shift the samples on all seismic traces to the time they would have if the valley were not present the most difficult part of this project was finding a good model the model is composed of two parts the depth of the sea f

removal of scattered guided waves from seismic data near surface scattered waves form a major source of coherent noise in seismic land data most current methods for removing these waves do not attenuate them adequately if they come from other than the inline direction we present a wave theory based method for removing scattered guided waves by a prediction and removal algorithm we assume that the near surface consists of a laterally varying medium in which heterogeneities are embedded that act as scatterers we first estimate the dispersive and laterally varying phase slowness field by applying a phase based tomography algorithm on the direct groundroll wave subsequently the near surface heterogeneities are imaged using a least squares criterium finally the scattered guided waves are modeled and subtracted adaptively from the seismic data we have applied this method to seismic land data and found that near surface scattering effects are attenuated

a method to analyze and verify deep crustal reflections offshore costa rica a multichannel seismic reflection profile across the oceanic crust seaward of the middle america trench off the nicoya peninsula costa rica shows discontinuous low frequency events at 6 5 to 7 0 s these events might first be interpreted as reflections from the moho however careful analysis of the seismic data suggests that these events represent three dimensional 3 d scattered energy from the rough basaltic basement velocity analysis indicates that root mean square rms velocities for these deep reflection events are too low to emanate from the moho also the ghost separation caused by the streamer depth decreases for increasing record time suggesting that incident angle for these reflections increases with time furthermore these events are approximately 13 db stronger than would be expected for a moho reflection common depth point cdp stacking and velocity filtering were used to attenuate the scattered noise and sideswipe from the basalt the results show a 21 db total reduction of s

seismic imaging of upper crustal basement faults in the skagerrak sea abstract the continental upper crystalline crust appears almost non reflective on many deep seismic reflection profiling sections typically only the major faults and lithological boundaries are imaged whereas smaller scale faults are usually not identified a deep seismic survey 0 16 s twt covering the skagerrak sea was undertaken in 1987 although the northeastern part of the skagerrak has only thin or no sediment cover the data in the depth range 0 6 s twt were reprocessed to commercial exploration standards close inspection of these high quality sections provides evidence of abundant moderately steep dipping 20 50 faults that can be traced to depths of 10 13 km fault geometry which can be inferred at profile intersections is in accordance with the general tectonic fabric observed on land and beneath the skagerrak sea these areas were deformed during the proterozoic sveconorwegian orogeny and during the formation of the permian oslo rift due to post permian erosion of the skagerrak sea proper the relative age and movements of the basement faults could not be determined this study shows that under favorable conditions faults in the upper crystalline crust are mappable by seismic means such measurements have the potential for resolving variations in block geometry with depth and also recent seismotectonic movements

charge structure in volcanic plumes a comparison of plume properties predicted by an integral plume model to observations of volcanic lightning during the 2010 eruption of eyjafjallajokull iceland observations of volcanic lightning made using a lightning mapping array during the 2010 eruption of eyjafjallajokull allow the trajectory and growth of the volcanic plume to be determined the lightning observations are compared with predictions of an integral model of volcanic plumes that includes descriptions of the interaction with wind and the effects of moisture we show that the trajectory predicted by the integral model closely matches the observational data and the model well describes the growth of the plume downwind of the vent analysis of the lightning signals reveals information on the dominant charge structure within the volcanic plume during the eyjafjallajokull eruption both monopole and dipole charge structures were observed in the plume by using the integral plume model we propose the varying charge structure is connected to the availability of condensed water and low temperatures at high altitudes in the plume suggesting ice formation may have contributed to the generation of a dipole charge structure via thunderstorm style ice based charging mechanisms though overall this charging mechanism is believed to have had only a weak influence on the production of lightning

lightning location relative to storm structure in a leading line trailing stratiform mesoscale convective system 1 horizontal and line normal vertical cross sections and composite images of dallas fort worth lightning detection and ranging ldar ii vhf radiation sources and radar reflectivity over a 30 min period provide a unique perspective on lightning pathways within a leading line trailing stratiform llts mesoscale convective system mcs on 16 june 2002 the overwhelming majority of vhf lightning sources occurred within the leading convective line in a bimodal pattern in the vertical assuming that vhf source density maxima were most likely associated with positive charge then the ldar ii observations suggest that the gross charge structure of the convective region of the mcs was characterized by a tripole with net positive charge centered at 4 5 km agl 3 c and 9 5 km agl 35 c and net negative charge centered roughly in the relative minimum of the vhf source density maximum at 7 km agl 17 c a persistent lightning pathway and inferred positive charge zone sloped rearward by 40 50 km and downward by 4 5 km from the upper vhf source maximum in the convective line through the transition zone and into the radar bright band of the stratiform region in the stratiform region vhf lightning sources and inferred positive charge were concentrated in three layers centered at 4 5 6 and 9 km agl 2 c 11 c and 31 c respectively consistent with past electric field studies of symmetric llts mcss positive cloud to ground lightning flashes in the stratiform region were initiated in the convective line and followed the slanting pathway from the top of convective cores to the stratiform precipitation where they were horizontally extensive layered and highly branched the sloping lightning pathway was identical to hypothetical trajectories taken by snow particles these observations provide further support for the advection of charge on snow along the sloping pathway and the in situ generation of charge in the horizontal lightning layers as primary contributors to electrification and positive lightning production rearward of the convective line

