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Joined Double Difference Earthquake Location and Estimation of Vp/Vs-Ratio from Earthquake Clusters

Description: 

A commonly used method to determine the vp/vs ratio within spatial closely distributed earthquakes is the approach proposed by Lin and Shearer (2007). There, pairs of differential P- and S-arrival times measured at the same station are used to estimate the vp/vs ratio within the earthquake cluster. The vp/vs ratio is the slope of a line fitted to differential P- and S- times after subtraction of the mean value over all stations. This statistical approach is highly dependent on the geometry of the earthquake locations and the station distribution. Only in a medium with a homogeneous vp/vs ratio, the estimated vp/vs ratio has no bias, as shown by Palo et al. (2016) and cannot be accurately accounted for, which limits the usage of “Lin and Shearer”.

Here we present a new method to overcome these limitations as we invert directly for the vp/vs ratio after a precise location, e.g. with the double-difference earthquake location of Waldhauser and Ellsworth (2000). Our approach is based on the ansatz of the relative location presented by Fréchet (1985). We use P and S differential times and invert directly for P-velocity and vp/vs ratio. We can combine the double difference relocation of the earthquake hypocentres with our estimation of the vp/vs ratio in an iterative inversion process to improve locations and velocity estimates. We test our method with synthetic data in a 2D and 3D subduction zone setting and apply it to a dataset of an earthquake cluster at the seismogenic interface in the subduction zone offshore Ecuador.

Session: Advances in Reliable Earthquake Source Parameter Estimation [Poster]

Type: Poster

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Runa

Student Presenter: Yes

Invited Presentation: 

Poster Number: 32

Authors