A Statistical Analysis of the Major and Microearthquakes Along the East-Anatolian Fault

In order to evaluate past and present earthquake activity along the East Anatolian Fault between Karliova and Maras, the distribution in time and space of earthquakes was investigated. The investigation dealt with an interval of 75 years for largemagnitude earthquakes, and with a period of 105 days for microearthquakes occurring in a limited area. The most active regions of the fault zone are around Bingöl in the north, the Lake Hazar in the middle, and Adiyaman in the south. Along the fault zone the average Richter magnitude of earthquakes is about 5, the hypocentral depth about 25 kilometers, the period of occurrence (determined by spectral analysis) about 11 years, and the b-value for the magnitude range of 7>M>4 approximately 0.5. The microearthquake recordings around Lake Hazar indicated a daily average of 5 events with magnitudes less than 3. The composite fault plane solutions confirmed a lefthand strikcslip motion for most of the secondary faults. The average daily energy release of 10 16 erg and explicit alignment of strain release contours with the fault are some of the indications of the continuous tectonic activity in this region even in this quiet period. An 11 and 27 days periodicity of microearthquake activities has been obtained from spectral analysis. A close correspondence in epicentral distribution exists between major earthquakes and the present microearthquakes.