Quality Analysis of High‐Frequency Air‐Gun Shot Seismic Recordings in the Juan de Fuca Plate

Sampath Rathnayaka; Haiying Gao

doi:10.1785/0220180274

The Vancouver Island Seismic Project: a co-CRUST onshore–offshore study of a convergent margin

Canadian Journal of Earth Sciences ◽

10.1139/e83-065 ◽

1983 ◽

Vol 20 (5) ◽

pp. 719-741 ◽

Cited By ~ 25

Author(s):

R. M. Ellis ◽

G. D. Spence ◽

R. M. Clowes ◽

D. A. Waldron ◽

I. F. Jones ◽

...

Keyword(s):

Velocity Structure ◽

Deep Ocean ◽

Crustal Thickness ◽

Vancouver Island ◽

Seismic Structure ◽

Secondary Phases ◽

Juan De Fuca Plate ◽

Deep Crust ◽

Air Gun ◽

Juan De Fuca

The seismic structure of the British Columbia continental margin has been investigated using four reversed refraction profiles. The profile across strike extended 350 km from the volcanic arc on the continent to the deep ocean of the Juan de Fuca Plate; the three profiles along strike were located on Vancouver Island, on the continental shelf, and in the deep ocean on the Juan de Fuca Plate. Interpretation of the profile along Vancouver Island yields a well constrained model for the upper crust with velocity increasing from ~5.3 km/s at the surface to ~6.4 km/s at 2 km depth to ~6.75 km/s at 15.5 km depth where the velocity increases sharply to ~7 km/s. The velocity structure of the deep crust and the crustal thickness are poorly constrained. Four possible velocity functions, based on ambiguous first arrivals and (or) secondary phases interpreted as Moho reflections, are presented. The preferred one includes a deep crustal low velocity zone with a crustal thickness of 37 km; models with a constant 7.1 km/s deep crust require thicknesses of 52 km. Preliminary results from the profile across strike show the dip of the basement towards the continent steepens from approximately 1.4° immediately west of the continental rise to ~4° beneath the rise. Sediment velocities increase as the sedimentary layer thickens towards the shelf. The Moho, with velocity near 8 km/s, appears to dip at similar angles in this region; the dip is ~6° from the edge of the shelf to the central portion of Vancouver Island; here there is an abrupt thickening of the continental crust by about 10 km with a flat-lying Moho to the east. This suggests a contact between subducting oceanic Moho and continental Moho. A small positive velocity gradient is required in the mantle.Two short reflection lines, one using explosives and the other a large air gun fired in an inlet, were recorded on a land-based multichannel reflection system. These were run to test the feasibility of obtaining coherent reflections to upper mantle depths in this complex geological environment, and of acquiring deep reflection data in coastal areas with an air-gun source. The preliminary explosion section showed reflections near 4.4 and 6.8 s. The depths of these reflections correspond closely to the 15.5 km crustal refractor and the top of the subducting oceanic lithosphere, respectively. Dip on the deeper reflector is close to that estimated from the refraction profile. Without stacking or velocity filtering, the air-gun recordings on a line adjacent to the explosion profile show arrivals of energy at similar times.

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Multiple Brain Abscesses by an Air Gun Shot: A Case Report

Arquivos Brasileiros de Neurocirurgia Brazilian Neurosurgery ◽

10.1055/s-0041-1731063 ◽

2021 ◽

Author(s):

Mohammad Jamali ◽

Iman Ahrari ◽

Keyvan Eghbal ◽

Arash Saffarrian ◽

Abbas Rakhsha ◽

...

Keyword(s):

