Sub-bottom Profiler Data Research Articles

A more complete and detailed glacial history of the northwestern Chukchi margin—Implications for the existence and evolution of the East Siberian-Chukchi ice sheet

It is speculated that an united East Siberian-Chukchi Ice Sheet (ESCIS) existed on the East Siberian-Chukchi margin during the Pleistocene era. However, details regarding the frequency of its occurrence and the intensity of each glaciation remain unclear. Critical information lies in the northern part of the East Siberian-Chukchi margin because this region preserves relatively complete glacial landforms and deposits, especially in areas of deep-water depths. In this paper, new full-coverage multibeam data from the outer shelf–ocean basin on the western side of the Chukchi Rise of the northwestern Chukchi margin are presented, and more complete submarine glacial landforms in this area are identified. In addition, we provide a more detailed interpretation of the entire glacial strata using a compilation of new sub-bottom profiler data. Interpreted glacial landforms and buried glaciogenic debris flows (GDFs) indicate that the western side of the Chukchi Rise was affected by the Chukchi Ice Sheet. Overall, the glacial landforms can be divided into two categories, i.e. those in an ice stream setting on the Southwestern Margin and an inter-ice stream setting on the Northwestern Margin. However, in the current inter-ice stream area, large old gullies and GDFs persist, indicating dynamic changes between the ice stream and inter-ice stream zones. Since the onset of glaciation began around ∼0.8 Ma, the study area has experienced a total of nine glaciations, including three intense glaciations, five intermediate glaciations, and 1 mild glaciation. Through a comparison with the GDFs on the eastern slope of the Arliss Plateau which locates further west of the Chukchi Rise, we infer the existence of at least four unified ESCISs during the Quaternary.

Changes in marine sedimentation patterns in the northeastern South China Sea in the past 35,000 years

In the continental margin of the northeastern South China Sea, the sea level fluctuations since the Last Glacial Maximum have profoundly impacted the sedimentary environment. Our sub-bottom profiler data show a sedimentation process change from deposition to erosion during the Last Glacial Maximum. After the widespread erosion, the sedimentation process returned depositional throughout the Holocene, probably due to the rise of the sea level. This sedimentary process results in a widespread sedimentary unconformity in the continental slope, providing a benchmark for the end of the Last Glacial Maximum. Analyzing the sediment cores, we affirm that the change in current intensity is the primary factor controlling the sedimentary environments. The current intensities strengthened during the eustatic lowstand and weakened during the highstand periods, leading to alternating erosional and depositional processes. The widespread distribution of the erosive surface represents a regional-scale change in the sedimentary environment instead of a local event.

Japan Trench event stratigraphy: First results from IODP giant piston coring in a deep-sea trench to advance subduction zone paleoseismology

The International Ocean Discovery Program (IODP) Expedition 386, Japan Trench Paleoseismology, represents the first utilization of giant piston coring (GPC) within scientific ocean research drilling. This allowed for a Mission Specific Platform (MSP) multi-site, multi-hole, shallow subsurface coring in an ultra-deep water subduction zone trench. The primary objective of the expedition was to investigate the concept of submarine paleoseismology in the Japan Trench, which involves studying long-term records of deposits in the deep sea that can provide insights into past earthquake events. In this paper, we compile and interpret initial shipboard data and results to (1) establish first-order event stratigraphic correlation of thick event beds (> 50 cm in thickness) between sites, (2) test previously published event-stratigraphic predictions of earthquake-related event deposits as proposed based on high-resolution hydro-acoustic subbottom profiler (SBP) data, and (3) derive SBP-scale event deposits age estimates to (4) discuss the advantages and limitations of giant piston coring for scientific drilling operations and the potential of new event stratigraphy results for advancing submarine paleoseismology.The findings of the study identified a total of 77 SBP-scale event beds across 15 sites along a trench-parallel transect spanning over 600 km. These event beds exhibit clear expressions in SBP data, with approximately 49 % matching precisely with SBP units previously identified by Kioka et al. (2019a). For the remaining 51 % of SBP-scale event beds, thin, acoustically-transparent bodies were observed between high-amplitude horizons, for which SBP-based seismic interpretation alone would not be definitive. Consequently, the study concluded that the SBP-scale event-stratigraphy observed in IODP 386 cores validates the event-bed mapping conducted by Kioka et al. (2019a) and improves SBP interpretation for event beds in the 0.5 to 1 m thickness range.The initial age constraints obtained from shipboard radiolarian biostratigraphy enable us to provide rough estimates of event ages by linearly interpolating between previously dated events occurring less than 2000 years ago and a datum around 11,000 years ago reported in four boreholes from trench basins in the Southern, Central, and Northern Japan Trench. Inter-site stratigraphic correlation reveals distinct SBP-scale event stratigraphies for the trench segments located to the north and south of the structurally complex “boundary area” at approximately 39.3–39.4°N, which is hypothesized to potentially act as a persistent rupture barrier for megathrust earthquakes. We observe more frequent but thinner event deposits in the Southern and Central Japan Trench, and fewer but thicker event beds in the Northern Japan Trench. This spatial variation may be related to the different seismogenic behavior of the various asperities along the Japan Trench megathrust and/or to differences in the response of slope sediments to earthquake shaking. However, here-presented investigations at the SBP-scale level are deemed too simplistic for robust application of the “submarine paleoseismology” approach. The extensive and high-quality dataset from IODP GPC, coupled with the encouraging initial correlation results presented here, leads us to hypothesize that further detailed studies can identify and characterize event deposition dynamics at the micro-facies level, refine sediment provenance, and constrain precise event ages necessary for evaluating synchronicity in paleoseismological interpretation. These studies will also enable robust exploration of along-strike correlations or variations, facilitating the extraction of paleo-earthquake signals from Japan Trench event stratigraphies.

