the response of the southwest western australian wave climate to indian ocean climate variability knowledge of regional wave climates is critical for coastal planning management and protection in order to develop a regional wave climate it is important to understand the atmospheric systems responsible for wave generation this study examines the variability of the southwest western australian swwa shelf and nearshore wind wave climate and its relationship to southern hemisphere climate variability represented by various atmospheric indices the southern oscillation index soi the southern annular mode sam the indian ocean dipole mode index dmi the indian ocean subtropical dipole iosd the latitudinal position of the subtropical high pressure ridge strp and the corresponding intensity of the subtropical ridge stri a 21 year wave hindcast 1994 2014 of the swwa continental shelf was created using the third generation wave model simulating waves nearshore swan to analyse the seasonal and inter annual wave climate variability and its relationship to the atmospheric regime strong relationships between wave heights and the strp and the stri a moderate correlation between the wave climate and the sam and no significant correlation between soi dmi and iosd and the wave climate were found strong spatial seasonal and inter annual variability as well as seasonal longer term trends in the mean wave climate were studied and linked to the latitudinal changes in the subtropical high pressure ridge and the southern ocean storm belt as the southern ocean storm belt and the subtropical high pressure ridge shifted southward northward wave heights on the swwa shelf region decreased increased the wave height anomalies appear to be driven by the same atmospheric conditions that influence rainfall variability in swwa

determining crustal structure beneath seismic stations overlying a low velocity sedimentary layer using receiver functions the receiver function rf technique has been widely applied to investigate crustal and mantle layered structures using p to s converted ps phases from velocity discontinuities however the presence of low velocity relative to that of the bedrock sediments can give rise to strong reverberations in the resulting rfs frequently masking the ps phases from crustal and mantle boundaries such reverberations are caused by p to s conversions and their multiples associated with the strong impedance contrast across the bottom of the low velocity sedimentary layer here we propose and test an approach to effectively remove the near surface reverberations and decipher the ps phases associated with the moho discontinuity autocorrelation is first applied on the observed rfs to determine the strength and two way traveltime of the reverberations which are then used to construct a resonance removal filter in the frequency domain to remove or significantly reduce the reverberations the filtered rfs are time corrected to eliminate the delay effects of the sedimentary layer and applied to estimate the subsediment crustal thickness and vp vsusing a h k stacking procedure the resulting subsediment crustal parameters thickness and vp vs are subsequently used to determine the thickness and vp vs of the sedimentary layer using a revised version of the h k stacking procedure testing using both synthetic and real data suggests that this computationally inexpensive technique is efficient in resolving subsediment crustal properties beneath stations sitting on a low velocity sedimentary layer and can also satisfactorily determine the thickness and vp vs of the sedimentary layer

complexity of the deep san andreas fault zone defined by cascading tremor seismic tremors can be used to distinguish plate boundaries analysis of tremors occurring deep beneath the san andreas fault may identify the boundary between the north american plate and the preserved remnant of a subducted slab

deep water measurements of container ship radiated noise signatures and directionality underwater radiated noise from merchant ships was measured opportunistically from multiple spatial aspects to estimate signature source levels and directionality transiting ships were tracked via the automatic identification system in a shipping lane while acoustic pressure was measured at the ships keel and beam aspects port and starboard beam aspects were 15 30 and 45 in compliance with ship noise measurements standards ansi asa s12 64 2009 and iso 17208 1 2016 additional recordings were made at a 10 starboard aspect source levels were derived with a spherical propagation surface affected or a modified lloyd s mirror model to account for interference from surface reflections surface corrected ship source depths were estimated from spectral differences between measurements at different beam aspects results were exemplified with a 4870 and a 10 036 twenty foot equivalent unit container ship at 40 56 and 87 of service speeds respectively for the larger ship opportunistic ansi i

