Trench Survey and Fault Displacement at Cheonbuk-myon Area along the Northern Part of Ulsan Fault System

울산단층계 북부 천북면 일대의 트렌치 조사와 단층변위

Quaternary fault movement of the Ulsan fault system was interpreted by aenal photograph, field survey and trench excavation. The geomorphological evidences associated with active fault are clearly shown at Cheonbuk-myeon area, northern part of Ulsan fault system. In the trench wall one reverse fault(N 50$^{\circ}$E, 70$^{\circ}$E) is identified between basement rock (Miocene mudstone) and gravel deposits Another thrust fault (NS) extends up to the red and light brown soil layers. Middle terrace surface shows cumulative vertical displacements of about 3 to 7 m. The horizontai displacement of the red soil by faulting event is about 1.8 to 2.4m. The age of the fault activity is younger than that of the soil layer, which is roughly estimated to be late Quaternary (about 100Ka)