Seismic Reflection Study of a Shallow Aquifer During a Pumping Test

Abstract

Seismic reflection surveys were used to follow the drawdown in a shallow aquifer during a pumping test. Using severe analog low‐cut filters and 1/4‐m geophone spacings, 335 Hz reflections were obtained from the top of the saturated zone 2.7 m deep. The reflections moved down in time as the saturated zone dropped in response to pumping. The dominant frequency and bandwidth both dropped during pumping indicating a more diffuse reflecting boundary. Slight pullups of reflectors at specific locations on the CDP sections may indicate a higher elevation of the capillary fringe and therefore finer sediments in those locations. Other potential applications of this technique include mapping cones of depression and detecting and delineating perched‐water tables.

Seismic reflections from depths of less than two meters

“…However, until about 15 years ago, the reflection method was not used routinely to extract geologic and hydrologic information from the earth's subsurface at depths of less than 30 m. Due to interference caused by the nearly simultaneous arrival of several wave types near the seismic source, reports of successful imaging at depths of less than 10 m have been limited to a very small number of refereed publications, including papers by We report here developments in near-surface seismic-reflection surveying that have led to the detection and evaluation of seismic reflections at depths of less than 2 m. We obtained three distinct seismic reflections from the upper 2.1 m of flood-plain alluvium in the Arkansas River valley, an area in which only a single reflection was observed from the water table at a depth of 2.6 m with a two-way traveltime of 22 ms during shallow seismic surveys undertaken in 1986 (Birkelo et al, 1987 …”

Shallow seismic reflection section—Introduction

“…The data in the figure display two reflections: a "deep" reflection representing the top of the saturated zone at 2.6 m below the surface, which was examined in detail by Birkelo et al (1987), and a newly detected (1997) shallow reflection at a depth of slightly more than 1 m. These data were collected in the Arkansas River valley near Great Bend, Kansas, where more than a score of test wells have been drilled in one small area over the past 15 years, providing excellent geologic and hydrologic "ground truth. "…”

“…The data from Birkelo et al (1987) were collected with a 30.06-rifle source fired directly into the earth's surface through an air-blast containment device. The data in the figure were obtained with a .22-caliber rifle source using subsonic, .22-caliber, short ammunition.…”

Source-Dependent Frequency Content of Ultrashallow Seismic Reflection Data

“…However, shallow (less than 10 m) reflection seismology has only become possible recently due to improvements in equipment, survey design, and processing procedures (Steeples and Knapp, 1982). Today, there are very few examples of seismic reflections from less than 3-m depth in the refereed literature (e.g., Birkelo et al, 1987;Steeples et al, 1995;Bachrach and Nur, 1998), and only one example showing reflections from less than 1-m depth (Baker et al, 1999a).…”