# Earthquake Location Information

## SeisComP

**Events in GeoNet's catalogue from 2012 are determined using the SeisComP earthquake analysis system. It features two location techniques, LocSAT and NonLinLoc. Since 2023 GeoNet upgraded seiscomp3 to later versions now using a generic "SeisComP" name**

SeisComP 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

SeisComP can produce many of the standard estimates of magnitude type. GeoNet combines these into a summary magnitude, denoted **M**, which consists of a weighted average of the individual network magnitude types and attempts to be a best possible compromise between all magnitude types for a range of earthquake sizes and distances. 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. It applies more specifically to small to moderate events at close and regional distance.
- \(M_{w(mB)}\): 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. It applies more specifically to moderate to large events at regional to global distance.

Summary magnitude for GeoNet is then defined as:

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