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Shocking events. Despite new technologies and decades of research, the ability to predict earthquakes remains tantalizingly out of reach. Some researchers recently proposed that information gathered during foreshocks, the smaller earthquakes that precede an earthquake, might provide information about the triggering event for an impending earthquake in time to provide warning and avoid catastrophe.

However, a recent study by Rachel Abercrombie, a CAS associate professor of earth sciences, and Karen Feltzer, a former BU student now at UCLA, casts doubt on that possibility. Their research indicates that all related earthquakes — foreshocks, mainshock, aftershocks, and multiplets (groups of earthquakes of comparable size) — are triggered by a single mechanism.

The researchers analyzed earthquake statistics from the International Seismological Center, the National Earthquake Information Center, and the California Council of the National Seismic System. They classified events that occurred in a cluster as foreshock, mainshock, aftershock, or doublet (two earthquakes of comparable size). Their reasoning was that if all of the shocks in a cluster resulted from the same trigger, then the rate that aftershocks and doublets occur in a region should vary linearly — that is, where aftershock rates are low, doublet rates should also be low; aftershock and foreshock rates should vary in like manner. The researchers found that although the number of aftershocks depends upon the size of the mainshock, the size of the aftershocks does not. They further found there is nothing to stop a small earthquake from triggering significantly large earthquakes, nor is there any way to predict when a small event will trigger a larger one.

According to Abercrombie, scientists studying the 1992 Landers (California) earthquake and the 2002 Denali (Alaska) earthquake determined that the quakes generated seismic waves that traveled through the ground and created dynamic stresses that in turn triggered earthquakes thousands of miles away. Abercrombie’s work is primarily focused on the factors governing the beginning and rupture of earthquakes. “The data does not seem to support the existence of a relationship between how the earthquake begins and how big it becomes,” she says.

This research was reported in the February 2004 issue of the Bulletin of the Seismological Society of America.

Overcoming barriers. Colorectal cancer is the second most common cause of cancer-related death in the United States. The American Cancer Society predicts 146,940 new cases and 56,730 deaths this year. But even in the face of these numbers, a majority of Americans skip such recommended screenings as fecal occult blood testing (for hidden blood in the stool) and flexible sigmoidoscopy and colonoscopy, which involve the insertion of a flexible tube into the rectum to see the inside of the colon. Although men and women are at equal risk for this cancer, women are more likely to bypass endoscopic screening, considered to be the most effective in identifying cancer and precancerous growths, or polyps.

Francis Farraye, a MED associate professor of gastroenterology, recently concluded two studies designed to provide a better understanding of the barriers that prevent patients from participating in colorectal cancer screenings.

In one study Farraye and his team surveyed women awaiting mammography, a group they

considered “highly motivated” to participate in health screenings. Among the 551 women surveyed, half reported having had a sigmoidoscopy or colonoscopy — and of these, 93 percent did so based on the recommendation of their primary-care provider. Although the women had colorectal screenings at a higher rate than the national average, those who had not had the screenings most often cited a primary-care provider’s failure to recommend them as the reason they had not been screened.

Primary-care providers also figured in a second study, which surveyed 554 people, men and women. Women reported significantly more embarrassment and fear about endoscopic screening than men. The responses showed, however, that the women were more willing to consider having an endoscopic exam if a long-term primary-care provider recommended the procedure. A large number also said that being able to go to a female endoscopist would positively influence them to undergo screening.

Farraye is also collaborating with Tracy Battaglia, a MED assistant professor of medicine and an investigator in the school’s Women’s Health Research Unit, in exploring barriers to colorectal cancer screening among members of minority groups.

"Research Briefs" is written by Joan Schwartz in the Office of the Provost. To read more about BU research, visit


15 May 2003
Boston University
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