Disaster History
What causes them, where risk concentrates, and what the historical record shows about the gap between what we know and what we have built.
The Hazard
An earthquake is the sudden release of energy stored in the Earth's crust along a fault, a fracture where tectonic plates meet, grind, or pull apart. The energy release produces seismic waves that radiate outward, shaking the ground at the surface. The shaking can last seconds to minutes depending on the earthquake's magnitude and depth. The damage, depending on what was built and how, can last decades.
Earthquakes cannot be predicted in the way that hurricanes or winter storms can be forecast. There is no reliable short-term warning system that can tell a community days in advance that an earthquake is coming. The ShakeAlert early warning system, deployed on the West Coast, can provide seconds to tens of seconds of warning after seismic waves are detected and before stronger shaking arrives at a location. That window is enough to stop a train, open a firehouse door, or drop and take cover. It is not enough to evacuate.
The United States Geological Survey estimated in 2023 that earthquakes cost the nation approximately $14.7 billion annually in building damage and associated losses. More than 143 million Americans live in areas with meaningful seismic risk. The geographic distribution of that risk is broader than most people assume: while California and Alaska have the highest hazard, the New Madrid Seismic Zone in the central U.S., the Cascadia Subduction Zone in the Pacific Northwest, the Wasatch Front in Utah, and the Charleston, South Carolina region all carry significant risk.
The Richter and Moment Magnitude Scales
Below 2.0
Micro-earthquakes, not felt. Hundreds of thousands occur annually across the U.S.
2.0 to 3.9
Minor. Often felt locally but rarely causing damage.
4.0 to 4.9
Light. Felt widely. Minor to no damage in well-built structures.
5.0 to 5.9
Moderate. Can cause significant damage to poorly constructed buildings.
6.0 to 6.9
Strong. Destructive in populated areas. Major damage to vulnerable structures.
7.0 to 7.9
Major. Serious damage over wide areas. The 1994 Northridge quake was 6.7; the 1989 Loma Prieta was 6.9.
8.0 and above
Great. Can cause severe damage hundreds of miles away. The 1906 San Francisco earthquake is estimated at 7.9.
Risk Geography
Seismic hazard is highest on the West Coast and in Alaska, but significant risk exists in the central and eastern U.S. as well. Understanding which fault systems threaten a region is the starting point for meaningful preparation.
Cascadia Subduction Zone
The Cascadia fault runs 700 miles offshore from northern California to British Columbia. A full Cascadia rupture, similar to those that have occurred roughly every 200 to 500 years, would produce a magnitude 8 to 9 earthquake and a major tsunami. The last full rupture was January 26, 1700. Infrastructure and building stock in the Pacific Northwest is largely not prepared for this event.
San Andreas and Related Faults
The San Andreas system, running 800 miles along California, produces the earthquakes most associated with seismic risk in public consciousness. The fault has multiple segments with distinct rupture histories. The southern segment, which has not ruptured in over 300 years, is considered overdue for a major earthquake. The 1906 San Francisco and 1989 Loma Prieta earthquakes were products of the northern segment.
New Madrid Seismic Zone
The New Madrid zone produced a sequence of massive earthquakes in 1811 and 1812 estimated at magnitude 7.0 to 8.0. The zone sits under some of the oldest and most vulnerable building stock in the country, in a region with less seismic awareness than the West Coast. A repeat event would affect more people with less preparation than any comparable event in California.
$14.7B
Estimated annual U.S. earthquake losses in building damage (USGS/FEMA 2023)
USGS/FEMA 2023 report
143M+
Americans living in areas with meaningful seismic risk
USGS/FEMA estimate
37
States that have experienced earthquakes exceeding magnitude 5 in the last 200 years
USGS historical data
1906
Year of the Great San Francisco Earthquake, still the reference event for West Coast seismic planning
USGS
What History Shows
The 1906 San Francisco earthquake and fire killed an estimated 3,000 people and destroyed 28,000 buildings. It remains the reference event for U.S. seismic risk, not because the science has stood still since then, but because it established the pattern that every subsequent major earthquake has followed: we know the hazard exists, we build vulnerable structures anyway, and we are surprised by the consequences. The Uniform Building Code, developed in part in response to 1906, has been revised continuously since then. Buildings constructed under modern seismic codes perform dramatically better than older stock. Most of the building stock in seismically active areas is old.
