The estimation of geoacoustic properties from broadband acoustic data, focusing on instantaneous frequency techniques

The compressional wave velocity and attenuation of marine sediments are fundamental to marine science. In order to obtain reliable estimates of these parameters it is necessary to examine in situ acoustic data, which is generally broadband. A variety of techniques for estimating the compressional wave velocity and attenuation from broadband acoustic data are reviewed. The application of Instantaneous Frequency (IF) techniques to data collected from a normal-incidence chirp profiler is examined. For the datasets examined the best estimates of IF are obtained by dividing the chirp profile into a series of sections, estimating the IF of each trace in the section using the first moments of the Wigner Ville distribution, and stacking the resulting IF to obtain a composite IF for the section. As the datasets examined cover both gassy and saturated sediments, this is likely to be the optimum technique for chirp datasets collected from all sediment environments

Optimal Processing of Marine High-Resolution Seismic Reflection (Chirp) Data

Chirp frequency-modulated (FM) systems offer deterministic, repeatable source-signatures for high-resolution, normal incidence marine seismic reflection data acquisition. An optimal processing sequence for uncorrelated Chirp data is presented to demonstrate the applicability of some conventional seismic reflection algorithms to high-resolution data sets, and to emphasise the importance of a known source-signature. An improvement of greater than 60dB in the signal- to-noise ratio is realised from correlating the FM reflection data with the transmitted pulse. Interpretability of ringy deconvolved data is enhanced by the calculation of instantaneous amplitudes. The signal-to-noise ratio and lateral reflector continuity are both improved by the application of predictive filters whose effectiveness are aided by the repeatability of the Chirp source.<br/

Frequency dependence of acoustic waves in marine sediments

In situ techniques provide the most reliable method of examining the geoacoustical properties of marine sediments. In the past, individual in situ surveys have only been able to examine compressional waves over a maximum frequency range of 100 Hz to 50 kHz. A new in situ acoustic device, the Sediment Probing Acoustic Detection Equipment, or SPADE, has been developed, which can emit a variety of pulses, e.g. tonal and swept-frequency, over a continuous frequency range of 10 - 100 kHz. Data from a recent field trial are analysed to obtain the in situ velocity and attenuation over frequency increments of 5 kHz between 10 - 75 kHz. Results imply that scattering is a dominant attenuation mechanism from 10-75 kHz and the media is dispersive for frequencies between 60 and 70 kHz and below 20 kHz. Biot theory cannot accurately model the observed velocity and attenuation

Lithosphere Structure and upper mantle characteristics below the Bay of Bengal

The oceanic lithosphere in the Bay of Bengal (BOB) formed 80–120 Ma following the breakup of eastern Gondwanaland. Since its formation, it has been affected by the emplacement of two long N-S trending linear aseismic ridges (85oE and Ninetyeast) and by the loading of ca. 20-km of sediments of the Bengal Fan. Here, we present the results of a combined spatial and spectral domain analysis of residual geoid, bathymetry and gravity data constrained by seismic reflection and refraction data. Self-consistent geoid and gravity modeling defined by temperature-dependent mantle densities along a N-S transect in the BOB region revealed that the depth to the Lithosphere-Asthenosphere boundary (LAB) deepens steeply from 77 km in the south to 127 km in north, with the greater thickness being anomalously thick compared to the lithosphere of similar-age beneath the Pacific Ocean. The Geoid-Topography Ratio (GTR) analysis of the 85°E and Ninetyeast ridges indicate that they are compensated at shallow depths. Effective elastic thickness (Te) estimates obtained through admittance/ coherence analysis as well as the flexural modeling along these ridges led to the conclusions: i) 85°E Ridge was emplaced in off-ridge environment (Te = 10–15 km); ii) the higher Te values of ?25 km over the Afanasy Nikitin Seamount (ANS) reflect the secondary emplacement of the seamount peaks in off-ridge environment, iii) that the emplacement of the Ninetyeast Ridge north of 2°N occurred in an off-ridge environment as indicated by higher Te values (25-30 km). Furthermore, the admittance analysis of geoid and bathymetry revealed that the admittance signatures at wavelengths &gt;800 km are compensated by processes related to upper mantle convection

Modern pollution signals in sediments from Windermere, NW England, determined by micro-XRF and lead isotope analysis

High resolution geochemical (Itrax micro-XRF and wavelength dispersive XRF) data, radiochronology (210Pb and 137Cs analyses) and ultra-high precision double-spike lead isotope measurements from lacustrine sediment cores are used in combination with historical research of former mining landscapes to investigate modern pollution signals in sediments from Windermere, the largest lake in the English Lake District. The sediment record suggests that while most element concentrations have been stable, there has been a significant increase since the 1930s in lead, zinc and copper concentrations. Double-spike lead isotope measurements reveal a mixture of natural lead, and three major contributory sources of anthropogenic (industrial) lead, comprising gasoline lead, coal combustion lead (from coal-fired steam ships) and lead derived from Carboniferous Pb–Zn mineralisation (mining activities). A number of up-system sediment traps have limited the amount of mining related heavy metals entering Windermere, and as a result, periods of metal workings do not correlate with peaks in heavy metals. Increases could also be due to flood-induced metal inwash or weathering of bedrock in the catchment. Application of these non-destructive and high precision analytical techniques provides new insights into the pollutant depositional history of Windermere

A 500 year sediment lake record of anthropogenic and natural inputs to Windermere (English Lake District) using double-spike lead isotopes, radiochronology, and sediment microanalysis

