Technical Reports by Polina Lemenkova
Technical report, 2024
Seismographs have recorded ground motion since the end of the 19th century until digital recordin... more Seismographs have recorded ground motion since the end of the 19th century until digital recordings became available in the 1970s. Pre-digital seismic records were typically created by using ink on white paper, scratching black-smoked paper, or by using light on photographic paper. With most of these legacy seismic data now stored in archives and exposed to physical decay, several projects in the last 20 years started to dedicate resources to digitising them to preserve and exploit the unexplored scientific wealth they contain and, in turn, introduce them into the age of modern seismology. This effort has become increasingly important due to the increasing risk of permanently losing those ageing paper seismograms combined with their recently found exclusive potential in recovering the global oceanic climate for the last century. The Royal Observatory of Belgium (ROB) possesses a vast archive of legacy seismic data, some of which has recently been scanned. Our project used computer vision and recently developed machine learning approaches to digitise waveform data extracted from these scanned images. This process results in the creation of calibrated and time-coded seismic time series, which can subsequently be disseminated to the scientific community via international web services following seismic community-defined standards. By providing access to continuous seismic data spanning the past century following the FAIR principles (findability, accessibility, interoperability, and reusability), the project aims to facilitate the investigation of historical oceanic climates using seismic data and to improve the accessibility to tools necessary for the digitization efforts across various institutes, observatories, and universities. Furthermore, the broad availability of quantitative observational data from around the world will significantly enhance existing oceanic wave models of the 20th century, contributing to climate research. We meticulously compiled all the information on the seismic archive of the ROB, along with its metadata. Our decision to concentrate on Galitzin data was informed by the instruments' high response in the microseismic frequency band, rendering them ideal proxies for sea state analysis. We developed an algorithm to vectorize and extract digital seismic waveforms from scanned seismograms using traditional computer vision techniques, supplemented by a distinct module leveraging deep neural networks to address more complex scenarios, such as line inter-crossing induced by high-amplitude events like earthquakes. We also developed a tool to compare vectorized waveforms with theoretical microseismic ground motions derived from the WaveWatch III oceanic models, facilitating initial validation of the time series. The work conducted within this project is continually evolving to ensure its enduring utility for the widest possible audience. Furthermore, the project has made significant contributions to the broader scientific community through the establishment of working groups, participation in international initiatives, provision of training courses, and ongoing contributions to a book chapter.
Geomorphological landforms of the oceanic trenches, their formation and variation of the geometri... more Geomorphological landforms of the oceanic trenches, their formation and variation of the geometric shapes is a question of special importance to the scientific community in marine geology. The actuality of this question has significantly increased since the beginning of the rapid development of the IT tools and methods of the advanced data analysis, yet its understanding remains patchy. Since the majority of the oceanic trenches are located along the margins of the Pacific Ocean, it plays a central role for their analysis and understanding their formation oceanic trenches. Specific geological conditions, presence of the tectonic subduction zones, vast territory of the Pacific Ocean with complex circulation system, extension of the ’Ring of Fire’, a seismically active belt of the earthquakes and volcanic, make the trenches of the Pacific Ocean highly sensitive to the factors affecting their formation which cause variations in their geomorphic shape forms. In this context, the most representative indicators of the variations in the deep-sea trenches are geological and tectonic factors, such as dynamics of lithosphere crust affecting speed and intensity of plates subduction, magnitude and frequency of the submarine volcanoes causing active sedimentation. Nowadays, studying marine geological phenomena and complex processes by programming and scripting has been a powerful method. Rapid development of the advanced methods of data analysis presented such effective tools as GMT, Octave/MATLAB, R and Python. It is particularly efficient when applied to the massive amounts of marine geological data. Big data processing by advanced scripting is a crucial approach, as algorithms of libraries give access to the accurate and rapid data analysis. Specific information about distant and hard-to-reach deep-sea trenches can be gained for precise visualization and analysis of their submarine geomorphology from local to regional and global scales. However, there is a lack of uniformity in studying deep-sea trenches, a shortage of systematic mapping of the Pacific trenches and a lack of understanding of the geomorphological variation between the trench profiles in different parts of the ocean: southern and northern, eastern and western, and their response to the geological and tectonic local settings