Data Services Products: 3dtraveltimes regional & teleseismic 3D travel times using LLNL-G3Dv3

Summary

Regional and teleseismic travel times using 3D raytracing through the LLNL-G3Dv3 P-wave velocity model.

this page is for DPWG review & is under development, subject to change

Description

The Lawrence Livermore National Labs Geophysical Monitoring Programs (GMP) group developed the LLNL-G3Dv3 model (Simmons et al., 2012) designed to accurately predict seismic travel times at regional and teleseismic distances simultaneously. The model provides a new image of Earth’s interior, but the underlying practical purpose of the model is to provide enhanced seismic event location capabilities. The LLNL-G3Dv3 model is based on ~2.8 million P and Pn arrivals that are re-processed using a global multiple-event locator called Bayesloc. The 3D travel times provided in this data product are calculated using 3D raytracing through LLNL-G3Dv3. The 3D travel times for P and Pn arrival times predicted using LLNL-G3Dv3 have smaller residuals to observations than those predicted by the 1D model AK135 on average, however the ability of the model to accurately predict travel times is data dependent and varies across regions. Users are encouraged to read the citation for further details (Simmons et. al., 2012).

The model and easy to use Earth3D raytracing package are available on the LLNL Global 3-D Seismic Tomography page.

The LLNL-G3Dv3 project was funded by the Ground-based Nuclear Detonation Detection (GNDD) program within the National Nuclear Security Administration (NNSA).


NNSALogo



Resources
On <6 CPUs (java-based Earth3D automatically multithreads using free CPUs) using a total of 1.5G of memory, ~7000 travel time calculations takes ~1hr.
Calculating a single 3d travel time on 1 CPU takes ~1 sec after about 10 sec for model loading.

3D travel times at IRIS

The IRIS DMC uses Earth3D along with the LLNL-G3Dv3.e3d P-wave model to calculate 3D travel times for all Mw6.0+ events within a few hours of origin time at all BHZ and LHZ stations held at IRIS (list of >3000 stations updated weekly to add new stations). Multi-pathing occurs when 3D raytracing; the travel times calculated represent only the minimum travel times.
Magnitude threshold and how far back we backfill are TBD with guidance from the DPWG.

Phase travel times calculated
P — First-arriving direct (non-reflected) P-wave (0 to about 99 degrees)
Pg — P-wave restricted to bottom in the upper crust or shallower (0 to 5 degrees, unstable beyond 5 degrees)
Pb — P-wave restricted to bottom in the lower crust (0 to 7 degrees, may be unstable in complex regions)
Pn — P-wave restricted to bottom in the upper mantle above the transition zone (0 to about 25 degrees)
Ptz — P-wave restricted to bottom in the transition zone (12 to about 30 degrees)
Plm — P-wave restricted to bottom in the lower mantle (16 to about 99 degrees)
PmP — P-wave reflected from the Moho (0 to about 5 degrees)
pP — P-wave depth phase reflected off the surface of the solid part of the model (1 to about 100 degrees)
pwP — P-wave depth phase reflected off the top of the water layer if one exists, same as pP otherwise (1 to about 100 degrees)
PP — Double P-wave turning in the lower mantle and reflecting from the solid surface(about 53 to 180 degrees)
PwP — Double P-wave turning in the lower mantle and reflecting from the top of the water layer if it exists (53 to 180 degrees)
PcP — P-wave reflected off the outer core (0 to about 99 degrees)
PKPdf(alias PKP or PKIKP) — P-wave bottoming in the inner core (115 to 179 degrees)
PKPab — P-wave bottoming in the middle of the outer core (about 145 to 177 degrees)
PKPbc — P-wave bottoming in the deep outer core (about 145 to 155 degrees)
PKPcd(alias PKiKP) — P-wave reflecting from the inner core (upto about 155 degrees)

S phases or other tomography models?
Earth3D is able to calculate 3d travel times through any model after a needed binary file is calculated using an appropriately formatted input file (takes a few hours).
The DMC could (with permission from model authors) precomute these binary files for other tomography models and make them available to users. 3d travel time could be precalculated by IRIS through different select models, though caveats may exist, e.g. models optimized for 1d raypaths.
3d travel time residuals using 1d raypaths in spherical models is a possibility.
Ellipticity corrections to 1d travel times for various phases are another possiblity.

Example output files

2008.05.12.06.27.59.TT.txt
2012.08.14.02.59.38.TT.txt
2013.05.24.05.44.48.TT.txt

The columns are:

SrcLat, SrcLon, SrcDepth, StatLat, StatLon, StatDepth, Phase, Network, Station, 1D travel time, “EARTH3D”, 3D travel time, Receiver-side water correction, Source-side water correction, Distance, Azimuth, UniqueID

example of 3d travel times text file

Note: Phase = “P” refers to the first arriving P-wave whether it be Pg, Pn, Pb…

Accessing files
The text files of travel times will be made available through SPUD ( example product in SPUD ). Command line downloading of the textfiles and bundles through SPUDservice will be made available along with examples.

Future directions?:
-A webservice similar to the Taup webservice could be set up. Whether precalculating travel times or calculating them on the fly is ???
-psuedo 3d travel times for spherical models using 1d rays
-ellipticity corrections to 1d travel times
Pie-in-the-sky version: IRIS is able to provide 1d and 3d travel times through a WS for different tomography models in EMC, given author consent.

Citations and DOIs

References

Simmons, N. A., S. C. Myers, G. Johannesson, and E. Matzel (2012), LLNL-G3Dv3: Global P wave tomography model for improved regional and teleseismic travel time prediction, J. Geophys. Res., 117, B10302, doi:10.1029/2012JB009525.

Credits

  • LLNL-G3Dv3 and Earth3D were developed at Lawrence Livermore National Labs by Nathan Simmons, Eric Matzel, Steve Meyers, & Gardar Johannesson.
    LLNL Global 3-D Seismic Tomography webpage.
  • Development of LLNL-G3Dv3 was supported by the Office of Nuclear Detonation Detection (NA222) within the National Nuclear Security Administration (NNSA).
  • IRIS DS staff implemented and are responsible for the usage and results from codes used in this data product.
  • Alexander Hutko

Contributors

Nathan Simmons
Lawrence Livermore National Laboratory

Categories

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