Path Calibration Studies in and Around the Indian Subcontinent

Abstract

We have developed one-dimensional crustal models for the regions of Peninsular India, northeast India and parts of the northwest Pakistan by modeling regional seismograms recorded up to 12 deg. distance. We modeled regional seismograms recorded at several stations in the Indian subcontinent, NIL (Nilore, Pakistan) and LSA (Lasha, China). We modeled teleseismic pP and sP phases to constrain depths and the amplitude variation of the pP, sP and P waves to constrain focal mechanisms of earthquakes. These crustal models are now being used to develop travel-time curves for seismic phases (P and S) so that they can be used in the seismic event location programs. We have also identified a set of possible GT10 and GT25 events using the data base from the ISC catalog and local contacts. For some events the locations determined using travel times from local networks and regionalized velocity models are found at several tens of kilometers away from the ISC and EHB hypocenters -- especially for small events. Often travel times exhibit residuals relative to a crustal structure used in their locations. To investigate how well this can be calibrated in the region surrounding the Indian subcontinent, we used a few GT10 events from the northeastern India and analyzed their travel times to the seismic stations that operate in the Indian subcontinent. We computed travel-time residuals by subtracting the IASP91 travel times from the observed travel times and by subtracting the IASP91 travel times from the travel times computed for 2D cross-sectional paths obtained from a preliminary 3D model of the region. This 3D model was constructed by placing the crustal model of Mooney and Laske on the mantle structure from Grand s tomographic model extrapolated to P wave velocities using a constant Poisson s ratio. We used a modified shortest path algorithm to calculate these travel times in this study.

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Document Details

Document Type
Technical Report
Publication Date
Sep 01, 2000
Accession Number
ADA572547

Entities

People

  • Bradley B. Woods
  • Chandan K. Saikia
  • Hong K. Thio

Tags

DTIC Thesaurus Topics

  • Abstracts
  • Algorithms
  • Asia
  • Boundaries
  • Broadband
  • Buildings And Structures
  • Calibration
  • Databases
  • Digital Data
  • Earthquakes
  • Epicenters
  • Pakistan
  • Residuals
  • Surface Waves
  • Three Dimensional
  • Travel Time
  • Waves

Fields of Study

  • Environmental science

Readers

  • Seismology