long term acoustic monitoring at north sea well site 22 4b highlights first study using long term passive acoustic monitoring of methane seeps at well blowout site 22 4b seep acoustic temporal variations correlated with ocean tides major acoustic transient event recorded on 8 december 2011 with high temporal resolution abstract marine seeps produce underwater sounds as a result of bubble formation and fragmentation upon emission from the seabed the frequency content and sound levels of these emissions are related to bubble size distribution and emission flux providing important information on methane release from the seafloor long term passive acoustic monitoring was used to continuously record seep sounds over a 7 month period within the blowout crater at the abandoned well site 22 4b in the central north sea also recorded were water column fluid velocities and near seafloor water conductivity temperature and pressure acoustic signatures were primarily from 1 to 10 khz key features were relatively broad spectral peaks at about 1 0 1 5 2 2 3 1 3 6 and 5 1 khz temporal variations in spectral levels were apparently associated with tides the recordings also documented a series of major episodic events including a large and persistent increase 10 db in overall sound levels and spectral broadening on 8 december 2011 the acoustic temporal pattern of this event was consistent with other recorded large transient events in the literature and the major event was correlated with dramatic changes in other measurements including increased water column fluid velocities increased pressure and decreased salinity indicating real changes in emission flux observed seabed morphology changes reported elsewhere in this special issue also likely were related to this event these data demonstrate the dynamic nature of marine seepage systems show the value of monitoring systems and provide direct supporting evidence for a violent formation mechanism of many widespread seep associated seabed features like pockmarks

the monopulsed nature of sperm whale clicks traditionally sperm whale clicks have been described as multipulsed long duration nondirectional signals of moderate intensity and with a spectrum peaking below 10 khz such properties are counterindicative of a sonar function and quite different from the properties of dolphin sonar clicks here data are presented suggesting that the traditional view of sperm whale clicks is incomplete and derived from off axis recordings of a highly directional source a limited number of assumed on axis clicks were recorded and found to be essentially monopulsed clicks with durations of 100 micros with a composite directionality index of 27 db with source levels up to 236 db re 1 micropa rms and with centroid frequencies of 15 khz such clicks meet the requirements for long range biosonar purposes data were obtained with a large aperture gps synchronized array in july 2000 in the bleik canyon off vesteralen norway 69 degrees 28 n 15 degrees 40 e a total of 14 h of sound recordings was collected from five to ten independent simultaneously operating recording units the sound levels measured make sperm whale clicks by far the loudest of sounds recorded from any biological source on axis click properties support previous work proposing the nose of sperm whales to operate as a generator of sound

spectral wave characteristics over the head bay of bengal a modeling study information on spectral wave characteristics is an essential prerequisite for ocean engineering related activities and also to understand the complex wave environment at any given location to the best of our knowledge there are no comprehensive studies attempted so far to study the wave spectral characteristics over the head bay of bengal a low lying deltaic environment the present study is an attempt to describe the spectral characteristics of wave evolution across different locations over this deltaic region based on numerical simulations therefore it implements a multi scale nested modeling approach using two state of art wave models wam and swan and forced with era interim winds spanning the year of 2016 model computed integrated wave parameters are validated against wave rider buoy data as well as remotely sensed saral altika and merged altimeter data analysis of the monthly averaged one dimensional spectrum reveals a single peak during the southwest monsoon and existence of double peaks from november to january and occasionally up to march variance energy density undergoes inter seasonal variation and attains its maxima during the month of july transformation of swell wave energy as a function of depth is found to be mostly associated with physical processes such as wave bottom interaction and attenuation by opposing winds during the northeast ne monsoon fetch restriction for the evolution of wind seas from the ne modification in wind shear stress by opposing swells and bottom effects remarkably contribute to the reduction in wind sea energy at shallow water depths this study indicates that the influence of swells is higher along the eastern side of the basin as compared to the western side and marginally higher variance is also observed over the east except during february april the two dimensional wave spectra exhibit differential wave systems approaching from various directions attributed to a reflected swell system from the south southeast throughout the year southwest swells reversing wind seas following local winds and reflected wind seas from the land boundary

