Thread by @USGS_ShakeAlert

#ShakeAlert focuses on eq shaking which is controlled by 3 main factors: magnitude, distance from the rupturing fault, and local ground conditions. These factors play a role in how hard and for how long a region will shake. @IRIS_EPO video explains #USGSRemembers #LomaPrieta

@IRIS_EPO Generally, the closer to an earthquake the stronger the shaking you will feel. The Cypress St. viaduct along the Nimitz Freeway (I-880) was 55 miles away from the #LomaPrieta EQ. Why did the viaduct experience such heavy shaking, which caused its tragic collapse? (1/2)

During an earthquake, loose, soft soil will shake harder and longer than hard rock. Valleys will shake harder than mountains because of their sediment fill. Watch this video from @IRIS_EPO: iris.edu/hq/inclass/ani…
#USGSRemembers (2/2)

@IRIS_EPO Getting out rapid information about an earthquake that has already begun is critical. A #ShakeAlert is a data package USGS makes available to 60+ partners so they can deliver alerts to people and/or trigger automated actions such as slow a train or protect a water supply.

A #ShakeAlert is one of the many earthquake information products offered by the USGS Advanced National Seismic System (ANSS). Other products include ShakeMap, National Hazard Maps, and Did You Feel It? Learn more about ANSS at: earthquake.usgs.gov/monitoring/ans…

Compared to other ANSS products, #ShakeAlert is first out of the gate. All of the products serve important roles in contributing critical information about earthquakes and their effects. Learn more about ANSS products at: earthquake.usgs.gov/monitoring/ans…

All components of the #ShakeAlert System must work quickly to get alerts to their destination. The USGS ANSS component in dark blue (ground motion detection by seismometers to issuing the ShakeAlert) are the first steps in the process.

Once ground motion is detected by seismic stations, information is sent in a fraction of a second to a #ShakeAlert processing center. There are 3 centers, 1 in Washington and 2 in California. ShakeAlert software makes very quick decisions from an early snapshot of the earthquake.

#ShakeAlert software is very sophisticated and works very fast. Pretend you are a ShakeAlert processing center. Is this snapshot of ground motion data an earthquake? (Answer will follow)

If you said yes - you've issued a successful ShakeAlert! Good job! This record is from the M6.0 South Napa earthquake on 8/24/14. Learn more about this earthquake at: earthquake.usgs.gov/earthquakes/ev…

In seconds, the #ShakeAlert system produces a package that has information about the location, initial magnitude, and estimated shaking intensity across the affected region. This information will help ShakeAlert partners make decisions about alert delivery.

The ShakeAlert system continues to refine these ground motion estimates and updates ShakeAlerts as the earthquake grows and more sensor data become available.