A high-resolution record of pollution is preserved in recent sediments from Windermere, the largest lake in the English Lake District. Data derived from X-ray core scanning (validated against wavelength dispersive X-ray fluorescence), radiochronological techniques (210Pb and 137Cs) and ultrahigh precision, double-spike mass spectrometry for lead isotopes are combined to decipher the anthropogenic inputs to the lake. The sediment record suggests that while most element concentrations have been stable, there has been a significant increase in lead, zinc, and copper concentrations since the 1930s. Lead isotope down-core variations identify three major contributory sources of anthropogenic (industrial) lead, comprising gasoline lead, coal combustion lead (most likely source is coal-fired steam ships), and lead derived from Carboniferous Pb–Zn mineralization (mining activities). Periods of metal workings do not correlate with peaks in heavy metals due to the trapping efficiency of up-system lakes in the catchment. Heavy metal increases could be due to flood-induced metal inwash after the cessation of mining and the weathering of bedrock in the catchment. The combination of sediment analysis techniques used provides new insights into the pollutant depositional history of Windermere and could be similarly applied to other lake systems to determine the timing and scale of anthropogenic inputs

Geometry and slip rate of the Aigion fault, a young normal fault system in the western Gulf of Corinth

The Aigion fault is one of the youngest major normal faults in the Gulf of Corinth, Greece, with an immature displacement profile. Based on geometry, slip rate and comparison with regional faults, we estimate the fault system length at ~10 km. We find the slip rate of the fault system is ~3.5 ± 1 mm/yr decreasing to ~2.5 ± 0.7 mm/yr close to its eastern tip. Complex fault geometry and displacement profiles on the shelf east of Aigion are consistent with the latter as the eastern tip location. Analysis of slip on this fault system and the established fault to the south (Western Eliki Fault) suggests that slip was transferred rapidly but not homogeneously between the two faults during the period of contemporaneous activity. Together with a lack of evidence of lateral propagation at the eastern fault tip in the last 10–13 k.y., we suggest that the fault developed and established its current length rapidly, within its 200–300 k.y. history. These results contribute to our understanding of the process of northward fault migration into the rift and the development of new normal faults

Assessing debris flows using LIDAR differencing: 18 May 2005 Matata event, New Zealand

The town of Matata in the Eastern Bay of Plenty (New Zealand) experienced an extreme rainfall event on the 18 May 2005. This event triggered widespread landslips and large debris flows in the Awatarariki and Waitepuru catchments behind Matata. The Light Detection and Ranging technology (LIDAR) data sets flown prior to and following this event have been differenced and used in conjunction with a detailed field study to identify the distribution of debris and major sediment pathways which, from the Awatarariki catchment, transported at least 350,000 ± 50,000 m3 of debris. Debris flows were initially confined to stream valleys and controlled by the density and hydraulic thrust of the currents, before emerging onto the Awatarariki debris fan where a complex system of unconfined sediment pathways developed. Here, large boulders, clasts, logs and entire homes were deposited as the flows decelerated. Downstream from the debris fan, the pre-existing coastal foredune topography played a significant role in deflecting the more dilute currents that in filled lagoonal swale systems in both directions. The differenced LIDAR data have revealed several sectors characterised by significant variation in clast size, thickness and volume of debris as well as areas where post-debris flow cleanup and grading operations have resulted in man-made levees, sediment dumps, scoured channels and substantial graded areas. The application of differenced LIDAR data to a debris flow event demonstrates the techniques potential as a precise and powerful tool for hazard mapping and assessment

The solution to the Tullock rent-seeking game when R > 2: mixed-strategy equilibria and mean dissipation rates

In Tullock's rent-seeking model, the probability a player wins the game depends on expenditures raised to the power R. We show that a symmetric mixed-strategy Nash equilibrium exists when R>2, and that overdissipation of rents does not arise in any Nash equilibrium. We derive a tight lower bound on the level of rent dissipation that arises in a symmetric equilibrium when the strategy space is discrete, and show that full rent dissipation occurs when the strategy space is continuous. Our results are shown to be consistent with recent experimental evidence on the dissipation of rents. An earlier version of this paper circulated under the title, No, Virginia, There is No Overdissipation of Rents. We are grateful to Dave Furth and Frans van Winden for stimulating conversations, and for comments provided by workshop participants from the CORE-ULB-KUL IUAP project, Purdue University, Pennsylvania State University, Rijksuniversiteit Limburg, and Washington State University. We also thank Max van de Sande Bakhuyzen and Ben Heijdra for useful discussions, and Geert Gielens for computational assistance. An earlier version of the paper was presented at the ESEM 1992 in Brussels and the Mid-West Mathematical Economics Conference in Pittsburgh. All three authors would like to thank CentER for its hospitality during the formative stages of the paper. The second author has also benefited from the financial support of the Katholieke Universitieit Leuven and the Jay N. Ross Young Faculty Scholar Award at Purdue University. The third author benefitted from visiting IGIER where part of the paper was written. The third author also benefitted from grant IUAP 26 of the Belgian Government

Sound Studies Meets Deaf Studies

Sound studies and Deaf studies may seem at first impression to operate in worlds apart. We argue in this article, however, that similar renderings of hearing, deafness, and seeing as ideal types - and as often essentialized sensory modes - make it possible to read differences between Sound studies and Deaf studies as sites of possible articulation. We direct attention to four zones of productive overlap, attending to how sound is inferred in deaf and Deaf practice, how reimagining sound in the register of low-frequency vibration can upend deafhearing dichotomies, how “deaf futurists“ champion cyborg sound, and how signing and other non-spoken communicative practices might undo phonocentric models of speech. Sound studies and Deaf studies emerge as fields with much to offer one another epistemologically, theoretically, and practically