Thread by @USGS_ShakeAlert

Hi everyone, it’s #ReseachFriday! This week’s focus is on #ShakeAlert alerting regions! This study looked at using the 2019 Ridgecrest earthquakes to find an optimal alerting strategy. pubs.geoscienceworld.org/ssa/bssa/artic…

So, the #ShakeAlert system detects an earthquake, it uses ground motion models (GMMs) to determine the size of the alert region using earthquake source estimates as input (generally, magnitude and location).

The authors first found which GMM predicts shaking intensities that match the average observed intensity with distance from USGS Did You Feel It? (DYFI?) reports on the Ridgecrest earthquakes. Here's the DYFI map from the M7.1 Ridgecrest earthquake.

DYFI? Reports are those reports that people fill out on the USGS website after they feel an earthquake. More here about those reports: earthquake.usgs.gov/data/dyfi/

Using the average-expected intensities in the alert region process is great, but ground motions vary for all sorts of reasons and there will be people who experience larger-than-expected shaking. The authors wanted to find a way to include these locations inside the alert region.

They did this by incorporating GMM uncertainties in the alert region calculation. In weather forecasts, if you’re told that you might experience 0-2 inches of rain, you’re going to bring your umbrella with you just in case! The authors took a similar approach here.

By picking the size of the alert region based on the maximum possible shaking at that location instead of just the average, the alert region can be expanded to include the locations that experience larger-than-expected shaking.

This can reduce the number of missed alerts, when people should have received an alert but didn’t. By incorporating uncertainty we can get 94% of the population who needed alerts for the Ridgecrest EQs inside the alert regions (assuming magnitude is estimated correctly).

And this is one way we are working to improve the #ShakeAlert system. Great work Dr. Jessie Saunders who is a USGS Mendenhall Postdoc. Paper is available at: pubs.geoscienceworld.org/ssa/bssa/artic… @IRIS_EPO

And oh yes - we know it should be #ResearchFriday. Happy Friday everyone!😀