Introduction

We designed and completed a very high-resolution 3-D seismic survey at Moss Landings, California. The survey was part of an ongoing series of experiments being conducted by one of the authors (Ran Bachrach of the Stanford Rock Physics and Borehole group, SRB) exploring the resolution limits of shallow/environmental reflection seismology particularly with regards to detection and monitoring of viscous fluid contaminants. This project is also part of an on-going collaboration between SRB and SEP.

Figure  shows a 2-D shot gather in the study area. The hyperbolic water-table reflector is clearly visible at 20 ms traveltime. Unfortunately the very shallow reflectors in the sand above the water-table only appear on the near offset traces, as they are masked by the direct arrival and the water-table refraction at larger offsets.

 

conventional Figure 1 2-D shot gather in the study area.

The water-table itself is only 2-3 m below the surface, so shallower reflections are not visible on offsets greater than about 3 m. The desire to record useful information on all sixty of the available channels, and physical limitations due to the size of the geophones forced us into a 3-D geometry. Moving to 3-D also gives us the potential to image structures that are not usually visible with conventional 2-D geometries.

As an aside, the full 3-D dataset is less than 220 Mb in size, and so provides an excellent test bed for SEP's in-house processing system, SEPlib3D.