Dr. Xin LIU, an assistant professor at the Department of Earth Sciences at the University of Hong Kong (HKU), led a team of international scientists along with seismologists from the US and China in developing a new method called differential ambient noise tomography. This method allows researchers to visualize rocks with fluids more effectively, leading to potential advancements in the discovery of water and oil resources, as well as applications in urban geological hazards, tsunami early warning systems, and understanding the water cycle. The findings were published in the journal «Nature Communications.»
The method utilizes a portable instrument called a «seismometer» to record the Earth’s natural vibrations, making it an easy and cost-effective way to study urban and ocean areas. In the study, 42 seismometers were placed along a line that crosses the Los Angeles basin from Long Beach to Whittier Narrows.
The researchers found that rocks at a depth of 1 to 2 kilometers near the Newport-Inglewood fault, a fault that causes earthquakes, contain a significant amount of fluids. These rocks have small holes filled with fluids, which may explain the occurrence of small earthquakes in Long Beach, California. The abundance of fluids within these small holes reduces friction along the fault plane, allowing the two rock blocks on each side to slide more easily and generate small earthquakes.
The article suggests that differential ambient noise tomography can be used to find water and oil resources without the need for expensive drilling. This novel method generates images of the ground covered by seismometers, revealing the speed at which seismic waves travel in soil and rocks. In some places, the seismic wave travels much more slowly compared to other regions at the same depth, indicating the presence of fluid. As water and oil are fluids in rocks, this method can identify rocks containing such fluids.
«Previously, it was difficult to find underground aquifers or deep fluid deposits without drilling multiple expensive wells or expensive seismic surveys with loud artificial sounds that are not environmentally friendly on land or in the ocean. Using only weak seismic noise records made by two dozen seismometers on land or on the sea floor, our new technique can create images containing fluid information within rocks and pinpoint the location and depth of fluid-rich rocks,» said Dr. Liu, the lead author of the journal article.
Additionally, this innovative method can be used to create detailed images of the ground in urban areas and ocean depths, serving various purposes, such as assessing urban geological hazards, implementing early warning systems for tsunamis, and improving our understanding of the water cycle under the seafloor. In urban environments, a series of land seismometers can be deployed over the area of interest. In the ocean, a line of ocean bottom seismometers (OBS) can be installed on the seafloor to record bottom vibrations. In both cases, a detailed image is created just below the line of seismometers, providing information about the location of loose soils/sediments and rocks containing fluids that are directly related to regions with slow seismic wave velocity.
«In conclusion, this innovative method has the potential to revolutionize our approach to discovering and using water and oil resources, improving urban safety measures, and deepening our understanding of the environment. Its direct impact on our daily lives ranges from efficient resource exploration to effective disaster preparedness and promotion of sustainable environmental management practices. This scientific breakthrough holds great promise for shaping a better future for all of us,» added Dr. Liu.