Acoustic Rapid Detection Technology and Its Application for Rare Earth Element (REE)-Rich Sediments in the Pigafetta Basin of the Western Pacific

This study aims to investigate the stratigraphic features and rare earth element (REE) mechanisms of deep-sea REE-rich sediments in the West Pacific Pigafetta Basin using acoustic rapid detection technology. Through an analysis of sub-bottom profile data and synthesis of existing studies, this study reveals the acoustic properties and thickness distribution of the REE-rich sediments. Acoustic spectral records identify three distinct acoustic facies: opaque (O), transparent (T), and laminated (L). This study maps the thickness and spatial distribution of the REE-rich sediment layer in the research area, ranging from approximately 6 to 36 m in thickness. Regions with REE-rich sediments exceeding 30 m in depth are identified, showing concentrated distribution along the northwest–southeast axis and a contiguous zone in the southwest corner of the study area. The method employed in this study can determine the potential bottom boundary of the REE-rich layer by assessing the thickness range of the sedimentary layer, overcoming limitations of traditional sampling methods. Furthermore, the thickness distribution characteristics of the REE-rich sedimentary layer in the study area provide valuable insights for future research on resource evaluation and estimation.

Seabed characterization based on the statistical classification using the seabed reflection amplitudes of sub-bottom profiler data

The seabed reflection amplitudes (SRAs) extracted from the sub-bottom profile have a strong correlation with the types and physical properties of the seabed sediments. In this paper, the SRAs distribution of classified seabed sediments is statistically obtained by calibration with seabed sampling results, discovering that SRAs on different seafloor sediment types exhibit Rayleigh distributions with varying parameters. Firstly, SRAs are compensated and enhanced, to improve their identification. Then, a novel classification method based on K–S test was proposed. This method measures the maximum distance between the cumulative distribution functions (CDF) of the unknown seabed and the calibrated sediment SRAs to check whether unknown samples belong to any of the known types. This proposed method only requires a small amount of seabed samples to automatically classify the seabed with high accuracy, and the model is simple, robust, and provides classification confidence.

Sub-Bottom Sediment Classification Employing a Multi-Attribute Temporal Convolutional Network

Sub-bottom profile data have the potential to characterize sediment properties but are seldom used for offshore site investigations because of uncertainties in rock-physics models. Deep-learning techniques appear to be poised to play very important roles in our processing flows for the interpretation of geophysical data. In this paper, a novel deep learning-based method for this task is proposed in which a nonlinear mapping between the observed data and sediment types is learned using a multi-attribute temporal convolution network (MATCN). Firstly, empirical mode decomposition (EMD) is employed for the original data, and intrinsic mode functions (IMFs) with multiple time scales are generated. Based on different IMFs, instantaneous frequency (IF) data under different IMFs can be obtained, while instantaneous phase (IP) and instantaneous amplitude (IA) data are obtained based on the original data. IF, IA and IP data are called attribute data, and are highly related to the attenuation, reflection, and interior structure of the sediment. Thus, IA, IF, and IP are used as the inputs, and a 1D convolutional neural network (CNN) and a time convolution network (TCN) are used to extract sequential features. Different feature representations are then fused. Combining cross-entropy loss function and class-edge loss function, the network is encouraged to produce classified results with more continuous sediment distributions compared with the traditional loss function. The real-data experiments demonstrate that the proposed MATCN has achieved good performance with an F measure greater than 70% in all cases, and greater than 80% in most cases.

