Publication Date:
2004
Description:
Earthquake hazard in the Marmara Region, Turkey has been investigated using
time-independent probabilistic (simple Poissonian) and time-dependent probabilistic
(renewal) models. The study culminated in hazard maps of the Marmara Region depicting
peak ground acceleration (Peak ground acceleration) and spectral accelerations (SA)'s at
0.2 and 1 s periods corresponding to 10 and 2% probabilities of exceedance in 50 yrs.
The historical seismicity, the tectonic models and the known slip rates along the faults
constitute the main data usedin the assignment. Based on recent findings it has been
possible to provide a fault segmentation model for the Marmara Sea. For the main Marmara
Fault this model essentially identifies fault segments for different structural,
tectonic and geometrical features and historical earthquake occurrences. The damage
distribution and pattern of the historical earthquakes have been carefully correlated
with this fault segmentation model. The inter-event time period between characteristic
earthquakes in these segments is consistently estimated by dividing the seismic slip
estimated from the earthquake catalog by the Global Positioning System-derived slip rate
of 22+/-3 mm/yr. The remaining segments in the eastern and southern Marmara region are
also identified using recent geological, geophysical studies and historical earthquakes.
The model assumes that seismic energy along the segments is released by characteristic
earthquakes. For the probabilistic studies characteristic earthquake based recurrence
relationships are used. Assuming normal distribution of inter-arrival times of
characteristic earthquakes, the 'mean recurrence time', 'covariance' and the 'time since
last earthquake' are developed for each segment. For the renewal model, the conditional
probability for each fault segment is calculated from the mean recurrence interval of
the characteristic earthquake, the elapsed time since the last major earthquake and the
exposure period. The probabilities are conditional since they change as a function of
the time elapsed since the last earthquake. For the background earthquake activity, a
spatially smoothed seismicity is determined for each cell of a grid composed of cells of
size 0.005degree~0.005degree. The ground motions are determined for soft rock (NEHRP B/C
boundary) conditions. Western US-based attenuation relationships are utilized, since
they show a good correlation with the attenuation characteristics of ground motion in
the Marmara region. The possibility, that an event ruptures several fault segments (i.e.
cascading), is also taken into account and investigated by two possible models of
cascading. Differences between Poissonian and renewal models, and also the effect of
cascading have been discussed with the help of Peak ground acceleration ratio maps.
Keywords:
Earthquake hazard
;
Fault zone
;
NAF
;
Marmara
;
region,
;
peak
;
ground
;
acceleration
;
Peak ground acceleration
;
SDEE
