Earthquakes - Geotechnical Engineering Investigation - page 907

the peak inertial force imparted by strong shaking to a structure founded on the ground
surface and to the peak shear stress induced within the ground itself. Peak vertical ground
acceleration (PVGA) and peak horizontal ground velocity (PHGV) are used in some engineer-
ing analyses to characterize the damage potential of ground motions to buildings. The peak
horizontal ground displacement (PHGD) may be used in the analysis of retaining walls, tun-
nels, and buried pipelines.
It is noted, however, that the recorded peak ground acceleration (PGA) is for an accelero-
graph placed at a particular location with particular conditions. Since accelerographs are
now placed in arrays in many locations, isobars of recorded “ g s” can be prepared.
Earthquakes with strong ground motions, recorded as of 1975, are summarized in
Table 11.3. In the United States, El Centro (1940) remained for many years the severest
ground motion recorded (0.32 g ). The recording station was located 4 mi from the fault
break. During the Parkfield event (1966) of M

5.6, accelerations of 0.5 g were recorded,
but the acceleration was a single strong pulse. During the San Fernando quake (1971,
M 6.5), an accelerograph registered the highest acceleration ever recorded at that time: in

the 0.5 to 0.75 g range with peaks over 1.0. The instrument was located on the abutment of
the Pacoima Dam, about 6 mi south of the epicenter, which was undamaged. Local topog-
raphy and the location, are believed to have influenced the very high peak acceleration
(Seed et al., 1975). PGA

≈ 0.8 g was recorded for the Northridge event (1994, M w 6.7) and

the Kobe event (1995, M w 6.9).

Network installations in the United States as of 2002 are given in Figure 11.8.
Improvements in the instrument and costs has resulted in installations worldwide, and as
of the year 2000 over 10,000 instruments were operating worldwide. The USGS is
installing new networks under the “Advanced National Seismic System” (ANSS) with

TABLE 11.3
Earthquakes with Strong Recorded Ground Acceleration a

Recording Station Horizontal Component Maximum Remarks

Distance to Acceleration

Epicenter (E) or (% gravity)

Fault (F), km

May 16,1968, Japan; magnitude 7.9

Hachinohe ca. 200 (E) N-S 24 Port area. Small shed

E-W 24 Soft soil

July 21, 1952, Kern County, California; magnitude 7.7

Taft 40 (E) N21°E 15 In service tunnel between

S69°E 18 buildings. Alluvium

October 17, 1966. Peru; magnitude 7.5

Lima 200 (E) N08°E 42 Small building. Coarse

N82°W 27 dense gravel and boulders

April 13, 1949, Puget Sound, Washington; magnitude 7.1

Olympia 16 (E) S04°E 16 Small building. Filled land

S86°W 27 at edge of Sound. Focal

depth h 50 km

December 11, 1967, India; magnitude 6.5

Koyna Dam 8 (E) Along dam axis. 63 Dam gallery

Normal dam axis. 49

( Continued )