A:
A seismometer is the
internal part of the
seismograph, which may
be a pendulum or a
mass mounted on a
spring; however, it is
often used
synonymously with
"seismograph".
Seismographs are
instruments used to
record the motion of
the ground during an
EQ--installed in the
ground throughout the
world and operate as
seismographic network.
The first one was
developed in 1890. The
earliest "seismoscope"
was invented by the
Chinese philosopher
Chang Heng in A.D.
132. This did not
record earthquakes,
however. It only
indicated that there
was one occurring.
A seismograph is
securely mounted onto
the surface of the
earth so that when the
earth shakes, the
entire unit shakes
with it, EXCEPT for
the mass on the spring
which has inertia, and
remains in the same
place. As the
seismograph shakes
under (in the example
below) the mass, the
recording device on
the mass records the
realtive motion
between itself and the
rest of the
instrument, thus
recording the ground
motion. In reality,
these mechanisms are
no longer manual, but
instead work by
measuring electronic
changes produced by
the motion of the
ground with respect to
the mass.
