Figure 3 1906
Another earthquake with movement along the same fault in 1906 causes further offset of the course of the stream.
Soil and sand will continue to bury and cover up parts of the 1857 (b), and the 1906 (c) offset. A shallow trench
(line G-H) cut parallel to and south of the fault in 1994 might show the following relationship (Figure 4) on the
southern side of the trench:
SECTION VIEW
Ground surface
Figure 4 Trench Log 1, 1994
The rate of movement and timing of earlier earthquakes can be determined from the age of the sand and gravel
deposits in the stream channel.
If a second longer and deeper trench is excavated in the area of trench G-H, the following log might be obtained
(Figure 5):
SECTION VIEW
Figure 5 Trench Log 2, 1994
A G U
/
F E M A
86
S
E I S M I C
S
L E U T H S
