Slip distribution of the 1973 Nemuro-oki earthquake estimated from the re-examined geodetic data

Takuya Nishimura

doi:10.1186/bf03352973

Abstract

AbstractGeodetic data, including leveling, tide-gauge, triangulation/trilateration, and repeated EDM data, from eastern Hokkaido, Japan, were re-examined to clarify the crustal deformation associated with the 1973 Nemuro-oki earthquake. We inverted the geodetic data to estimate the slip distribution on the interface of the subducting Pacific plate. The estimated coseismic slip, potentially including afterslip, showed a patch of large slip (i.e., an asperity) near the epicenter of the mainshock. The moment magnitude of the Nemuro-oki earthquake was estimated to be 8.0 from the geodetic data, which is comparable to the 2003Mw= 8.0 Tokachi-oki earthquake. The estimated slip distribution suggests a 50 km-long gap in the coseismic slip between the 1973 Nemuro-oki and the 2003 Tokachi-oki earthquakes. The slip area of the 2004Mw= 7.0 Kushiro-oki earthquake, estimated from GPS data, was located at the northwestern edge of the Nemuro-oki earthquake, which implies that the area may have acted as a barrier during the Nemuro-oki earthquake. The postseismic deformation observed by leveling and tide-gauge measurements suggests that the afterslip of the Nemuro-oki earthquake occurred at least in a western and northern (i.e., deeper) extension of the asperity on the plate interface.

Highlights

The Kuril Trench is known as one of the most intensive areas of seismic activity in the world
4.1 Slip distribution of the 1973 Nemuro-oki earthquake and its relation to the Tokachi-oki earthquake Comparing the estimated slip distribution and the epicenters of the aftershocks that occurred in 1973 (Fig. 7), we found that most of the aftershocks occurred in the region where the slip was estimated to be 1–2 m, beyond the slip peak
Because our data included postseismic deformation over a few years, the wider slip region of our model suggested that afterslip occurred in the deeper part of the plate interface, as discussed in Section 4.3 and proposed by Kasahara and Kato (1980)

Summary

Introduction

The Kuril Trench is known as one of the most intensive areas of seismic activity in the world. We first examined the geodetic data, including leveling, triangulation/trilateration, and repeated distance measurements, and adjusted these data for interseismic deformation in order to clarify the horizontal and vertical deformations associated with the 1973 Nemurooki earthquake. We estimated the slip distribution of the 2004 Mw = 7.0 Kushiro-oki earthquake that occurred near the source area of the Nemuro-oki earthquake using coseismic GPS displacements. The 1973 Nemuro-oki earthquake occurred during the period of transitioning from the use of triangulation to trilateration to measure the horizontal locations of control points, i.e., survey markers. The distance changes in AK4–AK2 and AK3–AK2 were converted to +5.9 and +4.6 microstrain, respectively (a positive value represents an extension) These data have never been used for the modeling of the 1973 Nemuro-oki earthquake, they are conducive to estimating the slip distribution because the. While the vertical displacements at the Kushiro and Nemuro (Hanasaki) tide-gauge stations were −1.6 and −4.9 cm, respectively, they were predicted to be 0.1 and −2.5 cm

Discussion

Spatial relation with the 2004 Kushiro-oki earthquake

Afterslip model of the 1973 Nemuro-oki earthquake

Conclusion