Field comparison of shallow seismic sources

TLDR

Choosing a shallow seismic source is a pivotal decision, and prior work indicates that any source could dominate comparisons depending on site characteristics. This paper presents data to help select a shallow seismic source that best meets project goals, especially when the water table is near the surface. Data from 15 shallow seismic sources were collected and displayed as seismograms and amplitude spectra at a single New Jersey site, using an objective format to compare sources across a three‑order‑of‑magnitude energy range. Two strong reflections at ~100 and 130 ms likely delineate the top and bottom of an 80‑m‑deep clay unit at the site.

Abstract

Choosing a seismic source for a shallow reflection survey can be the most pivotal decision for the engineering geophysicist. The intent of this paper is to present data that will assist in selection of a shallow seismic source best meeting the goals within the constraints of specific projects, particularly in areas where the water table is near the surface. The data were collected (and displayed as seismograms and amplitude spectra) for 15 different shallow seismic sources in October, 1985, at a single site in New Jersey; they show the different characteristics of each source. Considering the almost three orders of magnitude difference in total source energy between the largest and smallest source, we chose a display format that presented the data as objectively as possible, while still allowing direct source‐to‐source comparisons. Two strong reflections at about 100 and 130 ms probably mark the top and bottom of a clay unit 80 m below the surface at this site. Our previous work and that of our colleagues suggests that, given a specific set of site characteristics, any source could dominate the comparison categories addressed here.