NonLinLoc

The NonLinLoc (Non-Linear Location) package is a set of programs for velocity model construction, travel-time calculation and probabilistic, non-linear, global-search earthquake location in 3D structures, and for visualisation of 3D volume data and location results. Many of the programs operate with a 3D Grid structure which defines a specific, gridded, rectangular volume (Non-GLOBAL mode) or spherical section (GLOBAL mode).

IMPORTANT: The active NonLinLoc repository has been transferred to: https://github.com/ut-beg-texnet/NonLinLoc

Please be aware of this change and the new URL.

Citation

If you use the NonLinLoc package in your work, please cite the following papers:

• Lomax A., Virieux J., Volant P., Berge-Thierry C. (2000) Probabilistic Earthquake Location in 3D and Layered Models. In: Thurber C.H., Rabinowitz N. (eds) Advances in Seismic Event Location. Modern Approaches in Geophysics, vol 18. Springer, Dordrecht. https://doi.org/10.1007/978-94-015-9536-0_5

• Lomax A., Michelini A., Curtis A. (2014) Earthquake Location, Direct, Global-Search Methods. In: Meyers R. (eds) Encyclopedia of Complexity and Systems Science. Springer, New York, NY. https://doi.org/10.1007/978-3-642-27737-5_150-2

If you use NLL-SSST-coherence or any of its components, please cite:

• Lomax, A. & Savvaidis, A. (2022) High-Precision Earthquake Location Using Source-Specific Station Terms and Inter-Event Waveform Similarity. Journal of Geophysical Research: Solid Earth, 127, e2021JB023190. https://doi.org/10.1029/2021JB023190

For other A. Lomax NonLinLoc publications, see http://alomax.net/pub_list.html

Install complete NonLinLoc distribution software package

Clone or download ZIP from this repository https://github.com/alomax/NonLinLoc

Set output bin/ directory, if you have not already done this:

cd src
rm bin
# either do this:
mkdir bin   # bin/ is a subdirectory of src/
# or this:
ln -s <my_favorite_bin_path> bin   # bin/ is somewhere else

To build:

cd src
rm CMakeCache.txt
cmake .
make

See http://alomax.net/nlloc and http://alomax.net/nlloc -> tutorials for further information

To bulid debug: edit CMakeLists.txt to comment out Release build type and uncomment Debug bulid type:

#set(CMAKE_BUILD_TYPE Release)
set(CMAKE_BUILD_TYPE Debug)

then:

cd src
rm CMakeCache.txt
cmake .
make

Thanks to Gilles Celli (European Center for Geodynamics and Seismology) for creating and debugging the NonLinLoc CMake build system.

Documentation

• Future documentation (incomplete): http://alomax.net/nlloc/docs
• Legacy documentation (more extensive): http://alomax.net/nlloc
• Users guides and additional information: see doc/ directory in this repository

Additional information

NEW! NLLoc-SSST-coherence

NLL-SSST-coherence is an enhanced, absolute-timing earthquake location procedure, iteratively generates traveltime corrections to improve multi-scale precision and uses waveform similarity to improve fine-scale precision.

For details, see:

• Lomax, A. & Savvaidis, A. (2022) High-Precision Earthquake Location Using Source-Specific Station Terms and Inter-Event Waveform Similarity. Journal of Geophysical Research: Solid Earth, 127, e2021JB023190. https://doi.org/10.1029/2021JB023190

• Lomax, A., & Henry, P. (2023). Major California faults are smooth across multiple scales at seismogenic depth. Seismica, 2(1). [https://doi.org/10.26443/seismica.v2i1.324] (https://doi.org/10.26443/seismica.v2i1.324)

Example/Tutorial: Files and instructions for running NLL-SSST-coherence for a subset of Parkfield events [https://zenodo.org/doi/10.5281/zenodo.4756709] (https://zenodo.org/doi/10.5281/zenodo.4756709)

NLLoc_func_test program demonstrating running NLLoc through a function call

Install as above. TODO: how to build GNU_SOURCE with cmake?????

Build with:

GNU_SOURCE=-D _GNU_SOURCE

and comment the line:

#GNU_SOURCE=

Unpack demo files: unpack: NLL[VER]_func.tgz To run:

cd nll_func
./run_func.sh

To clean

rm -rf out/*
cd ..

See nll_func/run_func.sh for more detail.

ttime_func_test program demonstrating reading values from 2D or 3D grid file through a function call

Install as above.

Unpack demo files: unpack: NLL[VER]_func.tgz To run:

cd ttime_func
./run_func.sh
cd ..

See ttime_func/run_func.sh for more detail.

IMPORTANT NOTES

Grid2GMT (2023.02.19)

Grid2GMT now supports GMT 5 and 6 (thanks to https://github.com/sean0921). See src/CMakeLists.txt for details on how to set GMT version when compiling.

GMT 4 may work correctly when compile is set up for GMT 6.

Covariance errors (2014.10.30)

Applies to: LOCSEARCH MET and LOCSEARCH OCT The algorithm for calculating the covariance of the PDF scatter sample used in NLLoc was subject to precision errors when the expectation of the scatter sample (e.g. the event location) was far from the origin of the NLL coordinates system relative to the extent of the PDF scatter sample. Several tests indicate that "Far from the origin" is of the order of 1000 times the extent of the PDF scatter sample.

Errors in covariance will affect the ellipsoid and ellipse, standard-errors (erh, erz, etc.).

For teleseismic locations (NLL GLOBAL mode) errors with the old algorithm occur primarily in longitude (X), increasing with expectation longitude and occasionally becoming large towards longitude +/-180deg. For local studies in rectangular coordinates where the NLL coordinates origin is far from the network and target sources, the errors may be large. This may be the case, for example, for a micro-seismic study using a regional, metric-based cartesian grid coordinate system with origin far from the study area. For local studies in rectangular coordinates where the NLL coordinates origin is within or near the network and target sources, the errors should be very small or negligible.

The algorithm for calculating the covariance of the PDF scatter sample used in NLLoc v.6.03.00 and later does not have these precision errors and is valid for locations far from the origin of the coordinate system.