Ground Movements along the Himalayan Arc Derived from GPS Observations (1995-2019)

Date

2020-12

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Abstract

This study depicts GPS-derived ground movements associated with long-term fault creeping and large earthquakes within the Indian-Asian plate boundary zone. To delineate these signals, a stable geodetic reference frame of the Indian Plate (IND20) was produced using the 7-parameter Helmert transformation. IND20 was based on over two decades of continuous GPS daily solutions at six GPS sites (GOA1, HYDE, IISC, LCK4, MPUR, and NPGJ). Linear least squares and MIDAS velocity estimates in IND20 agreed overall, but some stations differed due to limitations on MIDAS’s algorithm. Also, IND20 proved to be a better stable Indian plate reference frame to use for geodetic studies compared to recent Indian plate Euler poles. The long-term tectonic trends with respect to IND20 show the Eurasian plate is moving towards the Indian plate at a rate up to 1.4 cm/yr directed southwest with 0.3-0.6 cm/yr uplift along the Himalayan arc (1997-2015) and 2.1 cm/yr directed southeast with 0.3 cm/yr uplift along Southern Tibet (1995 to 2019). Bhutan Himalayas show up to 0.7 mm/yr southeast motion in IND20 (2004-2015). Greatest strain accumulation is in northern Nepal where the strain accumulation rate is up to 1 cm/yr directed southward and 0.6 cm/yr up (1995-2015). The subsidence in Kathmandu (10.8 cm/yr in IND20; 2014-2019), Dhaka (1.1 cm/yr in IND20; 2003-2011) and Thimphu (0.3 cm/yr in IND20; 2004-2015) isn’t long-term tectonic movement, but instead are likely a consequence of aquifer compaction due to groundwater withdrawal. Seismic displacement from the 2008 Mw 6.3, 2011 Mw 6.9, and 2015 Mw 7.8 earthquakes indicate east dipping normal faulting, left-lateral strike-slip faulting and northeast dipping thrust faulting, respectively. The earthquakes occurred at different depths along different faults and faulting mechanisms suggesting the partial decoupling of strain between the Indian and Eurasian plates is intercontinental and intracontinental. Post-seismic deformation increased ground motion by a maximum of 1.9 cm/yr south, 0.7 cm/yr west, and 0.9 cm/yr up (CHLM; 2015-2019; IND20) and is still ongoing near many sites in Nepal. The 2008 Mw 6.3 and 2011 Mw 6.9 earthquakes exhibited no post-seismic deformation. No noticeable pre-seismic deformation was observed in any of the earthquakes.

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Keywords

GPS, Geodesy, Indian Plate Reference Frame, Indian and Eurasian Plate Collision, Earthquakes, Long Term Crustal Movement

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