Generalized Bancroft algorithm for locating earthquakes with P- and S-wave arrival times

Bulletin of the Seismological Society of America
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Abstract

Because of similarities between locating an earthquake with seismic stations and locating a Global Positioning System (GPS) receiver from satellites, the Bancroft algorithm developed for GPS processing can be used to locate earthquakes. Such an approach to earthquake location differs from the conventional method of choosing an initial or trial solution and then iteratively improving the solution until convergence. The Bancroft algorithm has the advantage of being a direct, noniterative solution but with the disadvantage of only being able to accommodate a homogeneous velocity model. An additional limitation of the standard Bancroft algorithm is that it considers arrival times in a medium with a single propagation velocity. This poses no problem for GPS processing because electromagnetic waves travel at the speed of light; however, for seismic waves it means the algorithm can be applied to collections of either P‐ or S‐wave arrival times. Here, I show how the Bancroft algorithm can be generalized to handle both P‐ and S‐wave arrival‐time measurements simultaneously. I also show how to accommodate depth‐varying P‐ and S‐wave velocity models. I apply the generalized Bancroft algorithm to microearthquakes beneath Tanaga Volcano in Alaska and compare standard locations from the widely used HYPOINVERSE location code to Bancroft locations and to the output of HYPOINVERSE when setting the trial location to the Bancroft location. I find the Bancroft locations outperform the results from the other methods for shallow earthquakes near sea level, where a quantity known as the geometric dilution of precision is large and linearized approaches such as HYPOINVERSE are expected to struggle.

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Publication type Article
Publication Subtype Journal Article
Title Generalized Bancroft algorithm for locating earthquakes with P- and S-wave arrival times
Series title Bulletin of the Seismological Society of America
DOI 10.1785/0120240058
Volume 115
Issue 2
Publication Date January 07, 2025
Year Published 2025
Language English
Publisher GeoScienceWorld
Contributing office(s) Volcano Science Center
Description 12 p.
First page 367
Last page 378
Country United States
State Alaska
Other Geospatial Tanaga Island
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