SM2.4 | Ocean bottom seismology throughout the years: instrumentation, processing and interpretation
EDI
Ocean bottom seismology throughout the years: instrumentation, processing and interpretation
Convener: Maria TsekhmistrenkoECSECS | Co-conveners: Ana MG Ferreira, Janneke de LaatECSECS, Afonso LoureiroECSECS, Stephen Hicks
Orals
| Thu, 27 Apr, 16:15–18:00 (CEST)
 
Room -2.91
Posters on site
| Attendance Thu, 27 Apr, 08:30–10:15 (CEST)
 
Hall X2
Posters virtual
| Attendance Thu, 27 Apr, 08:30–10:15 (CEST)
 
vHall GMPV/G/GD/SM
Orals |
Thu, 16:15
Thu, 08:30
Thu, 08:30
The oceans cover about 71% of the Earth's surface, yet our current picture of the structure and dynamics of the oceanic crust and mantle is mainly based on seismic data recorded in islands or in the continents.

Detailed seismic observations of the sub-oceanic Earth’s interior require the use of ocean-bottom seismometers (OBS), but large OBS deployments - both in numbers of instruments and area covered - remain a major endeavour due to technical, logistical and financial challenges.

A zoo of OBS arrays and other passive ocean-bottom geophysics (e.g., geodesy, magnetotelluric) has been deployed in the last two decades, which led to fascinating new discoveries about the crust and mantle beneath the seafloor in many regions worldwide. Despite great technological advances and improved data processing procedures, some challenges persist.

OBS deployments and recovery are more demanding than anticipated by (first-time) PIs and consist of many challenges obscured by a lack of communication between scientists. Recurring issues include missing or erroneous response files or the challenge of systematically exploring the wealth of information recorded by the OBS datasets. Most processed data sets are not released for several years (if at all). This stagnates the exploration of OBS datasets in the community and reduces its usage to just a few research groups.

We invite contributions from the global ocean-bottom geophysics community to share knowledge, experience, lessons learned and scientific achievements from OBS experiments. We welcome reflections on all aspects, from early stage planning, different kinds of OBS or amphibian devices, experiment design, deployment and recovery tactics, pre- and post-data processing and analysis (e.g., software), to publishing data reports and final scientific outputs (e.g., tomography, receiver functions, ambient noise studies, earthquake source analysis, etc). We also encourage contributions beyond seismology, such as from seafloor environmental sensors (e.g., using submarine cables), magnetotellurics, geodesy, ocean acoustics and marine mammals studies.

Orals: Thu, 27 Apr | Room -2.91

Chairpersons: Maria Tsekhmistrenko, Ana MG Ferreira, Afonso Loureiro
16:15–16:20
16:20–16:40
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EGU23-4581
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ECS
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solicited
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Virtual presentation
Helen Janiszewski, Zachary Eilon, Joshua Russell, Brennan Brunsvik, James Gaherty, Stephen Mosher, William Hawley, and Sloan Coats

The proliferation of broadband ocean bottom seismometer (BBOBS) deployments over the last two decades has generated key datasets from diverse marine environments, improving our understanding of tectonics and earthquake processes. In turn, the community of scientists using this data has expanded. This growth in BBOBS data collection is likely to persist with the arrival of new seismic seafloor technologies, and continued scientific interest in marine and amphibious targets. However, the noise inherent in OBS data poses a challenge that is markedly different from that of terrestrial data. As a step towards improved understanding of the sources of variability in this noise, we present a new compilation and analysis of BBOBS noise properties from 15 years of US-led seismic deployments. We find evidence for similarity of noise properties when grouped across a variety of parameters, with groupings by seismometer type and deployment water depth yielding the most significant and interpretable results. Instrument design, that is the entire deployed package, also plays an important role, although it strongly covaries with seismometer and water depth. We find that the presence of tilt noise is primarily dependent on the type of seismometer used (covariant with a particular subset of instrument design), that compliance noise follows anticipated relationships with water depth, and that shallow, oceanic shelf environments have systematically different microseism noise properties (which are, in turn, different from instruments deployed in shallow lake environments). We discuss implications for the viability of commonly used seismic analysis techniques, and future directions for improvements in the efficiency of analysis of BBOBS data.

How to cite: Janiszewski, H., Eilon, Z., Russell, J., Brunsvik, B., Gaherty, J., Mosher, S., Hawley, W., and Coats, S.: Understanding Broadband Ocean Bottom Seismometer Noise: Fresh Insights and Future Directions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4581, https://doi.org/10.5194/egusphere-egu23-4581, 2023.

16:40–16:50
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EGU23-8267
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On-site presentation
Frederik J. Simons, Sirawich Pipatprathanporn, Joel D. Simon, and Jessica C. E. Irving

Since the launch of the first third-generation MERMAID in 2018, sixty-seven autonomous freely-drifting mid-column hydrophones have been afloat in the Pacific Ocean,  the South China Sea, and the Mediterranean. Over fifty-five instruments remain alive and well, and are continuing to report short, triggered, waveform segments of acoustic pressure variations, with six instruments directly reporting acoustic spectral densities. A new model equipped with a conductivity-temperature-depth (CTD) sensor is due for deployment (four new units). Over these last few years, many thousands of teleseismic arrival-times have been reported, and associated with global earthquake catalogs, so that their travel-time residuals with respect to global reference models can be determined in view of making tomographic models, especially of the area around French Polynesia, the original launch focus of the EarthScope-Oceans (ESO) fleet. The data stream has been flowing into the EarthScope (IRIS) data management center (DMC), and reporting short segments around first-arriving phases and the calculation of travel-times have become routine applications.

We briefly review those successes, but we focus on the latest data types (spectral densities computed in-situ rather than time-domain seismograms transmitted via satellite), on the codesign of MERMAID as an acoustic float with an environmental CTD sensor, on the latest modeling efforts at matching waveforms with synthetically computed pressure seismograms, and on the rich set of continuous records that were requested from MERMAID's one-year buffer in the hours and days immediately following the Hunga Tonga Hunga Ha'apai eruption, recorded by over twenty instruments over a wide epicentral distance and backazimuthal range.

