September 6, 2011

Two Cents: Natural Disasters

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How was the recent earthquake in Virginia different from those in more earthquake-prone regions? What caused the earthquake to occur?

The vast majority of earthquakes worldwide, such as those in Japan and Chile, occur on the boundaries between the plates that make up the rigid outer shell of the Earth. The Virginia earthquake was unusual in that it occurred in the middle of the North American plate that stretches from the Mid-Atlantic Ridge to the San Andreas Fault. Although such earthquakes are rare, we know that they occur from time to time. Charleston, South Carolina experienced a much larger, magnitude 7.3 earthquake in 1886 which rang church bells as far away as Chicago! The crust of the earth is full of fractures and even a small amount of stress loading these weak planes over time can cause them to slip suddenly when friction along them is overcome. – Prof. Richard W. Allmendinger, Earth and Atmospheric Sciences

The eastern U.S. has a long history of earthquakes, but we don’t have large ones very often.  In fact, the last earthquake in this region as large as the August 23 event in Virginia was in 1944 in upstate New York.  There are faults all over the eastern U.S. — just look in the gorges — many of them are leftover from the time hundreds of millions of years ago when the Appalachian mountains were built.  But an area of active research is what causes stress to build up on these ancient faults to the point that they fail in an earthquake.  In earthquake prone regions like the western U.S., you are close to a boundary of moving tectonic plates that build up the stress.  But here in the east, we are thousands of miles from a plate boundary.  There are several hypotheses about the causes of stress in the east and the data that is being collected from the Aug. 23 event will help us test some of these hypotheses.   – Prof. Matthew Pritchard, Earth and Atmospheric Sciences

Can the recent natural disasters be seen as the beginning of a trend or were they more isolated incidents?

With the exception of hazards linked to climate change, there seems little evidence that the rate of natural disasters is increasing or decreasing with time. However, our society’s vulnerabilitiy to such events is clearly increasing with time as populationg increases and is increasing concentrated in the urban environment, and as we become more dependent upon relatively fragile infrastructure. – Prof. Larry Douglas Brown, Earth and Atmospheric Sciences

There is nothing particularly unusual about the frequency of earthquakes and other natural disasters recently, and the timing of the Virginia earthquake and Hurricane Irene is pure coincidence. Earthquakes have a tendency to occur in clusters because many faults in the crust are very close to the point of failure. An earthquake in one area changes the state of stress on surrounding areas, making them more likely to fail and even the propagation of seismic waves over large areas can cause minor temporary perturbations in the stress field surrounding distant faults. Also, truly random processes happen with irregular spacing between events, not at a uniform interval. In general we do know that the larger a disaster, the less frequently they tend to occur, so for example large asteroid impacts such as that responsible for the extinction of the dinosaurs 65 million years ago, tend to be separated in time by tens of millions of years and eruptions of super volcanos like Yellowstone occur only several hundred thousand years apart. Humans have yet to see truly catastrophic natural disasters like those (nor are we likely to see them any time soon), though there is abundant evidence in the geological record that such thing have happened repeatedly in the geological past. – Prof. Richard W. Allmendinger, EAS

Climate scientists have linked anthropogenic climate change (or change in average weather conditions and manifested in global warming, changing patterns of precipitation, melting glaciers and loss of sea ice, sea rise, desertification, extinction of species, and reduced air quality) to an increased incidence of extreme events. These events include tornados, tropical storms,windstorms, ice storms, severe droughts, periods of extreme heat and cold, etc. Flooding has occurred periodically in this part of the country even before climate change was discernible.

Some venerable residents of the Schoharie Valley can recall a dozen serious floods. The most recent, however, was by all accounts the worst. In the short run we will all need to prepare for an increased incidence of extreme events and develop appropriate response plans, even as historically episodic events recur. In the long run we will need to adopt more sustainable lifestyles that can slow the pace of climate change and mitigate its effects. – Prof. Kieran P. Donaghy, CRP

Why was the earthquake felt over such a large region?

Earthquakes in the east can be felt over a much larger area than in the west — and this is primarily due to the fact that out in the tectonically active west, the rock is warm and attenuates seismic energy more than the cold rock of the east.  When an earthquake happens in the east it is like ringing a good metal bell and the waves travel a long distance while in the west it is like ringing a wooden bell that gives off a short thud. – Prof. Matthew Pritchard, EAS

What kind of infrastructure must be built to deal with such natural disasters?

More robust, resilient, and sustainable infrastructure must be built to withstand the damages imposed by natural and anthropogenic disasters. Planners and engineers are well aware of this state of affairs. The American Society of Civil Engineers has regularly issued a report card indicating where public infrastructure systems are deficient; the ASCE has also suggested sound principles for guiding infrastructure system design, construction, and maintenance. Countries which are susceptible to frequent disasters, such as earthquakes, have adopted stricter building codes in their cities and for their infrastructure systems. Unfortunately, many of our bridges and dams in the US, which are particularly vulnerable to flooding, are in dangerously poor condition. In brief, we know what to build and how to maintain it, but we lack the political will to make the capital investments. In this time of fiscal retrenchment, in which the US is spending a smaller percentage of its GDP on public infrastructure than at any time since the Eisenhower Administration, we may need to bring into being infrastructure banks to capitalize the necessary investments. Such institutions can reduce the risk of private investors in public-private partnerships. – Prof. Kieran P. Donaghy, City and Regional Planning

How might atmospheric changes affect the paths of hurricanes in the future?

It is thought that a warmer climate in the future might favor the development of more intense hurricanes, but it is not known how a changing climate would affect the paths of these storms.  There appears to be a natural, multi-decadal clustering of the paths of these storms, and we are now in a pattern where more of these storms are striking the east coast of the United States than they were a few decades ago.  The source of this pattern, or even if it is real, is not known. – Prof. Stephen Colucci, Earth and Atmospheric Sciences

How can we best plan for natural disasters through infrastructure and policies?

Geologists tend to say that earthquakes don’t kill people, buildings kill people. Earthquakes in poor countries, such as Haiti, tend to cause a disproportionate loss of life because of inadequate or non-existent building codes, insufficient economic resources to spend the extra money to build safer buildings, and in some cases endemic corruption and dysfunctional political process which allows people to construct substandard buildings despite adequate codes. Thus, in the U.S., we need to make sure that we understand the seismic risk in all parts of the country, that we have building codes that are adequate for the level of risk, and that those building codes are appropriately enforced. – Prof. Richard W. Allmendinger, EAS

We can prepare for natural disasters by developing robust, resilient, and sustainable infrastructure systems that are also well integrated and that are likely to survive likely combinations of events. (It is difficult to be prepared for all contingencies.) We can develop better networks of first-responders and support services and better protocols for responding once disasters have struck. (Since 9/11, many Homeland Security programs at the state and federal level have done just this.) We can probably do a better job of anticipating certain types of disasters and rehearse appropriate response behavior. We can anticipate where food, water, and critical supplies will be needed and store resources accordingly. Cornell is very fortunate to have some of the leaders of research on disaster preparedness and response strategies in Linda Nozick, Mark Turnquist, and Carmen Rawls, all in the Department of Civil Engineering. – Prof. Kieran P. Donaghy, CRP

Original Author: Seyoun Kim