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ShakeAlert

ShakeAlert is an earthquake early warning (EEW) system managed by the United States Geological Survey (USGS) that detects significant earthquakes throughout the West Coast of the United States rapidly enough to deliver alerts to users and automated systems before strong shaking arrives.^[1] The system serves more than 50 million residents and visitors across California, Oregon, and Washington, aiming to reduce the impact of earthquakes by providing seconds to minutes of warning time to take protective actions, such as dropping, covering, and holding on, or automating responses like slowing trains and closing water valves.^[1] Developed over more than a decade by the USGS in partnership with institutions including the California Governor’s Office of Emergency Services, the California Institute of Technology, the University of Washington, and the University of Oregon, ShakeAlert leverages an existing network of seismic sensors to monitor and analyze earthquake activity in real time.^[1] Public alerts are now delivered via compatible mobile apps, wireless emergency alerts on smartphones, and integrated services, with the system becoming fully operational for public use in California in 2019 and expanding to Oregon and Washington thereafter.^[2] As of 2025, ShakeAlert remains online and continuously tested, contributing to broader global efforts in EEW alongside systems in countries like Japan, Mexico, and Taiwan.^[3]

History and Development

Origins and Early Research

The concept of earthquake early warning (EEW) systems emerged from global efforts to mitigate seismic risks, with pioneering implementations in Mexico and Japan serving as key inspirations for later developments. Mexico's Seismic Alert System (SASMEX) began operations in 1993 as the world's first public EEW network, using coastal sensors to provide up to 60 seconds of warning for Mexico City following the devastating 1985 Michoacán earthquake.^[4] In Japan, the nationwide EEW system, managed by the Japan Meteorological Agency and integrated into the J-Alert framework, launched in 2007, building on earlier railway-specific alerts dating back to the 1960s and providing seconds to minutes of advance notice using a dense network of over 1,000 seismic stations.^[4] These systems demonstrated the feasibility of rapid seismic detection and public alerting, motivating similar initiatives in seismically active regions like the U.S. West Coast, where subduction zones and strike-slip faults pose significant threats.^[5] In the United States, formal research into an EEW system began in 2006, led by the U.S. Geological Survey (USGS) in collaboration with universities such as the University of California, Berkeley; the California Institute of Technology (Caltech); and the University of Washington, along with other partners including state seismic networks.^[6] This effort focused on addressing the high seismic hazards along the West Coast, particularly in California, Oregon, and Washington, where urban populations and infrastructure are vulnerable to events from the San Andreas Fault and Cascadia Subduction Zone.^[5] The initiative built on prior experimental tests, such as short-term EEW prototypes in Oakland in 1989 and southern California in 1997, but emphasized scalable, integrated detection using existing seismic networks.^[7] The urgency for a U.S. EEW system was underscored by major earthquakes that exposed vulnerabilities in unprepared regions. The 1994 Northridge earthquake (magnitude 6.7), a blind-thrust event in the densely populated Los Angeles area, caused 57 fatalities, over 8,700 injuries, and approximately $20 billion in damage, revealing the limitations of reactive response and spurring investments in predictive technologies like EEW.^[7] Similarly, the 2001 Nisqually earthquake (magnitude 6.8) in the Pacific Northwest resulted in one death, hundreds of injuries, and $2 billion in losses across Washington state, highlighting the need for warnings in areas with deep intraslab events and limited surface rupture visibility.^[8] These disasters emphasized the potential life-saving value of seconds-long alerts for actions such as dropping, covering, and holding on, or automating safety measures in transit and industry.^[9] Early milestones in ShakeAlert's development included prototype testing in 2007 under the California Integrated Seismic Network (CISN) framework, which integrated real-time data from regional seismic arrays to validate initial alerting capabilities.^[10] By 2010–2012, field trials in California expanded this prototype, conducting end-to-end simulations with test users to refine alert delivery and performance metrics, such as detection latency under 5 seconds for moderate events.^[11] During this period, foundational algorithms were developed, including the Earthquake Point-source Integrated Code (EPIC) at UC Berkeley, which uses P-wave arrivals from multiple stations to estimate epicenter and magnitude, and the Finite-Fault Rupture Detector (FinDer) at Caltech, designed to model extended ruptures for larger earthquakes.^[12] Research identified several technical challenges, particularly in accurately detecting P-waves—the faster initial seismic signals—and estimating magnitude in the critical first few seconds before destructive S-waves arrive.^[13] For blind thrust faults, like that underlying the Northridge event, hidden subsurface ruptures complicated early magnitude scaling, as initial P-wave amplitudes often underestimated final event size, leading to potential under-alerting for inland urban areas.^[14] These issues drove iterative improvements in algorithm robustness, focusing on ensemble processing from distributed stations to enhance reliability amid variable fault geometries and noise.^[15]

