principles and applications of microearthquake networks

222 8. Applications for Earthquake Prediction
suggested that the locations and the focal mechanisms for the foreshock
pair and for the main shock pair were identical. However, the P-wave
spectra were consistent with a northwest direction of rupture for the
foreshocks, and a southeast direction of rupture for the main shocks.
Ishida and Kanamori (1980) examined the spectra of some pre-1949
background earthquakes and of foreshocks preceding the magnitude 7.7
Kern County, California, earthquake of July 21, 19.52. The frequency of
the spectral peak was found to be systematically higher for the foreshocks
than for the events occurring before 1949. They suggested that this result
was consistent with a model of stress concentration around the eventual
hypocenter of the main shock.
Note Added in Proof
In May, 1980, a symposium on earthquake prediction was held in New
York, hosted by the Lamont-Doherty Geological Observatory of Columbia
University. A collection of 51 research papers from this symposium
has just been published:
Simpson, D. W., and Richards, P. G., eds. (1981). "Earthquake Prediction,
an International Review,'' American Geophysical Union, Washington,
D.C.
Major topics in this volume include: seismicity patterns, geological
and seismological evidence for recurrence times along major fault zones,
seismic and nonseismic long-term and intermediate-term precursors to
earthquakes, short-term and immediate precursors to earthquakes, theoretical
and laboratory investigations, and reviews of national programs
in Japan, China, and the United States.