1. First we will look at the
northwest
fault map. The northern part of this area is dominated by the
right-lateral motion along the San Andreas fault (shown in red). Here,
the plates are sliding past one another in almost the exact orientation
of this great fault -- the land on the left (west) side of the San Andreas
fault is moving toward the northwest, and the land on the right (east)
side of it is moving southeast. The southern part shows the western end of
the Transverse Ranges, created by the compression of the "Big Bend" of
the San Andreas fault. Some faults in this area also work to
move material laterally out of the way of that compressional force.
Among them is the Garlock fault (shown in bright yellowish-green
in the lower right corner of the map), the longest left-lateral
fault in southern California.
Given this information, how many tries do you need to find:
2. Next, we'll go to the
Mojave fault map.
The southern part of this map -- the area around the "Big Bend" of
the San Andreas, is the site of compression and of some motion conjugate
to that of the San Andreas fault (again, in red). Near the top
of the map lies the left-lateral Garlock fault, also conjugate in
motion to the San Andreas fault. The Garlock fault marks the northern
boundary of the Mojave -- to its north, the tectonic environment
changes. Throughout the middle of the map, the faults are influenced
primarily by the Eastern California Shear Zone, an area marked by
right-lateral slip trending southeast to northwest -- roughly parallel
to that part of the San Andreas not involved in the "Big Bend" --
which connects with the San Andreas left of center just off the bottom
of the map. You will note that near center at the bottom, the
San Andreas fault splits up, denoted with slightly different
shades of red. We will see this again on the southern fault map.
Knowing this, see how many tries it takes to find:
3. Now, on to the Los Angeles area fault map. Los Angeles sits south of the "Big Bend" of the San Andreas. At the very top of the map, you can see the intersection of the Garlock and San Andreas faults. The action of the Garlock fault is probably responsible for the low number of faults north of this stretch of the San Andreas fault. To the south, however, things are not at all simple. Compression, in a roughly north-south direction, is the dominant force in this area, but as with the Garlock fault, some faults here also work to move material away from the collision zone. Along the bottom of this map, and in the lower left-hand corner the influence of the "Big Bend" begins to fade. One more hint before you start: the long, blue fault in the middle of the map is the steeply-dipping San Gabriel fault. Only the western section of this fault seems to show recent surface rupture.
Keeping all this in mind, how many tries do you need to find:
4. The southern
fault map is the next game board.
The northern part of this map covers the confusing split
of the San Andreas fault zone in the San Gorgonio Pass area (north
and northwest of Palm Springs). The strands of the San Andreas fault
(shown in different shades of red) rejoin near Indio, at the southeastern
end of the Big Bend. Around this area, the effects of the Big Bend
are reflected in nearby fault motions. The rejoining of
the San Andreas strands occurs near the point where the Eastern
California Shear Zone (which we saw on the Mojave map) branches off
from the plate boundary. The rest of the map is dominated by
right-lateral shearing motion of the plates in a
northwest-to-southeast direction. One of the largest right-lateral
faults in southern California is the San Jacinto fault, shown here
in purple, with numerous branches. Note how this major right-lateral
fault intersects with the San Andreas fault. How might such an
intersection affect faults within the acute intersecting angle --
in other words, what kinds of stresses would result from this
intersection?
5. Finally, look at the
Basin and
Range fault map. This is a tectonic region bounded to the south
by the left-lateral Garlock fault, and to the west by the
Sierra Nevada fault zone, a large zone of normal faulting shown in
dark blue (the Independence fault, in a brighter blue, is a part
of this fault zone). The region is characterized by extension
in a roughly east-west direction and by right-lateral shearing
in a north-south direction. Consequently, right-lateral
and normal slip dominate, often combining to yield right-normal
faulting. You will note that the San Andreas is not visible on this
map, and yet the right-lateral shearing transferred to this region
by the Eastern California Shear Zone reveals the nature of the
plate boundary a few hundred kilometers away. One last tip:
paying attention to the topography can really help you on this map.
With this knowledge as your guide, how many attempts will it take you to find: