Learning from Earthquakes - Earthquake Engineering for Structural Design - page 77

defined. There are some main faults along the Circum-Pacific Ring and
Alpide-Himalayan belt, which regularly produce great earthquakes.
- The positions of blind faults producing intraplate earthquakes are more
difficult to be detected, being inactive for many years, but potentially they
occur in near stable continental regions. The presence of a recently
discovered, inactive until now, blind fault in the western area of Timisoara
City, Romania, (Fig. 3.3) creates many problems to structural designers.
The 1976 Tangshan China earthquake (250,000-660,000 fatalities) is an
example of the damaging potential of this earthquake type. Unfortunately,
the geological basis for intraplate seismogenesis is still poorly understood.
A truth is established concerning these earthquake types: the presence of a
fault potentially indicates a possible earthquake, but it is not sure that this
will occur in the future.
- The interplate earthquakes occur in some very long fault zones, which
appear to be segmented. So, the sources move from a segment to another,
the case of the San Andreas, Mexican and Anatolian faults being
significant for these migratory earthquakes. Figure 3.4 shows the case of
the Anatolian fault, where the produced earthquakes advance from East to
West, indicating the strike-slip direction of the fault movement.
- Generally, the boundary plate contacts are characterized by the presence of
many parallel or diffuse faults, which can produce large earthquakes at the
same level as the principal fault. The well-known San Andreas Fault has
some parallel faults as Hayward, Rodgers, Calaveras, Greenville, and San
Gregory. One can see that the probability now of the occurrence of a
strong earthquake (the waiting Big One ) is higher for Hayward fault than
for San Andreas (Fig .3.5).
Figure 3.3 The map of Timisoara City, Romania, with the inactive, until now,
Western fault