Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

R. K. Singh ¹, Rajesh Prakash ¹, A. K. Shukla ¹, A. K. Bhatnagar ¹, H. N. Srivastava ²

Affiliations
1 India Meteorological Department, New Delhi - 110 003, IN
2 128, Pocket-A, Sarita Vihar, New Delhi - 110 044, IN

Abstract

Seismicity pattern has been examined prior to the occurrence of the six earthquakes (M ≥ 54) during the period 1965 to 2005. This includes the damaging earthquake of Gilgit 1972 Pattan 1974 and Muzaffarabad earthquake 2005. The results were interpreted with reference to (i) pattern of occurrence of past earthquakes (ii) energy released event wise and cumulative energy released year wise. It was interesting to note that all these earthquakes were preceded by quiescence followed by increase in seismicity before the occurrence of main earthquake. An alternative interpretation of the data prior to the occurrence of the great Muzaffarabad earthquake (October 2005) suggested a sequence of double quiescence as reported in Uttarkashi (1991) and Chamoli (1999) earthquakes in Uttaranchal. The focal mechanism solution of an earthquake during February 2004 and October 2005 revealed significant changes in the orientation of P and T axis. It was interesting to find that the value of 'b' in Gutenberg-Richter frequency magnitude relationship decreased markedly during 1985-1994 and almost recovered prior to the occurrence of Great Muzaffarabad earthquake m accordance with the Dilantancy Diffusion model of earthquakes.

Keywords

Seismicity Pattern, Muzaffarabad Earthquake, B-value.

Full Text

     

Rajesh Prakash ¹, J. P. Shrivastava ²

Affiliations
1 India Meteorological Department, New Delhi - 110 003, IN
2 Department of Geology, University of Delhi, Delhi - 110 007, IN

Abstract

Understanding of seismicity and seismotectonics of Delhi and adjoining areas is essential as these areas lie in the seismic zone IV and are geologically confined to the Delhi Fold Belt (DFB), juxtaposed to the Himalayan Frontal Thrust Fold Belt. Owing to the set-up, seismicity in this area is ascribed to the Himalayan Thrust System and activation of DFB Fault Systems. Considerably improved instrumental seismic monitoring in this area and data analysis had resolved three regions of pronounced seismicity that lie close to Sonepat, Rohtak and western part of the NCT Delhi, attributed to activation of various portions of the fault systems of the DFB. Based on seismic telemetry network data, the seismicity pattern analysis revealed that the Mahendragarh Dehradun Sub-Surface Fault (MDSSF) and Delhi Sargodha Ridge (DSR) are the two major zones of structural importance for the nucleation of seismicity in this region. These revelations were corroborated with the fault plane solution of the earthquakes. The dominant mechanism in nucleation of seismicity in DFB is the thrust with minor strike slip. The seismicity and seismotectonics of Delhi and adjoining areas endemic to activation of DFB is reviewed and presented in this paper.

Keywords

Earthquake, Seismicity, Seismotectonics, Fault Plane Solution, b-Value, Delhi.

Full Text