Dominant Frequency vs Resolution Calculator: How Attenuation Degrades Seismic Resolution With Depth

Convert dominant frequency and velocity to wavelength and resolution, model how frequency and resolution degrade with depth due to attenuation, or solve for the surface frequency needed to resolve a target bed at depth. Everything updates live.

A brand new broadband survey with sixty hertz of dominant frequency at the surface sounds impressive, and it is, right up until that same signal has traveled three seconds down through several kilometers of rock. By the time it reaches a deep target, most of that high frequency content is gone, absorbed by the earth itself, and the effective resolution at the target is nowhere near what the source suggested. This tool works through that relationship directly.

Start with a plain frequency and velocity to get wavelength and tuning thickness. Move into the depth model to see exactly how much resolution is lost by a chosen depth, given a starting frequency and a quality factor for the rock. Or solve backward from a target bed thickness at a known depth to find the surface frequency that would actually be required to resolve it once attenuation has done its work.

Why Dominant Frequency Is Not a Fixed Number

Seismic energy loses its higher frequencies faster than its lower ones as it travels through rock, a process controlled by intrinsic attenuation and commonly described using a quality factor called Q. A high Q rock, tight and well consolidated carbonate is a common example, preserves frequency content well and lets a signal keep much of its bandwidth even after a long travel path. A low Q rock, unconsolidated sand or anything charged with free gas, strips high frequencies out aggressively, sometimes within a single second of travel time.

This tool models that decay with a simplified exponential relationship, effective frequency equals the surface frequency multiplied by the exponential of minus pi times the surface frequency times travel time divided by Q. It is an estimation model rather than a full physical derivation, real attenuation depends on the complete wavelet spectrum and on a Q profile that typically changes with depth and lithology rather than staying constant, but it captures the core behavior well enough to plan around.

What This Means for a Deep Target

Because dominant frequency keeps falling as travel time increases, wavelength keeps growing, and tuning thickness grows right along with it. A bed that would be comfortably resolved near the surface can sit well below tuning by the time the same wavelet reaches three kilometers down, using nothing more than ordinary attenuation.

Take a sixty hertz source traveling through rock with a quality factor of one hundred. At five hundred meters the tuning threshold is already close to fifteen meters. By fifteen hundred meters it has grown to about thirty two meters. By three thousand meters it is nearly seventy five meters. A four meter reservoir sand that shows up clearly on a well log at fifteen hundred meters was never going to be a distinct, separately timed reflection on the seismic section, no matter how good the acquisition was.

Solving It Backward: What Frequency Does a Target Actually Need

Survey design conversations often start from the wrong end of this problem, picking a source and hoping the resolution works out. The more useful question is the reverse one: given a target depth, a target bed thickness, an estimated velocity, and an estimated Q, what surface frequency would actually be required to resolve that bed once attenuation has run its course.

This tool solves that equation numerically, since the surface frequency appears on both sides of the attenuation relationship and cannot be isolated with simple algebra. Enter the depth, velocity, Q, and target thickness, and the required surface frequency comes back directly, along with a flag if the target genuinely is not achievable at that depth and Q, however high the surface frequency is pushed.

Common Mistakes

Quoting a single dominant frequency for an entire seismic volume, when the effective frequency at a deep target can be a small fraction of the frequency measured near the surface.

Assuming resolution problems at depth are purely an acquisition or processing shortfall, when a genuinely low Q interval along the raypath can be the dominant cause.

Comparing tuning thickness calculated with a surface frequency number against a target bed at depth, rather than using the effective frequency actually expected to survive to that depth.

Treating the exponential decay model here as an exact physical result rather than a practical estimation tool for planning and quick checks.

Who Uses This

Geophysicists planning acquisition parameters who need a realistic estimate of achievable resolution at a specific target depth, not just at the surface.

Seismic processors and interpreters explaining to a project team why a shallow interval resolves cleanly while a deep target of similar thickness does not.

Students and early career geoscientists building intuition for how attenuation, quality factor, and vertical resolution connect to one another.

Anyone comparing prospects in a low Q setting, such as a known gas charged interval, against prospects in a high Q carbonate section at a similar depth.

Try It Above

Use the quick convert tab for a plain frequency and velocity check, move to the depth model to see resolution fall off across a full depth profile for a chosen source frequency and Q, or use the solve surface frequency tab to work out what a specific deep target actually requires.

Related Calculators and References

Continue building your workflow with the Vertical Resolution Calculator. For background on the formulas used above, see SEG Wiki: Seismic resolution.