Waveform modeling was not a design goal for MERMAID, but we discuss an innovative approach to circumvent the computational burden involved in matching the global earth ocean-bottom response to teleseismic earthquakes (computed using an axisymmetric spectral-element code) to the local oceanic mid-column pressure response, including the effects of bathymetry (computed using a local two-dimensional spectral-element modeling step). We applied our method, which is based on precomputed Green's functions via the publicly available code Instaseis and on a custom data base of ocean-floor-to-water-column response functions computed using SPECFEM-2D, to a set of over one thousand waveforms, after dynamically selecting the optimal bandwidth based on adaptive signal-to-noise considerations to steer clear of the noise generated by the ocean wave heave. The correlation between synthetics and observations is as high as 0.98, with a median of 0.72, and very coherent across the array, allowing for the determination of cross-correlation travel times and opening up MERMAID seismograms to conduct full-waveform tomography of Earth's mantle.

Similarly, volcanic monitoring was not a design goal for MERMAID, but in recovering, on-demand, the many hours of continuous records of the Hunga Tonga Hunga-Ha`apai eruption, we have obtained a unique data set from which are piecing together a detailed picture of the eruption sequence. We discuss signal correlations and disparities within and across the South Pacific Plume Imaging and Modeling (SPPIM) array, and address, in particular, path-dependent effects due to "bathymetric occlusion", the influence of seafloor topography on the coherent propagation of hydroacoustic energy over large distance ranges.

How to cite: Simons, F. J., Pipatprathanporn, S., Simon, J. D., and Irving, J. C. E.: MERMAID Tales: Travel-Times, Waveform Modeling, Infrasonic Spectral Densities, and Volcanic Eruptions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8267, https://doi.org/10.5194/egusphere-egu23-8267, 2023.

16:50–17:00
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EGU23-15012
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ECS
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On-site presentation
David Naranjo, Laura Parisi, Sigurjón Jónsson, Philippe Jousset, Dieter Werthmüller, and Cornelis Weemstra

The timing of the recordings of ocean-bottom seismometers (OBSs) is critical for accurate earthquake location and Earth model studies. GNSS signals, however, cannot reach OBSs deployed at the ocean bottom. This prevents their clocks from being synchronized with a known reference time. To overcome this, we developed OCloC, a Python package that uses time-lapse cross-correlations of ambient seismic noise to synchronize the recordings of large-scale OBS deployments. By simultaneously quantifying deviations from symmetry of a set of lapse cross-correlations, OCloC recovers the incurred clock errors by means of a least-squares inversion. In fact, because non-uniform noise illumination patterns also break the symmetry of (lapse) cross-correlations, we introduce a distance-based weighted least-squares inversion. This mitigates the adverse effect of the noise illumination on the recovered clock errors. Using noise recordings from the IMAGE project in Reykjanes, Iceland, we demonstrate that OCloC significantly reduces the time and effort needed to detect and correct timing errors in large-scale OBS deployments. In addition, our methodology allows one to evaluate potential timing errors at the time of OBS deployment. These might be caused by incorrect initial synchronization, or by rapidly changing temperature conditions while the OBS is sunk to the sea bottom. Our work advances the use of OBSs for earthquake studies and other applications.

How to cite: Naranjo, D., Parisi, L., Jónsson, S., Jousset, P., Werthmüller, D., and Weemstra, C.: Determining clock errors of ocean-bottom seismometers: an ambient-noise based method designed for large-scale ocean bottom deployments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15012, https://doi.org/10.5194/egusphere-egu23-15012, 2023.

17:00–17:10
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EGU23-12825
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On-site presentation
Thomas Bornstein, Dietrich Lange, Jannes Münchmeyer, Jack Woollam, Andreas Rietbrock, Grace Barcheck, Ingo Grevemeyer, and Frederik Tilmann

Detecting phase arrivals and pinpointing the arrival times of seismic phases in seismograms is crucial for many seismological analysis workflows. For land station data machine learning methods have already found widespread adoption. However, deep learning approaches are not yet commonly applied to ocean bottom data due to a lack of appropriate training data and models. Here, we compiled a large and labeled ocean bottom seismometer dataset from 15 deployments in different tectonic settings, comprising ∼90,000 P and ∼63,000 S manual picks from 13,190 events and 355 stations. We adapted two popular deep learning networks, EQTransformer and PhaseNet, to include hydrophone recordings, either in isolation or in combination with the three seismometer components, and trained them with the waveforms in the new database. The performance is enhanced by employing transfer learning, where initial weights are derived from models trained with land earthquake data. Our final model, PickBlue, significantly outperforms neural networks trained with land stations and models trained without hydrophone data. The model achieves a mean absolute deviation (MAD) of 0.06 s for P waves and 0.10 s for S waves. We integrate our dataset and trained models into SeisBench to enable an easy and direct application in future deployments.

How to cite: Bornstein, T., Lange, D., Münchmeyer, J., Woollam, J., Rietbrock, A., Barcheck, G., Grevemeyer, I., and Tilmann, F.: PickBlue: Seismic phase picking for ocean bottom seismometers with deep learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12825, https://doi.org/10.5194/egusphere-egu23-12825, 2023.

17:10–17:20
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EGU23-11602
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ECS
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Virtual presentation
Roberto Cabieces, Andres Olivar-Castaño, Thiago C. Junqueira, Jesús Relinque, Jiří Vackár, Cristina Palacios, and Katrina Harris

Integrated Seismic Program (ISP) is a graphical user interface designed to facilitate and provide a user‐friendly framework for performing diverse common and advanced tasks in seismological research. ISP is composed of six main modules for earthquake location, time–frequency analysis and advanced signal processing, implementation of array techniques, seismic moment tensor inversion, receiver function computation and and a new module for ambient noise tomography.

