Seismic Data Acquisition Techniques and Seismograph Mechanics

Seismic Data Acquisition and Seismograph Principles

Key Requirements for Seismic Data Acquisition

The acquisition phase also requires:

• Regional geological knowledge
• Design and recording parameters (energy source and geophones)
• Instrumental control
• Monitoring of recorded information
• Optimization of recording parameters
• Third-party damage control
• Design of operational logistics
• Control and storage of explosives
• Survey monitoring
• Sending tapes to the processing center
• Control and approval of invoices

Determination: Propagation of seismic wave velocities, which are essential elements for entering the depth domain (regardless of the time domain).

Proper Geophone Placement

In terms of location and planting of the geophones, one should always follow the direction of the plumb line (always vertical). Improper placement can lead to:

1. Attenuation of seismic waves
2. Wavefront distortion
3. Increased noise levels

Establishing Reference Velocity

A reference velocity is also needed. Where logs are available, the reference velocity is calculated through a study of plotting average speed values, depending on the depth of the low reference level.

The Necessity of Static Corrections

Static corrections should also be applied. Since the land surface is not completely flat and the media where waves propagate are not completely isotropic due to surface variations, it is necessary to perform these static corrections, which have two purposes:

• To refer recording times to an imaginary plane of constant height, recognized as a datum, which is considered to have a height of 0.
• To subtract the time delay.

Equipment Verification

At this stage, it is also necessary to review all the equipment used to ensure compliance with all requirements specified by the manufacturer.

Understanding Seismograph Fundamentals

The Principle of the Pendulum

A seismograph is a device of varying design and construction used to measure and record ground vibrations at shallow or deep levels. These vibrations may occur from natural phenomena, intentional works, explosions, or atmospheric disturbances, as in the case of artillery fire. Its main feature is a highly balanced device or suspension that responds with great sensitivity to external vibrations.

Seismograph Design and Function

At one end of the device, a marking pen records the oscillations on special paper. This paper is arranged on a rotating element driven by clockwork. The most basic design is the simple pendulum.

Earth-Pendulum Interaction and Resonance

The relationship between the movement of the earth and the pendulum or spring depends on the relationship between the natural period and the period of the reported instrument movement, as well as the damping of the system.

When the natural period is the same or very close to the period of the ground, the seismograph will trigger a resonance that increases the amplitude of the response. Because they are limited to specific frequency bands where resonances occur, it is necessary to synchronize the pendulum's length or the spring's constant and mass with the desired frequency range. Using the principle of the pendulum, seismograph motion can be synchronized.