The death and devastation caused by major earthquakes around the world can only worsen in the years to come, as urban development and unprecedented population growth compound the lethal effects of natural seismic hazards, experts say.
Big earthquakes strike regularly -- with about 18 measuring a magnitude 7.0 or greater every year on average, and four or five above the very dangerous 7.6 level. The recent destructive temblors in Turkey, Greece and Taiwan do not signify any increase in quake activity.
What has changed is that more and more people are living near faults. With the global population expected to pass the 6 billion mark next month, there are fewer unpopulated places for quakes to strike. With ever more people to accommodate, there is more multistory construction in vulnerable fault zones as well.
As a result, destructive earthquakes such as those of the past several weeks "are the wave of the future," said seismic expert Kerry Sieh of the California Institute of Technology.
"There are 40 cities of a million or more people within [62 miles] of a major plate boundary, and all those are good candidates for a large event. Our exposure to the hazard is increasing."
Some experts suggest that in recent decades, the world has experienced a lull in the most severe earthquakes -- those of magnitude 8.0 or greater. If so, even more destruction is to be expected when the lull ends.
Taiwan is shaken by dozens of quakes every year, caused by the inexorable crush of two major tectonic plates that squeeze the island from the east and west at the relatively rapid rate of several centimeters a year, building up seismic energy like the tension in a coiled spring.
Tuesday's disaster in Taiwan was the most recent in a series of damaging urban earthquakes in just over a decade.
Devastating tremors killed at least 16,000 people during a 7.4 earthquake in Turkey in August. At least 122 people died during a 5.8 temblor in Athens, Greece, several weeks later. More than 6,400 people died in a 1995 quake in Kobe, Japan. The 1994 Northridge earthquake in Los Angeles and the 1987 Loma Prieta temblor near San Francisco were among the most costly natural disasters in U.S. history.
Millions of earthquakes occur around the world annually. Most are too small to be felt. An average of 3,000 magnitude 5.0 quakes are recorded each year.
The destruction caused by an earthquake is unpredictable.
Tuesday's Taiwanese earthquake, at 7.6, was roughly twice as powerful as the 7.4 quake that racked Turkey last month. But the death toll may be only one-tenth as high, in large part because construction codes in Taiwan were more strictly enforced than in Turkey, several experts said.
Other factors can also make a huge difference. Several seismic hazard experts say that if the epicenter of the Northridge earthquake had been a few miles to the south, more directly under the downtown area, or if it had occurred during the day, the death toll might have reached the thousands, rather than the dozens, with damages of $100 billion or more.
Officials in Taiwan said that temblor could have been even more deadly, had its timing and location been slightly different.
"We roll the dice every time," said earthquake hazard analyst Charles Kircher.
But as urban boundaries expand to accommodate growing populations, those dice are being weighted for disaster. "We get closer to known faults and put more people on top of the faults," Kircher said.
"There has been a fourfold increase in the world's population since the 1906 San Francisco quake, and, if you look at the numbers, most of the million people who have died this century in earthquakes have died in poorly built urban areas."
While better construction can save many lives, some experts worry that quake-specific engineering solutions will foster the belief that it is safe to build in areas with a high potential for earthquakes, thereby making the long-term hazard worse.