More shakers felt in Mexico.

More shakers felt in Mexico

For several moments last week, residents in Mexico City and four Mexican states thought nightmare had returned. Seven months after a magnitude 8.1 earthquake demolished parts of Mexico City, killing about 9,500 people (SN: 9/28/85, p. 196), another large quake shook Mexico. But this time, the most trouble the earthquake and its two aftershocks caused were a few blackouts and some panic.

According to the National Earthquake Information Center in Boulder, Colo., the April 30 quake registered magnitude 7 and its epicenter was located in the Pacific about 250 miles southwest of Mexico City--in the same area as the Sept. 19 shaker. However, the New York Times reports that the National Autonomous University of Mexico has said the quake measured magnitude 6.5 and was centered 380 miles southwest of Mexico City. A smaller quake reportedly occurred in the same region on May 4.

Since the September quake, seismologists have been most concerned that an area to the southeast, closer to Acapulco, might experience a large earthquake in the next five to 10 years. Had last week's quake occurred in that region, it might have signaled increased stress in that area. But so far, says Hiroo Kanamori at Caltech in Pasadena, based on its location and size as reported by the Earthquake Information Center, the earthquake does not appear to be unusual or a cause for worry; it is not uncommon for a magnitude 7 quake to occur in the same area several months after a much larger event.

Still, it will be a few months before seismologists will have studied all the details of the two recent quakes to learn their full significance. As the 100 satellite-telemetered stations of a planned Global Seismographic Network are erected around the world over the next five to 10 years, adds Kanamori, seismologists will be able to study and interpret such seismic events much faster than they do now.