Stress drop and its relation to tectonic and structural elements for the meizoseismal region of great 1905 Kangra earthquake of the NW Himalaya

Investigations of micro- and low-magnitude earthquakes in the Kangra-Chamba region of the NW Himalaya were performed to evaluate the relationship between earthquake source, seismicity, stress drop, tectonics, and structure. The seismic events were recorded by a dense local network of 21 permanent/temporary stations during 2004–2005. The earthquake source parameters using spectral analysis were calculated for refined epicenters obtained by Local Earthquake Tomography method. We applied two approaches of spectral analysis for earthquake data and the box-counting fractal dimension for structural elements in order to understand the seismogenesis of the region properly. These two methods giving inter-dependable results were used for the study area that extends from latitude 31.5°N–33.5°N and longitude 75.5°E–77.5°E in the epicenter zone of devastating 1905 Kangra earthquake. The seismic moment of these earthquakes (1.5 ≤ Mw ≤ 4.8) is between 1.21E + 18 dyne-cm and 1.44E + 23 dyne-cm causing circular deformation of radius in the range 0.12–1.15 km based on Brune’s circular model. The study reveals that low value for the capacity fractal dimension (D <Subscript>0</Subscript> of 0.678) and seismically intense clustering of 135 earthquakes with low stress drops generally below 10 bar but up to 26 bar. Evaluated low stress drop of small size earthquakes and low D <Subscript>0</Subscript> of structural elements has led to the identification of nature of brittleness of the crust and proneness to high strain accumulation that indicates the presence of an asperity/barrier in the fault zones. The variation of b value and 3D seismic velocities supports the presence of asperity zone. Copyright Springer Science+Business Media Dordrecht 2013