Methane gas flares in the forearc basin of the Andaman-Nicobar subduction zone

Gas hydrates deposits in the Andaman forearc basin are inferred from seismic data and confirmed by drilling/coring during the NGHP-01 expedition. We present new evidence of gas flares in the Andaman forearc basin, detected through water column image (WCI), subbottom profiling, and high-resolution seismic data acquired onboard RV Sindhu Sadhana (SSD-085) in November-December 2021. The gas flares are located over an elongated sedimentary ridge, featuring two prominent mounds (M1 and M2) with distinct geological features. Compressional tectonics induced by the Diligent fault (DLF) formed the ridge with varying slopes and elevations. Gas flares observed above the mound M1 in WCI and sub-bottom profiler data. Seafloor samples reveal carbonate rocks with visible pores, indicating gas/fluid migration or burrows. The regional seismic profile delineates three sedimentary sequences: folded and faulted strata, mass transport deposits, and horizontal-to-sub-horizontal sedimentary layers. Additionally, we observed a bottom simulating reflector (BSR), indicating potential subsurface gas hydrate deposits. Detailed high-resolution seismic data revealed complex fault systems near bathymetry mounds (M1 and M2), which may serve as pathways for vertical fluid/gas migration.

Inversion of Sub-Bottom Profile Based on the Sediment Acoustic Empirical Relationship in the Northern South China Sea

This study focuses on the inversion of sub-bottom profile (SBP) data in the northern South China Sea using an empirical relationship derived from sediment acoustic data. The sub-bottom profile is primarily utilized for various marine applications, such as geological mapping and resource exploration. In this research, we present a study conducted in the northern slope canyon of the South China Sea. Firstly, we obtained the seabed reflection coefficient from sub-bottom profiles obtained by the autonomous underwater vehicle (AUV) detection system. Secondly, we utilized the acoustic empirical relationship in the northern South China Sea to establish relationship equations between the seabed reflection coefficient and the porosity, density, and average particle size of the sediment at a main frequency of 4 kHz (the AUV shallow profile main frequency). Then, using these equations, we were able to invert the physical parameters such as porosity, density, and average particle size of the seabed surface sediments. Finally, the inverted results are compared and analyzed by using the sediment samples test data. The overall deviation rate of the inverted physical parameters is within the range of ±10% when compared. The inverted results closely match the measured values, accurately reflecting the dynamic changes in the physical properties of seabed surface sediments. Notably, the average grain size is a direct indicator of the sediment particles size with smaller particles found in deeper water. The variation characteristics of sediment physical parameters align well with the variation of sediment types in the canyon, which is consistent with changes in the water depth, topography, and hydrodynamic conditions of the area. This further demonstrates the reliability of the inversion results.

Magmatism at an ultra-slow spreading rift: high-resolution geomorphological studies of a Red Sea Rift segment in Hadarba Deep

The mid-ocean rift in the Red Sea is one of the youngest rifting systems on Earth. Only recently, state-of-the-art methods and modern deep-sea instruments have been used to explore this young and unique volcanic system. During the first autonomous underwater vehicle surveys of the Red Sea Rift in Spring 2022, we collected multibeam bathymetry, backscatter, sub-bottom profiler data, and water column data over a 9 km long ridge segment in the Hadarba Deep between 22.49°N and 22.56°N to investigate the volcano-tectonic processes of this ultra-slow spreading segment (12 mm/year spreading rate). The high-resolution hydroacoustic data was used to (1) delineate and quantify the geometry of tectonic structures and individual lava flows, (2) define lava flow morphology and eruption style, (3) estimate relative ages of flows and features, and (4) retrace the evolution of the volcanic activity. In addition, the geochemistry of several young lava flows provides information on the relation between the different magma that supply these eruptions. About 90 eruptive units with variable sedimentary cover have been identified within the 43 km2mapped region. The oldest lava flows are buried under 3 to 4.2 m of sediment, indicating ages of up to ~30 ka based on average sedimentation rate estimates (~14 cm/ka), while the youngest eruptions are covered by<10 cm of sediment, and are thus younger than 700 years. Three volcanic phases have been identified based on changes in flow morphology and distribution, and tectonic pattern. All three axial phases have an average eruptive frequency of ~100-250 years. The segment displays an overall low tectonic extension (<10% of the total extension) and low vertical offset. Our geomorphological maps, analyses, and statistics reveal a moderately faulted, ultra-slow spreading MOR segment in the Red Sea with a surprisingly large amount of magmatic extension, implying that the segment has been underlined by a large magma supply for at least 15 ka. All these observations provide valuable implications for the formation history of the Red Sea Rift and the formation of ultra-slow spreading crust.

