Electroseismic Research

    My current dissertation research focuses on developing the electroseismic method as a tool for environmental studies and other shallow applications.  I am conducting controlled field experiments (these could be called field-scale lab experiments, though that might be a stretch) in order to improve data acquisition techniques, and am using the resulting data in the development of data processing routines.  My goal is to determine a reliable protocol that can be followed under a variety of circumstances to collect, process, and interpret electroseismic data, providing subsurface information beyond what is possible with commonly used geophysical techniques.

What is the electroseismic method?

    As sound travels through a fluid-containing porous medium, it causes the relative motion between the grains and the fluid.  Because a small charge separation exists at the grain-fluid boundary, this relative motion creates a larger-scale charge separation within the seismic wave.  This charge separation creates an electric field (termed the "coseismic field") within the seismic wave, a field that can be measured directly.  In addition, when the seismic wave hits an interface in material properties, the charge separation becomes asymmetric, resulting in (approximately) an occilating electric dipole at the interface.  The field from this dipole can be measured remotely, and is termed the "interface response".

What's so great about the electroseismic method?

    Because the interface response is produced at any interface in material properties, the electroseismic method offers the possibility of imaging very thin layers in the subsurface.  These layers are generally invisible to the seismic method but are of great interest to a hydrogeologist characterizing contaminant flow in a reservoir, for instance.  In addition, the electroseismic response is highly dependent on soil and fluid chemistry, so is sensitive to variables such as pH and salinity that are important in site characterization.

    I am carrying out experiments at a site located at Pride Mountain Vinyards in St. Helena, CA.  (Many thanks to Jim and Carolyn Pride for the use of their land, tractors, backhoe, etc).  At this site, I have constructed a wet sand-filled trench 2 m deep, 18 m long, and about 65 cm wide in an otherwise roughly homogeneous material (clay-rich soil).  With the seismic source (10 lb sledge, until I upgrade to something better...) on one side of the trench and the electrode dipole receivers on the other side, I "image" the trench from the side.  The key to this experiment is the horizontal interface, because the described acquisition geometry lets me record the interface response from the ditch prior to the arrival of the coseismic field.  Because I know exactly what I'm trying to image (the joys of building your own geology), I am able to better interpret the data.
    The electroseismic response is rather weak compared with background noise, so it is necessary to use a high number of stacks of hammer blows at each shot point.  Generally I use 50 or 100 hammer strikes per shot.  This has led to a large amount of hammer swinging since August, 2001.   My arms would have long since fallen off if it weren't for the help of many suckers who I lured into the task with promises of free food and beer.   (One of the advantages of being surrounded by graduate students...)  Check out The Hammer Swinger's Page of Fame.

Links (updated Feb 2007)