A Hammer-Impact, Aluminum, Shear-Wave 

Source

Open-File Report 2007-1406

U.S. Department of the Interior

U.S. Geological Survey
A Hammer-Impact, Aluminum, Shear-Wave Seismic 

Source 

By Seth S. Haines 

Open-File Report 2007–1406 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2007 

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Haines, S. S., 2007, A Hammer-impact, aluminum, shear-wave seismic source, U.S. Geological Survey 

Open-File Report 2007-1406, 5 p., available only online at http://pubs.usgs.gov/of/2007/1406/. 

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Contents 

Abstract................................................................................................................................................................................1

Introduction .........................................................................................................................................................................1

Source design .....................................................................................................................................................................2

Discussion and Conclusions.............................................................................................................................................4

Acknowledgments..............................................................................................................................................................5

References Cited ................................................................................................................................................................5
A Hammer-Impact, Aluminum, Shear-Wave Seismic 

Source 

By Seth S. Haines 

Abstract 

Near-surface seismic surveys often employ hammer impacts to create seismic energy. Shearwave surveys using horizontally polarized waves require horizontal hammer impacts against a rigid 

object (the source) that is coupled to the ground surface. I have designed, built, and tested a source 

made out of aluminum and equipped with spikes to improve coupling. The source is effective in a 

variety of settings, and it is relatively simple and inexpensive to build. 

Introduction 

Near-surface shear-wave seismic surveys typically employ horizontally polarized (SH) waves 

because they are more easily distinguished from compressional (P) waves, and they generally do not 

convert to P waves as readily as vertically polarized shear (SV) waves. We can create SH waves in 

many different ways, but the most common involve inputting horizontal ground motion at the earth’s 

surface. We record the resulting energy with horizontal geophones. Both the source and the geophones 

are oriented perpendicular to the SH-wave survey transect. 

An optimal SH-wave source allows for the creation of two opposite polarities of seismic energy 

for better identification of true SH-wave energy. It should give repeatable results, providing virtually 

identical energy with each usage. The source must employ an efficient coupling mechanism so that 

maximum energy, with broadband frequencies, enters the ground. This is generally accomplished with 

some combination of mass holding it down and spikes holding it laterally stable. Finally, the source 

must be convenient and simple to use, readily transportable, and able to provide a brief cycle time so 

that surveys can be conducted quickly. 

Various workers have used a number of different horizontal sources over the years. Hasbrouck 

(1983) describes what is often referred to as the “golf shoe” source (fig. 1); it is made of heavy steel, has 

a spiked base, and offers good repeatability with proper use. The golf shoe weighs approximately 40 

kg, and thus can lead to difficult logistics for an extended field campaign. In addition, the vertical 

impact face results in a swing geometry that some people find awkward; this awkwardness can result in 

diminished strike-to-strike repeatability and reduced data quality. The wooden source shown in figure 1 

provides a lightweight alternative (14 kg) that has proven quite effective in some circumstances (for 

example, the studies described by Ellefsen and others, 2007). We find that this wooden source is most 

effective on pavement or hard ground, but that coupling is not optimal on rough ground, which is likely 

caused by the absence of spikes. In addition, the wooden source is not sufficiently durable to withstand 

years of use, and the location of the impact face almost directly between the legs of the hammer swinger 

is awkward for many people. Pugin and others (2006) present SH high-frequency data that were 

collected using hammer impacts on a roller that is coupled to the ground with the weight of a vehicle. 

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Liu and others (1996) describe an air-powered impulsive SH source that is also weighted with a vehicle. 

Ghose (2002) describes SH data acquisition using a horizontal vibrator source. Each of these sources 

has its advantages, but none is clearly superior under all circumstances. In order to provide a repeatable, 

convenient, hammer-impact, SH source for use in our near-surface surveys, I created a new source. 

Figure 1. The steel golf shoe source (a) and the wooden source with metal strike plates (b). 

The aluminum source described here was designed to provide a comfortable strike stance for the 

hammer swinger, which leads to improved repeatability and overall data quality. The source is 

inexpensive to construct and simple to use. Weight is kept to a minimum (25 kg) while retaining the 

strength necessary for extended use and repeated hammer impacts. This report describes the design and 

construction of this source, and concludes with some suggestions for improvements on the current 

design. 

Source design 

The source is built primarily from 2-cm thick 6061-T6 alloy aluminum plate. The original 

version was constructed entirely from this material, but the use of thicker aluminum block for the 

impact plates is a substantial improvement in the current version that is described here. One piece of 

plate (Figures 2a and 3) makes up the base, with holes for the ground-coupling spikes. The holes are 

counter-sunk on the bottom to provide space for the nuts that attach the spikes. Two longitudinal rails 

are welded to the base plate and provide rigid support for the impact plates. The rails are made out of 

aluminum plate, and their design is shown in Figure 2b. The impact plates (Figure 2c) must be made of 

thicker material in order to withstand a long period of use and abuse; aluminum deforms considerably 

when subject to thousands of hammer impacts. A 15 x 24 x 10 cm aluminum block, machined to shape, 

has proven effective and long-lasting. These blocks are bolted to the longitudinal rails using 17-cm 

long, 1.5-cm diameter (5/8 inch) grade-5 bolts, in order to facilitate replacement of the impact plates. 

