All the time. Many regions that experience tropical cyclones are also seismically active. East Asia, New Zealand, Mexico, and the western Caribbean all lie in the Pacific Ring of Fire, a swath of earth that suffers from frequent and powerful quakes. * Since earthquakes are so common in those areas—in the last week, events of magnitude four or greater were registered in Indonesia, Japan, Fiji, Vanuatu, Tonga, New Guinea, the Philippines, and Aruba—they often coincide with typhoons and hurricanes.
As for the connection between the two, there is no reason to believe that an earthquake can cause a hurricane. There are, however, some tantalizing clues suggesting that hurricanes might contribute to earthquakes. Massive changes in atmospheric pressure, for example, are widely thought to cause slow earthquakes—weak tremors that last for hours or days rather than unleashing their full power over a few moments. At least one earth scientist believes hurricanes and typhoons can set off more destructive earthquakes as well. At the 2010 American Geophysical Union meeting, Shimon Wdowinski of the University of Miami argued that the abnormally heavy 2008 hurricane season caused enough land erosion to shift the pressure on the earth's crust, triggering the massive 2010 quake in Haiti. He pointed out that strong storm seasons also preceded large quakes in Taiwan in 1996 and 2009. At this point, however, Wdowinski's theory hasn't yet gained widespread acceptance, and most earth scientists still see no connection between hurricanes and large earthquakes. (Nor would the theory explain last week's coincidence, in which the quake came first.)
Earthquakes may not cause hurricanes, but they can set off several other natural disasters. As the last decade has amply shown, earthquakes cause tsunamis, which are often more devastating in terms of human deaths than the inciting quake. Earthquakes also trigger mudslides and landslides, in part because they increase the pressure on water-soaked soil. (This phenomenon, known as liquefaction, can cause entire buildings to keel over sideways, even without a landslide.)
If the fault along which an earthquake occurs lies directly beneath a volcano, the shaking can cause an eruption. That's probably what set off Chile's Cordón Caulle in 1960 and Hawaii's Mount Kīlauea in 1975. Many seismologists and vulcanologists believe that earthquakes can cause more distant volcanoes to erupt as well, although the hypothesis is unproven. The leading theory is that earthquakes either compress magma reservoirs, increasing pressure on the walls, or expand the reservoirs, causing cracks and fissures that enable the hot liquid to break through.
There are other possible combinations. Hurricanes often bring tornados. (Hurricane Irene unleashed tornadoes on Virginia, Maryland, Delaware, and New Jersey.) Tropical storms sometimes trigger landslides, because the heavy rains make the earth unstable. Volcanic eruptions can also cause landslides, as parts of the mountain collapse. If that collapse occurs near the coast, the huge piles of earth slamming into the ocean can, in turn, result in a tsunami.
Cosmic impacts may be the granddaddy—or the Kevin Bacon—of natural disasters. Some earth scientists believe that the largest extinction in the planet's history was the result of a meteor that struck the earth, causing worldwide earthquakes that in turn set of massive volcanic eruptions. Landslides and tsunamis almost certainly followed.
Got a question about today's news? Ask the Explainer.
Explainer thanks Shimon Wdowinski of the University of Miami. Thanks also to reader Amanda Perez for asking the question.
Correction, Aug. 30, 2011: This article originally stated that Australia is within the Pacific Ring of Fire. New Zealand is in the Ring of Fire, but Australia is not. (Return to the corrected sentence.)