SEISMOTECTONIC STUDY OF NW HIMALAYAS USING HYPODD

Devika S Kumar

Department of Earth Sciences, Pondicherry University, Puducherry 605014

Sushil Kumar Rohella

Scientist 'F' & Head, Wadia Institute of Himalayan Geology, Dehradun 248001

ABSTRACT

The geology of Himalayas is a record of the most dramatic and visible creations of the modern plate tectonic forces. The Himalayas which stretch over 2400 km are the result of an ongoing orogeny – the result of continent-continent collision of tectonic plates. An insight into the occurrence and processes related to earthquakes has always been challenging for earth science community. The study of these earthquakes is not only important for mitigating the seismic hazards but also to unveil the spectrum in the evolution of the magnificent Himalayan mountain chain. One of the most striking aspects of the Himalayan orogeny is the lateral continuity of its major tectonic elements namely The Shivaliks, The Lesser Himalayas, The Higher Himalayas and The Indus Suture Zone. Thus, in this context analysis of earthquakes using modern methods has been taken into account in which Seisan software and HypoDD for location of earthquakes has been incorporated. The method used here for location of earthquake hypocenters is a double-difference algorithm known as hypoDD, which solves for event hypocenters and origin times using differential travel-time data from catalogue phase picks and waveform cross correlations. In the present study, one year data of nine stations situated in the North-Western Himalaya for the year 2017 has been used.

Earthquake waveforms are analysed and further processedd using the SEISAN software. With Seisan it is possible, using local and global earthquakes, to enter phase readings, locate events, edit events, determine spectral parameters, seismic moments etc. This software has been used to generate the basic observable data for further processing and implications. Locating an earthquake is a classic and an active research subject. HypoDD is a Fortran computer program package for locating and relocating earthquakes with the double-difference algorithm. The DD technique takes advantage of the fact that if the hypocentral separation between two earthquakes is small compared to the event-station distance and the scale length of velocity heterogeneity, then the ray paths between the source region and a common station are similar along almost the entire ray path . This method uses relative travel times between linked event pairs and iteratively adjusts the locations of the events to minimize the sum of travel-time residuals.

Keywords: North-Western Himalaya, Seisan, HypoDD, Location