RSTT (Regional Seismic Travel Time) is a seismic velocity model and computer software package that captures the major effects of 3-dimensional crust and upper mantle structure on regional seismic travel times. The RSTT program interface is easy to use, requiring only the input of two positions in/on the Earth (event and station locations) to compute the travel time between the specified points. RSTT was designed to be incorporated into real-time event location systems where travel times must be calculated in ~milliseconds on conventional computer hardware. RSTT is designed to work seamlessly with travel time predictions for teleseismic P-waves that are based on the ak135 model, and RSTT is particularly useful for low magnitude events where regional stations close azimuthal gaps in network coverage. Therefore, RSTT enables regional stations to complement a teleseismic monitoring network. RSTT was written in C++ and runs on Linux, Mac and Sun systems with interfaces from Java, C, and FORTRAN languages provided. Test data are included in the release package.
The RSTT 3D Earth velocity structure parameterization is based on a global tessellation of nodes (Figure 1). Velocity profiles (velocity vs. depth) at each node are interpolated to render a 3-dimensional crust that overlies a laterally variable representation of upper mantle velocity. The mantle velocity parameterization is specified by the velocity at the crust-mantle boundary and a linear velocity gradient as a function of depth.
Figure1. Example of a global tessellation. Inset shows nominal 1° (~111 km) node spacing for RSTT 3D velocity representations.
Specifying upper mantle velocity with a linear gradient constrains the mantle ray path to an analytic form (Figure 2), which dramatically increases computational efficiency of the travel time calculation. Tests suggest that this particular RSTT algorithm and geometrical parameterization is applicable for computing travel times for ray paths out to approximately 1,600 km.
Figure 2. Components of the RSTT Pn/Sn travel time calculation (left). Pn ray path through the RSTT unique parameterization (right).
Any velocity representation in RSTT's data format is inherently global in extent and a regional travel time can be computed anywhere for the standard regional phases (Pn, Pg, Sn, and Lg) that are used in monitoring. In order to improve travel time prediction accuracy over conventional models/methods (e.g. ak135 model), the tomographic velocity representation must be "tuned" for each region. RSTT velocity representation tuning is accomplished by first constructing a best approximation of the 3-dimensional structure of the Earth's crust and upper-most mantle based on previous studies. Then velocities - but not layer interfaces - are adjusted using tomographic imaging methods (Figure 3). Therefore, care must be taken to ensure that layer depths are accurate.
Figure 3. Upper mantle P-wave velocity across Eurasia after tomography
RSTT tomography has been conducted throughout Eurasia to optimize prediction accuracy for Pn, Pg, Sn, and Lg phases. RSTT tomography in North America for Pn has also been completed. The eventual goal is to extend RSTT tomography for all four regional phases (Pn, Sn, Pg, Lg) to the rest of the globe.
Peer reviewed paper on Eurasia Pn tomography in the Bulletin of the Seismological Society of America (BSSA): Myers, Stephen C, Michael L Begnaud, Sanford Ballard, Michael E Pasyanos, W Scott Phillips, Abelardo L Ramirez, Michael S Antolik, Kevin D Hutchenson, John J Dwyer, Charlotte A. Rowe, and Gregory S. Wagner, A Crust and Upper-Mantle Model of Eurasia and North Africa for Pn Travel-Time Calculation, Bulletin of the Seismological Society of America, Vol. 100, No. 2, pp. 640-656, April 2010, doi: 10.1785/0120090198.
Paper on Pg, Lg, and Sn tomography in Eurasia and Pn tomography in North America in the Monitoring Research Review (MRR): Myers, Stephen C, Michael L Begnaud, Sanford Ballard, Abelardo L Ramirez, W Scott Phillips, Michael E Pasyanos, Harley Benz, Raymond P Buland, A Regional Seismic Travel Time Model for North America, presented at the National Nuclear Security Administration's 2010 Monitoring Research Review under Contract No. DE-AC52-07NA273441, DE-AC04-94AL85002, DE-AC52-06NA253963.
Early peer reviewed paper on RSTT technique in Geophysical Research Letters (GRL): Phillips, W. S., M. L. Begnaud, C. A. Rowe, L. K. Steck, S. C. Myers, M. E. Pasyanos, and S. Ballard, Accounting for lateral variations of the upper mantle gradient in Pn tomography studies, Vol. 34, L14312, 2007, doi:10.1029/2007GL029338.
Regional Seismic Travel TIme (RSTT) Software Summary Sheet
The gz tar files contain the Earth model and code.(Note: SLBM stands for Seismic Location Baseline Model and is the name of a previous version of RSTT and has not been changed for coding reasons)
When you open the gz file you will see a software directory tree similar to the one below.
Please register (or unregister) by sending an email to: firstname.lastname@example.org. Registration is optional, but registered users will be notified of software updates and other noteworthy events related to RSTT development.
Stephen Myers (Lawrence Livermore National Laboratory) - email@example.com Michael Begnaud (Los Alamos National Laboratory) - firstname.lastname@example.org Sanford Ballard (Sandia National Laboratories) - email@example.com Leslie Casey (DOE/NNSA/NA-22) - Leslie.Casey@nnsa.doe.gov