Spatial and temporal variability in Holocene trough-fill sediments, King Haakon Trough System, sub-Antarctic South Georgia

The climate in the South Atlantic sector of the sub-Antarctic, and therefore on and around the island of South Georgia, is dependent on the Southern Hemisphere Westerlies (SHW) and the Antarctic Circumpolar Current (ACC). The SHW and the ACC, in turn, are strongly controlled by climate variability in the Southern Hemisphere. Accordingly, thick sediment sequences in the troughs across South Georgia's continental shelf serve as valuable archives for past climate variations in the Southern Ocean. Since Holocene climate fluctuations led to only minimal oscillations in glacier margin positions within the fjords, the entire shelf was exposed to dynamic ocean currents since at least 10 ka BP. Its depositional systems are therefore a suitable target for the reconstruction of Holocene dynamics of both the SHW and the ACC. Sub-bottom profiler data and radiocarbon ages from four gravity cores from the south-western South Georgia continental shelf provide evidence for a complex interplay between island run-off and ocean currents intruding into a unique cross-shelf trough system during the last ∼10 ka. The data reveal several prominent changes in sediment and Holocene climate dynamics, the most significant occurring between 8 and 7.7 cal ka BP and between 2.6 and 2.2 cal ka BP. Both of these time periods represent transitions from warmer to cooler and windier conditions in South Georgia and the Southern Hemisphere. Our record from the King Haakon Trough System is the first highly resolved Holocene archive from the marine realm on the south-western South Georgia continental shelf and suggests several large-scale Southern Hemisphere climate changes during the mid-to late Holocene.

Assessment and Characterization of Woji Creek Riverbed in Port Harcourt, Rivers State, Nigeria, Utilizing Side Scan Sonar Technology

Woji Creek plays a crucial role in vessel navigation, supports diverse flora and fauna habitats, and sustains local livelihoods. However, human activities and natural events have led to changes in its riverbed over time. Given its significance for coastal stability and geomorphology, there is a pressing need to classify, evaluate, and ensure its environmental sustainability. The primary objective of this study is to employ side scan sonar technology to classify and assess the riverbed of Woji Creek in Port Harcourt, Nigeria. The study aims to classify the riverbed, analyze water depth variations, evaluate navigational suitability, and determine turbidity levels within the creek. To achieve these objectives, the methodology involved acquiring Side-Scan Sonar (SSS) and Sub-bottom profile data. These datasets underwent backscatter processing to create geocoded backscatter images. Feature points were extracted and matched from these images to derive riverbed classification, depth categories, water volume distribution, and river turbidity analysis. The riverbed classification revealed the presence of three primary sediment types: Clayey Silty Sand, Silty Clay, and Silty Sand, each with distinct implications for navigation. Shallow, Moderate, Deep, and Very Deep areas were identified within Woji Creek, each influencing navigational conditions. Additionally, the water volume distribution analysis provided essential insights into depth limitations and route planning.
 Moreover, the assessment of river turbidity identified low, moderate, and high turbidity zones, reflecting water clarity and suspended particle levels. These findings serve as invaluable decision support tools for navigation planning and management in Woji Creek, offering comprehensive insights into the riverbed, depth suitability, volume distribution, and water quality. Leveraging this data can enhance strategic decision-making processes and contribute to the sustainable management of this vital waterway.

