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Considerations for Optimally Combining Local, Regional, and Teleseismic Data in Single Event Locations

Description: 

The U.S. Geological Survey National Earthquake Information Center’s (NEIC) mission requires that it rapidly estimates earthquake locations using a spatially diverse set of seismic stations and a wide range of phase arrival-time observations. In some cases, like for many midocean ridge earthquakes, the NEIC primarily uses a distributed set of teleseismic observations. In other cases, such as for small domestic earthquakes, the NEIC uses a small set of local-to-regional observations. In most cases, the NEIC must rely on a varied combination of local, regional, and teleseismic arrival-time observations.

Given the heterogeneity of potential observations, it is challenging to ensure data is optimally weighted to ensure high-quality event locations and minimize potential velocity model and observation density biases. The NEIC locator currently uses a range of techniques aimed at improving event locations, including decimating dense observations, down weighting correlated observations, and weighting observations based on expected arrival-time uncertainties. Many of these techniques were developed before NEIC had access to a robust set of local observations, and therefore are less appropriate for the current state on NEIC’s monitoring system. As a result, locations can underweight local observations and overweight regional observations that may have large velocity model biases. Here, we leverage a global catalog of calibrated earthquake locations to evaluate how to optimally combine observations at local to teleseismic distances. We re-evaluate how phase, distance and azimuth effect the covariance of arrival-time observations. We also re-evaluate phase specific arrival-time statistics (e.g., bias, spread). We demonstrate the effect of changes to these underlying statistics in the results from the NEIC locator.

Session: It’s All About Relocation, Relocation, Relocation

Type: Oral

Date: 4/20/2023

Presentation Time: 04:30 PM (local time)

Presenting Author: William L. Yeck

Student Presenter: No

Invited Presentation: 

Authors