Geoscience Reference
In-Depth Information
(a)
N
(b)
N
E
W
W
E
(c)
Figure 4.54.
(a) Directions of first motion for an earthquake that occurred in Iran. •,
compression (positive); ◦, dilatation (negative). (b) Directions of first motion for an
earthquake that occurred in the Eastern Atlantic. (c) An equal-area (Schmidt) net.
12. Figures 4.54(a) and (b) give the directions of first motion for two earthquakes, plotted
on equal-area projections of the lower focal hemisphere. For each earthquake, do the
following.
(a) Draw the two perpendicular planes that divide the focal sphere into positive and
negative regions.
(b) Find the strike and dip of these planes.
(c) Plot the horizontal component of strike.
(d) Discuss the mechanism of the earthquake.
N.B. Yo u will need to photocopy and enlarge the equal-area projections.
