I am working on a project about seismic wave analysis these days. For reading data containing seismic waves, it comes up to several format, and the one I get in touch frequently is miniSEED.

miniSEED is famous of its simplicity compared to its superset SEED, which stands for Standard for the Exchange of Earthquake Data. The biggest difference between them is that miniSEED only contains a header – to carry necessary information about the data – and the values representing the amplitude of the seismic wave. [1] As usual, numerous libraries support to read and write miniSEED data in ease. For instance, libmseed is provided by IRIS team to let people to manipulate miniSEED data and create their own binding on other programming languages.

Why I Write This Post

Seismology is a fresh new area to me, and I think getting familiar with the data manipulating tool is a good start for realizing what seismologists are doing.
Compared to the version before 3, libmseed made a great number of changes in order to support the newer version standard of miniSEED (or miniSEED 3.x). [2] And writing this post makes not only some records what I have done for porting this library but also a brief introduction for others to use this work.

Installation

Installation of libmseed will be quite easy, and it has almost no dependencies (though strictly, glibc).

Unix-like System

Type these commands will be sufficient:

$ make
$ sudo make install # to install libmseed so that you can link against to other programs

After you install the necessary files, you can choose one of the following ways to let the runtime linker where the libmseed is:

Add libmseed into LD_LIBRARY_PATH environment variable (e.g., .bashrc file).
```
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/path/to/libmseed/shared/lib
```
Create a new *.conf file in /etc/ld.so.conf.d/: [3] For instance:
```
/etc/ld.so.conf.d/99local.conf
```
with just:
```
/usr/local/lib
```
After the modification you have to run:
```
$ sudo ldconfig
```

Windows System

Type the comand instead:

$ nmake -f Makefile.win

Then add the library path to compiler setting may be work.

Linking against to Other Programs

Assume you put libmseed.h in /usr/local/include and the shared libraries in /usr/loca/lib, you can link libmseed in the following way for instance:

$ gcc -I/usr/local/include -o main main.c -L/usr/local/lib -lmseed

Demo

In this part, I am going to demoinstrate how to read the infomation of header and the values of each record. The demo procedures are shown as follows:

Clone the repo written by me.
Compile it.

Run with the following command:

$ make
$ ./libmseed_hello_world <your miniSEED file> 

After running the above commands, you should get the following output (take test.mseed provided by libmseed as example):

...
XFDSN:IU_COLA_00_L_H_1, 4, 512, 135 samples, 1 Hz, 2010,058,06:50:00.069539
XFDSN:IU_COLA_00_L_H_1, 4, 512, 188 samples, 1 Hz, 2010,058,06:52:15.069539
XFDSN:IU_COLA_00_L_H_1, 4, 512, 126 samples, 1 Hz, 2010,058,06:55:23.069541
XFDSN:IU_COLA_00_L_H_1, 4, 512, 156 samples, 1 Hz, 2010,058,06:57:29.069539
XFDSN:IU_COLA_00_L_H_1, 4, 512, 138 samples, 1 Hz, 2010,058,07:00:05.069539
XFDSN:IU_COLA_00_L_H_1, 4, 512, 132 samples, 1 Hz, 2010,058,07:02:23.069539
XFDSN:IU_COLA_00_L_H_1, 4, 512, 110 samples, 1 Hz, 2010,058,07:04:35.069539
XFDSN:IU_COLA_00_L_H_1, 4, 512, 131 samples, 1 Hz, 2010,058,07:06:25.069539
XFDSN:IU_COLA_00_L_H_1, 4, 512, 135 samples, 1 Hz, 2010,058,07:08:36.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 117 samples, 1 Hz, 2010,058,07:10:51.069539
XFDSN:IU_COLA_00_L_H_1, 4, 512, 114 samples, 1 Hz, 2010,058,07:12:48.069539
XFDSN:IU_COLA_00_L_H_1, 4, 512, 117 samples, 1 Hz, 2010,058,07:14:42.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 123 samples, 1 Hz, 2010,058,07:16:39.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 123 samples, 1 Hz, 2010,058,07:18:42.069539
XFDSN:IU_COLA_00_L_H_1, 4, 512, 142 samples, 1 Hz, 2010,058,07:20:45.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 130 samples, 1 Hz, 2010,058,07:23:07.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 127 samples, 1 Hz, 2010,058,07:25:17.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 120 samples, 1 Hz, 2010,058,07:27:24.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 118 samples, 1 Hz, 2010,058,07:29:24.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 108 samples, 1 Hz, 2010,058,07:31:22.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 107 samples, 1 Hz, 2010,058,07:33:10.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 107 samples, 1 Hz, 2010,058,07:34:57.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 110 samples, 1 Hz, 2010,058,07:36:44.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 103 samples, 1 Hz, 2010,058,07:38:34.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 103 samples, 1 Hz, 2010,058,07:40:17.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 104 samples, 1 Hz, 2010,058,07:42:00.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 105 samples, 1 Hz, 2010,058,07:43:44.069536
XFDSN:IU_COLA_00_L_H_1, 4, 512, 103 samples, 1 Hz, 2010,058,07:45:29.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 103 samples, 1 Hz, 2010,058,07:47:12.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 106 samples, 1 Hz, 2010,058,07:48:55.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 103 samples, 1 Hz, 2010,058,07:50:41.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 103 samples, 1 Hz, 2010,058,07:52:24.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 110 samples, 1 Hz, 2010,058,07:54:07.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 103 samples, 1 Hz, 2010,058,07:55:57.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 108 samples, 1 Hz, 2010,058,07:57:40.069538
XFDSN:IU_COLA_00_L_H_1, 4, 512, 32 samples, 1 Hz, 2010,058,07:59:28.069538
...

