scholarly journals Along-Arc Heterogeneity of the Seismic Structure Around a Large Coseismic Shallow Slip Area of the 2011 Tohoku-Oki Earthquake: 2-D Vp Structural Estimation Through an Air Gun-Ocean Bottom Seismometer Experiment in the Japan Trench Subduction Zone

2018 ◽  
Vol 123 (6) ◽  
pp. 5249-5264 ◽  
Author(s):  
R. Azuma ◽  
R. Hino ◽  
Y. Ohta ◽  
Y. Ito ◽  
K. Mochizuki ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Structural Estimation ◽  
Japan Trench ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Seismic Structure ◽  
Air Gun ◽  
Slip Area

Migration-Based Local Event-Location Workflow for Ocean-Bottom Seismometer (OBS) Records in Subduction Zones: A Practical Approach for Addressing a Large Number of Events

2021 ◽  
Author(s):  
Shinji Yoneshima ◽  
Kimihiro Mochizuki
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Real Data ◽  
Japan Trench ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
S Waves ◽  
Local Earthquakes ◽  
Ocean Bottom Seismometers ◽  
Event Location

ABSTRACT An efficient event-location workflow is highly desired to analyze large numbers of local earthquakes recorded by ocean-bottom seismometers (OBSs) in subduction zones. The present study proposes a migration-based event-location approach for evaluating OBS records to examine local subduction-zone earthquakes. This approach can significantly reduce the amount of manual time picks compared with conventional methods. The event-location workflow was designed to detect arrival onsets of both P and S phases. Synthetic tests have shown that the proposed migration-based event-location method is robust against different types of noise, such as environmental noise and local spike noise. This workflow was then applied to real OBS data in the off-Ibaraki region at the southern end of the Japan trench. The results show that this approach is applicable to real data from subduction-zone events: It gives reasonable agreement with manual time picks for both P and S waves and reasonable error bars, and it demonstrates a clear down-dip trend of seismicity. The results also show fair agreement with event distributions from previous studies of the off-Ibaraki region. This proposed workflow can be used to examine the seismicity of local earthquakes around the subduction zone using OBSs. This approach is especially effective when the seismicity is high and/or in cases in which long-term OBS monitoring has recorded a large number of events.

Seismic structure of the extended continental crust in the Yamato Basin, Japan Sea, from ocean bottom seismometer survey

2013 ◽  
Vol 67-68 ◽  
pp. 199-206 ◽  
Author(s):  
Kazuo Nakahigashi ◽  
Masanao Shinohara ◽  
Tomoaki Yamada ◽  
Kenji Uehira ◽  
Kimihiro Mochizuki ◽  
...  
Keyword(s):  
Continental Crust ◽  
Japan Sea ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Seismic Structure ◽  
Yamato Basin

Crustal structure across the Southwest Newfoundland Transform Margin

1988 ◽  
Vol 25 (5) ◽  
pp. 744-759 ◽  
Author(s):  
B. J. Todd ◽  
I. Reid ◽  
C. E. Keen
Keyword(s):  
Continental Crust ◽  
Transition Zone ◽  
Crustal Structure ◽  
P Wave ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Structure Information ◽  
Grand Banks ◽  
Air Gun ◽  
Transform Margin

A seismic-refraction survey providing deep crustal structure information of the continent–ocean boundary across the South-west Newfoundland Transform Margin was carried out using large air-gun sources and ocean-bottom seismometer receivers. Continental crust ~30 km thick beneath the southern Grand Banks (P-wave velocity = 6.2–6.5 km/s) thins oceanward to a 25 km wide transition zone. In the transition zone, Paleozoic basement of the Grand Banks (5.5–5.7 km/s) is replaced by a basement of oceanic volcanics and synrift sediments (4.5–5.5 km/s). Seaward of the transition zone the crust is oceanic in character, with a velocity gradient from 4.7 to 6.5 km/s and a thickness of 7–8 km. Oceanic layer 3 is absent. No significant thickness of intermediate-velocity (>7 km/s) material is present at the continent–ocean transition, indicating that no under-plating of continental crust has taken place. The continent–ocean transition across the transform margin is much narrower than across rifted margins, supporting the theory that formation of the transform margin is by shearing of continental plates.

scholarly journals Crustal-scale depth imaging via joint full-waveform inversion of ocean-bottom seismometer data and pre-stack depth migration of multichannel seismic data: a case study from the eastern Nankai Trough

