Geoacoustic Data Research Articles

MONITORING OF CHANGES IN THE STRESS-STRAIN STATE OF GEOENVIRONMENT AT THE PETROPAVLOVSK GEODYNAMIC TESTING SITE BASED ON THE MULTI-INSTRUMENTAL BOREHOLE AND GPS DATA DURING THE ACTIVE PHASE OF PREPARING THE ZHUPANOVSKY EARTHQUAKE (JANUARY 30, 2016, Mw 7.2)

The paper presents the results of comparative analysis of the data regarding the multi-instrumental borehole monitoring data of changes in the geoenvironment stress-strain state and GPS data obtained in the time vicinity of the close strong Zhupanovsky earthquake. The purpose this study was to assess the feasibility of using GPS measurements on routine basis for effective monitoring of strong Kamchatka earthquakes in the area of Petropavlovsk-Kamchatsky. The Zhupanovsky earthquake active phase was chosen as a "test" time interval for comparing GPS and borehole monitoring data. This earthquake has been the strongest seismic event since 2000 in terms of the ratio of the earthquake focus length to the hypocentral distance. The time series borehole electromagnetic and geoacoustic data were compared with the dilatation series reflecting the relative changes in the area of a triangle composed of Kamchatka GPS observation network located in the Petropavlovsk geodynamic testing site. The analysis indicates a high degree of consistency in these time series. GPS data obtained during the active phase of the earthquake preparation is agree with the results of mathematical modeling expected values of volumetric strain on the daylight surface on the eve of the earthquake. A joint analysis of borehole and GPS data made it possible to specify the time limits for the stages of change in the stress-strain state of geoenvironment and to resolve ambiguity of interpretation of the electromagnetic and geoacoustic borehole measurement results at the final stage of preparing the Zhupanovsky earthquake.

A Clone Selection Algorithm Optimized Support Vector Machine for AETA Geoacoustic Anomaly Detection

Anomaly in geoacoustic emission is an important earthquake precursor. Current geoacoustic anomaly detection methods are limited by their low signal-to-noise ratio, low intensity, sample imbalance, and low accuracy. Therefore, this paper proposes a clone selection algorithm optimized one-class support vector machine method (CSA-OCSVM) for geoacoustic anomaly detection. First, the interquartile range (IQR), cubic spline interpolation, and time window are designed to amplify the geoacoustic signal intensity and energy change rules to reduce the interference of geoacoustic signal noise and intensity. Secondly, to address the imbalance of positive and negative samples in geoacoustic anomaly detection, a one-class support vector machine is introduced for anomaly detection. Meanwhile, in view of the optimization capabilities of the clone selection algorithm, it is adopted to optimize the hyperparameters of OCSVM to improve its detection accuracy. Finally, the proposed model is applied to geoacoustic data anomaly detection in nine different datasets, which are derived from our self-developed acoustic electromagnetic to AI (AETA) system, to verify its effectiveness. By designing comparative experiments with IQR, genetic algorithm OCSVM (GA-OCSVM), particle swarm optimization OCSVM (PSO-OCSVM), and evaluating the performance of the true positive rate (TPR) and false positive rate (FPR), the experimental results depict that the proposed model is superior to the existing state-of-the-art geoacoustic anomaly detection approaches.

Depth-Dependent Seabed Properties: Geoacoustic Assessment

Offshore geoengineering requires reliable sediment parameters for analysis and design. This study proposes a robust framework for effective stress-dependent geotechnical and geoacoustic properties for seabed analysis based on geophysical models, new experimental data, and extensive data sets compiled from published studies that cover a wide range of marine sediments and depths. First, effective stress-dependent porosity versus depth profiles are computed using compaction models that are valid for a wide stress range. Then, P- and S-wave velocity data are analyzed in the context of effective stress-controlled density, shear stiffness, and bulk modulus within a Hertzian-Biot-Gassmann framework. Finally, this study selects six distinct “reference sediments” that range from clean sands to high-plasticity clays and assigns self-consistent compaction and shear stiffness properties using well-known correlations reported in the literature in terms of specific surface, plasticity, and grain characteristics. Results show that robust physical models for compaction and stiffness adequately predict depth-dependent geotechnical and geoacoustic properties according to sediment type. The asymptotic void ratio at low effective stress eL determines the sediment density ρo at the sediment–water boundary. New experimental studies show that the characteristic asymptotic sediment density ρo at very low effective stress σz′→0 controls the high-frequency acoustic reflection used for bathymetric imaging. The proposed analysis of geoacoustic data can be used to obtain first-order estimates of seafloor sediment properties and to produce sediment-type seafloor maps.

