Since the September 12 4.7 earthquake centered just north of Malibu, the valley has been hit by a series of smaller, but nonetheless frequent shakers.
Seismologist Lucy Jones, following the September 12 quake, said, “We need to remember that the quiet of the last 25 years is not representative of the long-term Southern California pattern. And we should get used to having more than we’ve seen recently.”
With ongoing tremors and the possibility of another big earthquake, California residents should take advantage of the free ShakeAlert App offered by the U.S. Geological Survey.
The ShakeAlert Earthquake Early Warning System detects significant earthquakes quickly enough so that alerts can be delivered to people and automated systems potentially seconds before strong shaking arrives. The purpose of the system is to reduce the impact of earthquakes to save lives and property.
The USGS works with licensed technical partners who use USGS-issued ShakeAlert Messages to alert people to take a protective action or to trigger automated actions. These automated actions could include slowing trains, closing water valves, turning on backup generators, issuing public announcements, and many others.
For individuals their slogan “because seconds matter” means the alert may give residents time to take cover, hold on and stay safe during shaking.
The system does not predict earthquakes. ShakeAlert detects ground movement after an earthquake has already begun, and then issues messages to rapidly alert people.
It detects earthquakes when a rupturing fault sends out different kinds of waves that send energy away from the epicenter, like ripples on a pond. The fastest-moving seismic waves (primary or P-waves) travel about 3.6 miles per second and generally don’t produce strong shaking. P-waves are followed by slower moving, more damaging waves (secondary or S-waves) and surface waves that travel about 2.5 miles per second.
The ShakeAlert seismic network detects the P-wave (that first felt wave) and immediately transmits data to a processing center, where the estimated location, size and expected shaking of the quake are determined. The goal of earthquake early warning is to send out a ShakeAlert-powered alert before damaging shaking arrives.
The system is designed to work because P-waves travel almost twice as fast as the surface waves, and today’s telecommunications systems are many times faster than seismic waves.
Both of these factors make it possible for alerts to reach people before strong shaking arrives.
However, those directly above or very near the earthquake origin are not likely to receive an alert before shaking is felt because there may not be enough time to detect, confirm and send an alert to those close to the epicenter before the S-waves arrive. That is the reason some residents close to Malibu reported that they did not receive an alert on their phone on September 12.
Alert delivery will come by other public and private means (internet, radio, television, cellular), including Wireless Emergency Alerts – think of an AMBER Alert – delivered by FEMA’s Integrated Public Alert and Warning System.
There are several ways to get ShakeAlert-powered alerts on your cell phone. The MyShakeTM app was developed by UC Berkeley and is sponsored by the California Governor’s Office of Emergency Services. MyShake is available for free in the Apple iTunes and Google Play stores. Google provides a ShakeAlert-powered earthquake alert feature for cell phones using the Android operating system
To get information about downloading the ShakeAlert visit.usgs.gov/faqs/how-do-i-sign-shakealertr-earthquake-early-warning-system.
