By Randy Welch, Region VIII External Affairs
Hurricanes are monitored from hurricane-prone Miami, tornados are monitored from tornado-prone Norman, Okla., and earthquakes are monitored from Golden, Colo., nestled against the Rocky Mountains.
"We're in Golden because Colorado has a lower earthquake hazard than areas like California,” says Paul Earle, operations director of the National Earthquake Information Center, part of the U.S. Geological Survey. “We want to be far away from earthquakes so we can keep reporting on them if the regional centers go down. We can keep getting the important signals from the seismometers by satellite.”
The system uses 2000 seismic monitors around the world to gather information. A dozen regional “seismic centers” monitor activity in their areas and feed information to the NEIC. The NEIC monitors earthquakes around the globe, backs up the regional centers, and covers areas with no regional center. It shares the data and products with US and foreign networks, the White House, media, academics, and aid organizations such as USAID and the Red Cross.
More than 100,000 earthquakes of Magnitude 3 or greater on the Richter Scale occur every year – an average of about 275 a day. But the President’s inbox is not being flooded with notifications. NEIC just tells the White House about those that may cause significant damage, which is only a handful worldwide each year.
Anyone can sign up to receive email notices about earthquakes, choosing the area and the size of earthquakes they want to know about on the USGS Website. The free service currently has about 350,000 subscribers.
But one of the first things earthquake watchers need to know is that the widely used Richter scale is not a good way to measure earthquakes. The Richter scale measures the back and forth swings on an old-style seismometer that measures only a narrow frequency band, and is calibrated to Southern California, Earle explains. For earthquakes larger than 6 on the scale, it gives a low estimate of the actual size of the event.
“The real key is the ‘seismic moment,’” says Earle. “The ‘moment (or energy) magnitude scale,’ referred to as Mw, is tied to a value similar to the original Richter scale. However, the Mw scale is more physical. For example, an Mw 6.0 earthquake is roughly 100 square kilometers in area and slips about a meter.”
An initial reading of a quake is done automatically by the computers, but a seismologist is always on duty to remove bad data or add more data and provide a revised assessment of the larger earthquakes.
A more down-to-earth way of measuring an earthquake is its intensity, or the amount of shaking it generates. The public can actually help report shaking and damage levels by going online to a program called “Did You Feel It?” Anyone can click through the different seismic events listed there to report on the one they know. Shaking is measured on a scale of “not felt” all the way up to “extreme,” and damage goes from “none” to “very heavy.” The raw data from the public is color-coded and can be added to a “Shake Map” so people can see how widespread the shaking was and seismologists can determine the quake’s shaking intensity and extent. Based on the reporting, FEMA and other organizations can decide the size of response that may be necessary.
Another system – Prompt Assessment of Global Earthquakes for Response – provides worldwide estimates of fatalities and economic loss based on the losses from recent past earthquakes in each country. Another system, ShakeCast, alerts observers to potential damage by overlaying the Shake Map with the types of buildings in the area and what building codes were used during their construction. This shows which structures need the most immediate attention. For example, there are thousands of overpasses in California. There is no way every overpass can be examined after every earthquake. By using ShakeCast, vulnerable overpasses are highlighted for repairs.
Mitigation is vital, says researcher David Wald, who led development of the “Did You Feel It?” ShakeMap, ShakeCast and PAGER systems.
“In the 1994 Northridge earthquake, we had 33 fatalities,” he points out. “A comparable earthquake in Pakistan would kill at least 1000 times more, roughly 33,000. The building codes in California started after 1933. A lot of places were built with wood framing plus sheetrock and plywood, which is flexible yet strong. On the other hand, that also means it is more difficult to take steps now that will save lives in California than it is in Pakistan. And across the globe, the situation is getting worse as populations move to more dense urban areas often dominated by poorly built structures, and some right on faults.”
Once a quake hits, of course, it is too late to mitigate. And the idea a doorway is the safest place to be is a myth from a post-earthquake photo that showed a doorway as the only thing left standing.
In the U.S., Wald advises sticking with the tried and true: wherever you are, if you feel the ground shaking, “duck, cover and hold on.”