Stanford Geophysicists Map What Lies Beneath Southern California Using High-Resolution Sensors

BY ZACHARY ROMANO
Researchers at Stanford University are identifying hidden dangers beneath Earth’s surface in Southern California by measuring body waves from human activity on city streets and sidewalks. Body waves are the seismic waves that only move through the interior of a solid, as opposed to “surface waves,” which only move on the surface. Throughout Long Beach, seismic sensors had been placed around the area for routine monitoring of earthquake and tremor activity. Using these devices, the researchers calibrated them to filter out background noise waves and hone in on these body waves. The maps generated from the seismic data visualize more than half a mile beneath the Earth’s surface.

For nearly 15 years, scientists have worked towards developing the technology that could effectively filter out the unwanted background noise. Previously the technology was quite costly and the seismic sensors lacked the precision to measure the low amplitudes of body waves, especially against the interfering noise. Body wave tomography itself, however, has been used for decades to track earthquakes and explosions. With the help of geospatial and GIS technologies, the maps visualizing these body waves are quite insightful. In Long Beach, the maps accurately show the location of the Newport-Inglewood Fault. The research team also discovered the rock types adjacent to the fault line which could be useful information to certain practitioners.

THOUSAND OF SEISMIC SENSORS (RED DOTS) WERE PLACED AROUND LONG BEACH, CALIFORNIA FOR THE STUDY. THE BLUE STAR INDICATES THE REFERENCE RECEIVER. MAP: NAKATA ET AL, 2015.

Southern California can certainly benefit from this new tool to understand the subsurface of the Earth. Two large seafloor faults, the Santa Cruz-Catalina Ridge and Ferrelo Fault, are presently shifting and have the ability to create an 8.0 earthquake with tsunami potential 90 miles of the coastline. The DailyMail reported that “the ridges, valleys and other signs they found along the Santa Cruz-Catalina Ridge Fault suggest that the fragmented, blocky crust has been lifted upward, while also slipping sideways like the plates along the San Andreas Fault do.” Researchers can create noise images in real-time and use time-series analysis of these images to have a more detailed knowledge of fault lines and their movement, even on a small-scale.

BY MAPPING OUT THE SEISMIC WAVES GENERATED BY HUMAN ACTIVITY, RESEARCHERS ARE ABLE TO CREATE A MAP OF UNDERGROUND CONDITIONS. IMAGE: NAKATA ET AL, 2015.

Another practical application deals with the observation of sinkholes. This can allow researchers to see what areas are at high risk of sinkholes and, in turn, minimize the destruction and number of victims. With a very dynamic crust in California, this higher resolution seismic sensor can now inform emergency preparedness strategies and allow experts to better understand the timeline of a major earthquake.

More:


Nakata, N., Chang, J. P., Lawrence, J. F., & Boué, P. (2015). Body wave extraction and tomography at Long Beach, California, with ambient‐noise interferometry. Journal of Geophysical Research: Solid Earth, 120(2), 1159-1173. Retrieved from: http://onlinelibrary.wiley.com/doi/10.1002/2015JB011870/full

Source: GIS Lounge - Maps and GIS

The most precise 3D map of Earth’s interior

By Aleks Buczkowski




Seismologists from University of California, Berkeley, have come up with an interesting project. They’ve analyzed paths of seismic waves and based on that created the first-ever detailed 3D map of the Earth’s interior.

The 1,800-mile thick mantle under the Pacific Ocean contains rising plumes of hot rock that fan out at the surface to stationary hotspots, where they generate island chains as Earth’s crust moves due to plate tectonics. Scott French image.

The model shows mantle plumes (where the hot rock flows) starting at the bottom of the core-to-mantle boundary and climbing to the top, where they connect to volcanic hotspots in the Earth’s crust. The model precisely connected volcanic island chains like Hawaii, Samoa and Iceland. Of course it isn’t perfect. It didn’t link plumes to some volcanoes, such as the one at Yellowstone National Park but still it is the most precise scan of the Earth’s interior ever made.

Most of the known volcanic hotspots are linked to plumes of hot rock (red) rising from two spots on the boundary between the metal core and rocky mantle 1,800 miles below Earth’s surface.

Previous attempts to map mantle plumes have detected pockets of hot rock rising in areas where plumes have been predicted, but it was unclear whether they were connected to volcanic hotspots at the surface or at the roots of the plumes, deep below the surface of the planet.

Creating this kind of high-resolution CT of Earth, requires significant computing resources. Scientists used very accurate numerical simulations of how seismic waves travel through the mantle, and compared their predictions to the ground motion actually measured by detectors around the globe. The analysis required 3 million CPU hours on supercomputers, and tool couple of weeks of computing.

It is interesting that we are thinking about exploring Mars but we still now so little about what’s beneath us.

source: Berkeley News and Geoawesomeness