Earthquake

Scientists release first global earthquake hazard map
Associated Press, Dec. 15, 1999

Much of the world's population lives on potentially shaky ground, scientists said Tuesday after releasing the first map detailing the entire planet's earthquake hazard zones. The ominously colorful document offers few surprises: Southern California, southeastern Hawaii, Turkey, Taiwan, Iceland and the India-China border are most likely to experience strong shaking in the future, researchers said. "Active tectonics make outstanding scenery and people want to live there," said Kaye Shedlock of the U.S. Geological Survey. "You just have to recognize what your hazards are. You have to mitigate them and know what you are dealing with."

The map, which was developed by 500 scientists over seven years, offers developing countries new information that can be used to update or establish building codes. Some nations in Africa, for example, never compiled such data. "We can say today that as a result of this program, more than half the countries of the world have a new generation of seismic hazard maps," said Domenico Giardini of the Swiss Seismological Service in Zurich. As much as 15 percent of the planet's land is in zones of high or very high hazard, which is defined as a 10 percent chance or greater of violent shaking within the next 50 years, Shedlock said. Roughly 40 percent of the Earth's land is considered low hazard.

Specifically, the map attempts to predict the probability of peak ground acceleration, a force that is most likely to damage low-rise residential buildings. Future maps are being compiled that will detail hazard areas for larger structures like high-rises. "This map only provides part of the story," Giardini said. "You can easily live in a high-risk area if you have a well-built house." In most cases, the hazardous areas are near faults that define the boundaries of the Earth's tectonic plates. Entire continents and oceans ride on the plates, which grind against, smash into or separate from each other, producing quakes and volcanoes.

In California, the San Andreas Fault slices through the state where the Pacific and North American plates meet. Turkey, which has been devastated by several large quakes this year, is at the juncture of the Eurasian, African and Arabian plates. One of the largest red marks is along the India-China border, where India is literally smashing into Asia, producing the still-growing Himalayas, the tallest mountains in the world. Hawaii, however, is a different story. The island in the middle of the Pacific plate is prone to large quakes caused by underground volcano-related collapses. The greatest hazard areas, which are colored red or brown on the map, contains half the world's largest cities. Efforts are now under way to determine exactly how many people live in the most dangerous areas. It will be up to individual governments to determine how to use the new information. Developments planned in the most hazardous areas should receive the closest scrutiny, the geologists said. "If we've done our job right, the end result of this is going to be a lot more detailed site-specific hazard maps," Shedlock said.

The map project was launched in 1992 by the International Lithosphere Program with support from the United Nations' International Decade for Natural Disaster Reduction. It was unveiled at the fall meeting of the American Geophysical Union. Researchers combined existing hazard maps, data from recent and historical quakes as well as other records that stretch back 2,000 years. Biblical passages were used for parts of the Middle East. The work was easy in the United States, where the law requires hazard maps to be updated every five years. It was much more difficult in less developed countries, Giardini said.