WIDE ANGLE REFLECTIONS AND THEIR APPLICATION TO FINDING LIMESTONE STRUCTURES IN THE FOOTHILLS OF WESTERN CANADA

Geophysics ◽  
1960 ◽  
Vol 25 (2) ◽  
pp. 385-407 ◽  
Author(s):  
T. C. Richards
Keyword(s):  
High Velocity ◽  
Seismic Event ◽  
Critical Distance ◽  
Western Canada ◽  
Wide Angle ◽  
Normal Reflection ◽  
Theoretical Evidence ◽  
Strong Seismic Event

Experimental and theoretical evidence is presented to show that a strong seismic event, occurring late in a record and at distances beyond the critical distance, is a wide angle reflection: and not a refraction from a high velocity limestone formation. The evidence includes studies of the effects of anisotropy on the velocities along reflected and refracted paths and of the variation of amplitude of the event with distance. The paper also describes how the results of broadside wide angle reflection shooting may be combined with normal reflection shooting to map strongly dipping limestone structures. An application to a profile through a foothills well in Western Canada is included.

scholarly journals Surface-wave images of western Canada: lithospheric variations across the Cordillera–craton boundary

2018 ◽  
Vol 55 (8) ◽  
pp. 887-896 ◽  
Author(s):  
Taras Zaporozan ◽  
Andrew W. Frederiksen ◽  
Alexey Bryksin ◽  
Fiona Darbyshire
Keyword(s):  
Surface Wave ◽  
Phase Velocity ◽  
Upper Mantle ◽  
High Velocity ◽  
Western Canada ◽  
Low Velocity ◽  
Phase Velocities ◽  
Slave Province ◽  
Upper Mantle Structure ◽  
Tectonically Active

Two-station surface-wave analysis was used to measure Rayleigh-wave phase velocities between 105 station pairs in western Canada, straddling the boundary between the tectonically active Cordillera and the adjacent stable craton. Major variations in phase velocity are seen across the boundary at periods from 15 to 200 s, periods primarily sensitive to upper mantle structure. Tomographic inversion of these phase velocities was used to generate phase velocity maps at these periods, indicating a sharp contrast between low-velocity Cordilleran upper mantle and high-velocity cratonic lithosphere. Depth inversion along selected transects indicates that the Cordillera–craton upper mantle contact varies in dip along the deformation front, with cratonic lithosphere of the Taltson province overthrusting Cordilleran asthenosphere in the northern Cordillera, and Cordilleran asthenosphere overthrusting Wopmay lithosphere further south. Localized high-velocity features at sub-lithospheric depths beneath the Cordillera are interpreted as Farallon slab fragments, with the gap between these features indicating a slab window. A high-velocity feature in the lower lithosphere of the Slave province may be related to Proterozic or Archean subduction.

Damage Due to Cavitation and Sub-Cooled Boiling Bubble Collapse

1968 ◽  
Vol 183 (1) ◽  
pp. 31-50 ◽  
Author(s):  
F. G. Hammitt
Keyword(s):  
Shock Wave ◽  
High Velocity ◽  
Wave Model ◽  
Bubble Collapse ◽  
Spherical Shock Wave ◽  
Cavitation Damage ◽  
Present Evidence ◽  
Theoretical Evidence ◽  
Shock Wave Model ◽  
Spherical Shock

The possibility of the applicability of spherical symmetry to cavitation and highly sub-cooled bubble collapse is considered in the light of present photographic and theoretical evidence, and it is concluded that such symmetry is unlikely in situations of engineering importance. Rather an asymmetry which generates a high-velocity microjet is a more likely mode of collapse. The present evidence relative to the importance of microjet impact as opposed to the classical spherical shock-wave model for cavitation damage is examined and some new experimental evidence presented. It is concluded that the microjet model is most likely of predominant importance in cavitation damage. Some estimates for the pertinent parameters of such microjets are presented.

