Field Instrumentation - Geotechnical Engineering Investigation - page 331

(a)

(e)

(h)

(j)

(m, n, q, x, r)

FIGURE 4.43
Instrumentation to monitor fault movements. Legend: (a) precise leveling and GPS; (e) tiltmeter; (h) strain
meter; (j) accelerometer; (m) deflectometer; (n) shear-strip indicator; (q) acoustical emission device; (r)
piezometer; (x) stress meter.

4.5.7 Fault Movements

Objectives
Earthquakes have been associated with fault rupture (see Section 11.3.1), which may be
preceded by ground warping, slippage along the fault, and increase in ground stresses
and pore-water pressures. Fault monitoring is still in its experimental stages; eventually,
some basis for predicting or anticipating rupture may be developed (see Section 11.2.8).

Instrumentation
Ground warping and fault movements on local and regional scales are monitored by sev-
eral groups: NASA's Jet Propulsion Laboratory at Caltech, the U.S.G.S., and the California
Geological Survey. The source data include information from GPS ( Section 4.2.2) and Insar
data ( Section 2.2.3) as well as land-based and field geologic data (Chamot, 2003).
Surface indications of displacement along the San Andreas Fault are monitored by an
early warning system set up by NOAA's Earthquake Mechanism Laboratory at Stone
Canyon, California (Figure 4.43). The system consists of an interconnected 20 m triangular
array of mercury pools set in piers attached to Invar rods to monitor tilting (e) and strain
meters consisting of three 30-m-long extensometers (h) to measure creep (Bufe, 1972).
Accelerometers (j) set on the surface monitor ground motion accompanying fault activity.
Subsurface deformations may be monitored with deflectometers (m) and shear strips (n)
installed in boreholes across the fault, set to sound alarms if desired. Stress meters (x) mon-
itor stress increase, as does the acoustic-emissions device (q) on a qualitative basis, when
set in or near the fault zone. Piezometers (r) set in the fault zone monitor water pressures
that may indicate stress changes in the rock mass.

References

Blackwell, G., Pow, D. and Klast, L., Slope Monitoring at Brenda Mine, Proceedings of the 10th Canadian
Rock Mechanics Symposium , Kingston, Ontario, Sept., 1975, pp. 45-79.
Brawner, C. O., Case examples of instability of rock slopes, J. Assoc. Prof. Eng., British Columbia,
Feb. 26, 1975.
Broms, B. B., Landslides, Foundation Engineering Handbook , Winterkorn, H.P. and Fang, H.-Y., Eds.,
Van Nostrand Reinhold Publishers, New York, 1975, chap. 11.