РЕГРЕСІЙНИЙ АНАЛІЗ СЕЙСМІЧНИХ І ГЕОФІЗИЧНИХ ПАРАМЕТРІВ ТА ЙОГО ЗАСТОСУВАННЯ ДЛЯ ДОСЛІДЖЕННЯ СЕЙСМІЧНОСТІ ЗАКАРПАТСЬКОГО РЕГІОНУ

The purpose of this work is to interpret the experimental data (deformation, geoacoustic and earthquake parameters) and to establish their relation with the seismicity of the Transcarpathian region using statistical (regression) analysis. The correlation of geophysical parameters is described, namely: deformation, geoacoustic emission and seismic characteristics of magnitude and energy class.For construction of the statistical (regression) model, geoacoustic and deformation data for the period of 2014, as well as data of the seismological catalog provided by the seismicity department of the Carpathian region (Subbotin Institute of Geophysics of NAS of Ukraine) were used. The statistical model of seismicity is built to analyze various geophysical parameters and to establish their relationship with each other by means of regression analysis.This interconnection will give an opportunity to understand how seismicity influences the change of various environmental parameters of the Transcarpathian region. The deformation and geoacoustic data used in the work were obtained at the mode geophysical station (MGS) "Beregove" and the observation point "Janoshi" (Transcarpathia). The basic regression analysis formulas used to construct a linear statistical model are given. According to the seismic catalog, a graph of dependence between energy class (K) and magnitude (MD) for the period 2002–2016 was constructed, which confirmed their dependence, as well as a histogram of seismic activity for the period 2002–2016, from which it follows that the largest number of events was in 2015. The tables, on which graphs of seismicity dependence on deformation and geoacoustics, are presented. The relationship between the magnitude (MI) and the offset shift (lg DP) in depth (h) is shown. Studies were conducted for different depths: 1) up to 2 km, 2) from 2–5 km, 3)5–10 km and 4) from 10 km or more. The results showed that the greater the depth, the greater the relationship between the magnitude (MI) and the offset shift (lg DP) is. Such studies are needed to identify the effect of seismicity on the change of other environmental parameters, in particular, temperature, characteristics of earthquake foci, which will allow building an existing model of seismicity of the Transcarpathian region.

Geoacoustic Model of Coastal Bottom Strata off the Northwestern Taean Peninsula in the Yellow Sea

In the shallow coastal area, located off the northwestern Taean Peninsula of the eastern Yellow Sea, geoacoustic models with two layers were reconstructed for underwater acoustic experimentation and modeling. The Yellow Sea experienced glacio-eustasy sea-level fluctuations during Quaternary period. Coastal sedimentation in the Yellow Sea was characterized by alternating terrestrial and shallow marine deposits that reflected the fluctuating sea levels. The coastal geoacoustic models were based on data from piston, grab cores and the high-resolution 3.5 kHz, chirp seismic profiles (about 70 line-kilometers, respectively). Geoacoustic data of the cores were extrapolated down to 3 m in depth for geoacoustic models. The geoacoustic property of seafloor sediments is considered a key parameter for modeling underwater acoustic environments. For simulating actual underwater environments, the P-wave speed of the models was adjusted to in-situ depth below the sea floor using the Hamilton method. The proposed geoacoustic models could be used for submarine acoustic inversion and modeling in shallow-water environments of the study area.