Recently the Ambient Noise Tomography module has been upgraded with a tool specifically designed to synchronize Ocean Bottom Seismometers (OBSs) and to denoise the OBSs seismogram of the vertical component from tilt and compliance noise. The new tool has extensively been tested with data from UPFLOW project (https://upflow-eu.github.io).

In addition, several support tools are available, allowing the user to create an event database, download data from International Federation of Digital Seismograph Networks services, inspect the background noise, and compute synthetic seismograms.

ISP is written in Python3, supported by several open‐source and/or publicly available tools. Its modular design allows for new features to be added in a collaborative development environment.

How to cite: Cabieces, R., Olivar-Castaño, A., C. Junqueira, T., Relinque, J., Vackár, J., Palacios, C., and Harris, K.: Integrated Seismic Program (ISP): A New Python GUI‐Based Software for Earthquake Seismology and Seismic Signal Processing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11602, https://doi.org/10.5194/egusphere-egu23-11602, 2023.

17:20–17:30
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EGU23-5724
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ECS
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Virtual presentation
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Susana Gonçalves, Philippe Schnürle, Marina Rabineau, Alexandra Afilhado, and Maryline Moulin

We image the Moho discontinuity and deeper crustal layers by applying the Reverse Time Migration (RTM) method to wide-angle seismic (WAS) data that were acquired along two different profiles in the NW and SE offshore Brazil. The application of this method is quite uncommon to ocean bottom seismometers (OBS) data due to the OBS wide spacing deployment and low folds. Also, we applied the method to each OBS without making any assumptions on the type of propagation generated inside the model. The long offset of the refractions obtained, allows us to image deeper crustal layers.

Being able to obtain an image of these deeper layer is useful when MCS streamer data are not available or, even when they are, do not image the same depths.

We analyze the effectiveness of the RTM method when applied to the reflectivity of the WAS data. We can image the structures by cross-correlating the forward and backward wavefields given by the acoustic seismic equation. This allows us to use each interface crossed by a ray as a source but also as a receiver.

The velocity models used to perform RTM were previously obtained by applying a procedure of two-dimensional forward ray-tracing followed by a damped least-squares travel time inversion.

The results obtained have an unexpected large contribution from the wavefield traveling as refractions within the earth. We obtain strong and continuous refractors for depths that correspond to the basement and the Moho discontinuity. As we move inland, the refractors that correspond to the Moho discontinuity disappear due to the move of this discontinuity to deeper depths. 

The obtained results are promising for a wide range of applications at a crustal scale seismic exploration, with wide-angle seismic data.

Funding: This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL

How to cite: Gonçalves, S., Schnürle, P., Rabineau, M., Afilhado, A., and Moulin, M.: Reverse Time Migration of offshore wide-angleseismic data: an efficient method to image deep crustal structures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5724, https://doi.org/10.5194/egusphere-egu23-5724, 2023.

17:30–17:40
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EGU23-8862
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ECS
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On-site presentation
Yann-Treden Tranchant, Valérie Ballu, Denis Dausse, and Laurent Testut

Ocean bottom pressure (OBP) records are an important source of information for monitoring seafloor motion due to tectonic and magmatic processes, such as earthquakes and volcanic eruptions, at a centimeter-level precision. Although centimeter-level resolution is commonly accessible with high-resolution sensors;  monitoring seafloor deformation of a few centimeters through time with OBPs is challenging due to the instrumental drift and the existence of oceanic variations at different timescales.

In the context of the Mayotte volcanic crisis, which occurred in the western Indian Ocean in 2018 and was characterized by a series of more than 10,000 small-magnitude earthquakes and a subsidence of tens of centimeters (Peltier et al., 2022), three RBR Ambient-Zero-Ambient (A0A) drift-controlled pressure gauges were consecutively deployed in 2020, 2021 and 2022 for seafloor vertical deformation monitoring. The A0A system allows the in-situ estimation of the instrumental drift  by periodic venting from ocean pressures to a reference atmospheric pressure (Wilcock et al., 2021). Since no significant vertical ground displacements are recorded by ground GNSS stations since 2020, the overall objective of this study is to assess the calibration method of these innovative pressure gauges, reduce the oceanic “noise” in corrected OBP records and thus discuss our ability to observe any seafloor deformation in the Mayotte region.

To do so, we investigated the use of numerical models, including available global ocean circulation reanalyses (OGCMs) and barotropic simulations, in order to better understand the relative influence of each processes evolving at different timescales, to reduce the oceanic “noise” in drift-corrected OBP records and thus improve our ability to derive accurate estimates of seafloor motion in the Mayotte region. In addition, we exploited temperature and salinity collected by repetitive glider transects to validate OGCMs in the region and quantify the contribution of unresolved fine-scale processes, such as sub-mesoscale eddies, to OBP records. 

Our results provide valuable insights into the feasibility of using numerical modeling for improving the accuracy of OBP-based monitoring in the context of the Mayotte seismic crisis as well as for other seafloor deformation monitoring. It also has important implications for future A0A deployments and in the perspective of the planned MARMOR seafloor cabled observatory.

References 

Peltier, Aline, et al. "Ground deformation monitoring of the eruption offshore Mayotte." Comptes Rendus. Géoscience 354.S2 (2022): 1-23.

Wilcock, W. S., Manalang, D. A., Fredrickson, E. K., Harrington, M. J., Cram, G., Tilley, J., ... & Paros, J. M. (2021). A thirty-month seafloor test of the A-0-A method for calibrating pressure gauges. Frontiers in Earth Science, 8, 600671.

How to cite: Tranchant, Y.-T., Ballu, V., Dausse, D., and Testut, L.: Observability of Seafloor Deformation in OBP Records: an A-0-A Experiment in the Context of the Mayotte Volcanic Crisis, Using Ocean Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8862, https://doi.org/10.5194/egusphere-egu23-8862, 2023.

