Using geochemical and sedimentological properties of a sediment core IK2 from the 210 m deep Karamursel Basin of the Izmit Gulf, temporal evolution of pollution and sources of trace elements (As, Co, Cr, Cu, Hg, Pb and Zn) were investigated. The core sequence extends back to AD865 and includes four mass-flow units (THU-1 to THU-4 from top to base) that were triggered by major earthquakes of AD 1999, 1509, 1206 and 865. The vertical profiles of elements and total organic carbon (TOC) in core IK2 display the highest enrichments in THU-1 that was triggered by the 1999 Izmit earthquake (Mw 7.4). The profiles also display massive erosion of sediments below THU-1, belonging to the industrial period. Principal component analysis (PCA) of geochemical data from core IK2 showed three clusters: (1) PC1 (Co, Cu, Zn, Hg, TOC); (2) PC2 (As, Cr); (3) PC3 (Al). Enrichment of PC1 elements in THU-1 indicates that the unit represents the contaminated surficial sediments remobilized mainly from the relatively steep slopes of the Karamursel Basin by the earthquake shaking. Strong correlation between TOC and Cu, Zn, Hg, Co suggests additional contamination sources, such as the seepages from the disrupted industrial pipelines, oil refinery and storage tanks, following the earthquake. Moderate enrichment in Pb, and As severe enrichment in Zn and very severe enrichment in Hg in the THU-1 sediments occurred in the last century, but significantly magnified by the devastating 1999 Izmit earthquake and early diagenetic processes.