Foundation–structure systems over a rupturing normal fault: Part I. Observations after the Kocaeli 1999 earthquake

Triggered by reactivation of the strike-slip North Anatolian Fault, the disastrous Mw 7.4 Kocaeli (Turkey) earthquake also produced normal faulting in the pull-apart basin of Gölcük. Surface scarps from such faulting reached almost 2.5m in height. Several structures were crossed by the surface rupture. As expected, many of them either collapsed or were severely damaged. But, surprisingly, several structures survived the outcropping dislocation essentially unscathed. In fact, in some cases the surface rupture path seemed to have deviated, as if to “avoid” rupturing directly underneath a structure. In other cases damage was substantial even though the fault rupture was “masked” by the near-surface soil and did not create a scarp. The rigidity and continuity of the foundation appears to have been one of the crucial factors affecting structural performance. Interestingly, the examined structures were supported on a variety of foundation types, ranging from isolated footings, to rigid box-type foundations, to piled foundations. The paper outlines a reconnaissance of the area, providing a documented description of the observed interplay between the rupturing fault, the soil, and the structure, along with the results of soil exploration and geological trenching. In the companion paper, Part II, each system is analysed numerically to confirm the conclusions of the present paper, reveal the main aspects of Fault Rupture-Soil-Foundation-Structure Interaction (FR-SFSI), and help develop deeper insights into the mechanics of successful performance of structures built on top of such faults.