LAB 1 : Examine Seismic Data

A seismic data must be carefully looked into by geophysicists for the first time such as its header, which contains information and paramaters value used to acquire data. The data is usually saved in many types of data formats such as the typical SEG-Y or Seismic Unix formats.

Seismic data and its header information are stored in MATLAB data format file called SeismicData.mat. The dataset that will be used consists of a 2D land line from east Texas, USA. Followings are some important parameters about the data.

• ·           Number of shots = 18
• ·         Source type = dynamite in 80-100 ft depth holes
• ·         Number of channels per shots = 33
• ·         Receiver type = Vertical component geophones
• ·         Array type = 12-element inline
• ·         Number of traces in line = 594
• ·         Receiver interval = 220 ft
• ·         Shot interval is variable
• ·         Time sampling interval = 2ms
• ·         Number of time samples per trace = 1501
• ·         Data format = SEG-Y
• ·         Byte swap type = Big endian
• ·         Data file name = data.sgy
• ·         Geometry has already beed set up and recorded in the trace headers
• ·         Uphole times at shot locations have been recorded in the trace headers
• ·         An 8-64 Hz bandpass has been applied to the data in the field.

After loading the data, the variable H is found out to be 1x594 structure array with many fields:

Number of traces per shot

Receiver information per seismic trace

Source of elevation profile for each trace

Stacking chart plot of the Seismic data

 There are many ways to display seismic sections including seismic shot gathers and CMP gathers and the most commonly used displays are:

        1.      The wiggle display
        2.      The variable area display
        3.      And The variable density display

Figure 5-7 shows an example of shot gather number 8 displayed using variable area display scheme and variable density display scheme in both gray and colors respectively. To extract these, we used the function extracting_shots.m

1.              Load SeismicData.mat
2.              Shot_num=8;
3.              P=0;
4.              [Dshot,dt,dx,t,offset] = extracting_shots(D,H,shot_num,p);

  

Figure 5: Variable are display

Figure 6: Grayscaled variable density display

   

Figure 7: colored variable density display

                      

Figure 8 displays a group of seismic shot gather concatenated together using the same function extracting_shots.m. As for this example, we extract shot gathers number 4-6 by the code of

         Mwigb (Dshot, scale, offset, t)

Variable area display at seismic shot gathers 4-6