quakes can drop land

We often think of sea level as the height of water relative to the land. But geologists know that the land is also in motion, somewhat complicating measurements of rising sea level. (Alaska, which is tectonically rising, records less apparent sea level rise than elsewhere, for example.) In cases where land is subsiding, sea level rise may actually seem augmented. And no part of the Earth underwent a quicker subsidence than areas of coastal Japan during the great quake of 11 March 2011.

As a recent story confirms,

The March 11 earthquake that hit eastern Japan was so powerful it pulled the entire country out and down into the sea. The mostly devastated coastal communities now face regular flooding, because of their lower elevation and damage to sea walls from the massive tsunamis triggered by the quake.

One of my professors of geology remembers camping on a beach the night of the 1992 Mendocino earthquake, and finding in the morning that the coastline had been visibly uplifted, exposing mussell-covered rocks now well-above the high tide line, dooming their sessile molluscan tenants.

While we human like to imagine the solid land as solidly fixed in one place, the reality is far more complex, though our short life spans rarely allow us to the opportunity to observe changes first hand. This the nature of deep time; we can see the long term effects of geologic changes but usually only indirectly observe them occurring.

Japan is an exception:

Some areas in Ishinomaki moved southeast 17 feet (5.3 meters) and sank 4 feet (1.2 meters) lower.

"We thought this slippage would happen gradually, bit by bit. We didn't expect it to happen all at once," says Testuro Imakiire, a researcher at Japan's Geospatial Information Authority, the government body in charge of mapping and survey.

The now permanent situation in Japan should give those of us who live in California a moment of pause to reflect on how quickly the land around may one day change.