7. International Earth Science Colloquium on the Aegean Region, no.0, ss.79-83, 2020 (Düzenli olarak gerçekleştirilen hakemli kongrenin bildiri kitabı)
The Bodrum-Kos earthquake initiated a long-lasting debate on the dip of the fault plane where authors give arguments
both on a south-dipping and north dipping planes. Here, we contribute to the subject by using Coulomb stress change
estimation technique as a tool to discriminate between the two nodal planes. The stress changes associated with a
mainshock primarily dependent on the properties of the source model.
A large variety of fault planes solutions have been derived for the Bodrum-Kos mainshock mechanism showing faults
striking from NNW-SSE to NNE-SSE, rakes indicating oblique to pure normal faulting and also mechanisms
portraying from shallow to steeply dipping planes.
As such, here we first try to establish a source model based on near-field data and then use that model to estimate the
Coulomb stress changes. The resulting stress maps estimated for the optimally oriented strike-slip and normal faults
are compared with the aftershock distributions to see which of the nodal planes provide better correlation with the
region of increased stresses.
A near-field five-station strong motion network located in Bodrum Peninsula has been used to infer a rupture model
for the July 20th, 2017 Bodrum-Kos earthquake. The accelerometric stations of the local network are located on the
hanging wall of the plane extending northeast from its surface trace located offshore Kos island. The data used have
been augmented including nearby accelerographs operated by AFAD and NOA-EIDA node.
Thus acquired mainshock accelerograms have been integrated twice to get displacements which were then inverted to
their sources to retrieve source parameters for the mainshock through searching for the best CMT location on a 3-D
grid scheme. The results indicate that the best CMT point is located at 6 km depth and shows predominantly normal
faulting mechanism with a considerable strike-slip component; where left-lateral strike-slip motion has been derived
on the nodal planes striking NW-SE and dipping NE, while the sense of motion is right-lateral-strike-slip on the plane
extending NE-SW and dipping SW.
A 50x20 km fault plane has been parameterized to have 40 elements each of 5x5 km size; 10 of them are located along
the strike and 4 along the dip. Ultimately, the best fit CMT parameters have been utilized to get a slip distribution
model where the moment release on each sub-fault is derived; essentially, needed for Coulomb failure stress
The results indicate that the Coulomb stress changes associated with the northeast dipping nodal plane show very well
fit between the aftershock distributions taking place to the NE of the ruptured fault plane and the region of increased
coulomb failure stress changes estimated for the optimally oriented normal and strike-slip faults. Despite the distance
to the ruptured fault plane and the time delay since the origin of the mainshock those off-fault events can be classified
as aftershocks taking into account space and time window length for Mw=6.6 event.