## 1 Introduction
A clear example of this occurred during the 2015 Gorkha earthquake in Nepal, where many URM houses collapsed not because of original construction flaws, but due to extra stories and rooftop rooms added over time, often without any seismic reinforcement. Similar cases have been reported in Mexico and Iran, where post-earthquake surveys revealed that informal structural additions were a key factor in building failures. These kinds of modifications are not just cosmetic upgrades or extra rooms. They are significant structural changes that typically fall outside the scope of building codes and engineering oversight. Because of that, they often go unaccounted for in design assumptions and risk models, quietly increasing vulnerability until a major event exposes the weakness [14; 15; 16; 17; 18; 19]. Apart from changes brought on by occupants, the usage of mortar in conventional masonry construction creates a major structural flaw. The Turkish Academy of Sciences (TUBA) [20] emphasizes that resident families typically blend local earth or sand, at times integrating straw for earthen blocks, or utilize unrefined riverbed aggregates for stone walls. This type of mortar demonstrates poor cohesion and limited tensile strength, exacerbating shear or corner fractures when subjected to lateral forces from seismic events. On a global scale, [PERSON] [4] noted that the compressive strength of mortar should correspond to the compressive strength of the blocks to facilitate proper load distribution and mitigate joint sliding. Nonetheless, the modifications made by occupants seldom replicate the mortar specifications (if any were present) of the original construction. Rather, resident families often opt for less expensive, friction-based bonding agents that, upon enduring recurrent vibrations, deteriorate, particularly in proximity to expansions or corners. A further complicating factor is ring beam omission or partial usage. The TMS 602 [12] suggests ring beams or confining elements at critical horizontal intervals to tie walls together and prevent out-of-plane disintegration. Similarly, the TBEC (2018) [13] mandates horizontal ties or belts in larger masonry walls to forestall vertical separation. Occupant expansions, however, seldom see ring beams installed at the new roof-wall interface. Instead, occupant families typically lay wooden joists or, in some cases, steel beams directly on top of unreinforced walls, ignoring the ring beam concept. Observations from the 2023 Kahramanmaras events confirm that occupant expansions lacking ring beams frequently collapsed outward, generating large debris fields that hampered rescue efforts [20]. Similar patterns were observed worldwide in older masonry expansions without ring beams, including post-quake reconnaissance in the 2009 L'Aquila quake, the 2011 Christchurch (New Zealand) event, the 2017 Puebla-Morelos (Mexico) quake, and 2017 Kermanshah (Iran) quake [9; 21; 22; 23; 24]. In each case, occupant expansions or partial additions aggravated the dwellings' vulnerability. In conclusion, occupant expansions, low-grade mortar, and absent ring beams collectively represent the trifecta behind older masonry collapses in eastern Turkiye, particularly in adobe or stone-based building types. Substantial occupant expansions in rural communities produce structural anomalies that code-based design does not anticipate, while occupant acceptance remains elusive if solutions appear expensive or culturally incongruent. Meanwhile, major seismic events highlight these deficiencies with stark clarity. If occupant expansions remain invisible to policy or occupant expansions are neglected in code-based vulnerability frameworks, older masonry in eastern Turkiye will remain perpetually at risk, yielding tragic outcomes whenever large quakes strike. Moreover, post-earthquake onsite investigations significantly enhance the development of more seismically resilient structures for future seismic events.