Abstract
Since their development in the 1960s, seismic arrays have given a
new impulse to seismology. Recordings from many uniform seismometers
in a well-defined, closely spaced configuration produce high-quality
and homogeneous data sets, which can be used to study the Earth's
structure in great detail. Apart from an improvement of the signal-to-noise
ratio due to the simple summation of the individual array recordings,
seismological arrays can be used in many different ways to study
the fine-scale structure of the Earth's interior. They have helped
to study such different structures as the interior of volcanos, continental
crust and lithosphere, global variations of seismic velocities in
the mantle, the core-mantle boundary and the structure of the inner
core. For this purpose many different, specialized array techniques
have been developed and applied to an increasing number of high-quality
array data sets. Most array methods use the ability of seismic arrays
to measure the vector velocity of an incident wave front, i.e., slowness
and back azimuth. This information can be used to distinguish between
different seismic phases, separate waves from different seismic events
and improve the signal-to-noise ratio by stacking with respect to
the varying slowness of different phases. The vector velocity information
of scattered or reflected phases can be used to determine the region
of the Earth from whence the seismic energy comes and with what structures
it interacted. Therefore seismic arrays are perfectly suited to study
the small-scale structure and variations of the material properties
of the Earth. In this review we will give an introduction to various
array techniques which have been developed since the 1960s. For each
of these array techniques we give the basic mathematical equations
and show examples of applications. The advantages and disadvantages
and the appropriate applications and restrictions of the techniques
will also be discussed. The main methods discussed are the beam-forming
method, which forms the basis for several other methods, different
slant stacking techniques, and frequency-wave number analysis. Finally,
some methods used in exploration geophysics that have been adopted
for global seismology are introduced. This is followed by a description
of temporary and permanent arrays installed in the past, as well
as existing arrays and seismic networks. We highlight their purposes
and discuss briefly the advantages and disadvantages of different
array configurations.
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