Cascadia

Is Cascadia Waking Up?

I have no idea how common this pattern might be, but in the last year or two of watching the Cascadia, that fault zone has largely been silent. Now it’s getting 4.x scale events around the perimeter. (It’s that triangle just off the Oregon / Washington / British Columbia coastline).

North Amercia 8 October 2010

Original Image with clickable quake details

We are getting a load of quakes along the Aleutian Islands and into Alaska. More activity has been rampant along the South American coast. California is lit up fairly well too (and I note that the line of activity that starts down in Baja with a boat load of quakes is, in N. California, following the Hayward / Calaveras system that is prone to going ‘a few years’ after a great quake on the San Andreas and that we had that 7.2 Loma Prieta quake a couple of decades back…).

Then the activity heads out to sea and to the Cascadia (where you can see the San Andreas split and the faults go on both sides of a small plate).

Maybe it’s just me, but it sure looks like we’ve had a load of stress relief all along the N. American side of the Pacific and on down to South America; except the Cascadia. And it is now starting to get some modest quakes…

I wouldn’t panic about it just yet, but if this pattern continues and escalates into the 5.x range, I’d then expect it to be a series of ‘fore shocks’ and get prepared for a problem.

Live Map

The above map is a static map (though the clickable link is live). This map is the present live map:

North America Quake Map - Live from the USGS

California

Current quake map in California

Original Image, with captions and description. The original is interactive with clickable regions for ‘close ups’.

This map shows the line of quakes starting down in Baja (where we had some large ones a few months back) and running up the San Andreas. But where it used to follow the San Andreas up the peninsula and out the backside of Marin, it’s now following the Hayward Calaveras system a bit more inland. That fault system goes under such things as Oakland and the University of California at Berkeley (where you can visit the sports stadium and see how ‘creep’ has offset the two halves of it… yes, the stadium is built straddling the fault… you can see it in the below picture.)

Berkeley Stadium Fault Creep Artifacts

Original, and even larger, image

The wiki does a pretty good write up on the Hayward / Calaveras system. This link is to the Hayward portion description:

http://en.wikipedia.org/wiki/Hayward_Fault_Zone

The USGS is giving a 62% probability. I’d start ratcheting that up a bit, were it up to me, and move a bit more of the probability over into the East Bay:

S.F. Bay Area Quake Probability

Original Image

But back on the Cascadia…

It may well be that we get both. The Loma Prieta quake only loosened the souther bit. From about Los Gatos / Santa Cruise and a bit south. Leaving the part under San Francisco and out to sea still stressed. The wiki says that often a great quake on the Cascadia sets off the San Andreas. I’d bet it can also set off the Rogers / Hayward / Calaveras set as well…

From the wiki:

San Andreas Fault connection

Studies of past earthquake traces on both the northern San Andreas Fault and the southern Cascadia subduction zone indicate a correlation in time which may be evidence that quakes on the Cascadia subduction zone may have triggered most of the major quakes on the northern San Andreas during at least the past 3,000 years or so. The evidence also shows the rupture direction going from north to south in each of these time-correlated events. The 1906 San Francisco earthquake seems to have been a major exception to this correlation, however, as it was not preceded by a major Cascadia quake.

Prediction of the next major earthquake

Recent findings concluded the Cascadia subduction zone was more hazardous than previously suggested. The feared next major earthquake has some geologists predicting a 10 to 14% probability that the Cascadia Subduction Zone will produce an event of magnitude 9 or higher in the next 50 years, although the most recent studies suggest that this risk could be as high as 37%. Geologists have also determined the Pacific Northwest is not prepared for such a “Colossal” earthquake. The tsunami produced may reach heights of approximately 30 meters (100 ft).

This, of course, also means that the probability of a 7.x or 8.x is even higher than that, as you get more quakes as they get ‘smaller’…

WHEN (and it is a when) that sucker lets loose, it’s going to be one heck of a ride, and that ride will reach all the way down to where I live. The good news is that I’m where it will run out of steam, as this part of the fault has already let loose… And I’m located modestly far from both the San Andreas and the Hayward / Calaveras. With the Loma Prieta quake as my standard, I’m also shown to be on favorable ground (thanks to inspecting some USGS soil and quake / shake maps prior to buying… So I’m not too worried about me. But it will be one heck of a mess from San Francisco / Berkeley all the way to Vancouver.

The Whole World Quake Map

A bit of “context”:

World Quake Map - Live from the USGS

Original Map with clickable details

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