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.

In quest of the flank

Geophysics ◽  
1989 ◽  
Vol 54 (6) ◽  
pp. 701-717 ◽  
Author(s):  
Ken Larner ◽  
Craig J. Beasley ◽  
Walt Lynn
Keyword(s):  
Seismic Data ◽  
Field Data ◽  
Velocity Structure ◽  
Velocity Variation ◽  
Wide Angle ◽  
Lateral Velocity ◽  
Time Migration ◽  
Recent Developments ◽  
Ray Bending ◽  
Accurate Imaging

Primarily through synthetic and field data examples, this paper reviews the benefits of recent developments in time migration of seismic data and reveals limitations, some of them fundamental, that keep elusive the goal of imaging steep events with full accuracy. Even where velocity varies only with depth and, hence, time migration should suffice, accurate imaging of very steep events requires that the velocity structure be known with considerable precision and be finely sampled in depth. This sensitivity of migration accuracy to detail in velocity structure is attributable to the sensitivity of ray bending for wide‐angle rays to detail in the velocity structure. Also, interestingly, the presence of ray bending at interfaces is seen to enhance the steep‐event accuracy of some algorithms (e.g., phase shift and cascaded finite‐difference) while it degrades the accuracy of others (for example, conventional Kirchhoff summation and the frequency‐wavenumber domain method of Stolt). Of the various time‐migration schemes, a cascading of the Stolt method is the most efficient while having steep‐event accuracy in the presence of significant vertical velocity variation. Its behavior in the presence of even mild lateral velocity variation, however, differs greatly from that of the other methods and must be taken into account. A case involving 3-D migration of 3-D survey data shows how different issues in imaging of the subsurface (two‐pass versus single‐pass 3-D migration and algorithm choice in the presence of mild lateral velocity variation) can become intertwined in practice and lead to confusion as to which of the issues is essential for accurate imaging of the subsurface.

THE CRUST AND UPPER MANTLE STRUCTURES IN CENTRAL ANATOLIA, TURKEY, CONSTRAINED BY GRAVITY AND SEISMIC DATA

2020 ◽  
Author(s):  
Yagmur Yilmaz ◽  
◽  
Alain Plattner ◽  
Rezene Mahatsente ◽  
Ibrahim Çemen ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Seismic Data ◽  
Central Anatolia ◽  
Crust And Upper Mantle

scholarly journals Structure and evolution of the Atlantic passive margins: A review of existing rifting models from wide-angle seismic data and kinematic reconstruction

2021 ◽  
Vol 126 ◽  
pp. 104898
Author(s):  
Youssef Biari ◽  
Frauke Klingelhoefer ◽  
Dieter Franke ◽  
Thomas Funck ◽  
Lies Loncke ◽  
...  
Keyword(s):  
Seismic Data ◽  
Wide Angle ◽  
Passive Margins

scholarly journals Subglacial water-sheet floods, drumlins and ice-sheet lobes

1999 ◽  
Vol 45 (150) ◽  
pp. 201-213 ◽  
Author(s):  
E.M. Shoemaker
Keyword(s):  
New York ◽  
Lake Michigan ◽  
New York State ◽  
Ice Sheet ◽  
Lake Ontario ◽  
High Water ◽  
Green Bay ◽  
Subglacial Lake ◽  
Western Lake ◽  
Subglacial Lakes

AbstractThe effect of subglacial lakes upon ice-sheet topography and the velocity patterns of subglacial water-sheet floods is investigated. A subglacial lake in the combined Michigan–Green Bay basin, Great Lakes, North America, leads to: (1) an ice-sheet lobe in the lee of Lake Michigan; (2) a change in orientations of flood velocities across the site of a supraglacial trough aligned closely with Green Bay, in agreement with drumlin orientations; (3) low water velocities in the lee of Lake Michigan where drumlins are absent; and (4) drumlinization occurring in regions of predicted high water velocities. The extraordinary divergence of drumlin orientations near Lake Ontario is explained by the presence of subglacial lakes in the Ontario and Erie basins, along with ice-sheet displacements of up to 30 km in eastern Lake Ontario. The megagrooves on the islands in western Lake Erie are likely to be the product of the late stage of a water-sheet flood when outflow from eastern Lake Ontario was dammed by displaced ice and instead flowed westward along the Erie basin. The Finger Lakes of northern New York state, northeastern U.S.A., occur in a region of likely ice-sheet grounding where water sheets became channelized. Green Bay and Grand Traverse Bay are probably the products of erosion along paths of strongly convergent water-sheet flow.

scholarly journals Geometry of the Deep Calabrian Subduction (Central Mediterranean Sea) From Wide‐Angle Seismic Data and 3‐D Gravity Modeling

2020 ◽  
Vol 21 (3) ◽  
Author(s):  
David Dellong ◽  
Frauke Klingelhoefer ◽  
Anke Dannowski ◽  
Heidrun Kopp ◽  
Shane Murphy ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Seismic Data ◽  
Gravity Modeling ◽  
Wide Angle ◽  
Central Mediterranean ◽  
Central Mediterranean Sea

scholarly journals Improved Detection Using Negative Elevation Angles for Mountaintop WSR-88Ds. Part III: Simulations of Shallow Convective Activity over and around Lake Ontario

2007 ◽  
Vol 22 (4) ◽  
pp. 839-852 ◽  
Author(s):  
Rodger A. Brown ◽  
Thomas A. Niziol ◽  
Norman R. Donaldson ◽  
Paul I. Joe ◽  
Vincent T. Wood
Keyword(s):  
New York ◽  
Flow Direction ◽  
New York State ◽  
Lake Ontario ◽  
Heavy Snowfall ◽  
Land Area ◽  
Lake Effect ◽  
Northern Side ◽  
Low Altitude ◽  
The Difference

Abstract During the winter, lake-effect snowstorms that form over Lake Ontario represent a significant weather hazard for the populace around the lake. These storms, which typically are only 2 km deep, frequently can produce narrow swaths (20–50 km wide) of heavy snowfall (2–5 cm h−1 or more) that extend 50–75 km inland over populated areas. Subtle changes in the low-altitude flow direction can mean the difference between accumulations that last for 1–2 h and accumulations that last 24 h or more at a given location. Therefore, it is vital that radars surrounding the lake are able to detect the presence and strength of these shallow storms. Starting in 2002, the Canadian operational radars on the northern side of the lake at King City, Ontario, and Franktown, Ontario, began using elevation angles of as low as −0.1° and 0.0°, respectively, during the winter to more accurately estimate snowfall rates at the surface. Meanwhile, Weather Surveillance Radars-1988 Doppler in New York State on the southern and eastern sides of the lake—Buffalo (KBUF), Binghamton (KBGM), and Montague (KTYX)—all operate at 0.5° and above. KTYX is located on a plateau that overlooks the lake from the east at a height of 0.5 km. With its upward-pointing radar beams, KTYX’s detection of shallow lake-effect snowstorms is limited to the eastern quarter of the lake and surrounding terrain. The purpose of this paper is to show—through simulations—the dramatic increase in snowstorm coverage that would be possible if KTYX were able to scan downward toward the lake’s surface. Furthermore, if KBUF and KBGM were to scan as low as 0.2°, detection of at least the upper portions of lake-effect storms over Lake Ontario and all of the surrounding land area by the five radars would be complete. Overlake coverage in the lower half (0–1 km) of the typical lake-effect snowstorm would increase from about 40% to about 85%, resulting in better estimates of snowfall rates in landfalling snowbands over a much broader area.

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