Step 1: Survey location and seismic source
This "brute-strength" experiment was conducted at an aquifer storage and recovery (ASR) site in the Abu Dhabi Emirate. ASR consists in injecting water into an aquifer in order to produce it later on: a wide variety of seismic and non-seismic methods can be used to help delineate the aquifer. In April 2011, a seismic survey was conducted at this ASR site: a seismic receiver line consisting of both one-component (1C) and three-components (3C) geophones was deployed over 1.2km. The source line was 3.6km long, extending 700m West and 1,700m East of the receiver line.
The key idea behind this experiment was to record seismoelectric data simultaneously with seismic data to take advantage of the powerful seismic source used for seismic imaging. Three separate seismoelectric spreads were deployed, each array consisting of 49 electrodes separated by 4m. The first two spreads were deployed at the eastern end of the seismic receiver line, while the third spread was centered on the receiver line.
The source used here was an 80,000 lb peak force tracked DX-80 Desert Explorer Vibrator.
Step 2: Seismoelectric and seismic super-gathers
Figure shows the seismoelectric and seismic super-gathers created from 8 records acquired with a 1m source spacing. Both recordings look fairly similar as several seismic events have seismoelectric counterparts, exhibiting similar slope and intercept time values: these are coseismic or type-I waves. But horizontal arrivals can also be seen on the seismoelectric recordings, as highlighted by the white arrows in the left-hand side gather at 32ms and 47ms: these arrivals correspond to waves travelling at velocities several orders of magnitude greater than seismic velocities. Also, they exhibit reversed polarities on either side of the shot point at x=0. Last but not least, they appear at early times, that is, before the reflected coseismic waves reaches the receivers at the surface. These characteristics indicate that these arrivals correspond to the type-II interface response.
Step 3: Zoom on Interface responses
Figure shows a close-up view of the recordings seen on the previous display. The first 100ms for offsets comprised between x=60 and x=100m are displayed here for the seismoelectric recording on the left-hand side. The corresponding seismic recording is displayed to the right. The white arrows indicate two interface responses. Note that these events of zero slowness have no equivalent in the seismic recording. The recording shown here is a super-gather, which means that it is a combination a several recordings: random electrical noise is cancelled through this stacking process which confirms the flat events highlighted here are indeed interface responses.
