Crustal deformations associated with the great Sumatra-Andaman earthquake deduced from continuous GPS observation

Abstract

We analyzed continuous GPS data from more than 20 sites in Asia, Australia and islands in Indian Ocean in order to detect crustal deformations associated with the Sumatra-Andaman earthquake of December 26, 2004. Coseismic steps can be recognized at sites about 3,000 km away from the epicenter such as Kunming in south China, Quezon in Philippines, and Diego Garcia Island in central Indian Ocean. The largest displacement of about 26 cm is found at Phuket in Thailand about 600 km away from the epicenter, about twice as large as that at Sampari, the nearest site in northern Sumatra. These observations suggest that as large slip as 14 m occurred beneath the Nicobar Islands. Large postseismic displacements are observed at Phuket and Sampari after the mainshock, but the former is three times larger than the latter. This suggests that the spatial distribution of afterslip is different from the coseismic slip distribution. The temporal variation of postseismic displacements can be explained by a logarithmic function derived from rate-state dependent friction law with short characteristic time. The area where coseismic displacements from the Nias earthquake of March 28, 2005 are detected is much smaller than that from the December mainshock, but displacement at Sampari is larger than that during the mainshock. These displacements suggest less than 4 m slip on a shallow dipping thrust fault and resultant moment release is smaller than that estimated from seismological data. Finally, total moment released by afterslip amounts to 3.83 × 10 22 Nm which is equivalent to Mw 8.99 for about five months, including the afterslip for the Nias earthquake.

Coseismic Slip and Afterslip of the GreatMw 9.15 Sumatra–Andaman Earthquake of 2004

“…Very-Far-Field (Ͼ1100 km from the Source) Data Many more-distant IGS stations throughout southeast Asia recorded a measurable coseismic signal (Banerjee et al, , 2007Catherine et al, 2005;Hashimoto et al, 2006;Kreemer et al, 2006a;Ohta et al, 2006;Vigny et al, 2005). Stations as far as 3000 km from the epicenter moved as much as 1-2 cm.…”

Combined logarithmic and exponential function model for fitting postseismic GNSS time series after 2011 Tohoku-Oki earthquake

“…Attempts have been made to use function fitting regression analysis to investigate postseismic deformation (Takahashi et al 2004;Hashimoto et al 2006;Nishimura 2014). The time series of a postseismic deformation is commonly fitted by a logarithmic or exponential decay function.…”

Review of the source characteristics of the Great Sumatra–Andaman Islands earthquake of 2004

“…Data from Lay et al (2005) and to be sheared off parallel to the subduction zone from Myanmar to Sumatra, termed the Andaman microplate ). Banerjee et al (2005), Catherine et al (2005), Vigny et al (2005) and Hashimoto et al (2006) use far-field GPS data to constrain fault slip during the December mainshock. Using far-field GPS sites about 400-3,000 km from the rupture, they derived a slip model for this earthquake with a maximum slip of 30 m. Banerjee et al (2005) estimates the average slip along the rupture to be~5 m. Hashimoto et al (2006) suggests that coseismic slip as large as 14 m occurred beneath the Nicobar Islands.…”

“…Banerjee et al (2005), Catherine et al (2005), Vigny et al (2005) and Hashimoto et al (2006) use far-field GPS data to constrain fault slip during the December mainshock. Using far-field GPS sites about 400-3,000 km from the rupture, they derived a slip model for this earthquake with a maximum slip of 30 m. Banerjee et al (2005) estimates the average slip along the rupture to be~5 m. Hashimoto et al (2006) suggests that coseismic slip as large as 14 m occurred beneath the Nicobar Islands. Gahalaut et al (2006) improved slip resolution and rupture characteristics using coseismic displacements derived from near-field GPS.…”