Assessment of the temporal and spatial dependence of reverberation mechanisms for KOREX-17

Mid-frequency reverberation data were obtained over a 9-day period off Geoje Island, Republic of Korea, complemented by transmission loss and backscatter measurements. The reverberation data were collected using the Autonomous Reverberation Measurement System (ARMS), a benthic lander with a source and receive array mounted on a rotation stage in order to collect reverberation data as a function of bearing angle. The ARMS was repeatedly deployed in roughly the same location over the course of the experiment. The surficial sediments close to the ARMS are known to be composed primarily of mud with occasional rock outcrops. Beyond a range of 2 km, the sediment composition is uncertain and a geoacoustic measurement survey has been planned to collect additional data in this region. Using contemporaneous measurements of the sea surface directional wave spectrum and the currently limited geoacoustic data, modeling is used to estimate the relative importance of sea bottom and surface reverberation. [Work supported by of the Office of Naval Research.]

Implications from a clay/silt suspension model of mud for data from the Seabed Characterization Experiment

Mud-like marine sediments may be modeled as a suspension of flocculated clay particles in water, in which silt particles are embedded in the clay flocs. Recent calculations based on this model [Pierce et al., New Orleans ASA] produced new predictions for the frequency-dependent phase speed and attenuation of compressional waves. For phase speed, very good comparisons between model predictions and archival data were found. Comparisons will be presented using geoacoustic data from sediment cores extracted from the New England Mud Patch. For attenuation, predictions using Gaussian distributions of silt particle radius were calculated. An approach will be described for producing a frequency-dependent effective particle radius to account for size-distribution effects using single-particle attenuation expressions. The influence of non-Gaussian size distributions on the effective radius and on the frequency intervals of near-linear attenuation behavior will be shown. An environmental model for a WHOI AUV track d...

Mesophotic Coral Ecosystems: A Geoacoustically Derived Proxy for Habitat and Relative Diversity for the Leeward Shelf of Bonaire, Dutch Caribbean

Current trends demonstrate coral reef health in serious decline worldwide. Some of the most well preserved coral reefs in the Caribbean basin are located in the waters surrounding Bonaire, in the Dutch Caribbean. In many places on the leeward side on islands dominated by trade winds, the shallow reef systems extend into deeper water where they are known as Mesophotic Coral Ecosystems (MCE). Autonomous Underwater Vehicles (AUVs) were used to collect geoacoustic data of these leeward reefs at multiple sites as part of an ocean exploration project. AUV swath bathymetry and side-scan sonar data were analyzed for depth, acoustic backscatter intensity, seafloor slope and rugosity. These geomorphic metrics were then used as inputs to generate a composite synthetic index of bottom-type to delineate MCE features. A confusion matrix statistical analysis of the acoustic class map showed an overall accuracy of the acoustic classes at 66%, with accuracy of the hard coral class the highest at 83% and the sandy-bottom class the lowest at 55. The hard coral class was also the statistically most reliable, at over 80%, with the noise class coming in as the least reliable. This morphologic habitat index is a potentially useful new tool in quantifying the extent of MCE located in proximity to Marine Protected Areas (MPAs).

Geoacoustic model of the transverse acoustic variability experiment area in the northern East China Sea

Transverse Acoustic Variability Experiment (TAVEX) is a joint ROK-US acoustic experiment for testing transverse acoustic variability in the northern limit of the East China Sea. TAVEX was performed in a water depth of 70–90 m around 32°30 to 40N, 125°20 to 30E, about 150 km southwest of Cheju Island, in August 2008. Purpose of this paper is to provide geoacoustic models of the TAVEX area, integrated and detailed as available. Two geoacoustic models of three layers were reconstructed, located at 32°40N/125°30E and 32°30N/125°30E of the northern East China Sea, respectively. The models were based on the data of the high-resolution subbottom and air-gun seismic profiles with cores. Geoacoustic data of the cores were extrapolated down to a depth of 100 m of the geoacoustic models. For actual underwater experiments, the P-wave speed of the models was compensated to in situ depth below the sea floor using the Hamilton method.

