Coastal deformation associated with the 2007 Noto Hanto earthquake, central Japan, estimated from uplifted and subsided intertidal organisms

Yasuo Awata,Tomoo Echigo,Shinji Toda,Masanobu Shishikura,Haruo Horikawa,Takashi Azuma,Heitaro Kaneda

doi:10.1186/bf03352869

Abstract

AbstractThe March 25, 2007 Noto Hanto earthquake (Mj= 6.9,Mw= 6.7) generated vertical crustal movement along the northwestern coast of the Noto Peninsula, central Japan. Soon after the event, we estimated the pattern and amount of coseismic coastal movement based on uplifted and subsided intertidal sessile organisms. Our observations reveal a broad 20-km-wide asymmetric zone of surficial deformation above and across the south-dipping source fault, with a steep north-facing frontal limb and a gentle south-facing back limb. The maximum coseismic uplift was approximately 40 cm at the crest of the zone of deformation. The result of forward modeling suggests that the top of the south-dipping source fault is buried at a depth of approximately 2 km, and that 1.2 m of slip on the fault provides the best fit to our surface observations. Our results demonstrate that traditional field investigations should be combined with modern instrumental observations such as GPS and InSAR to obtain the most effective and reliable spatio-temporal estimates of crustal movement associated with large earthquakes.

Highlights

March 25, 2007, a large earthquake occurred in the vicinity of the Noto Peninsula on the Japan Sea side of central Japan
No active faults have been mapped onshore in this region except for the north-northeast-striking Sakami Fault (Research Group for Active Faults of Japan, 1991), which is located further to the south. These observations suggest that the 2007 earthquake can be ascribed to a rupture of the F-14 Fault near the coastline of the Noto Peninsula
The amount of coseismic uplift associated with large earthquakes is normally estimated from the vertical extent of mortality of intertidal organisms, which becomes visible days or weeks after the earthquake (e.g., Nakamura et al, 1964; Carber et al, 1994; Meghraoui et al, 2004); in the present study we focused on the zonation of living colonies and succeeded in promptly determining the pattern and amount of minor vertical crustal movements of less than 40 cm

Summary

Introduction

March 25, 2007, a large earthquake occurred in the vicinity of the Noto Peninsula on the Japan Sea side of central Japan. No active faults have been mapped onshore in this region except for the north-northeast-striking Sakami Fault (Research Group for Active Faults of Japan, 1991), which is located further to the south. These observations suggest that the 2007 earthquake can be ascribed to a rupture of the F-14 Fault near the coastline of the Noto Peninsula. The western Noto Peninsula, where tidal variation as small as 30–40 cm facilitates the recognition of minor coastal deformation, is indicated by the generation of small tsunamis, the magnitude and focal mechanism of the main shock, and the distribution of aftershocks. In an effort to promptly determine the coastal deformation and source fault parameters, we conducted an urgent field survey of uplifted and subsided intertidal sessile organisms in the mezoseismal region

Methods

Fault Model Estimated from Coastal Movements

Discussion