Monthly GRACE detection of coseismic gravity change associated with 2011 Tohoku-Oki earthquake using northern gradient approach

Jin Li,Wen-Bin Shen

doi:10.1186/s40623-015-0188-0

Abstract

We demonstrate that the coseismic gravitational changes due to the 2011 M w = 9.0 Tohoku-Oki earthquake are detectable by GRACE with only 1-month data after the earthquake, which is also supported by a simulation test using the seismic-signal-contained observations synthesized with the signals of a dislocation model prediction. The commonly used destriping to filter correlated errors in GRACE coefficients tends to distort the true coseismic signals in both amplitude and spatial pattern. In order to better retrieve coseismic gravitational signals, we apply a northern gravity gradient approach with the filter of spatial averaging and without destriping. The coseismic northern gravity gradient changes of Tohoku-Oki earthquake are extracted from the monthly data of April 2011, which reveal a positive-negative-positive spatial pattern and agree with the model prediction. The northern gradient approach provides an efficient means to detect coseismic signals and potentially constrain fault slip models with large-scale gravitational changes using limited time span of monthly GRACE solutions.

Highlights

Gravity Recovery and Climate Experiment (GRACE) level 2 data released with monthly spherical harmonic (SH) coefficients are contaminated by northsouth stripe errors, and the stripe errors are related with the correlated errors among the SH coefficients (Swenson and Wahr 2006)
It could be inferred that the gravity-change approach with the filter of destriping plus spatial averaging may not work well for detecting coseismic signals with only 1month GRACE data set, as the signal-to-noise ratio (SNR) for the observation is relatively weak for this case
A more practical and commonly used representation of the postseismic gravitational changes for GRACE observation is to apply the negative exponential function with a given relaxation time constant (e.g., Han et al 2008; de Linage et al 2009; Li et al 2014) to describe the asthenosphere rheology of earthquake region. We demonstrate by both synthetic tests and real-data case studies that the coseismic gravitational changes due to the 2011 Tohoku-Oki earthquake are detectable by GRACE with only 1-month data after the earthquake

Summary

Introduction

Chen et al (2007) and Heki and Matsuo (2010) used a filter including destriping first and spatial averaging to reduce noises and retrieve seismic signals associated with large earthquakes. Several other previous studies employed destriping to extract the coseismic gravitational changes due to 2011 Tohoku-Oki earthquake (e.g., Matsuo and Heki 2011; Zhou et al 2012). Destriping would distort and reduce real signals while suppressing

Methods

Results

Discussion

Conclusion