Python - How to transform counts in to m/s using the obspy module

Question

I have a miniseed file with a singlechannel trace and I assume the data is in counts (how can i check the units of the trace?). I need to transform this in to m/s. I already checked the obspy tutorial and my main problem is that i dont know how to access the poles and zeros and amplification factor from the miniseed file. Also, do I need the calibration file for this?

Here is my code:

from obspy.core import *
st=read('/Users/guilhermew/Documents/Projecto/Dados sismicos 1 dia/2012_130_DOC01.mseed')
st.plot()

Thanks in advance, Guilherme

EDIT: I finally understood how to convert the data. Obspy has different ways to achieve this, but it all comes down to removing the instrument response from the waveform data. Like @Robert Barsch said, I needed another file to get the instrument response metadata. So I came up with the following code:

parser=Parser("dir/parser/file")
for tr in stream_aux:
    stream_id=tr.stats.network+'.'+tr.stats.station+ '..' + tr.stats.channel
    paz=parser.getPAZ(stream_id, tr.stats.starttime)
    df = tr.stats.sampling_rate
    tr.data = seisSim(tr.data, df, paz_remove=paz)

Im using the seisSim function to convert the data. My problem now is that the output dosen't look right (but i cant seem to post the image)

Answer 1

This is clearly a question which should be asked to the seismology community and not at StackOverflow! How about you write to the ObsPy user mailinglist?

Update: I still feel the answer is that he/she should ask directly at the ObsPy mailing list. However, in order to give a proper answer for the actual question: MiniSEED is a data only format which does not contain any meta information such as poles and zeros or the used unit. So yes you will need another file such as RESP, SAC PAZ, Dataless SEED, Full SEED etc in order to get the station specific meta data. To apply your seismometer correction read http://docs.obspy.org/tutorial/code_snippets/seismometer_correction_simulation.html

Answer 2

To get it in real-life units and not counts, you need to remove the instrument response. I remove instrument response using this code:

# Define math defaults
from __future__ import division #allows real devision without rounding

# Retrieve modules needed
from obspy.core import read
import numpy as np
import matplotlib.pyplot as plt

#%% Choose and import data
str1 = read(fileloc)
print(str1) #show imported data
print(str1[0].stats) #show stats for trace

#%% Remove instrument response

# create dictionary of poles and zeros
TrillC = {'gain': 800.0,
        'poles': [complex(-3.691000e-02,3.712000e-02),
                  complex(-3.691000e-02,-3.712000e-02),
                  complex(-3.739000e+02,4.755000e+02),
                  complex(-3.739000e+02,-4.755000e+02),
                  complex(-5.884000e+02,1.508000e+03),
                  complex(-5.884000e+02,-1.508000e+03)],
        'sensitivity': 8.184000E+11,
        'zeros': [0 -4.341E+02]}
str1_remres = str1.copy() #make a copy of data, so original isn't changed
str1_remres.simulate(paz_remove=TrillC, paz_simulate=None, water_level=60.0)
print("Instrument Response Removed")

plt.figure()
str1_remres_m = str1_remres.merge()
plt.plot(str1_remres_m[0].data) #only will plot first trace of the stream

As you can see I have manually defined the poles and zeros. There is probably a way to automatically input it but this was the way that I found that worked.

Remember each instrument has different poles and zeros.

The number of zeros you use depends on what you want your output to be. Seismometers are normally velocity (2 zeros)

• 3 zeros = displacement
• 2 zeros = velocity
• 1 zero = acceleration