Instrument Response Reomoval

Usage Questions
1

Hi there,

I have an XML file for my station and am trying to convert counts to displacement (m) using obspy. I also did separate counts to velocity (m/s), and integrated to displacement (m). After simulating to WA seismometer using gains 1, magnification (V) 2800, and damping factor (h) 0.8/km, I measured the mean maximum displacement on two horizontal components to put into the Oman Local Magnitude Scale equation below:

ML = logAwa(R) +0.95logR + 0.0011R− 3

Paper link: Determination of a local earthquake magnitude scale for the Sultanate of Oman | Arabian Journal of Geosciences | Springer Nature Link

I noticed that for my recorded event with (epicenter ~890 km, depth 10 km, reported local network ML 4.61), the measured mean maximum amplitude from two horizontal components is around 41 micrometers; however, for a similar event (epicenter ~960 km, depth 10 km, and magnitude 4.59), their mean maximum amplitude is around ~1300 micrometers. For this, my calculated ML is 2.40, while the reported one is 4.61. This is a 2.21 ML difference from the reported ML because my measured mean maximum displacement on the WA seismometer is way less than it should be. Can you please guide me on where I am making the mistake? It must be with the amplitude measurement on the simulated WA seismometer, or earlier, with my Instrument response removal step. I can not figure it out myself so far. Please help. Thanks

Best,

Muhammad Awais

2

if you remove the instrument response to recover displacement (e.g. st.remove_response(inv,output=’DISP’) are the resulting amplitudes similar to the reported 1300 um?

3

also note that ML for >400 km distance is probably not super-super adapted…