The findings come from the University of Miami Rosenstiel School of Marine and Atmospheric Science, and they confirm what seasoned weather observers like farmers, fishermen and ranchers have long suspected; weather can cause earthquakes, if it is extreme enough.

One of the severe weather patterns identified are tropical cyclones, or hurricanes, which Rosenstiel researchers say can cause earthquakes even years later. In fact, according to the study’s lead author, Dr. Shimon Wdowinski, the kind of precipitation generated by a hurricane or cyclone is a “trigger.”

Impossible as it seems at first glance, the study results make perfect sense when examined in depth. Dirt is heavy. Water makes dirt heavier. When torrents of rain fall on the ground in the vicinity of a fault line, the results can be mudslides or rapid erosion of soil, leaving the fault line thousands of tons lighter as a result.

After an interval, which can be as little as a few days or as long as a few years, this “lighter” landmass allows the fault beneath it – no longer compressed – to rise up, often catastrophically. To the earth, this lifting can be equated to taking a deep breath after something moves off its chest. 

As the study demonstrates, the weather/earthquake connection relies on two features; the presence of faults (see map) and the presence of hurricanes or typhoons. But if you doubt the weight of earth, especially wet earth, as being sufficient to suppress fault action, go outside, fill a bucket with dirt, pour in enough water to make mud and then lift it. Or try.

Dr. Wdowinski and team used a much more scientific method, of course. They tracked the occurrence of earthquakes and tropical cyclones (also called hurricanes, or typhoons, depending on their location) in and around Taiwan over a 60-year time span.

Then they made the same comparison with Haiti (2010 earthquake, 2008 tropical storms) – a comparison supported by similar research at the California Institute of Technology, Pasadena, where graduate student Thomas Ader confirmed that earthquakes in his home state were more likely to occur in dry winter months; i.e., when the dirt weighs less.  

Unfortunately, Dr. Wdowinski and his group’s discovery, that heavy rain events usually preceded earthquakes by less than four years, is valuable only as scientific observation. It won’t do much to predict earthquakes, since the areas where they are prevalent are often visited by heavy rains in a yearly fashion – a fact on which farmers rely to grow their crops.

There are exceptions, of course. California, for example, can no longer rely on its multi-year drought to keep earthquakes at bay, since that officially ended in March of 2011. Expect a big one in California this summer?

In New Zealand, where a lot of rain during the season is typical, it’s hard to use Dr. Wdowinski’s observations to understand why the city of Christchurch and surrounding areas continue to experience secondary quakes after a massive shakeup that reverberated for most of the day on February 22 of 2011. To date, the area has experienced a total of 118 quakes in excess of 4.5 magnitude, or more than 1,000 ranging from 3.5 to 5 on the Richter scale.

This was a followup to the so-called Canterbury earthquake (7.1) of September 2010, and experts are now suggesting that the more recent quakes are caused by a new fault line subsequent to the “liquefaction” of the earth – a recent discovery which does little to reassure New Zealanders, I’m sure.   

In fact, work at the University of California, Berkeley (which sits atop the Hayward Fault) suggests that fault mapping and earthquake science is still in, if not its infancy, certainly in its adolescence, with more reliable earthquake mapping and predictors yet to come.

We can only hope.