A seiche is a wave in a lake, reservoir, or bay that is caused by earthquake shaking. A large earthquake can generate low, rolling waves in the earth that are imperceptible to people. These waves, which may originate from an earthquake thousands of miles away, can cause the water body to “slosh” back and forth. In extreme cases, the oscillating water body can cause shoreline inundation. For example, the northern hemisphere’s largest recorded earthquake (Prince William Sound, Alaska, in 1964) produced seiching in lakes and bays over a thousand miles away and sunk fishing boats in a Louisiana harbor.
While California law does not require disclosure of seiche hazard zones, some shoreline municipalities along inland lakes and reservoirs have designated seiche runup zones in their General Plan Safety Element, which a prospective buyer may consider to be material to a property transaction.