# Earthquake Location Information

## SeisComP3

Events in GeoNet's catalogue from 2012 are determined using the SeisComP3 earthquake analysis system. It features two location techniques, LocSAT and NonLinLoc.

SeisComP3 is seismological software for data acquisition, processing, distribution and interactive analysis. As part of its origin location functionality, it employs two locations techniques:

• LocSAT uses a one-dimensional model of the crust. See Bratt, S., and W. Nagy (1991): The LocSAT program, Science Applications International Corporation, San Diego. The evaluationmethod is LOCSAT and the current model definition is earthmodel iaspei91.
• NonLinLoc is a software package that can use three-dimensional models of the crust. We have used the model described in Eberhart-Phillips, D.; Reyners, M.E.; Bannister, S.C.; Chadwick, M.P.; Ellis, S.M. 2010 Establishing a versatile 3-D seismic velocity model for New Zealand. Seismological research letters, 81(6): 992-1000. The evaluationmethod is NonLinLoc and the current model definition is earthmodel nz3drx.

### Magnitudes

SeisComP3 can make many of the standard estimates of magnitude. GeoNet combines these into a summary magnitude, denoted M, which consists of a weighted average of the individual magnitudes and attempts to be a best possible compromise between all magnitudes for a range of earthquake sizes. Currently we only use two magnitude estimates:

• $$M_{Lv}$$: Local magnitude calculated on the vertical component using a correction term to fit with the standard M$$_L$$. The maximum distance for which this is computed is 8 degrees.
• $$M_{w(mB)}$$: Estimation of the moment magnitude $$M_w$$ based on $$mB$$ using the Mw vs. mB regression of Bormann and Saul (2008). The minimum distance for which this is computed is 5 degrees.

Summary magnitude for GeoNet is then defined as:

$$M = \frac{2 * M_{Lv} + (0.4 * number\_of\_stations(M_{w(mB)}) - 1) * M_{w(mB)}}{2 + (0.4 *number\_of\_stations(M_{w(mB)}) - 1)}$$