Seismic structure of the Central Metasedimentary Belt, southern Grenville Province

1994 ◽  
Vol 31 (2) ◽  
pp. 243-254 ◽  
Author(s):  
C. A. Zelt ◽  
D. A. Forsyth ◽  
B. Milkereit ◽  
D. J. White ◽  
I. Asudeh ◽  
...  
Keyword(s):  
Seismic Data ◽  
High Velocity ◽  
Hanging Wall ◽  
New York State ◽  
Lake Ontario ◽  
Wide Angle ◽  
Seismic Structure ◽  
Lateral Velocity ◽  
Crust And Upper Mantle ◽  
Grenville Province

Crust and upper-mantle structure interpreted from wide-angle seismic data along a 260 km profile across the Central Metasedimentary Belt of the southern Grenville Province in Ontario and New York State shows (i) relatively high average crustal and uppermost mantle velocities of 6.8 and 8.3 km/s, respectively; (ii) east-dipping reflectors extending to 24 km depth in the Central Metasedimentary Belt; (iii) weak lateral velocity variations beneath 5 km; (iv) a mid-crustal boundary at 27 km depth; and (v) a depth to Moho of 43–46 km. The wide-angle model is generally consistent with the vertical-incidence reflectivity of an intersecting Lithoprobe reflection line. The mid-crustal boundary correlates with a crustal detachment zone in the Lithoprobe data and the depth extent of east-dipping wide-angle reflectors. Regional structure and aeromagnetic anomaly trends support the southwest continuity of Grenville terranes and their boundaries from the wide-angle profile to two reflection lines in Lake Ontario. A zone of wide-angle reflectors with an average apparent eastward dip of 13° has a surface projection that correlates spatially with the boundary between the Elzevir and Frontenac terranes of the Central Metasedimentary Belt and resembles reflection images of a crustal-scale shear zone beneath Lake Ontario. A high-velocity upper-crustal anomaly beneath the Elzevir–Frontenac boundary zone is positioned in the hanging wall associated with the concentrated zone of wide-angle reflectors. The high-velocity anomaly is coincident with a gravity high and increased metamorphic grade, suggesting northwest transport of mid-crustal rocks by thrust faulting consistent with the mapped geology. The seismic data suggest (i) a reflective, crustal-scale structure has accommodated northwest-directed tectonic transport within the Central Metasedimentary Belt; (ii) this structure continues southwest from the exposed Central Metasedimentary Belt to at least southern Lake Ontario; and (iii) crustal reflectivity and complexity within the eastern Central Metasedimentary Belt is similar to that observed at the Grenville Front and the western Central Metasedimentary Belt boundary.

VELOCITY SPECTRA AND DIFFRACTION PATTERNS

Geophysics ◽  
1971 ◽  
Vol 36 (2) ◽  
pp. 415-417 ◽  
Author(s):  
W. L. Dinstel
Keyword(s):  
Diffraction Pattern ◽  
High Velocity ◽  
Source Analysis ◽  
Vertical Projection ◽  
Common Depth Point ◽  
Normal Reflection ◽  
Diffraction Patterns ◽  
Velocity Spectra ◽  
Correlation Factors

Analysis of velocity spectra in Tertiary sand‐shale sequences sometimes shows anomalously high velocity events, with high correlation factors, deep in the section. One source of these events may be diffraction patterns. Figure 1 shows a model where a velocity gather is centered over a diffraction source; the diffraction acts like a normal reflection common depth point. Calculations yield the expected velocity of 7500 ft/sec. In Figure 2, the velocity gather is centered 6000 ft on the ground horizontally from the vertical projection of the diffraction source. Analysis of the data of Figure 2 results in a velocity which is quite a bit too high. Various combinations of velocity, depth, and offset produce varying degrees of error. The velocity computed from a spectrum not centered over a diffraction pattern is always too high, when we assume that the diffraction source is in the plane of the section.

