Fundamentals of the *** reflection point multiple superposition method

From the discussion in Chapter 2, it can be seen that the *** reflection point time-distance curve is a hyperbola, which is symmetrical to the time axis of the *** center point. Since each of the *** reflection point channel sets is a reflected wave from the same point (as shown in Figure 2-1-8), they have similar waveforms. Because of the different gun check distances at each reception point, there is a travel time difference between the channels, i.e., there is a normal time difference. If these original recorded channel sets are directly added together, the reflected wave energy will partially cancel each other, failing to achieve the purpose of multiple overlays to enhance the reflected wave signal. Therefore, in the channel set before the superposition, must eliminate the channel set due to the different distance between the gun check and the reflected wave generated by the time difference between the receiving point, so that the receiving point of the reflected wave travel time are corrected to *** center point of the vertical reflection time t0, and then the superposition of the superposition of the channel for the superposition. This causes the reflected wave to be strengthened and the interfering wave to be weakened accordingly, as shown in Figure 4-1-1.

From the second chapter of equation (2-1-22), *** reflection point time distance curve equation:

Reflection wave seismic exploration principles and data interpretation

Normal time difference Δt is

Reflection wave seismic exploration principles and data interpretation

Figure 4-1-1 *** Reflection point superimposition method principle schematic diagram

The above equation shows that The normal time difference Δt is related to the gun check distance x, wave velocity v, and the vertical reflection time t0 at the center point of ***. When the speed v and t0 are certain, the normal time difference Δt increases with the increase of the gun checking distance x.

Generally, we subtract the travel time of each superimposed channel at the *** reflection point from its normal time difference, which is called normal time difference correction, also known as dynamic correction. The essence of the dynamic correction is the hyperbolic shape of the *** reflection point time-distance curve corrected to become a straight line t = t0, that is, the *** reflection point channel set of the reflected wave travel time are corrected to become the vertical reflection time at the center of the **** t0. With the *** gun point dynamic correction amount of the formula is similar to the derivation of the formula, can be obtained *** reflection point time-distance curve of the amount of the dynamic correction of the approximate formula for the

Reflected-wave seismic survey principles and data interpretation

Reflected-wave seismic survey principle and data interpretation

For the obtained *** reflection point time distance curve with formula (4-1-2) or formula (4-1-3) for dynamic correction will produce two situations: ① for a reflected wave, different gun check distance of the superposition of each time are corrected to the *** center of the vertical reflection time t0, the time distance curve is flattened, superimposed on the first reflected wave is strengthened, see Figure 4-1-1 (a), the time distance curve is flattened, the superposition of the wave is strengthened, see the first reflected wave. 1(a). ② For the regular interference wave, due to the propagation path and propagation speed are different, its time-distance curve and the time-distance curve of the primary reflection wave are different, its time difference with the vertical reflection time t0 at the center point of the *** is

Reflected Wave Seismic Exploration Principles and Data Interpretation

Because of the Δt interference ≠ Δt primary wave, after the dynamic correction, there still exists a residual time-difference Δt, which is

Reflected wave seismic exploration principles and data interpretation

Because of the regular interference wave by the normal time difference correction, there is a residual time difference; superimposed, there is always a part of the energy to cancel each other, so it is suppressed.

From the above analysis, we can get *** reflection point of the principle of multiple superposition: it is the use of the effective wave (a reflected wave) and the rule of interference waves (multiple waves) by the dynamic correction after the existence of the residual time difference between the difference to highlight the effective wave, suppression of the interference wave, to improve the information signal-to-noise ratio.