Investigation of the Co-seismic gravity field variations caused by the 2004 Sumatra-Andaman earthquake using monthly GRACE data

Abstract

Gravity Recovery and Climate Experiment (GRACE) observations have been used to detect the co-seismic and post-seismic gravity field variations due to the M w =9.3 Sumatra-Andaman earthquake that occurred on December 26, 2004. This article focuses on investigating some gravitational effects caused by this huge earthquake. We computed the geoid height changes, the equivalent water height (EWH) changes, and the gravity changes using the GRACE Level-2 monthly spherical harmonic (SH) solutions released by University of Texas Center for Space Research (UTCSR). The GRACE results agree well with the prediction by a dislocation model and are consistent with the results obtained by some previous scholars. In particular, we calculated the three components of the gravity gradient variations and found that they can recover the seismic-related signature more sensitively due to a certain degree of amplification of the signals. A positive-negative-positive mode predominates in the spatial distribution of the horizontal components of the gravity gradient variations, which is possibly attributed to the anomalies in the crustal density distribution caused by the uplift-subduction effect of the dip-slip earthquake. Moreover, the latitude components of the gravity gradient changes show strong suppression of the north-south stripes, which is due to the along-orbit measurements of the two GRACE satellites. We conclude that the positive-negative-positive mode in latitude gravity gradient changes would be a more sensitive feature to detect the deformations of some major dip-slip earthquakes by GRACE data.

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

“…We also calculate the coseismic northern gravity gradient changes in the region of interest, for both the model prediction and synthetic data retrieval. The northern gravity gradient changes are evaluated from the derivative of the associate Legendre function according to the spherical harmonic expansion of Earth's gravity field (e.g., Li and Shen 2011), based on the model and GRACEsynthetic SH coefficients, respectively. After spatial smoothing, the model-predicted northern gravity gradient changes are shown in Figure 3a,b,c, with the filters of 300 km Gaussian smoothing only, P3M6 destriping plus 300 km Gaussian smoothing, and Duan09 destriping plus 300 km Gaussian smoothing, respectively.…”

“…gradient changes on the north-south stripes, the signals in Figure 4d are less contaminated by stripes than those in Figure 4b. Since GRACE observations are of anisotropic sensitivity due to the along-orbit measurements of the two near-polar-orbit satellites, the signal-to-noise ratio (SNR) in the longitudinal direction should be higher (Li and Shen 2011). The positive-negative-positive gradient changes in the near field of Figure 4c range from '+2.6 to −2.9 to +1.2' × 10 −13 s −2 and coincide quite well with the 'true signal' as shown in Figure 3a for both amplitude and spatial pattern.…”

“…Nevertheless, destriping would distort and reduce real signals while suppressing stripes. Li and Shen (2011) found that the horizontal components of gravity gradient changes exhibit positivenegative-positive features due to the mass variations of a large thrusting earthquake and recommended a northern (latitude-direction) gravity gradient approach to detect the coseismic effects more efficiently due to the anisotropic sensitivity of GRACE observations. Later, Wang et al (2012b) demonstrated the potential of gravity gradient approach in a more general sense.…”

Seismologic applications of GRACE time-variable gravity measurements

“…Some other studies try to extract seismic signals using different quantities other than the commonly used geoid, equivalent water height (EWH) or gravity of the GRACE time-variable gravitational field. These other GRACE field quantities include gravity gradients, vertical deflections, and gravitational gradient tensors (e.g., Li and Shen 2011;Sun and Zhou 2012;Wang et al 2012a), which are sensitive to small-scale signals.…”

GRACE detection of the medium- to far-field coseismic gravity changes caused by the 2004 MW9.3 Sumatra-Andaman earthquake

“…The Gravity Recovery and Climate Experiment (GRACE) has detected the gravitational effects of three large earthquakes since its launch in 2002, which include the 2004 M W 9.3 Sumatra-Andaman earthquake (e.g., Han et al, 2006;Chen et al, 2007;de Linage et al, 2009;Li and Shen, 2011), the 2010 M W 8.8 Chile earthquake (Han et al, 2010;Heki and Matsuo, 2010;Zhou et al, 2011), and the 2011 M W 9.0 Tohoku (Japan) earthquake (Matsuo and Heki, 2011;Han et al, 2011;Wang et al, 2012;Sun and Zhou, 2012;Zhou et al, 2012). However, these previous studies discussed only the GRACE detection of near-field gravity changes, and the effects of far-field variation seems to be ignored.…”