GPS measurements of postseismic deformation in the Andaman‐Nicobar region following the giant 2004 Sumatra‐Andaman earthquake

Abstract

We report GPS measurements of postseismic deformation from 22 campaign‐mode and one continuous GPS sites in the Andaman‐Nicobar region following the great Sumatra‐Andaman earthquake of 26 December 2004. Large horizontal displacements toward west to southwest, varying in magnitude from 10 to 40 cm, and with uplift reaching 16 cm, occurred in the region in the first year after the earthquake. The observed motion decreased logarithmically in the subsequent year. We suggest that in the Andaman region, frictional afterslip occurred farther downdip of the coseismic rupture, while in the Little Andaman and Nicobar regions, the coseismic rupture and afterslip patch partly overlapped. The afterslip was mostly aseismic and did not contribute to the aftershocks. The aftershocks and postseismic displacements appear to follow a similar relationship, although with different decay times. The temporal dependence of the two differs only by a term linear in time. Thus the temporal evolution of the afterslip seems to be consistent with a mechanism governed by frictional afterslip. Available rates of interseismic and postseismic deformation and coseismic static offsets allow us to approximately estimate a return period of about 400 years for great earthquakes in the Andaman region.

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

“…Scholz (1990), Marone et al (1991), and Scholz (1998) all proposed that the afterslip increases logarithmically with time. Freed et al (2007) and Gahalaut et al (2008) also used a logarithmic function to fit GPS displacement time series. Furthermore, the postseismic surface deformations determined by Maxwell viscoelastic rheologies exhibited an exponential-like relaxation phase (Hetland and Hager 2006).…”

Weak Tectono-Magmatic Relationships along an Obliquely Convergent Plate Boundary: Sumatra, Indonesia

“…In fact, while in the inter-seismic period the kinematics of GSF may be predominantly dextral, in the co-and (to a lesser extent) post-seismic cycle the arc may experience significant arc-normal extension. This has been observed not only after the 2004 Sumatra mega-earthquake (Subarya et al, 2006;Gahalaut et al, 2008;Shearer and Burgmann, 2010), but also in NE Japan after the 2011 Tohoku mega-earthquake (Ozawa et al, 2011;Simons et al, 2011;Takada and Fukushima, 2013) and in Southern Chile after the M9.5 1960 and the M8.8 2010 Maule mega-earthquakes (Barrientos and Ward, 1990;Wang et al, 2007;Vigny et al, 2011;Pritchard et al, 2013). In the latter two cases, mega-earthquakes promoted the transient (co-and postseismic) inversion of the major tectonic structures, also affecting magmatic activity (Singer et al, 2008;Takada and Fukushima, 2013).…”

“…GPS data in the northern part of Sumatra show that the coand post-seismic displacement after the 2004 M9.2 SumatraAndaman mega-earthquake was characterized by significant SW motion (several tens of cm of co-seismic displacement, plus tens of cm in the first year after the earthquake) of the volcanic arc region (Subarya et al, 2006;Gahalaut et al, 2008;Shearer and Burgmann, 2010). The 2004 mega-earthquake was followed, 1 month later, by a seismic swarm in the Andaman Sea north of Sumatra (Kundu et al, 2012) and volcanism, as testified by a submarine eruption .…”

Indian National GNSS Programme: Crustal deformation measurements in the Indian Sub-continent

“…In general, the horizontal and vertical deformation rate decreased from east to west. Gahalaut et al (2008) and Paul et al (2007) presented the estimates of postseismic measurements using GPS. The ongoing measurements suggest that the postseismic horizontal deformation in the Andaman-Nicobar region occurred in the west to southwest direction and most of the sites experienced uplift.…”