Implementation Timeline

ShakeAlert's implementation unfolded in distinct phases, focusing on progressive expansion from limited testing to widespread public access across California, Oregon, and Washington. Phase 1, spanning 2015 to 2018, involved initial deployment for advanced users, including pilot testing in the Pacific Northwest starting in 2015 and expansion to select technical users such as transportation and utility managers by 2017.^[2] In fall 2018, the U.S. Geological Survey (USGS) declared the system "ready to roll," enabling automated delivery of alerts to over 60 institutional partners for operational use without public dissemination.^[2] This phase emphasized system reliability and integration with existing seismic networks, laying the groundwork for broader rollout while restricting access to vetted organizations to refine performance.^[16] Phase 2, initiated in 2019, marked the transition to public alerting, beginning with California's first statewide testing on October 17, 2019, which delivered alerts via apps and other channels to evaluate real-time performance.^[17] This beta period gained critical real-world validation during the July 2019 Ridgecrest earthquake sequence, where the system issued timely alerts for the magnitude 6.4 and 7.1 events, providing seconds of warning and demonstrating robustness under high-magnitude conditions.^[18] In 2020, ShakeAlert evolved to Version 2.0, incorporating enhancements such as the EPIC (Earthquake Prediction and Information Center) and FinDer (Finite Fault Detector) algorithms, which improved latency by reducing processing times and boosted accuracy in magnitude estimation and rupture characterization.^[19]^[16] Public expansion continued into 2021, with integration into the Wireless Emergency Alerts (WEA) system enabling automatic notifications to compatible mobile devices.^[20] Oregon activated statewide public alerts on March 11, 2021, followed by Washington on May 4, 2021, completing West Coast coverage.^[21]^[22] By mid-2021, ShakeAlert achieved general availability, serving more than 50 million residents and visitors through diverse delivery mechanisms.^[21]

Funding and Partnerships

ShakeAlert's primary funding comes from federal appropriations to the U.S. Geological Survey (USGS) through the Earthquake Hazards Program, with Congress allocating $161.8 million for earthquake early warning (EEW) capabilities from fiscal year (FY) 2006 to FY 2024, including $130.7 million in base funding and $31.1 million in capital investments.^[23] In FY 2024, the USGS allocated $28.6 million specifically to ShakeAlert operations and development within the broader $163.5 million National Earthquake Hazards Reduction Program (NEHRP) budget. This federal support is supplemented by nonfederal contributions totaling $135.5 million from 2012 to 2024, primarily from state sources such as California's $110.1 million (including investments from the California Earthquake Authority and Cal OES), Oregon's $8.5 million for seismic infrastructure, and Washington's $1.2 million via emergency management allocations to the Pacific Northwest Seismic Network (PNSN).^[23] Private philanthropy has also played a role, with the Gordon and Betty Moore Foundation providing $10.1 million in grants to support system research and deployment.^[23] By 2025, cumulative investments in ShakeAlert exceed $300 million when combining federal, state, and private sources, enabling the system's expansion to over 1,500 seismic stations across the West Coast.^[23] Funding challenges include heavy reliance on annual congressional appropriations, which have varied and occasionally fallen short of full operational needs, prompting incremental build-out rather than comprehensive completion.^[19] In response, the Senate passed S.3606 in December 2024 to reauthorize NEHRP for FY 2024 through FY 2028 at $175.4 million annually across participating agencies, but the bill did not become law; reauthorization efforts continued in 2025 with new bills introduced in Congress, providing ongoing oversight for USGS-led EEW efforts like ShakeAlert.^[24]^[25] The USGS serves as the lead operator of ShakeAlert, coordinating with a network of partners under the Advanced National Seismic System (ANSS).^[26] Key academic collaborators include the California Integrated Seismic Network (CISN), encompassing institutions like the University of California, Berkeley, and the California Institute of Technology (Caltech), as well as the PNSN at the University of Washington and Central Washington University, which manage regional seismic monitoring.^[6] State emergency management agencies—such as California's Office of Emergency Services (Cal OES), Oregon's Office of Emergency Management (OEM), and Washington's Emergency Management Division (EMD)—contribute to alert dissemination and public outreach.^[20] Private sector involvement includes integrations with technology firms, notably Google's partnership for delivering ShakeAlert notifications via Android's Earthquake Alerts system. Governance is structured around USGS oversight within the NEHRP framework, with the Core Committee (CoreCom) providing strategic coordination among federal, state, and academic stakeholders to evaluate resources and align implementation plans.^[20] This committee, comprising representatives from the USGS, principal state agencies, and university partners, addresses operational priorities and fosters collaboration on technical enhancements.^[20] In California, the Earthquake Early Warning Advisory Board under Cal OES offers additional state-level guidance on system integration and user adoption.^[23]

