DOI: 10.5061/dryad.j9kd51c9s
title: Hales discontinuity in the southern Indian continental lithosphere: seismological and petrological models

description: We model the shear wave velocity structure of the
 Hales-discontinuity beneath the Eastern Dharwar Craton and
 Southern Granulite Terrain in Southern India using P-wave
 receiver function (P-RF) analysis and joint inversion with Rayleigh wave
 phase velocity dispersion. For this study we use data from seismological
 stations HYB, GBA and KOD. We isolated P-RFs where the Hales
 phase is distinct and model them using joint data analysis.
 We also use common conversion point stack profiles constructed by
 depth migrating P-RFs through the velocity model and show that
 the Hales discontinuity is undulatory in nature. We perform petrological
 modeling of the Hales discontinuity and fianlly propose a geodynamic model
 for its evolution. 
description: Seismological analysis we use broadband teleseismic data from the
 Geoscope station Hyderabad (HYB) and the Indian Institute of Astrophysics
 & University of Cambridge temporary network stations Gauribidanur
 (GBA) and Kodaikanal (KOD). Stations HYB had been operated for a period of
 18 years (1989-2007). Broadband data for HYB was downloaded from the Data
 Management Center of the Incorporated Research Institutions in Seismology
 (IRIS-DMC). GBA was operated from 1998 to 2001, and KOD was operated from
 2002 to 2006. Both stations were equipped with Guralp CMG-3T seismometer
 (120~s--50~Hz flat velocity response), with Reftek data logger at GBA and
 Guralp Data and Communication Module (CMG-DCM) at KOD. The station
 location and time stamp to the recorded data were provided by Global
 Positioning System (GPS) receiver connected to the seismometer.
 In this study we use teleseismic earthquakes with magnitude
 greater than 5.5, in the distance range of 30 to 90 degree to model the
 sub-crustal lithospheric mantle structure. A total of 604, 52 and
 44 seismograms from HYB, GBA and KOD, respectively, have been used for
 P-wave receiver function (P-RF) analysis.   The three
 component broadband waveforms are pre-processed by rotating the horizontal
 components (North-South and East-West) into radial and tangential
 directions using <br> the back-azimuth angle. The vertical component
 waveform is deconvolved from the radial and tangential components to
 remove source and propagation effects, except for those immediately
 beneath the station. This deconvolved radial waveform contains the effects
 of the structure beneath the receiver site and is termed the P-wave
 receiver function. We use the iterative time domain deconvolution
 technique where the P-RF is created using a spike train, constructed by
 cross-correlating the radial with the vertical component waveform. This
 spike train is convolved with the observed vertical component waveform to
 form a synthetic radial component waveform. The synthetic and <br>
 observed radial component waveforms are compared in the least-squares
 sense and a misfit value calculated. Based on this misfit, the spike
 train is iteratively updated. Once the misfit value fall below an
 acceptable limit (chosen as 0.001 in this study) or the maximum number of
 iterations (set at 200) are completed, the process stops. This iteratively
 updated best fitting spike train is the computed P-wave radial receiver
 function. Observed waveforms have high frequency noise, which are
 eliminated using a low-pass filter. This also assists in stabilizing the
 time domain deconvolution process. A Gaussian filter of width 2.5 (corner
 frequency $\sim$0.46~Hz) is used as this low pass filter \citep{Ammon91}.
 The P-RF obtained through the iterative time domain deconvolution is
 assessed for quality by the percentage fit to the observed radial
 waveform. In this study we use P-RFs with fit of 70\% and
 above.  This dataset is the best P-RFs obtained from
 the analysis described above. 
description: Software needed: Seismic Analysis Codes: http://ds.iris.edu/files/sac-manual/