+ Moment Tensor
istiMT:
This module automatically computes 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). It 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 a rupture length and propagation estimate using a sliding-window FK-analysis method. This computation, like istiMT, relies on a magnitude threshold 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 to determine how the rupture progresses over time. The standard QuakeML message format does not suppport the result, and so instead, an “event” object is created, notifying the end-user that the computation has been 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 a 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 to set the initial parameters and also requires access to the Green’s functions that istiMT uses. The resulting computation is not part of the QuakeML standard, 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 give a more accurate idea of the earthquake characteristics, particularly concerning tsunamigenic earthquakes.
While SeisComP has a very nice interface for adding new magnitude types, ISTI could not 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 required 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.
