## 3 Observed Damage Mechanisms in Eastern T\(\ddot{\text{u}}\)rkiye's Masonry Buildings
### Failures at Corners and Orthogonal Wall Intersections  
The failure of corners and intersections formed by orthogonal walls represents a common mode of failure in masonry constructions found in eastern Turkkiye. In the presence of lateral seismic forces, inadequate interlocking, a deficiency or absence of vertical confining elements, and inconsistent detailing at L-, T-, or cross-shaped junctions significantly increase the vulnerability of these regions to sudden out-of-plane movements or corner disintegration [45]. The fundamental geometry of masonry corners, typicallycharacterized by substantial unreinforced edges converging at right angles, intensifies stress concentrations, especially during bidirectional ground shaking. As a result, the edges of walls are prone to rotate outward, leading to partial collapses that compromise structural integrity and produce dangerous debris fields. Empirical observations consistently indicate that corner failures are intricately associated with two primary deficiencies. Firstly, masons frequently neglect to ensure the proper toothing or keying of perpendicular walls, resulting in vertical seams or discontinuities at the juncture [45]. This issue stems from inadequate craftsmanship, where the builder fails to systematically interlace bricks or stones, and occupant expansions, wherein newly constructed perpendicular partitions are simply placed against rather than securely bonded to existing walls [41]. During significant horizontal ground motion, these unbonded seams serve as planes of vulnerability; separation commences at mid-height or near the eaves, leading to the detachment of substantial triangular or indiscrete trapezoidal corner segments. Secondly, the lack of vertical confining elements, such as boundary tie columns, considerably exacerbates the deficiency of interlocking. Although partial interlocking of components may exist, in the absence of a substantial reinforced concrete (RC) or steel boundary element, the corner remains essentially unrestrained, allowing for out-of-plane rotation. Once fissures develop in the corner region, whether induced by out-of-plane bending or diagonal shear, there is no secondary confinement to restrict movement or maintain the corner's structural integrity [46]. As a result, cracks can swiftly advance from one surface to another, leading to complete corner \"spalling\" and localized failure. Field evidence indicated that cracks typically started at vertical seams where orthogonal walls lacked toothing or interlocking, often just below roof eaves or around unconfined window corners. From these points, fractures propagated diagonally downward or vertically along mortar joints, leading to the progressive detachment and outward rotation of entire corner segments under repeated lateral shaking. In addition to their inherent structural disjunction, corner failures incite a cascade of adverse effects that jeopardize neighboring wall panels and floor diaphragms. Corners are typically pivotal nodal points essential for facilitating \"box action\", enabling the transfer of lateral loads across perpendicular planes [39]. Upon the fracturing or outward rotation of a corner, the overall capacity for distributing lateral forces experiences a significant reduction. Adjacent walls become isolated components vulnerable to out-of-plane instability, and roof/floor systems secured at that corner face the risk of partial detachment or progressive collapse in response to further seismic activity or aftershocks [4]. The insights derived from the 2020 Sivrice and 2023 Kahramanmaras earthquakes provided an abundance of case studies illustrating scenarios wherein multi-story stone or  
Figure 13: Damage due to heavy earthen roofs. brick masonry structures demonstrated significant corner degradation. In buildings devoid of ring beams or horizontal tie beams, corner separation often coincided with the outward rotation of the upper segments of perpendicular walls.