A Report On Land Streamers: The Last Geophone You Will Ever Plant?

Seismic surveying gives some of the best sub-surface images of any geophysical technique. Since the ground supports a wide variety of particle motions, there are many different types of seismic waves, all which carry information about the subsurface.

But the improved resolving power of seismic imaging comes with some costs. Surveys can be time consuming and labor intensive, particularly for measuring the reflected portion of the wavefield. High resolution surveys can require great care planting geophones to ensure good coupling necessary for high-frequency recording.

The seismic marine industry is capable of recording large volumes of high-resolution data that have long been the envy of land geophysics. While land surveys involve tedious hours slogging through swamps, dragging across deserts and sometimes spending as much as 5 minutes to plant a single geophone in hardpan or hard rock, marine surveys are conducted by effortlessly dragging hydrophone streamers behind boats. The coupling between the streamer and the water is excellent and the 'mobile array' permits the collection of massive amounts of high-frequency data that produces some of the best seismic images recorded.

Marine streamers have been so effective that there is widespread interest in developing a similar concept for land. There are many challenges to overcome: higher background noise, cross coupling between geophone elements, geophone orientation, mechanical wear not to mention logistics concerns like dodging traffic on roads. But because the earth supports many different modes of vibration, land streamers have some attractive benefits. Not only can land surveys measure P waves, but also shear waves and surfaces waves, vibration modes that do not propagate in a marine environment. The measurement of surfaces waves with land streamers may be particularly appropriate since surface waves can be as much as an order of magnitude larger than body waves. And unlike the kilometer long streamers deployed in marine surveys, streamers for shallow land surveys can be relatively short and have very closely spaced geophones, a requirement for shallow surveys that currently makes their cost prohibitive for many applications.

Several innovators have been exploring the use of land streamers, and we bring you a brief report on their activities:

The Future

High-resolution seismic data acquisition is expensive and time consuming. Land streamers appear to provide a fast and comparatively economical method to collect the large volumes of data at close sensor spacings required to resolve near-surface velocity structure and provide a seismic image of the subsurface. It is clear that coupling is a major issue, but used prudently in situations where sensors can make good contact, land-streamers can provide excellent results. This is particularly true when reflections are already coherent and anomalies generated by the streamers are more obvious. Perhaps the use of multiple streamers would allow identification of localized coupling problems. Click here for references...........

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