Seismic Energy Sources explained

You have already either heard or sense about Earth's Vibration (Earthquake)!. In Earthquake seismology when we talk about seismic source, geologically it is from stress released by brittle fracturing of long termed strained rock. However in seismic exploration (reflection and refraction), this seismic energy is from artificial devices such as vibrators and dynamite, just to mention a few.

Since there is an important relationship between Energy and frequency, then Energy should vary inversely to time. Hence it is true that if we say an ideal seismic source creates a wavelet that has short duration and high energy and not otherwise. This is because short duration improves survey resolution and higher energy produces a higher amplitude wavelet making it easier to detect the seismic signal within background noise.

Here down today I would like to convey to you through this post, a brief about these seismic energy sources. Let's continue together!

What are seismic Energy Sources?

Seismic Energy Source can be defined as any device, equipment or tool that can be used to generate seismic Energy.

Most common energy Sources depend upon where (environment) at which the seismic survey will be conducted, such as Land survey, have seismic energy sources compared to Marine seismic survey.

We can classify seismic energy sources based on various factors,

Based on Environment

This is where seismic survey (seismic data acquisition) is conducted. It can either be Land seismic survey or Marine seismic survey

Land Vs Marine energy sources

Land Seismic Sources: Are the one at which their operations take place at dry areas such as desert or any other terrestrial area. Examples: Sledge Hammer, Drop weight, Impulsive devices like shotguns.

Marine Seismic Sources: These involve their operations below or at the surface of water bodies. Example: Air gun, dynamite.

Based on Nature of Operations

Impulsive Sources: These apply a huge force in a short period of time.

Non - Impulsive sources: These apply a force at gradual periods of time. Such that the force can be constant under a long period of time.

Explosives Vs Non - Explosives

Explosives sources apply the explosion mode of operation in which the explosive chemicals are detonated with electrical charges within drill holes (6 - 30m). The energy may be sufficient to be used in survey, however the drawback of this source is that there are some restrictions on explosive handling, logistics and storage. Also environmental safety regulation must be adhered to since it is a destructive source. Example dynamite.

Non - Explosive Sources operate without the use of explosion, they can either be Vibrators like Vibroseis, small - electromechanical vibrators or drop weight, Sledge hammer. They can be used in town since they are non destructive.

Common used Seismic energy sources

Vibrators: we can define it as any device that can generate vibrations from mechanical means. I would like to talk about Vibroseis before going to the discussion. Let's first briefly prerequisite the basics of physics laid behind the vibrator. For any body to vibrate it should be at equilibrium position, then if the force is applied to disturb the body it will start to oscillate to and fro from its mean position. This is known as a forced vibration example of an oscillating spring.

Vibroseis:These use Vibrating impact technology that produces seismic energy into the ground via a vehicle (truck) - mounted vibrating Base plate. When the sent energy is received by the receiver they produce a signal known as sweep signal (see figure 1 below). The maximum of applied (Peak) force is 105 lbf, however this may vary depending on the capacity of Vibroseis itself. The energy frequency produced is between 10 - 80 Hz. Sweeping signals from different layers and points are added together to produce an output signal with high signal to Noise ratio, so that resolution can be improved.

Figure 1: Vibroseis wave train

This is the most applied source for seismic reflection exploration in desert or in some dry cities where the ground is hard sufficient to compensate for the overall weight of the truck. However the source is limited to areas which are remote or those with enough moisture or subsurface is highly weathered and eroded with more underground caverns, sinkholes that may cause sinking of the truck during operation.

Another limit is that it is expensive to operate due to site preparation (seismic line clearance) especially in Forest regions and trucks are heavy that require expensive logistics. Hence it is limited only to Large land Seismic surveys rather than small ones.

Airgun: This uses the simple principle that the high pressure bubble (10 - 15MPa) is electrically released from the air compressor into a submerged part of the water in order to produce a very high pressure with small operation. The pressurized water after being bounced at some boundary at seabed then will cause effect to the seismic receiver (hydrophones) placed at the water surface.

The frequency of the released wavelet can be controlled by using the air vent with different volumes depending on survey objectives.

It's only the basics about these seismic energy sources as the aim of this blog title described.

Thanks for reading this! And share if you liked

You can Follow this blog on Telegram group to gain more benefits.

Your Support is also welcomed! If you found this content helpful to you!

Don't hesitate to check a simple list below for Electrical resistivity or Seismic equipment and tools that may assist your work.

BASIC SEISMIC TOOLS

- 3D Components - Geophones, detector, vibration sensors

- GD - One Geophone and Exploration equipment

- GDH - 4.5 Seismograph and Vibration sensors

- Seismic receiver

BASIC RESISTIVITY EQUIPMENTS and TOOLS