Tilt records prior to the 2011 off the Pacific coast of Tohoku Earthquake

Hitoshi Hirose

doi:10.5047/eps.2011.05.009

Abstract

The 2011 off the Pacific coast of Tohoku Earthquake was an unexpected megathrust event with magnitude 9.0 along the Japan trench. Hi-net tilt records prior to the great earthquake are examined in order to determine whether a precursory tilt change is observed in the short-term (~days) and medium-term (~a month) for confirming a preslip hypothesis and the effectiveness of an earthquake prediction method based on that hypothesis. For a quantitative reference to the observation, the detectability of the tilt observation for interplate slip on the subducting Pacific plate is also evaluated. In this study, no clear signal of preseismic tilt change or preslip is found in the records. This means that there is no preslip larger than moment magnitude (Mw) 6.2 on the deeper extension of the earthquake source area on the plate interface or larger than Mw 7.3 near the hypocenter.

Highlights

The 2011 off the Pacific coast of Tohoku Earthquake (M 9.0) occurred at 14:46 on March 11 (Japan Standard Time, JST) along the Japan trench where the Pacific plate is subducting beneath overriding northeastern Japan
Hi-net tilt records prior to the great earthquake are examined in order to determine whether a precursory tilt change is observed in the short-term (∼days) and medium-term (∼a month) for confirming a preslip hypothesis and the effectiveness of an earthquake prediction method based on that hypothesis
The Hi-net tiltmeters have successfully detected the tilt deformations caused by slow slip events (SSE) in the southwest Japan subduction zone (e.g., Obara et al, 2004; Hirose and Obara, 2005)

Summary

Introduction

The 2011 off the Pacific coast of Tohoku Earthquake (M 9.0) occurred at 14:46 on March 11 (Japan Standard Time, JST) along the Japan trench where the Pacific plate is subducting beneath overriding northeastern Japan. Doi:10.5047/eps.2011.05.009 hoku Earthquake observed with high sensitivity accelerometers (tiltmeters) at National Research Institute for Earth Science and Disaster Prevention (NIED) Hi-net stations in order to examine possible preseismic deformation. The detectability of the Hi-net tilt observation for slip on the plate interface is evaluated for a quantitative measure of the observation This is important to test the effectiveness of a short-term earthquake prediction strategy based on the monitoring of preslip with crustal deformation observations, and to constrain a physical process immediately before a dynamic rupture initiation of an earthquake. 2. Tilt Data before the Mainshock NIED Hi-net tiltmeter records (Okada et al, 2004; Obara et al, 2005) are used to investigate possible crustal deformations before the earthquake (in this paper, times are presented in Japan Standard Time, JST). The focal mechanism solution of the March 9 event shows a shallow thrust

HIROSE

Discussion