Finally, a rope may be tied through the holes in the rails to provide a carrying handle. 

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Figure 2. Sketches of the components of the source. Base plate (a) and rails (b) are made of 2-cm thick 

aluminum plate. Impact plates (c) are made of aluminum blocks. Spikes (d) are made of steel bolts with 

the heads cut off. Note that I now recommend eliminating or reducing the size of the holes in the rails. 

The hole configuration leads to weakness that results in deformation. 

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Figure 3. Photos of the source (a) with spikes removed, and the source in use for field data collection (b). 

After several thousand impacts, the rails show considerable deformation (c), indicating that the holes 

weaken the source. The holes were previously circular, but now all are deformed. The rope handle and 

some spikes are also visible. 

The ground-coupling spikes are made of 1-cm diameter (3/8 inch) bolts, with the head cut off 

and the remaining smooth section machined to a moderate point (Figure 2d). A half-thickness nut on 

the threaded part of the spike rests against the underside of the source base plate, and a lock washer and 

nut on the top side of the base plate hold the spike in place. I use two different spike lengths 

depending on conditions. For hard ground, gravel and cobbles, etc., I find 5.5-cm long spikes to be 

effective. For softer soils, grassy areas, etc., I find the longer 10.5-cm spikes to be preferable. The 

spikes are easily changed, or removed for use on pavement or other such surfaces. 

Discussion and Conclusions 

The source is effective and has proven reliable through two years of usage. The basic design is 

very functional, but the durability has room for improvement even in this second version. It has 

withstood approximately 10,000 impacts and remains functional, but it does show signs of failure 

(figure 3c). The primary change that I would make for future versions is to redesign the hole pattern in 

the rails. Removing material saves weight and also allows for a rope handle to be threaded through. 

But the current configuration of holes weakens the rails so that they deform laterally after extended use. 

Smaller holes, with larger amounts of aluminum between them, would create a more durable source. 

Perhaps it would be best to drill only small holes for the rope handle, and otherwise leave the rails 

intact. 

The current impact plate design is very strong and has deformed very little after extended use. 

However, I suspect that the same would be true for a somewhat modified design. I would try making 

the plate thinner (perhaps 8 cm total thickness instead of 10 cm) in order to save weight. 

Clearly, the impact plates would not need to be nearly as thick if they were made of a different 

material. Because the impact plates are bolted, rather than welded, to the aluminum framework, the use 

of other materials is feasible. I don’t necessarily advocate a different design, but it is something to 

consider. Steel is one option, although it rings very loudly when struck with a hammer – an 

inconvenience that can become more of a major issue over the course of an extended survey. Also, steel 

is considerably more dense than aluminum, so it would be difficult to avoid a weight increase. 

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The source described here provides one option for near-surface SH surveys. I find it to be wellsuited to a variety of applications, and consider it my standard choice for most surveys. It is light 

enough that it can be readily moved between locations, it is inexpensive to build, and it provides 

consistent data with a high degree of strike-to-strike repeatability. 

Acknowledgments 

I am very grateful to Paul Wigton, as well as to Carl Stoddard and Roy Kipfinger for help with 

the construction and improvement of this seismic source. 

References Cited 

Ellefsen, K., Burton, B., Lucius, J., Haines. S., Fitterman, D., Witty, J., Carlson, D., Milburn, B., and 

Langer, W., 2007, Field demonstrations of five geophysical methods that could be used to 

characterize deposits of alluvial aggregate: U.S. Geological Survey Scientific Investigations Report 

2007-5226. 

Ghose, R., 2002, High-frequency shear wave reflections from shallow subsoil layers using a vibrator 

source: sweep cross-correlation versus deconvolution with groundforce derivative: Society of 

Exploration Geophysicists 72nd Annual International Meeting, Expanded Abstracts. 

Hasbrouck, W. P., 1983, Sketches of a hammer-impact, spiked-base, shear-wave source: U.S. 

Geological Survey Open-File Report 83-917, 7 p. 

Liu, H., Maier, R., and Warrick, R., 1996, An improved air-powered impulsive shear-wave source: 

Bulletin of the Seismological Society of America, v. 86, p. 530-537. 

Pugin, A., Sargent, S., and Hunt, L., 2006, SH- and P-wave seismic reflection using landstreamers to 

map shallow features and porosity characteristics in Illinois: Symposium on the Application of 

Geophysics to Environmental and Engineering Problems, Proceedings, p. 1094-1109.