Execute with the -D option will output the values of each records:

$ ./libmseed_hello_world -D test.mseed
XFDSN:IU_COLA_00_L_H_1, 4, 512, 135 samples, 1 Hz, 2010,058,06:50:00.069539
-502676     -504105     -507491     -506991     -505093     -506634  
-507449     -506132     -504335     -503581     -504801     -502676  
-499117     -502521     -508058     -508719     -506640     -503213  
-501518     -503297     -504019     -503973     -505239     -505618  
-505363     -508445     -512396     -510357     -503344     -499292  
-500644     -499573     -497070     -496368     -494254     -495751  
-498163     -498512     -503053     -504862     -502569     -505073  
-508702     -510540     -510995     -509509     -510162     -509896  
-506668     -505275     -501772     -499662     -504604     -506787  
-508899     -511028     -506260     -506356     -507500     -502717  
-501599     -499809     -497380     -499415     -499962     -501449  
-506331     -508451     -507561     -505771     -504482     -504974  
-502925     -499716     -499168     -497727     -496606     -497632  
-498311     -501691     -506977     -508209     -509408     -510606  
-507239     -504164     -503331     -501325     -498815     -499063  
-500754     -501606     -502901     -505046     -506651     -506710  
-505258     -502673     -502796     -505352     -504242     -503463  
-505552     -506242     -505771     -504268     -503942     -504831  
-505228     -505811     -504930     -503956     -502634     -501069  
-503523     -505187     -502566     -502208     -502309     -499495  
-498321     -497806     -498092     -499768     -499282     -500757  
-506604     -509557     -508944     -510178     -509697     -505212  
-499533     -495590     -496168  
XFDSN:IU_COLA_00_L_H_1, 4, 512, 188 samples, 1 Hz, 2010,058,06:52:15.069539
...

And execute with the -s will show the brief summary like this:

$ ./libmseed_hello_world -s test.mseed
...
Records: 107, Samples: 12600

Explanation of Code

Let’s deep dive into libmseed’s functions!

First, to read one record from a miniSEED file, we can use ms3_readmsr(). The function will read a record into a struct of type MS3Record **. What’s more, you can set the flag using |= operator then pass the flag to this function so that it performs certain actions. In here I pass MSF_VALIDATECRC and MSF_UNPACKDATA to let the function performs both validate the data using CRC and unpack the data into MS3Record type.

Then, as a computer engineer, I always concern about the length of data and its values. Here I will divide into two parts to tell you where the length and values reside:

The length of data is the numsamples variable in MS3Record.
The values of data is the datasamples1 variable in MS3Record`.
- The most interesting part is that the type of values is void. I guess is for storing different types easily in C.

Next, we want to output each element of the values. To output the message, libmseed provides a handy function called ms_log(). Besides, you can pass int to level parameter for different message level.

Note that when doing any manupulation of values, you should always get the type of them (sampletype if using MS3Record) then cast them to appropiate type. It is also a good practice in C that the programming must know what type of the variable is.

Eventually, you should clean up what you have allocated in C. The library provides the following approach to clean MS3Record struct:

ms3_readmsr (&msr, NULL, NULL, NULL, 0, 0);

Conclusion and Thoughts

In this post, I introduce what is miniSEED and libmseed. Also, I demonstrate how to easily read the miniSEED file with explanations of necessary functions. I hope this post will be a great introduction to those who are working on seismic wave and people who want to port version 3 and above of libmseed to other programming language and platform.

References

[1] http://ds.iris.edu/ds/nodes/dmc/data/formats/miniseed/

[2] https://github.com/iris-edu/libmseed/blob/master/ChangeLog#L62

[3] https://stackoverflow.com/questions/17889799/libraries-in-usr-local-lib-not-found