Identification of earthquake precursors in the hydrogeochemical and geoacoustic data for the Kamchatka peninsula by flicker-noise spectroscopy

Abstract. A phenomenological systems approach for identifying potential precursors in multiple signals of different types for the same local seismically active region is proposed based on the assumption that a large earthquake may be preceded by a system reconfiguration (preparation) on different time and space scales. A nonstationarity factor introduced within the framework of flicker-noise spectroscopy, a statistical physics approach to the analysis of time series, is used as the dimensionless criterion for detecting qualitative (precursory) changes within relatively short time intervals in arbitrary signals. Nonstationarity factors for chlorine-ion concentration variations in the underground water of two boreholes on the Kamchatka peninsula and geacoustic emissions in a deep borehole within the same seismic zone are studied together in the time frame around a large earthquake on 8 October 2001. It is shown that nonstationarity factor spikes (potential precursors) take place in the interval from 70 to 50 days before the earthquake for the hydrogeochemical data and at 29 and 6 days in advance for the geoacoustic data.

A Digital System for the Acquisition and Processing of Geoacoustic Data

In the autumn of 1969 we accepted delivery of three TC-200 digital data acquisition systems from Teledyne Geotech. These systems can record up to 16 channels of long period, digital data with a specified sampling rate (currently 1 per second) on magnetic tape in an ‘IBM compatible’ format. Identifying headers are automatically written at the beginning of each file on tape and Universal Time is written each minute. The actual dynamic range of the recoding system is about 66 dB, but an operating range of 120 dB is automatically assured by the use of binary, gain-ranging amplifiers. The systems have been tested and are now operating satisfactorily at Blacknest Laboratory near Reading in England, at the University of Alaska and at a field site east of Dallas, Texas.

The structure of the incoherent sediments in the Ita Mai Tai Guyot (Pacific Ocean) based on geoacoustic profiling data

The results of geoacoustic studies carried out by the acoustic MAK-1M system in the southeastern Ita Mai Tai Guyot (Magellan Seamounts, Pacific Ocean) are discussed. The obtained geoacoustic sections characterize the incoherent part of the sedimentary sequence with high resolution. The geoacoustic stratification is well correlative with the deep-sea drilling data: the acoustic units are reliably correlated with the lithostratigraphic units defined in the cores of DSDP holes 200 and 202. Three geoacoustic units are distinguished in the sedimentary section (from the top downward): unit I corresponding in age to the terminal Miocene (Messinian)-Quaternary; unit II correlated with the Late Miocene (Tortonian); unit III accumulated in the Early Eocene-Early Miocene. The acoustic basement is composed of reefogenic limestones that were formed at different stages of the guyot’s development through the Aptian-Turonian to Late Paleocene-Eocene. The sonar images allow the distribution of the incoherent carbonate sediments to be contoured along the periphery of the summit’s plateau.

Fluid seepage and mound formation offshore Costa Rica revealed by deep-towed sidescan sonar and sub-bottom profiler data

Our analysis of geoacoustic data from the Middle American margin provides an insight into the formation and evolution mechanisms of mound structures observed on the continental slope offshore Costa Rica. Based on high-resolution deep-towed sidescan sonar and sub-bottom profiler (SBP) data six different mound and fluid seepage structures at the Hongo mound field are characterized in detail. The Hongo mound field is located on the lower continental slope offshore Nicoya peninsula in the prolongation of the subducting Nicoya fracture zone. The mounds have oval to circular shapes with diameters of 500–1600 m and relief heights of 60–100 m. High backscatter anomalies near the mound summits indicate carbonate precipitation and focused fluid seepage activity within the last 10 ka. The data do not show evidence for mud extrusions and the structures were probably formed by a combination of carbonate precipitation and mud diapirism. Based on seismic stratigraphy analysis, mud diapirism is at least active since 42.5–57 ka and average vertical growth rates vary between 6–24 cm/ka. However, if diapirism represents the dominant mound evolution mechanism, mound heights of 80 m point to much older mound ages of 330–1330 ka.

