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Abstract:
We provide a preliminary report on seismicity before and after the 2023 M7.8 and M7.5 earthquake sequence.
One feature for seismicity during 2013-2022 was the 2020 M6.8 earthquake (data from KOERI-RETMC, in Bogazici University). Aftershocks since the M6.8 earthquake suggest that the south end of the M6.8 rupture was close to the north end of the M7.8 rupture. Another feature is a seismic swarm on and around the fault segment, from which the M7.8 rupture was initiated. On this segment, an area of large slip (~1.3 m) was overlapped with this swarm. Since late 2022, this swarm was activated, with a clear decrease in the Gutenberg-Richter b-value to b=0.7~0.8, indicative of an increase in stress. In-depth analyses to verify whether the b-value in the large-slip area pronouncedly decreased preceding its occurrence need to be performed, as in the case for the 2011 M9 Tohoku-oki earthquake in Japan (Nanjo et al., 2011).
Comparing with the stress imparted by the M7.8 and M7.5 earthquakes (Toda et al., 2011, 2023), we noted the lack of post-M7.5-quake seismicity at the zone of increase in stress beyond the north end of the M7.8 rupture and that this area lacking in seismicity closely matched to the area of the M6.8 rupture. Future activation that extends to the north on the East Anatolian Fault is unlikely. We will tackle the question whether parts of this fault farther to the north, beyond the M6.8 rupture area, and next to the south of the M7.8 rupture area, may show future activation.
