Collecting more than just seismic data along the Cascadia fault
An example of seafloor morphology data collected using a multi-beam echo sounder shows that an undersea canyon near Port Grace, Washington erodes the sea floor.
In R/V’s main laboratory Marcus Lances, You will find a series of monitors — 46 to be exact! -All display information about the data we are collecting.Although many screens are dedicated to monitoring Seismic data As with the instruments related to the acquisition of seismic data, there are two screens that display data related to the multi-beam echo sounder. The multi-beam echo sounder is an instrument installed on the hull of the ship, which can emit sound waves in a fan shape below the ship. The sound waves travel through the water to the bottom of the sea and return to the instrument. The time required for sound waves to return is used to determine the depth of the seafloor, which provides us with information about the shape of the seafloor-called bathymetry. This information complements the deep underground imaging provided by seismic data.
Figure 1: Pictures of the two screens dedicated to the multi-beam echo sounder in the main laboratory. The screen on the left shows an overlay and a window for adjusting parameters. The right screen displays data in real time in two different formats.
Two monitors dedicated to multi-beams allow us to control and view the data being collected. One of the screens displays multi-beam data in a map view, allowing us to view the coverage area and set the parameters of the instrument (Figure 1, left screen). The other screen is divided into two windows, displaying data in real time (Figure 1, right screen). The top window shows the sea bottom reflectivity, which is a measure of seabed hardness or roughness. The bottom window displays the data as side bars, which is essentially a side view of the data, as if we were looking at it from behind the ship.
Figure 2: A 3D perspective view of southern Oregon, with geomorphological annotations and fan view images of methane leakage.More information about methane leakage exploration and seafloor mapping is available from NOAA Pacific Ocean Environmental Laboratory.
Figure 3: Annotated water column bands of multi-beam data where methane leakage has been identified.
What are we looking for in multi-beam data? In Figure 2 below, we can see the dynamic environment of the ocean floor in southern Oregon, where gullies, waterways and landslides are photographed along this small part of the edge. In addition to seafloor imaging, modern multi-beam systems can also image bubbles in the water column.Methane leakage can be seen in the new data set, corresponding to Previously identified leakage May contain helium leaking from the mantle. The new imaging technology (Figure 3) allows researchers to better locate the location of these methane exudates from the seafloor.
Figure 4: Coverage of the new multi-beam bathymetry data collected during our survey. As of June 30, the ship has collected about 26,500 square kilometers of new data, and the rainbow-colored part outlines the survey area.
A careful review and interpretation of the multibeam and sonar data from previous research shows Thousands of methane leaks All scattered on the edge of Cascadia. During our expedition, we confirmed the locations of some of the previously drawn leaks through multi-beams, but also identified some new leaks. With a careful eye, you can find these methane leaks in real time through the side-scan window. However, compared with the spatial coverage of multi-beams, the leakage is very small, so they are really easy to miss and disappear from the screen in the blink of an eye. Therefore, we mainly confirm and identify methane leakage in the processing steps of multi-beam data. When processing data, we can stack and filter to more accurately image and locate methane leaks (Figure 3).
Multi-beam data can reveal many important and interesting insights about the ocean floor. Combining the new multibeam data collected during this voyage is another step towards obtaining a complete high-resolution map of the sea floor and a catalog of methane leaks along Cascadia.
Jeff Beeson is an assistant professor/senior researcher at NOAA Pacific Marine Environmental Laboratory and Oregon State University.
Michelle Lee is a graduate student at Columbia University’s Lamont-Dougherty Earth Observatory.
