Evidence of geohazards in South Africa: a rock slide on Tafelberg road (Table Mountain). Photo courtesy of Vaughn Thompson
Evidence of geohazards in South Africa: another rock slide episode within siliciclastic Cape Supergroup of South Africa, near Cape Town. Photo courtesy of Vaughn Thompson
An earthquake in Haiti brings widespread death and destruction. A volcano erupts in the Philippines and 50,000 evacuate. A massive landslide destroys homes in San Diego.
Dangerous stuff, geology.
In the United States, geological hazards are monitored and studied by the U.S. Geological Survey. The USGS Geologic Hazards Team has its headquarters in Golden, Colo.
It works in earthquake-hazard, landslide-hazard and geomagnetism programs and partners in the Global Seismographic Network (GSN). Additional earthquake research and monitoring is conducted in USGS offices in Menlo Park, Calif., Seattle and Anchorage, Alaska.
The GSN provides worldwide monitoring of the Earth, with more than 150 seismic stations distributed globally.
“In the case of Haiti, we have a sub-network of nine stations in the Caribbean (at the time of the Jan. 17 earthquake). There is literally not a seismometer in Haiti, so all the activity has to be monitored remotely,” said AAPG member David Applegate, USGS senior science adviser for earthquakes and geologic hazards in Reston, Va., and formerly was director of the American Geological Institute’s Government Affairs Program, working closely with AAPG on policy initiatives.
Monitoring earthquakes and gathering data make up a significant part of the USGS hazards mission, essential for issuing emergency notification.
“We try to get the fastest information and the richest information out to the emergency responders as quickly as possible,” Applegate noted.
“For the Haiti earthquake, we issued the magnitude 7.0 estimate within 20 minutes,” he added. “We also were able to say at least two million people were exposed to violent shaking.”
Haiti: In the Field
Geologists also are early responders following a destructive earthquake, but in a different sense.
Paul Mann, another AAPG member, is a senior research scientist for the Institute for Geophysics at the University of Texas at Austin. He and a fellow scientist traveled to Haiti after the January earthquake to conduct fieldwork.
“He and I are both involved in rapid response. I’ve just spent five days down there measuring the fault,” Mann said.
“It was sort of like being in World War II. Everything was wrecked. All the buildings were blocks of concrete,” he recalled.
Also, he said, people afraid to live indoors were staying outside everywhere – usually under makeshift tents made of bedspreads stretched across string.
Mike Jacobs, speaking as president of AAPG’s Division of Environmental Geosciences, shared the concern.
“We as geologists, of course, are aware of the geological risks of living and working in certain regions and can make educated decisions on whether or not we choose to accept those risks,” he said. “The tragedy with Haiti is that it is populated by some of the poorest people on this earth – and even if they were aware of the risk, they most likely had no choice on whether or not to accept it.
“Many paid the price with death and suffering,” Jacobs said, “and my prayers and thoughts go out to them.
According to Mann, scientists need to react quickly to study indicators of recent earthquake activity, “ephemeral effects that are important but not permanent.
“It’s a very good example of teamwork in trying to get down there while these indicators still exist,” he said. “Some of those will disappear with the first heavy rainstorm.”
Mann was able to travel to the epicenter fault area, detailing the near-site effects and discovering the ground had not ruptured from the quake.
“That’s an important piece of information to have. It shows what happened to that fault during the earthquake,” he said.
The Haiti quake involved an 80-kilometer section of the 600-kilometer Enriquillo-Plantain Garden Fault, which stretches from Jamaica to the Dominican Republic, Mann said.
Movement of the adjacent plates builds up fault stress very slowly, but inexorably. Earlier measurement and calculation had shown about two meters of stress built up on the fault, Mann noted.
“If you release two meters of stress on this fault you would get a 7.2 magnitude earthquake, so it was just a little smaller than we thought,” he said.
Mann was frequently interviewed by national media after the quake as one of a small group of scientists who’d produced studies warning of the possibility of a major earthquake in Haiti.
“‘Predicted’ would be too strong a word, because they didn’t say anything about when that earthquake might happen,” Mann said.
“The real fear now,” he added, “is that the movement of this 80-kilometer section has increased the stress on the adjacent parts of the fault.”
‘A Very Young Science’
Although earthquake science has made impressive advances, it has not reached the point of predicting the time of an event, or even narrowing down the possibility into a short timeframe.
“That has proven elusive,” Applegate conceded.
“Instead, what we focus on are medium- and long-range forecasts,” he said.
For the USGS, that means an assessment of a quake’s likely intensity and probability in a 30-year to 50-year period.
As an example, Applegate cited a 2008 joint forecast by the USGS and other agencies that predicted a 99 percent likelihood in the following 30 years for a quake of 6.7 magnitude or greater in California, with the two most likely candiates for a major earthquake being the Hayward Fault in the San Francisco Bay area or the southern section of the San Andreas Fault.
“It’s still a very young science. We seem to know more from every earthquake, but we still have a long way to go before we have a good handle on the predictability,” said Carol Prentice, a paleoseismologist for the USGS Western Earthquake Hazards Team in Menlo Park.
“What you don’t know is if an earthquake is going to happen now, or will the strain accumulate for another 100 years and it will be a bigger earthquake,” she added.
Earthquake researchers focus on Late Holocene geology and events, conducting fieldwork for measurement of current and past activity. A major technique “is to cut trenches across faults to see where earthquakes have occurred,” Prentice said.
They also conduct surface studies of fault areas, aided by remote sensing technology that can image through vegetation.
“The most exciting thing these days is LIDAR,” she said. “It’s a remote sensing device that actually looks through trees.”
While some areas of the world are well-studied, Haiti is in an area not nearly as well understood seismically, Prentice noted.
“The studies that need to be done just haven’t been done,” she said. “We never got the funding to do it.”
The USGS also conducts a Volcano Hazards Program, with a network of five major volcano observatories and other resources, and with additional research conducted at the Menlo Park Science Center.
“Unlike earthquakes, volcanoes have proven to be fairly predictable. We’re in the process of developing a national volcano early warning system,” Applegate said.
Beyond the immediate effects of a volcano eruption, the event can have longer-lasting and far-reaching consequences. For instance, “there have been several cases where aircraft have flown into a volcano ash cloud and lost engines, sometimes all four engines,” he noted.
But earthquakes remain unpredictable, and right now scientists are studying the geological aftermath of the Haiti quake. Researchers often say the most likely place to expect earthquakes is where earthquakes have struck before.
“This quake is not the worst earthquake that could have happened. That’s what is so stunning. This earthquake broke to the west, so the bulk of the seismic energy was directed away from the city,” Applegate said.
“The fault has not done all that it’s going to do. As rebuilding takes place, we can say with high certainty that structures need to be able to withstand at least the amount of shaking we saw in the last event,” he added.
Earthquake risk is measured not only by the likelihood of an event, but also by the amount of destruction that might result.
“An important point to make is that there are a lot of major cities located near active geologic faults. And as population grows in areas of activity, the risk grows,” Prentice observed.
That’s one reason she thinks earthquake forecasts, even with limited certainty, are a valuable tool.
“If you hear there’s a 68 percent chance of rain,” she said, “you might bring an umbrella.”