vertical mantle flow associated with a lithospheric drip beneath the great basin rapid surface uplift or subsidence and voluminous magmatic activity have often been ascribed to regional scale downwelling of lithospheric mantle however because lithospheric drips sinking plumes of cold and dense lithosphere are relatively small and transient features direct evidence of their existence has been difficult to obtain moreover the significant vertical mantle flow that should be associated with such structures has not been detected here we integrate seismic anisotropy data with tomographic images to identify and describe a lithospheric drip beneath the great basin region of the western united states the feature is characterized by a localized cylindrical core of cooler material with fast seismic velocities and mantle flow that rapidly shifts from horizontal to vertical our numerical experiments suggest that the drip can be generated by gravitational instability resulting from a density anomaly of as little as 1 and a localized temperature increase of 10 the drip tilts to the northeast opposite to the motion of the north american plate in the hotspot reference frame and thereby indicates northeast directed regional mantle flow seismic anisotropy data for the great basin region of the western united states coupled with tomographic images help delineate a northeast dipping lithospheric drip numerical experiments suggest that the drip could have formed owing to gravitational instability triggered by a density increase of about 1 and a temperature increase of about 10

along strike translation of a fossil slab abstract the isabella anomaly is a high seismic velocity anomaly beneath the southern central valley of california that has previously been interpreted to represent a lithospheric drip or delaminated sierra nevada root however recent work suggests that the anomaly is a remnant slab left over from cenozoic subduction attached to the pacific plate underneath the edge of the north american plate this hypothesis requires the slab to translate hundreds of kilometers along strike while remaining intact and attached to the pacific plate despite drag from the surrounding asthenosphere and overriding lithosphere we use 3 d finite element models to simulate this scenario and calculate the viscosity ratio between the slab and the surrounding asthenosphere required for the slab to translate undeformed the required viscosity ratio increases with increasing downdip extent of the slab and decreases with increasing slab dip for geometries approximating that of our proposed slab the required ratio ranges from 10 2 to 10 4 given the thermal and petrologic history of the slab mantle flow laws predict viscosity contrasts greater than or equal to these requirements as such we conclude that along strike translation of a remnant slab is feasible and serves as a possible explanation of the isabella anomaly the significance of this finding extends beyond our general understanding of subduction dynamics in that the presence of such a slab could have implications for the water budget of the san andreas fault and its role in aseismic slip

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

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

three dimensional tracking of cuvier s beaked whales echolocation sounds using nested hydrophone arrays cuvier s beaked whales ziphius cavirostris were tracked using two volumetric small aperture 1 m element spacing hydrophone arrays embedded into a large aperture 1 km element spacing seafloor hydrophone array of five nodes this array design can reduce the minimum number of nodes that are needed to record the arrival of a strongly directional echolocation sound from 5 to 2 while providing enough time differences of arrivals for a three dimensional localization without depending on any additional information such as multipath arrivals to illustrate the capabilities of this technique six encounters of up to three cuvier s beaked whales were tracked over a two month recording period within an area of 20 km 2 in the southern california bight encounter periods ranged from 11 min to 33 min cuvier s beaked whales were found to reduce the time interval between echolocation clicks while alternating between two inter click interval regimes during their descent towards the seafloor maximum peak to peak source levels of 179 and 224 db re 1 pa 1 m were estimated for buzz sounds and on axis echolocation clicks directivity index 30 db respectively source energy spectra of the on axis clicks show significant frequency components between 70 and 90 khz in addition to their typically noted fm upsweep at 40 60 khz

three dimensional seismic velocity structure of the northwestern united states 1 we present a high resolution three dimensional p wave tomography model for the northwestern united states major features of the model include clear well resolved images of the juan de fuca gorda slab to depths of at least 500 km reduced velocities beneath newberry volcano and north central oregon increased velocities beneath the idaho batholith and a deep slab like eastward dipping feature of increased velocities beneath nevada we find no evidence for a mantle plume in this region and demonstrate that suggested disruption of the juan de fuca slab beneath oregon in the vicinity of newberry volcano is an inversion artifact we interpret the primary features of this new model within the framework of post laramide tectonomagmatism and the continuing tectonic evolution of the cascadia subduction zone a model explaining the regional tectonomagmatic history consistent with the imaged seismic velocity structure is one driven by mantle flow responding to the evolving subduction system

