principles and applications of microearthquake networks

9. Discussion
Microearthquake studies have grown tremendously in the last two decades.
The use of microearthquakes as a tool in understanding tectonic
processes was recognized in the 1950s. Permanent networks and portable
arrays were developed specifically for studying microearthquakes. Telemetry
transmission was tested and proved feasible. In the 1960s, instrumentation
development for telemetered microearthquake networks
was started. Many data acquisition and processing procedures were automated,
including hypocenter locations by computers.
With funds available for research in earthquake hazards reduction (especially
for earthquake prediction), many microearthquake networks
were established in the 1970s. Telemetry transmission and centralized
recording systems were improved. Much effort went into streamlining
data acquisition and processing procedures, but progress has been slow.
More intensive use of computers to analyze microearthquake data increased
our knowledge about the distribution of microearthquakes and
their relation to the faulting process. However, we also learned that microearthquake
networks can generate far greater amounts of data than
can be coped with effectively. To help solve this problem, a combined
effort by the USGS and several universities to develop interactive computing
facilities for microearthquake networks has been undertaken by
P. L. Ward and colleagues (1980). There is also an increasing use of
digital electronics and microprocessors to collect, process, and analyze
microearthquake data (see, e.g., Allen and Ellis, 1980: Prothero, 1980).
The capital cost for either a permanent station or a temporary station is
about $SoOO. The total operating cost for a permanent station is also about
$5000 per year, and that for a temporary station may be a few times more.
Given a limited amount of financial support, it may not be effective to
operate a dense microearthquake network of permanent stations over a
large area. An alternative is to have a relatively sparse network of permanent
stations and to use a mobile array of temporary stations that provides
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