Actually it is is not a role in all cases. You can find a good quality land seismic survey.

But in general, the partial difference (if found) may be due to that fact that the subsea strata is more compacted and pressurized than in land.

Thanks for your answer! For the shallow strata (and not for deep strata) onshore, I have surveyed many papers but have not found clear images. I think most of the shallow subsea sediments are also unconsolidated and soft.

It is not a general case. However, where the formation penetrated by seismic wave is not dense and compacted, quality of seismic reflection data will be low. This observation is likely caused by this reason.

I agree with Nyako Jimmy George, "It is not a general case." However, one must remember that the fold increases with time until the full fold is attained - the rate of increase depends on the geometry, but always long offset traces lack shallow data.

Dear Johnny Zhang: I will try to answer your question, following your keywords “not so clear” such as an equivalent of both, vertical and lateral seismic resolution. If I am right, the resolution is a function of the bandwidth of the seismic. I understand you are talking about the capacity to distinguish both top and base reflections. Therefore, I can say you that the differences are related to the noise.

Noise is an inherent feature of seismic data, especially in land acquisition.

Land acquisition habitually experiences crucial difficulties that drastically reduce SNR and bandwidth: the important back dispersion/scattering in the near subsurface wave energy. Thinking you that more than 60% of the energy of a surface source (impulsive or Vibro) can end up in the near-surface rather than imaging reflections (thinking for example in volcanic environments conditions, basalts, topography dramatically variations and thickness of weathering). You may be thinking about problems that are associate with surface noise: many Rayleigh waves; correlation noise; not enough energy; wind-noise; ground-roll noise; weathering effect; planting of geophones is a non-trivial issue and environmental problems such as wind (I live in Patagonia!) or frozen conditions in the surface. The coherency of ambient seismic noise recorded during surveys and the resulting implications for the effectiveness of geophone arrays; the better noise attenuation, the more bandwidth, and lateral/vertical resolution, the clearer imaging. Combining these problems can improve basic imaging very challenging, for example, using very low-frequencies to resolve shallow horizons and complement conventional seismic imaging.

The acquiring seismic data offshore (marine) has problems associated with, e.g., the free-surface ghost effect is probably the main factor that can strongly impact the data bandwidth dependent on the streamer and source depths; keeping the streamer at a constant depth; the position of multiple gun arrays, and every hydrophone group in multiple streamers; swell noise; passing-vessel-noise, streamer hit, etc. Each noise type has a different origin, coherency, and frequency content.

Expanding the bandwidth of surface seismic data, particularly towards low frequencies, is essential for improving resolution. Broader band signals, both in land and marine have marked benefits for imaging deeper targets, imaging through absorptive overburdens, and, inversion for rock properties.

Best regards, Mario E. Sigismondi

Dear Nyakno jimmy George Ernest Berkman Mario Emilio Sigismondi

Thank you for your answers. Here I would like to emphasize again that the question is trying to discuss the "shallow strata" (e.g., 0-500m subsurface). The question came from my impression of seismic images of marine and on land from literature or internet surveys-- I cannot find a clear reflection seismic profile for shallow sediments on land (with a clear show of sediment or aquifer structures; if you know one, please show me) whereas there are numerous good cases for marine surveys (for example, a marine reflection profile https://www.usgs.gov/media/images/multichannel-seismic-reflection-profile) .

Yes, Dr. Sigismondi's answer is important for my understanding. From the answer, the seismic resolution seems critically related to the source excitation ways (in his Land acquisition part).

So the question is why the marine way through airguns (or sparkers and boomers) in ocean water has a good source excitation for subsea reflections? why the airgun way does not generate fewer unwanted waves as the surface source (impulsive or Vibro) on land? If we have a way of using airguns on land, the same quality of seismic data can be obtained (if do not consider other factors).

Thank you!

There is a publication by R. D. Miller etal, Geophysics, 1986, v51 n11, that compares several seismic sources and discusses your problem. I believe noise and coupling are the biggest problems. I once tested a small air gun that required a shallow drilled hole that was filled with water. We took numerous shots, summed them all, and had very good data. As I recall we had to sum a least 25 air gun shots before the noise canceled and the signal added. The problems were the cost of the well, and the requirement that the hole lost water and had to be continually refilled - it was just not practicable! I presently recommend the use of a modified Buffalo Gun in a 3 ft auger hole.

Yes, the ocean is a filter for S waves, so, as the seismic acquisition is designed to acquire P waves, at sea they will be naturally filtered, but in o shore seismic aquisicion they will be registered as noise. A three component acquisition can help you to improve seismic image.

Thank you all very much for the answers. These days I have investigated this question. I think some words from an interview of Dr. Oz Yilmaz when introducing his new book by Andrew Geary in a Seismic Soundoff episode (Episode 123: Land Seismic Case Studies with Oz Yilmaz) may be very helpful for this question in addition to @Mario Emilio Sigismondi's answer:

"...There were many challenges regarding the near surface to confront the complexity and heterogeneity of the near surface, give rise to travel time and amplitude distortions associated with subsurface reflections and surface waves that consume most of the seismic source energy leaving very little to penetrate into the subsurface. To understand the wave phenomenon in the near surface in close proximity. I conducted numerous engineering seismology projects that required detailed seismic characterization of the near surface."

"... marine seismic source and receivers are deployed on a flat datum, in a water layer that represents on a macro scale, essentially a homogeneous medium. In comparison, land seismic source and receivers are deployed on any regular topography over a near surface that often represents a heterogeneous medium. This difference between marine and land seismic exploration has an enormous impact on the quality of the data acquired ..."

"....What is the one challenging problem in land seismic in land seismic exploration, they have to are acquired over an irregular topographic surface and complex near surface, the near surface is defined as the depth interval. Below the free surface, up to a few 100 meters of thicks, composed of a low velocity soil column and unconsolidated, heterogeneous, and weather layers of rock, or to deleterious effects of the near surface: A. the near surface causes distortions of subsurface reflection travel times and amplitudes and B. the near surface gives rise to dispersive surface waves and guided waves, which can severely mask subsurface reflections in recorded data..."

https://seg.org/podcast/Post/12564/Episode-123-Land-Seismic-Case-Studies-with-Oz-Yilmaz