Abstract
In contrast to most of the coseismic gravity change studies, which are generally based on data from the Gravity field Recovery and Climate Experiment (GRACE) satellite mission, we use observations from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) Satellite Gravity Gradient (SGG) mission to estimate the coseismic gravity and gravity gradient changes caused by the 2011 Tohoku-Oki Mw 9.0 earthquake. We first construct two global gravity field models up to degree and order 220, before and after the earthquake, based on the least-squares method, with a bandpass Auto Regression Moving Average (ARMA) filter applied to the SGG data along the orbit. In addition, to reduce the influences of colored noise in the SGG data and the polar gap problem on the recovered model, we propose a tailored spherical harmonic (TSH) approach, which only uses the spherical harmonic (SH) coefficients with the degree range 30–95 to compute the coseismic gravity changes in the spatial domain. Then, both the results from the GOCE observations and the GRACE temporal gravity field models (with the same TSH degrees and orders) are simultaneously compared with the forward-modeled signals that are estimated based on the fault slip model of the earthquake event. Although there are considerable misfits between GOCE-derived and modeled gravity gradient changes (ΔVxx, ΔVyy, ΔVzz, and ΔVxz), we find analogous spatial patterns and a significant change (greater than 3σ) in gravity gradients before and after the earthquake. Moreover, we estimate the radial gravity gradient changes from the GOCE-derived monthly time-variable gravity field models before and after the earthquake, whose amplitudes are at a level over three times that of their corresponding uncertainties, and are thus significant. Additionally, the results show that the recovered coseismic gravity signals in the west-to-east direction from GOCE are closer to the modeled signals than those from GRACE in the TSH degree range 30–95. This indicates that the GOCE-derived gravity models might be used as additional observations to infer/explain some time-variable geophysical signals of interest.
Highlights
Because satellite gravity observations are not limited to Earth’s surface conditions, and can cover the whole Earth quickly, they provide an independent way to detect the coseismic effects of large earthquakes, which is a good complement for other earthquake measurements, and are of great scientific significance.A new generation of satellite gravimetry missions, including CHAMP (CHAllenging Minisatellite Payload) [1], GRACE (Gravity field Recovery and Climate Experiment) [2] and Gravity field and steady-state Ocean Circulation Explorer (GOCE) (Gravity field and steady state Ocean Circulation Explorer) [3], have been successfully implemented to detect global static and time-variable gravity signals
To extract the coseismic gravity signals from the recovered global gravity field models, we proposed tailored spherical harmonic (TSH) coefficients according to the influences of colored noise in the Satellite Gravity Gradient (SGG) data and the polar gap problem on the recovered models
The radial gravity gradient changes from the derived monthly time-variable gravity field models before and after the earthquake show obvious steps before and after the earthquake, whose amplitudes are at a level over three times that of their corresponding uncertainties, and significant
Summary
Because satellite gravity observations are not limited to Earth’s surface conditions, and can cover the whole Earth quickly, they provide an independent way to detect the coseismic effects of large earthquakes, which is a good complement for other earthquake measurements (e.g., surface deformations), and are of great scientific significance.A new generation of satellite gravimetry missions, including CHAMP (CHAllenging Minisatellite Payload) [1], GRACE (Gravity field Recovery and Climate Experiment) [2] and GOCE (Gravity field and steady state Ocean Circulation Explorer) [3], have been successfully implemented to detect global static and time-variable gravity signals. The detection of coseismic gravity change signals using GRACE data has been widely studied. Long-to-medium-wavelength coseismic and post-seismic gravity changes from large-scale earthquakes (e.g., the 2004 Sumatra-Andaman Mw = 9.1, 2010 Maule Mw = 8.8, 2011 Tohoku-Oki Mw = 9.0) have been adequately detected by the GRACE mission [4,5,6,7,8,9,10,11,12,13,14,15,16,17]. A few studies have focused on inferring the coseismic gravity change signals from simulated data [24,25,26] or real GOCE observations [27,28,29]
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