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  • OceanRep  (7)
  • OceanRep: Article in a Scientific Journal - without review  (7)
  • 1
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    Investigating subduction zone processes in Chile (2006)
    AGU (American Geophysical Union)
    In:  Eos, Transactions American Geophysical Union, 87 (27). pp. 265-272.
    Details
    Publication Date: 2017-02-17
    Description: The highly active subduction zone of southern Chile was the source region of the 1960 Valdivia megathrust earthquake (Mw= 9.5), the largest earthquake ever recorded.This region is currently under investigation by the multidisciplinary TIPTEQ (From the Incoming Plate to Mega-Thrust Earthquake Processes) project, which is studying the structure, state, and deformation of the subduction zone lithosphere. Over 90 days, from December 2004 to February 2005,TIPTEQ scientists on cruise S0181 of the German research vessel (R/V Sonne acquired a broad variety of geophysical and geological data in the research area offshore Chile between 35°S and 48°S (Figure 1).These data include active and passive source seismics, heat flow probing, magnetics, magnetotellurics for studying Earth conductivity, highresolution multibeam bathymetry, and sediment probes from gravity cores.
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
  • 2
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    Constraining the maximum depth of brittle deformation at slow- and ultraslow-spreading ridges using microseismicity: REPLY (2020)
    GSA (Geological Society of America)
    In:  Geology, 48 (5). e502.
    Details
    Publication Date: 2020-11-05
    Type: Article , NonPeerReviewed
    Format: text
    DOI: 10.1130/G47542Y.1
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    OceanRep: Article in a Scientific Journal - without review
  • 3
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    In situ lower crustal accretion by melt sill injection revealed by seismic layering (2021)
    In:  (Submitted) Research Square Preprints .
    Details
    Publication Date: 2021-11-24
    Description: Oceanic crust is formed at mid-ocean spreading centres by a combination of magmatic, tectonic and hydrothermal processes. The crust formed by magmatic process consists of an upper crust generally composed of basaltic dikes and lava flows and a lower crust presumed to mainly contain homogeneous gabbro whereas that by tectonic process can be very heterogeneous and may even contain mantle rocks. Although the formation and evolution of the upper crust are well known from geophysical and drilling results, those for the lower crust remain a matter of debate. Using a full waveform inversion method applied to wide-angle seismic data, here we report the presence of layering in the lower oceanic crust formed at the slow spreading Mid-Atlantic Ridge, ~7-12 Ma in age, revealing that the lower crust is formed mainly by in situ cooling and crystallisation of melt sills at different depths by the injection of magma from the mantle. These layers are 400-600 m thick with alternate high and low velocities, with ± 100-200 m/s velocity variation, and cover over a million-year old crust, suggesting that the crustal accretion by melt sill intrusions beneath the ridge axis is a stable process. We also find that the upper crust is ~400 m thinner than that from conventional travel-time analysis. Taken together, these discoveries suggest that the magmatism plays more important roles in the crustal accretion process at slow spreading ridges than previously realised, and that in-situ lower crustal accretion is the main process for the formation of lower oceanic crust.
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.21203/rs.3.rs-145281/v1
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    OceanRep: Article in a Scientific Journal - without review
  • 4
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    PickBlue: Seismic phase picking for ocean bottom seismometers with deep learning (2023)
    Details
    Publication Date: 2023-05-11
    Description: 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 an extensive 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 propose PickBlue, an adaptation ot the two popular deep learning networks EQTransformer and PhaseNet. PickBlue joint processes three seismometer recordings in conjunction with a hydrophone component and is trained 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. PickBlue significantly outperforms neural networks trained with land stations and models trained without hydrophone data. The model achieves a mean absolute deviation (MAD) of 0.05 s for P waves and 0.12 s for S waves. We integrate our dataset and trained models into SeisBench to enable an easy and direct application in future deployments. KEY POINTS • We assembled a database of Ocean Bottom Seismometer waveforms and manual P and S picks, on which we train PickBlue, a deep learning picker. • Our picker significantly outperforms pickers trained with land-based data with confidence values reflecting the likelihood of outlier picks. • The picker and database are available in the SeisBench platform, allowing easy and direct application to OBS traces and hydrophone records.
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
  • 5
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    Disparate crustal thicknesses beneath oceanic transform faults and adjacent fracture zones revealed by gravity anomalies (2022)
    GSA (Geological Society of America)
    Details
    Publication Date: 2023-01-16
    Type: Article , NonPeerReviewed
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    OceanRep: Article in a Scientific Journal - without review
  • 6
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    Broad fault zones enable deep fluid transport and limit earthquake magnitudes (2022)
    Details
    Publication Date: 2023-02-03
    Description: Constraining the controlling factors of fault rupture is fundamental to understanding the earthquake cycle. Fluids can influence earthquake locations and magnitudes, although the exact pathways of fluids through the lithosphere are not well-known. Ocean transform faults are an ideal laboratory to study the factors controlling fault ruptures and fluid pathways given their relative simplicity. Here, we analyse seismicity recorded by the Passive Imaging of the Lithosphere-Asthenosphere Boundary (PI-LAB) experiment, centred around the Chain Fracture Zone. We find that earthquakes beneath mapped morphological transpressional features occur deeper than the brittle-ductile transition predicted by simple thermal models but elsewhere occur shallower. These features are characterised by multiple parallel fault segments and step overs, high b-values, gaps in large historical earthquakes, and seismic velocity structures consistent with hydrothermal alteration. This suggests that broader fault damage zones preferentially facilitate fluid transport into the lithosphere. Although this cools the mantle, it also reduces the potential for large earthquakes at punctuated locations (barriers). These barriers divide the transform into asperity segments that are shorter, thereby limiting the earthquake magnitudes in these regions.
    Type: Article , NonPeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
  • 7
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    From Symmetric Rifting to Asymmetric Spreading - Insights into Back-Arc Formation in the Central Mariana Trough (2024)
    Details
    Publication Date: 2024-06-21
    Description: The Mariana Trough is the youngest back-arc basin in a series of basins and arcs that developed behind the Mariana subduction zone in the western Pacific. Active seafloor spreading is ongoing at a spreading axis close the Mariana Arc resulting in a pronounced asymmetric configuration (double rate to the west 2:1) at 17° N. The formation of back-arc basins is controlled by the subducting slab, which regulates the temporal development of mantle flow, entrainment of fluids and hydrous melts together with the magma generation. To better understand the formation process of back-arc basins and the asymmetry of the central Mariana Trough, we combined 2-D P-wave traveltime tomography results together with high-resolution bathymetric data. Here, we show that the crust in the central Mariana Trough is 6.5-9.5 km thick, which is unusual for oceanic crust. The lower crust exhibits average seismic velocities of 6.5-7.2 km/s. High-velocity anomalies (7.4-7.9 km/s) in the lower crust at the margins of the Mariana Trough indicate that magmatic accretion process was affected by hydrous melting during rifting. While the Mariana Trough developed from a rather symmetric rifting (0.89:1) to a strongly asymmetric seafloor spreading stage (5.33:1), the contribution of hydrous melts declined and the opening direction changed. The asymmetric plate motions and the temporal change of the slab component influenced strongly the formation of the back-arc basin.
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
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