Alkan, Hamdi; Öztürk, Serkan; Bektaş, Özcan; Büyüksaraç, Aydın

The Marmara Region is an active tectonic region in northwestern Türkiye, which comprises some important strike-slip active fault mechanisms and important tectonic units, located near the western part of the North Anatolian Fault Zone. In the historical and instrumental period, the Marmara Region experienced large/devastating earthquakes. Considering this continuous activity, in this study, we investigate the tectonic structure and performed future seismic hazard estimation of the region based on some seismotectonic parameters. For this evaluation, we plot the Coulomb stress change maps of 1912 Mürefte-Şarköy, 1953 Yenice-Gönen and 1999 İzmit mainshocks with the earthquakes (MW ≥ 4.5) that occurred in the study region after 2003. For the estimation of b-value, occurrence probabilities and return periods of earthquakes, we used a homogenous local seismicity catalogue consisting of 119.029 events for the period between 1912 and 2023. In the findings of this study, the lower b-values and increasing Coulomb stress changes which are trigger stress failure compatible are observed in the west and northwest of the Marmara Sea. In contrast, the higher/moderate b-values and decreasing Coulomb stress values are observed in the east and southeast of the Marmara Sea. The results of probability assessments show that an earthquake with Mw = 6.5 may occur with a probability of 98% in the west of the Marmara Sea after 2025. As a remarkable fact, a comprehensive assessment of these types of variables will supply important findings for earthquake hazard and potential in the study region.

Senkaya, Mustafa; Alkan, Hamdi; Öztürk, Serkan; Büyüksaraç, Aydın

The 6 February 2023 Mw 7.7–7.6 Kahramanmaraş earthquake sequence has significantly impacted the East Anatolian Fault zone, including the city of Malatya and its immediate surroundings. In addition to the aftershocks of February 2023, the Mw 5.9 Kale earthquake that occurred on October 16, 2024, further underscores the ongoing seismic activity in the region. This study analyzes the distribution of b-values derived from a comprehensive dataset comprising 14,549 earthquakes and the Coulomb stress variations associated with the aftershocks of the February 2023 sequence and the Kale earthquake. The primary objective of this analysis is to enhance the understanding of the tectonic setting that contributed to the occurrence of the Kale earthquake. The findings indicate that the low b-values and stress transfer through the Pütürge segment toward the unnamed fault near Kale are significant contributing factors to the occurrence of the Kale earthquake. Additionally, positive stress variations from Doğanşehir to Malatya’s city center suggest a potential fault oriented toward the city center that may increase the current earthquake hazard. Furthermore, the distribution of seismic events around Malatya suggests a possible barrier supported by previous magnetic data analysis between Malatya and Kale. Lastly, the observed stress variations for the Kale earthquake indicate the likelihood of upcoming seismic events in both the northeast and southwest directions of the Kale.