Synthetic Seismogram Modeling of Crustal Seismic Record Sections from the Koyna Dss Profiles in the Western India

  1. Robert F. Mereu,
  2. Stephan Mueller and
  3. David M. Fountain
  1. V. G. Krishna,
  2. K. L. Kaila and
  3. P. R. Reddy

Published Online: 9 APR 2013

DOI: 10.1029/GM051p0143

Properties and Processes of Earth's Lower Crust

Properties and Processes of Earth's Lower Crust

How to Cite

Krishna, V. G., Kaila, K. L. and Reddy, P. R. (1989) Synthetic Seismogram Modeling of Crustal Seismic Record Sections from the Koyna Dss Profiles in the Western India, in Properties and Processes of Earth's Lower Crust (eds R. F. Mereu, S. Mueller and D. M. Fountain), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM051p0143

Author Information

  1. National Geophysical Research Institute, Hyderabad 500007, India

Publication History

  1. Published Online: 9 APR 2013
  2. Published Print: 1 JAN 1989

ISBN Information

Print ISBN: 9780875904566

Online ISBN: 9781118666388

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Keywords:

  • Earth—Crust—Congresses;
  • Geophysics—Congresses

Summary

Two deep seismic sounding profiles, each about 200 km long, were recorded in the east-west direction in the Koyna region of the Western India by the National Geophysical Research Institute CKlquiring wide angle crustal se ismic data in the analog form. the analog DSS records, acquired by continuous profiling, have been digitized and assembled into trace normalized record sections which are displayed in the form of reduced travel time with reduction velocity of 6 km/sec. Travel times and relative amplitudes modeling, with the aid of synthetic seismograms, of the record sections obtained in the eastern and western directions on the northern profile as well as a record section in the eastern direction on the southern profile reveal consistent models of the crustal velocity structure with minor lateral variations in the Koyna region. the prominent features of the crustal velocity models inferred in this region include low velocity layers (LVL) in the upper crust (6.0 to 11.5 km depth) as well as in the lower crust (26.0 to 28.0 km depth) and at least 2 km thick transitional Moho at 35.5 to 37.5 km depth. However, the Moho is 1–2 km deeper along the southern profile. the upper crustal LVL, with its top at 6–7 km depth in these models, is consistent with the observed seismic activity concentration at 4–5 km depth and an appreciable reduction of seismic activity at greater depths in the Koyna region. the inferred crustal velocity models are also consistent with the essentially aseismic nature of the lower crust in this region. the two low velocity layers, in the upper and the lower crust in th is region, may suggest rheological stratification of this part of the lithosphere with levels of increased ductility at those depths. the reflected phase PMP, from the Moho boundary, is relatively strong only beyond 90–100 km recording distance while it is almost suppressed in the subcritical distances on the record sections considered in the present study. Further the PS converted waves from the Moho are also not observable at the appropriate times in these record sections thus substantiating the transitional nature of the Moho, which is at least 2 km thick, in the Koyna region. the Pn phase, well recorded as the first arrival beyond 165 km recording distance, reveals an uppermost mantle P velocity of 8.25 km/sec in this region.