Download Earthquake Catalogs from Global CMT website

In seismology, we always need to download and check the event information about the events. This python script can download the event catalog from the website to the local computer for the given range of time.

Running this program is very simple:

The user just needs to input the time range for the earthquakes e.g., 2000/05-2009/08.

 

Requirements: Python 3

To download the program, please click here.

Calling SAC(Seismic Analysis Code) (in Perl)

For seismologists, using a SAC for sac data manipulation is essential (though there are few alternatives). Here, we see how can we call SAC from a perl script:

#!/usr/bin/perl
open(SAC, "| sac ") or die "Error opening sac\n";
print SAC qq[
echo on
*fg seismogram    #sample seismic signal in SAC's memory
fg sine 2 npts 2000 delta 0.01
*fg impulse npts 100 delta 0.01
bandpass bessel corner 0.1 0.3 npole 4
ppk
fft
plotsp am
save sine_fft.pdf
];
print SAC "quit\n";
close(SAC);

Example script to call SAC functions in perl

Some utilities to deal with sac data format

In seismology, we usually have to deal with the sac data format (binary data format). This data format can be dealt easily and efficiently with the SAC software provided by IRIS. But if we want to use this data in other software for instance MATLAB, then we may need to convert the data in alphanumeric format or to install additional functions.

Here, we show how can we deal with the sac data file format.

1. If you have sac installed on your system, then you can make use of the sac’s “convert” command to convert the data from alphanumeric format to sac format, back and forth.
2. There are several other functions and libraries available online to deal with the sac data file format directly in MATLAB. For example, Mike Thorne’s Software, Frederik J. Simons Repository
3. Here we give some useful utilities:

prem is a simple program to return the PREM velocities and density for an input depth. Using this you don’t need to check manually what is the PREM velocity at a particular depths.

This can be compiled using the following steps:

g95 -c getprem_mod.f90

g95 prem.f90 -o prem ./getprem_mod.o

mkdir -p ~/bin

mv prem ~/bin

sachead returns the value of specified sac header. So, you don’t need to read the data with sac to get its header information. If you have sac already installed in your computer then you don’t need this utility as there is a utility “saclst” which does the same job.

usage: >> sachead sacfile headervariable

To compile this utility,

g95 -c mod_sac_io.f90

g95 sachead.f90 -o sachead mod_sac_io.o

mkdir -p ~/bin

mv sachead ~/bin

sac2xy converts the sac file from binary to alphanumeric format

usage: >> sac2xy sacfile outputfile

For compilation,

g95 -c mod_sac_io.f90

g95 sac2xy.f90 -o sac2xy  mod_sac_io.o

mkdir -p ~/bin

mv sac2xy ~/bin

To add these programs into the path of your system,

open “~/.bashrc” file using your favourite text editor

add the following line to it

export PATH=$PATH:~/bin

close the .bashrc file and restart your terminal window or run “.  ~/.bashrc” command

Or directly from the terminal,

type

echo “export PATH=$PATH:~/bin” >> ~/.bashrc

Mac users can add the following lines to the file ~/.bash_profile

C-shell users can edit the ~/.cshrc file.

echo “setenv PATH $PATH\:/~/bin” >> ~/.cshrc

We list some MATLAB functions which can be used directly to import sac data in MATLAB:

1. load_sac : To read header and sac data
2. rmean : To remove mean from the read sac data
3. rtrend : To remove linear trend from the data
4. cos_taper : Applies a 10% cosine taper
5. bp_bu_co : Bandpass filter using butterworth filter implementation

Tool to download large HTML file

Sometimes when you need to download catalog data using a web browser (Chrome, Firefox, etc.), it will take some time and might cause crash or lag. Here is some ways to do it:

I. Using wget
+ Install if you do not have in terminal:

yum install wget

or

sudo apt-get install wget

+ Basic commands:

wget –output-document= {output file}  {link to download}

E.g:wget ‐‐output-document=filename.html example.com

Details of how to use it can be find here or here.

II. A simple python code

All you need to do it install python and tqdm package using

pip install tqdm

Or run the sh file which I have already written the code to install tqdm package.

Run ./download.sh or python download.py to run, example below:

You can download this small utility here.