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Earthquake Imaging: Smartphones, Drones, Lasers, and Radars
Every ad for a cellphone includes a plug about its camera. We want the images we take to have depth, beauty, and quality – achieved with a simpler technique. And we especially want better resolution.
In the earthquake science world, an image is worth a thousand words (and significant publications). How well we can see or measure something on a map, a photo, or in a simulation may mean the difference between validating a hypothesis or stumbling upon a major, unexpected breakthrough.
Earthquake scientists constantly look for opportunities to gather data at finer spatial scales using DSLR cameras attached to drones or balloons, aerial or ground laser scanning lidar, radar technology (InSAR), satellites, and even smartphones.
“We need a resolution fine enough to capture earthquake phenomena at the scale in which they operate.” said Ramon Arrowsmith, Professor of Geology at Arizona State University and long-time SCEC community scientist. “If your ruler is too big for the subject, how can you measure it accurately?” For example, the details of an earthquake surface rupture, and the subsequent landscape response, require one to characterize fractures, landform elements, warps, and other features at sub-meter scales.
And given costs, weather conditions, emergency response efforts, and other conflicting priorities, it may take time to deploy people and technology to affected areas.
For example, following the 2010 M7.2 El Mayor Cucapah (Baja California) earthquake, it took 3-4 months before planes equipped with lidar could be deployed to collect data. According to UC Davis Professor and SCEC community scientist Mike Oskin, “Ideally, we want an aircraft to fly over a rupture area within 3-4 days, not months.” With increasing existing coverage of high-resolution topographic data, scientists can analyze the differences from before and after scans of affected areas. Capturing the ephemeral aspects of a rupture before and right after an event allows for better understanding of fault zone processes.
Even so, many revelations were made with data obtained from lidar about the El Mayor Cucapah earthquake. This event resulted from a “keystone” fault responsible for rupturing many other faults, as verified by the surface rupture seen along smaller faults in the high-resolution data – something not easily identified by the naked eye in the field. (See Oskin M., Arrowsmith J., Corona H., Elliott A., & Fletcher J., “Near-Field Deformation from the El Mayor–Cucapah Earthquake Revealed by Differential lidar (2012)", Science. DOI: 10.1126/science.1213778.)
Source: UC Davis News Room / KeckCAVES
“Surveying the 2014 Napa Earthquake was a slightly different story,” says Oskin. Airspace was restricted to emergency response, and ground deformation from that M6 earthquake was at the decimeter level – a challenge to measure from the air. In this case, a smartphone proved to be a handy, cost-effective, and non-disruptive method for surveying. Smartphones were used to take photos from various angles, and the photos were then layered together to yield a high-resolution, 3D model of “structure from motion.” Airborne, terrestrial and mobile laser scanning was also applied effectively by the U.S. Geological Survey. (DeLong et al, 2015; Hudnut et al, 2014)
With all these tools and techniques, one can imagine the amount of data present. In the geosciences, collaborating to share and analyze data is key. Thus, innovative applications and environments are always popping up and evolving to help scientists make sense of the vast amounts of data.
Take for example OpenTopography.org, hosted at the San Diego Supercomputer Center in collaboration with UNAVCO and Arizona State University. It is an open and organized environment for collecting and tools for processing high-resolution topographical data. In 2016, more than 53 thousand jobs from over 16 thousand users were run through OpenTopography.org. Its collections include lidar coverage for most of the active faults in western North America.
As technology that fits in our hands continues to improve – along with how we process the obtained data – so will the future of earthquake imaging. So better resolution means better ways to characterize seismic hazard, thus giving better information to those who build infrastructure, ultimately saving lives, reduce injury, and mitigate economic loss.