Brain Injury ◽

Brain Injuries ◽

Good Condition ◽

Signs And Symptoms ◽

Low Velocity ◽

Penetrating Brain Injury ◽

Air Gun ◽

Gun Shot ◽

Brain Abscesses ◽

Air Gun Pellet

Abstract Introduction Low-velocity penetrating brain injury is not prevalent. In some conditions such as childhood, and with the penetration of a pellet in weak spots of skull, low-velocity penetrating brain injury is expected; however, high-velocity projectiles have also been reported as the cause of severe brain injuries. One of the complications of penetrating brain injury is infection, in which different types of microorganisms play a role. The Streptococcus genus is the leading cause of abscess formation in non-traumatic patients. Multiple brain abscesses are not common. Case Presentation A 10-year-old boy with penetrating brain injury caused by an air gun pellet, who developed signs and symptoms of high intracranial pressure 18 days after the trauma. After the imaging scans and the detection of multiple brain abscesses and severe brain edema, prompt surgical intervention was performed for all three lesions in a single operation. The culture of a pus specimen was positive for Streptococcus species, and, with adequate antibiotic therapy, the patient was discharged from the hospital in good condition. Conclusion Brain injury with air gun shot is not prevalent. The penetration of a low-velocity air gun pellet in weak points of the skull (such as the orbit, the squamous portion of the temporal bone, and the cranial suture), specially in children, can cause significant brain injuries.

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Depth dependent azimuthal anisotropy beneath the Juan de Fuca plate system

10.1002/essoar.10502070.1 ◽

2020 ◽

Author(s):

Zachary C Eilon ◽

Donald W. Forsyth

Keyword(s):

Azimuthal Anisotropy ◽

Juan De Fuca Plate ◽

Juan De Fuca ◽

Plate System

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The northern limit of the subducted Juan de Fuca Plate system

Journal of Geophysical Research Atmospheres ◽

10.1029/98jb02140 ◽

1998 ◽

Vol 103 (B11) ◽

pp. 26949-26961 ◽

Cited By ~ 17

Author(s):

John F. Cassidy ◽

Robert M. Ellis ◽

Costas Karavas ◽

Garry C. Rogers

Keyword(s):

Northern Limit ◽

Juan De Fuca Plate ◽

Juan De Fuca ◽

Plate System

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Blended acquisition with dispersed source arrays

Geophysics ◽

10.1190/geo2011-0480.1 ◽

2012 ◽

Vol 77 (4) ◽

pp. A19-A23 ◽

Cited By ~ 46

Author(s):

A. J. Berkhout

Keyword(s):

High Frequency ◽

Spatial Sampling ◽

Acquisition Process ◽

Air Gun ◽

Seismic Acquisition ◽

Sampling Intervals ◽

Source Array

Blended source arrays are historically configured with equal source units, such as broadband vibrators (land) and broadband air-gun arrays (marine). I refer to this concept as homogeneous blending. I have proposed to extend the blending concept to inhomogeneous blending, meaning that a blended source array consists of different source units. More specifically, I proposed to replace in blended acquisition the traditional broadband sources by narrowband versions — imagine coded single air guns with different volumes or coded single narrowband vibrators with different central frequencies — together representing a dispersed source array (DSA). Similar to what we see in today’s audio systems, the DSA concept allows the design of dedicated narrowband source elements that do not suffer from the low versus high frequency compromise. In addition, the DSA concept opens the possibility to use source depths and spatial sampling intervals that are optimum for the low-, mid-, and high-frequency sources (multiscale shooting grids). DSAs are considered to be an important step in robotizing the seismic acquisition process.

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Detecting gas leakage using high-frequency signals generated by air-gun arrays

Geophysics ◽

10.1190/geo2016-0483.1 ◽

2017 ◽

Vol 82 (2) ◽

pp. A7-A12 ◽

Cited By ~ 4

Author(s):

Martin Landrø ◽

Fredrik Hansteen ◽

Lasse Amundsen

Keyword(s):

High Frequency ◽

Field Experiments ◽

Water Layer ◽

Sampling Interval ◽

Acoustic Energy ◽

Storage Site ◽

High Frequency Signal ◽

Gas Leakage ◽

Temporal Sampling ◽

Air Gun

Recent field experiments have demonstrated that marine air-gun arrays create acoustic energy greater than 1 kHz. We have suggested to use the high-frequency signal as a source to look for gas leakage at, for instance, a producing hydrocarbon field, or a [Formula: see text] storage site in which the field is covered by permanent acoustic sensors at the seabed, often referred to as a permanent reservoir monitoring field. The only needed modification is that the temporal sampling interval for the receivers is decreased to 0.1 ms (in contrast to the normal sampling interval of 1 or 2 ms), to ensure that the system is capable of recording signals up to 5 kHz. We suggest using numerous fixed receivers at the seabed to detect a gas chimney by simple high-pass filtering and subsequent transmission type analysis of the recorded signals. We think this method might serve as an elegant, precise, and very cost-effective way to detect gas leakage into the water layer.

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