A Shaky Situation With Dangerous Potential

June 17, 2005 — -- Seismologists study earthquakes, and they will be the first to tell you their science is very young and sometimes very frustrating. Mother Earth is still hiding many details of how giant blocks of her crust move and grind and bump into each other, the type of planetary movement called plate tectonics that pretty much provides the energy for all earthquakes.

This week California got rattled several times, and whenever a series of large quakes gets our collective attention (especially whenever the word tsunami is attached), questions arise of how they might be related to each other. That's a very legitimate question, but it's fraught with scientific uncertainty.

Thursday's quake near San Bernardino, Calif., for instance, was very close to (if not right on) the famed San Andreas Fault, which runs through San Francisco (Daly City to be exact) and then southeastward all the way to and beyond the Los Angeles area. Tuesday's temblor, however, was offshore to the west of Eureka, Calif., many hundreds of miles northwest of San Bernardino, and at first blush completely unconnected with the San Andreas.

But recent geologic history has too often taught us things we hardly suspected, and because all of us (including seismologists and geophysicists) are always looking for patterns, it's tempting to think that two quakes in California in two days may be a harbinger of more to come.

One may beget another, so to speak.

When we're thinking about a second quake in the same area, that's well understood and entirely possible. Most West Coasters, especially, know that even a large quake could be what's known as a foreshock of what could be a following larger quake.

And, there's the question of pressure along any of the myriad faults which underlie the Los Angeles area. Did it increase or decrease? One highly experienced seismologist was asked that exact question Thursday: Did the quake in San Bernardino relieve or increase the stored, dynamic tension along the San Andreas?

His answer: Yes and no. In other words, no one knows.

We know that both sides of the San Andreas Fault are continuously creeping in relation to each other, and there is substantial evidence that the fault "breaks" and causes a major earthquake north of the Los Angeles area near Fort Tejon Pass about every 140 years, and that the area last broke nearly 150 years ago (meaning it may be overdue).

But the answer is that at this stage, seismology can't tell us whether what happened yesterday near San Bernardino increased or decreased the potential for that somewhat overdue great quake. It could, in other words, be foreshock, or an aftershock, or completely unrelated.

Additional Danger to Consider

But how does the Eureka area offshore quake connect?

Even though the Eureka event was somewhat to the north of where the San Andreas Fault goes out to sea, there is no serious seismological suspicion that one could trigger the other. Yet again, it's a young science, and after all, it's the same Earth.

But the potential worry about Eureka is something entirely different, and almost everyone outside of seismology missed it. That offshore quake (initially measured in the low 7s on a different scale called Moment Magnitude) occurred at the southern end of the most dangerous quake-producing fault affecting any part of the United States: The Cascadia Subduction Zone -- an area that has Vancouver, Seattle/Tacoma, Portland, and even Northern California in its crosshairs. In other words, while all the news was about tsunami alerts, the quake may have been banging away on a hair-trigger to the north.

Technically, the Eureka event was what seismologists call a "strike-slip" earthquake, very different (in terms of how the ocean floor moves) to what created the massive tsunami near Sumatra last December. Nevertheless, when any large earthquake occurs on the ocean floor near our shores, a tsunami alert is exactly the right thing to issue, and we all need to take it very seriously.

But here's the question: Could that quake near Eureka perhaps serve as some sort of a trigger for the incredibly damaging "great" earthquake we know is stored along the Cascadia Subduction Zone?

Probably not. Hopefully not. The Eureka quake technically occurred along what's known as the northern Gorda Plate, which is under massive tectonic pressure from three sides, and these shallow quakes are not unusual. BUT … the fact that it's even close to a massive subduction zone that has been storing energy for 300 years (since the last break) is worrisome, and in the first hours after the Eureka quake was reported, those of us who are not scientists but who, as journalists, have followed and written about the Cascadia Subduction Zone were very worried that what we don't know seismologically might hurt us.

In other words, while alerts were ping-ponging around the West Coast about the tsunami potential from that offshore quake, many of us thought we should be talking with equal caution about putting the entire Pacific Northwest on alert lest one quake trigger the other.

Reminder to Get Prepared

And what is that potential subduction zone quake?

In a phrase, worse than the massive quake that mauled the sparsely unpopulated state of Alaska in 1964. The Cascadia Subduction Zone is the point where the westward-creeping North American Continental tectonic plate collides and overrides the Juan de Fuca Plate, a process that has shoved the ocean floor down at an angle beneath us so far that eventually it melts and comes back up to form volcanos like Mount St.Helens, Mount Rainier, Mount Hood and Mount Shasta.

It's a slow process moving at about 4.3 centimeters per year (you wouldn't want to set up bleachers and sell tickets to watch it), about the speed our fingernails grow. But the collision zone runs 800 miles from the northern offshore area of Canada's Vancouver Island all the way south to -- guess what -- the Eureka, Calif., area, where it gets jumbled up with the pressures of the Gorda tectonic plate.

And February of the year 1700 was the last time it broke, roiling the Northwest for perhaps as much as four-and-a-half minutes of massive shaking as the coastline dropped up to five feet in altitude and a massive Sumatra-class tsunami roared inland within minutes.

All that will occur again, but seismology is too young to be able to predict whether it's coming in 10 minutes or 100 years. But here's the point: It's locked and loaded and dangerous to the tune of potentially killing thousands and costing hundreds of billions of dollars in a three-state area, along with temporarily wiping out the ability of ports like Vancouver, Seattle, Tacoma, and Portland to function for many months.

With that type of threat, any earthquake of any kind occurring near the Cascadia zone should get us all on high alert just in case the dots are connected.

Why is this vital? Not to scare, but to remind all those officials in all those states of all the things they have not yet done to prepare their buildings and ports and citizenry for the inevitable.

It was Will Durant who wrote that "Civilization exists by geologic consent, subject to change without notice." The long-deceased residents of Italy's Pompeii -- as well as the mauled citizens of coastal Asia -- can confirm that.

(For some good graphic depictions of these zones from the U.S. Geologic Survey, go to: http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/Maps/map_juan_de_fuca_subduction.html,and http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/Maps/map_plate_tectonics_cascades.html. An excellent article on the same subject from Oregon State University can be found at: http://oregonstate.edu/dept/ncs/newsarch/2005/Jun05/earthquake.htm.)

John J. Nance, ABC News' aviation analyst, is a veteran 13,000-flight-hour airline captain, a former U.S. Air Force pilot and a lieutenant colonel in the Air Force Reserves. He is also a New York Times best-selling author of 17 books, including the non-fiction title, "On Shaky Ground," about earthquakes and is a licensed attorney, a professional speaker, and a founding board member of the National Patient Safety Foundation. A native Texan, he now lives in Tacoma, Wash.