System Design and Technology

Detection Methods

ShakeAlert's detection capabilities are grounded in a comprehensive seismic monitoring network that captures ground motion in real time across the U.S. West Coast. The core infrastructure comprises approximately 1,675 seismic stations operated by the U.S. Geological Survey (USGS), universities, and state agencies, including networks such as the Advanced National Seismic System and regional systems like the California Integrated Seismic Network (CISN), which contributes over 400 stations in California alone. These stations form a dense array designed to sense earthquake initiation promptly, enabling the system's early warning functionality.^[7]^[19] The network employs two primary sensor types: strong-motion accelerometers and broadband seismometers. Strong-motion accelerometers are optimized for recording high-amplitude ground accelerations during intense shaking, providing critical data on potential damage levels. Broadband seismometers, in contrast, detect a broader spectrum of seismic signals, including the initial primary (P)-waves that propagate faster than the secondary (S)-waves responsible for most structural harm; this allows detection of an earthquake's onset several seconds before stronger shaking arrives at distant sites.^[7]^[27] Seismic data is transmitted in real time through telemetry systems utilizing internet and radio links, achieving end-to-end latencies of under 5 seconds from sensor detection to arrival at central processing facilities. Complementing these seismic sensors, over 1,100 GPS (Global Positioning System) stations have been integrated to measure co-seismic surface deformations, enhancing detection accuracy for large-magnitude events where traditional seismometers may saturate. This geodetic data provides complementary insights into fault rupture dynamics, improving overall system reliability for significant earthquakes.^[19]^[28] A key limitation in detection arises from blind zones, where shallow crustal earthquakes near the epicenter evade early sensing due to finite station spacing, typically resulting in radii of several kilometers without sufficient coverage. These gaps are exacerbated in regions with lower network density, potentially reducing warning times for proximal populations.^[29] To mitigate such challenges, targeted infrastructure upgrades have expanded the network, including the addition of over 100 new stations by 2023 to densify coverage in urban high-risk zones like the Los Angeles Basin and reduce blind zone vulnerabilities. These enhancements, part of broader efforts to reach a target of 1,675 stations by 2025, have bolstered detection thresholds in densely populated areas.^[30]^[31]

Algorithms and Processing

The ShakeAlert system employs a suite of algorithms to rapidly analyze seismic data and generate earthquake early warnings. The primary algorithms include the Earthquake Point-source Integrated Code (EPIC), which estimates earthquake location, magnitude, and peak ground motion for point-source events using P-wave data from multiple stations.^[32] EPIC triggers on P-wave arrivals exceeding a threshold at least four stations and requires 40% of nearby stations to activate, providing initial estimates within seconds.^[12] Complementing EPIC is the Finite-Fault rupture Detector (FinDer), a finite-source algorithm that models extended ruptures by estimating rupture length, orientation, and propagation using spatial distributions of peak ground acceleration (PGA) from triggered stations.^[32] For magnitude estimation, the Virtual Seismologist (VS) method applies a Bayesian network to integrate observed phase arrivals, network geometry, and prior earthquake probabilities, yielding probabilistic estimates of magnitude, location, and ground-motion distribution.^[33] These algorithms feed into an ensemble approach implemented in ShakeAlert Version 2, where a Solution Aggregator module combines independent outputs from EPIC, FinDer, and VS to produce a consensus source estimate, reducing uncertainties and mitigating false positives through multi-algorithm agreement.^[32] The processing pipeline operates across regional hubs at the University of Washington (Seattle), USGS Menlo Park (California), and Caltech/USGS Pasadena (California), with central aggregation at USGS facilities to ensure redundancy and low-latency computation.^[32] Incoming seismic data undergoes real-time hypocenter location estimation within 3-5 seconds of the event origin, followed by magnitude updates every second as additional waveforms arrive, enabling iterative refinements during the alert pause period.^[8] Alert issuance relies on key parameters such as predicted PGA thresholds, with warnings triggered for expected values exceeding 0.01g, corresponding to light shaking (Modified Mercalli Intensity IV).^[34] False positive rates are minimized by requiring consensus across algorithms and incorporating quality checks, such as sufficient station triggers and magnitude stability.^[32] In ShakeAlert Version 3, deployed in 2024, enhancements focus on offshore detection through Bayesian grid-search location methods paired with machine learning models like PhaseNet-DAS for precise P- and S-wave picking on distributed acoustic sensing data, alongside empirical scaling laws for rapid magnitude estimation based on peak strain rates. Version 3 also incorporates real-time GNSS data for improved detection of large-magnitude events.^[35]^[36] These updates improve accuracy for submarine events, providing up to 6 additional seconds of warning near coastal faults like the San Gregorio.^[35] This yields typical lead times of 5-60 seconds, depending on distance from the epicenter and rupture characteristics, allowing users to take protective actions before strong shaking arrives.^[37]

