San Diego didn’t get a ShakeAlert. Here’s why we weren’t supposed to
All ShakeAlerts are not the same. There are three different notification systems and only one is currently working.
Author: Brandon Lewis, Reporter
Published: 4:44 PM PDT July 6, 2019
Updated: 6:07 PM PDT July 6, 2019

SAN DIEGO — When the first of a series of earthquakes rolled through San Diego July 4, some residents questioned why they didn’t get a notification.

Just a week earlier, most phones countywide buzzed with an alert that tested the Wireless Emergency Alert (WEA) system that would send ShakeAlerts, but the system isn’t ready to go live.

What is a ShakeAlert?
Across the country, the U.S. Geological Survey has ground sensors that detect primary and secondary waves. There are 45 in San Diego County.

When a sensor detects primary waves from a significant earthquake, it triggers an alert to the USGS. A ShakeAlert would then take that data and send a notification to you that secondary waves, which cause shaking, are imminent.

Are all ShakeAlerts the same?
No, there are three different notification systems. Only one is currently working.

1) ShakeAlert LA – This is the only functioning system and only serves Los Angeles County. It is set to notify residents when shaking above a magnitude 5.0 is imminent within the county. This is an app-based system that requires users to download an app.

2) ShakeAlert – This is a statewide app that is still in development. It would send notifications based on a user’s location. It would require users to download an app.

3) ShakeAlert WEA – This is the system that was tested last week. It would send a notification to all phones within a designated area based on the geolocation of the device. It would work similar to an AMBER Alert and would not require users to download any additional programs.

Why are there so many systems?
"What we found with Wireless Emergency Alerts is that not everyone receives them. Not everyone is going to download the app, so the idea is to create multiple platforms and multiple ways that people can receive messages about earthquakes," said Holly Porter, Director of the County Office of Emergency Services. “During a disaster, just by its very definition, systems are overwhelmed. technology fails. We want people to have all the options available to them to receive a potential alert and warning."

When will San Diego start getting ShakeAlerts?
The ShakeAlert app should be available statewide in late 2019. The WEA is still undergoing testing.

What was the WEA test last week?
"We tested that system to see if it's fast enough. If it could possibly be used to send out an alert for an earthquake early warning," said Porter. "[We’re testing] what platform will be fast enough once those primary earthquake waves are detected by sensors to quickly get an alert to public before secondary waves arrive."

If the system were working, would I have received a ShakeAlert Thursday or Friday?
Likely not because the shaking in San Diego County wasn’t severe enough to warrant notification.

What magnitude earthquake will trigger a ShakeAlert in San Diego?
That’s still being decided.

Will San Diego have our own ShakeAlert App?
No, we will be part of the two statewide alerting systems.

ShakeAlert LA was set to send an alert to residents during a 5.0 or greater magnitude earthquake. The city later said, based on feedback from residents, it would lower the threshold.

Some researchers are advocating for a high threshold to avoid desensitizing the public. They argue it should be reserved for earthquakes when lives or property are at risk. Others want a lower threshold, so residents can be prepared for any earthquake that might affect them.

The threshold for the statewide ShakeAlert is still being debated.

"It's looking for that sweet spot where we want to alert people when there's protective action recommendation you want them to take when there's possible damage, but not over alert to the point the alerts don't really mean anything," said Porter. "We want the alerts to be meaningful and we want to give people notice of what they can do at that moment to protect themselves."

LOCAL
Understanding the probability of future earthquakes and aftershocks
Seismologists warn that large aftershocks are expected to continue for days or longer, following Thursday and Friday's earthquakes in the Ridgecrest area.
Author: Heather Hope, Reporter
Published: 6:32 PM PDT July 6, 2019
Updated: 6:33 PM PDT July 6, 2019

RIDGECREST, Calif. — Seismologists say the shaking in southern California may not be ending anytime soon after having major back-to-back quakes.

