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README_EarthquakeSeisToolsMATLAB.txt
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This collection contains MATLAB scripts associated with the publication:
Plourde A.P. and M. R. Nedimovic (Submitted). Earthquake depths, focal
mechanisms, and stress in the Lower St. Lawrence Seismic Zone.
Seismological Research Letters.
and was last updated February 3, 2021.
Many of the MATLAB scripts have fairly detailed descriptions of their function
within themselves; however, this documentation is far from complete. Most of
the codes have been thoroughly tested, but I make zero guarantees that they
function as intended. Testing was mostly performed on WINDOWS with
MATLAB 2017a. There may be slight modifications required for operation with
other versions of MATLAB or in UNIX or MAC environments, especially for codes
that read or write external files.
Please feel free to send any questions or bug reports to:
- Alexandre P. Plourde
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% SET UP
To use these codes, I recommend adding the following lines to your MATLAB
startup.m file, modifying dr0 to your MATLAB home directory.
dr0 = 'YOUR_MATLAB_PATH\';
addpath(dr0);
addpath([dr0,'EQ_FocalMech_MT\']);
addpath([dr0,'EQ_Plotting\']);
addpath([dr0,'FocMechAPP\']);
addpath([dr0,'hypoAPP\']);
addpath([dr0,'hypoDD\']);
addpath([dr0,'hypoTD\']);
addpath([dr0,'Numerical_Methods\']);
addpath([dr0,'Signal_Processing\']);
clear dr0
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% GENERAL INFO
Although many of the core functions in this package can be used indepently,
the "driver" files provided (COMING SOON) are designed to initially read in
earthquake hypocenter, station coordinates, and phase data from "hypoDD" format
event.dat, station.dat, and phase.dat files (see hypoDD manual ---
Waldhauser [2001] USGS Open File Report) and save them in a MATLAB ".mat" file.
This file can then be reloaded to by "driver" scripts to compute waveform
differential times, hypocenters, focal mechanisms, stress, etc., with the
results of each analysis being appended to the ".mat" file.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% SELECTED FUNCTION INFO
% -- FocMechAPP
Estimates a focal mechanism and standard error (in degrees) using
two types of constraints P-wave first-motions and P-SV-SH absolute amplitude
ratios. It requires a pre-defined uniform grid of focal mechanisms, which can
be created with "createSDRgrid.m"---because this is a bit slow, I recommend
saving the grid in a .mat file. The function computes a relative probability
for each grid-point focal mechanism, and finds the solution that minimizes the
standard error angle. See the drivers "FirstMotionAutopick.m" and
"record_PSVSH.m" for guidance in creating input data from earthquake waveforms.
% -- hypoAPP
Estimates an earthquake hypocenter from P and S arrival times
and a 1D layered gradient velocity model. It minimizes an L1 misfit defined
as a weighted sum of absolute travel time residuals. The method uses iterative
grid-searches, each testing a 3D grid of potential hypocenters, centered around
an initial estimate. It returns a best-fit hypocenter and 95% confidence
intervals in each direction (E,N,Z).
% -- hypoDD
An implementation of the double-difference earthquake relocation method
"hypoDD" by Waldhauser and Ellsworth (2000,BSSA). It also includes functions
to read/write files related to running the original hypoDD software.
% -- hypoTD
Estimates earthquake hypocenters with pick-based and waveform-based
differential travel-times, based on the "triple difference" or
"double-pair double-difference" of Guo and Zhang (2017,GJI).
hypoTDX.m is the most recently updated and most flexible version of
the main function.
% -- StressInvV2014
Estimates the tectonic stress tensor from focal mechanisms. Standard error
angles on each focal mechanism can be input, allowing robust uncertainty
estimates of the stress tensor. The name owes to its inspiration from the
algorithm of Vavrycuk (2014,GJI).
%%%%%%%%%%%%%%%%%%%%%%%%%%
References
Guo, H., and H. Zhang (2017). Development of double-pair double di erence earthquake location
algorithm for improving earthquake locations. Geophysical Journal International, 208, 333-348.
doi:10.1093/gji/ggw397.
Vavrycuk V. [2014]. Iterative joint inversion for stress and fault orientations from focal
mechanisms. Geophysical Journal International, 199, 69-77, doi:10.1093/gji/ggu224.
Waldhauser F and Ellsworth WL. [2000]. A double-difference earthquake location algorithm:
Method and application to the Northern Hayward Fault, California. Bulletin of the
Seismological Society of America, 90, 1353-1368, doi:10.1785/0120000006.