Aligning microseismic reflections for imaging

In search of P-reflections

The reader will, of course, have observed that we have only shown a shear reflection in the above. Looking at the direct arrivals, we can see that the direct P waves are weaker than the direct S waves, so it should not be surprising that the reflected P waves may be quite weak.

We used our running window cross-correlation program to cross-correlate direct P arrivals with whole seismograms with the hope of finding P-reflections. Results of such an approach can be seen on Figure 4(b). We can see in this figure that on the original seismogram, the P reflection seen at around 2.2s was not apparent and was actually brought up by the cross-correlation of the direct P with the whole seismogram. It turns out that the stronger the P arrival we use in cross correlations, the more likely we are to find an arrival that can be a P-reflection.

Bonner0209,B0209-p
Figure 4. a) seismogram with P-reflection not strong enough to be seen b) cross-correlation result with direct P-wave, with a possible reflection appearing at about 0.23s.

Aligning microseismic reflections for imaging