Seismologists warn that large aftershocks are expected to continue for days or longer, following Thursday and Friday's earthquakes in the Ridgecrest area.

RELATED: Powerful 7.1 magnitude earthquake shakes southern California

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"We are really likely to see a six-size event in the next few days on the next week, we're expecting large earthquakes on all the faults in Southern California," said Dr. Egill Hauksson of the CalTech Seismological Laboratory.

The USGS reports there have been nearly 1,500 earthquakes and aftershocks in 24 hours with over 500 having a magnitude of at least 2.5.

“For a while, Ridgecrest was known as the Earthquake capital of the world because they used to have so many small earthquakes,” Hauksson said.

RELATED: San Diego didn’t get a ShakeAlert. Here’s why we weren’t supposed to

Hauksson says there is a three percent chance for another seven or greater quake to hit and a 27 percent chance for a magnitude 6. The chance of a magnitude 5 or higher is 96 percent, with as many as eight likely to occur.

"With these earthquakes, we are lucky, that the energy in them is mostly going to the north away from Los Angeles," said Hauksson, who does not believe the earthquakes were caused by fracking in Kern County.

Although Ridgecrest in Kern County is more than three and half hours away from San Diego, the impact of its quakes can still leave a mark.

RELATED: Governor Newsom issues statement on California earthquakes

"Earthquakes at this distance can cause some damage in very isolated cases, especially if the ground is very soft and saturated with water,” Hauksson said.

USGS geologist Nicholas Van Der Elst says the Ridgecrest area’s activity is “going to be higher for the foreseeable future, for years, these aftershocks are going to be trickling along.”

Seismologist Doug Given of USGS for 40 years states these quakes are a reminder that Californians live in earthquake country.

"Could be that this kind of earthquake that we just experienced it happens every thousand years or so and we just got lucky, that it wasn't more impactful in the populated areas,” Given said

How fast does the earthquake information get posted to the website, get sent out via the Earthquake Notification Service (ENS), ATOM feeds, etc?

USGS earthquake information mechanisms are all triggered by the same system, so they all receive the information at the same time. The time it takes for the system to receive the information primarily depends on the size and location of the earthquake:

An earthquake in California is processed and posted to the system in 2.5 minutes (on average). This is because our seismic network is very extensive in California, where there are many earthquakes and many people.

An earthquake in the U.S. outside of California (where seismic networks are not as dense), is typically posted within 8 minutes.

An earthquake outside the United States, where the seismic network is sparse in some areas, takes 20 minutes (on average) to process and post. Our webpages with realtime information are cached for 60 seconds, so there might be an additional delay of up to 60 seconds for the webpage to be updated.

From the time each system receives the information to the time you receive the information is the same for all systems, usually within a few seconds (unless there are network problems), except for the Earthquake Notification System (ENS) and the earthquake feeds, which can vary.

Since ENS has many thousands of accounts, all customized to receive different notifications, the time between ENS receiving the information and you receiving your notification can vary quite a bit. A large earthquake that generates many notifications might take up to 45 minutes to reach the last account on the list. A small earthquake that generates fewer notifications will take only a matter of several minutes to reach all accounts. The time it takes for the notifications to be sent depends on the capacity of the machines that send the email.

Social media outlets, such as Twitter, might be able to broadcast the occurrence of an earthquake faster than the USGS can using our standard mechanisms, but they cannot provide any quantitative data such as location and magnitude.

For the various Feeds, we cache different feeds for different lengths of time, so it depends on the feed you access. We try to balance data volume, how often the data in the feeds change, and server load so:

GeoJSON 7-days and less feeds are cached for 1 minute
Other 7-day and less feeds are cached for 5 minutes
30-day feeds and searches are cached for 15 minutes
Event pages (and geojson detail feeds) are cached for 1 minute for the first 7 days after an event, and for 15 minutes after that

The Earthquake Map/List/Search interface uses GeoJSON feeds.