Along-strike variation in slab geometry at the southern Mariana subduction zone revealed by seismicity through ocean bottom seismic experiments

SUMMARYWe have conducted the first passive Ocean Bottom Seismograph (OBS) experiment near the Challenger Deep at the southernmost Mariana subduction zone by deploying and recovering an array of 6 broad-band OBSs during December 2016–June 2017. The obtained passive-source seismic records provide the first-ever near-field seismic observations in the southernmost Mariana subduction zone. We first correct clock errors of the OBS recordings based on both teleseismic waveforms and ambient noise cross-correlation. We then perform matched filter earthquake detection using 53 template events in the catalogue of the US Geological Survey and find >7000 local earthquakes during the 6-month OBS deployment period. Results of the two independent approaches show that the maximum clock drifting was ∼2 s on one instrument (OBS PA01), while the rest of OBS waveforms had negligible time drifting. After timing correction, we locate the detected earthquakes using a newly refined local velocity model that was derived from a companion active source experiment in the same region. In total, 2004 earthquakes are located with relatively high resolution. Furthermore, we calibrate the magnitudes of the detected earthquakes by measuring the relative amplitudes to their nearest relocated templates on all OBSs and acquire a high-resolution local earthquake catalogue. The magnitudes of earthquakes in our new catalogue range from 1.1 to 5.6. The earthquakes span over the Southwest Mariana rift, the megathrust interface, forearc and outer-rise regions. While most earthquakes are shallow, depths of the slab earthquakes increase from ∼100 to ∼240 km from west to east towards Guam. We also delineate the subducting interface from seismicity distribution and find an increasing trend in dip angles from west to east. The observed along-strike variation in slab dip angles and its downdip extents provide new constraints on geodynamic processes of the southernmost Mariana subduction zone.

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Long offset ocean bottom node full-waveform inversion and multi-azimuth tomography for high-resolution velocity model building: North Sea, Utsira High

10.1190/segam2020-3428806.1 ◽

2020 ◽

Author(s):

Adriana Citlali Ramirez ◽

Simon Baldock ◽

Dhiman Mondal ◽

Jan Gromotka ◽

Matt Hart

Keyword(s):

High Resolution ◽

North Sea ◽

Model Building ◽

Waveform Inversion ◽

Velocity Model ◽

Full Waveform Inversion ◽

Ocean Bottom ◽

Full Waveform ◽

Velocity Model Building ◽

Long Offset

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Imaging the Deep Galicia margin using three-dimensional full waveform inversion

10.5194/egusphere-egu2020-5559 ◽

2020 ◽

Author(s):

Bhargav Boddupalli ◽

Tim Minshull ◽

Joanna Morgan ◽

Gaye Bayrakci

Keyword(s):

High Resolution ◽

Travel Time ◽

Waveform Inversion ◽

Three Dimensional ◽

Velocity Model ◽

Normal Faults ◽

Full Waveform Inversion ◽

Ocean Bottom ◽

Time Model ◽

Full Waveform

Imaging of hyperextended zone and exhumed continental mantle rocks can improve our understanding of the tectonics of the final stages of rifting. In the Deep Galicia margin, the upper and lower crust are coupled allowing the normal faults to cut through the brittle crust and penetrate to the mantle leading to serpentinization of the mantle. Localized extensional forces caused extreme thinning and elongation of crystalline continental crust causing the continental blocks to slip over a lithospheric-scale detachment fault called the S-reflector. &#160;A high-resolution velocity model obtained using seismic full waveform inversion gives us deeper insights into the rifting process. In this study, we present results from three dimensional acoustic full waveform inversion performed using wide-angle seismic data acquired in the deep water environments of the Deep Galicia margin using ocean bottom seismometers. We performed full waveform inversion in the time domain, starting with a velocity model obtained using travel-time tomography, of dimensions 78.5 km x 22.1 km and depth 12 km. The high-resolution modelling shows short-wavelength variations in the velocity, adding details to the travel-time model. We superimposed our final model, converted to two-way time, on pre-stack time-migrated three-dimensional reflection data from the same survey. Compared to the starting model, our model shows improved alignment of the velocity variations along the steeply dipping normal faults and a sharp velocity contrast across the S-reflector. We validated our result using checkerboard tests, by tracking changes in phases of the first arrivals during the inversion and by comparing the observed and the synthetic waveforms. We observe a clear evidence for preferential serpentinization (45 %) of the mantle with lower velocities in the mantle correlating with the fault intersections with the S-reflector.

