I'm a PhD student researching seismic amplification in a NZ sedimentary basin. I hope that somebody will be able to help me in my interpretation of the 2D seismic lines that traverse the basin. As per the attached image, I am somewhat baffled by the amount confusion in the seismic signals below the surface(shown within red rectangles) that are appearing where I would expect a regular stratigraphic sequence. I have attempted to delineate fault lines but I don't know how successful I am in this aspect. I point out that the mid formation (250-1250m) is consolidated marine sediments, above this mostly sediments from a volcanic source (silts, sands and pebbles mostly unconsolidated).
While the region has historically been understood as passive in terms of seismic activity, this may not be the case as this research may prove.
One of the suggestions for the signal complexity is that the surface region has been so fractured by seismic activity that the resulting unsorted and unstratified volcanic sediments impair the clarity of the signal that is penetrating below.
I hope that someone with experience may have an answer.
Dave,
You really have your hands full with these lines. First I would clean things up. The black lines do not go with this version of the line. Way too many faults at this stage, you can see the offset on the one near 790 but the others are mostly vertical noise trains.
It looks like you have two wells posted. I guess that is where the lithology information about 250-1250m came from. You need to transfer a few key stratigraphic markers from the wells to the line more accurately. I would be surprised if the line was in depth. Look up time-depth conversion.
From the well picks, identify a nearby seismic peak or trough (blue or red) and follow it as far as you can, just estimate fault displacement and extrapolate with the dip across the vertical noise trains. Do three or four horizons in in a half hour (there will be many refinements later).
It looks like you have two cross-line intersections. You need to transfer the three or four horizons as points on the intersecting line and go from there as you did on the first line. A real test is if you can make a loop back to the first line from the others. That is where refinements come it, and estimates of fault offset.
At first glance the structure looks like a graben. I would think of normal and transverse faults not reverse. The data quality is poor which is unusual in marine sediments except very consolidated. Shallow volcanic rocks could certainly be to blame, but I would not think fractured by earthquakes, more likely heterogeneous. Actual volcanic flows can wreck havoc.
Not sure what seismic amplification is all about, perhaps earthquakes. It may not be relevant, but this line looks highly processed and relative amplitudes would have to be looked into carefully.
Best Regards,
Jim Ballard
More information about the seismic data is imperative. It looks like old data that current data processing techniques may enhance.
Dave,
Saw your 2D line by chance; nicely complex!
I concur with Jim that post-stack cleaning up of the lines would be helpful. Different interpretation platforms provide different tools. I would recommend filtering in the FK domain. Are the lines migrated?
A comment, the shallow overburden does not contain spark of high reflectivities, supporting an acoustically relatively homogenous interval. Note that you have limited fold at shallow times, i.e. the stack is from a limited number of traces there.
The seismic contains reflective and non-reflective sequences; have an acoustic impedance log and synthetic made of a well if possible. As a rule of thumb, reflective packages relate to sequences with contrasted lithologies, i.e. carbonates interbedded with shales or volcanics with clastics. Transparent units are likely to be more homogenous.
Keep fault geometries simple.
Try to interpret some horizons across the sections and flatten - unflatten the section along those horizons, it may help you figure out what the seismic contains.
Shallow heterogeneities may lead to a cascade of poor imaging, as do fault zones. Imaging of faults on 2D seismic lines running oblique to faults are challenging for fault imaging.
Good luck with your project.
Thomas.