Seismic Tomography (Refraction & Reflection) in Pomona

For a standard refraction tomography survey with a 230-foot spread and 24 geophones, costs in Pomona typically range from US$2,400 to US$5,300 depending on the number of shot points, site access conditions, and whether we need to mobilize traffic control on city streets. Reflection work with longer spreads and a higher-energy source runs toward the upper end of that range or slightly beyond, especially if we're shooting multiple overlapping lines for 3D coverage.

For refraction, the rule of thumb is that the depth of investigation reaches about one-third to one-fifth of the total geophone spread length. With a 575-foot spread, you can typically image down to 115–190 feet in the alluvial soils common in Pomona. Reflection profiling can go much deeper—300 to 1,000 feet or more—depending on the source energy and the acoustic impedance contrast between the sediment layers and the basement rock.

Not always. If you're designing shallow foundations or a basement less than 30 feet deep, refraction alone usually gives you everything you need: bedrock depth, rippability, and velocity for site classification. Reflection becomes valuable when you have a deep excavation, a tunnel alignment, or when the geotechnical borings suggest a complex buried channel geometry that refraction can't resolve because of a velocity inversion—where a soft layer sits beneath a stiffer one.

IBC site classification requires a Vs30 value—the average shear wave velocity in the top 100 feet. Seismic refraction gives you Vp directly, and we can convert to Vs using calibrated Poisson's ratios from the local geology. However, for a direct Vs measurement, we often run a MASW line along the same spread. The combined Vp and Vs dataset lets us compute Poisson's ratio, dynamic moduli, and a defensible Site Class (A through F) that can be submitted to the City of Pomona Building Department without pushback.

A single refraction line with a 2-person crew takes about 2 to 4 hours on site, including layout, shooting, and breakdown. A reflection survey with multiple shot points might take a full day. The source—usually a weight drop or accelerated impact hammer—creates a brief thump at each shot location, but there's no drilling, no trenching, and no lasting disturbance. We can work on asphalt, compacted soil, or even landscaped areas with minimal impact.