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The marine activities performed within the TOMO-ETNA experiment

Annals of Geophysics ◽

10.4401/ag-7081 ◽

2016 ◽

Vol 59 (4) ◽

Author(s):

Mauro Coltelli ◽

Danilo Cavallaro ◽

Marco Firetto Carlino ◽

Luca Cocchi ◽

Filippo Muccini ◽

...

Keyword(s):

High Resolution ◽

Structural Model ◽

Seismic Refraction ◽

Velocity Model ◽

Ocean Bottom ◽

Etna Volcano ◽

Remotely Operated Vehicle ◽

Reflection Seismic ◽

Air Gun ◽

Mt Etna

The TOMO-ETNA experiment was planned in order to obtain a detailed geological and structural model of the continental and oceanic crust beneath Mt. Etna volcano and northeastern Sicily up to the Aeolian Islands (southern Italy), by integrating data from active and passive refraction and reflection seismic methodologies, magnetic and gravity surveys. This paper focuses on the marine activities performed within the experiment, which have been carried out in the Ionian and Tyrrhenian Seas, during three multidisciplinary oceanographic cruises, involving three research vessels (“Sarmiento de Gamboa”, “Galatea” and “Aegaeo”) belonging to different countries and institutions. During the offshore surveys about 9700 air-gun shots were produced to achieve a high-resolution seismic tomography through the wide-angle seismic refraction method, covering a total of nearly 2650 km of shooting tracks. To register ground motion, 27 ocean bottom seismometers were deployed, extending the inland seismic permanent network of the Istituto Nazionale di Geofisica e Vulcanologia and a temporary network installed for the experiment. A total of 1410 km of multi-channel seismic reflection profiles were acquired to image the subsurface of the area and to achieve a 2D velocity model for each profile. Multibeam sonar and sub bottom profiler data were also collected. Moreover, a total of 2020 km of magnetic and 680 km of gravity track lines were acquired to compile magnetic and gravity anomaly maps offshore Mt. Etna volcano. Here, high-resolution images of the seafloor, as well as sediment and rock samples, were also collected using a remotely operated vehicle.

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A reflection-based efficient wavefield inversion

Geophysics ◽

10.1190/geo2019-0664.1 ◽

2021 ◽

pp. 1-53

Author(s):

Chao Song ◽

Tariq Alkhalifah

Keyword(s):

