short notes about seismic stratigraphy

this kind of information may be obtained either from surface exposures and outcrops,

or from the subsurface via well logs and cores
another important source of information otfen used in stratigraphic and

basin studies is SEISMIC data

seismic surveys provide information about the geology that lies beneath the Earth's surface.

This is achieved by sending seismic waves into the subsurface and recording

the reflected or refracted energy that returns to the surface.

A reflection is produced where a seismic wave encounters an interface that reflects part of the wave's energy back to the surface.

Notice that, for seismic data, the vertical scale is measured in time

, not in depth. Two-way time (TWT) is the time for a seismic wave to

travel down to a reflector and back to the surface.

The extent which a surface reflects seismic energy is a function of

quantity called ACOUSTIC IMPEADANCE

.... or to be more precise, it depends on the CONTRAST in acoustic impeadance across the surface

little or no contrast in acoustic impeadance

marked contrast in acoustic impeadance:REFLECTION

The seismic line opposite shows strong reflectors, indicating high acoustic

impeadance contrast. as well as more opaque areas that suggest low contrast

it is believed that seismic reflectors approximate to time lines

i.e.

A sharp facies change across a bedding plane is likely to be associated with a sharp impeadance contrast, leading to reflection of seismic waves

in effect, reflection are only generated from stratigraphic surfaces (e.g. bedding contacts) across which there is a contrast in acoustic impeadance.

In stratigraphic studies, seismic is particularly useful for illustrating large scale stratal geometries.

In addition, changes in the character or reflections can be used to provide information about lateral variability in lithology and/or depositional process.