Microstrain stability of Peninsular India 1864–1994 |
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Authors: | J Paul F Blume S Jade V Kumar P S Swathi M B Ananda V K Gaur Roland Burgmann Roger Bilham B Namboodri Dave Mencin |
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Institution: | (1) CSIR Centre for Mathematical Modelling and Computer Simulation, NAL Belur Campus, 560037 Bangalore, India;(2) CIRES, University of Colorado, 80309-2016 Boulder, CO, USA;(3) University of California, Davis, USA;(4) UNAVCO, Boulder, Colorado, USA;(5) Survey of India, Southern Circle, Bangalore |
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Abstract: | We report the results of the South Indian Strain Measuring Experiment (SISME) designed to determine whether strain related
to microseismicity in the past century may have deformed the networks of the 19th century Great Trigonometrical Survey of
India (GTS). More than a dozen GTS points were measured between Mangalore, Madras, and Kanyakumari in southernmost India using
GPS geodesy to determine regional deformation. Detailed measurements were made near two of the original baselines of the survey
to determine the reliability of dilatational strain data for the network. The regional measurements revealed negligible regional
dilatational (+ 11.2 + 10 microstrain) and shear strain changes (0.66± 1.2μradians) in the southernmost 530 km of India. In
addition to these measurements, we determined the rate of northward and eastward motion of a point in Bangalore (1991–1994)
in the ITRF92 reference frame to be 39 ± 3.5 mm/year, and 51 ± 11 mm/year respectively. This is consistent with NUVEL-1A plate
motion estimate for India. Simultaneous measurements to a point near Kathmandu reveal that the Indian plate and the Southern
Himalaya are moving approximately in unison, placing an upper limit on the rate of creep processes beneath the lesser Himalaya
of ≈6 mm/year, and suggesting relatively rigid behavior of the Indian plate north of Bangalore. The stability of the Indian
plate is confirmed by the absence of significant changes in the lengths of the two baselines at Bangalore and Cape Comorin,
which, within the limits of experimental error have not changed since 1869. The measurements place an upper limit for recent
deformation in the southern peninsula, and hence a lower limit for the renewal time for intraplate earthquakes in the region
of approximately 10,000 years, assuming shear failure strain of approximately 100 μradians. This, in turn, implies that recurrence
intervals for Peninsular Earthquakes far exceed the length of the written historic record, suggesting that the characterisation
of seismic recurrence intervals from historical studies is likely to be fruitless. In contrast, the SISME experiment demonstrates
that the noise level of geodetic studies based on 19th century GTS data is less than 0.02 μstrain/year, providing considerable
scope for delineating regions of anomalously high seismogenic strain, by GPS measurements at all available trig points of
the 19th century GTS survey. |
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Keywords: | GPS measurements south Indian trigon deformation strain rate plate velocity |
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