# 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:

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