SeismoTectonic Regime Earthquake Calculator (STREC)

This library and set of tools was created to provide functionality to automatically determine the tectonic region of an earthquake (Subduction,Active,Volcanic,Stable), and the distance to the tectonic regions to which it does not belong.

In addition, STREC provides a tool that, in subduction zones, returns information on the subducting interface, using the USGS Slab1.0 model (https://earthquake.usgs.gov/data/slab/models.php).

GLOSSARY

In STREC we defined a number of terms that may not be commonly understood, so they are explained here. These terms may be different from the Garcia paper upon which this software is originally based.

• Tectonic Region: One of Subduction, Active, Volcanic, or Stable. We have split up the globe into these four regions, such that any point on the globe should fall into one and only one of these regions.

  • Subduction: A tectonic region defined by one plate descending below another (e.g., the western portion of the United States).

  • Active: A tectonic region which experiences crustal deformation due to plate tectonics.

  • Volcanic: A tectonic region which is dominated by volcanic activity. This also includes what are referred to as "hot spots".

  • Stable: Tectonic regions which unlike Active regions, do not experience crustal deformation (e.g., the interior of the Australian continent.)

• Oceanic: Another region, not exclusive with the four Tectonic Regions, that indicates whether the point supplied is in the ocean (i.e., not continental).

• Continental: The opposite of Oceanic.

• Focal Mechanism: A set of parameters that define the deformation in the source region that generates the seismic waves of an earthquake.

• Tensor Type: The short name for the algorithm used to generate the moment tensor used to determine focal mechanism, Kagan angle, etc. This is usually a short code like Mww (W-phase), Mwr (regional), Mwb (body wave), or composite, which indicates that there is no computed moment tensor, so a composite of historical moment tensors around the input coordinates is used instead.

• Tensor Source: When available, this is usually the network that contributed the moment tensor, followed by the ID used by that network (e.g., us_2000bmcg).

• Kagan Angle: An single angle between any two moment tensors or in our case, between a moment tensor and a subducting slab.

• Composite Variability: When the moment tensor solution is of type composite, a scalar value describing the variability of the moment tensors used to determine the composite.

• Distance to [Region]: The great circle distance from the input coordinates to the nearest vertex of [Region] polygon.

• Slab Model Region: We currently use Slab 1.0 subduction models (Hayes 2012), which are currently provided for 13 regions around the globe. These regions are described in detail here: https://earthquake.usgs.gov/data/slab/models.php

• Slab Model Depth: The best estimate of depth to subduction interface.

• Slab Model Depth Uncertainty: The best estimate of the uncertainty of the depth to subduction interface.

• Slab Model Dip: The best estimate of the dip angle of the subducting plate.

• Slab Model Strike: The best estimate of the strike angle of the subducting plate.

INSTALLATION

Currently, the easiest way to install STREC is to use the install script found in this repository.

Pre-requisites

• You should be comfortable using a terminal window in general, and the bash shell in particular.

• You should have either Anaconda

  https://www.anaconda.com/download/

  or Miniconda

  https://conda.io/miniconda.html

  installed on your system. In theory, this code should work on Windows, but has not been tested on that platform.

• You should have git installed on your system. On Linux or Mac OS, you can determine this by typing:

  which git

  If you see a response that indicates you have git installed on your system (something like /usr/bin/git), then you are set. If not, install git by using the package manager for your system (Linux) or visiting this page:

  https://git-scm.com/download

Installing STREC In a New Conda Environment

• Download the STREC source code by running the following command:

  git clone https://github.com/usgs/strec.git

  This will create a directory called strec below your current working directory.

• Run the installer script by typing:

  cd strec;bash installer.sh

• Activate the STREC virtual environment by running this command:

  source activate strecenv.

  You will need to add this command to your bash profile file (~/.bash_profile or ~/.bashrc), or re-run the command when you open a new terminal window.