crustal structure and composition of the southern foothills metamorphic belt sierra nevada california from seismic data the foothills metamorphic belt is an accreted terrane consisting of paleozoic and mesozoic metamorphic rocks that separates the great valley from the sierra nevada batholith in northern and central california until recently the only available geophysical data for this area were reconnaissance refraction surveys and gravity and magnetic data new insights into the structure of the deep crust are provided by the interpretation of a seismic reflection profile cc 2 acquired in 1984 by the u s geological survey at the southern end of the foothills metamorphic belt our interpretation is constrained by a new seismic velocity model derived from coincident microearthquake data earthquake hypocenters that occur at unusually great depths of 12 to 30 km make the data set particularly useful for obtaining deep crustal velocity information the velocity model shows velocities of 5 2 to 6 3 km s 1 for the upper 12 km of the crust and 6 7 to 6 8 km s 1 from 12 km to an estimated moho at 32 km the upper crustal velocities correspond to metamorphic rocks and serpentinites of the foothills metamorphic belt as well as to diorites and granodiorites of the sierra nevada batholith while the lower crustal velocities are interpreted to represent intermediate to mafic granulites the majority of the earthquake hypocenters as well as a 6 7 km s 1 layer in the velocity model corresponds in depth to thick zones of west dipping midcrustal reflections that may represent major shear zones formed during the late jurassic nevadan orogeny or synbatholithic ductile shear zones that accommodated crustal extension associated with batholith intrusion these reflections are truncated updip by an inferred subvertical contact that coincides with the western edge of the sierra nevada batholith and the southward trace of the bear mountains fault zone the updip truncation of midcrustal shear zones and high lower crustal velocities indicate that strike slip faulting and magmatic underplating can be important processes during the docking and welding of an accreted terrane

tracking dolphin whistles using an autonomous acoustic recorder array dolphins are known to produce nearly omnidirectional whistles that can propagate several kilometers allowing these sounds to be localized and tracked using acoustic arrays during the fall of 2007 a km scale array of four autonomous acoustic recorders was deployed offshore of southern california in a known dolphin habitat at 800 m depth concurrently with the one month recording a fixed point marine mammal visual survey was conducted from a moored research platform in the center of the array providing daytime species and behavior visual confirmation the recordings showed three main types of dolphin acoustic activity during distinct times primarily whistling during daytime whistling and clicking during early night and primarily clicking during late night tracks from periods of daytime whistling typically were tightly grouped and traveled at a moderate rate in one example with visual observations traveling common dolphins delphinus sp were tracked for about 10 km with an average speed of 2 5

mantle provinces under north america from multifrequency p wave tomography this is a survey of mantle provinces large scale seismic anomalies under north america from the surface down to 1500 1800 km depth the underlying p velocity model was obtained by multifrequency tomography a waveform based method that systematically measures and models the frequency dependence of teleseismic body waves a novel kind of three dimensional rendering technique is used to make the considerable structural complexities under north america accessible in the transition zone and below the north american mantle is dominated by seismically fast provinces which represent distinct subduction episodes of the farallon plate i attempt to date and interpret the various slab fragments by reconciling their present positions with paleotrench locations from plate tectonic reconstructions and with major geologic surface episodes differences in vertical sinking velocity have led to large vertical offsets across adjacent coeval slabs some of the mantle provinces have not been discussed much previously including 1 a seismically slow blanket overlying the oldest farallon subduction along the eastern continental margin 2 a transition zone slab coeval with the laramide orogeny ca 80 60 myr which i discuss in analogy to the stagnant slab subduction style commonly found in the western pacific today 3 the lower mantle root of present day cascadia subduction which may have started out as intraoceanic subduction 4 a lower mantle slab under arizona and new mexico the last material to subduct before strike slip motion developed along the san andreas boundary and 5 two narrow plate tears thousands of kilometers long one of which is the subducted conjugate of the mendocino fracture zone