Coverage and Infrastructure

ShakeAlert's primary coverage encompasses the states of California, Oregon, and Washington, providing earthquake early warning to over 50 million residents and visitors in these regions. The system prioritizes high-risk seismic zones, including the San Andreas Fault system in California, which poses threats to major urban centers like Los Angeles and the San Francisco Bay Area, and the Cascadia Subduction Zone extending from northern California through Oregon and Washington, capable of generating magnitude 9+ megathrust earthquakes. This geographic focus addresses the West Coast's most seismically active areas, where tectonic interactions between the Pacific and North American plates drive frequent and potentially destructive events.^[38]^[39]^[19] The monitoring network comprises approximately 1,675 seismic stations operated by the U.S. Geological Survey (USGS) and partners, including about 1,100 geodetic stations for enhanced ground deformation detection, achieving full operational status as of 2025. Station density varies by region to optimize detection speed and accuracy: in high-population urban areas like the Bay Area, spacing averages about 10 km to enable rapid initial alerts, while seismic source zones threatening population centers aim for 20 km intervals, and lower-risk rural areas maintain 40 km spacing. Offshore regions remain sparser, relying on limited integration of existing instruments to extend coverage beyond coastal boundaries. This tiered density ensures efficient resource allocation, with denser networks supporting faster warning dissemination in populated zones.^[7]^[19]^[40] Central to the system's reliability are three primary data processing centers located at the USGS facilities in Menlo Park and Pasadena, California, and the University of Washington in Seattle, which handle real-time seismic data ingestion, analysis, and alert generation in a distributed architecture. These centers feature redundant communication pathways, backup power supplies, and failover mechanisms to maintain continuous operation during events, minimizing downtime risks from power outages or network disruptions. For offshore monitoring, particularly along the Cascadia Subduction Zone, ShakeAlert incorporates data from ocean bottom seismometers (OBS) deployed through partnerships like the Ocean Observatories Initiative, supplemented by hydrophones for acoustic detection of submarine events; this feeds into broader tsunami alerting coordinated with the National Oceanic and Atmospheric Administration (NOAA).^[40]^[41]^[42] Despite these advancements, coverage gaps persist, notably in southern Oregon where station density is lower than in California, potentially delaying alerts in remote areas, and in northern Baja California, Mexico, which lies outside the system's operational boundary due to its focus on U.S. territory and lack of integration with Mexico's SASMEX network. Plans to address these include expanding rural instrumentation through additional station deployments and collaborations to achieve target spacings, enhancing overall network resilience without extending beyond current state borders.^[19]^[7]

Alert Delivery and Users

Distribution Mechanisms

ShakeAlert warnings are disseminated through a structured core delivery system managed by the U.S. Geological Survey (USGS). Initial messages are published to the USGS Alert Queue, a central distribution hub that routes alerts to licensed partners and redistributors via redundant servers located in key facilities such as Seattle, Menlo Park, Berkeley, and Pasadena. From there, alerts are forwarded to collaborators like the Federal Emergency Management Agency's (FEMA) Integrated Public Alert & Warning System (IPAWS) for broader public dissemination, ensuring a seamless transition from earthquake detection to end-user notification.^[19] The protocols for these messages emphasize speed and precision, utilizing XML-formatted data packets that include critical parameters such as expected shaking intensity (measured in Modified Mercalli Intensity or MMI), estimated time until shaking arrival, and the earthquake's location (latitude, longitude, and depth). This format allows for rapid parsing by receiving systems, with a targeted end-to-end latency of less than 5 seconds from detection to delivery in high-density areas, enabling timely protective actions. Messages are updated iteratively as new data refines estimates of magnitude and extent, particularly for events exceeding magnitude 6.5.^[19] Distribution occurs across multiple channels tailored to different needs, including API feeds for application developers and web services for enterprise systems, which support machine-to-machine integrations for automated responses. For public alerts, messages are broadcast to nationwide cell carriers such as AT&T, Verizon, and T-Mobile via Wireless Emergency Alerts (WEA), adhering to a 360-character limit approved by the Federal Communications Commission (FCC) to accommodate more detailed information without overwhelming users.^[19] To ensure reliability during seismic events, the system employs geographically distributed redundant servers with automatic failover mechanisms, minimizing downtime even if primary infrastructure is affected by shaking. Integration with major carriers provides robust cellular and Wi-Fi pathways, while diverse telemetry options like satellite and microwave links offer backup routing. For user comprehension, alerts incorporate the ShakeIntensity scale, translating MMI levels into accessible descriptors such as "Light" for minimal effects (MMI IV) or "Moderate" for noticeable shaking that may displace objects (MMI V).^[19]