total lightning signatures of thunderstorm intensity over north texas part i supercells abstract it is shown that total lightning mapping along with radar and national lightning detection network nldn cloud to ground lightning data can be used to diagnose the severity of a thunderstorm analysis of supercells some of which were tornadic on 13 october 2001 over dallas fort worth texas shows that lightning detection and ranging ldar ii lightning source heights quartile median and 95th percentile heights increased as the storms intensified most of the total cloud to ground and intracloud lightning occurred where reflectivity cores extended upward within regions of strong reflectivity gradient rather than in reflectivity cores a total lightning hole was associated with an intense nontornadic supercell on 6 april 2003 none of the supercells on 13 october 2001 exhibited a lightning hole during tornadogenesis the radar and ldar ii data indicated updraft weakening the height of the 30 dbz radar top began to descend approximately 10 min 2 volume scans before tornado touchdow

evolution of lightning activity and storm charge relative to dual doppler analysis of a high precipitation supercell storm abstracta high precipitation tornadic supercell storm was observed on 29 30 may 2004 during the thunderstorm electrification and lightning experiment observational systems included the oklahoma lightning mapping array mobile balloon borne soundings and two mobile c band radars the spatial distribution and evolution of lightning are related to storm kinematics and microphysics specifically through regions of microphysical charging and the location and geometry of those charge regions lightning flashes near the core of this storm were extraordinarily frequent but tended to be of shorter duration and smaller horizontal extent than typical flashes elsewhere this is hypothesized to be due to the charge being in many small pockets with opposite polarities of charge close together in adjoining pockets thus each polarity of lightning leader could propagate only a relatively short distance before reaching regions of unfavorable electric potential in the anvil however lightning extended tens of kilome

crustal structure of the midcontinent rift system in eastern lake superior from controlled amplitude analysis of glimpce deep reflection seismic data the reprocessing of line f of the glimpce deep marine reflection seismic survey according to controlled amplitude principles provides new insights on the crustal structure of the midcontinent rift

distribution of magma beneath the east pacific rise near the 9 03 n overlapping spreading center from forward modeling of common depth point data we have reprocessed six cross axis and three along axis common depth point cdp profiles near the 9 03 n overlapping spreading center osc to understand the relationship between axial magma chamber amc width and seafloor morphology travel time modeling of the amc reflector reveals an asymmetric distribution of melt across the 9 03 n osc the variation of modeled amc width beneath either osc limb is minimal but the width increases nearly fourfold across the offset attaining an estimated maximum width of 4 15 km near the 9 17 n ridge axis discontinuity additionally melt distribution underlying the eastern rise limb is not symmetric with respect to the rise axis neovolcanic zone but is displaced toward the western rise flank depth migration based on a continuum velocity model consistent with postcritical reflections from the base of layer 2a places the skewed amc reflector beneath a nearly constant thickness sheeted dike section which dips 10 away from the rise axis to confirm amc continuity beneath the western rise flank we use the maslov synthetic seismogram method to show that amplitude enhancement of the amc reflector is consistent with a continuous melt body underlying a thickening extrusive layer analysis of along strike cdp profiles indicates an amc which is neither overlapping nor discontinuous when projected onto the along strike plane identifying intracrustal events on along axis cdp lines however requires extreme caution we have modeled out of plane scattering using a kirchhoff formulation and we show that a coherent event identified beneath the overlap basin results from diffraction off the amc which lies nearly 3 km to the west of the profile we attribute the asymmetric pattern of melt to a decoupling of melt supply from preexisting weaknesses in the brittle upper crust in this model melt ascends upward buoyancy forces until deflected by the impermeable sheeted dike complex melt then migrates updip beneath the base of the sheeted dikes toward the neovplcanic zone where fissuring produces a temporary conduit for emplacement discrete jumps in modeled amc width toward the overlap basin represent a further displacement defocusing of melt supply western amc edge relative to the neovolcanic zone eastern amc edge the asymmetric pattern of melt therefore represents a gradual en echelon accommodation of melt supply across the 9 km of ridge axis offset at 9 03 n thus for asymmetric configurations amc width may not correlate solely with magmatic robustness but may signify the amount of decoupling which exists between melt supply and extrusive emplacement within the neovolcanic zone here we present a new model for osc development which invokes a significant component of cross axis melt migration moreover abrupt changes in amc width near ridge axis discontinuities e g 9 17 n deviation in axial linearity suggest that any along axis melt migration is confined to subsegments of the ridge and seem to preclude the segment length migration of melt proposed in some current models the transition of melt supply beneath the overlap basin might favor a continuous low velocity zone underlying this feature if true basin development may be related to the subsidence of a mechanically weak crustal lid the proposed model for osc development therefore views ridge axis discontinuities as the surficial response of misalignment and or defocusing of melt supply in the uppermost mantle