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The devastating earthquake that struck Haiti on January 12, 2010 came without warning. Despite decades of research, scientists don’t have a reliable method of predicting such temblors. In places like Haiti, which haven’t implemented modern building standards, casualties can run very high—in contrast with a place like California, where the October 17, 1989 Loma Prieta earthquake caused significant damage but only a few dozen deaths.

Still, San Franciscans are surely sympathizing with the latest Caribbean quake victims. In California, the question is always in the back of your head: When’s the next earthquake coming? Past experience shows that there is a 1 in 6.87 (14%) chance that some part of California will experience an earthquake of magnitude 6 or greater in a year. That’s as specific as it gets. No one knows when or where the next quake will be.

There was a period of time, from the 1960s to the mid-1980s, when many scientists were optimistic they would soon be able to reliably predict impending earthquakes. Two large-scale experiments were conducted, one along a fault near Tokyo and one along the San Andreas Fault between Los Angeles and San Francisco. The experiments were designed to detect subtle movements in the Earth’s crust, with the hypothesis that these movements would be predictive of impending larger disruptions. Both experiments failed to achieve the desired results.

In the case of the American study, scientists with the state of California and the US Geological Survey had predicted a significant earthquake would most likely occur in the region in the mid 1980s; it finally occurred in 2004, but instruments installed to detect precursors to the event, including foreshocks, failed to register any signal. There have been numerous other attempts at earthquake prediction which have also yielded disappointing results. According to Michael Blanpied, a scientist with the US Geological Survey, there is currently “no organization or government or scientist capable of successfully predicting the time and occurrence of an earthquake.” However, research into earthquake predictability has yielded valuable general information about the likelihood of earthquakes over a time span of many years, and that information has led to improved building codes in earthquake-prone regions.

There is one prediction we can make. The odds that an earthquake will occur somewhere in the world on any given day are 1 in 1 (100%). In fact, there are thousands of quakes a day even though humans don’t feel most of them.

All this seismic activity is thanks to plates of rock that fit together like puzzle pieces and make up Earth’s surface. These tectonic plates float atop the molten rock of Earth’s upper mantle. The border where two plates meet is called a fault, and as they move they push against one another. Eventually, there’s so much pressure that the fault “breaks.” When a fault breaks, one plate will slide beneath the other, or the two plates will scrape along in opposite directions. The result is an earthquake.

Earthquakes are essentially sound waves that emanate from the break and ripple outward through the earth, causing the ground to vibrate. The most well-known measurement of these waves is the Richter Scale, although for bigger quakes, scientists prefer the more accurate “moment magnitude” scale. The scales are a measure of wave strength. A 6 on the Richter scale is likely to cause damage in populated areas, and anything 7 or higher is classified as a “major” earthquake. Each higher number on the scale represents a ten-fold increase in the strength of the quake.

Where you live affects the odds of experiencing such momentous earthquakes. Faults like the San Andreas, where the North American and Pacific tectonic plates meet, are especially active. As a result, the West Coast states lead the nation in probability of a magnitude 6 or greater earthquake each year. After California, Alaska comes in second with a 1 in 9.36 chance, and the odds are 1 in 61.8 the citizens of Oregon or Washington will feel the earth move under their feet.

But the threat of a quake isn’t limited to the Western US. For example, an off-shore fault line gives Massachusetts 1 in 154.5 odds of experiencing a big earthquake—the same as Missouri, with its infamous New Madrid Fault.

While big quakes are relatively unlikely, that doesn’t mean we can just forget about them. Earthquakes are very expensive. Only 1 in 115 federal disaster declarations will be earthquake related, but1 in 15.57 catastrophe-loss dollars paid out by insurance companies goes to fixing quake damage.

Not to mention the international aid that goes to poorer countries—like Haiti—when they are badly rocked by an earthquake.