Seismic moment release along selected major transforms on the Central Indian Ridge,Western Indian Ocean,and its tectonic implications |
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| Authors: | M Radha Krishna |
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| Institution: | (1) Marine Geology Division, School of Marine Sciences, Cochin University of Science and Technology, Fine Arts Avenue, 682 016 Cochin, India |
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| Abstract: | A detailed seismicity map of the Central Indian Ridge for the period 1912–1993 is presented, and the earthquakes pertaining
to four major transforms offsetting the ridge are utilized to study the moment release pattern. The scalar moment release
for the period 1912–1993, and the summed moment rate tensors for both short period (1977–1993) and long period (1912–1993)
bring out a unified picture of moment release pattern.
The fraction of seismic slip calculated based on depths of 100°C and 400°C limiting temperatures suggests that the Marie-Celeste
transform requires a slip almost to a depth of 400°C isotherm to account for the observed moment, and the Argo transform requires
depth of faulting much above the 400°C isotherm. A very small fraction of slip is accounted seismically for Vema (53%) and
12° 12′S (23%) even to depths of 100°C isotherm, suggesting a very low order of moment release along these transforms.
The horizontal plate velocities and the corresponding strain rates obtained from moment tensor summation of long period data
(82 years) give rise to (V
y
y
; V
y
x
mm. yr−1) of 6.0 and 6.1 along Marie-Celeste, 1.3 and 0.50 along Argo, 0.06 and 0.06 along 12° 12′S, 1.6 and 0.25 along Vema transforms.
The corresponding strain rates (ε
y
y
;ε
y
x
× 10−15 S−1) are 12.7 and 6.8 along MarieCeleste, 6.9 and 1.4 along Argo, 0.27 and 0.14 along 12° 12′S, 7.3 and 0.58 along Vema transforms.
These results suggest that the strain rates were highest and almost all predicted motion is taken up seismically along the
Marie-Celeste transform. The strain rates are lower along Argo transform and the observed moment release require shallower
depth of faulting in order to slip to be accounted seismically. The Vema and 12° 12′S transforms are characterized by low
strain rates and less than 15 per cent of motion is accommodated seismically within the seismogenic layer. It is proposed
that the deficiency of moment release along the Vema and 12° 12′S multiple transform system may be due to most of the plate
motion occurring aseismically. |
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| Keywords: | Scalar moment release moment rate tensors strain rates major transforms Central Indian Ridge |
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