Solid Earth ◽  
2019 ◽  
Vol 10 (3) ◽  
pp. 765-784 ◽  
Author(s):  
Andrzej Górszczyk ◽  
Stéphane Operto ◽  
Laure Schenini ◽  
Yasuhiro Yamada
Keyword(s):  
Seismic Data ◽  
Nankai Trough ◽  
Waveform Inversion ◽  
Velocity Model ◽  
Full Waveform Inversion ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Depth Migration ◽  
Full Waveform ◽  
Air Gun

Abstract. Imaging via pre-stack depth migration (PSDM) of reflection towed-streamer multichannel seismic (MCS) data at the scale of the whole crust is inherently difficult. This is because the depth penetration of the seismic wavefield is controlled, firstly, by the acquisition design, such as streamer length and air-gun source configuration, and secondly by the complexity of the crustal structure. Indeed, the limited length of the streamer makes the estimation of velocities from deep targets challenging due to the velocity–depth ambiguity. This problem is even more pronounced when processing 2-D seismic data due to the lack of multi-azimuthal coverage. Therefore, in order to broaden our knowledge about the deep crust using seismic methods, we present the development of specific imaging workflows that integrate different seismic data. Here we propose the combination of velocity model building using (i) first-arrival tomography (FAT) and full-waveform inversion (FWI) of wide-angle, long-offset data collected by stationary ocean-bottom seismometers (OBSs) and (ii) PSDM of short-spread towed-streamer MCS data for reflectivity imaging, with the former velocity model as a background model. We present an application of such a workflow to seismic data collected by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and the Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER) in the eastern Nankai Trough (Tokai area) during the 2000–2001 Seize France Japan (SFJ) experiment. We show that the FWI model, although derived from OBS data, provides an acceptable background velocity field for the PSDM of the MCS data. From the initial PSDM, we refine the FWI background velocity model by minimizing the residual move-outs (RMOs) picked in the pre-stack-migrated volume through slope tomography (ST), from which we generate a better-focused migrated image. Such integration of different seismic datasets and leading-edge imaging techniques led to greatly improved imaging at different scales. That is, large to intermediate crustal units identified in the high-resolution FWI velocity model extensively complement the short-wavelength reflectivity inferred from the MCS data to better constrain the structural factors controlling the geodynamics of the Nankai Trough.

scholarly journals Application of the Stacked Refraction Convolution Section to 2D Ocean Bottom Seismometer Wide-angle Seismic Data Along the Tamayo Through Basin, Gulf of California

2021 ◽  
Vol 9 ◽  
Author(s):  
Antonio González-Fernández
Keyword(s):  
Seismic Data ◽  
Seismic Reflection ◽  
Gulf Of California ◽  
Constant Thickness ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Wide Angle ◽  
Travel Times ◽  
Air Gun ◽  
Refraction Seismic

The stacked refraction convolution section can be used as an interpretation tool in wide-angle refraction seismic data generated by air gun shooting and recorded by Ocean Bottom Seismometers (OBS). The refraction convolution section is a full-wave extension of the Generalized Reciprocal Method (GRM), a method frequently used in shallow refraction seismic interpretation, but not applied to deep crustal-scale studies. The sum of the travel times of the waves refracted in the same interface and recorded in a pair of forward and reverse profiles, time-corrected by the reciprocal time, is an estimation close to the two-way travel times of the multichannel seismic reflection sections, but with seismic rays illuminating the interfaces upwards. The sum of seismic traces is obtained with the convolution section. Furthermore, several pairs of convolved forward-reverse refraction recordings of the same area can be stacked together to improve the signal to noise ratio. To show the applicability of the refraction convolution section in OBS deep data, we interpreted the basement structure of the Tamayo Through Basin in the southern Gulf of California, offshore Mexico. We compared the results with both, a multichannel seismic section recorded in the same profile, and the previous interpretations of the same wide-angle seismic data modeled with ray tracing and tomography methods. The basement imaged by the stacked refraction convolution section is similar in geometry to that obtained by seismic reflection processing. The stacked refraction convolution section identifies the full extent of the basement and confirms the location of a nearly constant thickness volcanic layer in the northwestern half of the basin. However, only a small area of volcanic deposits is found in the shallower parts of the southwestern margin. We also show that the convolution process can be used to estimate the occurrence of lateral variations of seismic velocities in the basement, as a further application of the GRM to deep refraction data.

Sign in / Sign up

Export Citation Format

Share Document