Dipping layer reflection events and the common midpoint gather Environmental and Exploration Geophysics II Dipping layer reflection events and the common midpoint gather tom.h.wilson tom.wilson@mail.wvu.edu Department of Geology and Geography West Virginia University Morgantown, WV Tom Wilson, Department of Geology and Geography

Objectives for the day A shot record view of the dipping layer reflection Analysis of the dipping layer reflection The concept of normal moveout correction The problem posed by dipping layers Common midpoint sorting Tom Wilson, Department of Geology and Geography

Dipping Layer Reflection Event with Offset Apex Tom Wilson, Department of Geology and Geography

How do you find depth h, velocity V and dip ? Tom Wilson, Department of Geology and Geography

If you could not see the direct arrival then you could solve for V using either expressions for t0 or tapex. Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

This is referred to as a stacking chart This is referred to as a stacking chart. The significance of the name will become apparent later on. Tom Wilson, Department of Geology and Geography

Bring questions to class on Tuesday For next week at this time construct a stacking chart for a symmetrical split spread consisting of 12 geophones arranged 6 on each side of the source. Bring questions to class on Tuesday Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

The effect of the moveout correction on the traces in the common midpoint (CMP) gather is to create a composite normal incidence trace that effectively shares a coincident source and receiver at the midpoint shared by all the traces in the gather. We’ll discuss CMP data in more detail in a couple lectures. Tom Wilson, Department of Geology and Geography

Homework Construct a stacking chart for a symmetrical split spread consisting of 12 geophones arranged 6 on each side of the source (see handout). Bring questions to class next Monday. Chart is due next Wednesday. Complete your reading of Chapter 4. Dipping layer reflection events are covered on pages 183-186, with additional discussion on pages 186-196. The idea of common depth point sorting is discussed on pages 225 -229. We’ve talked tangentially about resolution (217-219) and velocity analysis (233-238). We will be talking about stacking of CDP gathers (238- 241) and migration (241-244). Discussions of migration will come later but it is helpful to be aware of the issues early on. Look over problems 4.1, 4.4 and 4.8. Tom Wilson, Department of Geology and Geography