Input for Bayesloc calculations for locating the 27 February 2022 Lop Nor earthquake

Steven J Gibbons, NGI
2022-04-04

The directories contained within this tar file contain all the files needed to calculate the location estimates
of the 2022-02-27 Lop Nor earthquake using the Bayesloc program with various sets of
inputs.
No output is included, only the input files:

bayesloc.cfg
arrival.dat
station.dat
origin_prior.dat
and any traveltime tables needed.

In each directory, the Bayesloc program is run by typing

bayesloc bayesloc.cfg

The directories are as follows:

(a) USGS_P1only_singleevent
    The following 5 files needed to locate using only the first P arrivals
    in the NEIC solution (see Data and resources)

    ak135_P1.dat  arrival.dat  bayesloc.cfg  origin_prior.dat  station.dat

(b) superset_singleevent
    The following 6 files needed to locate using a set of arrivals based upon
    the USGS arrivals, selected arrivals from the file ISC_info_20220402.txt,
    and manual picks made from open stations available from IRIS.

    ak135_P1.dat  ak135_S1.dat  arrival.dat  bayesloc.cfg  origin_prior.dat  station.dat

(c) 11 different directories
    fisk_900526
    fisk_900816
    fisk_920521
    fisk_920925
    fisk_931005
    fisk_940610
    fisk_941007
    fisk_950515
    fisk_950817
    fisk_960608
    fisk_960729

    In each of these directories, there are the files
    ak135_P1.dat  arrival.dat  bayesloc.cfg  origin_prior.dat  station.dat
    needed to locate one of the 11 nuclear explosions described in Fisk (2002)
    on an event by event basis.

(d) all_events_joint_USGSonly_fixedGT

    This solves for the location of the 20220227 event simultaneously with the
    locations of the 11 GT nuclear tests, using only those arrivals chosen from
    the USGS solution for the 20220227 event
    (i.e. the arrivals in the directory USGS_P1only_singleevent )

    This directory contains five files
    ak135_P1.dat  arrival.dat  bayesloc.cfg  origin_prior.dat  station.dat

(e) all_events_joint_superset_fixedGT

    This solves for the location of the 20220227 event simultaneously with the
    locations of the 11 GT nuclear tests, using the arrivals from the 20220227
    event "superset" (i.e. the arrivals in the directory superset_singleevent )

    This directory contains six files
    ak135_P1.dat  ak135_S1.dat  arrival.dat  bayesloc.cfg  origin_prior.dat  station.dat

The image "locations_panel.png" contains the output from each of the Bayesloc
calculations in these directories, plus a few others using the same input files but with
changes to the origin_prior.dat files such that the GT events are not fixed to the locations
specified by Fisk (2002).

Panel (a) displays the bulletin location estimates listed in the file
"ISC_info_20220402.txt" together with the GT locations of the nuclear tests provided by
Fisk (2002).

Panel (b) displays the results from the single event location runs: i.e. the outputs
from all of the directories

fisk_900526
fisk_900816
fisk_920521
fisk_920925
fisk_931005
fisk_940610
fisk_941007
fisk_950515
fisk_950817
fisk_960608
fisk_960729
superset_singleevent
USGS_P1only_singleevent

Panel (c) displays the locations when the files in the directory
all_events_joint_superset_fixedGT are run but with modifications
to the origin_prior.dat file to remove the 1 km lateral constraint on the GT
events. In addition, the brown points on this map are the output from
the directory all_events_joint_USGSonly_fixedGT but with the origin_prior.dat
modified to remove the constraints of the GT events.

Panel (d) displays the locations when the files in the directory
all_events_joint_superset_fixedGT are run as they are.
In addition, the brown points on this map are the output from
the directory all_events_joint_USGSonly_fixedGT.

In panels (c) and (d) the nuclear explosion locations are only displayed
for the calculations in the all_events_joint_superset_fixedGT directory.
The locations for these events obtained in the all_events_joint_USGSonly_fixedGT
directory are very similar.

Data and resources
------------------

The Bayesloc probabilistic multiple seismic event location software was obtained from
https://www-gs.llnl.gov/nuclear-threat-reduction/nuclear-explosion-monitoring/bayesloc
(last accessed April 2022).

The file ISC_info_20220402.txt is the output from a search of
http://www.isc.ac.uk/iscbulletin/
performed on April 2, 2022.  (ISC, 2022)

The National Earthquake Information Center earthquake report for the 27 February 2022 event is found on
https://earthquake.usgs.gov/earthquakes/eventpage/us6000h0k8/executive
(last accessed April 2022).

References
----------

Fisk, M. D. (2002). Accurate Locations of Nuclear Explosions at the Lop Nor Test Site Using Alignment of Seismograms and IKONOS Satellite Imagery. Bull. Seismol. Soc. Am. 92, 29112925. doi:10.1785/0120010268.

International Seismological Centre (2022), On-line Bulletin, https://doi.org/10.31905/D808B830