17:40–17:50
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EGU23-10225
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On-site presentation
Hongfeng Yang, Gaohua Zhu, Han Chen, and Aqeel Abbas

The Challenger Deep in the Southern Mariana subduction zone has attracted enormous attention of scientific investigators and explorers during recent decades. Since late 2016, near-field active and passive source seismic experiments has been carried out in the region by deploying Ocean Bottom Seismographs (OBS) in various terms. Both active and passive source tomographic images clearly indicate a well hydrous incoming plate, which is consistent with the observed pervasive normal faults in the out-rise region. Numerous earthquakes have been detected from the OBS recordings, and their locations delineate the subducting plate as well as deep out-rise faults, showing significant along-trench variations. Earthquake clusters are also found beneath the southwestern Mariana Rift and diminish sharply in the north. In addition to the scientific findings, we have discovered unexpected problems with the OBS data, particularly on the timing accuracies that are crucial on seismic records. To fix the various timing problems, we develop a framework of integrating travel times of teleseismic earthquakes and ambient noise cross correlations in different time segments. Such a framework could be applied on other OBS dataset suffering from irregular timing problems.

How to cite: Yang, H., Zhu, G., Chen, H., and Abbas, A.: Outcome and lessons from the Southern Mariana Ocean Bottom Seismic Experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10225, https://doi.org/10.5194/egusphere-egu23-10225, 2023.

17:50–18:00
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EGU23-9886
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On-site presentation
Nicholas Rawlinson, Tom Winder, Hrvoje Tkalcic, Joann Stock, and Mike Coffin

The Macquarie Ridge Complex (situated on the Australian – Pacific plate boundary, in the southwest Pacific Ocean) constitutes a unique geological site, being the only location on Earth where ‘normal’ oceanic crust protrudes above sea level within the ocean basin in which it formed. This raises fundamental questions, including what facilitates the obduction of oceanic crust in this locality (crucial for fully understanding the context around much-studied ophiolite complexes such as the Samail, Oman), and the conditions which led to the largest strike-slip earthquake of the 20th Century (Mw 8.2; May 23 1989).

To begin to answer these questions, an array of broadband ocean-bottom and land seismometers was deployed on and around Macquarie Island between October 2020 and February 2022. In this presentation, we summarise the data that were collected – and challenges faced – and show a preliminary catalogue of microseismicity for the duration of the deployment, generated using QuakeMigrate software. QuakeMigrate uses a waveform-based approach to earthquake detection and location, with advantages including improved performance in the presence of heterogeneous noise sources, during intense seismic swarms with small inter-event times, and in automating the processing of large quantities of continuous seismic data. Sophisticated time-domain algorithms allow us to maintain an appropriate detection threshold despite strongly varying noise levels (in the world’s stormiest ocean), varying numbers of operational stations, and in the presence of significant clipping issues on the ocean-bottom instruments’ horizontal channels.

We search for temporal variations in earthquake rates, and compute relative relocations (using GrowClust software) to produce high-resolution images of the faults on which the seismicity occurs. These results are interpreted in the context of the location of the most recent large earthquakes on this segment of the plate boundary, and together with complementary geophysical parameters including geodetic measurements and submarine and subaerial fault mapping.

How to cite: Rawlinson, N., Winder, T., Tkalcic, H., Stock, J., and Coffin, M.: Microseismicity of the Macquarie Ridge Complex, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9886, https://doi.org/10.5194/egusphere-egu23-9886, 2023.

Posters on site: Thu, 27 Apr, 08:30–10:15 | Hall X2

Chairpersons: Maria Tsekhmistrenko, Afonso Loureiro, Stephen Hicks
X2.95
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EGU23-11372
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Laura Parisi, Nico Augustin, P. Martin Mai, and Sigurjón Jónsson

The Red Sea (RS) is an ideal natural laboratory to study the transition from continental rifting to seafloor spreading because it is one of the youngest rift basins on Earth. The RS is an ultra-slow spreading rift with an opening rate that decreases from 15 mm/yr in the south, at the Nubian-Arabian-Danakil triple junction, to 7 mm/yr in the north where it connects to the Dead Sea transform fault. While the southern RS has a well-developed seafloor spreading ridge with an axis parallel to the rift bounding faults, images of the northern RS seafloor provide limited information because of thick evaporite layers covering the main tectonic features. Nevertheless, the northern rift axis is geometrically different as it is more oblique to the bounding faults than in the south. Furthermore, the transition between the southern and northern RS is sharp with a ~100 km rift axis offset, named Zabargad Fracture Zone (ZFZ). However, the current knowledge of the seismic activity, transform fault configuration, and the crustal and upper mantle structure of the ZFZ area is too limited to assess the seismic hazard associated with this rift offset and understand the role of the ZFZ in the RS development.

To fill this gap, we deployed the first broadband seismic network in the Red Sea, within the ZFZ, from November 2021 to November 2022. This network included 12 Lobster OBSs from the DEPAS pool (equipped with Güralp CMG-40T-OBS sensors), 2 additional Trillium Compact sensors deployed directly on the seafloor mounted on minimalist frames through a collaboration with the company Fugro, as well as 2 Trillium Compact Horizon and 2 posthole sensors deployed on islands and inland in Saudi Arabia, respectively.

The overall data recovery rate is above 90%. Also, our preliminary data analysis confirms some of the known issues of the Lobster OBSs and their sensors (strong self-noise at periods >10 s of the Güralp sensors and high-frequency harmonic noise due to head-buoy cable strumming). Furthermore, we conducted a systematic comparison of the noise recorded by different station configurations. We find that while Lobster OBSs with a head-buoy cable set free to strum generate strong noise at about 10 Hz and its overtones, Lobster OBSs with tight cable still display harmonic noise from 10 to 40 Hz that increases during bad weather conditions, probably due to resonance of other OBS elements. The Fugro OBSs, despite their minimalist deployment setup, show noise at 40 Hz that also resonates in bad weather. All the OBSs also display a peak of noise between 0.5 and 5 Hz (separated from the secondary microseismic peak). While such a noise peak is not recorded by the inland stations, it is well exhibited by the two island stations suggesting that this is due to locally ocean-generated seismic waves, but not by the OBS frames. At periods >10 s, the Fugro OBSs perform as well as the island and inland stations. In fact, waveforms of teleseismic earthquakes recorded by the Fugro OBSs and island and inland stations have comparable signal-to-noise ratios.

