The author has been involved in the stress state of earth's crust and analyzed the stresses through analytical solutions and finite element methods. For practical applications, he has developed various techniques for inferring the stress state in the earth's crust through utilization of geological features (i.e. striation, kinking, dyke intrusion, folding), damage zone formation around blasted holes, focal mechanism solutions and crustal deformation obtained from GPS. Furthermore, the Acoustic Emission technique was applied to the evaluation the stress state in Turkey and in Ryukyu Archipelago, Japan with an emphasis on earthquake prediction utilizing the variations of stresses in the earth's crust.
In-situ stresses are of great importance for the design and stability assessment of rock engineering structures. There are many in-situ stress inference techniques classified into broadly direct or indirect techniques (Amadei and Stephanson, 1997). The authors have been utilizing both direct and indirect techniques in an integrated manner to infer the in-situ stress state at various sites. Direct techniques are generally costly and they are only utilized for some important structures. The direct techniques utilize boreholes and assume that the surrounding rock behave elastically. However, the acoustic emission (AE) method can be used as a direct stress measurement method as it is less costly and it can be performed under well-controlled conditions in laboratory once sampling is done.
Indirect stress inference techniques utilizing borehole breakouts, fault striations and earthquake focal mechanism solutions are also proposed and used (Zoback and Healy 1992; Angellier, 1978; Aydan 2000a; Aydan and Kim 2002). Recently the author proposed a new stress inference technique utilizing damage zone around blastholes and it was applied to several sites in Japan and Turkey (Aydan, 2012, 2013a,b,c).
In this article the fundamentals of some of direct and indirect techniques developed by the author and his group are briefly explained. The applicability of direct and indirect techniques to estimate the in-situ stress state at various sites are presented and discussed. Then, the stress state estimates in a country-level are described.