Hydrothermal amorphous silica, barite and orpiment from the crater area of seamount (SM-13) off Nicobar island, Andaman sea: Indications for the development of a new hydrothermal field

The Andaman sea characterized by trench-arc-backarc elements (Andaman-Nicobar island-arc, the Andaman back-arc spreading center, the seamount complex, and the back-arc basin) is a complex active basin and is known for hydrothermal activity in some of the seamounts (subaerial and submarine) of the volcanic arc. In the present study, 13 submarine seamounts (SM1- SM13) in the southern Andaman volcanic arc, extending from 6°47′N: 94°43′E to 7° 56′ N: 94° 2.47′E, were surveyed onboard RV Sindhu Sadhana (November 2021) to find the evidences for the hydrothermal activity. Out of the 13 seamounts, at one crater seamount (SM-13) we have observed evidence for hydrothermal activity characterized by plumes rich in dissolved gases (mainly CO2) in the water column, live chemosymbiotic organisms (Bathymodiolus species), and neoforming minerals such as amorphous silica, barite and orpiment. We observed two plumes rich in dissolved gases (mainly CO2), called GP1 and GP2, in the water column at two different water depths i.e. 400 and 380 mbsl respectively. Geochemical analysis of the water samples shows enhanced TCO2 concentrations within the plumes rich in dissolved gases (mainly CO2) observed in sub-bottom profiler data, however, the dissolved methane concentrations do not show any enrichment when compared with ambient seawater concentrations. Apart from the enhancement in the TCO2 concentrations, pH and total alkalinity data also show fluctuations within the same depth zone which may be attributed to the hydrothermal plume exhausting from the crater seamount. The occurrence of live chemosymbiotic organism Bathymodiolus species indicate an active and continuous supply of H2S. The precipitation of neoforming hydrothermal minerals such as amorphous silica, tabular barite, and orpiment on the surface of the rock samples further supports the hydrothermal activity. Previous studies carried out in 2007 have reported hydrothermal ferromanganese oxides precipitated from low-temperature hydrothermal fluids (Surya prakash et al., 2012) and inferred SM-13 as a dormant submarine volcano (Kamesh Raju et al., 2012). However, after 14 years, we observe volatile emissions to the water column, hydrothermal mineral precipitation and live chemosymbiotic organisms from the same seamount. These observations of the present study infer development of a new hydrothermal field in the least explored Andaman Sea. This study adds up a new active site to the global hydrothermal inventory which may allow better estimation of global hydrothermal flux and its role in oceanic elemental cycle.

Pseudo-3D cubes from densely spaced subbottom profiles via projection onto convex sets interpolation: An open-source workflow applied to a pockmark field

High-resolution subbottom profiler (SBP) data are commonly recorded during academic or industrial surveys and analyzed as 2D profiles. However, there is growing interest in 3D imaging of the shallow seafloor subsurface, e.g., site surveys prior to the installation of offshore wind farms. Despite ongoing advancements in 3D systems, SBPs continue to be used mainly for 2D profiling. In other seismic imaging applications, “pseudo-3D” seismic cubes have been successfully generated from dense 2D seismic surveys. We developed a novel open-source Python-based workflow to interpolate densely spaced 2D SBP profiles acquired with a hull-mounted parametric SBP into pseudo-3D cubes. This workflow is applied to a study area on the Chatham Rise east of New Zealand’s South Island, comprising numerous seafloor pockmarks and subsurface paleo-pockmarks. Our workflow consists of two stages: (1) processing of individual 2D profiles to compensate for existing vertical offsets and (2) sparse data interpolation by applying the iterative projection onto convex sets algorithm. We correct the residual static effect caused by the sea state during acquisition, compensate for the varying tidal elevations, and apply vertical time shifts to individual profiles to correct misties at profile intersections. The interpolation of the binned sparse 3D cube is performed in the frequency domain using the fast Fourier transform and executed in parallel processes, which significantly increases the computational efficiency. We validate our workflow by testing different bin sizes, sparse transforms, thresholding approaches, and varying total iterations, which noticeably impact the resulting interpolation quality. Our developed workflow generates pseudo-3D subsurface images from densely spaced SBP profiles, with numerous potential applications for academic and industrial surveys.