How to cite: Parisi, L., Augustin, N., Mai, P. M., and Jónsson, S.: The first network of Ocean Bottom Seismometers in the Red Sea to investigate the Zabargad Fracture Zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11372, https://doi.org/10.5194/egusphere-egu23-11372, 2023.

X2.96
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EGU23-10019
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Highlight
Ana MG Ferreira and Miguel Miranda and the UPFLOW team

Deep upward mantle flow is key to bring volatiles to the atmosphere and to produce Earth’s largest melting events extending through hundreds of thousands of kilometres, which coincide with major extinctions and changes in the geodynamo. Without knowing upward flow, we cannot understand global mantle flow and directly link the Earth’s interior with the surface. Yet, while downward flow (at subductions zones) is well constrained by seismology, plume-like mantle upwellings that connect the deepest mantle to the surface are poorly understood. The goal of the UPFLOW project (https://upflow-eu.github.io/) is to develop new high-resolution seismic imaging approaches along with new data collection, and to use them to constrain upward flow in unprecedented detail. We conducted a large amphibian experiment in the Azores-Madeira-Canary Islands region, which is a unique natural laboratory with multiple upwellings that are poorly understood in general. UPFLOW deployed 50 and recovered 49 ocean bottom seismometers (OBSs) in a ~1,000×2,000 km2 area in the Azores-Madeira-Canary Islands region starting in July 2021 for ~13 months, with an average station spacing of ~150-200 km. These data will be combined with land data from over 30 seismic stations in nearby islands. The seismic deployment and recovery involved institutions from five different countries: Portugal (IPMA, IDL, Univ. of Lisbon, ISEL), Ireland (DIAS), UK (UCL), Spain (ROA) and Germany (Potsdam University, GFZ, GEOMAR, AWI). In addition to its scientific component, the experiment also had a substantial science outreach component, with participation from children from primary schools in the UK, Germany, Portugal, Spain and Ireland, facilitated by UCL’s GeoBus project. We discuss some of the activities conducted, such as the children’s naming of the OBSs, their drawings on how they imagined the OBSs, their stories on what may have happened to the OBSs during the experiment and zoom sessions including live calls to the ship. Names chosen included Neptune, Triton, Jelly, Caesar and Thor. The deployment (28 days offshore) and recovery (35 days offshore) of the OBS instruments was carried out during two dedicated expeditions with IPMA’s research vessel NI Mário Ruivo with the strong support of its skilled and highly motivated crew. 32 OBSs were loaned from the DEPAS international pool of instruments maintained by the Alfred Wegener Institute (Bremerhaven), Germany, while other institutions borrowed additional instruments (7 from DIAS, 4 from IDL, 3 from ROA, 4 from GEOMAR). Most of the instruments have three-component wideband seismic sensors and hydrophones, but three different designs of OBS frames were used. Initial data analysis shows high-quality data, notably a substantial decrease in noise levels in the vertical component long-period data (T>~30s). We show illustrative recordings of teleseismic events, a local seismic swarm, and long-period seismic signals as well as of non-seismic signals such as whales vocalisations and ships’ noise. We discuss the lessons learned from our international collaborative expedition, as well as possible future directions. 

How to cite: Ferreira, A. M. and Miranda, M. and the UPFLOW team: The UPFLOW experiment: peeking from the sea floor to the deep mantle with a ~1,500 km aperture array of 49 ocean bottom seismometers in the mid-Atlantic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10019, https://doi.org/10.5194/egusphere-egu23-10019, 2023.

X2.97
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EGU23-5928
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ECS
Afonso Loureiro, Carlos Corela, Maria Tsekhmistrenko, Miguel Miranda, and Ana Ferreira and the UPFLOW Team

Currently, Ocean Bottom Seismometers (OBS) have sensors comparable to those used on land stations. However, they are exposed to very different conditions that degrade the recordings. One major issue is being directly exposed to global and tidal oceanic currents that, depending on the water velocity flowing around the instrument, can excite parts of the frame or produce drag and lift effects due to vortex shedding. Any of these conditions is detrimental for signal integrity, either from variations of the instrument-to-ground coupling or by introducing unwanted energy that is unrelated with the seismic events the experiment is aimed at.

The UPFLOW project is aimed at understanding mid-plate, deep upward flow that cannot be explained by plate tectonics, but is critical for continental growth, for returning volatiles to the atmosphere and for producing Earth’s largest melting events. For this reason, 50 OBS of different types were deployed for a year in the North Atlantic Ocean, including several prototypes aimed at reducing the tidal-induced noise generated by water flowing around the instrument's frame.

In this work, we show the seasonal variation of the tidal-induced noise on different instrument types across the Madeira and Seine abyssal plains of the North Atlantic Ocean during neap and spring tides between July 2021 and July 2022. In some instances, where harmonics are detected, individual frame components of the OBS can be identified as a major contributor, paving way to finding mitigation solutions on future deployments.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020.

How to cite: Loureiro, A., Corela, C., Tsekhmistrenko, M., Miranda, M., and Ferreira, A. and the UPFLOW Team: Seasonal changes on tidal-induced noise on long-term OBS deployment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5928, https://doi.org/10.5194/egusphere-egu23-5928, 2023.

X2.98
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EGU23-8108
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ECS
Maria Tsekhmistrenko, Roberto Diaz, Katrina Harris, Frederik Tilmann, Frank Krüger, Ana Ferreira, and Miguel Miranda and the UPFLOW Team

We present preliminary results from the UPFLOW (Upward mantle flow from novel seismic observations; https://upflow-eu.github.io/) project and associated large-scale amphibian experiment. The UPFLOW project, funded by the European Research Council (2021-2026), led a passive seismology large-scale experiment in the Azores-Madeira-Canary region starting in July 2021 and ending in September 2022. 

