San Francisco may be known for its seismic activity, but it's not the most naturally dangerous place on the West Coast.

Our sister tech city Seattle wins that distinction, as it has more natural disaster threats than almost anywhere - earthquake, tsunami, volcanic eruption, landslide or lahar (mud or debris flow from a volcano).

Seattle has the Cascadia subduction zone and its potential for releasing another 9- or 9.5-magnitude megathrust earthquake in the next couple hundred years to thank for such distinction. Of course, there's also that bit about living in the shadows of massive volcanoes ... one of which recently exploded.

It is also interesting to consider that only relatively recently we all discovered just how dangerous our region is.

"We now know it to be much more dangerous than we thought it to be 30 years ago," said the host of the upcoming PBS NOVA series "Making North America" and director of the Smithsonian National Museum of Natural History Kirk Johnson.

Johnson grew up in Bellevue and recently chatted with us about our natural environs and his new show.

"When I left here in 1978, we didn’t really fear volcanoes erupting, and then Mount St. Helens blew up. We didn’t really think of these landslides that could bury towns, and then that happened. We didn’t really think about earthquakes. We thought the earthquakes were in California, and then we had the Nisqually earthquake. "And then with amazing geological sleuthing, we discovered the Cascadia one (the megathrust quake from 300 years ago that devastated the region and generated a massive tsunami). We didn’t really know about tsunamis. We didn’t really know about lahars. So all those things are real and were discovered by great (recent) geology investigations."

So we now say, he added, “Yeah, we live in a very active landscape that’s still under construction and depending on where you are and when you are there it can be very dangerous.”

Wild geology series

Johnson was in Seattle last week at the public television station KCTS as part of his tour promoting his upcoming NOVA series. ... and you thought looking at rocks all day was boring!

What PBS says about it:

Mighty, elemental forces molded North America—fiery eruptions, titanic floods, the grinding of great ice sheets, and massive impacts from space all shaped our homeland. The epic three-part series unfolds in a forgotten world that existed long before our own, crossed by long-lost mountain ranges, deserts the size of Africa, and vast inland seas spanning the length of the continent. Explore beloved landmarks like the Grand Canyon and Yellowstone National Park from the inside out as we witness the clash of nature’s creative and destructive forces. Hosted by renowned paleontologist Kirk Johnson, this spectacular road trip through a tumultuous deep past explores three fundamental questions: How was the continent built? How did life evolve here? And how has the continent shaped us? “Making North America” reveals the incredible story of a majestic continent.

Discovering the Great Danger

Now, of course, Seattleites and visitors to the region associate earthquakes with the Northwest as easily as California. In fact, Johnson said, he just happened to overhear a conversation in a Seattle restaurant about quakes in SeaTown.

"That's on our radar now," he said.

The NOVA crew and Johnson shot footage for the series in Willapa Bay with U.S. Geological Survey geologist Brian Atwater, one of the geologists who discovered the great megathrust earthquake and tsunami of January 1700, and then in Corvallis with OSU geology and geophysics professor Chris Goldfinger.

"I saw the direct evidence for what they saw that helped them understand what happened. It's quite compelling," he said of the Cascadia quake research. "These forests, the whole Northwest coast drops five feet in an instant, and that's going to be a shake. I wouldn't want to be here when it happens."

He added, more generally of regional dangers:

"Geology still bats last, and so you've got this amazing civilization, these great cities and all this technology but a 9.5 earthquake would be pretty amazing in a landscape like that.

"That's still only a part of the story. That's a couple of hundred years from now, but what about 100 million years into the future, what happens? What's the fate of North America, where's it going? It turns out that North America in a 175 million years ends up colliding with all the other continents making this one giant mega-continent."

OK, that's the big picture, but between San Francisco and Seattle, who has the most to fear from natural events?

"Seattle," Johnson said without much hesitation.

San Francisco has some earthquakes generated by the San Andreas fault, but (that recent terrible movie not withstanding) Seattle is threatened by a bigger fault ...

"Volcanoes," he added, "are a nice bonus. And the tsunami (from Cascadia Subduction quake)."

Jake Ellison can be reached at jakeellison@seattlepi.com. Follow Jake on Twitter at twitter.com/Jake_News. Also, swing by and *LIKE* his page on Facebook. If Google Plus is your thing, check out our science coverage here.