MODESTO — There's a huge difference between a prediction and an advisory.
The first says something definitely will happen. Remember the radio preacher in Oakland who predicted true Christians would go to heaven May 21, 2011?
When that didn't happen, he rescheduled. The world's next last day would be Oct. 21, 2011, beating the Mayan calendar thing by two months. Some folks actually bought into it, quitting their jobs and unloading their possessions.
Of course, doomsday didn't arrive. He chose not to rebook a second time, although he could have opted for a day-night doubleheader.
We're still here.
An advisory, meanwhile, merely suggests something might happen. High-wind advisories. Tornado advisories. Severe winter storm or hurricane warnings. Such are probabilities or strong possibilities that don't always materialize. But at least residents were given a heads-up.
Pennsylvania resident David Nabhan, who studies earthquake patterns and wrote a book on the subject, isn't predicting the end of the world. But he does believe there are certain times when Mother Nature is more likely to rearrange her furniture.
He suggests when earthquakes are more apt to occur. Why should you care about this here in the valley, where we might feel an occasional shaker but rarely if ever incur any damage? We'll get into that shortly.
Nabhan deals in windows of increased likelihood, as in "don't be surprised" if the West Coast gets a big quake on a probable day and within a three-hour window between 5 a.m. and 8 a.m. or 5 p.m. and 8 p.m.
He bases his advisories on historical data, plate tectonics, lunar and solar tides, solstices, and equinoxes. He also looks at the alignment of the sun, Earth and moon at the time of full or new moons an effect called a syzygy. Any word spelled with three y's needs to be taken seriously.
The shifting weight of the oceans against the Pacific, North American and South American plates, combined with Earth's internal heat and other aforementioned forces creates stress on the various earthquake faults along the West Coast. Those forces are stronger at certain times of the year, particularly when the moon is closer to Earth.
At some point, he said, that stress releases and Earth must quake.
Nabhan cites as evidence six major quakes ranging in Richter scale magnitude from 5.9 to 7.3, from 1933 to 1994. The Long Beach quake of 1933 happened at 5:54 p.m. The other five all happened in the early mornings between 4:51 and 7:43 a.m.
Since his chart doesn't include two other big earthquakes of the past 30 years, I checked them against his theory.
The Oct. 17, 1989, Loma Prieta quake (7.1) hit at 5:04 p.m. and the 1983 Coalinga quake (6.4) at 4:42 p.m.
Not mentioned: The great San Francisco earthquake, estimated at 7.7 or more, came at 5:12 a.m., April 18, 1906.
The 5.7 earthquake May 23 near Susanville? Boy, was he way, way off on that one. It happened at 8:47 p.m. a whopping 47 minutes beyond his three-hour evening window.
Nabhan isn't discouraged when his theories are frequently pooh-poohed by geologists, seismologists and others who are much better about pooh-poohing than predicting earthquakes in their own right. He's campaigning to get Gov. Jerry Brown to take his advisories seriously, giving the state's residents fair warning just in case the Big One happens according to his schedules.
Which brings us to the point of interest here in Modesto and the valley. The coast and Sierra are seismically active areas. The valley feels some of their pain whenever earthquakes hit on either side of us, but doesn't take the brunt of it.
"People want screaming headlines," Nabhan said. "Modesto is not at the heart of seismic activity."
Should there be a devastating earthquake along the coast, though, we'd notice.
"If the Port of Los Angeles were to shut down, Modesto would feel it," he said.
The Port of Oakland, too. The flow of goods and some food supplies would slow or stop for a time.
State and federal agencies implore such good-sense preparation through the Great California Shakeout, www.ready.gov and other public awareness tools that apply to floods and power failures, as well as earthquakes.
Getting valley residents to store food, drinking water and medical supplies is generally a tough sell, but something they need to take more seriously, said Hugo Patino of the Modesto Regional Fire Authority.
"There will be some residual effect for the valley," Patino said.
Which could include a flood of refugees should an earthquake devastate the Bay Area, he said.
"We have plans in place if we needed to provide shelter sites for emergency shelter," he said. "We have a lot of the background in place."
You know, just in case .
By Nabhan's calculations, the next best chances for a major earthquake on the West Coast will arrive on or about June 23, followed by another window July 22.
That isn't a prediction. It's an advisory.
The hardships or at least inconveniences unprepared valley residents face if the Big One hits?
That's a promise.
Jeff Jardine's column appears Sundays, Tuesdays and Thursdays in Local News. He can be reached at email@example.com, @jeffjardine57 on Twitter or at (209) 578-2383.