We recovered 49 (out of 50) OBSs deployed in a ~1,000×2,000 km2 area and with an average station spacing of ~150-200 km. Most instruments have three-component wideband seismic sensors (Trillium compact OBS version with a corner period of 120 s) and broadband hydrophones (type HTI-01 and HTI-04-PCA/ULF) with a corner period of typically 100 seconds. Three different designs of OBS frames were used LOBSTER, NAMMU and DUNE. We achieved data recovery rates of ~90-100% in 37 stations and ~50% in 6 stations, with only 7 stations being faulty, highly problematic or lost. 

We present various illustrative examples of seismic waveforms, spectrograms and data quality analysis from the recovered OBS data. Systematic probability power spectra density (PPSD) plots for all stations and over the whole deployment show a marked improvement in the quality of the long-period data (T>~30s) compared to previous experiments. 

We analyse the data performance as a function of the three models of OBS, recorder and seismometer types. Additionally, we present initial results from: (i) noise correlation analysis to quantify the clock skew during the deployment; (ii) estimation of horizontal component rotation angles from teleseismic data (body and surface waves); and, (iii) tilt and compliance analysis. 

Finally, we present an initial set of ~6000 multi-frequency body-wave travel time measurements generated with the UPFLOW OBS data and show a glimpse of preliminary body wave tomographic models built with this new dataset.

How to cite: Tsekhmistrenko, M., Diaz, R., Harris, K., Tilmann, F., Krüger, F., Ferreira, A., and Miranda, M. and the UPFLOW Team: UPLFOW ocean bottom seismometers data: preliminary performance report, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8108, https://doi.org/10.5194/egusphere-egu23-8108, 2023.

X2.99
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EGU23-1434
Investigation of Shallow Subsurface Stress State on the Accretionary Prism off Southwest Taiwan Using Ocean Bottom Seismometers
(withdrawn)
Win-Bin Cheng, Shu-Kun Hsu, and Jing-Yi Lin
X2.100
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EGU23-4854
Waveform similarity reveals the relationship among pressure, acceleration and velocity in shallow water: a study based on seismic records from different sensors
(withdrawn)
Zhen Jin and HuiTeng Cai
X2.101
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EGU23-5838
Yu Jin Sohn, Kwang-Hee Kim, Su Young Kang, Doyoung Kim, and Young-Cheol Lee

Pusan National University deployed sixteen ocean bottom seismometers (OBSs) in the eastern offshore of the southern Korean peninsula. The primary purpose of the OBS network is monitoring earthquakes in the eastern offshore to investigate potential fault systems in the offshore region which was formidable using limited apertures by land-based observations. A seismic network's performance highly depends on each site's background noise level. We analyze the nature of the ambient noise and site response for ocean bottom seismometers (OBSs) deployed in the 2021-2022 period. The power spectral densities (PSDs) of the OBSs exhibited dis-similar features from those of land-based stations; most temporary broadband seismic stations on land showed relatively lower background noise levels. In the meanwhile, OBSs showed higher background noise levels. We report the nature of ambient noise at various channels, water depths, spatial locations, temporal variations, extreme weather conditions, and their potential causes. In general, horizontal components are noisier than vertical components. For longer periods, horizontal components are larger by ~45 dB. The probability density functions (PDFs) of OBSs show that the noise level is within the range of McNamara’s model (2004) for higher frequencies (3.5~50 Hz) although they are still high. When examining long periods (> 20 s), the noise level is higher than what would be given by McNamara’s model. Although we do not observe diurnal or weekly variations in OBS, as expected, we observe varying degrees of seasonal variations in OBSs. Apparently, water depth is the most important factor in deciding noise levels and their seasonal variations. At shallow-depth OBSs, we observe a strong correlation between noise levels and wave heights estimated by the Korea Meteorological Administration (KMA). The ambient noise is down to -130 dB for the band from 5 to 15 Hz, which provides the best signal-to-noise ratio for local microearthquakes. We also present the horizontal-to-vertical spectral ratio (HVSR) of the ambient noise recorded by OBSs. They present significant amplifications at lower frequencies, which indicates large amplification by combined effects due to lower density and lower wave velocity at shallow sediments, and greater depths to major impedance contrast. We confirm that modeling HVSR of noise data recorded by a three-component OBS offers a fast and inexpensive method for site investigation in deep water with the potential of in situ seafloor sediment characterization.

How to cite: Sohn, Y. J., Kim, K.-H., Kang, S. Y., Kim, D., and Lee, Y.-C.: Seismic noise characteristics of PNU OBS network in 2021-2022, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5838, https://doi.org/10.5194/egusphere-egu23-5838, 2023.

X2.102
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EGU23-15911
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ECS
Mohammad-Amin Aminian, Eléonore Stutzmann, Jean-Paul Montagner, and Wayne Crawford

The ocean covers two-thirds of the Earth's surface, making it difficult to study the structure of the Earth in these areas.  The ocean, however, provides a pressure signal that can be used to study the oceanic crust, by measuring the seafloor deformation under this pressure signal.  We use continuous signals of seismic ground velocity combined with differential pressure at the sea floor recorded by ocean bottom stations (OBS).  By combining pressure and displacement data of the OBS, we can calculate the compliance function from the pressure signal of infra-gravity waves in the frequency band (0.003-0.03 Hz) . The displacement depends on the seismic properties of the earth's crustal layers, primarily its shear modulus.
The compliance function is very sensitive to the regions with a low shear velocity which makes it an excellent tool for investigating the earth crust for these regions.

To calculate the compliance function, the data must be preprocessed in several steps including glitch and earthquake removal, tilt correction, etc.
To remove earthquakes we used earthquake catalogs for large events and a recursive STA/LTA algorithm for local events. We use a comb
filter to remove hourly glitches  produced by the internal OBS system . 
Tilt noise is caused by deep ocean currents,  we minimize it on the vertical record by rotating the 3-component seismic data to an angle that minimize the variance of the vertical record, then by removing noise coherent with the horizontal components.

