Helmholtz-Centre Potsdam GFZ, the German Research Centre for Geosciences, is the license holder for SeisComP3 and developed the open source SeisComP3 program. ISTI has been developing new modules and modifying existing modules for the free open-source version of SeisComP3 since 2014.
Table of Contents
ISTI has created the following modules which can be added to an open source SeisComP3 system:
Moment Tensor – istiMT – This module serves to automatically compute a moment tensor given an earthquake of a sufficient magnitude (the exact value is configurable, but the default is to calculate the moment tensor given a 7.5 Mw magnitude). This module utilizes pre-computed Green’s functions from the National Earthquake Information Center (NEIC), and uses either the “WPhase” method, or the NEIC’s method for computing the focal mechanism based on the P-wave. In addition to the primary QuakeML focal mechanism message, the data and intermediary results are saved and packaged in an HDF5 file.
Array Processing – istiAP – This module calculates an estimate of rupture length and propagation using a sliding-window FK-analysis method. This computation, like that of istiMT, relies on a magnitude threshold in order to kick off computation (which is also set to a default of 7.5). A back-azimuth and apparent velocity are found for each window, which is then back projected onto the original hypocenter in order to attain an idea of how the rupture progresses over time. The result is not supported by the standard QuakeML message format, and so instead an “event” object is created notifying the end-user that the computation has completed and results are packaged and made available in the HDF5 format. Results are highly dependent on array geometry, so proper configuration of an array suitable for examining an earthquake at teleseismic distance is a prerequisite to attain meaningful results.
Finite Fault Solution – istiFFS – This module computes a finite fault solution that discretizes the rupture area to provide more insight into the earthquake characteristics. The module relies on having access to the information provided by the focal mechanism in order to set the initial parameters, and also requires access to the Green’s functions that are used by istiMT. The resulting computation is not part of the QuakeML standard, and so once again users are notified of results via an “event” placeholder object, and the actual results are stored and accessible in an HDF5 file.
Wave Magnitude – istiWM – This serves to calculate specific magnitudes (the mantle magnitude ‘Mm’, an “energy” magnitude ‘Me’, another version of the surface wave magnitude ‘Ms’, and a discriminating ration known as “theta”. These magnitudes are calculations based on slower traveling waves, but serve to give a more accurate idea of the earthquake characteristics, particularly as relating to tsunamigenic earthquakes.
While SeisComP has a very nice interface for adding new magnitude types, ISTI was not able to use the standard processing workflow which requires amplitude measurements to be made apart from the magnitude processing module. In our case, the products needed by the end user needed direct access to the data streams, which is only available to scautopick/scamp in the standard workflow.
The istiWM (for “wave magnitude”) workflow sees the module trigger calculations for origin calculations, as happens with the standard magnitude processor “scmag”, but then istiWM proceeds to lookup the time window of interest around the arrivals, calculating the magnitude and sending off the resulting QuakeML formatted product along with an auxiliary data file stored in the HDF5 format.
ISTI has updated the following core modules:
scevent – A function was added to find the nearest cities to an earthquake and report that information in the “event description”. This function was modeled after an existing method which provided the region the earthquake is in and draws from the same table of information that the regional description is located.
scautopick – Methods were added to roughly approximate pick polarity and wave first motion and pass that information along with the computed results.
scautoloc – ISTI modified the original association routine to deal with user-defined picks outside of the normal toolset provided by the standard GUIs. Specifically, logic was created to ensure the system could effectively “blacklist” picks from being further incorporated in automatic locations, as well as to ensure that a “dis-association” could be forced that prevented picks from being automatically associated with a particular event. ISTI also incorporated a QC method for “winnowing” out bad picks. While SeisComP already provides QC methods incorporating azimuthal gap, standard error, and a host of other metrics, this change allows looking at these metrics and attempting to attain a better solution by omitting picks before re-submitting to get a new location. Up to three picks may be omitted from the final solution, picks to be removed are determined via a naive “n squared” search over the set. This behavior was identified as requiring a large amount of system resources, and may be turned “on” or “off” in the configuration.
Consulting from ISTI
ISTI is available as a consultant to build custom SeisComP3 modules for you, or help deploy any of our modules to your environment.
Information on the SeisComP User License Agreement may be found here: https://www.seiscomp3.org/doc/