Regional considerations of Coastline change, tsunami damage and recovery along the southern coast of the Bay of Izmit (The Kocaeli (Turkey) earthquake of 17 August 1999)

Co-seismic phenomena along the south coastline included liquefaction, subsidence and tsunami. Construction on areas composed of fluvial and alluvial sediments as well as unconsolidated fill increased the risk by creating potential for amplification of seismic waves. Cyclic mobility liquefaction was common along the coastline, and level-ground liquefaction was observed. Flow liquefaction is held forth as a possibility in the Deǧirmendere submarine landslide. Damage to structures was markedly more in areas of unconsolidated sediments. One or more tsunami struck immediately after the event; the uniformity of tsunami impact indicating a wave coming from 310° suggests that submarine faulting was the major source of tsunami. Over 800,000 m² of subsidence resulted from sediment slumping, fault controlled subsidence, and possibly post-liquefaction sediment compaction. After a brief period of post-event abandonment, reclamation and use of coastal areas is well underway. This creates a tension between human desires pushing for quick and inexpensive re-inhabitation of the coastal areas, and the needs for zoning and building codes for risk reduction. In this high-risk area such contrary cultural mandates cannot yield ideal results. It is suggested that an alternative model of immediate post-event creation of parks and natural areas that would yield benefit is preferable in coastal areas rather than the enforcement approach currently favored.