About This Item
Share This Item
In the process of incorporating seismic coverage and well data into a single mappable interpretation, many seismic time sections were found to display data with improper static corrections for near-surface velocity anomalies. These anomalies originate in the glacial overburden, which exhibits sudden and sizable variations in thickness and seismicity through much of the Allegheny Plateau of southern New York. An expedient method to compensate for these variations was sought to use the seismic analog data.
Along the southern tier of New York, detachment structures have been
mapped in the Salina and overlying groups, whereas the top of the underlying Lockport Group has been mapped as a relatively smooth homocline dipping south. An appropriate method was selected that is dependent on the simplicity of the structural configuration at depth rather than the complexity of near-surface reflectors. The interface between the Vernon Shale (basal Salina) and the underlying Lockport carbonates is an easily identified reflector on seismic sections. By using the map of the Lockport surface as a reference, reflectors immediately above and below can be mapped using the travel times between reflectors and velocity analyses to calculate isopach information between reflectors. Additional reflectors can be mapped by adding or subtracting isopach information in an upward or ownward continuation manner.
This velocity correction involves digitizing the seismic reflectors and shotpoint map, making or obtaining subsurface regional maps of a reference horizon, and performing simple mathematical calculations on a microcomputer. Independent operators can use this inexpensive and straightforward method to rescue some analog seismic data that might otherwise be regarded as useless. Subtle zones of structural closure have been mapped where initial observations suggest the presence of chaotic deformation.
End_of_Article - Last_Page 1916------------