Change of stress patterns during 2004 M_W 9.3 off‐Sumatra mega‐event: Insights from ridge–trench interaction for plate margin deformation

Abstract

The Andaman-Sumatra subduction margin is identified as a complex tectonic transition zone between the Myanmar and Java regions. The Late Cenozoic evolution of various basins, faults, plate slivers, and the Andaman back-arc rift-transform system altered the boundary. The sharp changes in free air gravity anomaly, north-eastward swing of the Andaman Sea spreading ridge, increased dip of the subducting plate and the decrease in seismicity towards the north of the study area possibly account for increased interaction of the Ninetyeast Ridge (NER) against the Andaman Trench.Stress fields of the subducting plate were modified from semi-radial compression (SRC) during pre-seismic deformation to pure extension (PE), semi-radial extension (SRE), and strike-slip extension (SSE) during post-seismic deformation phase in the central segment. The co-seismic second energy burst, subsidence in the overriding plate, and subsequent reactivation of the Barren and Narcondum volcanoes also corroborate the transformation of the stress fields in the overriding plate into predominant extension. The dominant SRC stress in the subducting Indo-Australian lithosphere in the south changed to pure compression (PC) prior to the 2004 M W 9.3 mega-event.While the changes in stress field from SRC to pure strike-slip (PSS) in the north account for stress relaxation after the occurrence of the mega-event and the co-seismic~1,300km rupturing, the occurrences of uplift and subsidence in the northern part of the study area were possibly caused by inherited stress field from the Eastern Himalaya.The continued overall compression in the subducting Indo-Australian Plate in the south, under pre-and post-seismic deformation phases, is presumably correlated with the focal mechanism stress parameters of the 2004 mega-event, whereas the strikeslip-dominated movement in the overriding plate remained almost unchanged. The stress perturbations in the central segment are interpreted to be the result of interaction between the NER and Andaman-Sumatra Trench.

Earthquake Shocks Around Delhi-NCR and the Adjoining Himalayan Front: A Seismotectonic Perspective

“…The enormity of deformation of the orogenic process has resulted in the development of unconformity in the floor of the Bay of Bengal, folding and faulting in the equatorial Indian Ocean, and the evolution of basins and ridges near the foothills of the Himalayas-all in response to tectonic processes in the orogen that evolved during Miocene-Pliocene time (Cochran, 1990;Curray, 2005;Gordon, 2009). Thus, the active resistance to the under thrusting distributes and perturbs the stress fields up to the Indian Ocean, and accounts for occasional incidents of great intraplate earthquakes Aggarwal et al, 2016;Khan et al, 2016;Khan et al, 2020). Further, the excess weight of the orogeny is supported in parts by the strength of the Indian plate, which distributes the load by flexing down along the ∼1000 km laterally extended and isostatically over-compensated Indo-Gangetic Plains (e.g., Lyon-Caen and Molnar, 1983;Tandon et al, 2014).…”

Spatial Temporal Condition of Recent Seismicity In The Northern Part of Sumatra

“…Oblique subduction between Indo-Australia plate with a slip rate of 5 mm/yr beneath Eurasian generates the oceanic earthquake (Bradley et al, 2017;Liu et al, 2018). Several historical earthquakes that followed by a tsunami, such as 2004 Sumatra-Andaman M 9.0 (Lay et al, 2005, Khan et al, 2020, 2005 Nias M 8.5 (Meltzner et al, 2015), and 2012 Wharton Basin M8.2 and 8.1 (Hill et al, 2015).…”