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1 [1] (April 25, 2025)

handle is hein.crs/skealtehq0001 and id is 1 raw text is: Congressional Research Service Informing the legislative debate since 1914 Updated April 25, 2025 The ShakeAlert Earthquake Early Warning System Portions of all 50 states, as well as U.S. territories and the District of Columbia, are vulnerable to earthquake hazards (e.g., ground shaking) and associated risks (e.g., exposure of people or property to ground shaking) to varying degrees (Figure 1). Among the costliest U.S. earthquake disasters was the 1994 magnitude 6.7 Northridge earthquake in California, which caused about 60 fatalities and more than 7,000 injuries; left about 20,000 homeless; damaged more than 40,000 buildings; and caused an estimated $13-$20 billion in economic losses. Congress established the National Earthquake Hazards Reduction Program (NEHRP), involving the U.S. Geological Survey (USGS), National Science Foundation (NSF), Federal Emergency Management Agency (FEMA), and National Institute of Standards and Technology (NIST), in 1977 to reduce earthquake risks. In the NEHRP Reauthorization Act of 2018 (P.L. 115-307), Congress directed the USGS to implement an effective earthquake early warning system to reduce risks. Figure 1. USGS Seismic Hazard Model, 2023 Chance of slight orgreater) damaging _ earthquake shaking in 100 Iyears * >95 75-95 Alaska 50-75 25 50 <5 Z Source: Mark D. Peterson et al., The 2023 U.S. 50-State National Seismic Hazard Model: Overview and Implications, Earthquake Spectra, vol. 40, no. 1 (2024), DOI: 10.1 177/87552930231215428. Notes: Map displays the likelihood of damaging earthquake shaking (equivalent or greater than Modified Mercalli Intensity VI) in the United States over the next 100 years. Earthquakes cannot be predicted, nor can the potential for an earthquake to reoccur in areas with some seismic history be ruled out. The model uses existing faults and past earthquakes to forecast the probability of future earthquakes and uses the geology to estimate how much the ground shakes during an earthquake. Earthquake early warning (EEW) may reduce earthquake risks (i.e., reduce fatalities and injuries, as well as damage to structures and operations). EEW refers to sending a warning that an earthquake was detected and damaging ground shaking may be coming (Figure 2). An EEW received in tens of seconds to minutes before shaking may allow individuals to take protective actions and institutions to engage automated protective actions (Table 1). Figure 2. Schematic of the ShakeAlert System source: JnakeAlert. Notes: Once an earthquake starts (star labeled epicenter on a fault), the earthquake-sensing network (sensors) detects the P-waves (yellow curve and arrow) at sensors closest to the epicenter. The sensors transmit data to data processing centers. The centers process the data and, if the earthquake may be damaging, prepare alert messages with information about the earthquake's magnitude and location and what areas may receive intense shaking from the later-arriving, more damaging S-waves (red curve and arrow). Public and private communication pathways convert the alert messages into EEWs and send them to individuals and institutions in endangered areas. The USGS and other federal, state, academic, and private partners began public EEW on the West Coast via the ShakeAlert Earthquake Early Warning System in California in 2019 and in Oregon and Washington in 2021. There have been some feasibility studies about implementing ShakeAlert in Alaska, Hawaii, Nevada, and Utah. An EEW system consists of the following components (Figure 2 and Figure 3): * an understanding of earthquakes and faults to determine where to locate an earthquake-sensing network; * an earthquake-sensing network, including seismic and geodetic sensors, to detect the start of an earthquake; * robust and rapid telemetry; * data analysis and alert decisionmaking; https://crsreports.congress.gov

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