Don,

It's not fair to the original writer (in this case Lee Dye) if you don't clearly state where you are lifting quotes from. Plus, it would be helpful for others to know the source so they could refer to it for other purposes. This is more an ethical or legal matter rather than a mere formality (such as what tense to use in the first sentence of a science paper), so we should be careful about it.
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excerpt from
What We Still Don't Know About Earthquakes
Recent Tremblor in Alaska Highlights What We Know and Don't Know
By Lee Dye

The Unknowns: �eWhat�f and �eWhen?�f

We know what causes earthquakes. Quakes are caused by the sudden release of strain that builds up in the giant tectonic plates as they grind against each other while moving around the surface of the earth.

But we don't know specifically what triggers a quake. We do know it isn't the alignment of the planets, or radiation from space, or your grandmother's gout. The trigger probably varies with local conditions.

And nobody knows precisely when the next quake will occur. Instead of predicting quakes, scientists have settled for long-range forecasts.

So no reputable scientist is going to tell you that California's notorious San Andreas Fault is going to rip up that pricey landscape at 2 p.m. on Friday the 13th. The best they can do is say that some part of it is likely to break loose sometime in the next decade or so.

Faulty Timing

But there is some pretty convincing evidence that even those long-range forecasts are built on shaky ground. Most governmental agencies around the Pacific Rim base their engineering requirements on the idea that faults tend to rupture at fairly definable intervals. It's called the "time-predictable recurrence model," but it may well be dead wrong.

Geophysicists at Stanford University have taken a hard look at that concept and concluded that nature really isn't all that tidy when it comes to scheduling earthquakes. Jessica Murray and Paul Segall examined a famous section of the San Andreas Fault that runs through the farming village of Parkfield in central California.

Parkfield is the most instrumented fault zone this side of Tokyo because some decades ago scientists determined that it has ruptured on average once every 22 years since 1857. Since the last quake hit there in 1966, scientists began packing all sorts of gizmos into Parkfield in the mid-1980s. They reckoned that a quake of magnitude 6 should hit there by around 1987.

Most of those instruments are still there, and new experiments are being set up, but guess what? No earthquake. The shaker is way past due, but so far the score is San Andreas 1; scientists 0.

• ABC News