In this study, we used the French OBS of the Rhum-Rum experiment (Barruol and Sigloch, EOS, 2013) near La Reunion Island for 13 months in 2012, then calculated the compliance function. The crustal shear velocity structure below each station is then recovered by depth inversion of compliance.

How to cite: Aminian, M.-A., Stutzmann, E., Montagner, J.-P., and Crawford, W.: Determining the shear velocity structure of the oceanic crust from measurements of seafloor compliance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15911, https://doi.org/10.5194/egusphere-egu23-15911, 2023.

X2.103
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EGU23-14181
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ECS
Laura Hillmann, Susanne Hemmleb, Angelo Strollo, Javier Quinteros, Andres Heinloo, Christian Haberland, Martin Haxter, Mechita Schmidt-Aursch, Louis Ulmer, Anke Dannowski, Heidrun Kopp, and Wayne Crawford

Data from Ocean Bottom Seismometer (OBS) deployments nowadays are routinely integrated in federated seismological data centers, but often without following standardized procedures as recommended by the OBS community. This makes it difficult to locate and exploit these data mainly due to the restrictions imposed by the standard metadata format (stationXML) and the services.

In the context of the Helmholtz Metadata Collaboration (HMC), supported by OBS experts, we selected AWI and GEOMAR datasets to be archived at the GEOFON data center with standardized procedures according to the FDSN straw man proposal of W. Crawford for OBS data and metadata using also the OBSinfo tools developed at IPGP. In addition, a special emphasis was put on enhancing FAIRness for the selected datasets, for example identifiers of individual instruments were included, which are linked to instrument databases. Keywords were also added to make the data more easily findable and interoperable. From these experiences we formulated guidelines for OBS data management, which should help researchers to archive their OBS data consistently throughout EIDA data centers.

How to cite: Hillmann, L., Hemmleb, S., Strollo, A., Quinteros, J., Heinloo, A., Haberland, C., Haxter, M., Schmidt-Aursch, M., Ulmer, L., Dannowski, A., Kopp, H., and Crawford, W.: Enhancing FAIRness for OBS data within the eFAIRs project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14181, https://doi.org/10.5194/egusphere-egu23-14181, 2023.

X2.104
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EGU23-10745
Tae-shin Kim, Sung-Joon Chang, and Michael Witek

At the Mariana Trench, the Pacific plate with increasing age to the east is subducting beneath Philippine Sea plate. This subduction zone includes a volcanic arc, back-arc spreading center and many serpentinite seamounts. The Central Mariana Trench is investigated by using seismic data from 32 OBSs and 20 stations deployed in islands. Cross-correlating ambient noise records between station pairs yields fundamental-mode Rayleigh- and Love-wave dispersion curves at periods from 3 s to 35 s and at periods from 3 s to 20 s, respectively and used a 3D reference model consisting of Crust1.0 and ak135 to obtain more accurate inversion results. In particular, we also estimate group velocities between asynchronous station pairs by using permanent stations on great circle as virtual sources. By jointly inverting Rayleigh- and Love-wave dispersion curves, we calculate an S-wave isotropic and radially anisotropic velocity model, which has resolutions down to 70 km depth for isotropic S-wave velocity model and down to 40 km depth for anisotropic model. Low velocity anomalies are imaged due to the serpentinization and volcanic arc and high velocity anomalies are caused by the stagnation of fore-arc material. On the other hand, negative radial anisotropy are observed dominantly down to 15 km depth, which may be caused by vertical dykes responsible for many seamounts in this region.

How to cite: Kim, T., Chang, S.-J., and Witek, M.: S-wave isotropic and radially anisotropic velocity structure around the Mariana Trench inferred from ambient noise tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10745, https://doi.org/10.5194/egusphere-egu23-10745, 2023.

X2.105
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EGU23-11314
Ji-hoon Park, Sung-joon Chang, Michael Witek, Sang-Mook Lee, YoungHee Kim, Hisashi Utada, Hajime Shiobara, Takehi Isse, Nozomu Takeuchi, and Hiroko Sugioka

In the Western Pacific, there are unique geologic/tectonic features such as oldest oceanic crust in the Pacific, seamount chains derived from the Caroline hotspot, the Ontong-Java plateau which is the largest large igneous province, and complex plate boundaries between major and microplates. Investigation of isotropic and anisotropic velocity structure for this region is essential to our understanding of those unique features aforementioned. We estimate an S-wave isotropic and radially anisotropic velocity model beneath the Western Pacific by applying partitioned waveform inversion to three-component seismograms collected from the Incorporated Research Institutions for Seismology Data Managing Center, the Oldest-1 Array deployed in 2018-2019 by a joint Korean-Japan research team, and the Ocean Hemisphere network Project (OJP, NM, and SSP networks). We nonlinearly invert three-component waveforms from 17,038 raypaths (Mw > 5.5) with a 3-D reference model consisting of Crust1.0 and AK135 and resulting constraints are used for iterative least-squares inversion to build an S-velocity model. Our isotropic Vs model shows low-Vs anomalies at ~40 km depth beneath the Ontong-Java Plateau indicating a thick crust, at ~200 km depth beneath the Woodlark spreading center and Caroline seamount chain and at ~600 km depth beneath the center of the Eauripik rise. High-Vs anomalies are observed beneath the center of the Ontong-Java Plateau at 40-150 km depth and at ~50 km depth beneath the West Philippine basin, the Parece-Vela basin, and the Caroline basin. Overall positive radial anisotropy anomalies are observed in the Western Pacific, but the contrast of anisotropy was found in the Pacific plate, Philippine Sea plate, and Caroline plate at ~50 km depth. Negative radial anisotropy anomalies found in the Perace-Vela basin at ~30 km depth, and strong positive anisotropy anomalies are observed at the northern boundary of the Ontong-Java Plateau and beneath the Sorol trough and Caroline seamount chain.

