The Sakar and Strandzha Mountains are disposed in the South-East end of the Balkan Peninsula (on the both sides of the Bulgarian-Turkish boundary). They belong to the southeastern margin of the Bulgarian continental microplate. They are limit from North Thracian morphostructural zone to the North, the East Thracian morphostructural zone to the South and the Rhodopean morphostructural zone to the West. The observed mountain territory builds the Sakar-Strandzha morphostructural zone. It is divided by Sakar Dervent and Strandzha morphostructural areas. Every of them include morphostructural regions. They are composed by numerous Late Pleistocene-Holocene dome-like morphostructures. The relics from the Post Early Pleistocene concentric morphostructures are distributed in the entire zone. They were determined some archer and concentric Holocene mountain morphostructures.
The regional seismic activity (during the last 50 years) outlines three parts of the Sakar-Strandzha morphostructural zone. The western one - the Sakar part is moderate seismic active. The centred - Dervent part is practically seismic „calm“. The eastern one- Strandzha part show a very intensive seismicity. It can by given right in a future (after the necessary investigations) to divide the zone in three areas.
References  Tsankov, Ts. Morfostrukturen analiz. Izdatelstvo „Grafika 19“, Sofia, 2013 . ISBN 978-954-976434-5, p. 160.  Tsankov, Ts.; N. Spasov; K. Stoyanov, Neogensko-kvaternerna paleogeografia i geodinamika na Sredna Struma (Yugozapadna Bulgaria). Univ. Izdat. „Neofit Rilski“, Blagoevgrad, 2005, ISBN 954-680-365-0, Blagoevgrad, p. 199.  Tzankov, Tz., Sv. Stankova, R. Iliev, I. Mitkov. Late Quaternary morphostructuralgenerations in the east part of Balkan Peninsula, SocioBrains , 2018 , 41 , 188-197.  Tzankov, Tz., R. Iliev. Morphostructure
, R., Mitkov, I., Late Quaternary morphostructuralgenerations in the eastern part of the Balkan Peninsula. SocioBrains , 2018 , 41 , 188-197.  Tzankov, Tz.; Iliev, R., Morphostructure of the Rhodopean Mountain massif. Printing House „Grafika 19“, Sofia, 2015 .