Seismic wide-angle reflection and refraction
Geophysical investigation technique
- 1 min read
- 3 chapters
Explore on Lably
ToursExplore Lably’s 3D toursTheory
In comparison to the typical seismic reflection survey, which is restricted to relatively small incidence angles due to the limited offsets between source and receiver, wide-angle reflection and refraction (WARR) data are acquired with long offsets, allowing the recording of both refracted and wide-angle reflection arrivals.
Sign in to keep reading
2 more chapters are free with a Lably account.
Acquisition
The acquisition setup depends on the type of seismic source being used and the target of the investigation.
Receiver
The sound waves are normally recorded using 3-component seismometers, with ocean-bottom seismometers (OBS) used offshore. The three components allow the recording of S-waves as well as the P-waves that single component instruments can record. The offset range used depends on the depth of the target. For the top few kilometres of the crust, such as when investigating beneath a thick layer of basalt, a range of 10–20 km may be appropriate, while for the lower crust and mantle, offsets greater than 100 km are normally necessary.
Modelling
The processing approach used in standard seismic reflection profiling is not appropriate for wide-angle data. The main modelling approach used for WARR profiles is to match predicted travel times, based on the geology, with those observed in the data. An initial model of variations in seismic velocity is set up, based on whatever knowledge is available from other sources. A ray tracing algorithm is used to calculate the travel times and the model is adjusted iteratively to reduce the misfit between observed and modelled times. Most modelling uses P-waves, but S-waves are also modelled in some cases.