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.

Aktaş, Gülten

The present study aims to determine submarine structural elements by analysing high-resolution magnetic data sets and to examine the impact of geological surface structures characterizing Lake Sapanca. Lake Sapanca is located on the northern branch of the North Anatolian Fault Zone. The study area and its immediate surroundings are located within the most active tectonic structure of Turkey. A magnetic study was carried out in Sapanca Lake to reveal the structural elements that caused the formation of the lake. Diurnal corrections were applied to the magnetic data. During the analysis of the marine magnetic data set, there are variations in the mean field level of the magnetic field caused by the routing effects of ship noise on the measurements. To eliminate this noise effect, directional correction was performed. Then, de-stripping correction was also applied. It is essential to estimate the boundaries and depths of the structural features of the region. In order to elucidate the structural features of the region, different techniques such as tilt angle derivative, the total horizontal derivative of tilt angle derivative, Euler 2D deconvolution, horizontal gradient magnitude, and source edge detection were applied to magnetic data. 2-D modelling using GM-SYS in Oasis Montaj were performed. These techniques identified and mapped the edges of anomalous sources related to magnetic data corresponding to geological elements in the study area. The results allow us to image the submarine lineaments for the survey area. These structural lineaments are in E–W, NE–SW and NW–SE trends. These lineaments in our results are quite compatible with the faults in previous geophysical results. The E–W trending lineaments are related to the E–W trending faults in the region.

Öztürk, Serkan; Bayrak, Yusuf

A statistical analysis is made for the eastern part of Turkey in the beginning of 2009 by studying the phenomenon of seismic quiescence as a potential precursor of the main shocks. The results produced four areas having seismic quiescence in the beginning of 2009. These areas are observed to be centered at 39.96°N-40.69°E (around Aşkale, Erzurum), 39.36°N-39.74°E (around Ovaci{dotless}k, Tunceli), 39.02°N-40.52°E (including Elazi{dotless}ǧ and Bingöl), and 38.45°N-42.94°E (Van Lake). Based on the recent results showing 5 ± 1.5 years quiescence before the occurrence of an earthquake in this region, the future earthquake would be expected between 2009. 5 and 2010. 5. The future earthquake occurrence may reach 2012 if we consider the standard deviation of average seismic quiescence as ±1.5 years. We have found that the MW = 6.0 Elazi{dotless}ǧ earthquake on 8 March 2010, followed a seismic quiescence starting about 5 years before the main shock. Thus, special interest should be given to the other regions where the seismic quiescence is observed.

Öztürk, Serkan

Characteristics of seismic activity along the North Anatolian Fault Zone are analyzed between 1970 and 2010. Magnitude completeness changes between 2.7 and 2.9 in the North Anatolian Fault Zone. The frequency-magnitude distribution of earthquakes is well represented with a b-value typically close to 1. A clear decrease in temporal distribution of b-value is observed before the strong main shocks. Correlation dimension values are relatively large and the seismic activity is more clustered at larger scales in the North Anatolian Fault Zone. A statistical assessment is made in order to detect the current seismic quiescence anomalies in the beginning of 2010. Eight significant anomalous zones throughout the North Anatolian Fault Zone are detected. These are centered at: (1) 41.08°N-28.58°E (around Silivri), (2) 41. 47°N-29.51°E (in the Black Sea), (3) 40.69°N-29.78°E (including Izmit), (4) 40.26°N-26.46°E (around Gelibolu, Canakkale), (5) 40.59°N-31.03°E (including Duzce fault), (6) 40.86°N-35.30°E (around Amasya), (7) 39.48°N-39.74°E (around Erzincan), and (8) 39.06°N-40.50°E (around Bingol).