Implications of 3D Seismic Raytracing on Focal Mechanism Determination

Author:

Newrkla Katharina1,Shiddiqi Hasbi Ash12,Jerkins Annie Elisabeth3,Keers Henk1,Ottemöller Lars1

Affiliation:

1. Department of Earth Science, University of Bergen, Allègaten 41, N‐5007 Bergen, Norway, hasbi.shiddiqi@uib.no

2. ORCID ID: 0000‐0002‐8927‐0167.

3. NORSAR, Gunnar Randers vei 15, P.O. Box 53, N‐2007 Kjeller, Norway

Abstract

Abstract The purpose of this study is to investigate apparent first‐motion polarities mismatch at teleseismic distances in the determination of focal mechanism. We implement and compare four seismic raytracing algorithms to compute ray paths and travel times in 1D and 3D velocity models. We use the raytracing algorithms to calculate the takeoff angles from the hypocenter of the 24 August 2016 Mw 6.8 Chauk earthquake (depth 90 km) in central Myanmar to the stations BFO, GRFO, KONO, and ESK in Europe using a 3D velocity model of the upper mantle below Asia. The differences in the azimuthal angles calculated in the 1D and 3D velocity models are considerable and have a maximum value of 19.6°. Using the takeoff angles for the 3D velocity model, we are able to resolve an apparent polarity mismatch where these stations move from the dilatational to the compressional quadrant. The polarities of synthetic waveforms change accordingly when we take the takeoff angles corresponding to the 3D model into account. This method has the potential to improve the focal mechanism solutions, especially for historical earthquakes where limited waveform data are available.

Publisher

Seismological Society of America (SSA)

Subject

Geochemistry and Petrology,Geophysics

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