Tectonic geodesy revealing geodynamic complexity of the Indo-Burmese arc region, North East India

Abstract

The plate boundary between India and Sunda plates across the Indo-Burmese arc (IBA) region is probably the most neglected domain as far as the plate motion, crustal deformation and earthquake occurrence processes are concerned. Because of the limited or no geodetic measurements across the IBA region, debate continues on the most appropriate plate boundary model for the region. Subduction along this boundary occurred in geological past, but whether it is still active is a debatable issue. It is believed that the predominantly northward India–Sunda relative plate motion of about 36 mm/year is partitioned between the Indo-Burmese wedge (IBW) and the Sagaing Fault (SF). However, it is not clear how relative plate motion between India and Sunda plates is accommodated across the IBA region – whether localized, partitioned or distributed, and in particular what is the slip rate and mode of slip accommodation across faults in the region? In such cases, Global Positioning System (GPS) measurements of crustal deformation have proved to be the best and probably the only tool. Our detailed seismo-tectonic study, crustal deformation study using high precision GPS measurements of eight years, strain rate estimates, field studies, analytical and finite element modelling of GPS data from the IBW region in North East India provide evidence for present-day active deformation front (or the plate boundary fault) between the India and Burma plates. On the basis of our extensive studies, it is now suggested that the Churachandpur–Mao Fault (CMF), a geologically older thrust fault, accommodates motion of about 16 mm/year through dextral strike–slip manner. The motion across the CMF constitutes about 43% of the relative plate motion of 36 mm/year between the India and Sunda plates. The remaining motion is accommodated at SF. On the basis of modelling, which suggests low friction along the CMF, absence of low-magnitude seismicity along the CMF, lack of historic and great and major earthquakes on the CMF and regions around it, and field studies, it is proposed that the motion across the CMF occurs predominantly in an aseismic manner. Such behaviour of the CMF significantly lowers the seismic hazard in the region.