Temporal variability of gas seeps offshore New Zealand: Multi-frequency geoacoustic imaging of the Wairarapa area, Hikurangi margin

Cold seeps on Opouawe Bank, situated in around 1000 m water depth on the Hikurangi Margin offshore North Island. New Zealand, were investigated using multibeam bathymetry, 75 and 410 kHz sidescan sonar imagery, and 2–8 kHz Chirp sediment echosounder data. Towed video camera observations allowed ground-truthing the various geoacoustic data. At least eleven different seep locations displaying a range of seep activity were identified in the study area. The study area consists of an elongated, northward-widening ridge that is part of the accretionary Hikurangi Margin and is well separated from direct terrigenous input by margin channels surrounding the ridge. The geoacoustic signature of individual cold-seep sites ranged from smooth areas with slightly elevated backscatter intensity resulting from high gas content or the presence of near-surface gas hydrates, to rough areas with widespread patches of carbonates at the seafloor. Five cold seeps also show indications for active gas emissions in the form of acoustic plumes in the water column. Repeated sidescan sonar imagery of the plumes indicates they are highly variable in intensity and direction in the water column, probably reflecting the control of gas emission by tides and currents. Although gas emission appears strongly focused in the Wairarapa area, the actual extents of the cold seep structures are much wider in the subsurface as is shown by sediment echosounder profiles, where large gas fronts were observed.

Remote sensing of Tyrrhenian shallow waters using the adjoint of a full-field acoustic propagation model

Over the past two years the capabilities of adjoint-based inversion have been explored for applications both in geoacoustic inversion and shallow-water acoustic tomography. Starting from case studies based on the principles of optimal control theory the performance of adjoint modeling has been constantly improved to more realistic scenarios ever since. In particular, the concept of semi-automatic adjoint generation has been introduced for inversion of satellite ocean colour imagery and geoacoustic characterization of seabed properties. In the framework of a Maritime Rapid Environmental Assessment sea trial (MREA/BP07) that was conducted in the same area south of the island of Elba as the earlier Yellow Shark experiment (YS94), this paper examines the original YS94 geoacoustic data and the recent MREA07 oceanographic data to demonstrate adjoint-based acoustic monitoring of environmental parameters in Mediterranean shallow waters. First, the adjoint-generated environmental gradients are validated for an application in geoacoustic inversion where the bottom geoacoustic parameters of the layered seabed are determined from long range acoustic propagation data in the water column. Then, for the application in ocean acoustic tomography, the temporal variability of MREA/BP07 sound-speed field data is analyzed in terms of empirical orthogonal functions and the adjoint-based approach is used to track the time-varying sound speed profile of the experimental transect.

High-resolution geoacoustic inversion in shallow water: A joint time- and frequency-domain technique

High-resolution geoacoustic data are required for accurate predictions of acoustic propagation and scattering in shallow water. Since direct measurement of geoacoustic data is difficult, time-consuming, and expensive, inversion of acoustic data is a promising alternative. However, the main problem encountered in geoacoustic inversion is the problem of uniqueness, i.e., many diverse geoacoustic models can be made to fit the same data set. A key, and perhaps unique, aspect of this approach is the combination of data analysis in both the space-time and the space-frequency domains. This combination attempts to ameliorate the uniqueness problem by exploiting as much independent data as possible. In order to meet the stringent requirements of high spatial resolution and uniqueness, an entire method has been developed including a new measurement technique, processing/analysis technique, and inversion strategy. These techniques are described and then illustrated with a shallow-water data set. Sound-speed gradients in the upper few meters of the sub-bottom appear to be much higher (one order of magnitude) than generally assumed. And, although often ignored, a large density gradient was observed in the top layer that played an acoustically significant role.