Installing STREC in an Existing Conda Environment

Make sure you have the following dependencies already installed through conda or pip:

• numpy
• scipy
• pyproj
• pandas
• openpyxl
• xlrd
• xlwt
• pytest
• pytest-cov
• fiona
• h5py
• shapely
• obspy
• rasterio
• gdal

Then run the following commands:

• pip -q install https://github.com/usgs/MapIO/archive/master.zip
• pip -q install https://github.com/usgs/libcomcat/archive/master.zip
• pip -q install https://github.com/usgs/earthquake-impact-utils/archive/master.zip
• pip -q install https://github.com/usgs/strec/archive/master.zip

Using STREC

Subduction Selector

The subselect command gives you several pieces of information regarding the earthquake ID or location you input. Basic usage of subselect for single events is as follows:

• subselect -e LAT LON DEPTH to return information about an event based on hypocenter.
• subselect -d EVENTID to return information about an event based on ComCat event ID.

The output of subselect will look something like this:

For event located at 3.2950,95.9820,30.0:
	TectonicRegion : Subduction
	FocalMechanism : RS
	TensorType : composite
	TensorSource : composite
	KaganAngle : 10.685829986253886
	CompositeVariability : 1.1036343285450119
	NComposite : 50
	DistanceToStable : 481.143972927
	DistanceToActive : 481.143972927
	DistanceToSubduction : 0.0
	DistanceToVolcanic : 4864.56919929
	Oceanic : False
	DistanceToOceanic : 573.606960791
	DistanceToContinental : 0.0
	SlabModelRegion : Sumatra-Java
	SlabModelDepth : 34.91320037841797
	SlabModelDepthUncertainty : 11.31596851348877
	SlabModelDip : 14.680322647094727
	SlabModelStrike : 307.7746276855469
	SlabModelMaximumDepth : 55

subselect can also be used in batch mode, operating on input CSV or Excel files.

The NEIC libcomcat library and tools are installed along with STREC, so you can use the getcsv command to generate input files to use with regselect. For example:

getcsv ~/big_events_2016.xlsx -s 2016-01-01 -e 2016-12-31T23:59:59 -m 6.5 9.9 -f excel

will download basic event information for all magnitude 6.5 and greater events in 2016. This output can be directly piped into regselect, and the results saved back out to Excel:

subselect -i ~/big_events_2016.xlsx -f excel -o ~/subselect_events.xlsx

Data Used in STREC

There are three datasets that are included with STREC:

• Vector (GeoJSON format) data files that define the four mutually exclusive tectonic regions (Active, Stable, Volcanic, Subduction) and Oceanic.

• Database (SQLite format) of GCMT moment tensors that are used to determine composite moment tensors. This can be overridden by the user (see below).

• USGS Slab 1.0* subduction zone model grids (NetCDF4/HDF5 COARDS format). These models are described in detail on this page: https://earthquake.usgs.gov/data/slab/models.php

The moment tensor database can be overridden by using the strec_init command line tool (distributed with this repository), in one of two ways:

• Downloading up-to-date versions of the GCMT moment tensors
• Installing your own catalog of moment tensors.

To update to the most recent version of the GCMT moment tensors, do the following:

strec_init [DATAFOLDER]

where [DATAFOLDER] is the location where you would like the new SQLite database file to be located. STREC programs will recognize that this new file should override the data included in the repository by looking at a config file that strec_init will create in ~/.strec/strec.ini.

To use your own catalog of moment tensors, you must have a CSV or Excel file of earthquake and moment tensor data, with the following (exactly named) columns:

• time (YYYY-MM-DD HH:MM:SS for CSV)
• lat (decimal degrees)
• lon (decimal degrees)
• depth (km)
• mag (moment magnitude units)
• mrr (dyne-cm)
• mtt (dyne-cm)
• mpp (dyne-cm)
• mrt (dyne-cm)
• mrp (dyne-cm)
• mtp (dyne-cm)

and then run the following command:

strec_init -d [DATAFILE] -s [SOURCE]

where [DATAFILE] is the name of the aforementioned CSV/Excel file and [SOURCE] is the name of the originator of the moment tensor solutions ("gcmt", "us", "duputel", etc.)

As above, STREC will recognize this new data as the source of moment tensors by looking in the STREC ini file.

• • At the time of this writing, an updated set of subduction models is in preparation, and will hopefully be added to the repository soon.