in the places of formation. Therefore, this study develops a systematic approach to monitoring and comparative analysis of the geomorphological shape forms of the deep-sea trenches formed under specific geological and tectonic conditions along the margins of the Pacific Ocean. The study area encompasses Pacific Ocean, and more specifically, includes 20 selected target trenches: Aleutian, Mariana, Philippine, Kuril-Kamchatka, Middle America, Peru-Chile, Palau, Japan, Kermadec, Tonga, Izu-Bonin, New Britain, San Cristobal, Manila, Yap, New Hebrides, Puysegur, Hikurangi, Vityaz and Ryukyu. These are the major trenches of the Pacific Ocean and, therefore, the most representative for the geomorphological modelling. This study identifies tectonic plates formation, slab subduction, historical geological development, earthquakes and submarine volcanoes as the primary types of impact factors affecting trenches formation. Secondary factors include ocean currents, sedimentation and biota contributing to the sedimentation. Seafloor geomorphology in hadal trenches is strongly affected by a variety of factors that necessarily affect the shape of their landforms. Using data modelling, the shapes of the profiles transecting the trenches in an orthogonal direction were compared and analyzed in order to highlight the differences and variations in their geomorphology. The objective of this study is to perform a geomorphological classification of the shape forms of the trenches through ordering them into groups based on the common characteristics of the trenches’ landforms in plan and attaching labels to these groups. Following geomorphological profile shape types have been identifies and trenches are classified into seven types: U-formed (in plan), V-formed (in plan), asymmetric, crescent-formed, sinuous-formed, elongated, cascade-formed. For each type (U, V, asymmetric and so on) characteristic steepness sub-types are identified: strong, very strong, extreme, steep, very steep. Valley slopes are classified as follows: very high, high, moderate, low, based on the curvature degree. Size and valley slope classes are analyzed in the context of physical environment and tectonic and geological development of the area of trench formation. Technical aim of this research was to experiment with and extend current methods of geospatial modelling for geomorphological classification of the submarine landforms of the trenches. Using methods of the advanced data analysis is crucial for the precise and reliable data processing, since understanding seafloor landforms can only be based on the computer-based data modelling due to their unreachable location. The selection of the methodology, tools and algorithms is explained by research objectives and goals. The specifics of the marine geology consists in the high requirements towards data processing. Datasets were processed, computed and analyzed in semi-automatic regime by Machine Learning (ML) approaches, using advanced algorithms of data analysis and effective visualization through application of the advanced programming tools and Generic Mapping Tools (GMT) scripting toolsets. This study presents an automated workflow enabling large-scale profile cross-sectioning aimed at transect geomorphological mapping, quantitative comparative analysis and classification of the 20 trenches of the Pacific Ocean. The methodology of the GMT includes algorithms of sequential scripting for the cartographic visualization and mapping, automatic digitizing of the cross-section transect profiles, and geomorphic modelling of the trenches. In total 50 modules of GMT scripting toolset were trained on extensive datasets collected from 20 trenches across the whole region of the Pacific Ocean. Using high-resolution bathymetric datasets (General Bathymetric Chart of the Oceans (GEBCO), ETOPO1 and Shuttle Radar Topographic Mission (SRTM)), sample transects of the trenches were modeled, analyzed and compared. Variations in shape forms, steepness and curvature were analyzed by computed models for each trench. The tables were converted from QGIS plugins to Python libraries and R packages, and from GMT to Octave via AWK languages. The results revealed significant variation in the shape and steepness of the submarine geomorphology in 20 trenches of the Pacific Ocean. A strong correlation between the geomorphic profile shapes with geological factors and level of tectonic activities (earthquakes, volcanism, speed of tectonic plate subduction) and the scale of trench steepness, curvature and shape unevenness is confirmed and analyzed. Geomorphological structure of the trenches and dynamics of the tectonic plates subduction are analyzed and assessed at each trench regionally (north, south, west and east Pacific). The novelty of the study consists in presented systematic classification and comparative modelling of the geomorphic profiles of the deep-sea trenches by means of the sequential usage of the advanced scripting toolsets. Technical innovativeness consists in a combination of GIS, GMT, Python, AWK, R. The actuality of this research consists in its strongly multi-disciplinary nature demonstrating a combination of the following approaches: 1) systematic multi-source geospatial data analysis; 2) statistical data modelling and processing by libraries of the Python and R, AWK and Octave/Matlab; 3) geological literature analysis; 4) cartographic mapping and modelling by GMT shell scripts and visualization in QGIS. The research contributes to the studies on the seafloor of the Pacific Ocean. Technical scripts used for advanced statistical analysis are presented in full in the Appendix A for future replication and reproducible analysis in other trenches of the world ocean.