High Resolution ◽

Initial Velocity ◽

Waveform Inversion ◽

Synthetic Data ◽

Velocity Model ◽

Background Model ◽

Ocean Bottom ◽

Velocity Inversion ◽

Velocity Models ◽

Wavefield Inversion

Full-waveform inversion (FWI) is popularly used to obtain a high-resolution subsurface velocity model. However, it requires either a good initial velocity model or low-frequency data to mitigate the cycle-skipping issue. Reflection-waveform inversion (RWI) uses a migration/demigration process to retrieve a background model that can be used as a good initial velocity in FWI. The drawback of the conventional RWI is that it requires the use of a least-squares migration, which is often computationally expensive, and is still prone to cycle skipping at far offsets. To improve the computational efficiency and overcome the cycle skipping in the original RWI, we incorporate it into a recently introduced method called efficient wavefield inversion (EWI) by inverting for the Born scattered wavefield instead of the wavefield itself. In this case, we use perturbation-related secondary sources in the modified source function. Unlike conventional RWI, the perturbations are calculated naturally as part of the calculation of the scattered wavefield in an efficient way. As the sources in the reflection-based EWI (REWI) are located in the subsurface, we are able to update the background model along the reflection wave path. In the background velocity inversion, we calculate the background perturbation by a deconvolution process at each frequency. After obtaining the REWI inverted velocity model, a sequential FWI or EWI is needed to obtain a high-resolution model. We demonstrate the validity of the proposed approach using synthetic data generated from a section of the Sigsbee2A model. To further demonstrate the effectiveness of the proposed approach, we test it on an ocean bottom cable (OBC) dataset from the North Sea. We find that the proposed methodology leads to improved velocity models as evidenced by flatter angle gathers.

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Hybrid Velocity Model Building: 3D Ocean Bottom Cable (OBC) Orthorhombic Full Waveform Inversion (FWI) Depth Imaging of a Complex Geological Structure, Western Berau – Papua, Indonesia

Proc of Indonesian Petroleum Association 42nd Annual Convention ◽

10.29118/ipa19.g.601 ◽

2018 ◽

Author(s):

P. Santoso

Keyword(s):

Model Building ◽

Waveform Inversion ◽

Velocity Model ◽

Geological Structure ◽

Full Waveform Inversion ◽

Ocean Bottom ◽

Depth Imaging ◽

Full Waveform ◽

Velocity Model Building ◽

Complex Geological Structure

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Cloud Detection Based on High Resolution Stereo Pairs of the Geostationary Meteosat Images

Remote Sensing ◽

10.3390/rs12030371 ◽

2020 ◽

Vol 12 (3) ◽

pp. 371 ◽

Cited By ~ 2

Author(s):

Sahar Dehnavi ◽

Yasser Maghsoudi ◽

Klemen Zakšek ◽

Mohammad Javad Valadan Zoej ◽

Gunther Seckmeyer ◽

...

Keyword(s):

High Resolution ◽

Matched Filter ◽

Stereo Pair ◽

Cloud Detection ◽

Operating Characteristics ◽

Detection Techniques ◽

Infrared Imager ◽

Detection Approach ◽

Considerable Impact ◽

Image Pairs

Due to the considerable impact of clouds on the energy balance in the atmosphere and on the earth surface, they are of great importance for various applications in meteorology or remote sensing. An important aspect of the cloud research studies is the detection of cloudy pixels from the processing of satellite images. In this research, we investigated a stereographic method on a new set of Meteosat images, namely the combination of the high resolution visible (HRV) channel of the Meteosat-8 Indian Ocean Data Coverage (IODC) as a stereo pair with the HRV channel of the Meteosat Second Generation (MSG) Meteosat-10 image at 0° E. In addition, an approach based on the outputs from stereo analysis was proposed to detect cloudy pixels. This approach is introduced with a 2D-scatterplot based on the parallax value and the minimum intersection distance. The mentioned scatterplot was applied to determine/detect cloudy pixels in various image subsets with different amounts of cloud cover. Apart from the general advantage of the applied stereography method, which only depends on geometric relationships, the cloud detection results are also improved because: (1) The stereo pair is the HRV bands of the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) sensor, with the highest spatial resolution available from the Meteosat geostationary platform; and (2) the time difference between the image pairs is nearly 5 s, which improves the matching results and also decreases the effect of cloud movements. In order to prove this improvement, the results of this stereo-based approach were compared with three different reflectance-based target detection techniques, including the adaptive coherent estimator (ACE), constrained energy minimization (CEM), and matched filter (MF). The comparison of the receiver operating characteristics (ROC) detection curves and the area under these curves (AUC) showed better detection results with the proposed method. The AUC value was 0.79, 0.90, 0.90, and 0.93 respectively for ACE, CEM, MF, and the proposed stereo-based detection approach. The results of this research shall enable a more realistic modelling of down-welling solar irradiance in the future.

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