How to cite: Park, J., Chang, S., Witek, M., Lee, S.-M., Kim, Y., Utada, H., Shiobara, H., Isse, T., Takeuchi, N., and Sugioka, H.: S-wave isotropic and radially anisotropic velocity structure in the Western Pacific inferred from partitioned waveform inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11314, https://doi.org/10.5194/egusphere-egu23-11314, 2023.

X2.106
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EGU23-6910
Will Reis, James Lindsey, Dan Whealing, and Neil Watkiss

Seismologists have historically focused on land-based seismic research, due to the logistical and financial challenges presented by offshore installations. Guralp has developed technology which allows the seismology community monitor offshore seismicity with greater ease, improving global seismic data resolution. This is due to systems such as the Aquarius autonomous ocean bottom seismometer (OBS) and world-leading engineering advancements in Science Monitoring and Reliable Telecommunications (SMART) cables.

Autonomous free-fall OBS units allow users flexibility in deployment and ability to redeploy a number of times in different locations. The Guralp Aquarius functions at any angle without using a gimbal system, and can wirelessly transmit SOH and seismic data to the surface via an integrated acoustic modem. These features allow researchers to monitor and transmit data without offshore cabling, thereby reducing logistical challenges whilst maintaining some degree of real-time data transmission. Optional surface communications can be permanent (buoy-mounted), semi-permanent (wave-glider) or on demand (ship-of-opportunity or dedicated voyage).

Alternatively, cabled solutions give users access to high-resolution data in real-time via a physical link to an onshore data centre. As an example, the Guralp Orcus provides a complete underwater seismic station with observatory grade seismometer and strong-motion accelerometer in a single package. The slimline Guralp Maris also provides a more versatile solution, making use of the same omnidirectional sensor as the Aquarius and can be installed either on the seabed or in a narrow-diameter subsea borehole.

SMART cables show great potential for increasing the number of cabled ocean observatory deployments in the future with substantially reduced deployment costs to the research institute. Combining several applications into a single system, including seismic monitoring and telecommunications, large scale monitoring networks can be created cost effectively by combining efforts from several industries. Guralp is deploying a demonstration SMART Cable system to monitor volcanic and seismic activity offshore in the Ionian Sea in collaboration with Instituto Nazionale Di Geofisica e Vulcanologia (INGV). This will be the first practical demonstration of this technology and there are plans for additional projects in the future.

How to cite: Reis, W., Lindsey, J., Whealing, D., and Watkiss, N.: Novel Autonomous and Cabled OBS Solutions for Offshore Seismic Research, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6910, https://doi.org/10.5194/egusphere-egu23-6910, 2023.

Posters virtual: Thu, 27 Apr, 08:30–10:15 | vHall GMPV/G/GD/SM

Chairperson: Janneke de Laat
vGGGS.8
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EGU23-10875
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ECS
Xiaolong Ma, Hrvoje Tkalčić, Caroline Eakin, Nicholas Rawlinson, Thanh-Son Pham, Tom Winder, Robert Pickle, Millard Coffin, and Joann Stock and the Macquarie Ridge 3D Team

The Macquarie Ridge Complex (MRC) constitutes the boundary between the Indo-Australian and Pacific plates in the southwest Pacific Ocean. It accommodates the world’s most potent sub-marine earthquakes that are not associated with ongoing subduction. To better understand the nature of MRC and its associated earthquakes, we aim to explore the crustal structures using recordings from island-based stations and ocean bottom seismometers (OBS). In particular, these OBSs, which are deployed in the surroundings of Macquarie Island from October 2020 to November 2021, enable us to image the refined oceanic structures beneath the study area. In this study, we obtain the body-wave reflections by computing phase coherence autocorrelations of both ambient noise and earthquake data. Our preliminary reflection profiles by both methods reveal coherent reflected P waves that may be related to Moho and additional structures within the crust and upper mantle.

How to cite: Ma, X., Tkalčić, H., Eakin, C., Rawlinson, N., Pham, T.-S., Winder, T., Pickle, R., Coffin, M., and Stock, J. and the Macquarie Ridge 3D Team: Crustal Structure of the Macquarie Ridge Complex Constrained by the Ambient Noise and Earthquake Autocorrelograms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10875, https://doi.org/10.5194/egusphere-egu23-10875, 2023.

vGGGS.9
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EGU23-10662
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ECS
Thanh-Son Pham, Hrvoje Tkalcic, Xiaolong Ma, Robert Pickle, Jack Muir, Kenneth Duru, Tom Winder, Nicholas Rawlinson, Caroline Eakin, Millard Coffin, and Joann Stock and the Macquarie Ridge 3D Team

The Macquarie Ridge Complex, located at the boundary between Indo-Australian and Pacific plates in the southwest Pacific Ocean, hosts the largest sub-marine earthquakes in the 20th century, not associated with ongoing subduction. We deployed 27 ocean-bottom seismometers, of which 15 have been recovered successfully, to understand the origin of the sub-marine earthquakes and their potential earthquake and tsunami hazards to Australia and New Zealand. Additionally, we deployed five land-based seismometers on Macquarie Island.

We explore state-of-the-art processing methods to analyze the new seismic dataset from the retrieved seismic stations. One of the goals is to image the tectonic settings beneath the MRC. Here, we present a first-order tomographic model and its relevant uncertainty estimate of the region constructed from ambient noise surface waves using a probabilistic inversion framework. The tomographic image will be complemented with receiver-based imaging results such as those from P-wave coda autocorrelations and receiver functions to confirm the existence of possible geometries. The results are expected to supply a fresh understanding of the tectonic settings under the MRC and unpuzzle the origin of the significant underwater earthquakes in the 20th century.

How to cite: Pham, T.-S., Tkalcic, H., Ma, X., Pickle, R., Muir, J., Duru, K., Winder, T., Rawlinson, N., Eakin, C., Coffin, M., and Stock, J. and the Macquarie Ridge 3D Team: Probabilistic ambient noise imaging of the Macquarie Ridge Complex using ocean-bottom and land-based seismometers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10662, https://doi.org/10.5194/egusphere-egu23-10662, 2023.