In-situ update of geoparameter databases

Low- and mid-frequency system performance is often controlled and degraded by bottom interaction, especially in littoral regions. However, performance prediction models generally give unreliable estimates of bottom interaction. The poor estimates are most often due to the databases that drive the models rather than the model physics. In this study a new approach is taken in rapid environmental assessment for overcoming this problem. The concept is to use in-situ propagation data to extract geoacoustic information about the bottom which is then used to update the bottom database. An analogous approach has long been employed for the water column, where in-situ bathythermograph (BT) data are used to update historical databases. While techniques for screening/merging BT data are now under development, there are no comparable techniques for treating bottom geoacoustic data. In this paper, a high-level methodology for updating bottom databases with in-situ measurements is outlined. The methodology includes a series of critical questions sequenced to lead to decisions about the robustness of the historical databases in a given region and the potential for database update. Results of the methodology, i.e., the in-situ measurements, modeling, and resulting bottom geoparameter database updates, from several littoral areas, will be shown.

Broadband bottom-interacting acoustics in shallow waters

Understanding broadband acoustic propagation in shallow-water ocean environments presents a host of challenges for the acoustics community. Insufficient environmental and experimental data make quantitative assessments of predictive models very difficult. On the other hand, due to substantial cost incurred in obtaining the ground truth and high-resolution geoacoustic data, the information is usually limited to a single or at most very few geological cores in a region. For acoustic applications, geological data need to be converted to a set of geoacoustic parameters such as compressional and shear wave speeds, their attenuation profiles, and the bulk density of sediment. In recent years several experiments of broadband acoustic propagation in shallow-water environments have been performed using airgun sources in different water depths. These experiments have been conducted in regions with some geological information. A procedure to convert the measured geological parameters into geoacoustic data in conjunction with the empirical orthogonal functions (EOF) has allowed the creation of statistical and frequency-dependent sediment profiles suitable for propagation modeling. Parabolic equation (PE) and normal mode models have been used to assess the physics of sound propagation in these regions. The results of these investigations are summarized here with regards to the geoacoustic inversion in shallow-water regions.

Can Maximum Likelihood Estimators Improve Genetic Algorithm Search in Geoacoustic Inversion?

The principles for estimating sea floor parameters via matched-field processing (MFP)-based techniques are now well known. In pure MFP, source localization is often seen as a range-depth estimation problem while the use of MFP on geoacoustic estimation generally involves a computationally intensive optimization procedure. In the last few years, much effort has been devoted to developing new or improving upon existing search procedures to solve the optimization problem Little, or no, attention has been given to the ensemble MFP-optimization treating it as a single technique. The question addressed in this paper is centered on the relation between the MFP parameter estimator technique, defining the objective function and the search procedure used to optimize it. In particular, we are interested in questions like: Can a faster search or more accurate estimate be achieved with a "peaky" surface instead of a flat and ambiguous surface? Is the inversion process affected by cross-frequency estimators and model mismatch? Does the search procedure need to be modified, and if yes how to account for this "peaky" surface navigation? This paper attempts to answer these and other related questions in the context of the June '97 geoacoustic inversion workshop data set.

Evaluation of Biot–Stoll theory for conversion of geology to geoacoustic data in shallow water

A procedure for estimating acoustic-wave velocity and attenuation in ocean sediment using a minimum amount of geological and geotechnical data is demonstrated. First, the Biot–Stoll theory is presented. Next, various asymptotic formulas for the attenuation coefficient are derived for high, low, and intermediate frequencies. These expressions clearly isolate the effects of the intergranular Coulomb friction and fluid viscous dissipation on the attenuation of shear and compressional waves. Under the constraint of a minimum amount of geological and geotechnical information, a sequence of empirical equations is compiled to convert basic data, such as the blow count number from a standard penetration test or shipboard density, into sediment geoacoustic properties. As a demonstration, two well-known field cases, the Atlantic Generating Station (AGS) site and the Atlantic Margin Coring (AMCOR 6010) site, are examined. By incorporating the uncertainty involved in the data collection, the estimated geoacoustical parameters are provided with a standard deviation.