Nonlinear dynamic failure process of tunnel-fault system in response to strong seismic event

2013 ◽  
Vol 64 ◽  
pp. 125-135 ◽  
Author(s):  
Zhihua Yang ◽  
Hengxing Lan ◽  
Yongshuang Zhang ◽  
Xing Gao ◽  
Langping Li
Keyword(s):  
Nonlinear Dynamic ◽  
Seismic Event ◽  
Failure Process ◽  
Fault System ◽  
Dynamic Failure ◽  
Strong Seismic Event

scholarly journals A wide-angle outflow with the simultaneous presence of a high-velocity jet in the high-mass Cepheus A HW2 system

2010 ◽  
Vol 410 (1) ◽  
pp. 627-640 ◽  
Author(s):  
J. M. Torrelles ◽  
N. A. Patel ◽  
S. Curiel ◽  
R. Estalella ◽  
J. F. Gómez ◽  
...  
Keyword(s):  
High Velocity ◽  
High Mass ◽  
Wide Angle ◽  
Simultaneous Presence ◽  
Cepheus A

Hypothesis of strong seismic event origin in Rasvumchorr Mine on January 9, 2018

2018 ◽  
Vol 12 ◽  
pp. 74-83 ◽  
Author(s):  
A.А. Kozyrev ◽  
◽  
I.E. Semenova ◽  
O.G. Zhuravleva ◽  
A.V. Panteleev ◽  
...  
Keyword(s):  
Seismic Event ◽  
Strong Seismic Event

The Wide Angle Seismic Wave Field Analysis and Imaging Method below the High Velocity Shield Layers

2004 ◽  
Vol 47 (1) ◽  
pp. 102-109 ◽  
Author(s):  
Zhong-Ping HU ◽  
Lu-Ping GUAN ◽  
Lian-Xing GU ◽  
Liang-Shu WANG ◽  
Da-Li WU ◽  
...  
Keyword(s):  
Wave Field ◽  
Seismic Wave ◽  
High Velocity ◽  
Field Analysis ◽  
Imaging Method ◽  
Wide Angle ◽  
Seismic Wave Field

scholarly journals Seismic velocity structure of the Queen Charlotte terrace off western Canada in the region of the 2012 Haida Gwaii Mw 7.8 thrust earthquake

Geosphere ◽  
2020 ◽  
Author(s):  
M. Riedel ◽  
S. Yelisetti ◽  
C. Papenberg ◽  
K.M.M. Rohr ◽  
M.M. Côté ◽  
...  
Keyword(s):  
High Velocity ◽  
Velocity Structure ◽  
Seismic Refraction ◽  
P Wave ◽  
Seismic Survey ◽  
Western Canada ◽  
Crustal Material ◽  
Haida Gwaii ◽  
Wave Velocities ◽  
Refraction Data

A well-recorded Mw 7.8 megathrust earthquake occurred on 27 October 2012 under the Queen Charlotte terrace off the west coast of Haida Gwaii, western Canada. In this study, we supplement limited earlier seismic refraction work on the offshore velocity structure off Haida Gwaii with data from ocean bottom seismometers (OBS) operating between 6 December 2012 and 5 January 2013. The OBS recorded a portion of the aftershock sequence, and an active-source seismic survey was conducted in January 2013 to acquire seismic refraction data in the region of the Haida Gwaii earthquake across the Queen Charlotte terrace. P-wave velocity analyses using first-arrival tomography showed relatively shallow (2.0–3.0 km below seafloor) high-velocity material with values up to 4.0 km/s beneath the terrace. At the one OBS station seaward of the deformation front on the abyssal plain, refraction velocities of ~4.5 km/s indicated the top of the oceanic plate at ~1–2 km below the seafloor. At sev­eral OBS stations, converted shear-wave velocities were determined within the sediment cover using reflected arrivals. The S-wave velocities ranged from 0.5 to 1.5 km/s, and the corresponding P/S velocity ratio was between 3.0 and 4.2. The new refraction data confirm earlier interpretations of high-velocity material in the shallow terrace that may indicate fractured oceanic crustal material lies significantly above the location where a sub­ducted slab is thought to occur under the terrace. Transpressive deformation of the Pacific plate may explain these observations.

Sign in / Sign up

Export Citation Format

Share Document