Living safely on this vigorous earth
Science refines management of quake and hurricane risks
The growth of knowledge during the past millennium has moved our confrontation with nature out of the realm of helpless superstition into the arena of scientific understanding.
When hurricanes roared across Central America a thousand years ago, some locals blamed the evil deity Huracan. Now, we track his namesake storms with satellite vision.
When earthquakes struck without warning a thousand years ago, it seemed reasonable to suspect divine displeasure. Last December, an international project involving more than 500 scientists published the first global seismic-hazard map to guide earthquake-safe construction.
When volcanoes erupted a thousand years ago, they often seemed propelled by supernatural wrath. Now, suspect volcanoes are monitored from space and on-site by seismologists who track every burp of their rumbling magma.
Scientists now know that storms, quakes, and volcanic eruptions reflect the geophysical activity of a life-sustaining planet. That activity commands respect rather than fear. It challenges us to use our scientific knowledge to live safely on our vigorous earth. The new seismic-hazard map emphasizes this point.
Earth's surface is broken into large plates. Most earthquakes and many volcanoes occur where these plates bump together, rub past each other, or dive beneath or override one another. They also occur where new plate material forms - welling up along mid-ocean rifts. From there, the new seabed crust spreads outward until it dives beneath older plates that carry the continents. It then returns to the semi fluid mantle that underlies Earth's outer crust. Eventually, some of that material will again return to the surface along the ocean rifts or through volcanoes. The system recycles minerals and some atmospheric gases. Geophysicists believe that, without this plate tectonic action, Earth wouldn't sustain an environment hospitable for complex organic life.
The seismic-hazard map reflects this knowledge. Many high hazard areas lie along active plate boundaries. But in presenting this map last December, project coordinator Domenico Giardini, director of the Swiss Seismological Service in Zurich, distinguished hazard from risk. The map shows the probability of severe horizontal ground shaking over the next 50 years. That's hazard. Risk is the probability of such shaking causing damage. Dr. Giardini noted that the map tells people how much care they have to take in locating and building structures. Where there's high seismic hazard, zoning should be strict and building codes realistic. The bottom line, Giardini said, is that "you can live in tectonic safety if you have a well-built house."
The same can be said for volcanoes, severe weather, and other powerful natural systems. Geophysicists still have much to learn about these phenomena. But they now know enough to detail their hazards. Much of the damage from hurricanes is due to unwise coastal development and life-styles that ignore well-defined storm dangers. This can change.
Drought affects more people than any other natural hazard, according to the American Meteorological Society. Yet, the society notes: "Drought should not be viewed as merely a physical phenomenon. It is the result of an interplay between a natural event ... and the demand placed on water supply by human-use systems." This, too, can change as scientific knowledge is translated into sustainable water-use policies.
The last millennium brought a profound shift in humanity's concept of natural disaster. We now understand that these seemingly destructive forces are part of the geophysical system that sustains a liveable environment. We know their hazards. We cannot change them. But we can manage the risk that they present.
(c) Copyright 2000. The Christian Science Publishing Society