Radio hints precede a small U.S. quake....After a 5-year wait with radio receivers pressed firmly to the ground, Antony Fraser-Smith captured electromagnetic premonitions of a California earthquake a month before it struck last year. The finding offers the hope that scientists may one day predict some quakes by listening for electromagnetic pulses and other types of signals emanating from faults as they prepare to give way. An atmospheric physicist at Stanford University Stanford University, at Stanford, Calif.; coeducational; chartered 1885, opened 1891 as Leland Stanford Junior Univ. (still the legal name). The original campus was designed by Frederick Law Olmsted. David Starr Jordan was its first president. , Fraser-Smith grew interested in seismology seismology (sīzmŏl`əjē, sīs–), scientific study of earthquakes and related phenomena, including the propagation of waves and shocks on or within the earth by natural or artificially generated seismic signals. when one of his ultra-low-frequency radio receivers happened to record unusual electromagnetic emissions just before the 1989 Loma Prieta earthquake The Loma Prieta earthquake was a major earthquake that struck the San Francisco Bay Area of California on October 17, 1989 at 5:04 p.m. The earthquake lasted approximately 15 seconds and measured 6.9 on the moment magnitude scale (surface-wave magnitude 7.1). south of San Francisco San Francisco (săn frănsĭs`kō), city (1990 pop. 723,959), coextensive with San Francisco co., W Calif., on the tip of a peninsula between the Pacific Ocean and San Francisco Bay, which are connected by the strait known as the Golden . In hopes of catching another quake, the physicist set up two receivers over the San Andreas fault San Andreas fault, great fracture (see fault) of the earth's crust in California. It is the principal fault of an intricate network of faults extending more than 600 mi (965 km) from NW California to the Gulf of California. near the tiny town of Parkfield, where seismologists believe a magnitude 6.0 quake is imminent. He also stationed instruments near the San Andreas fault in Southern California Southern California, also colloquially known as SoCal, is the southern portion of the U.S. state of California. Centered on the cities of Los Angeles and San Diego, Southern California is home to nearly 24 million people and is the nation's second most populated region, and in the Bay Area. In November 1994, one of the Parkfield instruments started showing electromagnetic pulses 10 times the size of typical atmospheric signals. At around the same time, seismometers and other types of monitoring devices stationed at Parkfield also began picking up unusual signals, convincing Fraser-Smith that "things were heating up down there." He drove to Parkfield to repair his other receiver, which had stopped working. A week later, a magnitude 5.0 earthquake struck. His instruments in Southern California did not, however, pick up changes before the disastrous Northridge earthquake on Jan. 17, 1994. Fraser-Smith's modest success at Parkfield and other findings around the world have convinced skeptical seismologists to take a new look at electromagnetic monitoring of faults (SN: 10/21/95, p.260). |
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