Past is Prologue -- Southern San Andreas Fault Reliably Active
Seismologists have recorded earthquakes for a very brief amount of time, relative to the age and activity of the Earth’s faults. Therefore, in order to understand and forecast earthquakes along any fault, scientists must play the role of historical detective to unearth and identify clues to past activity. Katherine M. Scharer, a geologist at Appalachian State University in North Carolina, and colleagues at University of Oregon, US Geological Survey, and University of Nevada at Reno, ranked 316 “event indicators,” or evidence of past ground deformation, for the Southern San Andreas Fault located at Wrightwood, California, during 3000 to 1500 B.C. Scharer and her colleagues have carefully identified and documented 11, and as many as 14, major ground rupturing earthquakes. The frequency of the paleoseismic earthquakes is similar to those previously recognized by her co-authors for the past 1500 years, thus confirming that the most recent rate, an average of 111 years between major earthquakes, holds for the longer time interval stretching 5000 years. The authors’ painstaking work to gather and rank every piece of evidence allows other scientists to assess the quality and quantity of evidence for each prehistoric earthquake and reflects a valuable contribution to seismology.
Seismologists' Advance May Lead to Safer Buildings
As in many other branches of predictive sciences, one important task of seismology is to predict ground motion caused by disastrous earthquakes using physics-based quantitative models. Recent advances in seismology and cyber-infrastructure have made possible large-scale, high-resolution, physics-based predictive earthquake simulations. The largest and most detailed earthquake simulation so far is the "TeraShake" simulation for the Southern San Andreas Fault, which was completed two years ago by the Southern California Earthquake Center (SCEC) scientists. However, the accuracy of predicted ground motion depends heavily upon the accuracy of the underground Earth structure model used in any simulation. Authors Po Chen of Columbia University, Li Zhao of Academia Sinica in Taiwan, and Thomas H. Jordan of University of Southern California, report that they were able to improve the accuracy of the 3D Earth model used in the TeraShake simulation so that the predicted ground motion is accurate up to 1 Hz, which is the frequency most useful for designing high-rise earthquake-resistant buildings. Their research reflects one application of full 3D tomography (F3DT), a new method of producing three-dimensional images of the interior of the Earth.
Please cite the Bulletin of the Seismological Society of America, (Volume 97, Issue 4), as the source of this information.
The Bulletin of the Seismological Society of America (BSSA) is the premier journal of advanced research in earthquake seismology and related disciplines. It first appeared in 1911 and was issued on a quarterly basis until 1963. Since 1963, it has appeared bimonthly (in February, April, June, August, October, and December).
Journal
Bulletin of the Seismological Society of America