talc bearing serpentinite and the creeping section of the san andreas fault the section of the san andreas fault located between cholame valley and san juan bautista in central california creeps at a rate as high as 28 mm yr 1 ref 1 and it is also the segment that yields the best evidence for being a weak fault embedded in a strong crust serpentinized ultramafic rocks have been associated with creeping faults in central and northern california and serpentinite is commonly invoked as the cause of the creep and the low strength of this section of the san andreas fault however the frictional strengths of serpentine minerals are too high to satisfy the limitations on fault strength and these minerals also have the potential for unstable slip under some conditions here we report the discovery of talc in cuttings of serpentinite collected from the probable active trace of the san andreas fault that was intersected during drilling of the san andreas fault observatory at depth safod main hole in 2005 we infer that the talc is forming as a result of the reaction of serpentine minerals with silica saturated hydrothermal fluids that migrate up the fault zone and the talc commonly occurs in sheared serpentinite this discovery is significant as the frictional strength of talc at elevated temperatures is sufficiently low to meet the constraints on the shear strength of the fault and its inherently stable sliding behaviour is consistent with fault creep talc may therefore provide the connection between serpentinite and creep in the san andreas fault if shear at depth can become localized along a talc rich principal slip surface within serpentinite entrained in the fault zone

lithosphere asthenosphere interaction beneath the western united states from the joint inversion of body wave traveltimes and surface wave phase velocities summary the relation between the complex geological history of the western margin of the north american plate and the processes in the mantle is still not fully documented and understood several pre usarray local seismic studies showed how the characteristics of key geological features such as the colorado plateau and the yellowstone snake river plains are linked to their deep mantle structure recent body wave models based on the deployment of the high density large aperture usarray have provided far more details on the mantle structure while surface wave tomography ballistic waves and noise correlations informs us on the shallow structure here we combine constraints from these two data sets to image and study the link between the geology of the western united states the shallow structure of the earth and the convective processes in mantle our multiphase dna10 s model provides new constraints on the extent of the archean lithosphere imaged as a large deeply rooted fast body that encompasses the stable great plains and a large portion of the northern and central rocky mountains widespread slow anomalies are found in the lower crust and upper mantle suggesting that low density rocks isostatically sustain part of the high topography of the western united states the yellowstone anomaly is imaged as a large slow body rising from the lower mantle intruding the overlying lithosphere and controlling locally the seismicity and the topography the large e w extent of the usarray used in this study allows imaging the slab graveyard a sequence of farallon fragments aligned with the currently subducting juan de fuca slab north of the mendocino triple junction the lithospheric root of the colorado plateau has apparently been weakened and partly removed through dripping the distribution of the slower regions around the colorado plateau and other rigid blocks follows closely the trend of cenozoic volcanic fields and ancient lithospheric sutures suggesting that the later exert a control on the locus of magmato tectonic activity today the dna velocity models are available for download and slicing at http dna berkeley edu

shamal swells in the arabian sea and their influence along the west coast of india wave data collected off ratnagiri goa and dwarka along the west coast of india during winter season ne monsoon and early pre monsoon present distinct wave characteristics with periodicity ranging between 2 and 5 days associated with shamal events the notable wave characteristics during these events are an increase in wave height decrease in swell period and a common propagation direction northwest for wind sea and swell ifremer cersat blended winds clearly show the presence of strong northwesterly winds in the arabian peninsula and northwestern arabian sea which are associated with the winter shamal events the winds during such events generate large northwesterly swells shamal swells in the northwestern arabian sea and propagate towards the west coast of india in the nw direction with mean periods ranging between 6 and 8 s numerical simulations reproduce the shamal swells over the arabian sea and they can be traced all along the west coast of india however with lesser order of magnitude from north to south generation and propagation of shamal swells and their influence along the west coast of india have been described

