Earthquakes can trigger at least seven other types of natural disasters, including tsunamis, landslides, fires, flooding, volcanic eruptions, avalanches, and dam failures. While building collapse from shaking causes the majority of earthquake deaths (about 78%), these secondary disasters account for roughly one in five earthquake fatalities worldwide. In some events, the chain-reaction disasters cause far more destruction than the shaking itself.
Tsunamis
Tsunamis are the deadliest secondary effect of earthquakes. Between 1968 and 2008, tsunamis caused about 16% of all earthquake-related deaths globally, a figure heavily influenced by the 2004 Indian Ocean disaster. They form when an earthquake suddenly lifts or drops a section of the ocean floor, displacing the water above it into a series of fast-moving waves.
Not every undersea earthquake creates a tsunami. The quake generally needs to be magnitude 7.0 or higher, occur under or very near the ocean, and strike less than 100 kilometers (about 62 miles) below the surface. Deeper quakes are unlikely to move the seafloor enough to matter. For a tsunami dangerous enough to cross an entire ocean basin, the earthquake typically needs to exceed magnitude 8.0.
Most tsunami-generating earthquakes happen in subduction zones, where one tectonic plate is forced beneath another. When the edge of the overriding plate snaps upward and springs seaward, it raises the seafloor and the water column above it. That vertical displacement is what launches the wave. While other fault types can produce tsunamis, subduction zone quakes produce the largest and most destructive ones.
Landslides and Rockfalls
When you remove the 2004 Sumatra tsunami from the data, landslides become the single largest cause of non-shaking earthquake deaths, responsible for about 71% of secondary fatalities. Shaking destabilizes slopes that may have been marginally stable for years, sending rock, soil, and debris downhill in seconds.
Rockfalls, rock slides, soil falls, and disrupted soil slides are the types triggered by the weakest shaking, meaning they can happen even in moderate earthquakes. The vulnerable terrain ranges from steep overhanging cliffs of solid rock to nearly flat ground (slopes under 1°) made of soft, loose sediment. In mountainous regions, a single large earthquake can trigger thousands of landslides across a wide area simultaneously, burying roads, rivers, and communities.
Soil Liquefaction
Liquefaction happens when loosely packed, waterlogged soil near the surface loses its strength during shaking and temporarily behaves like a liquid. The USGS compares it to wiggling your toes in wet sand at the beach: the solid ground beneath a building can suddenly flow and shift. Structures sink, tilt, or collapse not because they were poorly built, but because the ground underneath them stopped being solid.
The conditions for liquefaction are specific. The soil needs to be sandy or silty, loosely packed, and saturated with water near the surface. Areas with high water tables, like riverbanks, coastal fills, and reclaimed land, are the most vulnerable. Liquefaction can also undermine dams, roads, and buried utilities, compounding the disaster well beyond the initial shaking.
Post-Earthquake Fires
Earthquakes rupture gas lines, topple electrical equipment, and knock over heating appliances, all of which can ignite fires in the minutes and hours after shaking stops. Following the 2024 Noto Peninsula earthquake in Japan, half of the shaking-triggered building fires were caused by electrical sources like wiring, appliances, and equipment. Others came from overturned oil heaters and even molten metal in factories.
What makes post-earthquake fires especially dangerous is that the same shaking that starts them also cripples the ability to fight them. In the city of Wajima after the Noto earthquake, damage to the water supply system left fire hydrants dry, collapsed buildings blocked access to underground water cisterns, and delayed detection allowed a fire in the downtown area to destroy roughly 240 buildings. Tsunamis can worsen the problem further: in the same event, fires broke out in a flooded building and a flooded car within the tsunami zone and spread to 18 additional structures.
Seiches and Inland Flooding
A seiche is a standing wave that forms in an enclosed or semi-enclosed body of water, like a lake, reservoir, or river, when seismic waves pass through the area. Think of water sloshing back and forth in a bathtub. Unlike tsunamis, which are generated by seafloor movement, seiches are set in motion by the ground vibrations traveling outward from the earthquake.
Seiches can occur surprisingly far from the earthquake itself. The 1959 Hebgen Lake earthquake in Montana triggered seiches detected on 54 stream gauges across Montana, Wyoming, Idaho, and Alberta, Canada, with the most distant one 545 kilometers from the epicenter. The 1964 Alaska earthquake caused water bodies to oscillate across much of North America, with waves as high as 1.8 meters (about 6 feet) reported along the Gulf Coast. The phenomenon was first documented after the 1755 Lisbon earthquake, when lochs across Scotland were observed sloshing without any local cause.
Earthquakes can also cause flooding more directly by triggering landslides into reservoirs, displacing water over dam crests, or by creating landslide dams that temporarily block rivers and then burst.
Volcanic Eruptions
Large earthquakes can sometimes trigger volcanic eruptions, but only under narrow conditions. The volcano must already be primed, meaning it has enough liquid magma stored inside and significant pressure in that storage region. If both conditions are met, a nearby earthquake above magnitude 6 can act as the final push. The shaking can cause dissolved gases to separate from the magma, similar to shaking a bottle of soda, rapidly increasing internal pressure and potentially setting off an eruption.
A volcano that isn’t already on the verge of erupting won’t be triggered by an earthquake, no matter how strong. This is why the connection between earthquakes and eruptions is occasional rather than routine. The USGS describes only “a few” large regional earthquakes as being clearly linked to subsequent eruptions or volcanic unrest.
Snow Avalanches
In mountainous regions with significant snowpack, earthquakes can release massive avalanches. Between 1899 and 2010, researchers identified 22 confirmed cases worldwide of earthquake-triggered avalanches, linked to earthquakes ranging from magnitude 1.9 to 9.2 at distances up to 640 kilometers from the epicenter. In extreme cases, thousands of large-scale avalanches have been released simultaneously by a single earthquake.
The low number of documented cases is somewhat misleading. About 3.1% of Earth’s land area sits in zones where both avalanche risk and seismic hazard overlap, a region roughly half the size of all avalanche-prone terrain. But these areas tend to be remote and uninhabited, so many earthquake-triggered avalanches likely go unwitnessed. The key factor is the internal structure of the snowpack: a snowpack that’s already unstable, with weak layers buried beneath heavier slabs, is far more susceptible to being shaken loose.
Dam Failures
Earthquakes threaten dams through several mechanisms, and a dam failure can turn a moderate earthquake into a catastrophic flood. For concrete dams, the primary danger is excessive cracking that leads to sliding or overturning, particularly in the upper half of the structure. Arch dams are most vulnerable at their abutments, the rock walls they press against, while buttress dams can tip under side-to-side shaking.
Embankment dams, built from compacted earth and rock, face a different set of risks. Shaking can cause the crest to settle and drop below the reservoir level, allowing water to overtop and erode the dam. Liquefaction in loose soils within or beneath the dam can cause massive deformation that continues even after the shaking stops, driven by gravity alone. Cracking from deformation can also create paths for water to seep through the structure, eroding it from the inside out. Even without direct structural damage, an earthquake-triggered landslide falling into the reservoir or a seiche wave within it can push water over the top.
The downstream flooding from a dam failure can arrive with little warning and affect communities many miles from both the dam and the earthquake’s epicenter, making it one of the more dangerous chain-reaction scenarios.