Maden, Nafiz; Yıldız, Burak

Seydi Ali Reis first mentioned the declination angle in his book titled Kitab-ı Muhit in 1554. Kitab-ı Cihannüma (1654), Füyuzat-i Mıknatisiye (1731), and Mârifetname (1757) gave the magnetic declination angle values in Anatolia. We have compiled magnetic declination data from 1500 to the present day in Anatolia and Istanbul. The plot of the magnetic declination angle was drawn for the first time using historical data between 1500 and 1947 for Istanbul. Three new magnetic declination maps for the periods of 1909–1910, 1970 and 2009 were produced for Turkey. The annual change map based on the data of 1970 and 2009 is also given for whole Turkey. The agonic line extending in NW-SE direction between Sinop and Antep divides Anatolia into two regions in 1910. The mean declination values obtained from qibla direction measurements made by the Presidency of Religious Affairs in all mosques give 3.11° E for 1970 and 4.74° E for 2009 in Turkey.

Öztürk, S.

Variations of the recent seismicity in and around the Central Anatolian region of Turkey were evaluated based on the seismic b-value, standard normal deviate Z-value, GENAS modelling, annual probabilities and return periods of the earthquakes. The catalog includes 16,702 earthquakes between 1974 and 2019 with magnitudes from 1.0 to 6.3. Time distribution of b-value shows that there is a tendency to decrease after the year of 2002 and b-value decreased from 1.58 ± 0.03 to 1.25 ± 0.05 at the beginning of 2019. Annual probabilities for magnitude ranges of 3.0–4.0 have the values between 3 and 30. Return periods for magnitude levels of 5.0–5.5 have the values from 5 to 20 years, and a value of 80 years for magnitude level of 6.0. The GENAS results show the significant temporal variations in the number of earthquakes smaller and larger than specific magnitude intervals by supplying the beginning periods of increases and decreases in the earthquake activity rate. Remarkable reductions in region-time distribution of b-value at the beginning of 2019 were detected in the regions covering Niğde fault and its vicinity along the south, west, northwest and southwest directions, among the Mut Fault Zone, Karsantı-Karaisalı Fault Zone and Karataş-Osmaniye Fault Zone, in and around Sürgü fault and along its northwest direction, between Sürgü fault and East Anatolian Fault Zone. Significant seismic quiescence areas in Z-value distribution include the northwest ends of the Tuzgölü Fault Zone and study area including Akpınar fault, the northeast of Salanda fault, between Salanda fault and the Central Anatolian Fault Zone, the northeast parts of the Central Anatolian Fault Zone, the west of Malatya fault, between Sürgü fault and the East Anatolian Fault Zone, the southeast end of the Tuzgölü Fault Zone, Karsantı-Karaisalı Fault Zone and its vicinity, the southwest of Tuzgölü. Thus, these anomaly areas observed in the Central Anatolian region and its vicinity at the beginning of 2019 may be one of the most likely zones for the next strong/large earthquake occurrences.