Geoscience Reference
In-Depth Information
Figure 4.16.
Jeffreys-
Bullen (J-B) travel-time
curves for an earthquake
focus at the surface, with
some modifications. Such
curves are usually
accurate to within a few
seconds. The epicentral
distance is the angle
subtended by the
earthquake epicentre and
seismometer at the centre
of the Earth. (After Bullen
and Bolt (1985).)
Figure 4.17.
Examples of
long-period earthquake
records. Z is the vertical
component and N (north)
and E (east) are the two
horizontal components.
Time marks (dots) are
every minute. The
recordings are made in
ink on a rotating drum -
hence the other traces
above and below the
earthquake. (a) Offshore
Nicaragua, focal depth
70 km, surface wave
magnitude 5.7, recorded
in New York. Note the
clear dispersion of the
Raleigh waves. (b)
Northern Chile, focal
depth 129 km, surface
wave magnitude 6.5,
recorded in New York.
(From Simon (1981).)
