Preprints
https://doi.org/10.5194/se-2019-191
https://doi.org/10.5194/se-2019-191

  27 Jan 2020

27 Jan 2020

Review status: this preprint was under review for the journal SE. A final paper is not foreseen.

An MCMC Bayesian full moment tensor inversion constrained by first-motion polarities and double couple percent

Mehrdad Pakzad1, Mahnaz Khalili2, and Shaghayegh Vahidravesh2 Mehrdad Pakzad et al.
  • 1Institute of Geophysics, University of Tehran, Tehran, 1435944411, Iran
  • 2Graduate Student of Geophysics, Institute of Geophysics, University of Tehran, Tehran, 1435944411, Iran

Abstract. Monte Carlo Markov chain (MCMC) samplings can obtain a set of samples by directed random walk, mapping the posterior probability density of the model parameters in Bayesian framework. We perform earthquake waveform inversion to retrieve focal angles or the elements of moment tensor and source location using a Bayesian MCMC method with the constraints of first-motion polarities and double couple percentage using full Green functions and data covariance matrix. The algorithm tests the compatibility with polarities and also checks the double couple percentage of every site before the time-consuming synthetic seismogram computation for every sample of moment tensor of every trial source position. Other than large earthquakes, the method is especially suitable for weak events (M < 4) that their focal mechanisms cannot be well-constrained by polarities or seismograms alone, unless a dense local network is available; something that is generally occasional. Two- and one-station solutions show more agreement with all-station solution if polarity and DC % constraints are employed. In order to examine the validity of the method, two events with the independent focal mechanism solutions are utilized. Furthermore, we also calculate data covariance matrix from pre-event noise and Green function uncertainty to obtain the errors of focal mechanisms.

This preprint has been withdrawn.

Mehrdad Pakzad et al.

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Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Mehrdad Pakzad et al.

Mehrdad Pakzad et al.

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This preprint has been withdrawn.

Short summary
Mechanisms of earthquakes' sources are essential for seismotectonic studies. We have used algorithms for sampling from probability distributions to retrieve focal mechanism and source location of seismic events. The inversion method uses earthquake records but constrain the solution by polarities and double couple percentage which also makes the calculations faster. Two- and one-seismic station solutions show more agreement with all-station solution if polarity and DC% constraints are employed.