Institutional Users

Institutional users of ShakeAlert primarily include operators of critical infrastructure sectors such as utilities, transportation systems, healthcare facilities, and educational institutions, who integrate the system to enable automated protective actions ahead of strong shaking. These organizations receive ShakeAlert messages through licensed technical partners, allowing for rapid responses like securing equipment or halting operations to minimize damage and ensure safety.^[1]^[7] Utilities, for instance, utilize ShakeAlert to automate valve closures and other safeguards; the City of Grants Pass in Oregon has implemented the system to prevent water loss by automatically closing valves serving over 10,000 customers. In transportation, Bay Area Rapid Transit (BART) employs ShakeAlert for automated train control, slowing vehicles to 27 mph and briefly stopping them upon alert receipt, a process that takes about 20 seconds from full speed. Similarly, Metrolink rail in Southern California integrates alerts to slow trains in affected counties. Ports benefit from early warnings to secure operations, with general applications allowing crane operators to safely disembark or halt machinery, as demonstrated in conceptual uses at major facilities like the Port of Los Angeles. Hospitals, such as Cedars-Sinai in Los Angeles, route alerts through public address systems and radios to coordinate staff responses and protect patients. Schools integrate ShakeAlert into safety protocols, with districts like Stanwood-Camano in Washington using public address systems to deliver alerts and incorporate them into regular earthquake drills.^[43]^[44]^[19] Access to ShakeAlert for institutional users occurs via a subscription model through USGS-licensed technical partners, who provide API-based delivery of ShakeAlert messages for integration into operational systems; this paid service enables customized automation without direct USGS infrastructure management. Benefits include seconds of warning to secure operations, potentially averting injuries and structural damage—such as preventing train derailments or equipment failures—while contributing to broader economic resilience by reducing losses from major events, estimated in benefit studies to offset implementation costs through mitigated disruptions.^[45]^[46]^[6] Notable case studies highlight practical applications: During the December 2022 magnitude 6.4 Ferndale earthquake, ShakeAlert successfully detected and alerted users, demonstrating reliable performance for institutional responses despite challenges like message pauses. In 2024, system updates including Version 3 algorithms enhanced detection accuracy and speed, improving API responsiveness for automated institutional actions such as those in rail and utility sectors.^[32]^[47] The USGS provides training resources to support custom response automation, including the ShakeAlert Tests, Drills, and Exercises Toolkit for planning institutional exercises, as well as messaging toolkits tailored for sectors like education to integrate alerts into preparedness programs such as the Great ShakeOut drill. These tools facilitate ongoing education and testing to ensure effective automated implementations.^[48]^[49]^[50]

Public Alerts and Mobile Integration

ShakeAlert delivers earthquake early warnings to the general public primarily through the Wireless Emergency Alerts (WEA) system, which automatically transmits geographically targeted, text-like messages to compatible mobile phones without requiring app downloads. Implementation began in California on October 17, 2019, and expanded to Oregon on March 11, 2021, and Washington on May 4, 2021.^[20] The WEA system reaches over 90% of mobile devices in the United States, including most smartphones manufactured after 2012, ensuring broad accessibility for residents in the covered regions.^[51] Complementing WEA, dedicated mobile applications provide enhanced, customizable alert options for users seeking more detailed information. The MyShake app, developed by the University of California, Berkeley, integrates ShakeAlert data to deliver personalized notifications based on user location and preferences, and has surpassed 4 million downloads by April 2025.^[52] Since August 2020, ShakeAlert has been integrated into the Android operating system, including Google Pixel devices, enabling direct earthquake early warnings through the OS starting in early 2021 for the West Coast. As of 2025, ShakeAlert is integrated into both Android and iOS operating systems for direct alerts on compatible devices, enhancing public reach.^[53] Push notifications from these platforms, including Apple's ecosystem, support bilingual messaging in English and Spanish, with opt-in features for sharing alerts with family members across devices.^[54] The public rollout of ShakeAlert alerts has demonstrated practical application, with 41 notifications issued between October 2019 and September 2023 for earthquakes of magnitude 4.5 or greater that produced light shaking. In response to feedback on message brevity, the Federal Communications Commission expanded WEA capacity in 2020 to support up to 360 characters, allowing inclusion of safety instructions such as "Drop, Cover, and Hold On" alongside basic event details.^[55] To promote inclusivity, ShakeAlert incorporates accessibility features tailored for diverse users, including audio alerts that provide audible warnings for visually impaired individuals via compatible phones and apps.^[56]

