14:15 〜 14:30
[S09-26] 2023年2月6日にトルコで発生したM7.8とM7.5の地震前後の地震活動について
On February 6, 2023 (UTC), a devastating M7.8 earthquake struck the East Anatolian Fault zone (EAFZ) bounding the Arabian and Anatolian tectonic plates. Nine hours later, a M7.5 earthquake occurred about 90 km NNW of the initial M7.8 earthquake. We provided a report on seismicity before and after the M7.8 and M7.5 earthquakes. To create it, we used three earthquake catalogs created by the Disaster and Emergency Management Authority (AFAD), Lomax (2023), and Kwiatek et al. (2023), to demonstrate that the result does not depend on the choice of catalog.
One feature of the seismicity before the M7.8 and M7.5 earthquakes is the 2020 M6.8 earthquake. 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 was the occurrence of two seismic swarms on and around the fault segment, from which the M7.8 rupture had initiated. On this segment, an area of a large slip (~1.3 m) overlapped with one of the swarms. The swarms began in mid-2022, and statistical analysis using the Epidemic-Type Aftershock Sequence model revealed that the occurrence rate after the start of the swarms (1.3 events of M1.5+ per day) was significantly larger than that before it (0.3 events of M1.5+ per day). We also observed a clear decrease in the Gutenberg-Richter b-value since the start of the swarms. This infers an increase in stress, assuming that the b-value is negatively correlated with differential stress.
We pointed out three features pertaining to seismicity after the M7.8 and M7.5 earthquakes. The first feature is the lack of post-M7.5-quake seismicity at the zone of increase in Coulomb stress imparted by the M7.8 and M7.5 earthquakes beyond the north end of the M7.8 rupture, noting that this area, which lacked seismicity, closely matched the area of the M6.8 rupture. The second feature is that due to stress transfer by the M7.8 and M7.5 quakes, future rupture was promoted around the south end of the M7.8 rupture, where the largest aftershock of M6.4 occurred on February 20, 2023. A map view that shows data of post-M7.5-quake seismicity until immediately before the M6.4 earthquake reveals a zone of low b-values around the future hypocenter. That zone coincided remarkably with the region where future rupture was promoted. The third feature is based on a comparison between the distribution of b-values based on seismicity after the M6.4 earthquake and the distribution of the faults of the M7.8 and M7.5 earthquakes. The spatial pattern in b generally shows high b-values around the causative faults (indicative of stress relieved by these earthquakes), except for two zones beyond the north end of the M7.8 rupture: one is the rupture area of the 2020 M6.8 earthquake and the other is a part of the EAFZ farther to the north, beyond the M6.8 rupture area. We will tackle the question of whether these two zones may show future activation.
One feature of the seismicity before the M7.8 and M7.5 earthquakes is the 2020 M6.8 earthquake. 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 was the occurrence of two seismic swarms on and around the fault segment, from which the M7.8 rupture had initiated. On this segment, an area of a large slip (~1.3 m) overlapped with one of the swarms. The swarms began in mid-2022, and statistical analysis using the Epidemic-Type Aftershock Sequence model revealed that the occurrence rate after the start of the swarms (1.3 events of M1.5+ per day) was significantly larger than that before it (0.3 events of M1.5+ per day). We also observed a clear decrease in the Gutenberg-Richter b-value since the start of the swarms. This infers an increase in stress, assuming that the b-value is negatively correlated with differential stress.
We pointed out three features pertaining to seismicity after the M7.8 and M7.5 earthquakes. The first feature is the lack of post-M7.5-quake seismicity at the zone of increase in Coulomb stress imparted by the M7.8 and M7.5 earthquakes beyond the north end of the M7.8 rupture, noting that this area, which lacked seismicity, closely matched the area of the M6.8 rupture. The second feature is that due to stress transfer by the M7.8 and M7.5 quakes, future rupture was promoted around the south end of the M7.8 rupture, where the largest aftershock of M6.4 occurred on February 20, 2023. A map view that shows data of post-M7.5-quake seismicity until immediately before the M6.4 earthquake reveals a zone of low b-values around the future hypocenter. That zone coincided remarkably with the region where future rupture was promoted. The third feature is based on a comparison between the distribution of b-values based on seismicity after the M6.4 earthquake and the distribution of the faults of the M7.8 and M7.5 earthquakes. The spatial pattern in b generally shows high b-values around the causative faults (indicative of stress relieved by these earthquakes), except for two zones beyond the north end of the M7.8 rupture: one is the rupture area of the 2020 M6.8 earthquake and the other is a part of the EAFZ farther to the north, beyond the M6.8 rupture area. We will tackle the question of whether these two zones may show future activation.