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Direction-Based P wave Traveltime Residual Estimation for some Stations Around Southern Thailand, Peninsular Malaysia, Singapore and Sumatra Using a New Ray Tracing Algorithm
  • Abel Uyimwen Osagie,
  • Ismail Ahmad Abir
Abel Uyimwen Osagie
University of Abuja

Corresponding Author:abel.osagie@uniabuja.edu.ng

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Ismail Ahmad Abir
Universiti Sains Malaysia
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Path dependent corrections relative to traveltimes have been demonstrated to improve event locations. Using available global velocity models, direction-based station corrections can be estimated in a region without calibration data. In this study, traveltime corrections have been obtained for 117 broadband seismic stations around southern Thailand, Peninsular Malaysia, Singapore and Sumatra region of Indonesia. A total of 82,325 first-arrival waves are obtained from 15,212 earthquakes that have occurred around the Sumatra Subduction Zone over five decades (1964 – 2018). The dataset is a combination of arrival time data from the Bulletin of International Seismological Centre and waveforms from the Incorporated Research Institutions for Seismology. A newly developed algorithm for three-dimensional ray tracing is used to compute traveltimes and raypaths. The corrections are based on the IASP91/AK135 velocity models at four back-azimuthal directions. The estimated residuals in seconds (s) ranges from -2.15 to 2.25 s for stations distributed around southern Thailand and a range of -0.76 to 1.60 s for stations within Peninsular Malaysia. A range of 0.59 to 1.08 s for stations within Singapore and -1.52 to 2.46 s for stations distributed around Sumatra (in Indonesia). Station PSI in Sumatra Island recorded the highest number with 4877 arrivals. Stations LEM, KLM and KGM show consistent high residual values at all calculated angles and distances. The result of this study will support routine location of hypocentral parameters within the region. The scheme is being implemented for use in the forward computational process of seismic tomographic inversion in the study area.