fossil slabs attached to unsubducted fragments of the farallon plate as the pacific farallon spreading center approached north america the farallon plate fragmented into a number of small plates some of the microplate fragments ceased subducting before the spreading center reached the trench most tectonic models have assumed that the subducting oceanic slab detached from these microplates close to the trench but recent seismic tomography studies have revealed a high velocity anomaly beneath baja california that appears to be a fossil slab still attached to the guadalupe and magdalena microplates here using surface wave tomography we establish the lateral extent of this fossil slab and show that it is correlated with the distribution of high mg andesites thought to derive from partial melting of the subducted oceanic crust we also reinterpret the high seismic velocity anomaly beneath the southern central valley of california as another fossil slab extending to a depth of 200 km or more that is attached to the former monterey microplate the existence of these fossil slabs may force a reexamination of models of the tectonic evolution of western north america over the last 30 my

trends of atlantic wave extremes as simulated in a 40 yr wave hindcast using kinematically reanalyzed wind fields abstract in this study seasonal extremes of wave height in the north atlantic are analyzed the analysis is based on a 40 yr 1958 97 numerical wave hindcast using an intensive kinematic reanalysis of wind fields changes in the ocean wave extremes are identified by performing the mann kendall test and are further related to changes in the atmospheric circulation sea level pressure by means of redundancy analysis the relationship between sea level pressure and ocean wave extremes is also used to reconstruct the seasonal wave statistics for the last century back to 1899 consistent with previous studies this high resolution atlantic wave hindcast also shows that the northeast north atlantic ocean has experienced significant multidecadal variations in the last century and it has indeed roughened in winters of the last four decades the winter wave height increases are closely related to changes in the north atlantic oscillation during the last four decades while showing trend patterns similar to

three dimensional seismic model of the sierra nevada arc california and its implications for crustal and upper mantle composition a three dimensional p wave velocity model of south central california from the coast ranges to the sierra nevada shows that the crust under most of the southern sierra nevada batholith has seismic velocities 5 9 6 3 km s below the continental average the crust is not much thicker on average about 35 km than in the adjacent great valley and basin and range province apart from a small northward thickening crustal root under the western sierra nevada that reaches a depth of 42 km crustal velocities above the continental average are observed beneath much of the great valley due to a high velocity body underlying the sedimentary basin and the foothills metamorphic belt 6 4 7 0 km s upper mantle velocities are generally low 7 8 km s but span a wide range 7 4 8 2 km s we display the velocity model in several cross sections and maps of moho depth and average crustal velocity the measured velocities in the upper and mid crust of the sierra nevada batholith are in good agreement with laboratory measurements on sierra nevada tonalites after corrections for density and temperature peridotite xenoliths from the eastern sierra nevada suggest strong upper mantle anisotropy which could explain some of the velocity heterogeneity in the sierra nevada mantle by the time cretaceous subduction related magmatism ceased the sierra nevada arc must have had a thick mafic lower crust yet a principal result of our work is that today the batholith has a crust of mainly felsic composition throughout a subcrustal layer with velocities below normal pn velocities 7 6 km s may indicate the presence of lower crustal material in eclogite facies

beaked whale and dolphin tracking using a multichannel autonomous acoustic recorder to track highly directional echolocation clicks from odontocetes passive hydrophone arrays with small apertures can be used to receive the same high frequency click on each sensor a four hydrophone small aperture array was coupled to an autonomous acoustic recorder and used for long term tracking of high frequency odontocete sounds the instrument was deployed in the spring of 2009 offshore of southern california in a known beaked whale and dolphin habitat at about 1000 m depth the array was configured as a tetrahedron with approximately 0 5 m sensor spacing time difference of arrival measurements between the six sensor pairs were used to estimate three dimensional bearings to sources both near seafloor beaked whales and near sea surface dolphins were tracked the tracks observed using this technique provide swimming and diving behavioral information for free ranging animals using a single instrument furthermore animal detection ranges were derived allowing for estimation of detection probability functions

