← Back to Sessions

Revising the Iaspei Ground Truth List

Description: 

Seismic events with well constrained hypocentres, referred to as “Ground Truth” events, are an important resource for benchmarking and testing new seismic velocity models and seismic event location techniques. Ground Truth events are relocated with ISCloc, using stations within 150 km of the event, and are categorised based on major axis of the error ellipse. Events that are determined to within 5 km are considered for the Ground Truth list. The current Ground Truth criteria require that candidate events have a station distribution with a maximum secondary azimuthal gap of 160° and balanced station distribution, as quantified by a ΔU value of less than 0.36. This is designed to ensure that an unbiased event location can be reliably constrained. Additionally, the existing criteria requires that there is at least one station within 10 km of the event, to ensure there is some reasonable depth resolution. We find that it is possible to improve the number of local stations and the secondary azimuthal gap for an event but degrade the ΔU value. As ISCloc and several other modern location algorithms, are able to account for unbalanced station distributions, we propose modifying these criteria in order to make them more inclusive, while not degrading the resulting location quality. In doing so we aim to improve the geographic distribution of events in the Ground truth list.

By replacing ΔU with a new measure referred to as the Cyclic Polygon Quotient (CPQ) we can consider more events for the Ground Truth list, including in areas of very dense seismic network coverage. In addition, the highly exclusive requirement that there is one station within 10 km of the event is augmented with the alternative requirement that there are stations reporting both P & S phase arrivals within 150 km of the event. We demonstrate that by modifying the Ground Truth criteria in this way we can increase the number and improve geographic distribution of Ground Truth events found without compromising the location accuracy of the identified Ground Truth events.

Session: Advances in Reliable Earthquake Source Parameter Estimation - I

Type: Oral

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Thomas

Student Presenter: No

Invited Presentation: 

Poster Number:

Authors