Deformation of Fluvial Terraces along the Western Margin of the Toyama Plain, Central Japan

Abstract

The Toyama Plain, central Japan, is a depression along the northward-flowing Zintsu River and Jogannji River. The western margin of the Toyama Plain is bounded by NNE- to NNW- trending Kurehayama fault. We estimated the formation age of fluvial terraces and the fault topography of the Kurehayama fault along the western part of Toyama Plain based on geomorphological and tephrochronological studies.
Late Quaternary fluvial terraces in the western part of Toyama Plain are divided into ten levels : terrace I to X in descending order. Terrace III is overlain by the Kikai-Tozurahara tephra (75-95 ka) and the Tateyama D tephra (95-130 ka), Terrace V is overlain by the DaisenKurayoshi tephra (43-55 ka), and Terrace VI is overlain by the Aira-Tanzawa tephra (22-25 ka), respectively.
The Kurehayama fault is a reverse fault extending for 20 km along the western margin of the Toyama Plain. The Kurehayama fault is characterized by fault scarps several meters high on late Quaternary fluvial terraces. Average vertical slip rates for the southern part of Kurehayama fault, Yatsuo area, are estimated at 0.08-0.41 mm/yr and vertical displacement at Terrace VI is more large northward. From the central to northern parts of Kurehayama fault, fault scarps 2 to 4 meters high on late Terrace IX and X, both terraces are Holocene terrace. Such a young offset implies that the last faulting events occurred since Terrace IX and X formed.