• journal_title：Geophysics
• Contributor：Ammanuel Fesseha Woldearegay ; Priyank Jaiswal ; Alexander R. Simms ; Hanna Alexander ; Leland C. Bement ; Brian J. Carter
• Publisher：Society of Exploration Geophysicists
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.1190/geo2011-0218.1
• journal_abbrev：Geophysics
• issn：0016-8033
• volume：77
• issue：2
• firstpage：B87
• section：Case Histories

Depth imaging in ultrashallow (<mml:math><mml:mrow><mml:mo form="prefix"><</mml:mo><mml:mn>50</mml:mn><mml:mrow><mml:mo> </mml:mo></mml:mrow><mml:mrow><mml:mo> </mml:mo></mml:mrow><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math><50  m) environments presents twofold challenge: (1) coda available for depth migration is very limited; and (2) conventional time processing with limited coda generally fails to estimate reliable velocity models for depth migration. We studied the combining of first-arrival traveltime inversion and prestack depth migration (PSDM) for depth imaging of ultrashallow paleochannel stratigraphy associated with the Bull Creek drainage system, Oklahoma. Restricted by a limited number of geophones (24) we acquired data for inversion and migration through two coincident profiles. The first profile for inversion has a wider survey-aperture (115-m maximum shot-receiver spacing) and consequently sparse CMP spacing (2.5 m), whereas the second profile for PSDM has denser CMP spacing (1 m) and consequently a narrower survey aperture (46-m maximum shot-receiver spacing). We also found that the velocity model from traveltime inversion of the wider-aperture data set is more preferable for depth-migration than the velocity model from time processing of the denser data set. The preferred depth image showed three episodes of incision whose chronological order is resolved through radio-carbon dating of terrace sediments. Results suggested that even with limited geophones, depth imaging of ultrashallow targets can be achieved by combining first-arrival traveltime inversion and PSDM through coincident wide- and narrow-aperture acquisitions.