Performance and Evaluation

Events During Development

During the development phase of ShakeAlert, prior to full public operations in 2021, the system underwent extensive testing through real-world earthquake events, demonstrating its capability to detect and characterize seismic activity rapidly while delivering alerts to beta users. One significant test occurred with the 2014 M_w 5.1 La Habra earthquake in California, where ShakeAlert detected the event in approximately 5.6 seconds and issued alerts to beta users, providing 10–20 seconds of warning time in areas like Los Angeles depending on distance from the epicenter.^[57]^[58] This event validated the performance of the Earthquake Point-source Integrated Code (EPIC) algorithm, which processed initial P-wave data to estimate magnitude and location effectively for point-source events.^[59] The 2019 Ridgecrest earthquake sequence in California, comprising an M_w 6.4 foreshock on July 4 and an M_w 7.1 mainshock on July 5, represented a more complex challenge due to its multi-fault rupture nature and provided the most rigorous pre-operational evaluation of ShakeAlert. The system detected both main events within 6.9 seconds of their origin times and generated alert messages available to pilot users, offering warnings ranging from 5 to 50 seconds before strong shaking arrived at distant sites.^[60] This sequence marked the first issuance of public test alerts through beta applications like ShakeAlertLA, though no widespread public notifications were triggered due to conservative thresholds; notably, there were no false negatives for significant events.^[60]^[61] The Ridgecrest sequence also included numerous aftershocks, with ShakeAlert processing 95 events of M ≥ 4.5 during the initial weeks, maintaining a system uptime of 99.5% amid the high seismicity.^[60] Overall, pre-2021 testing across such events achieved an average latency of 7.5 seconds for magnitude estimation, enabling timely alerts while keeping the false alert rate below 1%.^[60]^[30] Key lessons from Ridgecrest highlighted the need for enhanced finite-fault modeling to better handle complex ruptures, as initial point-source estimates underestimated magnitudes by up to 0.8 units, informing subsequent algorithm refinements without altering core detection methods tested earlier.^[60]

Operational Events

Since achieving general public availability in California in 2019 and expanding to Oregon and Washington in 2021, ShakeAlert has demonstrated robust operational performance in detecting and alerting for real earthquakes, issuing warnings that enable protective actions and automated responses. The system has processed numerous events, with alerts delivered via Wireless Emergency Alerts (WEA), mobile apps like MyShake, and institutional channels, serving over 50 million people across the West Coast. Performance metrics highlight rapid detection and high reliability for moderate-to-large events, though offshore and edge-of-network earthquakes present challenges in achieving optimal warning times.^[1]^[32] One early operational highlight was the July 8, 2021, M6.0 Antelope Valley earthquake in California, where ShakeAlert detected the event approximately 21 seconds after origin time using the FinDer algorithm, though sparse station coverage led to initial location inaccuracies and delayed public alerts in some areas. Despite these limitations, the system issued split alerts that informed users and triggered institutional measures, contributing to no reported injuries from shaking. This event underscored the need for denser seismic networks in rural regions.^[40]^[62] The December 20, 2022, M6.4 Ferndale earthquake offshore Northern California exemplified improved offshore detection capabilities, with ShakeAlert identifying the event in about 7.5 seconds using the EPIC algorithm and providing warnings of 0 to 23 seconds before strong shaking (MMI 6–8) in populated coastal areas. Alerts reached millions via WEA and apps, effectively activating responses such as train slowdowns and school drills, with no major disruptions reported. This performance validated the system's ability to handle subduction-zone-like events, delivering timely information that reduced potential impacts.^[32]^[63] In more recent operations, ShakeAlert conducted evaluations inspired by the 2024 M7.6 Noto Peninsula earthquake in Japan, using simulated real-time scenarios to test algorithm robustness against complex rupture sequences with multiple foreshocks. These tests improved finite-fault modeling for prolonged events, enhancing estimated shaking forecasts. Additionally, the March 3, 2025, M4.5 Orcas Island earthquake in Washington marked the system's first statewide WEA activation in the state, delivering average warnings of about 10 seconds to users in the Puget Sound region and demonstrating seamless integration with local emergency systems.^[64]^[65]^[66] The October 29, 2025, M5.4 earthquake offshore Oregon was detected and alerted, providing warnings to coastal areas and further validating offshore performance.^[67] From 2021 to 2025, ShakeAlert issued over 60 public alerts for significant events, achieving approximately 95% detection accuracy for M≥5.0 earthquakes within its core coverage area, based on analyses of 95 total M≥4.5 events through 2023 with minimal misses or false alarms. These operations have correlated with reduced simulated injuries in drills, as alerts provide critical seconds for actions like dropping to the ground. Delivery success rates exceeded 85% in urban zones, though rural gaps persist.^[32]^[7]^[40] Public response to ShakeAlert alerts has shown growing effectiveness post-2022, with studies indicating increased awareness and about 70% of recipients in surveyed events taking protective actions such as drop, cover, and hold on. Events like Ferndale boosted familiarity, leading to higher opt-in rates for apps and positive perceptions of alert utility in focus groups. This trend reflects ongoing education efforts, though overall baseline awareness remains below 50% in some demographics.^[68]^[69]^[32]

