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40 Years of Earthquakes in the Contiguous United States: 1980 - 2020

Every state and territory of the United State of America experiences earthquakes. In the contiguous states most of these earthquakes do not pose a tsunami risk as they do not lift or drop the seafloor. They are either too small, too far from a body of water, or move the underlying rock sideways. For these reasons two widely-felt earthquakes in March of 2020 also failed to generate tsunamis: the M5.7 Salt Lake City, Utah earthquake and the M6.5 Central Idaho earthquake. To put these two earthquakes in context this animation shows earthquakes in the contiguous United States for the previous forty years. Most earthquakes in the world, including those in the United States, are “interplate” earthquakes that occur at plate tectonic boundaries where large sections of the earth’s crust either grind past each other, pull apart, or slam together. With the exception of the Pacific Coast of southern California, the contiguous United States sits atop the North American Plate. This plate meets the Pacific Plate at the San Andreas Fault such that coastal California south of Mendocino rides atop the Pacific Plate, which moves northward relative to the rest of North America. North of Menocino, however, northern California, Oregon, and Washington State are colliding with the Juan de Fuca Plate (JdF) to produce a subduction zone capable of generating tsunamis with megathrust earthquakes. The last time this region produced a devastating tsunami, however, was 320 years ago. Offshore of the Pacific Northwest many earthquakes also occur along the boundaries between the Juan de Fuca Plate and the Pacific Plate. In the southeastern corner of the animation one more subduction zone also generates earthquakes where the North American Plate meets the Caribbean Plate at the Puerto Rico Trench. Earthquakes can also occur away from these plate boundaries throughout the contiguous United States. These are called “intraplate” earthquakes and they occur along faults within the North American continent. In recent years wastewater injection wells, a byproduct of hydraulic fracturing or “fracking” for hydrocarbon extraction, have also produced earthquakes in Oklahoma, north Texas, and eastern Wyoming. Some significant earthquakes in this 40 year period include: May 18, 1980 -- eruption of Mt. St. Helens (produced 820 ft. landslide-generated tsunami in Spirit Lake) Nov 8, 1980 -- M7.2 -- Northern California May 2, 1983 -- M6.5 -- Coalinga, California Oct 28, 1983 -- M7.3 -- Borah Peak, Idaho Apr 24, 1984 -- M6.2 -- Morgan Hill, California Jul 21, 1986 -- M6.4 -- Eastern California Nov 23, 1987 -- M6.2 -- California Oct 17, 1989 -- M6.9 -- Loma Prieta, California (small tsunami) Aug 17, 1991 -- M6.2 -- Honeydew, California Aug 17, 1991 -- M7.0 -- Offshore of Oregon Apr 22, 1992 -- M6.3 -- Joshua Tree, California April 25, 1992 -- M7.2 -- Cape Mendocino, California (small tsunami) Jun 28, 1992 -- M6.5 -- Big Bear, California Jun 28, 1992 -- M7.3 -- Landers, California Sep 2, 1992 -- M5.8 -- St. George, Utah Sep 20, 1993 -- M6.0 -- Klamath Falls, Oregon Jan 17, 1994 -- M6.7 -- Northridge, California Sep 1, 1994 -- M7.0 -- Northern California (small tsunami) Apr 14, 1995 -- M5.7 -- Marathon, Texas Oct 16, 1999 -- M7.1 -- Hector Mine, California Feb 28, 2001 -- M6.8 -- Nisqually, Washington Dec 22, 2003 -- M6.5 -- San Simeon, California Jun 15, 2005 -- M7.2 -- Offshore Northern California (small tsunami) Sep 10, 2006 -- M5.8 -- Gulf of Mexico, Florida Feb 21, 2008 -- M6.0 -- Wells, Nevada Apr 4, 2010 -- M7.2 -- Baja California (Mexico) Jan 9, 2010 -- M6.5 -- Eureka, California Aug 23, 2011 -- M5.9 -- Virginia Mar 10, 2014 -- M6.8 -- Ferndale, California Aug 24, 2014 -- M6.0 -- South Napa, California Sep 3, 2016 -- M5.8 -- Oklahoma Dec 8, 2016 -- M6.6 -- Ferndale, California Jul 5, 2019 -- M7.1 -- Ridgecrest, California Aug 29, 2019 -- M6.3 -- Oregon Coast Mar 18, 2020 -- M5.7 -- Salt Lake City, Utah Mar 30, 2020 -- M6.5 -- Central Idaho The National Tsunami Warning Center (NTWC) has the primary responsibility for issuing alerts for any tsunamis generated near the coastlines of the contiguous United States. NTWC will also alert these areas for dangerous tsunamis generated further away, such as the tsunami from Japan in 2011. Similarly the Pacific Tsunami Warning Center (PTWC) will alert the areas they serve--Hawaii, U.S. territories, and international partners--for any tsunami threat, including any tsunami generated off the coasts of the continental United States. These alerts will be posted to: https://tsunami.gov ----- Earthquake data from USGS/NEIC database: https://earthquake.usgs.gov/earthquak... Tsunami data from NOAA/NCEI Tsunami Database: https://www.ngdc.noaa.gov/hazard/tsu_... Plate boundaries from UTIG’s PLATES project: https://ig.utexas.edu/marine-and-tect...