Late Devensian to Holocene environmental change, Loch Lomond, UK: A seismic sedimentary record of deglaciation, paraglacial and postglacial landscape evolution

We present an interpretation of two-dimensional sub-bottom profiling data from Loch Lomond, Scotland, UK. Sediments deposited during and following the last glacier advance have been investigated for decades around the shores of Loch Lomond. For the first time, this study presents an interpretation of the subsurface providing a window into the late Quaternary and Holocene history of Loch Lomond and its surrounding. The seismic stratigraphy records the infill of the loch during the final stages of the Loch Lomond Stadial (LLS, 12.9–11.7 ka BP), through the Holocene and into the present day. Results reveal the presence of distinct seismic facies (SF) identifying four principal seismic horizons; SF-I, SF-II, SF-III, and SF-IV. The SF-I horizon represents the glaciated surface, interpreted as subglacial till (locally forming drumlins), glacial moraines or bedrock. Ice retreat was accompanied by glaciolacustrine sedimentation in a proglacial lake setting, depositing up to 44 m of laminated sediments and ice marginal fans (SF-IIa, b). A period of landscape instability followed with extensive deposition of mass transport deposits (SF-III). These deposits, characterised by chaotic seismic facies with an erosional basal surface, are up to 43 m thick and may represent up to 50 % of the sediment fill. SF-IV comprises finely laminated sediments deposited during the Holocene and highlights slower sedimentation rates in comparison to earlier phases of sedimentation. This study reveals new insights into the deglaciation of Loch Lomond, including previously unrecognised extensive mass transport deposits buried in the subsurface, associated with a period of paraglacial adjustment.

Developmental history of a newly discovered chain of paired mound and depression structures on the southwestern continental shelf of the Ulleung Basin, East Sea, Korea

A chain of paired mound and depression structures are presented in the southwestern continental shelf of the Ulleung Basin, East Sea, Korea. We integrate multibeam bathymetry to identify topographic features, sub-bottom profile and multi-channel seismic reflection data to confirm geological features, and piston cores to understand the sediments of the mounds and depressions. Paired structures occur with a northwest–southeast orientation at water depths between 130 and 150 m and have similar scales of 10–20 m in height and depth. The mounds consist of cold-water corals and authigenic carbonate with shelly sand, whereas, the surficial lithology of depressions are only composed of siliciclastic deposits. The mounds appeared to have grown from the depression based on the observation for morphological features in the cross-section profiles of the paired mound and depression structures. Seismic profiles show acoustic blanking anomalies and seismic chimneys, indicating that the topographic relief formed under the influence of gas seepage. The petrological and geochemical signature of carbonate chunks also displayed gas leak effects different from CWC. This study suggests a developmental history model with paired mound and depression structures, in which gas/fluid escape causes depressions and the selective coral growth creates mounds growing on one side of these depressions. The mounds had sufficiently grown, depressions would have been further developed in interaction with the bottom current.

Volcanic evolution of an ultraslow-spreading ridge

Nearly 30% of ocean crust forms at mid-ocean ridges where the spreading rate is less than 20 mm per year. According to the seafloor spreading paradigm, oceanic crust forms along a narrow axial zone and is transported away from the rift valley. However, because quantitative age data of volcanic eruptions are lacking, constructing geological models for the evolution of ultraslow-spreading crust remains a challenge. In this contribution, we use sediment thicknesses acquired from ~4000 km of sub-bottom profiler data combined with 14C ages from sediment cores to determine the age of the ocean floor of the oblique ultraslow-spreading Mohns Ridge to reveal a systematic pattern of young volcanism outside axial volcanic ridges. Here, we present an age map of the upper lava flows within the rift valley of a mid-ocean ridge and find that nearly half of the rift valley floor has been rejuvenated by volcanic activity during the last 25 Kyr.

Island formation adjacent to a large-scale slope failure in Central Peru: The Nazca Ridge subducted relief hypothesis

