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🇺🇸 Los Angeles

ShakeAlertLA — the City's Earthquake Warning App

Los Angeles released the first publicly available US smartphone app relaying earthquake warnings from the federal USGS ShakeAlert system, on the app stores from 31 December 2018. The sensors and the alert algorithm were federal; the city paid for the app and chose its alert threshold. It retired the app on 31 December 2020 for California's statewide MyShake.

Completed 📅 2018–2020 ✔ Editor-reviewed

✔ Reviewed by the 1001 Smart Cities editorial desk · 🔎 Last verified

🏛️ GovernanceSafety & securitySensors & IoTDigital government

📊 Impact

During the July 2019 Ridgecrest sequence — a M6.4 foreshock and a M7.1 mainshock, California's largest quake in 20 years — the app sent no public alert to Los Angeles County. A peer-reviewed USGS-authored analysis found the predicted shaking fell below the app's MMI 4.0 threshold, and that for the M7.1 an alert was warranted but ShakeAlert underestimated the magnitude by 0.8 units. The city cut the trigger from magnitude 5.0 to 4.5 on 14 August 2019. It reported 920,000 downloads over two years; no documented case of the app warning Angelenos before shaking was found.

🎓 Lesson

Los Angeles could set the alert threshold but not the accuracy behind it. At Ridgecrest both failed at once: the city's threshold was too high, and the federal algorithm underestimated the quake by 0.8 magnitude units.

Evidence🔬 Peer-reviewed
Scale🗺️ Regional
Cost≈$300k app contract (AT&T and the GRYD Foundation)
FundingCity of Los Angeles contract, with the Annenberg Foundation and the Mayor's Fund for Los Angeles as named partners

Sources

↗ City of Los Angeles Information Technology Agency (authority)The city's own account of the release, built on the USGS ShakeAlert system, and of the later lowering of the warning threshold from magnitude 5.0 to 4.5. Dates the release to 1 January 2019; the app reached the stores on 31 December 2018.
↗ Cal OES / Mayor Garcetti — retirement announcement (23 Dec 2020)Source of the 31 December 2020 retirement date, the self-reported 920,000 downloads and 100,000 alerts issued, the AT&T / Annenberg Foundation / Mayor's Fund partnership, and the statement that the statewide system pairs MyShake with Wireless Emergency Alerts.
↗ Chung et al., Bulletin of the Seismological Society of America (2020) — peer-reviewedBSSA 110(4):1904-1923, doi 10.1785/0120200032. Carries both load-bearing findings: no public alert was sent because predicted shaking was below the app's MMI 4.0 threshold, and for the M7.1 an alert was warranted but the point-source and finite-fault algorithms underestimated the magnitude by 0.8 units. Also confirms the app was the only publicly available alerting method at the time. Publisher pages block automated fetching (403); text verified via indexed abstract.
↗ GovTech — ShakeAlertLA adjusts alert thresholds after users complainLaunch threshold of magnitude 5.0 plus MMI IV, and the city's own rationale for setting it high: officials feared people would become apathetic and stop responding if it was set too low. Reports the MMI threshold as unchanged, which is why no revised intensity value is claimed here.
↗ NBC Los Angeles — threshold lowered (14 Aug 2019)Dates the change to Wednesday 14 August 2019 and attributes it jointly to Mayor Garcetti and the USGS: magnitude 5.0 down to 4.5.
↗ CBS Los Angeles — city council approves the app contract (19 Jun 2018)The $300,000 contract with AT&T and the GRYD Foundation for design, creation and deployment of the app.
↗ CBS Los Angeles — 'We hear you' (4 Jul 2019)The city's same-day response to the Ridgecrest non-alert, promising to lower the threshold.
↗ Nextgov — L.A.'s public earthquake-warning app is the first in the U.S. (Jan 2019)Independent support for the first-in-the-nation claim and for the partner list; also records that dozens of early users reported the iPhone app crashing at launch.
↗ LAist — the city points everyone to the statewide app (Dec 2020)Garcetti's stated reason, that ShakeAlertLA was a bridge to the statewide system, and confirmation that MyShake is operated by UC Berkeley.
↗ Temblor — earthquake early warning now and beyondThe only quantified Los Angeles performance figures found, and they belong to the successor app: at the M4.5 El Monte quake of 19 September 2020, MyShake sent 20,169 alerts, reached 80% of phones 3.5 seconds after receiving the ShakeAlert signal, and about half of alerted users were notified before the S-wave arrived. Also identifies WEA as FEMA's channel.
📎 Cite this project

1001 Smart Cities (2026). “ShakeAlertLA — the City's Earthquake Warning App” — Los Angeles, United States. The Smart City Atlas. https://1001smartcities.org/projects/la-shakealert-app/ (last verified 2026-07-26). Data: CC BY 4.0.

The underlying data is free to reuse with attribution — see the open data page.

🔗 Related projects

🇹🇷 Earthquake Early Warning & Seismic Monitoring Network · Istanbul Same hazard, opposite ends of the chain: Istanbul's seismic net halts trains and gas by itself; LA's app pushed a notification, or didn't. 🇯🇵 Tsunami-Alert Automatic Tide Gate Closure · Osaka A national alert closes Osaka's gates with nobody deciding; the same kind of national alert reached LA, and a city threshold stopped it. 🇵🇭 EFCOS: Metro Manila's Flood Telemetry and Floodway Gates · Manila Both put a number between sensor and response: Manila's crews open gates on a gauge; LA's threshold was set high enough that nothing fired. 🇺🇸 GeoHub Open Geospatial Data Platform · Los Angeles Another verified project from Los Angeles.

🧭 Explore the atlas

🏙️ Los Angeles Explore every verified project and the city's smart-city story. 🏛️ Governance Browse the main topic behind this project. 📖 Open data Information anyone is free to access, use and share, published by governments in machine-readable formats under an open licence. 📖 Adaptive traffic signals Traffic lights that retime themselves in real time from live sensor data to match actual traffic, instead of running a fixed pre-set schedule. 📖 ANPR (automatic number-plate recognition) Camera technology that reads vehicle number plates automatically, used to enforce road-pricing and clean-air zones without toll booths. 🪦 Why smart cities fail Read the wider analysis and comparison. 🚦 Showcase or use case — what does a smart city actually need? Read the wider analysis and comparison.

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