Subsurface mapping Subsurface survey techniques Physical methods of subsurface mapping Types of sub-surface mapping techniques

1. Physical methods of subsurface mapping
The following five types are mentioned below,
1. Seismic surveys:
Seismic survey arethe most common ones and the most usefultechnique for this
purpose. The Earth comprises of many different layers with various thicknesses
and densities.
In this method, a sourceof energy fromthe surfaceoccurs, waves of energy are
reflected and refracted back towards the surfaceat different velocities and times.
Geophones are placed all over the earth and record these seismic waves. These
waves are then sent to a seismogramthat generates a seismic station or basically
a 2D slice of the Earth below the surface.
Itis then further divided into Seismic Refraction, Seismic Reflection and Surface
wavesurvey.
SeismicReflection SurveyinSea

2. Benefits: This station tells us, types of rock, their depth, and the presenceof
unconformities. The reason that this is the mostcommon survey method is
because wecan create our own shock waves fromthe surfaceand get readings of
the Earth wherever we need them.
2. Gravity Surveys:
Such survey is generally done using gravimeters (an instrumentfor measuring the
difference in the forceof gravity fromone place to another), which measure
variations in the gravitational field on Earth. Denser rocks emit a greater
gravitational field allowing geophysicists to get a good idea of how deep these
certain rock layers are.
3. Magnetometer Surveys:
These surveys arecompleted by dragging or pulling a
magnetometer behind a ship or airplane. This magnetometer
detects slight shifts in Earth’s magnetic fields indicating how
deep certain magnetized rocks areburied.
4. Magneto-telluric or (MT) Surveys:
Itoperates on the principle that different rocks have different
electrical properties. Geophysicists measurethe naturally occurring flow of
electricity at different depths and usethat info to create electromagnetic images
of subsurfaceformations.
5. Magnetic and Electromagnetic Surveys:
These surveys allow geophysicists to get a better understanding and picture of
the configuration of subsurfacerock formations becauseof magnetic fields
emitted by minerals in different types of rocks. This typeof survey is very useful
to find faults.
MagnetometerSurvey