When modern science detects a Seattle Earthquake Zone fault right by your house

EARTHQUAKES ARE PERSONAL. Amid all the descriptions of generalized suffering lies your own story. And mine.

The reality of the Earth moving under my feet was brought home to me a long time ago by Bernard Hallet, now professor emeritus in the Department of Geological Sciences at the University of Washington. We’re mildly acquainted because we both live on Bainbridge Island, and one day when I ran into him, he was excited to convey to me that the hill I live on is home to a Seattle Earthquake Zone fault. “Close to your house,” he added. “We just found it.”

It happened like this: In the mid-1990s, our public utility district decided to map Bainbridge’s watersheds, something that required an intimate knowledge of surface elevations. Previously, such an effort had been considered useless because the island’s forests are so dense with understory that its contours are impenetrably shrouded. There was no point in sending anyone out to read the ground, because the ground wasn’t visible. In short, a nuanced map of the island’s surface elevations wasn’t possible — at least not until 1996, Hallet said, when the utility district hired a company called Airborne Laser Mapping (ALM) to make one.

ALM waited until snow had cleared the last leaves from the canopy, then went airborne with its new mapping equipment — a device called the Optech ALTM 1020. (Optech is now called Teledyne Optech, and its business is the production of laser-based survey instruments. Today those instruments are mostly mounted on drones, but in 1996, they took flight in airplanes.) It fired laser pulses at every point on the island, thousands per second, and these pulses, on hitting something solid, bounced back to it. Some bounced off treetops or limbs, but most pierced the canopy, penetrated the understory and bounced off the ground. In this way, the utility district got its map.

Elevation on the map was color-coded, with the deepest green representing sea level and the deepest red the island’s highest point. Inevitably, the eye is drawn to the map’s north and south running lines, which represent the gouging effect of northward-retreating fingers of glaciation. Those north and south running lines are so profuse that, unless a person looks closely, nothing much emerges of east/west significance. However, said Hallet, the map was magnified, manipulated and pondered until someone noticed a line running — as fate would have it — east and west across the hill I live on. All you have to do is walk north a little from your house, and you’re there, he told me. By the way: It’s an earthquake fault.

He seemed happy about it. In the manner of a geologist. Someone so inured to the volatility of the Earth that the discovery of an earthquake fault near my house was a source of joy.

I looked into it. Apparently, in the course of an earthquake — probably the most recent one on the newly discovered fault — the land under my house rose more than 20 feet.