The report presents an overview of the classification of morphological structures of the trenches... more The report presents an overview of the classification of morphological structures of the trenches of the Pacific Ocean, performed using advanced methods of data analysis, machine learning, modeling and mapping based on GMT. The study, aimed at analyzing the variability of morphological structure in the 20 deep-sea trenches of the Pacific Ocean, is an interdisciplinary approach that combines cartographic modeling and statistical data analysis.
Technical Report, 2006
This work presents the student technical report of the participant at Bathymetry group at the R/V... more This work presents the student technical report of the participant at Bathymetry group at the R/V ’Polarstern’ cruise, AWI. The expedition is organized to the western sector of Antarctica, the South Pacific (Bellingshausen Sea, Amundsen Sea). The main goal of the Bathymetry group was to conduct high-resolution multispectral surveys of the seafloor topography along the ship's route, map sampling points of the geological sampling, interpret gravimetric measurements and expand the World database of the seafloor mapping, in particular, updating seafloor topography data for an international map GEBCO. As a result of the work, the seafloor topography on selected areas of the Amundsen and Bellingshausen seas was surveyed and maped using Hydrosweep DS-2, Caris HIPS, GMT, ArcGIS. Technological workflow, research methodology and geological description of the study area are presented in the report. The report is written in Russian language.
Expeditionsprogramm, 2006
Gohl K., Uenzelmann-Neben G., Eagles G., Fahl A., Feigl T., Grobys J., Just J., Leinweber V., Len... more Gohl K., Uenzelmann-Neben G., Eagles G., Fahl A., Feigl T., Grobys J., Just J., Leinweber V., Lensch N., Mayr C., Parsiegla N., Rackebrandt N., Schluter P., Suckro S., Zimmermann K., Gauger S., Bohlmann H., Netzeband G., Lemenkova P. 2006. Deep crustal refraction and reflection seismics; Crustal & sedimentary structure & geodynamic evolution of the West Antarctic continental margin & Pine Island Bay. In: Berichte zur Polar- und Meeresforschung // Reports on Polar and Marine Research, 557: 117, p.20-30. ISSN: 1618-3193. Expeditionsprogram No75 of ANT-XXIII/4 Cruise. AWI fu ̈r Polar- und Meeresforschung, Bremerhaven, 11-12.
The reconstruction of the paleoclimatic and paleoceanographic development of the late Quaternary ... more The reconstruction of the paleoclimatic and paleoceanographic development of the late Quaternary south polar ocean and adjacent continental areas in high temporal and spatial resolution is the main goal of our long-term study. During this expedition the sedimentary budget of biogenic and terrigenous components and their variability will be investigated. One objective of this leg is to continue the studies of former expeditions to gather more detailed paleoceanographic information on the eastern Pacific sector of the Southern Ocean for reconstruction of the distribution of water masses, frontal systems and sea ice, as well as information on high export productivity areas and their impact on global climate evolution. Thus, it will help us to broaden our understanding of the impact of environmental processes in the Southern Ocean on global climate. The second objective is to investigate the response of the West Antarctic Ice Sheet (WAIS) to Quaternary climatic changes. This ice sheet represents the most instable portion of Antarctic ice. The distribution pattern of the WAIS and its development can be deciphered from the sediment deposition in the study area. Previous investigations indicated that the WAIS collapsed once or multiple times during the past 0.75 million years. However there are also controversial findings. Since marine-geological records of glaciomarine deposition proximal to the WAIS are sparse, the exact timing and boundary conditions for such an event, which would result in a rise of the sea level of 5-6 m, are not yet known. The reconstruction of environmental conditions based on a multiproxy approach (this includes the investigations of sediment composition, microfossil assemblages and isotopic measurement of biogenic components) and its stratigraphic dating should substantially add to the knowledge of the WAIS history and its stability during a possibly warmer climate in the future.
The RV Polarstern expedition ANTARKTIS-XXIII/4 (ANT-XXIII/4) began on 10 February 2006 from Punta... more The RV Polarstern expedition ANTARKTIS-XXIII/4 (ANT-XXIII/4) began on 10 February 2006 from Punta Arenas returning on 11 April 2006. The main goal of the expedition was to study glaciomarine sedimentation and the evolution of the tectonic-geodynamic setting of the southern Amundsen Sea and Pine Island bay. Crustal and sedimentary structures on the West Antarctic continental margin and Pine Island were surveyed using deep crustal refraction and reflection seismic geophysical methods.
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Technical Reports by Polina Lemenkova