• Biju John

      Articles written in Journal of Earth System Science

    • Electron spin resonance dating of fault gouge from Desamangalam, Kerala: Evidence for Quaternary movement in Palghat gap shear zone

      T K Gundu Rao C P Rajendran George Mathew Biju John

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      The field investigations in the epicentral area of the 1994 Wadakkancheri (Desamangalam), Kerala, earthquake (M 4.3) indicate subtle, but clearly recognizable expressions of geologically recent fault zone, consisting of fracture sets showing brittle displacement and a gouge zone. The fracture zone confines to the crystalline basement, and is spatially coincident with the elongation of the isoseismals of the 1994 mainshock and a 10-km-long WNW-ESE trending topographic lineament. The preliminary results from the electron spin resonance (ESR) dating on the quartz grains from the fault gouge indicate that the last major faulting in this site occurred 430 ± 43 ka ago. The experiments on different grain sizes of quartz from the gouge showed consistent decrease in age to a plateau of low values, indicating that ESR signals in finer grains were completely zeroed at the time of faulting due to frictional heat. The results show a relatively young age for displacement on the fault that occurs within a Precambrian shear zone. Discrete reactivated faults in such areas may be characterized by low degree of activity, but considering the ESR age of the last significant faulting event, the structure at Desamangalam may be categorized as a potentially active fault capable of generating moderate earthquakes, separated by very long periods of quiescence.

    • Geomorphic observations from southwestern terminus of Palghat Gap, south India and their tectonic implications

      Yogendra Singh Biju John G P Ganapathy Abhilash Abhilash George S Harisanth K S Divyalakshmi Sreekumari Kesavan

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      The region around Wadakkancheri, Trichur District, Kerala is known for microseismic activity, since1989. Studies, subsequent to 2nd December 1994 (M=4.3) earthquake, identified a south dippingactive fault (Desamangalam Fault) that may have influenced the course of Bharathapuzha River. Theongoing seismicity is concentrated on southeast of Wadakkancheri and the present study concentratedfurther south of Desamangalam Fault. The present study identifies the northwestern continuity of NW–SE trending Periyar lineament, which appears to have been segmented in the area. To identify the subtlelandform modifications induced by ongoing tectonic adjustments, we focused on morphometric analysis.The NW–SE trending lineaments appear to be controlling the sinuosity of smaller rivers in the area,and most of the elongated drainage basins follow the same trend. The anomalies shown in conventionalmorphometric parameters, used for defining basins, are also closely associated with the NW–SE trendingPeriyar lineament/s. A number of brittle faults that appear to have been moved are consistent withthe present stress regime and these are identified along the NW–SE trending lineaments. The currentseismic activities also coincide with the zone of these lineaments as well as at the southeastern endof Periyar lineament. These observations suggest that the NW–SE trending Periyar lineaments/faultsmay be responding to the present N–S trending compressional stress regime and reflected as the subtlereadjustments of the drainage configuration in the area.

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