localization of marine mammals near hawaii using an acoustic propagation model humpback whale songs were recorded on six widely spaced receivers of the pacific missile range facility pmrf hydrophone network near hawaii during march of 2001 these recordings were used to test a new approach to localizing the whales that exploits the time difference of arrival time lag of their calls as measured between receiver pairs in the pmrf network the usual technique for estimating source position uses the intersection of hyperbolic curves of constant time lag but a drawback of this approach is its assumption of a constant wave speed and straight line propagation to associate acoustic travel time with range in contrast to hyperbolic fixing the algorithm described here uses an acoustic propagation model to account for waveguide and multipath effects when estimating travel time from hypothesized source positions a comparison between predicted and measured time lags forms an ambiguity surface or visual representation of the most probable whale position in a horizontal plane around the array this is an important benefit because it allows for automated peak extraction to provide a location estimate examples of whale localizations using real and simulated data in algorithms of increasing complexity are provided

high frequency tail characteristics in the coastal waters off gopalpur northwest bay of bengal a nearshore modelling study over the years continued uncertainty amid 4 and 5 frequency exponent representation observed in the slope of the high frequency tail of a wind wave frequency spectrum is a major concern to comprehend the nature of the high frequency tail an effort has been made to assess the slope of the high frequency tail with measured data recorded for 3 years off gopalpur the study demonstrates that the high frequency slope of the spectra varied seasonally in the range of n 2 13 to 3 48 the swell and wind sea parameters calculated by separation frequency method shows that 64 6 of waves were dominant by swell and the rest 34 9 by sea annually single double and multi peaked spectra occur 12 23 71 80 and 15 37 annually to simulate wave spectra the nested wam swan model is forced with era interim winds and 1d wave spectra comparisons when performed proved to be encouraging from the comparisons of measured and theoretical spectra it is concluded that jonswap model could not describe the high frequency tail of measured spectrum as indicated by the very high scatter index ranging from 0 24 to 1 44 whether there exists a correct slope for the high frequency tail is still a question moreover the philosophy of a unique slope at any coastal location remains uncertain for the wave modelling community

seismic heterogeneity and small scale convection in the southern california upper mantle we invert traveltime residuals of teleseismic p and s phases for 3 d perturbations in vp vs and vp vs structures in the southern california upper mantle the tomographic inversion uses frequency dependent 3 d sensitivity kernels to interpret traveltime residuals measured in multiple frequency bands and recent advances in regional crustal thickness and velocity models to better isolate the mantle component of traveltime residuals in addition to separate vp and vs tomography we jointly invert the p and s data sets for vp vs perturbations by imposing a smoothness constraint on the lnvs lnvp field the regional upper mantle is very heterogeneous with the greatest amplitude of velocity and vp vs perturbations in the upper 200 km and mantle structures that correlate spatially with the major physiographic provinces of southern california our imaging improves the resolution of the geometry and amplitude of these features in addition to the major structures imaged and discussed in previous papers we find a large high velocity anomaly at depths between 340 and 500 km beneath the borderland transverse ranges and northern peninsular ranges this anomaly is separate from the well known uppermost mantle transverse ranges anomaly which extends no deeper than 175 200 km the strongest low velocity high vp vs anomaly is found beneath and west of the salton trough and is attributed to relatively high partial melt in the asthenosphere as a result of lithospheric thinning the magnitudes of vp vs and vp vs perturbations and knowledge of regional 1 d velocity and attenuation lead us to conclude that the asthenosphere contains up to 1 partial melt extending to depths as great as 150 200 km

receiver function studies in the trans hudson orogen saskatchewan teleseismic events were recorded on an array of three component broadband and short period seismographs in the trans hudson orogen over a period of almost 3 years receiver functions calculated from these data were used in a forward modelling study to derive the local shear wave velocity structure beneath 20 stations station ffc flin flon located within the flin flon belt was one of two stations situated on bedrock and produced the highest quality receiver functions the ffc velocity model correlates well with an interpretation of nearby reflection data and features a distinct lower crust interpreted as archean basement which cores the entire reindeer zone both radial and tangential receiver functions at ffc show strong evidence for a northeasterly dipping shallow boundary within rocks of the flin flon belt with a dip angle of 20 total crustal thickness is 37 km eighteen stations are situated on phanerozoic sedimentary cover ranging in thickness from 0 4 km to greater than 2 km receiver function