Limitations and Improvements

One key limitation of ShakeAlert is the existence of a blind zone near earthquake epicenters, where warning times are typically 5-10 seconds or less due to the rapid propagation of seismic waves outpacing detection and alert dissemination.^[70] This zone encompasses areas closest to the rupture, rendering alerts ineffective for immediate strong shaking in those locations. Additionally, the system has demonstrated challenges in accurately estimating magnitudes during evolving ruptures, as seen in the 2019 Ridgecrest sequence where the M7.1 mainshock was underestimated by 0.8 magnitude units, leading to underpredicted shaking intensities and missed public alerts in affected regions like Los Angeles County.^[18] Offshore earthquakes present further delays in detection, often due to sparse instrumentation and slower data telemetry, which can add several seconds to processing times compared to onshore events.^[40] False alerts remain rare, with a confirmed rate of approximately 1% for events of M≥4.5 between 2019 and 2023, primarily stemming from poorly located events at network edges rather than outright errors.^[32] However, even infrequent false positives can erode public trust, particularly when alerts interrupt daily activities without subsequent shaking. Coverage gaps in rural areas exacerbate these issues, as sparser seismic station density at network boundaries leads to higher location errors and missed detections, disproportionately affecting less densely populated regions that comprise a significant portion of the West Coast's geography.^[71] To address these challenges, ShakeAlert implemented Version 3 in March 2024, incorporating enhancements to core algorithms that improve performance in large earthquakes, including better handling of magnitude evolution and reduced false positives.^[72] A key upgrade involves Bayesian methods in the EPIC algorithm for offshore and out-of-network events, which refine initial estimates and aim to cut detection latency by up to 2 seconds through faster integration of sparse data.^[40] Machine learning classifiers have also been integrated to better distinguish aftershocks from noise, enhancing triggering reliability shortly after mainshocks.^[18] The U.S. Geological Survey conducts post-event analyses to evaluate ShakeAlert's performance, reviewing detection times, magnitude accuracy, and alert issuance against catalog data from sequences like Ridgecrest.^[73] User surveys, including those tied to the "Did You Feel It?" questionnaire, reveal feedback emphasizing the need for faster offshore alerts and clearer messaging to build confidence.^[74]^[75] Despite these limitations, particularly in mega-earthquakes (M8+), where initial underestimations could limit alert utility in subduction zone scenarios like Cascadia, ShakeAlert is projected to yield substantial economic benefits through reduced injuries, infrastructure damage, and downtime.^[76]^[77]

Future Plans and Expansions

System Upgrades

ShakeAlert underwent significant enhancements between 2020 and 2024 under Version 2, which integrated an ensemble of algorithms to improve detection accuracy and reliability. The system combined outputs from the Earthquake Point-Source Integrated Code (EPIC), the Finite-Fault Detector (FinDer), and the initial Geodetic First Approximation of Source and Teleseismic (GFAST) algorithms via a Solution Aggregator, allowing for more robust aggregation of seismic data to estimate earthquake parameters. These upgrades addressed limitations in point-source modeling by incorporating finite-fault detection capabilities in FinDer, enabling better tracking of rupture propagation in moderate to large events.^[12]^[78] Version 3, rolled out starting with version 3.0.1 on March 18, 2024, introduced further advancements, including the full integration of real-time Global Navigation Satellite System (GNSS) data through the GFAST-PGD algorithm to enhance magnitude estimation and rupture extent characterization for earthquakes exceeding magnitude 6.0, particularly in subduction zones. This version achieves initial alerts within 4-6 seconds of origin time for crustal events in densely instrumented areas, representing an improvement over prior latencies, with offline simulations demonstrating that approximately 90% of sites experiencing Modified Mercalli Intensity (MMI) VI shaking and 75% at MMI VII receive 10-40 seconds of warning for magnitude 7 scenarios. For larger events (M7+), performance simulations indicate 10-90 seconds of warnings at MMI VII-VIII sites, and up to 40 seconds at MMI VIII-IX for M8+ events, enabling more effective protective actions. Enhanced finite-source modeling in FinDer supports line-source estimates up to 1,362 km in length, improving predictions for extended ruptures. Full deployment of Version 3, including network expansions, is targeted for completion by the end of 2025.^[30]^[79]^[80]^[81] Additional upgrades in 2024 included Federal Communications Commission (FCC) approval for extending Wireless Emergency Alert (WEA) messages from 90 to 360 characters, incorporating URLs, Spanish-language options, and improved geotargeting to deliver more detailed ShakeAlert notifications via the Integrated Public Alert and Warning System (IPAWS). These changes enhance public alert clarity and accessibility for earthquake early warnings on the West Coast.^[7]^[82] Research following the 2022 M6.4 Ferndale earthquake highlighted the need for refined finite-source modeling, as the event provided only 0-12 seconds of warning at MMI VIII sites due to initial underestimation of rupture extent; subsequent analyses informed Version 3 enhancements to FinDer and GFAST-PGD for better handling of intraslab events. The U.S. Geological Survey (USGS) conducts ongoing annual system evaluations and updates through its Science and Technical Advisory Committee, ensuring iterative improvements aligned with operational performance data.^[79]^[81]^[80]

