GrowClust: A hierarchical clustering algorithm for relative earthquake relocation, with application to the Spanish Springs and Sheldon, Nevada, earthquake sequences

Daniel T. Trugman, Peter M. Shearer, & Ken D. Smith

Published September 8, 2016, SCEC Contribution #6649, 2016 SCEC Annual Meeting Poster #200 (PDF)

Accurate earthquake locations are essential for providing reliable hazard assessments, understanding the physical mechanisms driving extended earthquake sequences, and interpreting fault structure. Techniques based on waveform cross-correlation can significantly improve the precision of the relative locations of event pairs observed at a set of common stations. Here we describe GrowClust, a relative event relocation algorithm that can provide reliable relocation results for earthquake sequences over a wide range of spatial and temporal scales. The GrowClust method uses input differential travel times, cross-correlation values, and reference starting locations, and applies a hybrid, hierarchical clustering algorithm to simultaneously group and relocate events within similar event clusters. Requiring no explicit matrix inversion, the method is computationally efficient and capable of handling large data sets, and naturally applies greater weight to more similar event pairs. Additionally, GrowClust outputs robust location error estimates that are useful in interpreting the reliability and resolution of relocation results. As an example, we apply the GrowClust method to two prominent, recent sequences in western Nevada: the Spanish Springs and Sheldon earthquake swarms. These sequences highlight the future potential for applying the GrowClust relocation method on a much larger scale within Nevada and eastern California, where existing relocation results are sparse but vital for understanding the seismotectonics and seismic hazard of the greater Walker Lane region.

Key Words
earthquake location, Nevada seismicity, earthquake triggering, earthquake interaction, open-source software

Citation
Trugman, D. T., Shearer, P. M., & Smith, K. D. (2016, 09). GrowClust: A hierarchical clustering algorithm for relative earthquake relocation, with application to the Spanish Springs and Sheldon, Nevada, earthquake sequences. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology