Examination of an active submarine fault off the southeast Izu Peninsula, central Japan, using field evidence for coseismic uplift and a characteristic earthquake model

Akihisa Kitamura,Shigeto Kawate,Yuta Mitsui,Haeng Yoong Kim

doi:10.1186/s40623-015-0367-z

Abstract

Detailed mapping and radiocarbon dating of emergent marine sessile assemblages show that coseismic uplift occurred at 1256–950 BC, AD 1000–1270, AD 1430–1660, and AD 1506–1815 in the southern Izu Peninsula, central Japan. Employing a characteristic earthquake model, this study reconstructed the source fault for the uplift events from the spatial distribution of coseismic vertical displacements and historical documents. The source is inferred to be a reversal fault located about 3 km off the southern Izu Peninsula that is 25 km long and 13 km wide (strike = 250°, dip = 52° to the north) and slip of 2.7 m and has generated a Mw 7 class earthquake.

Highlights

Detailed mapping and radiocarbon dating of emergent marine sessile assemblages show that coseismic uplift occurred at 1256–950 BC, AD 1000–1270, AD 1430–1660, and AD 1506–1815 in the southern Izu Peninsula, central Japan
Kitamura et al (2015) examined the faunal compositions and 14C ages of emergent sessile assemblages at four sites in the southern Izu Peninsula (Fig. 2) and concluded that coseismic uplift occurred at 1256–950 BC, AD 1000–1270, AD 1430–1660, and AD 1506–1815
To model the source fault, we made assumptions: (1) the fault is a reverse fault with pure dip-slip movement, to account for the large coseismic uplift; (2) the upper edge of the fault is located along the cliff near the coast; and (3) the lower limit of the fault is at 10-km depth, which roughly corresponds to the lower limit of seismogenic layer in this region (Tanaka 2004)

Summary

Introduction

The Izu Peninsula in central Japan, which is located between the Sagami and the Suruga troughs and lies at the northern tip of the Philippine Sea (PHS) plate, is currently colliding with central Japan (Sugimura 1972; Somervill 1978; Nakamura and Shimazaki 1981; Arai and Iwasaki 2014, 2015) (Fig. 1). Many earthquakes have occurred along the active faults in this area (Sagiya 1999), including the AD 1930 North Izu. Emergent sessile marine invertebrates and raised coastal landforms, up to 3 m above mean sea level (amsl), occur at Shimoda in the southeast Izu Peninsula and appear to have been uplifted during seismic events (Fukutomi 1935; Ota et al 1986; Taguchi 1993; Kitamura et al 2014, 2015). Kitamura et al (2015) examined the faunal compositions and 14C ages of emergent sessile assemblages at four sites in the southern Izu Peninsula (Fig. 2) and concluded that coseismic uplift occurred at 1256–950 BC, AD 1000–1270, AD 1430–1660, and AD 1506–1815. Emergent sessile assemblages are incomplete at the other four sites, but Kitamura et al (2015) detected no significant difference in total uplift across the five sites

Methods

Results

KSM071

Discussion