Abstract
Chaotic blocks occur within a coherent zone of the Nishizaki Formation at Nishikawana to the southwest of Tateyama in southern Boso Peninsula. Based on detailed field observations and related laboratory studies the following facts were clarified, 1) the chaotic blocks are divided into 6 domains, 2) these domains are highly folded and faulted and generally overturned, 3) liquefied pumiceous sediments are found along fault zones between the adjacent coherent zone and the chaotic blocks, 4) the equivalent strata of the chaotic blocks are not found or correlated in the neighboring areas. The observations suggest that the chaotic blocks were emplaced by submarine landslide which was caused by liquefaction, and all the domains were subsequently stacked by thrust faults at the toe of the slide body. The domains were slid from S to N as shown by the fold axes analysis. This sliding direction is mostly perpendicular to the proto-Sagami Trough, suggesting that the submarine landslide have occurred on a forearc slope of the Izu Arc.
