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Earthquake Location

The phase pick information from run_seisbench.py is saved in event_picks.json in /FAST/utils/picking/event_picks.json and is used as input for finding the earthquake locations, starting with SeisBench2hypoinverse.py.

SeisBench2hypoinverse.py will format the needed earthquake information as input for HYPOINVERSE.

HYPOINVERSE is the standard location program supplied with the Earthworm seismic acquisition and processing system (AQMS). Read more about it here.

Make Changes to SeisBench2hypoinverse.py

  • Change output file name: 
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out_hinv_phase_file = 'EQT_19991015_test.txt' # Change file name for your dataset

Get Station List

You will need to edit eqt_get_station_list.py in /FAST/utils/location/ for your dataset:

  • Starting with getting the data
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# Hector Mine data
clientlist=["SCEDC"]
minlat=34.1
maxlat=34.9
minlon=-116.7
maxlon=-116
  • Choose channels you want to download
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chan_priority_list=["HH[ZNE12]", "BH[ZNE12]", "EH[ZNE12]", "HN[ZNE12]"] # Hector Mine data
  • Add event start and end time:
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tstart="1999-10-12 00:00:00.00" # Hector Mine data

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tend="1999-10-17 00:00:00.00" # Hector Mine data

Information About locate_events.hyp input files

Input files locate_events.hyp relies on:

  • CRH 1 ‘hadley.crh’
  • STA ‘station_list.sta’
  • PHS ‘EQT_19991015_test.txt’
  • SUM ‘locate_events.sum’
  • ARC ‘locate_events.arc’

hadley.crh is the velocity model input file. It approximates the p-wave speed (km/s) underground, at a given depth in km. You’ll need this to calculate earthquake locations from the phase pick times. The first column has p-wave speed in km/s. The second column has depth in km. The p-wave speed is 5.5 km/s at depths from 0 to 5.5 km, 6.3 km/s at depths from 5.5 to 16 km, 6.7 km/s at depths from 16 to 32 km, and 7.8 km/s at depths deeper than 32 km.

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POS 1.73                /P to S ratio

This line in the locate_events.hyp file tells you the ratio between p wave and s wave speed. S wave speed is always slower than p wave speed, so s picks are always later than p picks. You can divide the first column of numbers in hadley.crh by 1.73 to get the s-wave speeds; that’s what HYPOINVERSE does internally.

PHS ‘EQT_19991015_test.txt’ - that’s the all-important file your script generated, that has the approximate origin times and phase pick times from SeisBench.

STA ‘station_list.sta’ - this is the station file, which has the list of station names and their locations. There are scripts you can run to create this file shown in Tutorial.

Change File Name in locate_events.hyp

The output changed above in SeisBench2hypoinverse.py is used in locate_events.hyp

  • Change file name for your dataset in locate_events.hyp: 
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PHS 'EQT_19991015_test.txt' # Change file name for your dataset

Plotting HYPOINVERSE Location Results With PyGMT

IMPORTANT - PyGMT needs to be installed and run in a separate pygmt conda environment, since it is incompatible with the eq_fast conda environment.

Follow the steps in the tutorial section to user PyGMT.