principles and applications of microearthquake networks

8.1. Seistnicit~ Pritterns 199
made for their potential usefulness, but their success in predicting earthquakes
has been rather limited. Because of the extensive literature on
this subject and the impetus these early studies gave to the search for
other predictors, we have devoted a section to it. Temporal variations of
many other seismic parameters, such as b-slopes and focal mechanisms,
have also been investigated and will be summarized in a later section.
In this chapter, we discuss earthquake prediction based largely on data
from microearthquake networks, although many seismic precursors were
identified by using data from regional or global networks. In either case,
most precursors were not discovered until after the earthquakes had occurred.
One exception is the case for the recent Oaxaca, Mexico, earthquake.
An announcement of a forthcoming major earthquake near Oaxaca
was published in the scientific literature before its occurrence. By
studying seismicity patterns of shallow earthquakes located from teleseismic
data, Ohtake et id. (1977) identified a seismic gap along the west
coast of southern Mexico. This allowed them to estimate the magnitude
and the location of an earthquake that would occur in the gap. Because
they had no reliable basis for predicting the time of occurrence, they urged
that a program including monitoring microearthquake activity be carried
out in the Oaxaca region. On the other hand, Garza and Lomnitz (1978)
argued on the basis of statistical methods applied to the seismicity data,
that the evidence for a seismic gap near Oaxaca was inconclusive. However,
Garza and Lomnitz had no doubt that a large earthquake would
occur near Oaxaca sooner or later.
Following the suggestion by Ohtake et (11. (1977), a portable microearthquake
array was deployed in the Oaxaca region in early November,
1978 by K. C. McNally and colleagues. A major earthquake (M, = 7.8)
occurred within the array on November 29, 1978, as anticipated (Singh et
nl., 1980). According to McNally , the microearthquake array provided
unique data for studying the foreshock-main-shock-aftershock sequence.
Readers may refer to articles in Geojisica Internacional 17, numbers 2 and
3, 1978, for details.
8.1. Seismicity Patterns
At least three problems are involved in the st dy of seismicit I patterns
for earthquake prediction. First, can past occurrences of earthquakes be
used to predict a large earthquake? Second, can the search for spatial and
temporal patterns of seismicity be more systematic and more objective?
Can pattern recognition techniques developed in other scientific disciplines
be adapted to earthquake prediction research? Are the space-time