The 2011 off the Pacific coast of Tohoku Earthquake and its aftershocks observed by GEONET

Takuya Nishimura,Hiroshi Yarai,Hiroshi Munekane

doi:10.5047/eps.2011.06.025

Takuya Nishimura, Hiroshi Yarai + Show 1 more

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https://doi.org/10.5047/eps.2011.06.025

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Abstract

The large displacement induced by the 2011 M 9.0 off the Pacific coast of Tohoku Earthquake was observed by GPS stations of the permanent GPS Earth Observation Network system (GEONET) in northeastern Japan. The displacement was characterized by the eastward displacement and subsidence in the Pacific coastal area. The horizontal displacement exceeded 5.3 m, which is the largest ever detected by GEONET. The mainshock was followed by a sequence of aftershocks. We processed the GPS data through a kinematic positioning strategy to clarify the deformation, including the deformation caused by the mainshock, with high temporal resolutions. The offsets calculated from the kinematic coordinates separately depict the coseismic displacements of the mainshock, the largest aftershock, and the third largest. The fault model for these earthquakes suggests that the largest (M 7.7) and third largest (M 7.3) aftershocks ruptured the southern and northern extensions of the mainshock fault, respectively.

Highlights

The M 9.0 off the Pacific coast of Tohoku Earthquake occurred along the Japan Trench on March 11, 2011
The large displacement induced by the 2011 M 9.0 off the Pacific coast of Tohoku Earthquake was observed by GPS stations of the permanent GPS Earth Observation Network system (GEONET) in northeastern Japan
The focal mechanism from the Global CMT Project (Fig. 1) and the aftershock distribution published by the Japan Meteorological Agency (JMA) suggest that the 2011 Tohoku earthquake ruptured the plate interface between the subducting Pacific plate and the overriding Okhotsk plate

Summary

Introduction

The M 9.0 off the Pacific coast of Tohoku Earthquake (hereafter, the 2011 Tohoku earthquake) occurred along the Japan Trench on March 11, 2011. The GPS Earth Observation Network System (GEONET) is a permanent nationwide GPS array operated by the Geospatial Information Authority of Japan (formerly the Geographical Survey Institute, or GSI) It consists of more than 1300 continuous sites with a real-time transmission of 1-s data sampling. GEONET has recorded coseismic and postseismic displacements for many earthquakes that have occurred since 1994, including the earthquake off Tohoku. It has revealed plate motions and interseismic deformation along the plate boundaries In the sequence of the 2011 Tohoku earthquakes, several M > 7 aftershocks occurred within 1 h after the mainshock These aftershocks have the potential to cause displacements of more than several centimeters at the GEONET stations. A detailed analysis of the distribution of coseismic and postseismic slip as estimated from the GEONET data is summarized in another paper (Ozawa et al, 2011)

The 2011 Tohoku Earthquake As Revealed by GEONET

Coseismic Displacements and Their Fault Model

Conclusion