Digital Refraction Seismograph Seismic Survey Equipment For SASW/MASW Borehole Shear Wave Test

Digital Refraction Seismograph Seismic Survey Equipment For SASW/MASW Borehole Shear Wave Test

Application

    Explosive sources are artificial sources widely used in seismic exploration. At present, a series of ground sources have been developed, such as heavy hammers, continuous vibration sources, pneumatic sources, etc., but explosives are still the most important sources often used in land seismic exploration. In addition to explosive sources, offshore seismic exploration also widely uses air guns, steam guns, and electric spark detonation gas.

    Seismic exploration is an important means of exploring oil and natural gas resources before drilling. It is also widely used in coalfield and engineering geological surveys, regional geological research and crustal research. Since the 1980s, seismic exploration methods have also been selectively used in the exploration of certain types of metal mines.

Exploration process

    The seismic exploration process consists of three stages: seismic data acquisition, data processing and seismic data interpretation.

Exploration methods

      Including reflection method, refraction method and seismic logging (see borehole geophysical exploration). All three methods can be applied on land and sea.

    When studying very shallow or deep interfaces and looking for special high-speed strata, refraction method is more effective than reflection method. However, the application of refraction method must meet the specific requirement that the wave velocity of the lower layer is greater than the wave velocity of the upper layer, so the application scope of refraction method is limited. The application of reflection method only requires that the wave impedance of the rock layer changes, which is easy to meet, so the reflection method is widely used in seismic exploration.

Types of seismic waves

There are two main types of seismic waves: surface waves and body waves. Surface waves are only transmitted on the surface, while body waves can pass through the interior of the earth.

Body waves: They are transmitted inside the earth and are divided into P waves and S waves.

P waves: P stands for primary or pressure, which is a longitudinal wave. The direction of particle vibration is parallel to the direction of wave advance. Among all seismic waves, it has the fastest forward speed and arrives first. P waves can be transmitted in solids, liquids or gases.

S waves: S stands for secondary or shear, which has a forward speed second only to P waves. The direction of particle vibration is perpendicular to the direction of wave advance. It is a transverse wave. S waves can only be transmitted in solids and cannot pass through the liquid outer core.

Using the different transmission speeds of P waves and S waves and the travel time difference between the two, simple earthquake positioning can be performed.

Surface waves: Surface waves caused by shallow earthquakes are the most obvious. Surface waves have the characteristics of low frequency, high amplitude and dispersion. They are transmitted only near the surface and are the most powerful seismic waves.

Love Wave: The particle vibration direction is perpendicular to the wave's forward direction, but the vibration only occurs in the horizontal direction without a vertical component. It is similar to S waves, but the difference is that the lateral vibration amplitude decreases with increasing depth.

Rayleigh wave: Also known as ground roll, the particle movement is similar to that of sea waves. On the vertical plane, the particles vibrate in a counterclockwise elliptical shape, and the vibration amplitude also decreases with increasing depth.

Main technical indicators

Product Details