Assessing Components of Ground‐Motion Variability from Simulations for the Marmara Sea Region (Turkey)
Résumé
Recent studies have shown that repeatable travel-path terms make a
high contribution to the overall variability in earthquake ground motions. Having maps
of such terms available for a given recording site would, theoretically, allow removal of
this component from the aleatory variability of ground-motion models. The assessment
of such travel-path terms for a given site, however, relies on having recorded a rich set
of earthquakes at that site. Given the relative youth of strong-motion networks, the
assessment of such terms from observations is currently difficult for most parts of
the world. Ground-motion simulations provide an alternative method to assess such
terms. In this article, many dozens of earthquakes, distributed in a grid, are simulated
for the Marmara Sea region (Turkey), which borders the megacity of Istanbul and is an
area of high seismic hazard. Ground motions are simulated within a detailed 3D veloc-
ity structure model using a finite-difference method at 70 recording sites in the area
(
200
×
120
km
2
). Horizontal peak ground velocities from these simulations are re-
gressed to derive a ground-motion model. Next, residuals from this ground-motion
prediction equation are computed to assess repeatable source, site, and path terms
and various components of ground-motion variability. These components are similar
to those derived from real strong-motion data, thereby lending support to those esti-
mates as well as showing the worth of simulations for this type of exercise