Geographic and Capability Expansions

ShakeAlert's geographic expansions focus primarily on extending coverage to high-risk areas outside its current West Coast operations, with the most advanced plans targeting Alaska. The U.S. Geological Survey (USGS) released a Phase 1 Technical Implementation Plan in February 2025 outlining the addition of approximately 270 new seismic stations in Alaska, alongside upgrades to 160 existing stations and retention of 20 others, to form a 450-station network concentrated in populated regions such as Southcentral Alaska, Kodiak, Prince William Sound, Fairbanks, and Southeast Alaska.^[80] This expansion integrates data from the Alaska Volcano Observatory (AVO) to enhance earthquake detection and coordinates with the National Oceanic and Atmospheric Administration (NOAA) to improve the timeliness and accuracy of tsunami forecasts, as earthquakes and tsunamis in Alaska often occur together.^[80]^[83] If fully funded from the outset, limited public alerting could begin within four years of implementation, potentially achieving operational status around 2029.^[80] Interest exists in further geographic extensions to other seismically active U.S. regions, including Hawaii and Nevada, to address local tectonic and volcanic risks. For Hawaii, expansion could support monitoring of volcanic-tectonic events, complementing existing USGS volcano observatories, but Hawaii currently remains outside the ShakeAlert footprint, with only preliminary assessments conducted as of 2025.^[84] In Nevada, efforts toward expansion have advanced, including USGS purchases of approximately $1.5 million in new sensor equipment to improve the seismic network along the California-Nevada border and contribute data to ShakeAlert; however, as of November 2025, these projects have been put on standby due to a U.S. federal government shutdown disrupting USGS operations and funding.^[85]^[86] No specific pilots or timelines have been established for Hawaii beyond preliminary assessments.^[7] Potential cross-border collaborations, such as data sharing with Mexico's SASMEX system for events affecting Baja California, have been discussed but face technical incompatibilities, as SASMEX does not extend to that region and the systems differ in design.^[7] Capability enhancements aim to broaden ShakeAlert's scope beyond standalone earthquake alerts by integrating with complementary hazard systems. Coupling with NOAA's tsunami warning infrastructure is a priority, particularly for Alaska and the West Coast, where ShakeAlert's rapid earthquake characterization can inform near-real-time tsunami modeling and public messaging to ensure consistency.^[80]^[87] Plans also include exploring multi-hazard alerting for secondary effects like landslides triggered by earthquakes, building on state-level initiatives in Oregon that envision tying earthquake warnings to broader natural disaster responses.^[7]^[88] International data sharing is facilitated through platforms like Google's Android Earthquake Alerts, which incorporate ShakeAlert outputs into a global detection network, enabling broader EEW dissemination without a formal dedicated global consortium.^[89] Funding for these expansions relies on federal appropriations and partnerships, with the USGS Earthquake Hazards Program receiving $94.9 million in the fiscal year 2025 budget—an increase of $2.2 million—to sustain ShakeAlert operations and support planning efforts like Alaska's Phase 1.^[90] An additional $1 million was allocated specifically for Alaska implementation planning in collaboration with state partners.^[7] Collaborations with 146 Tribal Nations extend coverage to rural and underserved areas across the operational region, ensuring alerts reach diverse communities through integrated delivery mechanisms like wireless emergency alerts and apps.^[91] Key challenges include substantial costs and logistical hurdles, particularly in remote Alaskan terrains. The Phase 1 Alaska expansion is estimated at $66 million in capital costs (in 2024 dollars) for infrastructure and sensors, plus $12 million annually for operations and maintenance, driven by the need for helicopter access, harsh weather constraints limiting fieldwork to mid-May through mid-October, and unreliable telemetry due to sparse cellular coverage.^[80] Ensuring equitable alerting for underserved rural and tribal communities remains a priority, as limited telecommunications infrastructure may necessitate alternative delivery methods like radio broadcasts to bridge access gaps.^[80]

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