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# Finite-Fault Rupture Detector

Part of the EEW package.

The FinDer software is distributed by the Swiss Seismological Service (SED) at ETH Zurich. Access to the source code is limited to users who have an established collaboration with the SED. In other cases, compiled binaries (in a docker image) may be provided instead. Please contact Dr. Maren Böse (SED) for requests and further information.

The ground motion observed during large earthquakes is controlled by the distance to the rupturing fault, not by the hypocentral distance. Traditional point-source algorithms can only provide the hypocentral distance. The Finite-Fault Rupture Detector [1] (FinDer) Earthquake Early Warning algorithm (Böse et al., 2012) can determine fast and robust line-source models of large earthquakes in order to enhance ground-motion predictions for earthquake early warning (EEW) and rapid response. The algorithm quantifies model uncertainties in terms of likelihood functions (Böse et al., 2015), and can be applied across the entire magnitude range from M2 to M9 (Böse et al., 2018).

The FinDer algorithm is based on template matching, in which the evolving spatial distribution of high-frequency ground-motion amplitudes (usually peak ground acceleration, PGA) observed on a seismic monitoring network is continuously compared with theoretical template maps. These templates are pre-computed from empirical ground-motion prediction equations (GMPEs) for line-sources of different lengths and magnitudes, and can be rotated on-the-fly to constrain the strike of the earthquake fault rupture.

The template that shows the highest correlation with the observed ground-motion pattern is determined from a combined grid-search and divide-and-conquer approach (Böse et al., 2018). The resulting finite-source model is characterized by the line-source centroid, length, strike and corresponding likelihood functions. The model is updated every second until peak shaking is reached, thus allowing to keep track of fault ruptures while they are still evolving.

Compared to traditional point-source EEW algorithms, FinDer has a number of interesting features (see Böse et al., 2018 for details):

- Characterization of seismic ground-motions rather than earthquake sources;

- Consistent models and uncertainties for both small and large earthquakes;

- No magnitude saturation in large earthquakes;

- Applicable to complex earthquake sequences;

- No station averages, but true network solutions;

- Independent from traditional phase picker and pick associators;

- Unlikely to trigger during teleseisms;

- Enables joint seismic-geodetic real-time finite-fault models (e.g. for tsunami warning);

- Can resolve fault-plane ambiguities, including those of small earthquakes.

## Development

The implementation of FinDer proceeds in close collaboration of the Seismic Network group at the SED in ETH Zurich with the US Geological Survey (USGS) and the California Institute of Technology (Caltech).

## FinDer and SeisComP

FinDer has been implemented with an API. To integrate FinDer within SeisComP, a wrapper module scfinder uses this API. The scfinder module requires FinDer to be installed and SeisComP to be compiled from source.

The library version of the generic EEW pre-processing module sceewenv is used within scfinder to provide continuously updated envelope amplitudes to FinDer. FinDer outputs magnitudes (Mfd). Mfd is updated when significant changes are observed with updates continuing until a stable solution is reached.

An additional generic EEW module, sceewlog, creates log output and mails solutions once a new event is fully processed. It also provides an interface to send alerts in real-time using ActiveMQ. The Earthquake Early Warning Display [2] (EEWD, Cauzzi et al., 2016), an open-source java application, can receive and display EEW messages broadcast via ActiveMQ.

## FinDer in a Docker

See FinDer setup.

## EEW License

The SeisComP EEW modules are free and open source. They are distributed under the GNU Affero General Public License (Free Software Foundation, version 3 or later). For licence information on ETHZ-SED SeisComP EEW modules released before SeisComP v4.0.0 see the Timeline in EEW.

## References

Böse, M., Heaton, T. H., & Hauksson, E., 2012:

  Real‐time Finite Fault Rupture Detector (FinDer) for large earthquakes. Geophysical Journal International, 191(2), 803–812, doi:10.1111/j.1365-246X.2012.05657.x

Böse, M., Felizardo, C., & Heaton, T. H., 2015:

  Finite-Fault Rupture Detector (FinDer): Going Real-Time in Californian ShakeAlertWarning System. Seismological Research Letters, 86(6), 1692–1704, doi:10.1785/0220150154

Böse, M., Smith, D., Felizardo, C., Meier, M.-A., Heaton, T. H., & Clinton, J. F., 2018:

  FinDer v.2: Improved Real-time Ground-Motion Predictions for M2-M9 with Seismic Finite-Source Characterization. Geophysical Journal International, 212(1), 725-742, doi:10.1093/gji/ggx430

Cauzzi, C., Behr, Y. D., Clinton, J., Kastli, P., Elia, L., & Zollo, A., 2016:

  An Open-Source Earthquake Early Warning Display. Seismological Research Letters, 87(3), 737–742, doi:10.1785/0220150284

[1]

http://www.seismo.ethz.ch/en/knowledge/earthquake-data-and-analysis-tools/EEW/finite-fault-rupture-detector-finder/

[2]

https://github.com/SED-EEW/EEWD