Challenges for the Next Generation of Seismic Codes - Earthquake Engineering for Structural Design - page 472

These factors are:
- Earthquake magnitude is one of the fundamental parameters for characterizing
the ground motion. It must be determined using the recorded data for the site,
in function of the recurrence relationship. The magnitude must be specified for
each performance level. Referring to the maximum expected magnitude,
earthquakes can be classified as very strong (M > 8), strong (6.5 < M < 8),
moderate (4.5 < M < 6.5) and low (M < 4.5).
- Near-source effects are very great in case of crustal earthquakes, considering
all the characteristics of this special situation, in which the velocity of pulse,
period of pulse, number of pulses, vertical components, etc. play a very
important role in design provisions. In particular:
- Pulse type, in the sense that velocity pulse or acceleration pulse must be
considered;
- Number of pulses is very important to know if the ground motions are
characterized by much reduced number of pulses (only one or two pulses),
reduced (for 3 to 4 pulses) or by a large number of pulses (5 to 10 pulses or
more, in some special cases);
- Period of pulses, which can by very long (over 3 to 4 sec), long (1 to 3 sec)
and short (less than 1 sec).
- Spectrum type, characterized by corner period and amplification for short
periods, knowing that the differences in earthquake type are marked also by
this aspect, due to the importance of high vibration modes. Two normalized
spectra types are recommended to be used (available also in EUROCODE 8
(Fig. 10.1): Type 1 proposed for large magnitude earthquakes and Type 2 for
moderate magnitude earthquakes.
- Effects of soil conditions. In function on source type, the effects are different.
The effects can be very great, great and moderate.
- Duration of ground motions has a great influence on structure damage and
collapse type. It can be very long (over 90 sec), long (under 90 sec), moderate
(under 60 sec) and short (under 30 sec).