timing and structural expression of the nevadan orogeny sierra nevada california the nevadan orogeny was a very short lived event in the late jurassic that involved the deformation of a great variety of rock types and paleozoic and mesozoic terranes throughout the extent of the sierra nevada the nevadan structures show great variation in style but relatively constant orientations these relations can be explained by considering the prior histories of the various terranes slaty cleavages and tight folds are the characteristic main phase structures in the western belt of jurassic island arc volcanic rocks and flysch type sedimentary rocks a strip of phyllites and greenschists along the eastern edge of the belt apparently represents similar jurassic rocks that were deformed and metamorphosed at greater depths probably during underthrusting of the western belt beneath the central belt the central belt of paleozoic metasedimentary and metavolcanic rocks shows the most extreme variation in style of main phase structures from weak spaced to crenulation cleavages in the south where polyphase deformed rocks formed a structural basement to slaty and phyllitic cleavages and asymmetric to isoclinal folds in the north where most of the paleozoic basement rocks lack penetrative pre nevadan fabrics eastward directed thrust faulting apparently was important only in the northern part of the range where main phase deformation was most intense the eastern belt of jurassic and triassic magmatic arc volcanic and sedimentary rocks defines the core of a major synclinorium and the rocks contain penetrative slaty cleavages and asymmetric tight to isoclinal folds a late phase of nevadan structures consisting of northeast trending cleavages and minor folds also shows a marked variation in style from relatively intensely developed in the north to very weakly developed in the south the regional extent and geometry of the nevadan structures indicate that the nevadan orogeny involved underthrusting of island arc rocks on the west and significant crustal shortening in the central and eastern belts these features suggest that the nevadan orogeny resulted from the collision of the island arc western belt with an andean type arc eastern belt situated at the western edge of north america

an inverted continental moho and serpentinization of the forearc mantle volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back arc region but the forearc mantle in the corner of the wedge is thought to be significantly cooler here we explore the structure of the mantle wedge in the southern cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers we find very low shear wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an inverted continental moho which reverts to normal polarity seaward of the cascade arc this observation provides compelling evidence for a highly hydrated and serpentinized forearc region consistent with thermal and petrological models of the forearc mantle wedge this serpentinized material is thought to have low strength and may therefore control the down dip rupture limit of great thrust earthquakes as well as the nature of large scale flow in the mantle wedge

location of instruments on the seafloor by joint adjustment of instrument and ship positions the problem of determining accurate locations for arrays of underwater instruments is similar to the problem of locating local earthquakes by utilizing a limited number of receivers but is complicated by the fact that estimated errors in longitude and latitude of a given receiver ship position are nonzero and are typically correlated estimates of ship positions at sea are commonly determined by fixes from the navy transit navigation satellite system this system calculates position error ellipses which vary in size and orientation from fix to fix deviations in the orientations of the principal axes of the error ellipses from north south and east west result in the introduction of off diagonal elements in the ship position variance matrix tying each ship fix to a stationary array of ocean bottom seismometers obs s using acoustic ranging allows averaging of fixes thus solving simultaneously for ship and obs positions puts tight constraints on the system as a whole and especially on the relative positions of the obs s in addition to ship positions the data required to locate the instruments are two way travel times between the ship and transponders on the instruments and initial depth estimates of obs s read from the bathymetry the parameters which we solve for are the locations of the instruments including depth and of the ship at each fix the forward problem calculating acoustic travel times from distances between ship fixes and obs s is solved by a ray shooting algorithm this system of equations is linearized and transformed to diagonalize the covariances it is then solved iteratively by inverting the data jointly using singular value decomposition and step length damping the solution includes the covariances of the parameters we show calculations of positions of four obs s for deployments during three experiments including the rivera oceanic seismic experiment rose typical fix error ellipses 1 are 300 m by 200 m and resulting instrument position uncertainties are approximately 100 m relative instrument positions are accurate to about 50 m relative errors can be decreased to 10 to 20 m by using simultaneous rather than sequential ranging