Vertical tectonics and mass wasting activity along convergent margins are geodynamic processes commonly associated with the subduction of oceanic plate structures. At the Central Peruvian margin, the connection of the small Hormigas de Afuera Islands (HAI) (12°S) with a large-scale slope failure suggests the surficial expression of the subducted relief of the Nazca Ridge. This hypothesis is supported by the idea that the Tuamotu Ridge relief on the Pacific Plate is the analog of the subducted roughness of the Nazca Ridge based on their mirror-image location relative to the East Pacific Rise. Here, we use bathymetry, multichannel seismic data, subbottom profiling data and published findings to analyze the massive slope collapse near the HAI. At the shelf break, the HAI reflect uplift of the metamorphic basement and mark a N-S transition between post-Pliocene onlapping sediments and seafloor erosion of an uplifted, tectonically deformed sequence. W of the shelf break, the HAI scar is a trench-parallel, two-horseshoe-shaped escarpment in the upper slope (1300 m high and 1690 km2 area) that has lost mass with a total volume of 810 km3. Within this large escarpment, two cliffs show differences in size, seafloor morphology, and basement uplift. An embayment at the base of the HAI scar aligns with a downslope mass of 285 km3 volume in the middle slope. A bathymetric bulge of 800 m height characterizes the toe of this mass deposit. When the HAI are projected onto the Tuamotu Ridge northeastern flank, a seamount-shaped platform-like feature of 12,000 km3 is found. Our study area coincides with the well-known and highly coupled segment of the Central Peru subduction, which suggests an association with the history of large megathrust earthquakes in this area such as the great 1746 MW 8.8 Callao-Lima earthquake. Based on these findings, we postulate that the formation and spatial association of the small HAI with the HAI mass wasting result from the tectonic control imposed by the subducted roughness of the Nazca Ridge.

Sediments and bedforms of the Harle tidal inlet (Wadden Sea, Germany)

ABSTRACT The paper presents a map of sediment surface distribution and bedforms in the Harle tidal inlet, German Wadden Sea. Data collection, processing, and map editing were realized within the sublittoral mapping program of Lower Saxony national waters carried out by the NLWKN – Coastal Research Station. The map is the result of the combined use of multibeam echosounder, sub-bottom profiler, and ground-truth data. The sediment characterization is achieved by an unsupervised approach using an Object-Based Image Analysis (OBIA) on a normalized backscatter mosaic, verified by nineteen sediment samples. Morphometrical parameters and sub-bottom data provided important information to identify hard substrates and bedforms.

Application of acoustic classification in different sedimentary environments: A case study of the Gaoping slope in the southwest coast of Taiwan

• Acoustic remote sensing can be used to determine different types of sedimentary seabeds using quantitative classification. • Three attributes extracted from acoustic waveforms reveal four types of sedimentary seabeds. • The proposed method differentiates sedimentary seabed types with similar grain size distribution. • Core data from the offshore area of southwestern Taiwan validates the method. • This study provides a sensitive and robust quantitative method and reduces the uncertainty of manual identification between different seabeds. The sedimentary seabed properties are direct indicators of its stability, whose measure has several important implications in understanding and forecasting geological events. This study investigates the classification of sedimentary seabed types in different depositional environments using the three attributes: reflection coefficient (RC), similarity index (SI), and amplitude ratio (AR) values extracted from sub-bottom profiling data. Four sedimentary seabed types were evaluated automatically according to the waveforms in the horizontal and vertical directions. To infer the seabed properties, the attribute SI is used to identify the occurrence of homogeneity of sediment transportation in an area, while RC and AR are used to determine the seabed characteristics in terms of the variation of acoustic energy reflected from the sediment. To validate the results of this quantitative analysis method, sixteen seafloor sediment samples collected at different sites in the offshore area of southwestern Taiwan were analyzed. The automatic classification results suggest that the different sub-bottom profiling images are associated with the grain size distributions and compositions, such as the concentrated distribution, sand, silt, and clay percentages, and the mean bulk density. In addition, an inhomogeneous environment with similar grain size distribution can be identified. The proposed seabed classification is an effective method to study seabed characteristics, especially for identifying chaotic sediments.

Creep characteristics of muddy submarine channel slope instability

Creep is an important factor of muddy submarine channel slope instability. In this study, a sub-bottom profiler was used to monitor the continuous internal change of a muddy submarine channel slope in the laboratory to better understand the creep characteristics and mechanism of slope instability. The creep process was analyzed according to changes in the slope internal sound intensity. The results indicate a notable change of the creep characteristics during the slope instability process. Changes in the sound intensity time series decrease with increasing slope depth, and the fluctuation depth of the vertical sound intensity series varies during the slope creep process. The creep process of slope instability can be roughly divided into four stages based on the sub-bottom profile data: an expansion stage; an unstable expansion stage; a fracture stage; and a post-fracture development stage. An adjustment of the sediment microstructure in the slope is ascribed to slope creep deformation. This study highlights the prospects of high-resolution acoustic monitoring to detect and quantify the entire creep process of muddy submarine channel slope instability, which is of great significance for the evaluation and early warning prediction of channel slope instability.