ASCE 7-22 and the 2021 International Building Code require site-specific seismic hazard assessments for most commercial projects in Arlington. Sitting on the eastern edge of the Fort Worth Basin, the city's geology alternates between Cretaceous limestone, marl, and alluvial deposits from the Trinity River. These layers vary in stiffness and thickness within short distances, making a one-size-fits-all approach risky. Refraction tomography maps the P-wave velocity structure down to 30 meters, while reflection imaging resolves deeper stratigraphic boundaries. Before designing foundations or retaining walls, we recommend combining this survey with an ensayo SPT to calibrate velocity-to-strength correlations and a respuesta sísmica analysis for site class determination.
Refraction tomography maps P-wave velocity structure down to 30 meters; reflection resolves deeper stratigraphic boundaries critical for foundation design in Arlington.
Methodology and scope
A common mistake in Arlington is assuming the entire lot matches the geotechnical report from next door. The Eagle Ford Shale can be 2 meters deep in one corner and 12 meters in another. Refraction tomography uses a 24-channel geophone spread with a sledgehammer or accelerated weight drop source to generate a 2D velocity剖面. Reflection profiles, on the other hand, employ a larger source (minibang or Betsy gun) and deeper geophone arrays to image faults or karst features. We process the data using first-arrival picking and tomography inversion software. In clay-rich zones we integrate límites Atterberg to evaluate plasticity effects on velocity, and for roads or runways we link the results to CBR vial to correlate stiffness with bearing capacity.
Technical reference image — Arlington
Local considerations
The field crew sets up a 235-meter spread of geophones along Abrams Street or Green Oaks Boulevard, carefully avoiding buried utilities marked by Texas 811. A truck-mounted accelerated weight drop thumps every 5 meters, and the seismograph records arrivals in real time. In Arlington, afternoon thunderstorms can halt operations for hours. If a profile crosses the floodplain near the Trinity River, the loose alluvial sand transmits energy poorly, requiring multiple stacks per shot. Missing these low-velocity layers in the inversion can lead to underestimating liquefaction potential. We always record the raw shot gathers and check for near-surface static corrections before committing to a velocity model.
Sledgehammer (8 lb) or accelerated weight drop (100 lb)
Maximum depth of investigation
30–60 m (refraction), 100–200 m (reflection)
Processing software
SeisImager / Rayfract / ReflexW
Deliverable format
2D velocity剖面, interpreted cross-section, report with SPT correlation
Associated technical services
01
2D Refraction Tomography
P-wave velocity profiling using 24–48 geophones with a sledgehammer source. Ideal for site classification per ASCE 7, rippability assessments, and locating rock-head in the Eagle Ford Shale. Deliverables include velocity cross-sections and interpreted layer boundaries.
02
High-Resolution Reflection Survey
Deep imaging using a minibang source and 48-channel array. Detects faults, solution cavities, and stratigraphic pinch-outs below 30 meters. Processed with bandpass filtering, velocity analysis, and post-stack migration. Recommended for large infrastructure projects like bridges or hospitals.
03
MASW (Multichannel Analysis of Surface Waves)
Shear-wave velocity profiling for dynamic analysis. A 24-geophone array records Rayleigh waves from a sledgehammer; the dispersion curve is inverted to generate a Vs profile. Directly provides the average Vs30 for NEHRP site class A through F.
Applicable standards
ASTM D5777-18 (Standard Guide for Using the Seismic Refraction Method for Subsurface Investigation), ASTM D4428/D4428M-14 (Standard Test Methods for Crosshole Seismic Testing), ASCE 7-22 (Minimum Design Loads and Associated Criteria for Buildings and Other Structures, Chapter 20 – Site Classification)
Frequently asked questions
What is the difference between refraction and reflection seismic tomography?
Refraction tomography analyzes first-arrival travel times of P-waves to build a velocity剖面 of the upper 30–60 m. Reflection tomography uses reflected wave amplitudes and travel times to image deeper interfaces and structures, often below 30 m. Refraction is faster and cheaper for shallow layers; reflection is needed for deeper targets such as faults or bedrock topography. In Arlington, we typically run refraction first and only add reflection if the project requires deeper imaging.
How much does a seismic tomography survey cost in Arlington?
A standard 2D refraction survey with a 235-meter spread and report costs between US$2,450 and US$4,870, depending on site access, number of profiles, and required depth. Adding reflection lines increases the budget due to the larger source and longer processing time. Contact us for a detailed quote based on your specific scope.
Do I need seismic tomography if I already have soil borings?
Soil borings provide point-specific data, but they miss lateral variability between boreholes. Seismic tomography fills those gaps with continuous 2D profiles, revealing velocity changes that correlate with stiffness or rock quality. For Arlington sites underlain by variable marl and limestone, combining borings with tomography reduces the risk of encountering unexpected weak layers during excavation.
Location and service area
We serve projects across Arlington and its metropolitan area.