The 1964 Great Alaska Earthquake, at magnitude 9.2 the second-largest ever recorded, killed 131 people and caused $2.3 billion in damage (2023 dollars). Its scale exceeded any previous recorded earthquake in the U.S. The accompanying tsunami killed people as far away as Crescent City, California. The event drove the development of the Pacific Tsunami Warning Center and accelerated seismological research that produced modern understanding of subduction zone earthquakes.
The 1994 Northridge earthquake, magnitude 6.7, struck a Los Angeles suburb at 4:31 a.m. on January 17. It killed 57 people and caused $49 billion in damage, the costliest earthquake in U.S. history to that point. Northridge demonstrated that even moderate earthquakes, occurring in the wrong place at the wrong time, can produce catastrophic losses. It also accelerated seismic retrofit programs for concrete buildings and freeway structures that had been stalled by political inertia.
Detection and Response
ShakeAlert, USGS's earthquake early warning system for the West Coast, detects the initial P-waves from an earthquake and estimates the location and magnitude before stronger S-waves arrive at a given location. The system can deliver seconds to tens of seconds of warning, depending on distance from the epicenter. Those seconds are enough for automated actions: stopping trains, opening fire station doors, alerting hospital systems to pause surgeries.
For the general public, ShakeAlert warnings are delivered through Wireless Emergency Alerts on cell phones and through integration with some home automation systems. The warning time for locations near the epicenter may be zero. For locations farther away, the warning grows. No warning system changes what happens if you are in a vulnerable building when the shaking starts. Preparation before an earthquake determines most outcomes.
USGS's Did You Feel It? program collects reports from people who experience earthquakes, allowing rapid characterization of shaking intensity across wide areas. The National Earthquake Hazards Reduction Program coordinates federal earthquake research and preparedness activities across USGS, FEMA, NIST, and NSF. Building codes, updated by the International Code Council based on the latest seismic research, are the primary tool for reducing vulnerability in new construction.
During the shaking
Drop, Cover, Hold On
Get down on hands and knees. Take cover under a sturdy desk or table, or against an interior wall away from windows. Hold on until shaking stops. Do not run outside during shaking.
If no table is nearby
Cover your head and neck with your arms. Crouch near an interior wall. Stay away from exterior walls, windows, and anything that could fall.
If outdoors
Move away from buildings, streetlights, and utility wires. Once in the open, stay there until shaking stops.
After the shaking
Expect aftershocks
Aftershocks follow every significant earthquake. Some can be nearly as large as the mainshock. Be prepared to drop and cover again.
Check for hazards
Gas leaks, structural damage, and electrical hazards are the primary post-earthquake risks. If you smell gas, leave the building and call from outside.
Do not use elevators
Use stairs. Elevators may be damaged or lose power after an earthquake.
What You Can Do
The recurring lesson of earthquake history is that the gap between hazard knowledge and preparation is where deaths occur. Retrofitting a vulnerable building, securing heavy furniture and water heaters, and knowing the drop-cover-hold-on protocol are the three actions that account for the majority of preventable earthquake harm.
Landmark Events
April 18, 1906 - San Francisco, California
Magnitude 7.9. Roughly 3,000 deaths. 28,000 buildings destroyed, many by the fire that followed when water mains broke. The disaster established the modern understanding of strike-slip fault rupture and drove the first systematic seismic building code development in the U.S.
Case study coming soon
March 27, 1964 - Southcentral Alaska
Magnitude 9.2, the second-largest recorded earthquake in history. 131 deaths. Tsunami killed people as far away as Crescent City, California. Led to creation of the Pacific Tsunami Warning Center and transformed understanding of subduction zone earthquakes.
Case study coming soon
October 17, 1989 - San Francisco Bay Area
Magnitude 6.9, striking during Game 3 of the World Series. 63 deaths. The collapse of the Cypress Street viaduct in Oakland, where 42 people died, drove the largest highway retrofit program in California history.
Case study coming soon
January 17, 1994 - Northridge, California
Magnitude 6.7. 57 deaths. $49 billion in damage. Struck a suburban Los Angeles neighborhood at 4:31 a.m. Revealed unexpected vulnerabilities in welded steel moment frames and concrete structures. Accelerated retrofit programs that had been politically stalled.
Case study coming soon
The Archive
California
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Alaska
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Washington
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Oregon
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Utah
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Nevada
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Missouri
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Tennessee
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South Carolina
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Hawaii
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Puerto Rico
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Idaho
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Sources