Coseismic and post-seismic signatures of the Sumatra 2004 December and 2005 March earthquakes in GRACE satellite gravity

Abstract

International audienceS U M M A R Y The GRACE satellite mission has been measuring the Earth's gravity field and its temporal variations since 2002 April. Although these variations are mainly due to mass transfer within the geofluid envelops, they also result from mass displacements associated with phenomena including glacial isostatic adjustment and earthquakes. However, these last contributions are difficult to isolate because of the presence of noise and of geofluid signals, and because of GRACE's coarse spatial resolution (>400 km half-wavelength). In this paper, we show that a wavelet analysis on the sphere helps to retrieve earthquake signatures from GRACE geoid products. Using a wavelet analysis of GRACE geoids products, we show that the geoid variations caused by the 2004 December (M w = 9.2) and 2005 March (M w = 8.7) Sumatra earthquakes can be detected. At GRACE resolution, the 2004 December earthquake produced a strong coseismic decrease of the gravity field in the Andaman Sea, followed by relaxation in the area affected by both the Andaman 2004 and the Nias 2005 earthquakes. We find two characteristic timescales for the relaxation, with a fast variation occurring in the vicinity of the Central Andaman ridge. We discuss our coseismic observations in terms of density changes of crustal and upper-mantle rocks, and of the vertical displacements in the Andaman Sea. We interpret the post-seismic signal in terms of the viscoelastic response of the Earth's mantle. The transient component of the relaxation may indicate the presence of hot, viscous material beneath the active Central Andaman Basin

Post-seismic relaxation: An example of earthquake triggering in the Apennine belt (1915–1920)

“…Recently, possible effects of such a process, triggered by strong shocks, have been detected by means of space geodesy, radar interferometry and gravity measurements (e.g., Pollitz et al, 2006;Panet et al, 2007;Ryder et al, 2007;Ergintav et al, 2009;Ozawa et al, 2011). Moreover, several works suggest a causal link between the travelling post-seismic strain perturbation and earthquake triggering.…”

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

“…The gravity signature associated with this large earthquake in GRACE observations has already been detected by several studies (e.g., de Linage et al, 2009;Chen et al, 2007;Ogawa and Heki, 2007;Panet et al, 2007;Han et al, 2006). Han et al (2006) used the overflight Level-1 GRACE tracking data above the quake region and enhanced the signalto-noise ratio (SNR) by stacking the differences over 6 months and detected the gravity changes associated with the subduction and uplift.…”

“…Ogawa and Heki (2007) fitted the 4-year geoid height timeseries (2 years before and 2 years after the earthquake) with an annual and a semi-annual periodic terms, a coseismic jump, and a post-seismic relaxation and found a dominant-negative gravity anomaly in the Andaman Sea followed by a slow post-seismic rebound. Panet et al (2007) removed the interannual hydrological influences by using a global hydrological model, performed a continuous wavelet analysis of the geoid time-series, and discovered a short-term post-seismic effect located in the Andaman Sea and a large-scale effect still ongoing 9 months after the earthquake. de Linage et al (2009) used 4.6 years of GRACE observations, modeled the co-seismic changes by normalmode summation, and separated the co-seismic and post-seismic gravity changes associated with the Sumatra-Andaman earthquake.…”

Estimating geoid height change in North America: past, present and future

“…Co-and postseismic geoid changes for the Mw = 9.3 2004 Sumatra-Andaman earthquake have been evidenced from the GRACE satellites (de Linage et al 2009;Panet et al 2007) and used to constrain upper mantle rheology (Panet et al 2010). …”