Simplified Seismic Surveys for Non-Intrusive ASCE 7-22 Compliant Site Class, Critical-Zone Characterization, Fault Location, and Basin Structure

ASCE/SEI Standard 7-22 is in progress for adoption by countries, states, municipalities around the world in 2025. Chapter 20 describes new standards for determining seismic site class that encourage geophysical surveying rather than cone penetrometer or standard penetration testing. Invasive methods can fail to achieve compliance because of refusal or difficulty for intrusive methods to access sites. For non-intrusive geophysical surveying to achieve code compliance it is important for geotechnical engineers to employ geophysical survey methods effective at determining the time-averaged shear-wave velocity from the surface to 30 m depth, known as Vs30. Without such measurements, taking the default seismic site class may lead to over-design of building structures, inflated construction costs and extended project timelines. Code allowance of seismic surface-wave-arrays offers engineers the opportunity to perform one geophysical survey yielding Vs30 and site class along with a more comprehensive site investigation including assessments of the critical zone, depth to bedrock, fault location, and even P-wave velocity and Poisson’s ratio. ASCE 7-22 compliant surface-wave surveys, when processed and interpreted with Terēan software, will provide this full range of results. Most sites require less than one hour to complete for Vs30 measurement, including narrative report generation. This technology increases the ease of data collection with an untethered, triggerless hammer and the ability for the same array of 24, 4.5 Hz geophones to collect S- and P-wave data simultaneously, and simplifies seismic data acquisition by eliminating the need for hammer cables and surveying. Many case histories at scales from 5 m to 1000 m serve to demonstrate these rapid and comprehensive results, including assessments of basin structure to kilometer depths. Simpler geophysical surveys with more comprehensive results allow engineers and geologists to more efficiently complete safety and environmental assessments.