Civil Engineering Reference
In-Depth Information
FIGURE 3.11
Another view of the collapsed bridge north of Fengyuen caused by surface fault rupture
associated with the Chi-chi (Taiwan) earthquake on September 21, 1999. Note that the surface faulting has
created the waterfall on the right side of the bridge. (
Photograph from the USGS Earthquake Hazards
Program, NEIC, Denver.
)
collision zones (Fig. 2.7), the plates collide into one another, causing the ground surface to
squeeze, fold, deform, and thrust upward.
Besides uplifting, there could also be regional subsidence associated with the earth-
quake. There was extensive damage due to regional subsidence during the August 17, 1999,
Izmit earthquake in Turkey. Concerning this earthquake, the USGS (2000a) states:
The
M
w
7.4 [moment magnitude] earthquake that struck western Turkey on August 17,
1999 occurred on one of the world's longest and best studied strike-slip faults: the east-west
trending North Anatolian fault. This fault is very similar to the San Andreas Fault in California.
Turkey has had a long history of large earthquakes that often occur in progressive adjacent
earthquakes. Starting in 1939, the North Anatolian fault produced a sequence of major earth-
quakes, of which the 1999 event is the 11th with a magnitude greater than or equal to 6.7.
Starting with the 1939 event in western Turkey, the earthquake locations have moved both
eastward and westward. The westward migration was particularly active and ruptured 600 km
of contiguous fault between 1939 and 1944. This westward propagation of earthquakes then
slowed and ruptured an additional adjacent 100 km of fault in events in 1957 and 1967, with
separated activity further west during 1963 and 1964. The August 17, 1999 event fills in a 100
to 150 km long gap between the 1967 event and the 1963 and 1964 events.
The USGS also indicated that the earthquake originated at a depth of 17 km (10.5 mi)
and caused right-lateral strike-slip movement on the fault. Preliminary field studies found
that the earthquake produced at least 60 km (37 mi) of surface rupture and right-lateral off-
sets as large as 2.7 m (9 ft).
