Direction-Based P wave Traveltime Residual Estimation for some Stations
Around Southern Thailand, Peninsular Malaysia, Singapore and Sumatra
Using a New Ray Tracing Algorithm
Abstract
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.