Experimental Data

() present electroseismic experimental methods designed to record the coseismic field and the interface response separately. By imaging a vertical interface with the source and receivers on opposite sides of the target (Figure ), they record the interface response before the coseismic energy (Figure ). The target is a trench 342#3420.6m wide, 342#3422m deep, and 342#34218m long, lined with plastic, and filled with wet sand.

 

layout
Figure 3 Layout of field site. Note that source and receivers are on opposite sides of the target so that the seismic wave creates the interface response at the trench before reaching the electrodes and being recorded as the coseismic energy.

 

gen_data Figure 4 Generalized data, showing interface response arriving before coseismic energy. Note reversed polarity on opposite sides of shot point. (For simplicity, relative amplitudes are NOT correct.)

Approximately 80 shot records have been recorded at this site with various shot and receiver geometries. Shot gathers are generally stacks of 50 to 100 strikes of a 12 lb sledgehammer on a metal plate located 1 to 4 meters from one side of the trench. Recording geometries include 24 electrode dipoles (342#3421 meter wide) at 342#3420.7 m spacing located 1 to 4 meters from the other side of the trench. The interface response is recognizable before the coseismic arrival on every record, with varying clarity and strength. Arrival times and simple amplitude modeling confirm that the observed signal is indeed the interface response. Because the interface response shows virtually no moveout, and because it has reversed polarity on opposite sides of the shot point, it can be visually differentiated from the coseismic arrival and background electrical noise. These data, with the two effects recorded separately, provide a unique opportunity for development of a processing sequence to enhance the interface response and remove the coseismic signal.